Monthly Archives: November 2010

Engine Build #3: Top end

S3700155Now what in the hell is this? well, after i got the bottom end of the block assembled and went through my dial-in to set my camshaft and timing, it was time to start on the heads. on the oldsmobile v-8 cylinder heads, both the center exhaust posts of each head feed the exhaust crossover to the intake. good for cold weather/ not good for performance. Chevy cylinder heads would also use either one or both center exhaust ports for the same purpose, but it was not as severe as on the olds heads.  there are numerous ways to block these off using block-crete, epoxy, and there is also some kind of a goofy zinc alloy you can use(which can melt). the way i do it is melt down some scrap aluminum and pour it through the exhaust post openning until it fills just below the exhaust port on the back side. i melt the aluminum in a blacksmith’s ladle and use the rosebud on the acetylene torch for heat.  now it isn’t contoured at all for peak flow and there is a reason for this. if you contour it into a nice bowl shape, the edges of your plug will erode and flake causeing it to end up just like you see it anyways. the best i have found in doing this is to create a wall/plug of aluminum at the back of the exhaust port pocket and leave it. these are factory heads mind you.

 in this day and age if you want serious performance :buy aftermarket cylinder heads and say screw it. more often than not it is cheaper than jacking around fixing up factory heads. but here again, i am just seeking to improve a pair of factory heads a bit not re-invent the wheel.  on chevy heads for derby engines i have done this with good results, but just welding a plug into the intake seems to do about as much good on a chevy small block.

 Now the next step in fixin up my heads was to go throughS3700157 the valves.  Since i am on a budget i elected to do what i call a polish valve job, which is actually a service technique i learned in trade school from an old fart diesel mechanic i had as an instructor. basically you take lapping compound you can get at any parts store and spin it with a power drill instead of that ridiculous stick with a suction cup. i don’t have all day to mess with that shit. as you can see in the photo i have a quick-chuck style power drill. you put 3 or 4 dots of valve gringing compound on the face of the valve, stick it in as so and spin it with the drill at low speed; lifting and applying light pressure in 2 second intervals. you want to go low speed and yo don not want it to bark loudly or screech as it grinds. this causes vibration which will ruin the cut. after you grind, clean em off and check your valve action. your valves should pop closed and sit flush to the valve pocket. if it doesn’t that you may have bad valves or need to have everything sent to the machine shop. also while you’re at it, check your valve guides for excessive side play. if they are real sloppy your valves can stick open.

what you are doing by lapping the valves to the valve seats of the head is mating the two surfaces together to improve the seal of the valves. it also works to clean the carbon and other odd deposits off the seats. it is a cheap ass way of fixing up your cylinder heads rather than completely ignoring em after you go through the bottom of the block. this IS NOT an alternative to a valve job from the machine shop. regrinding the valve seats and valve faces completely is the right way to do this. a 3 angle valve job is also an excellent idea but i don’t really see the benefit of it unless you are going to be doing other port work on your heads and try to flow some serious cfm’s.

once you get your valves in order, it’s time for springs. although you can shim your springs according to wear, i always replace valve springs when i am replacing the camshaft. the valve spring tension must match the cam lift requirements otherwise you will have problems. i also replace my keepers every time. your retainer are a toss up. i elected to keep my rotators since they were factory. on chevy heads i usually omit the rotators in favor of solid retainers on both intake and exhaust. once you install your springs, take a rubber mallot and tap the springs to make sure the keepers seat fully into the retainers. you would rather have em shoot across the garage instead of comming apart and dropping a valve into your new engine!

it’s time to bolt on your heads. don’t get into a hurry here.  this is where the chevy and the olds engines really went two different directions. on your SBC’s, it can be as simple as bolting em on and setting your valve lash. on the oldsmobile: the rocker arms are not adjustable. actually they are a piece a shit. the aftermarket adjustable stuff isn’t much better it is usually re-fucked ford parts. so before you torque make sure your valvetrain will not bind- especially with an aftermarket camshaft.

for a non adjustable valve train: assemble your heads to your engine block with hand tightened head bolts. do not torque. put in a couple of push rods and a few rocker arms. check to make sure your valve lash is going to be spot on. you may need different pushrods or even convert to an adjustable valve train to make your camshaft work. you want a bit over zero lash for a hydraulic camshaft to preload the lifter(check your factory spec). converting to an adjustable rocker arm set up may or may not require some major machine work depending on what kind of heads you have to convert to an adjustable set up. this is why you don’t torque your heads until you know for sure.

if it looks good then roll it to maximum lift on both the intake and exhaust valve to check for valvetrain bind. now there are numerous ways to check for your valve clearance to the pistons and/or rocker arm bind.  the most unique way i have seen is using play-doh on the piston faces while swapping in solid lifters for checking. you then roll the engine over slowly and disassembe to check your pattern of valve to piston clearance in the play doh. .

 on a hydraulic lifter set up, an aggressive camshaft can be binding the valvetrainS3700161 during assemble and never know it as the lifters are collapsing as your spin the engine on the stand.  it will bind after start up and snap the front of the camshaft once you build enough oil pressure to pump the lifters fully. this can be due to either the valves hitting the pistons from incorrect piston: cam timing combination, valve spring coil bind, or the rocker arms are not slotted far enough and they bind on the pivots. a simple check is to stick a big pair of channel locks on the rocker arm at max lift of the valve and pull the rocker arm down until you have play on the push rods. this also checks for coil bind on the valve springs. i would not be doing the channel lock method on a race engine with aluminum rocker arms. this is a simple check that works well for a cheap build like this.

NOW, once you have ensured you valvetrain is going to be alright. torque your head to specification and assemble your valvetrain. start at the center of the head and work your way out. i torque the heads on in 3 stages: like 20-45-85 ft/lbs, have a sip of beer in between stages to give the head gasket time to crush.

i like to use the mr gasket head gaskets for oldsmobile they seem to hold up better over the fel pro. it’s also cheaper. for SBC, i tend to shy away from the metal head gaskets- especially on derby engines. even when using the ultra-copper i have had gasket sealing issues with stamp steel head gaskets. i had better results with the cheapo summit head gaskets for SBC over the stamp steel fel pro gaskets. it didn’t matter if it was a light or heavy casting heads either.

there ain’t much left to do on the olds at this point , but you chevy guys(and anyone else with an adjustable valvetrain) have to set valve lash. on these is do what is called the companion cylinder method. you basically take your firing order and chop it in half. so 1-8-4-3-6-5-7-2, 1 would be in the same position as 6, 8 the same as 5, and so on and so forth. this is how most engines for automotive work.

look at your rocker arms. you want to set your valve lash at or close to TDC compression of that cylinder that you are on to ensure you are not part way on a lobe. so to start, you bar the engine over looking at the rocker arms on #6. when the exhaust is just about finished and the intake rocker starts to move: you are at or near TDC of number 1 cylinder and can set your valve lash on both intake and exhaust of #1.

once set, you go about a 1/4 turn on the crank and watch the rockers on #5 to do the same thing as # 6  having both rocker arms in motion: this will center #8 at TDC compression and you can set both of those valves for lash. you just work your way down the line and should make 2 complete revolutions on the crankshaft ending up back at TDC#1 compression when finished.

the main reason i like doing it like this is because with aftermarket camshafts can be ground all over the place. so it may seem like you are on the bottom of the lobe and you really aren’t- causing lost performance from incorrect lifter preload.

Engine Build#2:Camshaft Dial-In


if you have never done this, or never even heard of this, it’s called camshaft dial-in. although not as many people do it as should, it is something i had to learn to do by force cause of this damn oldsmobile habit i have. unlike the aftermarket for chevy, olds performance products ore usually not right. i have only had two timing sets ever be spot on to there advertised markings. believe it or not the most consistent timing chains i have bought in recent years are the summit racing brand timing chains!

in a nutshell, your engine is a rotating assembly. your camshaft is designed to orchestrate your valve motion in relation to the rotational position of the crankshaft. by dialing in your camshaft, you are verifying that your camshaft and timing chain are going to fire off your valves at the right time and the proper lift to what you want. like i mentioned, there are numerous timing chains and camshafts out there, and they may or may not be made correctly. hell even my edelbrock cam was a bit off on the exhaust valve duration. a lot of your factory cams and bad replacements are ground retarded from the get go- and some of these multi position timing sets that actually sit 4 deg retarded at the 4 degree advanced markings!

Now, i could sit here and write out exactly how to do a cam dial in, but a quick google search will reveal some spot on articles on how to do it, as well as video’s you can watch on the web. you can buy complete kits to do this as well through summit or jegs. what i will do is point out a few things that i do whi;le going through the procedure.

there are a few ways of doing dial in, i use the intake centerline method with a dial indicator at the lifter. this eliminates all loss of lift through the valvetrain. yes, you can lose quite a bit of advertised lift through a poor valvetrain(like the olds). i use the large moroso degree wheel, a home-made pointer i made out of a bolt, and a piston stop i made from a piece of angle iron and a few bolts. i have a hydraulic lifter that has been welded solid with a plug so it does not collapse and throw off the measure of the dial indicator.

once i center my degree wheel to TDC #1, i position my dialS3700154 indicator directly on the lifter of either intake or exhaust # 1. you then zero the indicator and crank the engine around to .050″ lift at the indicator. look at your wheel and see how it corresponds with your cam card specs. if it is not spot on, note the degree’s of difference. this is the first sign of your cam timing being way off. i go through the process for both intake and exhaust lift. if all readings are off by about the same # of degree’s, adjust your timing chain…or in some extreme cases if it is off by 8 degree’s or more from the card on both intake and exhaust, shit can your timing chain.

as a rule of thumb, advancing your timing chain will usually help your bottom end power-retarding it pushed the power band up the rpm scale. for the most part, you should achieve correct cam timing with the timing set installed in standard position. if the cam is way retarded or advanced from the cam card while the timing set is installed straight up- call the manufacturer cause there is probably a reason for it, like valve clearance to the pistons for radical lift . do not plan on buying a cam and changing it at the timing chain from the get go. although it can be a neat way to save money- just save yourself a headache and buy the camshaft you want. use the timing set adjustments for fine tuning not overhauling the cam timing.

i quit buying used camshafts or anything without a timing card simply because you really don’t know what the hell you have. you can use this process to read an unknown cam or a camshaft you have ran for a few years to check for wear.

once i have my cam timing set, i wheel the engine to TDC#1 and remove the wheel. slide your dampener on(sometimes part way) and see where your ignition timing mark is located in relation to the true TDC location between your indicator and the groove on the dampener. you’re checking to see if the outer weight outer weight of the dampener has spun on the rubber and moved the mark. if this has happened, then you need to shit can your dampener. on the SBC chevy’s there were a few different balancers and timing covers so you can really mess up where you set your timing.

Engine Build #1: Bottom End


Well, i must be an idiot as i have decided to build myself yet another olds engine after i swore the damn things off.  I pretty much have given up on the 455 olds based engines as after about 10,000$ and 6 blocks. i have come to the conclusion the block itself has an achilles heal. the olds V-8 blocks like you see here have the thrust bearing at the center of the block. i theory is that on the 455’s, when that 80lb crankshaft is under major load like going down the track at the drag strip, the crank bends like a fishing rod flexing the block. the center thrust bearing aids in absorbing the thrust from the front 4 cylinders- but the back 4 cylinders have nothing to help it. basically the #4 main flex’s and shits out the main bearings. some engines do it- some don’t all i can say is balancing and camshaft selection are key with 455 longevity. also- buy a girdle for the bottom of the block. Better yet go buy a chevy based Merlin block and forget about it!!

Anyways, when i finally sold my 462 drag engine a few months back, i got this mid 70’s olds engine in on trade. last friday i tore it down and i have to tell ya, it is one of the cleanest Blocks i have ever seen.S3700146 it literally had a stock bore with no piston ring ridge on the cylinders. the Crankshaft was also spotless with normal wear on the all the bearings. so i elected to re-ring it for future use on a street car i have planned to putz around town in. i am using a mid 70’s 350 block, plain jane crankshaft and the original rods and pistons. the identifying mark on olds blocks sits right on the top of the block behind the timing cover. in the picture here to the right above is the serial number you would look for for the good olds 350 blocks. after 1976, the bottom of the block on most all but the diesel engines had large windows in the supporting cast iron of the block for the main journals making for a very weak block to begin with. in my opinion the only block stronger that these 350 olds blocks are the DX designation 350 olds diesel blocks of the early 80’s(which can be converted to gas).

Now to do up an engine right, your block, crank, heads, rods & pistons need to be checked for wear and damage.  things like journal diameter and cylinder bore wear and taper. if you do not have the machinist’s tooling to do it, find a GOOD machine shop(which can be hard to do) . if you are building a high dollar power plant, you should definitely have the block, crank, and heads magna-fluxed for cracks that cannot be seen by the naked eye. pretty much in my book any engine that will see over 350hp/ 5000rpm OR serious amounts of abuse should be checked. things like lifter valley crack can become major deals the more you push an engine to the limit.

 NOW, does this mean you cannot build an engine without a trip to the machine shop- of course not. in my case i started with a great core and have a 500$ budget to get the thing running, and it will not see serious abuse. if the machine shop is out of the question for whatever the reason….usually cost….here’s a list of things not to forget while tearing down, inspecting, and re-assembling you short block :

– i always check all 8 bores with a bore gauge for size and taper due to wear. visually check for pitting and wear to the top of the cylinder. slight ridge-ring is not a definite sign of needing machine work. a ridge reamer can take care of a lot of it. as a personal rule if it is over .010″ of wear you really ought to consider boring it out….however if you are building a loose derby motor, ring seal is not quite as critical so .010″-.015″ is not all bad. in that case the engine i built to run extremely hot and will actually run better as it runs hotter due to the tolerances tightening up. it’s a fine line- too much and you will have piston slap.

-always check the journals on the crankshaft with a micrometer and visibly look for hard wear and damage. you are checking for undersize and taper. if the bearings look bad- chances are the crank is screwed. even if it looks good, if your engine was making noise CHECK IT!  you never know when someone else has been into an engine haf-assed the assy with the wrong size bearings at some point in the past and it bites you in the ass(it happened to me years ago). if your sizes are not to factory spec, look over the crank for any markings on the ends. machine shops usually stamp an undersize on one end of the crank on the counterweight.

-check your pistons and the old rings. look for stuck rings. clean any and all carbon from the ring grooves with a piston ring groove cleaner so your new rings will not jam between the cylinder walls. make sure piston pins are free. check the rods for blue marks….some discoloration of the rods is fairly normal, blue indicates heat damage and it must be replaced.

-if you had spun main bearings or severe bearing damage, the alignment bore of the crankshaft in the block could be compromised and you will need to make a trip to the machine shop, or shit can the block if you have a pile of cores….LOL!

-if you are not replacing the camshaft take a pair of calipers and check EVERY lobe for wear. 90% of the time you will find one that is not up to snuff. always replace the timing chain. always dial in your camshaft. if you do not know how to do this- learn how to. over half of the timing chains on the market are not accurate, and camshafts may or may not be ground retarded in the timing from the get go. you can lose incredible amounts of performance because of this! on some applications it can cost you an engine at start up cause the valves hit the pistons!!

-stick your new piston rings into at least one of your cylinders with a piston to center them and check your piston ring end gap. excessive gap for a derby engine is not hyper critical. you just don’t want it to bind.

-if you are going to run it over 5000 rpm on a regular basis, having your rotating assy balanced is a good idea. if you are changing hard parts like rods & pistons and they are not factory replacement, you should definitely have everything re-balanced. new and oversize pistons are suppose to come from the manufacture already weighted to a factory piston weigh, but the quality control on some of these parts can be a little left to be desired.

-when you are installing engine bearings, do not touch the bearings with your fingers if you can help it. the acid from your fingers can put marks on the bearings. i put a glob of lubri-plate engine assy lube in the middle of the bearing and put it together. S3700149you don’t have to lick the bearings and fondle em like your having sex, you just need to throw some on there so it isn’t dry! i also use two pieces of 3/8″ fuel line with dowel rods stuck inside to not only guide the rod ends onto the crankshaft, but it also holds the bearings into the rod ends so they don’t fall out onto the floors while you are trying to install the pistons into the block leaving both hands free to run the piston ring compressor. always use red loctite on the connecting rod nuts.

carburetor #4:Edelbrock/AFB

When i was building my first drag motor, my 462 olds big block, i went with an edelbrock 750 cfm carb as well. off the top of my head i thing the referrence number was a 1407. these to be honest are a good carb that is a lot easier for tuning over the other two brands, but neither the mileage of a q-jet or the power of a holley. they are a good carb for the right application….and budget.

the Edelbrock carb that we see now days is basically a variation of an old carter/AFB design from years past. Hell even the new thunder series AVS carbs are nothing new they were around many years ago. the AVS stands for air valve secondary and fucnctions similar to the rear barrels on the other two brand of carbs i mentioned. never really messed with one yet so that’s what i know on em.

the AFB is very tuner/user friendly. it has float bowls on either side but only one fuel inlet. on either side of the air horn there are small taps which you can losen and pull the power valves out to change the metering rods. metering rods are the calibration over jets with these things, although you can remove the air horn and change the jets. the front barrels do most of the work and have the metering rods, the rear barrels are basically along for the ride and have an air valve with a counter weight rather than any kind of a vacuum signal to aid in preventing any kind of a lean condition when you bury the throttle.

for the street, putzing around on the weekend this is a great carb. the carb comes with a book that outlines which size rods/jets to install to change your mixture. the power valves also have different rated springs you can buy but i have found it doesn’t make that big of a difference. the baseplate is a squarebore pattern identical to the holley, but the smaller carbs like the 1405 have smaller primary’s and can fit directly to a spreadbore intake on occassion without a spacer or adapter. not always the case.

that bad part of these things is that when you crack the throttle wide open, especially at the drag strip, it coughs…..and the rear barrels don’t seem to do much. them weighted air valves on the back aren’t worth a shit for racing. ran great around town though. i literally toward the end just ran on the front barrels of the carb and left the rears unhooked….and only lost a 10th in the 1/4 mile!! that’s sad….and i tried every damn calibration i could get my hands on.

for derby, i have never tuned or ran one. i have been told if you install the off road kit into the float bowls they work well. i would still run it on the front barrels only. now all this being said, when you weigh in the price and ease of service, i wouldn’t be afraid of buying one for the right use. for racing or serious street-strip horsepower, you go another direction.

Carburetor #3: Holley

when it comes to all out performance and making horsepower, i really am a firm believer you have to run a holley carburetor. Back when i was drag racing i make the switch from an AFB style carb to a beat to shit-second hand holley 4160 vacuum secondary and literally gained damn near a full second in elapsed time in the 1/4 mile using the same cfm rated carburetor. that was all the proof  i needed to know.

 there are literally hundreds of different style holley or holley based style carbs in the world like the stuff from Barry Grant.  in my opinion though if you ever watch one of their training video’s, you will realize rather quickly the guys at pro- systems have their shit together also. i was going to spend a big chunk of money with them just before i got out of drag racing. i am no expert when it comes to carbs, but i know enough to hold my own. so instead of trying to dictate a bible on the holley i will just share some of my experiences with you guys. there are great tutorial books available through a lot of sources like summitracing. com

like i said above, the first carb i got into was a 4160 holley 4 barrel. i got it second hand off a big block chevy that came out of a 69 camaro my friend and i were restoring for an older lady years ago. the first kit i got was from quickfuel through the summit catalog. what a piece a shit that was and a complete waste of money. the power valve was WAY too big, the non-stick gaskets were about worthless, and it was missing some parts. i like to use the holley brand jet assortment kits, holley brand power valves and/or power valve block off plugs, and the moroso rubber gaskets for the metering blocks and float bowls. i have used the clear plastic plugs before in the floatbowls so you do not have to remove the plugs to set float level, but after a year or so they tend to yellow.

the 4160 is like night and day over the q-jet. basically it is a modular design consisting of float bowls, metering block(s), main body, and baseplate. with the removal of 8 screws the whole damn thing will fall apart. it is a 4 barrel carb, with dual float bowls but only one metering block.  the front half of the carb being your primary side, it will house the metering block and have the accelerator pump. the back side however is a vacuum secondary with no accelerator pump or metering block. instead they use a metering plate within the float bowl. you can get different caliber metering plates by the way if necessary. the back barrels are controlled completely off  the vacuum signal off the front booster venturi’s not the engine vacuum signal like the q-jet. this means that when you bury the throttle into the floorboard, you engine is drawing full flow through the front barrels. if the demand signal is strong enough it will begin to open the back two barrels as needed by your engine. that may or may not mean they have to open all the way. by doing this, once calibrated,  the carburetor cannot overfuel the engine like a 4150 double pumper can be known to do on the street. 

i ran my 4160 street strip. the front half is basically identical in construction to a 4412 or 4150 and is calibrated in much the same mannor. on the rear barrels i installed an aftermarket adjustable secondary so i could change spring tensions on the rear barrels. this allowed me to set the back barrels to open fully either lower or higher in the rpm range. 

for drag racing or anything else you run full throttle all the time, i found that removing the block off valve and increasing the size of the jets 4 or 5 sizes to make up for it is the way to go. the power valve on the holley is contained in the metering block. if you want to drive on the street at all i have found it is necessary not only for mileage but when i tried running without one i would get random detonation at different rpm AND the engine would overheat. at the drag strip it is pretty much the opposite. the power valve is an extra variable that will throw off your E.T.’s enough to take you our of the racing when your running brackets. this is why i know a lot of guys that will bring their jet kits with a power valve block off to the track with them and change it around for racing-then change it back to drive home.  at the derby, i believe the power valve is also a liability as it will hang up and blow out when the engine gets hot and/or backfires. so i chose to run a block off plug for derby aplication on holleys as well. that is no necessarily the case with a 2G for derby though. what works for one brand may not work on another. never assume!

the 4150 carbs are really the workhorse of the performance industry in my book. often referred to as the double pumper, it is basically two-2 barrel carbs that are joined like siamese twins at the center. the double pumper features both front and rear metering blocks and accelerator pumps. the 4150 can also come with a rear vacuum secondary in place of the rear accelerator pump. however, unlike the 4160 it has a metering block and may or may not have an extra set of idle mixture screws. you can get a 4150 in numerous performance configurations with both annular and downleg boosters, larger accelerator pumps, both front and rear idle mixture screws(referred to as 4 corner idling), as well as a performance main body with a nice contoured intake omitting the choke horn all together.

most of the time on the 4150’s for racing, you will run the front jets slightly larger then the rear jets as the velocity of forward acceleration will have a tendency to make the front cylinders lean out and the rear ones run rich. on a dominator set up for instance like pro stock, guys will run as many as 8 different size jets from the front of the engine to the rear just because of this. jet sizing is not quite that critical on a double pumper but it was a myth for years that the back jets had to be larger than the front, and that simply is not the case. the front barrels are always the workhorse. treat the carb with that referrence.

the 4412 2 barrel that pops up in both circle track and derby on occassion is basically the front half of a 4150 double pumper. usually 500cfm, i have dealt with a few of these and found that they are a good straight forward simple carb. however, i have a tendency to avoid them for derby myself as usually it will overfuel the engine. but i also know guys that make em work time and again. here again remove the power valve to control you fuel AND on these the accelerator pumps were like 50cc’s and can flood the engine when hot so don’t be afraid of playing with the eccentric cam on the throttle shaft.

worth mentioning, i run across old 3310 carbs. i have made these work well for derby by disabling the rear barrels entirely, installing a power valve block off plug, and rely’n solely on front jet caklibration and the front barrels to run. omit the choke. you end up with around 300 cfm or a bit less and works fairly well on a SBC for derby. a fuel filter is a definite must as the needle n seat stick pretty easy on these.

other than jet sizes and power valve, there are 3 other adjustments you really got to worry about. the float levels are set by an adjustment screw and nut at the top of the float bowl. while the engine is idling, take the sight plug out of the side of the bowl and adjust the screw up or down to set your fuel level at the bottom of the sight plug but you running out of the hole.  your idle mixture screws are located on either side of the carb and are usually gold at about 1/4 to 1/2 a turn out in most cases. so don’t start at 2 turns out.

one of the most critical  (and overlooked) though is after you set idle and timing, adjust your accelerator pump linkage(s). at idle position it shoul just kiss the pump cam lever and acc. pump lever below the float bowl. too lose and you will have a lag before you pump goes- too tight and you lose motion and not a full squirt into the engine also causing problems.

Carburetors #2: Rochester

well, like everyone else when i was in high school auto shop, some of the first carbs i was into were not by choice they were by necessity…..and they were the o so infamous quadrajet…I.E. quadrajunk carburetors. q-jet’s were not a bad carburetor for the most part. when they were right- they were damn near indestructable but when they fucked up….oh man what a piece a shit! and of course being that i went to high school in the early 90’s you can bet your ass i got to play with some of the E4M  electronic q-jet carbs when we had to make em work to get to school….ugh….and the dualjets….anyways i digress. this isn’t a tutorial on the history of the rochester carb division, just a bit on my knowledge of them.

lets start with the Q-jet. although they look the same for the most part over the years, they are all far from it. produced from the mid 60’s to the mid 80’s….and put on damn near every kind of gm car there was, when you run across one now you pretty much need to go by what the code is on the side of the main body to see what you exactly have. chevy and cadillac carbs had a side fuel  inlet to the right side of the engine/ BOP had a larger inlet the pointed straight out the front. as far as bolting up to the intake the carbs interchange- and the baseplate will also interchange with spreadbore carbs from holley. as far as exterior choke set ups they are all over the place. the cfm capacity was also all over the place from 500 to as much as 800cfm capacity from the factory and pretty much look identical on the outside.  most of the cfm capacity was dictated by the size of the rear barrels of the carb, the front barrels being the primary operating section of the carb and usually about 20-30% the size of the rear barrels. and most of the time you usually have to stand on the floorboard to open up the back barrels only to get a cloud of black smoke out the tailpipe. therefore when you miss on the cfm size like when you put a 750cfm off an olds on your SBC, it runs like a champ until you try to open up all 4 barrels.

the front barrels are  90% of a q-jets normal function. the float bowl sits at the front between the front barrels, directly behind the float,a vacuum operated metal power valve using metering rods  is located for main fuel metering.  the metering rods are forced into the center of the metering jets for the front barrels via vacuum. when engine load increases/vacuum decreases the rods pull out of the center of the jets allowing more fuel to enter the barrels. here now you can modify the q-jet for different applications with different size metering rods and jets….the jets are stamped with a number from the factory, as well as the metering rods. the air horn has to be removed to do this. it  is a real pain in the ass to remove the air horn compared to other carbs, it is not tuner friendly. ideally find the carb for your application to begin with and don’t fuck with it.

the rear barrels of the q-jet are very basic. simply 2 tubes hanging out  over two throttle blades and are fed by two jets at the bottom of the float bowl. the back barrels are openned through a progressive spring loaded linkage, usually start to open when the front barrels are damn near full open, and can be modified to open sooner in the rpm range with a bit of creativity. the primary metering device for the back barrels is the air valves located in the air horn directly behind the choke.  a vacuum canister usually hooked to the right front of the q-jet controls the rate at which the rear barrels take effect. this is resposible for the o-so -famous bogging sensation of the q-jet when you punch the throttle. a performance mod you can do to aid this is to drill the orifice in the vacuum can out a few drill bit sizes….or even let the rear air valves float freely without being hooked to the vacuum can at all.

the biggest problem with the q-jet in my book is the front throttle plate shafts. as they see almost all the work they wore out and got real sloppy in the base plate- which creates a vacuum leak that can come and go at any time and give you all kinds of shit like occassional detonation- backfire-hesitation-hanging throttle. back in the day there was no repair kit for this so we just cranked the idle mix screws out a bunch or partially wired the choke shut so we could get to school. also on the bottom of the float bowl supposedly the blocking plugs are prone to leak, but i never ran across one that did.

then of course there were the Q-jets which are referred to as the E4M carbs. basically they were an abortion. what it was is a failed attempt at making a carb work like fuel injection.  is in place of the vacuum controlled main metering valve it was an electric solenoid that pulsed the metering rods into the jets. the more often it pulsed the leaner it ran…the less frequent it pulsed the richer the mixture. this was, and is, know as pulse width. there are a throttle position sensor and an ignition control to the module in the distributor. modern fuel injection is based on the same principle of pulse width but it is much more efficient and solely relied on electronic injectors. these things were out of calibration and running like shit in lessthan 10,000 miles from the factory in some cases. they required a specialty tool for calibration called a sheppards staff if i remember right….and were damn near impossible to ever get right. your best bet was to usually hope the solenoid would short out and hope that the car didn’t smoke black.

another carb that i dealt with and still occasionally see is a dualjet rochester. it is basically a q-jet carb without the back barrels. variations of this were used from the late 70’s to the mid 80’s both with and without electronic bullshit. the non emmisions carbs were a pretty good carb, but the emissions carbs with the electronics were junk.

and then there is the very popular 2g and 2gv carbs. these are a very simple 2 barrel carb and also came in different calibrations and venturi sizes over the years for both big block and small block applications. there are no metering rods but a single metering valve in the bottom of the float bowl that was actuated by a separate vacuum actuated rod sticking into the float bowl from the air horn.  for the most part a very reliable carb and widely used in demo derby and street use. for all intensive purposes: not a good performance carb. to make serious power years ago they would use three of these things as a 6-pack to get enough cfm into the engine. now days you can get a large amount of cfm from a single 4 barrel so it becomes more of something for nostalgia than anything. if you are forced to use a stock carb for circle track or something like that, then there are places you can go to that will get the job done.  

these are the carbs that everyone claims to be a specialist so i will not elaborate but on a few things here:

– if you do not need a choke. make sure you plug the vacuum port of the base plate that draws hot air for the choke if you remove it.

-make sure the baseplate and throttle shaft are snug. also it seems that the throttle levers can losen.

-buy a rebuild kit from the referrence number on the side of the main body. this is what i do.  it will also show what it was originally for if you dig far enough.  you usually get the right gaskets as over the years the 2g did change slightly on some of the gaskets, but for the most part it didn’t change much, just enough to make it a pain.

–  only change jet sizes if you have a problem that nothing else can resolve. to make life easier you can drill and retap the jets to fit holley jets to make life easier.

Carburetor #1:Function Basics

well i haven’t written about this topic yet, so since i have time why not. most of my experience with carburetion is mostly for street/strip applications. i don’t really mess with a whole lot of carb’s for demo derby simply because so many people claim to be the cat’s ass at doing it….let em run with it. For the sake of arguement i am going to write according to performance oriented brands or styles: Holley, Rochester, and AFB/Carter/Edelbrock(which i will refer to as AFB for the rest of this as that was the original designation). i will probably write separate sections on each and my dealings with all of them.

The basic purposes of a carburetor are fuel atomization, air/fuel mixing, and air flow regulation, which all in turn govern engine speed and power output. in order for gasoline to burn properly in the cylinders/combustion chamber, it must be present in an atomized state and mixed with some amount of air. ideally for what most performance guys are going for, you would want 14.7 parts air to 1 part of fuel(as stated in other parts of the blog). obviously this is damn near impossible to accomplish in all driving condition. under heavy load/acceleration you would want more like a 11-12 to 1 ratio, and cruising or decelleration may yield 15-17 to 1 ratio’s of air to fuel. the carburetor must compensate as best as possible to most all driving conditions. have i lost you yet? stick with it i will get there…..

A carburetor basically has the job for atomizing the fuel going into the air intake charge of the engine as best as possible. it does this via carburetion with help of the venturi effect. for basic carburetion, think of how an old time perfume bottle works. as air passes over a tube, it draws liquid out  into an atomized state. to give you an even better idea you can try this experiment: take a glass full of water and stick a straw in it. then grab and air hose and hold it across the tip of the straw. it will draw the water out and spray it. it’s also the same principle as a paint gun. 

 the venturi effect is basically the same priciple they use for the cooling towers on a nuclear plant. it is basically a tube that narrows at the center and is referred to as a Venturi. at it’s narrowest point air flow will have a tendency to speed up creating a low pressure area with high air speed. by introducing fuel for carburetion at the narrow portion of the venturi for atomization, it is both drawn into the air stream  and atomized kind of like a double whammy. that is the basic principle of operation of a carburetor.  

Next we need a primary way of regulating engine speed. so we then put a throttle blade down the line to regulate engine speed  by controlling air/fuel amount entering the engine. you guys get the point  by now what is going on. if we had a governor and always wanted to run a constant speed(like most new push mowers)this would be pretty much all there is to the carb function. a fixed venturi and a throttle blade.  However, we aren’t going that direction and are from here on it going to talk about performance automotive carbs. we need to be able to vary the amount of fuel at different times for different driving conditions. this is where the carb starts to confound some people but really it isn’t that bad.  basically we are going to divide the carb into 5 main parts at this point: idle/low speed circuit, main metering circuit, choke, float bowl, and accelerator pump.

lets start with the main metering circuit as it is the one that does the bulk of the work.  obviously you have heard me talk about the venturi’s of the carb already. most carbs use 2 venturi’s. the first is the large outer venturi that makes up the bulk of the main body of the carburetor is there to simply regulate bulk air flow and usually. Air flow is measured  in cubic feet per minute of flow…..also known as CFM.  at wide open throttle the size of this venturi and the number of venturi’s(barrels) dictate air flow into the engine. if it is too large you will  lose performance overall as you will lose that low psi area i referred to earlier – too small and it will act like a restrictor plate. the CFM capacity of a carburetor must match the capacity of the engine for peak performance. i will get into that more toward the end.

the second venturi is a smaller venturi that hangs to the center of the first larger barrel. it is often referred to as a boost venturi and is where most of you fuel for operation flows through. if you are following along you probably figured out that by having two venturi’s you double that low psi effect for optimum atomization. fuel to the boost venturi is regulated by two things: Jet size and a main metering valve of some kind. the size of the jet regulates the amount of fuel entering the air charge going through the carb. it is the sole thing regulating fuel flow at wide open throttle: hence changing jet sizes at the race track.  however there is still a need to regulate this a bit  further based on engine load for average driving conditions. a metering valve with additional fuel flow regulation based off engine vacuum signal is also used. these are either done by use of something like a power valve or  metering rods.

next is the float circuit. it is basically like a toilet tank on the side of the carb. it’s job is to keep a small regulated amount of fuel on hand for all the circuits of the carb to draw on. there is a needle and seat valve inside the fuel inlet  of the car that is attached to a  float. the primary metering jets, metering valve, and accelerator pump all draw from this.

under sudden acceleration/movement of the throttle, the carb does not have enough time to shit fuel out of the main metering circuit to keep the car from stalling. to get around this we inject fuel via a small pump in the float bowl that shoots fuel directly into the large venturi area of the carb, and is referred to as an accelerator pump. this is usually adjustable via the linkage being manipulated somehow.

at idle or just off idle , we need minimal fuel and the throttle is almost completely closed. to create the same atomization, we introduce fuel at the edge of the throttle blades(point of peak vacuum at idle) which creates the same perfume bottle effect without the use of a venturi. the amount of fuel to this point varies as the idle point of the throttle blade can vary from one engine to the other, so the idle mixture is adjustable. to cite another section of the blog, your engine timing directly effects your idle mixture as it effects idle rpm and fuel demand. first timing-then idle rpm-then mess with the idle mixture screws.  just above the idle mixture ports are two small slots. these allow for a transition between main metering and idle mixture….and are hooked in with the idle mixture circuit.

and lastly when we have cold start conditions, an engine will need extra fuel to function until it reaches operating temperature. so we need to enrich overall mixture for a short time by”choking” the amount of air going into the engine, hence the blade on the top of the carb is called a choke. if a choke comes off too fast an engine can stall- if it sticks it will lack power and smoke black- run like shit. most of the bullshit that hangs to the outside of a carb is all related to the choke and cold run operation. in performance application we just rip it off and pump the accelerator quite a bit to make up for it so it will fire when you cold start.

now that you have some idea on how a carb works in about 5 paragraphs…LOL!….i will get into other things. for what most of the guys reading this blog are doing you pretty much have to fuck with 4critical adjustments: float level, jet size, metering  valves/springs and accelerator pump adjustment. these are all different per manufacturer. the overall most critical thing with a carburetor is have the right carb for the right job. this is where the 2g carbs work well for derby- and holley 4150’s work well for drag racing- and edelbrock carbs work great on the street rods.

ideally when buying a carb you want to have it at or just below the CFM capacity of the engine. this is done through use of a very simple formula that can be applied to most engine builds;

                          MAXIMUM  RPM X DISPLACEMENT

CFM= ————————————————-


so as an example if you run a 7000rpm set up with a 468 big block, you would need around 950cfm capacity carb. whereas with a 3000 stall 355 derby motor you would need more like 300 cfm carb, and would be a shining example of why the 2G carbs work well for derby use. always remember, you don’t make horsepower without feeding the horse.

Torque Converter Damage/ I.D. your converter

393394926well, one of my friends brought a tranny into my shop a few weeks back and i literally had to take a sledge hammer to it to get it out of the tranny. the whole center of the torque converter had dislodged and exploded the bearing. i actually watched him pull his car off the trailer at fall brawl and pull forward to lose all gears after 10 feet. not one of the best things in the world to witness as a transmission builder.

After going through the transmission it was obvious that the converter had ballooned- tearing itself apart internally and messing up the front pump assy. Ballooning is primarily caused by prolonged operation under excessive loading, very abrupt application of load, or operating a torque converter at very high RPM. the shape of the converter’s housing is caused to be physically distorted due to internal pressure and/or the stress imposed by centrifugal force. In drag racing, ballooning is something that high hp cars with a trans brake experience due to shock load of launch off the line. in derby, this happens when you slam shift with your foot on the throttle. in this case the guy got suck in a hole with a couple of imperials comming after him in his 74 buick…..can’t blame him!

in extreme conditions like a nitrous oxide set up with a trans brake, you would get a converter specifically made with what is called an anti-balooning plate, along with furnace brazing the internal fins. Basically the ballooning plate is a re-enforcement of the housing to help take the shock load. a lot of guys also refer to them as nitrous converters. However for most of us, Furnace brazing the internals of the converter alone is more than enough to strengthen up a converter- and reasonably priced.
as you will see in the pictures below, the balloon victim was a stock light duty converter. I took the converter over to my friends at Midwest converter and discovered a few things i didn’t know that are worth sharing. there are two different th400 13″ non lockup converters. look at the pictures side by side and you will see by the fin grooves of the first one they tilt to the left, and the other tilts to the right. light duty 400 converters….they called them V-6 converters have the fins tilted to the right at the edge and extremely light duty bearings internally. V-8 or heavy duty converters tilt to the left from the bottom up.


our friend with the 74 buick put in a weak converter from the get go. the sad thing is that he probably either bought it from a new parts supplier for cheap or pulled it out of a driver with a v-8. since the v-6 converters are pretty much worth nothing on core and cheap, they got used more often than not where they should not have been. And although a bit off topic i am under the impression that some of these cheap reman converters you get from your local cheapo parts house may be slightly ballooned from the get go. a dead giveaway that you are having a ballooning issue is the thing wobbles all over the place at idle, or a bad vibration. when a converter balloons it will not center between the pump and the center of the crankshaft.

393394925Here is a picture of the stator and front section (flex plate side) of the housing. as you can see all the fins absorbed damage, and the front support bearing is completely missing from the stator as it exploded and causes most of the damage to the fins. according to Dennis @ Midwest, what happened is the converter ballooned, caused the stator to dislodge and explode the bearing- which in turn caused all the fin damage. in a heavy duty/furnace brazed converter, these bearings are nearly double the size of this unit and all the fins ypou see are brazed in place not just crimped into the pieces that hold em together. the picture at the top of the page is of the snout side that faces the front pump. notice that the fins to the outside on both of the pics have the same effect like running your finger across radiator fins bending over the sheet metal. some of the fins are completely ripped out of place.

So what is the moral to the story……well there are several points here. A well built furnace brazed heavy duty converter is absolutely critical for demo derby. light duty, stock replacement, cheap reman, and used converters will take you out….and it will piss you off completely when it does. so no matter who builds your tranny, take caution if they want to sell you a converter that is not heavy duty. i use converters from Midwest, B&M, TCI,and Coan. Most all of them make a stock reman converter for around 75-100$ that is not furnace brazed. so don’t be mistaken that just cause it has a big name manufacture name on it that it is good to go. AND if you go to your local parts house you may indeed get just about anything for 75 bucks including the weak P.O.S that was described earlier in this post. food for thought good luck!