Category Archives: Engine Tuning - Page 2

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.

is 2.5 hrs run time on 6 gallons of gas possible

so, i read something on the internet about this. i was busy over the weekend and now cannot find the exact article, but i believe the claim was that the guy running at the end of the feature heat of a demolition derby  had 4 gallons of gas left in the tank after running 2 1/2 hrs in a feature event. The rules clearly state a 10 gallon fuel tank capacity. Many people have made the statement that this is clearly not right. So i decided to crunch a few number.

so lets start with the obvious we have the following variables:

6 gallons of gas consumed, which by weight can vary a bit with fuel quality,but a good average for the weight of pump gas is 6lbs per gallon, and there are 16 oz in 1lbs.
6 gal X 6lbs X 16oz = 576 oz of fuel consummed

the modern gasoline engines burn at a ratio of 14 parts air to 1 part of fuel. actually true stoichiometric mix ideally is 14.7:1 but it usually ends up being 14:1.

so basically we just need to plug and convert the figures. Air/fuel ratio, or AFR for short, is determined by the weight of air divided by the weight of fuel.
AFR= Mass of air / Mass of fuel

or to get what we are looking for

mass of fuel X AFR = mass of air used

576 oz X 14 = 8064 oz of air

the CRC book of chemistry defines air as 1.2 oz per cubic foot. there are many other variables that effect the actual weight, measured using a barometer commonly, as well as relative humidity, but for the end result in this case, it is not going to effect it as much as you think.

8064 oz of air / 1.2 per cubic ft =6720 cubic feet

now 2.5 hrs= 150 minutes

which then means the said car was consumming a whopping 45 CFM.

do i believe this is possible to do with a V-8 chevy, yes, at idle. honestly this is an average cfm for a given time frame so obviously at times we can have full throttle and dead idle situations.

One thing to keep in mind is at 14:1 AFR, that is IDEAL conditions to get that ratio. this is why auto makers use electronic fuel injection, and sensors like the mass air flow sensors and throttle position sensor to bring an element of precision to the metering process to the induction process that simply cannot be achieved with a carburetor- let alone a carb in a demo derby. Relative air weight is probably less in the midwest  than the figure i used as i believe the 1.2 oz number uses sea level. I believe it is a pointless arguement cause it is obvious that the numbers are so far off from making any kind of  real power worth bragging about is ridiculous.

so then lets go 10 gallon at 1 1/2hr. to spare you all the bullshit, it works out on paper to an average of 125cfm. this is a lot more believable number using a SBC with a 350cfm carb geared rear axle, and smart driving, for derby use in a 5-6000lb. station wagon.

you don’t make horsepower without feeding the horse. it’s that simple. so don’t let anyone bullshit ya!!!

Ignition wires/ Spark plugs

a very overlooked part of your engine is your ignition wires. Most people….and i have been guilty of this myself in the past…change the plugs, cap, and rotor but re-use old plug wires. if you are taking the time to change your plugs- change your wires don’t scrounge around the garage of find a dead motor in a corner of the barn to rob a plug wire, and have extra wires on hand for when you go to the track.

a hard lesson learned goes back to my buddy dave’s vega drag car. he had a set of crane ignition wires on his engine and had no problems for the first 2 years. well, after several drivetrain changes they kept running into inconsistent times at the track. they tried carbs-ignition boxes-distributors… one point they even tore down an engine i had built claiming i didn’t install the heads right……still had a problem. finally after several months someone walked over to the trailer one day at the track with a set of new wires and it was like night and day. they kept checking the wires for resistance and they checked fine….but never realized that constantly changing around the engine compartment had loosened the plug wire ends at the cap and was spark-arcing under hard accelleration along with cutting out spark. This is WAY too common around the pits at a demo derby. i see old wires that are duct taped, electrical taped, wadded together, and hell even cut wires while they are tuning a carb!!!

on a stock application a good set of wires should go 80-100,000 miles these days. for performance you need a good 8mm plug wire or bigger with sturdy ends at the plugs cause you will be pulling plugs a lot to read them. i will get into that later. i run and prefer Taylor spiro-pro 8mm wires. they are well built, easy to install, easy to use, and dress up an engine nice. the ends for the plugs are well built. MSD wires aren’t bad either. i avoid 7mm wires for performance. 9-10mm wires, as well as solid core wires, are usually overkill unless you have a magneto or something radical for an ignition system. you want a resistor core wire for an HEI style ignition. solid core wires can do funky things to the electronic ignition sometimes. not sure why.

I prefer buying the universal wire kits and make them to the lengths i want. By doing this you can route them nicely through looms to keep the wires from touching…..which is always a good idea…..and make it look nice. On a derby engine since you don’t have ends on yet you can route your wires through plastic wire loom, heater hose, or even hard tubing to protect the wires. it also makes it easier to route the wires around/under the header stacks without having the inevitable short wire that usually ends up burned off on a pipe.

Reading spark plugs is not something i am very good at but a necessary evil to see if the carb tuning is in the ballpark. Depending on the type of fuel you run it can be different from one engine to the next. Chosing the heat range of the plugs to run is also something to take into account when running alternative fuels or nitrous oxide as well. For street and derby application i start with a stock replacement spark plug and seek out a different heat range plug if i notice the electrodes are burning up and cooking the plugs….and it’s not something you have to deal with much outside of hardcore race engines. I hardly ever mess with it. If you are in the Zone of tuning, Cheap gas will have a white electrode, cam 2 will be an off purplish white color not ghost white. I always would play with timing and carb jetting/tuning before playing with heat range on the plugs. you want the plugs to run warm and clean, but not so hot they melt and crack. starting off or going to too cold of a plug can cause fouling issues and lack of performance. Also read your plugs after you have made a few runs and your engine is up to temp and ran UNDER LOAD. on a derby car, if you wanted to worry about it, you would beat on it for 10 minutes in the bean field.

I am a big fan of NGK V-Power spark plugs for just about everything. i seem to get the best compromise of longevity and performance for me personally. Platinum plug to me are usually overpriced for what you get. as a rule of thumb though i was taught that you use AC Delco for GM products, Motorcraft or Autolite for Ford stuff, and Champion plugs for a Mopar engine. This is a good rule of thumb and works. i am not a fan of Bosch plugs they suck for the most part.


ok i just read some stuff on-line about how to set an ignition system and set timing, so here are my opinions and techniques based on my experience and training. for arguement sake we will just refer to the GM HEI coil-in-cap distributors, but the same can be applied to an older ford duraspark or older CEI chrysler ignition systems(not lean burn they are junk).

Anyways, lets start with the coil. your ignition coil is what power’s the spark and does most of the work. It’s basically a transformer that has been modified to convert low voltage/ high amperage to high voltage/low amperage electrical current in order to just the gap at the spark plug(resistance/ohms). it contains two windings internally, a primary winding and a secondary. the primary winding is made of many small windings while the secondary winding is a larger winding with fewer coils. the primary is provided 12 volts to charge up. The primary circuit is then broken and reconnected rapidy via the distributor. this induces a high voltage in the secondary which follows the path to ground across the spark plug gap. obviously now we have to charge and break the primary electrical circuit rapidly for each cylinder- this is where your distributor comes in play. it’s job is to trigger the coil at the right time, distribute the spark, and alter the timing at which the coil fires according to engine load and rpm.

Older distributors did this pretty straight forward, they simply had a set of points based off 8 bumps on a cam(for a V-8) which openned and closed the primary circuit to the coil. the amount of charge time is referred to as dwell, and by varying your gap at the ignition points you effect the quality of spark and performance. these were fine but considered a high maintenance item. back in the day you were doing good to get 10,000 miles before needing a tune up.

In the early 70’s we saw the introduction of electronic ignition, which held your dwell time consistent without need for maintenance, as well as creating a more powerful spark. all of the big 3 did it differently but they all work on the same principles. HEI works via a pick up coil, reluctor wheel, and ignition module. The pick-up and reluctor create together make what is called a Hall Effect. This is used to trigger the spark. The hall effect is a slight voltage signal which is induced in a coil of wire as a magnet is passed infront of it. It works pretty much off the same principle as a magneto. On a GM HEI the pick-up is the piece with 8 points on it below the rotor in the same place as a set of points. you will also see the 8 pointed star on the dist shaft- this is the reluctor which replaces the cam. as the reluctor spins past the 8 points of the pick-up it induces a voltage signal 8 times per revolution. on a V-6 it would be only 6 points…get it?
This signal is sent to an ignition module which when takes battery voltage and dictates to the coil when to fire. on modern fuel injection systems the hall effect is still used in much the same way but usually uses crankshaft position as referrence and the on board computer dictates coil firing, along with fuel injection timing. now it is not hard to understand how having multiple ignition coils and shorter plug wires on modern engines to share the load and deliver a high quality spark is a no brainer on an electronic injection set up ….but i digress that is another arguement.

We have established how the distributor gets the spark going , but how does it alter it to make the engine run fine under all load/throttle positions. well, on most 79 and older electronic ignitions there are two advance circuits, a mechanical advance and a vacuum advance. after 1980 as computer controls were incorporated into vehicles the ignition modules were partially controlled by the computer and….it is a cluster fuck. for performance – again we are dealing with 79- older GM HEI distributors as well as aftermarket performance distributors which omit computer control of the ignition module.

Advancing or retarding timing by the distributor is done by altering the location of the pick-up coil or rotor in the distributor in relation to engine position- and we all know that we time an engine in relation to top dead center(TDC) of number 1 piston. the advance circuits work identical to how the governor and vacuum modulator work on a transmission. mechanical advance=governor/ vacuum modulator=vacuum advance. mechanical advance increase timing in relation to engine speed whereas the vacuum advance increases timing in relation to engine load.

Mechanical advance consists of two small flyweights under the dist. rotor held in by spring tension(2 small springs). as the speed of the engine increases the weights fly out and change the rotor position in relation to the dist cap terminals advancing timing. the amount of advance you get and at what rpm is referred to as advance curve. mechanical advance is altered by changing around weights and springs using aftermarket parts. this timing is a fixed timing once it is set up- it will only change with engine rpm. so once you get it where you want it, that’s where it’s at.

Vacuum advance is a low rpm load sensative advance for part throttle conditions and is hooked to the pick-up coil. A vacuum advance is suppose to be ported vacuum off the carb and gets no vacuum signal at idle. on some stock applications they also put in a vacuum heat switch to block off vacuum to the distributor until the engine reached operating temperature. just off idle, the engine vacuum is high and the canister of the vacuum advance will fully advance- full advance hovers around 52 deg before TDC. as you go to wide open throttle the vacuum advance has no effect cause it is dissengaging from lack of vacuum signal. if it did not your engine would detonate. upon decelleration the advance fully applies but does not detonate the engine as it is a no load condition. as the throttle opens up to compensate for heavy load-vacuum decreases. the vacuum advance does nothing during wide open throttle(WOT)or idle, and does very little above 2000 rpm other than save on gas. the primary job of the vacuum advance here again is to improve mileage and low rpm performance.

Base timing is set by simply unhooking the vacuum advance and using a timing light at idle. the mechanical advance is uneffected at it is not at a high rpm it is at idle. Stock application for timing on a chevy can vary between 4-12 degrees. i like to set base timing using and adjustable timing light so all i have to do is find the 0 deg TDC mark on the timing cover.

In all out drag racing/ serious performance application both the mechanical and vacuum advance are bypasses as they are unnecessary in most cases….or custom taylored with aftermarket ignition boxes. we then set base timing using an adjustable timing light. base timing of 28-35 deg is not uncommon. but here again these engines idle over 1100rpm.

For street performance, i like to run a full vacuum/mechanical advance but may taylor the mechanical advance to come into full timing at the point the powerband on my camshaft/engine hits……and now you can also follow how the right torque converter comes into play as well. everything has to work together and it mostly revolves around the cam you got. overlooking your ignition advance curves on a performance engine is like shooting yourself in the foot. it’s easy horsepower you just have to find it for your application.

For demo derby i prefer omitting the vacuum advance all together. Your not out for a sunday drive and usually it gets in the way of the distributor protector. i simply weld the actuating rod to the vacuum advance and cut the canister off. this keeps the pickup from flopping around. you can simply leave it unhooked as well. i then taylor the mechanical advance to the cam in the engine. i typically set base timing at 15-18 deg and may have a mechanical advance from 28-35 deg. on some engines, i set the distributor by setting it at final advance. i do this simply because the springs i use in some engines on the mechanical advance may vary the ignition timing at idle…….final timing is set by rev’n the engine to high rpm then adjusting the timing light and turning the distributor to set my final advance to where i want it. by doing this the mechanical advance has maxed out and your setting max timing.

if you unplug you vacuum advance and the engine stalls, chances are your base timing is messed up and the carb is jacked. by not having the correct base timing you are putting a halloween mask on the real problem and even though you may get it to work good enough to get around the block- in a derby or anywhere else it will rear it’s ugly head at the worst possible time. an engine should run properly at idle without any vacuum advance.

aftermarket ignition boxes like an MSD or mallory box come in all varietys and price ranges. basically they wire into the system in place of the stock ignition module and can alter just about everything to do with the ignition. i like MSD ignition coils and abuse them, other then that i have had a lot of problems with aftermarket ignition modules that fit in the distributor and either use the stock module or wire in an ignition box. i have ran both MSD and Mallory products as far as they go and they both have their plus and minus.

never weld on a distributor without removing the ignition module. as a matter a fact don’t weld anywhere on an engine without unplugging the ign module. even though the battery ios unhooked for some damn reason the current from the welder will find it and screw it all up!!

SBC Chevy Block casting numbers

Casting # Years
made Size HP levels
used for Notes
3703524 55 265 N/A Passenger
First 6 mos. used mech. cam not hyd.
3720991 56 – 57 265 N/A Truck/Pass
3731548 57 283 N/A N/A
3737739 58 – 61 283 220-290 2-Bolt mains/Truck/Pass
3849852 58 – 64 283 220-315 2-Bolt mains/Truck/Pass
3864812 62 – 64 283 230-315 2-Bolt mains/Truck/Pass
3959512 62 – 63 327 250 2-Bolt mains
62 – 64 327 250 2-Bolt mains
3858174 62 – 67 350, 327 & 302 210-350 2-Bolt mains/Truck/Pass
3782870 62 – 67 327 250-375 2-Bolt mains/Truck/Pass
3858180 62 – 67 327 250-375 2-Bolt mains/Truck/Pass
3791362 65 – 67 327 N/A 2-Bolt mains/Chevy II
64 – 67 350, 327 & 302 210-350 2-Bolt mains
65 – 67 283 N/A Truck/Pass
389257 67 – 69 302 N/A 2-Bolt mains
67 Small Journal (327 block)
68-69 Large Journal (350 block)
68 – 73 307 N/A Truck/Pass
3956632 69 307 200 2-bolt mains
3914660 68 327 210-275 2-bolt mains
68 – 69 327 210-300 2-Bolt mains
Corvette/Camaro/Hi PO
3914678 68 – 79 350, 327 &: 302 210-350 2-Bolt mains
68 – 76 350 210-300 2-bolt mains
3970014 68 – 79 350 200-255 2&4-Bolt main
68 – 79 350 & 302 250-300 4 bolt mains
Truck/Hi Perf
3970010 68 – 79 350 & 327 145-375 2&4-Bolt mains/Truck/Hi Perf
3932388 69 350 300 4-bolt mains
3951511 70 – 73 400 255-265 4 Bolt mains/HD Truck/Pass
330817 70 – 80 400 150-180 2-Bolt mains
360851 74 – 76 262 N/A Monza
74 – 76 400 150-265 2 Bolt Mains
++High Nickel Block
78 – 79 305 N/A Lt. Truck/Pass
14016379 78 – 79 350 N/A Lt.Truck/Pass
366245* 78 – 79 350 NA 4-Bolt mains
*Bowtie High Tin
Dipstick in Pan
79 – 82 267 N/A Passenger
80 – 84 305 N/A Lt. Truck/Pass
14010209 80 – 85 350 205 & up 2&4-Bolt mains
Passenger cars
14011064* 82 – 86 350 NA 4-Bolt mains/*Bowtie High Tin
14316379 86 – 88 350 205 & up 2&4-Bolt mains
1 piece rear main seal.