Monthly Archives: January 2010


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!!

Transmission Lines/ Cooler Loop Lines

one of the stupidest and unfortunately frequent failures and major source of burns is a transmission cooler line failure. how many times have you seen a cracked steel line, or better yet fuel line wrapped in duct tape or electrical tape!! also how many times have you put in the “aftermarket” derby hoses and fittings into your case and cracked the case….then told you tightened em too much. well we came up with something else.
381591038i use this on my test engine. basically these are aeroquip adapters and a signal loop line, the fittings are a part # FBM-2963 1/2-20 flare to -6AN fittings and i am using a -6AN metal braid line that has been pre made. not sure who made the line but they are available through summit racing on-line. you can even buy a short length of line and buy fittings to make the line yourself to whatever length you want. use steel fittings not aluminum for transmission lines. i am a big advocate for use of metal braid line for just about everything on a derby car. hydraulic lines get the job done just as well. i like this set up for a loop line simply because it’s durable and flexible so the tunnel of the car will not kink the steel line. obviously we know the fate of using rubber fuel line and hose clamps. never do that it’s fuel line….use it for fuel and vacuum. as stated in previous posts the fittings on a th350 and th400 are not a pipe thread they are a unique thread pattern from gm. you can get stuff close but to do it right you must use the original fittings w adapters.

I.D. your tranny according to oil pan shape

1 Aluminum Powerglide
2 TH200 (Metric), TH200C (Metric)
3 TH250, TH250C, TH350, TH350C, TH375B
4 TH375C, TH400, TH475, 3L80, 3L80HD
5 TH200-4R
6 TH700-R4, 4L60, 4L60E
7 4L80E

Th350 Lock-up /Non Lock-up

A lockup tranny basically is the short term used to describe a transmission with a locking clutch internally in the torque converter.

A non-lockup converter hydraulically locks at a certain rpm to create a drive source for the planetary gearset. together with gear reduction of different gears in the tranny, the converter provides an amount of torque multiplication to help get the car moving. it becomes unnecessary at highway speed for the converter to provide this added torque multiplication by slipping per say, but it still rotates a small amount under light load/cruising speeds. this eats away at your mileage

Iin the late 70’s is when we started seeing the first lock up clutch transmissions. it basically works just like a clutch in a manual transmission. At highway speed, usually around 45mph, the computer engaged the clutch in the torque converter to halt any and all excessive rotation of the converter to in effect create a solid drive source going to the tranny. obviously it can only be engaged at cruising speed cause if if didn’t ever release the engine would stall at the stoplight. also you need the added benefit of torque multiplication to get the car going. think of it this way…..a standard tranny has usually 5 speeds….an automatic for sake of arguement has 3. Since there is going to obviously be more of a gear/load jump the torque converter makes up the difference by creating torque multiplication. You can also start to realize how customizing how the converter is built and stall speed can really effect how your car performs can’t ya??

For derby use only, avoid running a transmission with a lock-up clutch. most of the time this clutch is already screwed up cause it came out of a car with years of abuse….especially something that was in around town a lot that cruised 45mph. the clutch dissintegrates and locks the torque converter up tighter than a crabs ass……and you’re dead in the water. even if you never engage the clutch it can still jam on ya as the tranny heats up.

When the Th350 first came out in the late 60’s, it is pretty obvious that they had planned on some kind of a lock-up clutch design in it’s future. In all there were 4 or 5 different versions of the th350. the the 250, 250c, 350, 350c, and 375B(somewhat rare). I believe the lock-up trannys started with gm in 1980 when the on-board computers came around, but i could be wrong. this line of transmissions underwent numerous changes every year of production. a dead giveaway you have a 250 or 250c is the output shaft is hollow….i avoid the 250 also because the clutch packs are pretty skimpy as it was a light duty tranny, along with a lousy gearset.

For derby use…..and for what i build the B-25 derby tranny’s out of, we want to use a non lock-up th350. Commonly they are longtail and have an input shaft that is fully splined to the end sticking out the front pump of the transmission. there are no electrical plugs in the case anywhere. Usually if it came out of a 70’s vintage tuna boat it’s a non-lockup.

700r4_establishing_bg A lock-up th350 transmission will look more like a 200R4 or 700R4. the input shaft sticking out of the front pump will resemble something like a manual transmission would have. instead of a fully splined input shaft there is a smooth arbor at the end of the shaft: narrower than the splines about 1/2″ long. this is the smooth arbor that engages the internal clutch of the lock-up converter. in addition, on the driver side toward the rear of the case there is a square electrical plug sticking out of the top of the case above the oil pan. if you find either of these things on a tranny, it’s a good bet you have a lock-up transmission. I have found that a lot of short shafts are prone to being lock-up trannys. now you can take the short shaft/tail housing out of a lock up tranny and put it in a non lock-up tranny, but other than that it is usually just easier to start with the right core to begin with. hope this helps.

Torque Converter Selection

One of the most overlooked and common failures of a derby transmission is the torque converter. quite often if you run a used converter, it is a crap shoot whether or not you get one that has some life left in it.

I always recommend running a new or rebuilt torque converter with any new transmission build. Stock converters are not furnace brazed and/or fully welded in most cases. when you beat on em hard, they will eventually come apart. A used converter in a new tranny can not only cross-contaminate the tranny with debris from the tranny that it came from, but if it does have internal damage it can create a frustrating overheating situation even though the fluid looked good when you pulled it from a working tranny.

i cannot tell you how many people called me completely pissed off that i fucked up their transmission, and come to find out they ran a bad converter….usually cause they got cheap shit. If you lean on a stock converter by slam-shifting, the stock tach welds(similar to how body seems are spot welded) usually bust apart. the stator sprag can also dissintegrate. when this happens you get the all too familiar,” i pulled onto the track and when the flag dropped nothing happened”…..” i have this noise comming from your tranny that sounds like bolts in a grinder even in park.” ……or,” My tranny lost all gears 10 minutes into the derby at the red flag , but when i gunned the engine and played with the shifter for a few minutes all my gears came back for the rest of the derby.” You pull the tranny and converter after the race and see nothing wrong with it…..hell fluid looks good you hear nothing rattling….stick a screwdriver down the neck and check the sprag it’s fine….but when you drain the fluid out of it finally you can hear a sound like wing nuts in an empty beer can.

The stall speed of the converter you chose mainly has to reflect the engine you put it behind….I.E the camshaft profile. if you run a common low hp/high torque derby built engine, your best choice is a 13″ truck converter with a stock or low stall. low stall creates less heat as compared to a high stall converter,plus you take full advantage of all the low end torque and 6-8 qts of fluid capacity!! Truck converters are usually heavier built to take abuse from towing/hauling and are easily idetified by 6 torque converter bolts to the flywheel.

Now if you are running a more radical camshaft that idles up over 1000rpm and has a higher rpm band, then of course you have no choice but to run a stall converter. For drag racing, the 11″ and smaller powerglide style converters accell for this application as it is smaller and creates less drag on the engine, creates a lock-up at a higher rpm to give you a good launch, and heat is a non-issue as you are only running for a short period of time.

Whether or not it’s for derby, drag racing, or heavy street……buy a quality converter if you can afford it. The guys at Coan engineering really have their shit together as far as converters go and can build pretty much whatever you want. A cheaper alternative to a Coan for derby applications is a Midwest Converter. affordable and well built for the price for low hp applications. B&M and TCI converters work well for the street/strip if you don’t buy the cheap line- you want a better furnace brazed converter like a holeshot B&M rather than a Tork Master as an example . I recommend having somekind of heavy duty converter for derby use. i have not had very much luck with the cheap light duty stock replacement car converters. As i stated earlier in this post, a cheap and easy solution it to run a 6 bolt truck torque converter, even though not all truck converters may be brazed/welded internally they seem to hold up better over a cheap 60-80$ replacement.

for you guys that run the ultrabell, you are pretty much stuck with a custom 11″ converter. For derby use Punisher and I have been trying out some built by Midwest performance made from a powerglide core with a turbo spline adapted internally to fit the th350-th400, and have them stall it as low as possible. with a 4.56 gear the poweglide custom converters seem to lock up around 1500rpm but they are intended to stall around 2000.

and finally….all th400 13″ converters are non-lockup converters. Th350 converters are 12″ factory and come both lock-up and non lock-up converters. 11″ converters came in powerglides originally, and are non-lockup. 11″, 12″, and 13″ non lockup torque converters all interchange and fit both the th400 and th350 non-lockup trannys. a lock-up clutch th350 DOES NOT interchange with anything else. A LOCK UP CLUTCH CONVERTER OUT OF A LOCK UP TH350, 200R4, 700R4, 4L60, or 4L80 WILL NOT FIT A TH400 OR TH350 NON LOCK-UP.

J.W. Bell Housing

374721910Well, when the bell housing breaks or you want to go with a sturdier upgrade to your transmission the ultrabell from jw performance or coan engineering is an excellent option. Installation is pretty straight forward you saw off the bell housing and remove enough material to bolt the ultrabell flush to the face of the front pump of the transmission. i use a sawzall to rough cut most of the bell housing off, then a cut off wheel on the angle grinder and a flap-wheel style grinding disc to polish edges of the aluminum to final fit the ultrabell to the pump/case.

On the th350 there isn’t much more to it then that, but the th400 did not always have 8 pump bolts cast into the transmission housing. most of your older 70’s vintage case had all 8 bosses under the front pump even if only 6 bolts are showing. quite often you can drill the extra 2 bolt holes in the pump itself through the backside of the pump. however your 80 & newer chevy th400’s only were cast with 6 pump bosses. you must have all 8 bolt bosses to make it work. you MUST use the bolts provided with the bell housing kit. they are hardened grade 8 and a special length.374721907

The advantage to the ultrabell is that it will not snap from torsional stresses of forward/reverse shifting. This same action also breaks the bell housing in snow plow trucks for the same reason. In normal installation, it WILL NOT make the tranny stronger in reguards to vertical stress from a distributor protector or anything else as the car bends upward. The housing can simply rip off the front pump if it gets pinched in a lateral direction. I am currently working on some improvements to keep this from happening, but it’s top secret right now…
the bell housing is meant for drag racing, and is intended to run an 11″ torque converter. you can make a 12″ converter fit with some machining. for derby i prefer to have a custom built low stall 11″ built so the engine starts to pull around 1100-1300 rpm.