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.

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