th400 help
04-29-2012, 06:52 PM
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th400 help ok gonn try to put the setup in as best I can:
99 trans am
408 prc 225s fast 102 direct port progressive. stand alone fuel system
th400 w/ yank convertor
moser 9 in 4.11 gear
3300 lbs
runs 6.1XX with 1.4 60 ft
heres the question: the car slows down the nitrous as we speed up the nitrous. on the dyno the graph climbs strong until it falls off well before the motor should quit pulling
the convertor data logs to be right. rear end is new. convertor is new and have been through 3 thinking it was the problem. motor is new and air fuel is dang near perfect all the way through. the only thing we are unsure of is the tranny. it was built by a local guy and chared 3000 for the swap. tranny parts and labor. is the transmission the problem? can a th400 swap be done to hold 1200hp for that money? could thramission slip be to blame? help!!!!
99 trans am
408 prc 225s fast 102 direct port progressive. stand alone fuel system
th400 w/ yank convertor
moser 9 in 4.11 gear
3300 lbs
runs 6.1XX with 1.4 60 ft
heres the question: the car slows down the nitrous as we speed up the nitrous. on the dyno the graph climbs strong until it falls off well before the motor should quit pulling
the convertor data logs to be right. rear end is new. convertor is new and have been through 3 thinking it was the problem. motor is new and air fuel is dang near perfect all the way through. the only thing we are unsure of is the tranny. it was built by a local guy and chared 3000 for the swap. tranny parts and labor. is the transmission the problem? can a th400 swap be done to hold 1200hp for that money? could thramission slip be to blame? help!!!!
04-29-2012, 08:02 PM
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can it be done..... maybe to be honest not likely but never know, depends on labor rate, and how over built he did it, and did he buy the converter...
but your real problem, the car slows down as you ramp up the nitrous is usually converter will cavitate as soon as you hit the nitrous. Remember stall of a converter is torque dependent, so when you hit the nitrous it wants to "wash out" meaning it becomes harder to couple. When you say the data logs seem to be right, what do you mean? what you should see is the driveshaft rpm and engine rpm should be as close to the same as possible when you cross the stripe. When you hit each stage you'll see the engine rpm will rise faster than driveshaft then it'll try to catch up again. unless you have an input shaft and output shaft/ d shaft couter you wont be able to decifer if the slip is in the trans or the coverter (unless you wanna take a guess or open both up).
If it slows down and there is less than 10% difference in engine rpm and d-shaft then its more likely a traction issue. On our car we always look for sharp changes in the driveshaft or if you have an accelerameter (g meter) look for any sudden rpm changes or the g forces to fall then pick back up again. because think there is no reason that a drive shaft should either speed up or slow down instantaneous unless it is slipping then gripping or if the tires are cutting loose.
but your real problem, the car slows down as you ramp up the nitrous is usually converter will cavitate as soon as you hit the nitrous. Remember stall of a converter is torque dependent, so when you hit the nitrous it wants to "wash out" meaning it becomes harder to couple. When you say the data logs seem to be right, what do you mean? what you should see is the driveshaft rpm and engine rpm should be as close to the same as possible when you cross the stripe. When you hit each stage you'll see the engine rpm will rise faster than driveshaft then it'll try to catch up again. unless you have an input shaft and output shaft/ d shaft couter you wont be able to decifer if the slip is in the trans or the coverter (unless you wanna take a guess or open both up).
If it slows down and there is less than 10% difference in engine rpm and d-shaft then its more likely a traction issue. On our car we always look for sharp changes in the driveshaft or if you have an accelerameter (g meter) look for any sudden rpm changes or the g forces to fall then pick back up again. because think there is no reason that a drive shaft should either speed up or slow down instantaneous unless it is slipping then gripping or if the tires are cutting loose.
04-30-2012, 05:41 AM
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Yeah he bought the converter but not the yank. 3 grand meant dropping the car off with a t 56 and picking it up with the 400. He put a spragless converter in what was then a street car. Track car now. According to yank the the rpms were supposed to fall a certain amount with every gear change and that data logs right.
04-30-2012, 06:20 AM
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I'm not sure but as well as I remember the ramp time is around a half second. In any case before the 60ft it full go for the whole run and jetted for a 300. Ill see if I can get whole of a Dyno sheet and put it up. Maybe a et slip or two from this weekend. Thanks for the insite so far by the way....
