Toymods Car Club Inc: Tech & Conversions => 1jz boost, stall, gearing

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Chris Davey
Forums Junkie

Location:
sunny coast, qld
Registered:
October 2002

1jz boost, stall, gearing	Thu, 29 September 2005 03:56

I have just checked my datalog from my last run at the drag strip and at 3500rpm there is absolutely no boost being produced. At 4200rpm there is around 1.5psi. Full boost isn't achieved until around 5800rpm. That is only in first gear though. From a roll in 2nd it will making a little positive boost from around 3000rpm full boost around 4100rpm. I think this is because of the diff ratio which is actually 4.875:1 not 4.6 as I think I may have written. I will be changing to 4.625:1 though ASAP. It seems as though there isn't enough load on the engine in 1st to make the turbo spool as it does in 2nd or 3rd. On the gear changes, the revs drop to 5200rpm. So from my understanding as long as the stall is lower than that then it shouldn't boil the trans fluid. Have been advised that there is little difference in efficiency between a 3500rpm and a 4200rpm stall? That is at part throttle driving. I have had conflicting information given to me. I rang accelerator high stall and he recommend me an 8” non lockup converter that is 4500rpm and should stall to 3800rpm on the foot brake. Then I rang Phil and TCE torque converters and he basically said that my turbo is too big and the diff is too short and 1st gear is too short. Turbo is HKS ta45s rated at 650hp .9turbine, .72 compressor, 65mm compressor wheel. Diff is currently 4.875:1 Mitsubishi diff. I can change to 4.625:1 but that is as tall as you can get. 1st gear in the auto is 2.831:1 whereas regular 3 speed autos are 2.3:1. So I had the idea of taking off in second as it is 1.5:1 and with the shorter diff would make it very close to a powerglide with 4.11’s but Mike from MV said that this will fry the box very quickly. I knew that the weak point is the 1-2 change but didn’t think it would be too bad starting off in second. He also said that a 4500rpm stall would be way too big and most guys use around 2800rpm. (Which I don’t think will be enough) He also said that it is most likely a gearing issue. I am also going from 25.5” tall tyres to 27.6” tall tyres to assist in taller gearing and hopefully more load on the engine. (Plus not having to change to OD at the end of the quarter) So does anyone have any suggestions? I am a bit stumped as to what I should do from here? [Report message to a moderator]

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