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6G Celicas Forums _ Forced Induction _ Why is that boost different in lower gears vs higher gears?

Posted by: ILoveMySilly97 Apr 29, 2016 - 12:48 PM

Just swapped in a 3sgte gen4 into my 97 GT. I was looking around to find the stock boost. I read we get peak boost at 14 psi in 3rd gear and up. But 7-8 psi in the 1st and 2nd gear.

Also why's it that it's different boost in the gears? What controls it or is it safe to make a mod to get even boost through the gears? I'm guessing that's what a boost controller is for?

Sorry for the rookie questions.

Posted by: richee3 Apr 29, 2016 - 1:34 PM

Longer gears make the engine work harder which spools the turbo more. My Supra, for instance, isn't fantastic in first gear but hauls ass in fourth.

Posted by: 98celi Apr 29, 2016 - 1:52 PM

QUOTE (ILoveMySilly97 @ Apr 29, 2016 - 1:48 PM) *
Just swapped in a 3sgte gen4 into my 97 GT. I was looking around to find the stock boost. I read we get peak boost at 14 psi in 3rd gear and up. But 7-8 psi in the 1st and 2nd gear.

Also why's it that it's different boost in the gears? What controls it or is it safe to make a mod to get even boost through the gears? I'm guessing that's what a boost controller is for?

Sorry for the rookie questions.

Trying to create even boost in all gears will destroy traction. Even with a dual clutch or in newer cases, a CVT still don't get consistent boost pressures. There's also external load contributors like road angle and wind resistance that you can only do so much about. Building on richees response. Turbo boost is based on the engines power band. The turbo won't spool up near as much in first because the duration is so short. 3rd gear is usually the best spool gear because the power band is long enough to feel full boost but short enough to feel the transmission torque. 4th gear output runs 1to1 with the engine (usually) so the transmission is less aggressive and the boost won't spool as fast.

Posted by: Box Apr 29, 2016 - 3:07 PM

Yup all about that engine load.

Posted by: ILoveMySilly97 Apr 29, 2016 - 3:38 PM

Aaaahhhh....I figure it was because of the engine load and duration. So when someone says "im boosting 14psi" that just means that's the highest boost their waste gate is set to then. So the gen4 is stock at 14psi.

Posted by: Batman722 Apr 29, 2016 - 8:10 PM

Did you disable the TVSV ? That sounds like your problem.
http://www.mr2oc.com/61-3sgte-turbo/369593-tvsv-location.html

Having the tvsv hooked up will restrict boost in the lower gears. Easy mod.

Posted by: Smaay May 3, 2016 - 8:45 AM

In amy's car, i removed all that crap. I have a single reference line from the turbo to the wastegate. I get about 15psi.

Posted by: texasnick Aug 30, 2016 - 2:32 PM

QUOTE (Batman722 @ Apr 29, 2016 - 9:10 PM) *
Did you disable the TVSV ? That sounds like your problem.
http://www.mr2oc.com/61-3sgte-turbo/369593-tvsv-location.html

Having the tvsv hooked up will restrict boost in the lower gears. Easy mod.


This is the reason why with everything stock, boost in 1st and 2nd is limited. It is controlled by the TVSV.

You will boost higher in higher gears due to the higher loading in higher gears, but the reason you are reading that there is a difference is due to the TVSV.

I have a bolt-on st205 and boost in 1st and 2nd is around 10 psi, 13 psi in 3-5.

Nick

Posted by: malpaso Aug 31, 2016 - 2:24 AM

Exactly as Dustin said. Bypass TVSV is the key. I did the same on my car 😊

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