sup guys, just finished up my 5sfte project. im in the middle of tuning right now and i stumbled on a small issue. im sure its something minor. but whats happening is that my turbo kicks in at 4k rpm and its only boosting around 3psi max lol



its feels great though. since i work all day and only rest on weekends its hard for me to diagnose at the time because by the time i get out of work its dark...
anyway im thinking it might be that i have too much free play on the wastegate actuator arm or a leak somewhere.

do you guys know what else it might be? would back pressure affect it? i ask because my down pipe is a 2.5" and drops down to a 2" to my stock exhaust

this is my first turbo project and its been a blast..... so help me guys! lol

specs on car:


94 gt
2.2 rebuilt
ported and polished
460cc injectors
Safc2
t3t4 external wastegate turbo 7psi spring
fairly large intercooler with 2.5 piping

2" exhaust is a bit of a restriction, but not kicking in till 4K is a larger issue.

hummm possible boost leak? i need to double check all my piping.... im assuming the turbo should kick in high 2k's or low 3k's rpms right?

thats about right with your turbo. maybe a little sooner.

Turns out i had too much play on my wastegate actuator.. Tightened it a bit more, now im boosting a good 8psi. Im tunning on that right now. Hopefully by next week I will be running a little more... Sweet!

yeah that will make a difference. also if you wanted to make a little more boost. put a washer behind the wastegate mount to make the actuator need more boost to open. a single washer will get you about 3 more psi

Cool, thanks for the tip. How thick though 1/8" or so? 12 psi on the t3t4 should be safe to run right? How many are you running on your celica and on what turbo?

start with a 1/16th you dont want to make a huge jump in boost. i think i ran my turbo about 10psi. the pistons are the weak link in the engine

The piston ringlands break long before the rods complain about power, if I'm not mistaken.

^^^ yep thats what i was saying

Thanks guys, I hear detonation is a b....im gona stay around 10-12psi max...if it blows then im goin forged next time lol

you could buy the engine that i rebuilt a few years ago. it probably only got 5000 miles on it.

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Detonation is not directly related with how much boost you're running really... just make sure you have a good fuel system (good, strong pump, big enough injectors, etc.) and don't use a SAFC if you're up above 8psi.. you need something that can modify fuel without messing with your timing, and even moreso, you need something to retard timing.

P.S. As long as your turbo is efficient where you want to run it, you have good enough fuel system and correct timing, you won't have any detonation.

This post has been edited by Syaoran: Mar 22, 2012 - 1:54 PM

Well I set my timing at 8 degrees. Wen im at full boost (8psi right now) the safc is set at -12% on high map. so im guessing timing is not advancing much, but I could be wrong.... I have a walbro 255 and 460 injectors. So far so good, im not seeing knock or hearing any funny noises. Im not finished tuning yet. Right now im staying on rich side 11.2 afr's at wot, im taking small steps up. Eventually I want to hit 11.9 afr im also putting together my water/meth kit for added protection :]

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There are too many variables for me to say for sure what it is, I dislike guessing. I'd also prefer not sending you on wild goose-chases if you get my drift.
There are a number of things, that come to mind from reading post X, Y or Z here.

1. Sounds as thou you are suffering from some restriction, it could possibly be a small vaccume leak or that the waste-gate is lose or the spring rate etc -

2. Depends on the specifications of a turbo-charger, T3/T4's come in a number of specifications. It would help to clearify A/R trim and inducer / exducer sizes are
housing inlet and outlet.

3. I don't know the complete layout of your exhaust system from the turbo-manifold back. If you are using the factory catalitic converter this could contribute to
partial restriction. However, most use a 2.5 ~ 2.8 all the way back, some use a tride and true 3 inch. A high flow catalist and 2.5 to 2.8 inch full length should is an aprox average.
( If you have a manual boost controller, set it back to a lowest setting ) when you free up the exhaust system ie reduce back pressure, you will flow more thus create more boost, thus this is why the waste gate is very important in controlling. A lot of guys have a restrictive system, and so they increase the boost achieve the desired boost level thru the power band, this is due partly because pressures increase as rpm increases.

I'll write a general article in the forced induction section look for it, should be a new post.

Regards,
Mick -