1jzgte overboosting ? and other issues

[Jonno2002]

this issue is getting anoying now, 1jzgte completely standard with 3" exhaust from downpipe back and fmic with short piping, boosts strait up to 15pound and hits the 14.7pound boost cut. ive taken the wastgate hoses off and tested them with compressed air and both gates work and arent stuck. ive read that exhaust and fmic can cause the boost to raise but surely not this much ? im actually at a loss what to do now, only thing left to try is putting a restrictor in the exhaust which i obviously dont want to do as it would defeat the purpose of having a nice exhaust.

anyone have and thoughts or comments ?

[MR2BOY23]

http://www.supramania.com/forums/showth ... ng-exhaust

Porting the wastegate sounds like the solution

[Jonno2002]

sounds fun, guess im getting the die grinder out then

[Py7h0n]

Far easier to fit a 2.5" section to the exhaust

[Jonno2002]

yougota be shitting me, pulled the turbos off and ported the wastegates and it still does it, i have a cursed 1j everythings $&#$% on it

[matt dunn]

When we first ran the AE101 Corolla with the std turbo's the only way we could ever get it to control the boost was to restrict the exhaust.

The big bore will be the problem. Fit a smaller pipe in it somewhere.

I think at one stage we actually welded a small 4 into 1 exhaust collector into the middle of one of the 4" pipes to fix it temporarily,
and it did.

Was not long till the whole turbo setup got the bin for some larger puffers and a bigger wastegate though,
but it did fix the boost issue for a few events.

[the fallen303]

thing i find interesting about this is i am running a modified turbo setup on my 1jz, but still retaining the ct12a's. have made custom manifold/exhaust for rear turbo and turned it around, and we're running twin 3" dump pipes for each turbo, and yet we don't get any issues with overboosting. from where the cat should be back is 2 3/4 inch, but even when i took the exhaust off for some work, it still didn't overboost. could possibly be from the changed layout of the turbos, with better dump pipes?

[Looonie]

I've got 3" exhaust from the factory y-pipe, straight through to a single rear muffler. Front mount intercooler with short piping (450x300 with 2.5" piping cold side and 3" piping hot side).

Stock motor, stock ECU. Boosts up to 11-12psi quickly and happily, sits there perfectly, no issues with overboost, spiking or fuel cut.

[Jonno2002]

maybe actuator then who knows but it hooked 5th gear on the skid pad last night so im $&#$% stoked no rb's doing 5th i saw haha

[YeMs]

how can you say 15psi is over boosting!! jz's love it, id be winding it up to 20

[Jebus]

This is what happens, just get a FCD.

[docTRD]

15pound aye hmm thats a few psi more than what i was getting with my 3" exhaust from the downpipe and large front mount. i was around the 11-12psi which looks like most people are achieving.
seems like you have something going on with yours im guessing turbo area ? even with no exhaust i never boost cut :p . and yea FCD and youl be laughing and going through plenty of tread haha

[Glancn]

nah all depends on age of engine/turbo condition. Mine would run 13-14 with straight 3" pipe, Now i have made custon dump pipe's it runs 1.15 bar.
I have a SAFC this eliminates the boost cut.

Just get a FCD this will fix the problem

[the fallen303]

doesn't fix the problem, just ignores it. does that sound like a good idea??? "ohh, i'm having boost control problems, so it's hitting boost cut... i know, i'll remove the boost cut!"

are you running a boost controller of any sort? where abouts are your wastegates getting their feed from? even though the wastegates are operating fine when you tested them, are they getting a proper pressure feed from the engine/turbo compressor housing, and are they actually opening and closing fully?

1jz's don't have the same overboosting problem 2jz's have, reason 2j's have the issue is the boost control only works through the front turbo, so essentially only uses one internal wastegate, so free it up too much, and it can't dump enough to control the boost. ct12a's still have an alright wastegate area, not the best, but still not bad enough to cause the issue you're having. did you notice any drop in boost when you ported out the wastegates? if not, then i'd be looking elsewhere.

for now, get a restrictor plate made up and see if that does alter the boost level at all.

is the on an engine from a conversion? so you've only ever run the 3" exhaust? when did the problem arise? did you change anything, then it started doing it, or has it just always done it since you got it running?

[Jebus]

doesn't fix the problem, just ignores it. does that sound like a good idea??? "ohh, i'm having boost control problems, so it's hitting boost cut... i know, i'll remove the boost cut!"

Good one, sounds about the same as "oh cool, just fitted a 3" exhaust and intercooler its going really good now but its hitting boost cut, I better restrict the exhaust to make it slow again"

[sergei]

doesn't fix the problem, just ignores it. does that sound like a good idea??? "ohh, i'm having boost control problems, so it's hitting boost cut... i know, i'll remove the boost cut!"

Good one, sounds about the same as "oh cool, just fitted a 3" exhaust and intercooler its going really good now but its hitting boost cut, I better restrict the exhaust to make it slow again"

If you have money for intercooler, 3" exhaust, and after that boost cut defender, you should approach this problem from proper angle: fix the overboosting in first place. All you need is either better down pipe design, or an external wastegate.

[the fallen303]

doesn't fix the problem, just ignores it. does that sound like a good idea??? "ohh, i'm having boost control problems, so it's hitting boost cut... i know, i'll remove the boost cut!"

Good one, sounds about the same as "oh cool, just fitted a 3" exhaust and intercooler its going really good now but its hitting boost cut, I better restrict the exhaust to make it slow again"

just saying, if it's just the exhaust etc thats raised the boost, and it's not much over cut, then sure, fit the defender, but if it's something else, he may not have any sort of boost control, so removing the cut could be bad, as could free boost, and damage either the turbo's or the engine itself.

find out exactly what is wrong first, then fit the defender, i'm not saying don't, i have one on mine, and run just over cut, but my control is nice and stable, and can comfortably sit it at 11-12 psi, or turn it up if i want.

get a restrictor plate made up, pretty cheap/easy to do, just slot it in a flange just after the dump pipe. then at least you can either confirm or eliminate the exhaust as being the problem. you can go from there about how you want to proceed.

[Jebus]

Yeh fair enough, weve done about 5 of these engine swaps into drift cars, all with straight 3" exhaust and they all just hit boost cut. We either use a FCD or SAFC and they usually have 13 - 15psi max, seems to be just what they do.