supra mkiv twin turbo overboosting!!!! help :)

[92mr2paddy]

my supra has recently got the cats removed as they were squished anyways from a useless driveway, got straight exhaust no mufflers and big front mount, runs 1.3+bar at 3rd gear upwards above 5k rpm, it has no boost control or bleed valve so should run only a few extra pound to stock levels?? faulty wastgate not opening al the way?? any help be appriciated, cheers pat

[sergei]

my supra has recently got the cats removed as they were squished anyways from a useless driveway, got straight exhaust no mufflers and big front mount, runs 1.3+bar at 3rd gear upwards above 5k rpm, it has no boost control or bleed valve so should run only a few extra pound to stock levels?? faulty wastgate not opening al the way?? any help be appriciated, cheers pat

I am not sure about supras, but that is very common when using stock turbp+stock wastegate without restriction in exhaust.

[the fallen303]

due to the design of the turbo seup on the mk4's, they only run a very small common wastegate for both turbos. when you replace the cats/dump pipe, there isn't enough restriction in the exhaust, and the wastegate can't dump enough gasses to control the boost. can get a restrictor plate made up to fit between the flanges of the dump pipe to restrict the exhaust enough that it drops the boost back down to acceptable levels, or get a good condition stock dump pipe put in it's place.

i can't remember the exact size for the restrictor plate, but a few people on here have done it before, gmcrae is one that comes to mind. they should be able to help. if not, make the restrictor about similar size to stock dump pipe, and should be enough.

[92mr2paddy]

swt cheers for that. i was hoping this wouldnt be the cause, guess ill have to jst throttle it to not overboost, haha will be going to single turbo some time next year so will eliminate the problem, cheers for the help anyway, any way to increase the flow of the standard gate???

[Snaps]

Drill it out a bit, I'm not completely sure on what it needs to be drilled out to, but it has been done before.

[YeMs]

thats not a problem.. its an advantage! haha

[BlakeNZ]

2" hole in restrictor plate.

[dnalunchie]

From reading a few local and overseas forums the best fix is just to have a 2.5inch down pipe and then larger exhaust after that, apparently with that it will run around 16-17psi which is safe (ish) but will still require a few cut defender thingy to stop it cutting out once it goes past the stock fuel map which I believe is 15psi

[sergei]

From reading a few local and overseas forums the best fix is just to have a 2.5inch down pipe and then larger exhaust after that, apparently with that it will run around 16-17psi which is safe (ish) but will still require a few cut defender thingy to stop it cutting out once it goes past the stock fuel map which I believe is 15psi

Fuel cut is there for a reason.
Fuel cut defender on MAP sensored vehicle will result in engine damage.
When it goes past fuel cut boost with fuel cut defender, the ECU will only supply fuel for whatever the fuel cut defender is limiting the signal (say 15psi), if you run above that, ECU will not compensate for extra air and you will end up running lean. Lean= lots of heat and detonation.

[Jebus]

Not on a JZ, my engine goes to 10.8:1 a/r at 15psi (stock with FCD clamping around 3.9-4v). Plenty of room for more boost there.

You could get a quick wideband check on the road if youre worried and once you go single turbo it will be fine.

[sergei]

Not on a JZ, my engine goes to 10.8:1 a/r at 15psi (stock with FCD clamping around 3.9-4v). Plenty of room for more boost there.

You could get a quick wideband check on the road if youre worried and once you go single turbo it will be fine.

Does it have AFM?

[Jebus]

MAP sensor, same as most/all JZ engines

[92mr2paddy]

yea i got a fuel cut defender and ive been told its fine to run around 17psi without leaning out too much, only thing is when the boost creeps higher u can tell the turbos arent supplying any more air and the car doesnt go faster at 1.3bar than at 1bar, apparently the stock turbos start creating too much heat above 15-16psi??

[Jebus]

Is the FCD adjustable or fixed? And is it a descent intercooler with good size pipes?

[FLAWLES]

MAP sensor, same as most/all JZ engines

bar the vvt-i 1jzgte
stupid afm's

[92mr2paddy]

no fixed fcd, intercooler massive 600x300x100 3inch piping, no lag even with this setup, but once 2nd turbo hits ''full'' boost it will rise quikly above the normal 1bar and climb,,,

[dnalunchie]

no fixed fcd, intercooler massive 600x300x100 3inch piping, no lag even with this setup, but once 2nd turbo hits ''full'' boost it will rise quikly above the normal 1bar and climb,,,

seriously, just try the restricter plate or smaller downpipe, easy, cheap fix and most likly will deal with the problem

[Jebus]

You have a good intercooler and exhaust just run 17psi and enjoy the extra power, $&#$% doing mods to make power then adding a restrictor plate to remove the power.

[MrOizo]

You have a good intercooler and exhaust just run 17psi and enjoy the extra power, $&#$% doing mods to make power then adding a restrictor plate to remove the power.

Putting it like that makes it sound like wiping your ass before taking a shiit - Makes sense though!

I have this same problem. When i took mine in for the exhaust after the conversion without front pipe it would cut fast and hard!

Now with the exhaust i have (3.25" down pipe then to 3") it goes up to 1bar, sits there and while building revs, it cuts. Always forget to feather the throttle instead WOT

[dnalunchie]

You have a good intercooler and exhaust just run 17psi and enjoy the extra power, $&#$% doing mods to make power then adding a restrictor plate to remove the power.

Putting it like that makes it sound like wiping your buttocks before taking a shiit - Makes sense though!

I have this same problem. When i took mine in for the exhaust after the conversion without front pipe it would cut fast and hard!

Now with the exhaust i have (3.25" down pipe then to 3") it goes up to 1bar, sits there and while building revs, it cuts. Always forget to feather the throttle instead WOT

would a Fuel cut defender not correct that problem or are you concerned with it going over 15psi?