long winded problem.. Any ideas would be much appreciated..

[BIGALR33]

Dear good people, I would greatly appreciate any help that you can offer. I don't know where to start so i'll try to explain..

This is a R33 Gtst and everything else other than mentioned is standard fitment.

Basically everything was fine up until i fitted exhaust, decat, downpipes and apexi filter jobby. Before i did this i was getting 0.5 bar boost on the actuator and then the boost solenoid was bleeding pressure from the actuator which was then increasing it to 0.7 bar boost. This was all fine and well. However, once i had fitted all the above gubbings i was getting more base boost and then once the boost solenoid opened, the boost was reaching levels where it started to create a massive flat spot . I assume that this was due to det and the knock sensor retarding the ignition.

So i disconnected the boost solenoid and blocked off the pipe so that no pressure was bled from the actuator. This seemed to work and i was getting 0.7ish bar at red line. it drove great and there seemed to be no problems...

Now the air has become cold, I am getting much more boost than before, around 0.8/0.9 bar and yet again it's causing problems. It doesn't do it when i've been in traffic and the intake temp is hotter.

I then found that i had an adjustable actuator on the car which was under quite a bit of preload on the spring (whilst wastegate closed) so i lenthened the actuator arm a bit. This was still holding the actuator closed but i figured it would open it sooner and further at the fully open position. This seemed to work, I had lost about 1 or 2 psi across the rev range but it was still too high. I lenthened it again and the wastegate is still closed as it should be with the actuator in the closed position. This time i had slightly more boost. in fact it was almost the same as before. Is this because there is now less preload on the spring and less pressure holding the wategate closed?
I thought this would again open the wastegate further at full boost and dump even more pressure but it didn't.

I figure this came about due to the improved efficiency of the intake and exhaust and the turbo spooling faster etc. but i don't know why the boost is not still 0.5 bar. Is this because my wastegate has become restrictive? Can it be ported or something?
I checked all the hoses for leaks and all seems well. I thought about putting the cat back on to see if this would help but i don't really want to go backwards..

I then lengthened the actuator so that there was no real pressure holding the wastegate closed. This drove much better. It began by showing almost no boost and then it crept up across the rev range upto about 0.7 bar by red line. Although it felt quite sluggish at lower rpms, once in the power band it performed ok. I guess the wastegate was pretty much open straight away and this caused the boost curve to become much slower. I guess this would over spin the turbo as its running alot faster but i am only assuming.. Is it safe to run the wastegate open for this much longer?

Any ideas would be much appreciated..

[Chris Wilson]

It's almost certainly because Nissan, like Toyota with the twin turbo Supras and the MR2 turbos use the stock exhausts restrictiveness in their calculations for wastegate sizing, so when you add a free flowing exhaust and a decat, the wastegate area, fully open, is no longer large enough to bypass enough exhaust gasses to keep the boost pressure in check. To do a quick test reinstate the stock cat and see what happens. You can sometimes "port" an integral wastegate to flow more gasses, or I can supply an exhaust restrictor ring to enable boost to be kept lower. This is better than keeping the cat, in so far as the cat retains a lot of heat energy near the engine, and cannot be quickly "tuned" like a hole in a steel plate, to give just the right amount of restriction. Don't get mislead into thinking an aftermarket boost controller can help, in such situations they can only raise the existing boost level still higher. HTH.

[BIGALR33]

This is what i had expected. I could easily make a plate to fit. Guess this would be the same size bore as the original exhaust? Didn't really want to do anything that was restrictive in any way but i guess it would be better than it is now. I think initially i'll stick the cat on and see what happens.. Is it just the size of the pipe going into and coming out of the cat that is restrictive or is it the cat itself?

[gtsgeorge]

hi, im new to the whole gtr register so sorry for anything i do wrong.

Big al. how did you get on with your boost problem cause i have exactly the same problem with my 1993 gts. i've got induction kit, exhaust, de-cat and adjustable wastegate actuator.
surely if the standard stage 1 tuning is to do the exhaust and induction only then it shouldnt really cause the problem.
any help you can give me would be great.

also, excuse my daftness but on the standard boost gauge, what are the numbers relating too? is it + 0.7 bar and - 0.7 bar?

[SteveC]

in negative terms the boost gauge reads mm/hg and positive reads in bar.

it is not possible to have a reading of less than ambient pressure on the negaive side when reading Bar so they use a different scale. bar would just read zero.

because gasses get out faster it changes the characterisitics of the exhaust tuning. this has an effect on the turbo and can cause overboosting.

hth
Steve

[gtsgeorge]

that makes sense, should've thought of that.
i've just been working on my engine again and have discovered that because of the shape of the rod on the hks actuator. it fouls on the wastegate arm when fully open. this causes it to not open fully when its clipped together. i bent my arm up slightly so the rod clears it and problem solved.

[BIGALR33]

Dude, I have tried everything, I want to fit a boost controller but even runnning on the 0.5 bar actuator i'm now getting 0.8 at the red line on some cold mornings. I put the cat back on and i still got boost creep. although it didn't boost quite so high, i didn't like the idea and took it back off. I fitted a set of iridium plugs and this gave me about 1 - 2 psi less boost. i guess that's maybe something to do with better combustion or something.. I'm thinking about porting the wastegate as i believe this may be too restrictive and see what happens..

The thing i can't get my head around is that i know people running much higher boost in higher spec cars than mine without any creep and they get flat 0.5 bar on the actuator. i can't believe there's that much difference in manufacturing tolerances on these?? surely one standard turbo should work the same as another?? if you add engine management, intercooler etc, then surely you are producing even more exhaust gas and faster spool etc, so why don't they have this same problem?

I don't get it..

[skylineman]

are you still having problems? I had the same thing when i fitted all the stuff. Have you a bleed valve or anything fitted? fitting that stuff will cause the boost to spike and even more so when the temp drops, when you floor it does it cut out? I would recommend a bleed valve to turn the boost down or a boost controller, Im running alot more mods now and, fitting the boost contoller did help. Hope any of this helps

jad

[LozGT]

Squire

I've got all the usual bolt on mods - intake, de-cat, downpipe, exhaust - but when I run it on just actuator I appear get a very flat 0.5 bar. If I use a bleed valve and adjust the boost I still don't appear to get any spike or creep of the magnitude you describe (as the intake cam advances I get a slight increase in boost) . However, I used a boost controller in the past (until it packed up) and when I did so my boost was very stable. I'd recommend getting one and also getting it set up on some rollers - just to guard against det-free running - for the boost you want to use. Now that I've typed the above I get the feeling that a number of straws have been clutched....

Cheers

See you around

[BIGALR33]

Hey Loz, hows it going? there you are!! I'll drop by and see you before the end of the week as I may have some stuff to drop off.. Skylineman, I cannot use any sort of bleed, the pressures i am getting are on the actuator with no bleed. this should give me 0.5 bar flat, as loz is getting, but i'm getting loads of creep. I don't understand why this is different betwen cars, I know there has been slight variations between standard turbo's such as compressor wheel material and so forth, but I wouldn't of thought the exhaust / wastegate side of things would have had a more restrictive design on a newer car..?? surely the castings would be the same for all gtst turbos?? The only thing i haven't tried is changing my actuator. I don't think this could be a problem but i guess there is a diaphram that could potentially leak?? has anyone experienced actuator failure?? I've never had fuel cut out before, guess it's not boosting high enough for that but it does occasionally reach 0.85 ish bar on the standard actuator.

[R32 Combat]

Al

I think the fuel cut is at 1.1bar.

I have a couple of GTR tubs sat about if you want to see it the actuators are the same. You could have a broken one or maybe the wastegate is warped.
From what you've done, it sounds like you've covered everything bar removing the turbo and inspecting it.

[gtsgeorge]

Big Al

i was thinking about your boost problem cause thats the same as ive got.
i disconnected the actuator arm and put the wastegate in the open position and went for a spin, it will run slighty over atmospheric but it does not over-boost. this proves that the wastegate CAN flow enough gases to prevent overboost. i also have an adjustable actuator on mine and i think that it is stopping the wastegate opening fully and causing it to creep up. disconnect your actuator rod, move the wastegate arm to the open position then try and put the rod onto it. if its the same as mine its not gonna happen.

what do ya think.

[BIGALR33]

Interesting.. I made the standard actuator adjustable by cutting the arm, threading each end and i drilled and tapped a bit of hex bar to couple these together. this allows me to adjust the length of the actuator arm. I haven't tried wiring the wastegate open but i have wound the arm so that the wastegate is barely held closed. This made the boost come on at very low pressure and it still increased to 0.7 bar by the red line. i guess it spooled up at such low boost pressure because the wastegate was not sealing closed due to no preload on the spring. i wonder if the actuator is not giving me enough travel to fully open the wastegate? could this be the result of a leak? i'll try wiring it open and see what happens.. Also thanks for the offer Andy, I may take you up on that if that's the cause. I take it the GTR actuator also has a 0.5 bar spring?

[R32 Combat]

The GTR actuator has, I think, a .6 spring.
LozGT might know. He's been with me when I've been faffing around with the GTR enough times.