Confirm My Exhaust Restriction :(

[666DAN]

OK every base has been covered with the car, no leaks in the piping, HKS actuator set at 15psi (and 11psi)

This is what I'm faced with (see below)....initial comments on my car was it's very quiet for a 3" turbo back system.

I'm convinced it's too much back-pressure slowing the turbine down and boost dropping off.

Comments please

[Fixxxer]

Do you have an EBC? And what sort of exhaust do you have?

Have a look at the exhaust, do you have a hi-flow cat, mandrel bends, how many and what kind of mufflers (design and diameter). Dropping boost usually means a restriction somewhere, my exhaust is pretty loud but holds 12psi all the way to redline. My rotor has a fairly muffled 3" system with some crush bends, and it can't hold onto the boost to redline.

Fixxxer

[666DAN]

Has a CES split dump, mandrel 3" the CAT should be a 3" highflow (installed by CES) doesn't have a hotdog it's a proper baffel toward the rear but the magnaflow twin tip is where I think I'm coming unstuck.

One run was done with EBC another with purely HKS actuator setting, also displayed the same behaviour with a turbotech bleedvalve, the stock actuator and trying an RB20 actuator.

I've got a nice free-flowing exhaust with cannon as a loaner to put on to confirm my suspicions.

[Tangles]

seems awefully similar to mine

190rwkw 14psi dropping to 12psi

manifold was cracked and replaced, rear Fujitsubo was causing a restricition - added a highflow 3inch Kakimoto muffler and all is fine now. Just got to retune it, soon hopefully.

[MANWHORE]

Hey Dan

One important thing that we need to know first. What turbo are you running?

I remember you telling me that its the slide highflow, but which one (rb25, rb25 oversize, vg, vg oversize).

Even the smallest one on 15 psi should make a fair amount more than that. On 15 psi, a car we did got around 225 rwkw (after tune).

Best way to find out, to just crack the catback off (including the cat) and see HOW restrictive it is

[666DAN]

It's the VG30 oversize, it pretty much looks like as the engine is starting to get going then the exhaust is restricting like hell.

I'd be expecting over 200rwkw at 11psi

A mate is giving me his system to try on the car, should answer the question instantly.

Whoever has heard my car would agree it's spookily quiet for 3" system

[Tangles]

Whoever has heard my car would agree it's spookily quiet for 3" system

so was mine.... centre to offset muffle, muffled big time. very quiet.

got a 2ndhand Kakimoto 3inch centre to centre straight thru muffler off a GTR. niiiiice. $65 delivered from WA.

welded it on, nice sound, restriction gone. set at 14psi but seen 15psi in a cold valley with foot down mashn the pedal.

stage1 slide rb25 highflow turbo

[R34GTX]

For what it's worth Dan, Me thinks it's not the exhaust...... With my stocka, and almost identical exhaust to yours I am getting 176rwkw.

OK every base has been covered with the car, no leaks in the piping, HKS actuator set at 15psi (and 11psi)

This is what I'm faced with (see below)....initial comments on my car was it's very quiet for a 3" turbo back system.

I'm convinced it's too much back-pressure slowing the turbine down and boost dropping off.

Comments please

[Haines]

Mine does this too

boosts to 12psi and tapers off to 9psi (got 195.5rwkws)

also a r34 gtt and also very quiet for a 3" turbo back exhaust

I thought maybe my cat had shit itself

im going to make a new cat section and try that out

[666DAN]

For what it's worth Dan, Me thinks it's not the exhaust...... With my stocka, and almost identical exhaust to yours I am getting 176rwkw.

It's not identical Pete, we've got different mufflers...yours is bigger. You've always had a better flowing exhaust than my one. You'r boost went through the roof after installing it, my stock turbo never really budged.

This is 100% exhaust restriction, I just wanted a few others to confirm.

Nothing else on the car can account for what's happening.

[kermit]

exhaust noise is controlled by slowing the gas down as it goes through the exhaust . quiet system equals restriction .

kermit ( i build exhausts )

[MANWHORE]

I suspect that it is exhaust restriction, but I don't think anyone can really say for certain.

When you knock the exhaust off and swap it with your friends, make sure you do the cat too. Some 'high flow' cats are not really high flow at all.

Your car is quite a bit down on power in terms of what it 'should' be making. After swapping exhausts, if you feel a lot more power, and response, then that means it was the exhaust

[ssshonky]

umm .. not sure why nobody has commented on this before

why dont you just disconnect your Exhaust from where it bolts onto the dump from the turbo ?

its going to be loud as hell .. and *might* run a bit lean .. but if the restriction is as massive as your leading it on to be .. a quick run on the dyno should be able to confirm if its pumping out much more horsepower. Even the " seat of the pants " dyno will tell you pretty quickly.

just support the remaining portions of the exhaust if your going to road test it and be careful and you should be ok ..

Obviously doing this on the dyno where you can keep an eye on mixtures etc will be the better way of doing it .

[BAMR33]

I suspect that it is exhaust restriction, but I don't think anyone can really say for certain.

When you knock the exhaust off and swap it with your friends, make sure you do the cat too. Some 'high flow' cats are not really high flow at all.

Your car is quite a bit down on power in terms of what it 'should' be making. After swapping exhausts, if you feel a lot more power, and response, then that means it was the exhaust

x2 'hi flow' cat is too much of general term everyone seems to be classifying their cats as, when most probably flow a lot less in comparison with quality hi flow metal cats that cost $350+

[MANWHORE]

umm .. not sure why nobody has commented on this before

why dont you just disconnect your Exhaust from where it bolts onto the dump from the turbo ?

its going to be loud as hell .. and *might* run a bit lean .. but if the restriction is as massive as your leading it on to be .. a quick run on the dyno should be able to confirm if its pumping out much more horsepower. Even the " seat of the pants " dyno will tell you pretty quickly.

just support the remaining portions of the exhaust if your going to road test it and be careful and you should be ok ..

Obviously doing this on the dyno where you can keep an eye on mixtures etc will be the better way of doing it .

I said that above in my first reply.

I always do that even if the power is where I expect it to be.

Every exhaust IS a restriction. What matters is whether it is a restriction at that power level. e.g. your quite 3" exhaust shoudl flow more than the standard exhaust. At standard pwoer levels, it is most likely that it won't pose much restriction at all. But then, at 200 rwkw, 250 rwkw, or 300 rwkw, the restriction will become evident

That's why I always take it off and do a back to back run just to see how much restriction there is.

[T04GTR]

ok. you need to unsrew your cat converter heat sensor and scre in a suitible fitting to mesure actual back pressure. also is it an apexi boost controler? cos they do that, it is electronic?

if its a bleed valve then thats normal. and all the vac lines to come from the inlet manifold or it will do that to.

[666DAN]

HKS actuator on it's own was doing this, in combo with a Profec B Spec II it's still doing it. I'm 99% sure it's the exhaust

[Bass Junky]

Put car on dyno, remove exhuast.

Then you will REALLY see how much an exhaust restricts the power on your car.

[666DAN]

Going back to CES today, they're going to have a look. He said they've had cars pull 300+ rwkw with my system, as I mentioned this one is different to my mates, who has the "same" GTt system.

[T04GTR]

ok.. try setting the boost controler to 4 pound higher. iff it still drops off the same amouint, then its the boost controler setting.

also adjust the gain to max, then adjust the boost setting. always the gain has to be max to stop the boost dropping off.