Confirm My Exhaust Restriction :(

[666DAN]

Well just got some more info, disconnected the wastegate pressure line. Car is free-boosting to 15psi (funnily enough what the actuator spring is set to) then boost tails off in much the same way.

ie must be the actuator....next question wtf can I do, what other option do I have for an internally gated turbo?????

[BAMR33]

Keep on winding the actuator up more and then going for a test drive. And if you've got an ebc that supports rpm based boost control you could overshoot the boost level where boost starts to drop off i.e. instead of aiming for 15psi where boost drops, aim for 18psi, it might average off to 15psi.

[666DAN]

New theory!!!!

For the actuator to be forced open, there needs to be some pressure up against it ie one side is a much higher pressure than the other side.

OK my dump pipe is 100% split, so the exhaust is about 2" in diamter and the dump has it's very own isolated 1" pipe....I'm thinking maybe the pressure across the actuator side is getting too high for the exhaust flow that the car is trying to push.

If I just threw a bellmouth dump pipe on I'd probably be better off as there is no chance of a pressure difference across the internal actuator as it's also seeing the pressure from the exhaust flow (unlike now as it meets way down the pipe where the exhaust pressure pretty low in comparison)

Feedback please

[darrinspencer]

If I just threw a bellmouth dump pipe on I'd probably be better off as there is no chance of a pressure difference across the internal actuator as it's also seeing the pressure from the exhaust flow (unlike now as it meets way down the pipe where the exhaust pressure pretty low in comparison)

Feedback please

You maybe right about the dump pipe being to small. Back to back testing on a neo stagea with a hks gtrs, which would be similar size to your hiflow, a bell mouth dump got 7rwkw more top end over the split dump pipe. The tuners believed the difference was caused by the split dump being too small.

Pm AFRO, he has a spare R34 GTT bell mouth dump for sale, or he may lend it to you. He lives at Rochedale

[666DAN]

You maybe right about the dump pipe being to small. Back to back testing on a neo stagea with a hks gtrs, which would be similar size to your hiflow, a bell mouth dump got 7rwkw more top end over the split dump pipe. The tuners believed the difference was caused by the split dump being to same.

Pm AFRO, he has a spare R34 GTT bell mouth dump for sale, or he may lend it to you. He lives at Rochedale

All over it like a fat kid on a smarty!

A CES HPC-coated stainless-steel split dump is coming to a "for sale" thread near you!!!!

[skylinecouple]

A long time ago I made a split dump for my R33 and only 3-4mths later everybody was making one.However I regret not making a bellmouth as I truly believe they are better.So yesterday I removed the split and replaced with my own bellmouth.It will go in to the hitman next week for a tune so should be interesting to see the result.If seat of the pants are anything to go by I`m right ,the power is much better up top.Doesn`t seem as crisp down low but remember ,no tune yet.

[cosworth1971]

I dont think a bellmouth will make any differance !!!my .02

[666DAN]

I dont think a bellmouth will make any differance !!!my .02

Why not? It makes sense as the pipe running behind the actuator is at low pressure with respect to the exhaust side, that's the only way it can be pushed open.

Bell mouth will equalize the pressure as there is no difference accross it then.

[nissan_gtr35]

Why not? It makes sense as the pipe running behind the actuator is at low pressure with respect to the exhaust side, that's the only way it can be pushed open.

Bell mouth will equalize the pressure as there is no difference accross it then.

By saying you are using a bell mouth dump pipe you are essentially implying that you want the wastegate and the turbine exhaust exits from the turbo to be contained within the same inlet chamber of the dump pipe, right? Unlike the split where there is the two seperate paths. If so without the split i think you may be right, as the difference 1" vs 2" diameter can (and i emphasise can) make is a good point. The single exhaust chamber in the combined dump pipe, will ensure the pressures are equal!!

Hope the change of dump pipe solves you problem, look forward to hearing the results.

[666DAN]

By saying you are using a bell mouth dump pipe you are essentially implying that you want the wastegate and the turbine exhaust exits from the turbo to be contained within the same inlet chamber of the dump pipe, right? Unlike the split where there is the two seperate paths. If so without the split i think you may be right, as the difference 1" vs 2" diameter can (and i emphasise can) make is a good point. The single exhaust chamber in the combined dump pipe, will ensure the pressures are equal!!

Hope the change of dump pipe solves you problem, look forward to hearing the results.

Eactly dude, that's what I'm going with...see dodgy picture Equal pressure all the way! I think the split may be a good idea with a stock turbo, but my one is realy trying to push some serious gas out of it, the split just isn't working methinks.

[cosworth1971]

Im a noob but will bet 1k on it that it doesnt help at all.

I have a bellmouth.

to hold 15 psi ur reversion may be anywhere in the flow path even inlet

dyno chart tells you u were fine at 10 psi ,maybe a leak after that?( i put clamps on all my hoses)things like orig boost guage may leak?

I could be wrong also

but ur right i dont like split dumps idea anyway but a split may have less presure on the exhaust side being seperate from the main exhaust presure?

u want less presure behind the flap and more pushing it open

like someone said bleed valves will taper off too if ur running dat

[666DAN]

Im a noob but will bet 1k on it that it doesnt help at all.

I have a bellmouth.

to hold 15 psi ur reversion may be anywhere in the flow path even inlet

dyno chart tells you u were fine at 10 psi ,maybe a leak after that?( i put clamps on all my hoses)things like orig boost guage may leak?

I could be wrong also

but ur right i dont like split dumps idea anyway but a split may have less presure on the exhaust side being seperate from the main exhaust presure?

u want less presure behind the flap and more pushing it open

like someone said bleed valves will taper off too if ur running dat

Yeah but inlet restriction doesn't push open a free-boosting actuator, the pressure was enough to overcome the HKS actuator set at 15psi, currently I don't need to run any pressure lines to it to make it open...no boost control whatsoever.

$1000 would be nice

[cosworth1971]

I was getting overboost and underboost mixed up

But im just trying to help!

****new theory!****

maybe at a certain point the exhaust where it meets the wastegate pipe will make the small wastegate pipe have vacuum!thus forcing the actuaotr flap open more than you want at high gas speeds....thus bleeding your boost off

how big is dump pipe it only looks 2 1/4 inch?or so..

but i still think split dump is not the prob

[T04GTR]

coool. you need a tighter wastegate spring.

its got to much backpressure in the turbine housing for your currant gate.

[T04GTR]

unusual. but thats trhe problem . usually it shout hit 2bar odd with no vac lines to it.

[Scooby]

Eactly dude, that's what I'm going with...see dodgy picture Equal pressure all the way! I think the split may be a good idea with a stock turbo, but my one is realy trying to push some serious gas out of it, the split just isn't working methinks.

the bellmouth might make a difference but if i follow what you're saying correctly, i don't think it will make it for the reasons you're suggesting. remember the whole reason we use splits to keep the w/g and exh seperate is so the w/g flow does not impede the exh flow. there is no turbo system that i'm aware of that uses pressure from the exh to keep the w/g closed. this would also suggest that when you are at wot the w/g operation woud be compromised by the exh gas flow by not letting it open.

the w/g is controlled by the actuator. the preload might be too low and be allowing some creep or there might be another issue with the intake side, but i guess you've checked thoroughly for obstructions etc? it would be unlike CES to make something that's not functional, unless the gas you're pushing through the hi flow is exceeding the capacity of the exhaust but they seem to be switched onto that sort of thing. also have you enlarged the wastegate orifice? can't speak from experience on this one but apparently some turbos with hi flow etc will exceed the capacity of the standard size wastegate.

good luck, intersted to hear how you get on

just saw your post re no w/g lines needed to make it open - now i reckon definately check out that actuator.

Edited July 29, 2007 by Scooby

[666DAN]

Yeah that's why it may be easier just to go to the bellmouth, equalize the exhaust and wastegate side and be done with it.....you really don't know how close I am to getting an EVO lol!!!!

A greater spring tension is just going to see me pushing more boost than I want to with the current gearbox....aghghg why can't things be simple!!!!

Yeah I went down to CES for a chat about it all. But maybe that's the issue, the setup is awesome for a fairly stock turbo, but once you get the exhaust pressures moving it's enough of a pressure difference to open the wastegate...we're only talking 15psi of load which in the scheme of things isn't much when you consider the pressure at the turbine.

I'll put a bellmouth on, then we can reconvine and discuss

[cosworth1971]

stock turbo lol maybe u dont have a impella no more lol

go back to 10 psi!

[Haines]

Mine does this on a stock turbo

boosts to 11psi then drops back to 9

I have a BOS split dump ,dont know how they compare to CES ones

does the R34's have some way of bleeding off excess boost that we dont know of

[skylinecouple]

Just so you know I have no problems with power or holding boost.The only reason I changed the split pipe to bellmouth is as an experiment because I`m a hopeless fiddler.But think about it,when the wastegate opens the only time the gases are not going in the same direction is when the flap STARTS to open.Thats when the gases are going sideways but only till the flap opens further then all gases are going in the same direction.Plus the Fact that the standard or high flow turbo is quite small in the turbine outlet area,putting a restriction in the way via a divider is causing more problems than it solves.Gas wants to expand when it is hot so why would you stop it by keeping it in a 2" pipe? Don`t forget,the wastegate opens after boost has been reached so the turbine will boost faster with less restriction via a bellmouth.Realistically,the turbine dump pipe on a high flow should be a 4" pipe to ,say,the rear side of the cat.Now that would be efficient at 20lbs of boost.

I remember a published experiment years ago involving a V8 holden and going from twin pipes to a single.The single gained some 15kws due to all the gases in the same pipe speeding up the gas flow.Just a thought.