Had the erst on the dyno 5 days ago and engine was running sweet and maybe done a few hundred miles with no issue
Today when i put my foot down sounds like theres way too much boost prersure and when i take my foot off get loads of chatter (sounds great but i i know its bad).
Over boosting?...cause - poor/weak actuator?
theres a bleed valve on there too

Any comments welcome



Not sure why its at 144 before anything done I thought everything was standard

 

ok then found the problem
It was the bottom boost pipe the clip was very loose and hose had slipped nearly off. The high 'chatter' made me think there was far too much boost there.
Forgot to nip it up from the recent engine change
A problem fixed that didnt cost me money

Note. I must check basics before I invent problems that dont exist

off topic ....how much extra hp would you get from a stainless backbox?
Tyring to work out why I pulled 144hp on the dyno from a standard engine and 2.5 magnex backbox only

 

I think 12psi may be more then standard boost. Not 100% sure on this though.
Also you have to take into account how accurate the dyno is.

 

std boost was 5 psi

 

You will now have to re check the boost level, if it has been set up with a big boost leak, which you have now fixed, the boost may well be far higher.

 

Disappointing that the tuner didn't do a pressure test before setting it up, you should now really have it setup again as James points out your boost could be far higher than you realise.

A stainless back box will give you 0 hp in your current state.

 

i wondered why my ears were popping on the 23rd, it was this turbo pumping up the universe

 

Im looking forward to coming to your spot for a setup next week all been well James

 

lol

 

Thanks for your reply folks
Engine runs and stars pretty sweet now, but will have to save up for another dyno run with hose nipped up.

How do you maintain a better turbo presure after the initial peak?

 

Use a decent EBC and/or fit a bigger turbo if boost is dropping because it can't flow enough air.

 

cheers again

EBC work on MFI?

 

As another suggestion I guess an external wastegate would be another method?

 

wont help at all if it cant maintain the desired pressure with the gate shut.

 

Maybe I am missing the point completely (please set me straight in this case) but I was under the impression that internal gates struggled to stay closed at full boost due to their size, something which is ultimately determined by the size of the turbine housing.

Christ, a number of factory external wastegates struggle to stay closed at higher RPM unless going for a refurbed unit (if they are old) or a dual port wastegate (this was my experience and others on a previous turbocharged car I owned).

 

not really a problem on an RST running 12psi though, -31 spring strength is more than enough to keep the gate shut,
If you did manage to get them holding onto some more boost you would end up running into fuelling issues, as the old mfi system doesn't really work that well and in order to maintain a safe AFR at a higher held boost pressure you would end up cruising rich.

 

Think about what holds the gate shut (internal or external)... a spring, if it is the correct pressure it will stay shut.

 

In which case, are you calling External and Dual Port Wastegates (External of course) useless, since the spring pressure in theory should deal with the lot?

I was under the impression (and my own experience) that external (moreso with DPWs) gave more control and with the latter, more force since the boost pressure itself also helps with keeping the wastegate shut.

I shall admit admitedly that a -31 actuator seems fine for most RSTs out there .

 

not useless at all, when used in the correct application they are very good but a massive overkill on something like an rs turbo.

external gates can be a great aid in boost control in instances like the T4 when even with the internal gate wide open they still make 15-20psi of boost as the internal gates are too small and not efficient enough to pass enough exhaust gas. an external gate of the correct size would cure this.

Also as external gates are often far better sized than internal systems,because they are not bound to casting sizes, they are more efficient in terms of flow, they will also make more power, because when the waste gate opens the engine in effect becomes a nasp, so a larger more efficient gate will increase ve when its open.

 

As James has explained, the purpose is better boost control and improved VE (less back pressure allows gasses to flow in and out easier and faster making the engine more efficient), nothing to do with being able to stay shut..... both internal and external gates will stay shut so long as the spring pressure is greater than the exhaust gas pressure trying to overcome it.

 

Yet again James and Karlos kill it
I had a good read to the technical sides and am now in mentally wealthier

 

It is always good to be learning in this game, that is all .

The exhaust flow is something I was aware of with External gates but not fully.

I was only referring to the wastegate being shut with my previous car (1991 Porker 944 Turbo). Running at 15PSi (over the stock 10PSi) it would very gently drop to 11PSi at the redline, something they all do even as standard. Shimming the wastegate (and plumbing in a 'boost profiler') helped but did not cure it. Going to a dual port wastegate did keep the car holding 15PSI to the top along with less turbo lag and another few horses at the top end as a result. I guess the principles were different there .

 

I think that's more to do with spring rates than anything else,
The dual port gates are good as you can neatly balance them and keep the gate shut rather than rely on pure spring pressure.
It cant reduce lag though really, once any gate is closed and stays closed you are relying on the physics of the turbo in terms of lag, if changing has made it spool faster etc, then the exhaust pressure must have been pushing the gate open I would guess.