A Question For You High Boost People

[Kinkstaah]

To add on to that - by 'slow leak' we are talking it'll drop 1psi every 3-4 seconds and otherwise hold air from an air compressor fine... an air compressor which is switched off once boost was reached. (so not constantly being fed, and leaking)

I showed trent on the dyno, this happens in Vacuum as well. You can be sitting at say, -10mmhg at a constant speed, and shift from 1-2-3-4 and the pressure in the manifold will change according to gear, regardless of anything else.

When testing with springs on the wastegate (no boost controller) the wastegate will OPEN at say, 15psi in 2nd, then open at 20psi in 3rd.

f**k me if anyone can explain how this is happening, all assumptions now assume it's an auto transmission thing, as opposed to anything turbo related.

[HarrisRacing]

What the ?!?!

Maybe the wastegate diaphragm is bad or something? Is the turbo in good shape?

I'm perplexed as well.

What exactly are you using to log / read boost? Mechanical gauge or electric?

Edited April 27, 2015 by HarrisRacing

[scotty nm35]

Well the pressure in the manifold will likely be changing with load/gearing, so the wastegate will open at different psi due to this pressure change behind the gate.

The diaphragm is perfect, I checked that when I swapped in the new spring. The turbo is brand new. Logging on the Haltech with a mechanical gauge as backup.

[XGTRX]

Where is your boost pressure sensor. It would be interesting to know the pressure before the intercooler to see if it's similar to that of the plenum.

[scotty nm35]

The Haltech was in the front reg fitting on the plenum, not sure where the mechanical one was plumbed.

The tuner just wants to see a consistent boost curve, he doesn't care if there is .5 or 50 psi drop over the cooler, but I agree, it must be close to maxing the core's flow. Wouldn't be hard to shove the mechanical onto the compressor cover and have a look Greg...

[XGTRX]

Maybe it's just the IC can't cope with the higher rate of boost increase in the lower gears

[dr phil]

How do you test whether a bov is leaking (a plumb back bov)? Do you just block off where it returns to the intake, and leave the return line open after the valve, pressurise the intake and see if it leaks?

[GTSBoy]

How do you test whether a bov is leaking (a plumb back bov)? Do you just block off where it returns to the intake, and leave the return line open after the valve, pressurise the intake and see if it leaks?

Piece of coke can sandwiched in the BOV's flange and gasket.

[Mitchee]

Where does the pressure source for the wastegate come from? Ive seen similar when its taken from the manifold and not from the compressor side.

Is the Haltech running Closed or Open Loop boost control? If its running Open Loop and the Base Duty table hasn't been configured correctly, it will have the exact symptoms you explain. The engine doesn't load up the same in the lower gears as it does in the higher gears where its tuned, so it uses a slightly different area of the table, which may command a lesser duty cycle on the solenoid.

Closed loop boost control with a correctly set base table will alleviate this.

[Kinkstaah]

Pressure source is about 1mm infront of the throttle body.

It happens in Closed loop.

It happens with a boost controller set to 0 duty (spring pressure) or the ECU wanting 0psi boost.

It happens in vacuum.

[XGTRX]

I still suspect an issue from the compressor to the plenum.

[scotty nm35]

It has all the hallmarks of an intake leak or restriction, but it was working fine before the engine build, and nothing else has changed afaik.

Greg, take a coke can to block the BOV on the next tune.

[Kinkstaah]

This behaviour has happened on multiple turbos, multiple engines, in multiple cars.

However, the Bov (which is an aftermarket Turbosmart BOV) has been consistent across the setup.

So I'll block it off for the sake of the argument, and report back at some time in the future, though obviously I will want to run a BOV in general, so if it 'fixes' it then I have no idea how to actually fix it.

[XGTRX]

An news on this?

[scotty nm35]

Greg has a larger turbo on the way, GTX35.

Seems the ported head and increased capacity now requires a larger turbo to get even the same power output he had before, a result of slowing the gas speeds down I assume. His 400kw external gate GTX3076 setup will be up for sale now I guess, perfect for an RB25.

[XGTRX]

Awesome, keep us updated on this. Really interested on the final outcome. Thanks.

[Leroy Peterson]

Greg has a larger turbo on the way, GTX35.

Seems the ported head and increased capacity now requires a larger turbo to get even the same power output he had before

Didn't the motor make the same power (or even 5kw more) than before? With 10psi less boost. (Partly due to compression ratio increase)

I just want to mention that the engine builders suggested the turbo was too small for the desired power figures, and so too did a Garrett rep who comes around the engine shop. I'm not saying a bigger turbo will sort every issue, but it was thrown out there as a suggestion pretty early on.

[Kinkstaah]

It initially made the same power (375kw) at 7-8 less boost but after fixing boost leaks and hunting everything down (and Trent upgrading his dyno so it can actually run WOT) for a full pull...

It made about 365ke, but peak power is at like 3900 rpm now.. Which it holds until about 6k then falls away and gets wavy and valve floaty. So the limiter is now lower and as mentioned, going a larger hot side.

The peculiarities of boost in gears remains in any case, nothing has changed in so far as the original post on the topic..