Duke

I'm suggesting that the engine will product a larger exhaust volume at higher rpms than lower rpms, so an exhaust leak before the turbo would hurt low end and midrange boost much worse than top end boost.
And looking at the chart this is not the case so I would rule out a pre turbo exhaust leak.

333pg333

Bit hard to say without testing backpressure. We only boosted the last motor to 25psi so perhaps we might have run into similar issues? Turbo, X-over, headers etc remain the same.

Not sure why a larger X-over would create more backpressure than a smaller one though? Assuming if anything it would slow the velocity down. Unless we're assuming it's overpower the turbo?

So we might have failed with the longer runners where the power starts to dip down lower than the motor was designed for...or that could be the b/pressure also having an effect.

Paulyy

not sure how applicable this is, but a lot of people use those turbos on RB25 with great successes and on Honda b18's

Do you have a different intake? if so, bolt it on and see what different it makes. if the curve moves, peaks change, then it's a possibility it's the intake.
If peaks barely change, and similar stuff is going on. probably be something else.

Strange though, i should be expecting similar power with current setup on similar boost.

333pg333

Well we've got the previous intake which has somewhat shorter, smaller runners and a not entirely dissimilar plenum.

Wonder if these ports are too big? But then they wouldn't fill on lower boost and not fill on higher I guess. Just need to get some pressure sensors in there first.

Paulyy

Patrick whats your cam intake duration? going to do some math.

Edit.

TurboTommy

Also curious as to not being able to make more boost.
Other than that, maybe consider lowering gear ratios which would be more suited to the higher RPMs; would address concerns with the lower torque at low/medium revs.

Also, is this a dry sump; or what have you done for oiling?
I know it's probably stated somewhere, but just wondering.

333pg333

Paul, I've sent you an gmail.

TT the gearing is stock 968 so it's pretty short. We've been running on 35 aspect ratio tyres but will test them against the 30 aspects too. Yes, dry sumped. Seeing approx 90psi pressure.

Penguinracer

Patrick - given that you're building a high-rpm 8 valve - are you anticipating high wear rates on the valve seats & stems?

Are you engineering the head to increase wear resistance (e.g. lighter valves & harder seats) or are you expecting to replace the valves & seats reasonably regularly as an operational overhead?

I hope you find the bottle-neck because you're really pushing 8 valve development in a rarely seen direction.

Tim

333pg333

Tim
All the hardware on this motor has been upspecced to race components. Can't really speak of wear rates but it doesn't see many hours per year.

mikey_audiogeek

Hi Patrick,
Any chance of a dyno run with the previous intake?

(the check is in the mail... )

Cheers,
Mike

Geneqco

Given the power produced by the last engine with same exhaust and turbo setup, I'm thinking, unless the turbo has been damaged, it's probably more to do with a boost pressure control issue - ie, wastegate/actuator/software setup or possibly an issue with the blow off valve.

Patrick, did you end up installing one of those wastegate sensor caps... it may provide some useful information:

http://www.turbosmart.com.au/news/kn...ate-sensor-cap

Also, if you want to get an idea of how intake manifold design affects things once the boost issue is sorted out, you obviously already have three to play with... if you'd like to play with a couple more, I have an SFR and a Powerhaus you could try on the dyno with if you wish.

333pg333

Thanks all. I do need to write some emails and reply individually to some of your thoughtful suggestions.

Been up early and attempted to do a test day at the track, lack of boost and spool notwithstanding. As quite often happens there was a very small raincloud that decided to open just over the track which worked in harmony with the guy that blew his motor at about T2 and drove all the way back to the pits on the racing line despite another small but highly visible cloud emanating from his exhaust. ie...not many laps today. However, yes it is laggy but not totally undriveable.

Scott we're headed in that direction. Going to modify the wastegate which was seeing high duty cycle at 20psi . It needs more spring and we're going to run another solenoid so as to run two and have much better control. We think we'll gain quite a few hundred rpm back in the onset of boost. We're also considering making a smaller Xover and potentially reviewing the turbo. We'll grab the low hanging fruit first and see what we find. A cheaper resolution would be ideal at this point. Also thanks for the generous offer of borrowing a different intake. From memory these are designed for the 2.5ltr flange? Be interesting to try a few but it's not quite Lego-like in terms of ease to swap around.

Geneqco

Glad you're sorting it out Patrick.
Yes, they are for the 8v head but I do understand they may nonetheless require some adjustments to line up with your present setup... from memory, SFR just lines up with stock but I did get some different IC pipes with Powerhaus for it to line up.

Paulyy

What's the Powerhause intake? didn't know they had them.

Geneqco

I'll take some photos.