4722 replies to this topic

[Duncan VXR]

Those cams and head work would match a bigger turbo better DG

[Dally868]

i have build few engines and we managed control boost with 38mm externall waste gate and still push 480 with gt30 on 1.75 with 400 pounds of torque which means turbo is working in a turbo map. your torque is way to low for that power u should be in 400s or high 300s.

[Nev]

I think the graphs will show the creep definitively. 

 

For the low power configuration (which is the only place this issue rears it's head), I have asked Chris to pull a bit of timing at high RPM to help reduce the power down. He thinks this will stifle the power down by about 10 or 15 BHP.

 

@Dally, I am not sure I understand you fully. The issue we have is wasting all the boost successfully at high RPM. The objective is to keep the torque flat from 4500 RPM to 8000 RPM.

 

@Duncan, yep in retrospect the engine breaths too well for a mid sized turbo. There is a lesson of economy to be gained there for anyone tuning their Z20LEx and switching to a mid frame turbo. Still it's satisfying for me to know the engine is all working very (perhaps too) efficiently. If I ever have reason to strip the exhaust manifold off I suppose I could get a 60mm waste-gate installed, but the hassle (and cost) would be significant.

 

 

Edited by Nev, 26 October 2013 - 05:15 PM.

[Dally868]

what i thought is if u are in map of your turbo or u have restriction on your set up. u should higher torque and keep it there. we used 50 mm waste gate on 600bhp car again no back pressure and flat torque curve but that is extra 120 bhp Im not sure if i explain that good enough

[cnrandall]

The waste gate issue is probably more down to exhaust manifold design and waste gate placement than purely waste gate size.  We use the MVR's on our build and for the LOTRDC race regs we have to peg the power back down to 260@ the hubs and the waste gates cope just fine with this.

[cnrandall]

Just looked at your blog and reminded myself of your exhaust configuration… You have the waste gate intake pipe at 90 degrees to the manifold and the exit feeds into the the wrong side of a bend (i.e. high pressure zone).  It ain't waste gate size that's your problem… 

[siztenboots]

will this be due to pressure differential between the two exhaust flow routes

[steveboyslim]

Those cams and head work would match a bigger turbo better DG

To a degree you are correct, but lesser cams and a head which does not flow so well (no big valve and/or no port job) can cause problems with surge else where in the rev range. Steve

[Nev]

Just looked at your blog and reminded myself of your exhaust configuration… You have the waste gate intake pipe at 90 degrees to the manifold and the exit feeds into the the wrong side of a bend (i.e. high pressure zone).  It ain't waste gate size that's your problem… 

 

Yes, very good point.

[siztenboots]

 

Just looked at your blog and reminded myself of your exhaust configuration… You have the waste gate intake pipe at 90 degrees to the manifold and the exit feeds into the the wrong side of a bend (i.e. high pressure zone).  It ain't waste gate size that's your problem…

  Yes, very good point.

 

will this be due to pressure differential between the two exhaust flow routes

[kontraman]

10 points to my good friend NEV and his wonderfoul project...

[VXT Tim]

Any update Nev?

[Nev]

I've had some rather gloomy news from the mapper

 

After doing the bulk of the mapping, the engine suddenly started to make a "thumping" sound from the lower half. In conjunction with the fact that it is still smoking (due to high crankcase pressure) it looks like I am going to have to extract the thing and investigate/rebuild it.

 

The engine still idles fine, but won't be happy to be driven, so JJJ is very kindly going to collect it on his trailer tomorrow for me; thank you Jimmy.

 

Until I open it up I won't know for sure what is causing the 2 problems, though I have my suspicions. At least it's winter time and I'm not losing any driving time.

 

Edited by Nev, 11 November 2013 - 09:04 PM.

[CocoPops]

Time for a new block? Taking what you've learnt and starting from fresh rather than a tired block? Build it how you want it from day one etc rather than trying to fix what you've got?

[Zoobeef]

Big ends? From a lack of oil of something else? :/

[Zoobeef]

Atleast its winter too!

[Nev]

Time for a new block? Taking what you've learnt and starting from fresh rather than a tired block? Build it how you want it from day one etc rather than trying to fix what you've got?

 

Yes, I think I might end up starting with a new block. However the current one does have waterway strengthing wedges and oil squirters, so perhaps I will risk re-boring it to 87mm if the crank and bores look ok. Until I open it up it's hard to know what to expect. The thumping could be a variety of things, top candidates IMO:

 

1. Rod big end bearing failure, possibly due to oil starvation.

2. Crank thrust bearing over-worn, causing crank to move laterally.

3. Lose crank timing gear wheel, not likely to make that kind of noise really at a guess.

4. Crank main bearing failure, not likely IMO as I've inspected them a couple of times and they looked great.

5. Lose con rod bolt or lose crank cap bolts.

6. Something else

 

The thing I am more concerned about is the high crank case pressures, this problem has dogged the engine for some time now and is irritating.

Edited by Nev, 11 November 2013 - 09:20 PM.

[Ormes]

[hairy]

Bu99er. Give us a shout if you need a pair of hands Nev.

[Duncan VXR]

That engine has given you some grief, what did Steve say as he built it, like you state its always had niggles? I had zacs engine off him which I was going to rebuild at some point if you want it let us know. Has the same work as yours to the block but std head setup Sure you will get it sorted nev, chin up sir DG