darek_u

I went to the dyno today. I just wanted to check how good my engine rebuild work was. I expected 230, 240 HP at the best delivered by the engine. What a surprise! Power measured was 270 HP and 370 Nm! I couldn't believe! But both runs were identical. Until now I was 200% convinced my car is bone stock but now I don't know. I rebuilt the engine myself - turbo is 26/8 (rebuild), head is stock (decked 2nd time to the limit, thicker 1.4mm head gasket used, grinded seats, lapped valves), compression 150 PSI on all cylinders, cam is stock (??? I don't know how to distinguish stock cam from NA), new ignition, stock rebuilt injectors, bottom end was in good shape - nothing was changed there. All usual stuff that needs to be replaced was replaced. I know that first suspect are chips inside DME and KLR - when I bought the car I was told these are stock. I noted that computer was opened at some stage in the past but I never reopened it again. the ONLY thing I did was adding one 0.8 - 1.0mm shim to the wastegate to compensate for 25 years of spring life. I don't know if I did right or wrong now but I did it.
My question is - can 25HP power gain be caused by one shim only? I know the easiest way to find out is just to open the DME but I don't feel comfortable with tearing apart this box. Before I'm forced to do it I prefer to ask. What are your opinions?
I would post dyno results but my scanner refused to cooperate. I'll have to see my friend tomorrow to use his scanner and try to post it.

lart951

there is not gain if you shim a good wastegate, what happens is that with time the stock wastegate starts to bleed and you need to run more boost to achieve the same power, once the wastegate is shimmed it holds the boost a little better and doesn't bleed boost as much

check my post 8 years ago

https://rennlist.com/forums/944-turb...ml#post2666718

Jherriott

Maybe shimming a stock wastegate holds the pressure in longer, giving you more boost? Maybe getting 1.0 Bar instead of 0.75 Bar?

darek_u

saying power gain I meant more boost that produced extra hp. correct me if I'm wrong here. on 3rd and 4th and pedal fully depressed boost gauge (stock) goes all the way to 2 bar mark or just below, like 1.95 I know it is inaccurate but on the other hand when I had system in safe mode for some time it stopped at 1.2 bar sharp, just as expected, so there is some accuracy in the gauge, at least in lower levels I think

lart951

did you guys bother to read the link I posted?

darek_u

yes I read your old post. so if wastegate has nothing to do with extra power I must have non stock chips installed.

TurboTommy

darek_u

Yes, of course, if you shim the wastegate there will be higher spring pressure which results in more boost. More boost = more hp all else being equal. The fact that your stock boost gauge is showing almost to the 2 bar mark is proof. I'm surprised, though, that a lowly 1mm shim would get you there.

Lart;
boost is boost
the so-called "bleeding" is relevent only to how quickly the turbo/wastegate combo can achieve full boost. Once the wastegate is open and reaches equilibrium the bleeding is a non-issue and power is determined by boost vs overall turbocharger efficiency

lart951

I disagree, that in theory will be true on a brand new wastegate, the spring after 30 years doesn't have the same strength as new and it bleeds, by adding the shim to all old wastegate all that you are doing is adding a little more resistance to the old spring and restoring some of the performance loss.

darek_u

I have to get the results scanned today and post them

333pg333

Sorry, is this hp gain to the wheels or crank? How was it measured? Assuming on a wheel dyno and it's showing 270whp. Add 15% as a rough guide = 310bhp. So 60bhp with a 1mm shim....??
What brand dyno?

darek_u

dyno is a wheel dyno, German V-tech. air temp 8-9 deg C, power measured at the crank as per DIN 7020 (that's what they told me), engine was run on 5th gear. i have to scan somehow these damn results...

lart951

5th gear dyno, are you sure?

TurboTommy

What do you mean by "bleeds", exactly?
I assume it means it now has less spring pressure holding it shut?

lee101315

All K26 turbo variants bleed off 3-5psi before red line, shimming the waste gate helps the spring keep the valve closed a little longer...helping reduce spool time. I've never owned a 951 with a K26 that didnt loose a few psi before redline, regardless of mods done. The only thing that made the car spool quicker was a tial 38mm wastegate, and the only thing that helped keep full boost to redline was a bigger turbo.

333pg333

Well certainly the ambient temps would have helped but I can't see 60bhp increase over stock 250bhp with a shimmed wastegate.