I run with trackmasters and hooked on driving.

Follow up to this old thread.

I built the motor using stock 11.2 high compression pistons, arrow rods, flame ring heads, custom cams with GT2 profile on exhaust and RS profile on the intake with 115 lobe centers.

I ran 10psi springs but saw 8 psi peak to 6 psi on the top end. After pulling apart the wastegates I found a torn diaphragm on one. I replace em and installed 7psi springs. Very happy with the performance. It feels like a NA GT3 motor.

Using 103 oct fuel I got these results.http://forums.pelicanparts.com/uploa...1423888479.jpg

Fantastic! I'm planning a similar build for my 964, but with e85. What turbo are you running? That dyno was at 7psi, correct?

Hey Pete, Bill, K24 .. summoning you back from the mists of time on this subject please!
Apologies in advance for my lack of knowledge on the science of cam timing and finer engine tuning details.
Just trying to consider the smartest/safest way forward.

Basically I'm wondering does it make sense to have a GT2 Evo cam in a NA 3.8 964 crankcase with 993 RS pistons, sleeves etc..?

PO seems to believe that the GT2 turbo cam is in the engine and that this was necessary as the RSR2 cam (per the invoice) was too hard to get a driveable, idle steady car so he had that switched. Shop say its very unlikely they'd put a turbo cam in NA car but can't say for sure as builder went to work at Ferrari and has since moved overseas.

Car is now on motec and idle is rock steady but tuner said that he wanted to keep advancing timing beyond 17deg but detonation prevented it and he feels compression must be very (too) high...invoice quotes 11.5:1. He thinks its much higher though.

POs quotes & invoices from 2008 rebuild show the 964 was upgraded to 993 RS pistons, sleeves etc... but no mention of heads or crank. Heads were skimmed - maybe too much? Could it be the compression is too high or is this somehow possibly related to the cam timing and GT2 evo cams? I wouldn't think the cam which controls the valve timing would impact on the static compression though it might on the dynamic ... and in this case maybe dynamic is the issue?

Can you guys give me some direction as I'm unsure of what I can or need to do. Car is running well but I want to keep it that way and am wondering if its safe to be at such a high compression or if there's something else that deserves a look.

I am running twin Garrett GT2860RS turbos with Tial 38mm external wastegates. Peak boost 8psi tapering to 6 psi.

I was running 10psi springs at the time of the dyno. Upon further inspection I found a torn wastegate diaphragm on one side. I suspect one turbo was doing all the work on the dyno that day.

I will be installing an EBC and converting to E85 next. That's when the fun really begins!!!

That's a bad combination. The GT2 EVO cams create a lot of static compression. With 3.8 P&C's the compression is closer to being true than the advertised 3.6 compression. It all depends on how they shimmed the cylinders and set squish. I could see how detonation would be an issue. What type of fuel do you run? Can you blend in some race gas?

I can't imagine why you would have trouble with RS cams and not GT2 EVO cams. The overlap of the GT2 cams is pretty bad from what I remember. If you run Motec I would just convert to speed density and ditch the MAF. Then you can run whatever Cams you want. With those P&C's Id run the supercups.

thanks K24 .. not using a MAF, just TPS and Map for barometric adjustment
... is that what you mean? but interesting re the cams thanks.

Yes...Speed density=MAP tuning.

With that I find it hard to believe they could not get the RS cams to idle and perform well at lower RPM's. Heck we run em on MAF cars with out issue.

Compression and cams are part of a matched set. You don't pick one not intended to work with the other. You start with desired RPM band where power is most important to you. The RS cams bump peak HP RPM (assuming proper supporting parts). One of the ways it does this is by closing the intake valve later. Because of this dynamic compression (the only one that really matters) is lower. You correct for this by adding more static compression.

I would start by doing a compression check and comparing it to stock. If you have GT2 cams and high compression that number will be pretty high.

Depending on what you find with the above I would look at matching cams to what you have for pistons and cylinders.

I assume you're twin plug?

I haven't tried the RSR cams yet ... that was when rebuild took place in 2008
and with a batch firing basic fuel mgmt system, not the M48 I have now ... so I'm glad you confirmed what I thought re RSR1 (or 2?) cams being manageable with the right ecu & map.

I think the PO spec was for an auto-x car and thus low rev torque might have been quite important
hence the choice for the GT2Evo cam?

Yes its a 964 re plugs ... and thanks for the input!

Lobe separation angle is going to be what's important with any of the discussed grinds. With the high compression you have I would run a 115 degree lobe separation angle on RS grinds. I ended up running a RS intake and GT2 exhaust profile with 115 lobe separation angles. That's one of the reasons torque is broad and flat. IMHO it's best to give up some of the peak torque in a street car in exchange for a broader RPM band. On the track you would want narrower power band with higher peak numbers from a narrow separation lobe angle.

http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx