michaelmount123

Gosh, if Robstah is out of medication, perhaps a few of us with extra can get some to him.

michaelmount123

I think Duke is spot-on with his tuning strategy. Dubai944: Since your cams are much 'bigger' than stock, you can also limit the amount of advance when the Vario is activated by limiting the travel of the tensioner. Keep in mind the more the cams are advanced, the closer the intake valve is to the piston. Make sure you have enough clearance!

If I were running a turbo 968 on the street I'd be using stock (NA) 968 cams and try the full Variocam scheme on the dyno.

Cheers.

Dubai944

Yes, Duke's idea makes total sense, rather than arbitrarily selecting different activation points, which is what the last tuner tried. Will definately do this next tuning session. I presume I have enough valve clearance with these cams otherwise it would have gone bang with the variocam running a long time ago!

How would you practically limit the tensioner travel?

michaelmount123

Hi Dubai,
I suppose you can consider any cams with lift and/or duration over stock to be aggressive. Yours, at 274, are very aggressive! The cams in the 968 referenced with the dyno sheets have 290 degrees on the intake and 280 on the exhaust. I don't think these (mine) are being fully utilized due to intake restriction. Smaller cams may well suit an engine like this, and if it's a street piece, the cams would be tailored to that application. The Porsche 4V is very responsive to bigger cams, but as you know, you've got to allow air in and air out to fully utilize them.

Is your engine turbocharged? Your avatar suggests that it is. If so, your cams are mighty big. If you've got lots of boost and wide lobe centers maybe they're fine, and maybe they were selected based on dyno results which is the only input you can rely on.

Typically, the larger the cam, the less benefit you'll get from varying the cam timing - which is what you've experienced. On the 968 you can limit the timing change by putting a spacer under the upper (moving) section of the tensioner. If you remove the solenoid you can shape the spacer so it's trapped when the solenoid is reinstalled.

I presume you're using something other than Motronics. Does anyone know if you disconnect the Vario with Motronic does the ECU go into any sort of limp mode? I put a resistor in the (unplugged) connector just in case.

Cheers

Dubai944

Michael,

Thanks very much for the input. My cams were originally installed when I was racing the car naturally aspirated. Intake duration as said is 274, lift is .44, Exhaust duration is 271 with .39 lift. This ran with stock 968 intake, throttle body and MAF, but Stahl headers and straight through big exhaust.

The car was later supercharged with a procharger and 951 intercooler, but I kept the cams. It now runs from a Motec standalone, no MAF. Since then I have decompressed the motor 9:1, and modified the supercharger drive significantly to achieve a reliable 10 psi, with potential for a bit more boost from the procharger still to come.

I have often wondered if sticking with the n/a cams is the best choice now that it is boosted, but was limited in Dubai in regard to finding tuning expertise. It is very responsive and pulls like a train up over 7500rpm but I have always felt it could make more outright power. The car is now back in Australia and I am hoping to finally get some more qualified input to maximise the setup.

Steve

michaelmount123

Odurandina: PLEASE change your avatar. She is terribly distracting.