Dubai944

I am looking into modifications required to fit my current supercharged 944 race car into various Australian motorsport categories so I can get the car back into some meaningful competition having shipped it back from Dubai where it ran as a GT car.

One option is to convert it to Improved Production spec, which would allow most of my current modifications with the exception of the supercharger setup if I convert it to 944 Turbo configuration.

Engine size and block is free within available replacements, so my current 3.0 block which was built for boost, arrow rods, 9:1 compression etc can stay, but head, inlet manifold, supercharger device and exhaust manifold must be as per manufacturers design spec. So the 16v head and mechanical charger would have to go and be replaced with a factory 8v head, turbo and manifolds.

The only head mods allowed are removal of metal, boost can be increased but the turbocharger has to be as per manufacturers specs. Exhaust is free after the charger.

My question is what combination of parts would be best for this conversion. I am not too familiar with the factory 8v heads and turbos. Did any of the 8v heads have bigger valves than others? Was there a 'best' version of the factory spec turbos or manifolds to use?

Anyone running a similar setup i.e. close to stock head, turbo and manifolds on a 3.0 block and can give me an idea of what sort of power I could tune to? I run a standalone Motec.

Dubai944

No comments? Maybe I am not asking the right question.

I guess most people who have gone to the trouble of running 3.0 blocks are also extensively modifying heads, turbos and manifolds.

I want to understand the effect of running stock spec 8v head, turbo and manifolds on a 3.0 litre motor. Can the flow restrictions be adequately offset with boost to still produce decent power on the bigger motor and what sort of torque curve am I likely to end up with for driveability etc?

Obviously the current 16V head, 968 manifold, cams and stahl header setup has decent flow, but boost is limited to 10-12 lbs with the supercharger. Would I be able to produce enough flow with a restrictive stock 8V turbo setup to comfortably match the curent power output and would I loose much in the way of throttle response compared to the current setup which acts just like a big N/A?

My 16V 968 head has 41cc chambers and the pistons I use give 9:1 compression. What are the chamber sizes on a stock 8V head? Am I likely to run into any valve clearance issues going to a stock 8V head?

JohnKoaWood

To run an 8V head on your 951 would require the head off an 89 NA (only 8V head that will align to the coolant jacket of your block).

Turbo, you will want a K26-8 (although this will be undersized for the 3L displacement IMHO)..

Perhaps PM Chris White, I know he has assisted a few Aussies in the past... he may have more ideas...

67King

I can't definitively say, but I think the cams make a lot more lift, and the valves are much larger in diameter, both of those factors are directionally wrong.

As John said, a K26 is going to be on the small side for a 3.0L. It may make some torque, but you may be out of turbo by 5,000 RPM. I honestly think you may be better off just going back to a 2.5L.

Paulyy

could you use the turbo from a 968 turbo s? or it has to be 944 specific? then you could run a k27 on that engine

Dubai944

Thanks. So valve clearance issues might stop it from being a simple head swap, and the K26 turbo is likely to be too small. I will check with the experts such as Chris White and Lindsey Racing to confirm. Will have to test the rules as far as whether 968 Turbo S factory specs could be applied.

Might be too much hassle all around... Option 2 - Fit LS6 and chase the Sports Sedans

333pg333

Why couldn't you use a 2.7 head? It fits straight onto the 3L block you have and comes with larger valves.

Dubai944

I guess the question is will the 2.7 head with the appropriate cams be compatible with the pistons I am currently using for valve clearance.

333pg333

Not sure, but don't think so. C/R is too high. Get some custom Wossners for about $1k.
Turbo choice is harder. Not sure if you could run the k27 as it wasn't on the 944 turbo. Seems odd that they'd let you run any capacity but stick with the same old turbo?

Dubai944

The rules allow for any replacement block of the same family, which alows the 3.0, but intake system has to be stock.

I was wondering if it was essentially just a head and manifold swap, but if it involves an engine rebuild there are other things I'd rather do.

Paulyy

don't the pistons in it now have 4 valve reliefs? if so that may not work with a 2valve head.

Dubai944

THe 968 pistons do have 4 valve relief and a wide central dish. I don't have any pics with me but the CR is 9:1 and from memory the dish was noticeably deeper than on the standard 968 piston. The 951 pistons I have seen pictures of appear to have a smaller central dish that is not any deeper so purely based on space available for valve extension the 968 pistons seem to have more room than the 951 pistons.

Can I just bolt on an 8V head and have the 968 pistons work with 2 valves? Maybe the valve lift is a problem, or the design of a 4 valve piston is the wrong shape for 2 valve fuel burn, I have no idea and need expert advice.

Yes I could change pistons, but if I don't need to it would save some time and cost.

333pg333

What are the 4v pistons from Steve? I mean, are they just stock 968 ones or did you get them made up?
In that you'd be refreshing the motor anyway during these changes, 'if' you had to change to a different piston it wouldn't be the end of the world. Sure, it's just extra cost, but not a lot.

If you chuck a V8 in there you're only going to be mid pack at best. If you can run a 3L with the 2.7 head and compete in Prod Sports then I think you'll be at the pointy end of your class. I'd still like to know what turbo the 968 and RS turbo ran? Although they mightn't let you use RS specs as there were only 4 made.

Paulyy

I think you're better off with new pistons. i don't think the 4 valve pistons will work properly with the 2 valve head.

From wiki.

Dubai944

The pistons are custom Wossners I had made. I just don't particularly want to rip apart a motor only recently built that runs perfectly well. More likely I would just build up my spare block in that case.

I can run the car as it is under QRDC rules which limits it just to Lakeside and Queensland Raceway. The category rules there are "two doors with a roof" but the competition doesn't seem too inspiring lol.

For anything serious as far as State Championships or National events I need to get it comply with a CAMS category. 2B Marque Sports Cars seems most logical. Also have to see what the State Sports Sedan level is as it might fare ok as is there without any mods. Certainly not at national level though, with all the 600hp, 900kg monsters there.