Star of the Art - 968/944 Engine Development

[Penguinracer]

Jon Mitchell down in Bournemouth is building some remarkable "big bore" 3, 3.2 & potentially 3.4 litre 968/944 motors using steel Nikasil coated wet liners. Running a Garrett Dual Ball-bearing turbo with a KKK #10 hotside - these engines are giving effortless torque.

I'm interested to hear from anyone who is developing their 968 /944 powerplant for big horsepower (e.g. 450+bhp).

What are the practical limits for what the four cylinder Porsche engines can produce & what the cars can effectively get to the ground?

[Thom]

On a 944 turbo I would be concerned with excessive low down torque as the VAG-derived gearbox has unexceptional bearings that may not be up the job of dealing with a lot more torque than what the engine is originally capable of delivering. Being quite away from the engine the gearbox has more kinetic energy to absorb compared to a non-transaxle car.

I am currently building a fairly "standard" 3.0 engine but I find my lightly upgraded 2.5 currently fast enough for the rest of the car (and it's got a great chassis with Motons, big sway bars, solid bushings, etc). I am not convinced it will really be worth it and it may well upset the excellent all round package the car already is.



PS : sorry I'm not aiming at 450+ bhp but only for something driveable with real world abilities. Unexploitable peak numbers are for lunatics IMHO and a 944/968 will never offer as much traction as a rear engined-car anyway, except perhaps with 600lbs of sand in the trunk.

Edited by Thom on Wednesday 23 May 17:47

[nick_968]

I dont think there is much point in going above 500hp in terms of reliability or driveablity. For a track car 400hp is probably about the optimum for the chassis but it all depends on how the torque is delivered. If the turbo comes in to hard to quickly this feels great in a straight line but is a nightmare to get the power down in a linear fashion out of the corners. From previous discussions 600hp has been mentioned but I dont think this is realistic or necessary. For me I would be happy with my car mapped to give 500hp at say 22psi, but I would want it on adjustable boost and for the most part would probably cruise around and do tracks with the boost turned down to 15 - 18 psi at around the 400hp mark. Power is only any good if you can use it and really much above 400 is just for straight line speed. It is possible to build a 400hp engine that runs at 15psi and it will be factory reliable, driveable and last 100k.

[diver944]

I have the first 3.2 that Jon and his engine builder Simon have put together and have just had it re-dyno'd at Weltmesiter now that it is nearly finished in terms of development and tuning. At 17psi of boost it yielded just under 400bhp and 480lbft of torque (650 Nm). Despite these pretty high figures for a late 80's car with no traction control or fancy suspension it is actually an absolute pussy cat to drive. Lag is hardly evident and the boost builds so smoothly and with such refinement that it is a much easier car to drive than it was when standard at 250bhp

The attached graph (blue lines) shows that peak torque is achieved in the midrange at 3500rpm, but currently drops away because there has been no work on the ignition timing yet. Jon is completing the tune next month and we are hopeful that at 18psi the car should make a similar power figure to the current torque and then hold it much closer to the redline. The internals of the engine were specced such that it can run safely at 30psi of boost as long as the fuelling and tune could match it. At that stage a conservative estimate would take it well over the 600bhp mark but I have no intentions to run anywhere near those looney levels as the gearbox simply could not take it for long and I have no intention to fork out on a new gearbox as well

Edited by diver944 on Thursday 24th May 19:09

[nick_968]

Paul, I know the internals are specced for higher horsepower, however I think you would run into other problems as 30 psi on a 3.2 is quite a feat. You would be flowing huge amounts of air and keeping the head down would become a major problem. I know you have no intention of running that kind of power but if you did I think there would be some changes you would have to make to make it trouble free. The factory studs are also only good up to 500hp. After that you need to go to ARP or Raceware.

[nick_968]

Oh and by the way, nice charts, you will be breaking 400hp with the extra 1 psi and I suggest you get the ignition done asap as with the bigger bores it will need different ignition timing to get the best combustion spread across the piston. Just a word of warning though, as has been said before on here it is torque that breaks gearboxes not hp and yours is seriously torquey. You must be getting very close to the limits of the 951 box. I know you do not beat on your car so hopefully it will last but its a fine line you are treading!!

[Thom]

650 N.m must taste very good indeed.
I presume rear wheels are spinning in the dry at least until fourth gear ?

[diver944]

Ahem yes, rear traction was a slight issue on the old Continental 255 tyres but I'm now runnning with 275 sized R rated Kumho V700's and that is soooo much better (in the dry). Of course more grip means more stress on that gearbox again. Arrrg what am I doing

[nick_968]

You love it Paul!! Keep pushing those limits!!

Oh how I wish I had a turbo like yours......I am waiting for Simon to develop the bits to make a full garrett work on our cars so I can get rid of my old fashioned turbo and get that nice spool up you have.