[Dubai944]

I know supercharging the stock 968 is well covered here in other posts, but there have been a few people interested in discussing pushing supercharger performance for whatever reason and that is what I am interested in. This is not a thread about which kit is better, or even about kits at all, it is just a discussion about the possibilities of pushing performance and what my experience is to date which might be of interest to some.



I have just rebuilt my race 968 engine, this time with 9 to 1 compression ratio in order to experiment with more boost out of the C2 procharger. From my experience the SFR kit I started with is inadequate in terms of belt setup to ever achieve much more than the advertised 7lbs of boost, the 6 rib belts and the high step up ratio of the procharger just will not work for any length of time without belt slip problems, especially at constant high rpm as in racing, however the C2 does have the potential to push 1100cfm of air and "theoretically' support a lot more boost and hp.Exactly what the limit is is up for debate.



I have installed a custom 7 inch crank pulley and 8 rib pulley set in an attempt to get less belt slip by running a bigger (3 inch) pulley on the charger. This also gears the charger to run closer to its maximum design at about 7200rpm. By contrast this gearing is spinning the charger at the same speed at just over 6000rpm as it used to achieve at 7000rpm, so boost is available earlier. To avoid overboosting I have installed a boost limiting valve from 928 motorsports, basically just a big spring check valve on the inlet side.



The car ran with this setup for the first time last week. An initial tune on the dyno was problematic because the injectors maxed out and it wasn't till later I realised I had set the fuel pressure using an incorrect calibration for the pressure sender in the Motec and we had actually tuned the car with about 1 bar less fuel pressure than we were reading. We didn't bother pushing the timing and contented ourselves to setup the lambda control. Boost was also down on what we expected, still 6-7lbs and we didn't know if it was the limit valve not working or what. So we didn't bother pushing the ignition timing, the dyno was aborted and we didn't get any useful power readings.



After discovering and fixing the fuel pressure issue, I had an opportunity to track test the car and by logging data and gradually adjusting the motec managed to scale the map back to compensate for the changed fuel pressure to the point where lambdas were in the ballpark of the dyno setup and injector duty cycles were back in a sensible range.



With a bit of belt adjustment boost was also coming in much earlier. Previously I would see nothing significant till around 4000rpm and barely hit 6-7 lbs at 7000rpm. With this setup I am now getting positive boost as low as 2000rpm, a solid 4lbs by 4000rpm, 6 lbs by 5500rpm, and a consistent 10lbs of boost by 7000rpm. Interestingly it would stay flat after that dropping just slightly through to redline at 7500. For this first track test that was as far as it would go regardless of the limit valve adjustment so I think there is still some belt slip issues going on even with the much bigger pulleys and belt width.



Happy with this result for a first time out, I decided to run a race as a further test to see how the car performed against the new cars in class which are a lot quicker than I was running against previously. In this new class I am racing against some very sorted GT4 Aston Martins and Maseratis, KTM X-Bows, Ginettas and Porsche Cup Cars. The poor old 944 now looks completely out of place, as does my privateer build it, fix it race it approach look against some very professional teams. However, to my surprise it actually performed well and I could even match some of the class cars for straight line speed. The early boost is great for getting out of the corners. Considering the tune is nowhere near right yet, and there is headroom for more boost if we can figure out how to get it, this is looking good. I hope to be back on the dyno for something more conclusive power testing in the next couple of weeks. For now here is the in-car video which gives some impression of the cars improved performance.



http://vimeo.com/20399968

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

It's amazing what can be wrung out of these old cars. I've always been a lot more impressed with seeing older, less expensive cars perform at a competitive level, than seeing some guy plunk down $125K on a new GT3 and go fast (duh).



It sounds like what you are trying to accomplish is very challenging, so congratulation on the rpomising initial results. I assume this is a pure race car, and not something you'd ever drive on the street, right?

Partial Post: Please Login or Register to read the full post.

[flash]

cool stuff - i love to see people pushing the limits



any idea what the output is relative to a motor with 11:1 and 7lbs? i mean, did you find that you are making more power overall, did it just move the curve, or was it nearly a wash?



what MAF are you using? or are you using one at all?

Partial Post: Please Login or Register to read the full post.

[Dubai944]

Lol! Definately a pure race car.



I once got stuck without a pickup truck and only because it is Dubai and it was early morning I decided in desperation to drive to the track, a distance of about 8km. I have 1200lb front springs and a very loud straight through exhaust, so you can imagine the spectacle as I drove my fully stickered race car down the main 8 lane freeway.... Dumb idea, never again!

Partial Post: Please Login or Register to read the full post.

[Dubai944]

Thanks Flash, hopefully more craziness to come.



In terms of power output, my butt dyno tells me it is making much more power overall and has moved the torque curve lower, but until I get back on the dyno for a proper tune who knows.



Our one aborted attempt at a dyno pull with the injectors maxed out and only 6lbs boost showing to just 6500rpm netted 251whp, which on the dynodynamics dyno is still pretty decent. With everything fixed at the track it was much stronger.



The only real indicator at the moment is the cars speed. On that track i was up about 10km/h on maximum speed on the straights compared to anything previously.



Edit: And no I don't run a MAF.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Does a metal spiral object that requires 1200 lb of force to deflect it one inch still qualify as a "spring?" Sounds like "post" might be more accurate <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />

Partial Post: Please Login or Register to read the full post.

[flash]

i'd love to see some data like the shape of the curve relative to the curve of an 11:1 motor, and especially intake temps - i'm not so much concerned with hp numbers or anything like that, but rather the comparison of 9.5 to 11 and 10lbs vs 6 or 7



i've been toying around with a new motor with 10lbs, and deciding what to do about CR and intercooler and all that obviously plays in



fun stuff either way though

Partial Post: Please Login or Register to read the full post.

[Dubai944]

I'll try and dig up some of the old dyno charts and also extract some logged data on intake temps etc.

Partial Post: Please Login or Register to read the full post.

[flash]

thanks - that will go a long way on telling me what to expect and which direction to head

Partial Post: Please Login or Register to read the full post.

[craigawoodman]

Where did you get the new crank pulley and SC pulleys made (or where they off the shelf)?

Partial Post: Please Login or Register to read the full post.

[Dubai944]

I designed the pulleys myself and had a local machine shop make them. Labour costs here are cheap. Then I took them home to Australia on holidays and had them hard anodised. Biggest challenge was wanting to keep the S2 harmonic balancer. The crank pulley now sandwiches between the balance shaft pulley and the balancer which sits inside the crank pulley.All held together with slightly longer bolts. 7 inches was as big as I could make fit and still keep the rear of the belt plane the same to avoid making new supercharger mounts. Timing belt covers are gone and also had to remove the power steering pump, which I replaced with a BMW mini electric pump.



Heres a couple of early pics of the crank pulley without the balancer yet in place:

Partial Post: Please Login or Register to read the full post.

[Dubai944]

Flash,



Here is an early dyno chart with the standard SFR kit setup achieving a maximum of 6-7lbs. The only other mods to the 968 engine at that time were cams, headers and it was being tuned with a Haltech interceptor attached to the Motoronic. Following that is a log chart from a track session with the same early setup which shows the manifold pressure curve (just subtract atmospheric, 14.5, for boost level), RPM, throttle position and inlet temperatures (just before the throttle body). Then a log setup with the new setup. You can see that with the new setup the boost levels are higher and earlier.With the new setup I am already getting 6-7lbs of boost at 5000rpm and 9-10 by 6300 which stays flat through to redline.



Inlet temperatures are much higher in the new setup, but this needs to be in context that the outside air temperature was approximately 10 degrees warmer that day and also it is from a mid race point instead of the earlier more leisurely track session where I wasn't pushing the car quite so hard. Obviously the intake temperatures are still higher with more boost and highlight the limitations of the stock 951 intercooler. Another cause may be that I have had to run the top radiator hose much closer to the intake pipe to clear the new belt setup, so some judicious insulating of the hard pipes might bring the inlet temps down a little as well. I don't have a dyno chart for the new setup yet, but I expect the curve to have moved a bit to the left with the earlier boost and the overall power output to be a fair bit higher.



With regard to the dyno figures which are on a Mustang Dyno, bear in mind the exact same setup dynoed at 308whp on a dynojet, so it is hard to do a comparison with other cars. As you say its the shape of the curves that are relevant. Unlike the street crowd, we prefer the dynos that show lower figures because our classes are based on power to weight <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />



Also I noticed I had a brain fade and said CR of 9.5 to 1 in my post last night, actually the new pistons are 9 to 1. I was originally going to do 9.5 to 1 then I changed my mind when I ordered them.



(You may need to go to the external link and use the magnifying glass to see the detail)



Dyno of previous setup - 7lbs boost





Logged Data from previous setup





Logged data from new setup

Partial Post: Please Login or Register to read the full post.

[savvas968]

hey Dubai 944,



if you ever visit Bahrain drop me a line

have a 944 turbo track car and couple of 968.

Would love exchanging ideas.

Partial Post: Please Login or Register to read the full post.

[Dubai944]

Cool. I lived in Bahrain for four years. I left before the track got built though.

Partial Post: Please Login or Register to read the full post.