[Dubai944]

For the interest of the supercharger crowd here is from the latest round of tuning just completed today on my supercharged 3.0. Current specs are S2 block with piston squirters, 968 head, Arrow rods, Wossner pistons 9:1 compression, big duration NA cams, stock 968 throttle body and intake. 72lb/hr injectors. Stahl headers 2.5 inch exhaust. Procharger C2 head unit and stock turbo intercooler. Tuned with a MoTeC stand alone.



The first chart shows power against boost level. My first question to myself is why is the boost level still flattening out at about 6000rpm. I have geared the supercharger to run at it's maximum design speed at the set rev limit of 7500rpm which I occasionally run to in the heat of racing. This is spinning the head unit much faster than the standard gearing used in any of the kits. The gearing has helped raise the boost levels down low which is good for a centrifugal charger, but in theory the C2 can flow 1100 cfm of air, so could it really just be running out of efficiency so early and just be too small? No compressor maps available from Procharger of course so not much chance of scientific assessment. I have gone a far as I am prepared to go making sure the supercharger can do it's best. Maybe it's just the inefficiency of the stock intercooler, or the intake manifold. Maybe the 928 motorsport boost limit valve which I have screwed completely shut is still opening slightly anyway and limiting the boost. Hmmm...







Anyway power level is acceptable and the torque curve is reasonably flat (see the second chart) so performance should be where it needs to be on the track. The curve looks ok but for some reason the chart scale is in dyno load of Lb. The third chart is apparently the calculated flywheel values (probably not very accurate) but at least shows torque in Ft/lb.

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[pmcrespo]

EPIC! I have such HP/TQ envy right now... :-) LOL....

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[craigawoodman]

Dubai - what type of belt are you running and what size drive pulley on the SC unit? I am running a 6-rib (double sided) and it still slips and I am nowhere near 10psi. Oh to be able to get 10psi.



Well done and top marks for persistence.

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[Dubai944]

I know what you mean. Stopping belt slip has been a three year battle, but I did win in the end. Two days of tuning and the belt stayed cool and tensioned the entire time. The boost trace has remained linear and repeatable over multiple runs which never happened previously when belt slip was still an issue, it would be all over the place.



This is what I have evolved to with my setup:



8 rib belt

7 inch oversized crank pulley so I can run bigger supercharger pulleys for the same gearing

3 inch supercharger pulley that gears the C2 procharger to run at maximum design speed at my rev limit (Could never have achieved that with the standard crank pulley)

Replaced the kit aluminum bracket and single idler with a stronger braced steel bracket with two idlers to eliminate any possibility of head unit flexing and maximise pulley wrap.



Other kits may or may not have the hardware design weaknesses mine did, so you may not need all these solutions, but from what I have seen, not only with supercharged Porsches but on most centrifugal charger installations for most cars, beating belt slip is the number one challenge to making decent boost levels from any of the head units. The solutions are always better belt wrap, bigger supercharger pulleys, eliminating flexing in the head unit mounting and wider belts.



This is the original bracket mount which originally used 6 rib belts (8rib shown here) and a single idler:







This is my modified bracket mount with 8 rib belts and twin idler:







This is installed in the car:







Of course now I am sure the belt slip is not the reason, I can see there is some form of restriction or inefficiency inherant in my intercooler or intake system that is limiting boost at 10psi. Theoretically it should be pumpig enough air to keep building boost a little higher. I was originally targeting 1 bar of boost and a genuine 400whp, but still a ways to go yet <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />

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[craigawoodman]

Ah, I also see some benefits of doing it on a 944 S2 engine. The plastic covers over the timing belt restrict the angles that the belt can go towards the supercharger. The Raptor unit can only spin one way and this necessitates a double sided belt (or destroying a single sided one by driving off the back of it - as supplied - not by Raptor, but by the kit vendor).



I really like the double idlers - it is something we were looking at, but with the plastic shroud issue, I don't think we can.



Where did you get the crank pulley from? Any spares?



Performance is a disease. Keep on keeping the bastards honest.

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[Dubai944]

It would fit the same with the 968 block, it was originally a complete 968 engine, but I damaged a bore early on and swapped to the S2 block. To fit everything I just removed all of the plastic timing belt covers. For a race car it's not an issue and has some advantages - easier inspection etc. The crank pulley I had made in Dubai. I have had a couple of pulleys made in Australia recently at a local machine shop and Australian prices are a bit higher, but not too bad. You might pay $200 for something similar I guess.



7 inches was as big as I could go without relocating th whole belt plane forward which wasn't really an option with the limited clearance to the radiator and the hassle of changing the alternator and charger mounts. Heres a few picture of the crank pulley. I had it made so the original S2 front pulley, which is also a harmonic balancer could bolt through the new shell onto the crank in it's original position.

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[Eric_Oz_S2]

Steve,



You mention "NA" cams. What are these exactly? I take it you are not running variable valve timing?



Eric

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[Dubai944]

Eric, the cams are race cams designed for a naturally aspirated engine. I fitted them previously when I was racing the car naturally aspirated. They are fairly big - 274 degrees of intake duration and 271 degrees of exhaust duration, and a bit more lift than stock. They effectively move the power band up the range making peak power closer to 7000rpm and the engine pulls very strongly up through 7500rpm. They have worked ok with the supercharger. I do have variocam connected on the 968 head but although we have tried different activation points it desn't seem to make much difference overall with these cams.



By the way, I had a run at Lakeside this morning - crikey, I forgot how narrow and short that track is..lol!

There were too many cars on the track at once and my speed was a lot higher than most of the other traffic so I spent most of the time trying not to run into anyone. I had a new quiet exhaust made for Lakeside and we tested both exhausts on the dyno. Unfortunately it seems the dyno guys didn't tighten the exhaust bolts and on the second session out it dropped on the track after 5 minutes running, so that was that. Still it will be fun to get back there next month a get a decent run at it.

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[Eric_Oz_S2]

Nasty dropping the exhaust. Bet that would have exceeded the 95 db limit.



I try to avoid Lakeside on those Saturday sprint things. The groups are always large and there is too much variance in car speed. If you can, you are better trying the midweek events. It's a pity you couldn't make it to the PCQ sprint last month. So did you crack the 1 min mark with all that traffic?

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[Dubai944]

No I never got any times at all. I realised during the first sesssion I forgot to reinstall the GPS aerial for the datalogger after repainting, so no track data..doh! I was going to use the stopwatch in the car to get a rough idea on the second session but then the exhaust fell off. It was pretty much bumper to bumper traffic anyway and there was never a clear lap so I doubt the times were very quick. Next time.

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[RS Barn]

Dubai944

Shoot me an email

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[Dubai944]

Finally got to give it a decent run at Lakeside.



The car is still setup for Dubai so it didn't like the bumpy old Aussie track. Slicks are old and my driving is rusty but it should be quick once I get it setup properly. Too much slow traffic to really get going, but it was fun and the engine is running nicely.



http://vimeo.com/47811338

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[Eric_Oz_S2]

Awesome stuff Steve. You should come to QR on Saturday. Not as fun as Lakeside but you will get a better run.

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[tamathumper]

Looked like a blast! Was it anything-goes day at the track? I could have sworn you passed a VW Golf, a Honda CRV, an old Toyota Celica, a Chevy Malibu, and a 1930's coupe?

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[Rap]

Yea I saw that 30's coupe. Was that blonde in the passenger seat Bonnie? Lol

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[Dubai944]

Yes it was kind of a weird group of cars. The 30s coupe thingy was cool.



Not the usual Ferraris, Lambos and Porsches we used to get at track days in Dubai..lol



Heres a link to a pic of that coupe

http://www.trackphotos.com.au/p759579984...#h251eca0d

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[craigawoodman]

Dubai,



Bloody quick time considering the amount of traffic that held you up. With new slicks, etc - it will be an absolute rocket of a time.



Well done.



Good to see a front engined 4 cylinder putting in those sort of lap times.

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[Dubai944]

Thanks Craig, based on best sector times from different laps the theoretical best lap was 56.3, so realistically 57s should be comfortable. A bit of setup change and a bit more familiarity with the track and hopefully I can do a bit better than that as well.

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[pmcrespo]

Nice!!!! Great driving!

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