nile13

I am actually assuming that power at high RPM would be the same, as supercharger would be switched off.
In actuality, supercharged and turbocharged versions have lower compression than their NA cousins, but with aftermarket supercharger, I assume that would not be the case.

graham_mitchell

Ok, I have never heard of such a kit. Regardless, that is not the case with any of the available Porsche-based supercharger kits. The supercharger is engaged at all revs.

nile13

Graham, I meant the factory installed superchargers and turbochargers. They have lower compression than NA engines. I think it's a longevity issue, but might be wrong.
Thanks for the info and Sachin's graphs, it was interesting to see!

Chris Berendes

holy cow,

i come back two hours after my first post and there is a huge discussion going on. Thanks for all the info.
I will have a look at all the supercharger threads and make up my mind.

@ Mr_Bock: If the supercharger kit gives me the power and torque of the TT but without the 4WD and the supposedly "bad" fuel consumption, then I have just found my next birtday present - I will have a look at some of your older posts

Chris

1999Porsche911

You are right. The old school of thought when you installed a blower was to reduce the static compression ratio of the engine which allowed you to increase the boost to amounts seen in Turbos. However, doing so with a supercharger would greatly reduce the lowend power at normal driving power even at WOT. You have to remember that a Centrefuge SC engine is not using any boost at all when vaccum is present. so you could cruise at 100 mph and not have any boost. As the throttle gets near WOT, the boost that had previously been simply recirculating in the blower, enters the engine and you have instant power.

For a ceterfuge blower on a low compression engine, you would have to spin that baby at some crazy RPM's in order to produce the kind of boost you need to get substantial power gains. So, now a days, it has become the prcatice (for those of us who have faith in the strength of their engine's componants) to keep the high static compression ration and induct a lower bost for power. i.e. a 996 with compression ratio of 11.3:1 with 6.5 psi boost gives you an effective compression ratio of about 16.3:1. You would have to boost a 9.4 static engine with 10.5 psi to get the same type of power but would have conciderable less bottom end torque.

It all boils dwn to what the boost will give you in the form of engine compression at a given rpm. A higher static compression engine will always give you far more power in the bottom end and at maximum RPM, both engines should be equal.

Chris Berendes

@ Graham: If I look at the graph and compare numbers at 4000 RPM then it seems like the torque is at about 210 vs. 260 without the supercharger. - is that right? Then, if I am at roughly 4000 RPM when doing 110 mph, that would give me lower power than in the reguar version?? Only benefit seems to be no drop-off over 5000 RPM

Thanks for clarifying this
Chris

graham_mitchell

That wasn't a very clear example, sorry. This graph shows the night and day difference between NA and supercharged. You have considerably more torque and power AT ALL TIMES. I hope that puts this matter to rest!



Yes, and that's one of the reasons why centrifuge superchargers are no longer popular and positive displacement superchargers are in favour - the latter always provides boost. I hope no-one gets confused by this - the 964, 993 and 996 TPC supercharger kits all use positive displacement superchargers.

Chris Berendes

Graham, thanks for that. Thats what I was hoping to hear!
Chris

Tour18

NOTHING, I repeat, NOTHING compares to positive displacement supercharging.

It will permanently alter your perspective on automobile performance... Permanently.

24FPS

nice.

scarry... but n i c e .