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supercharging an SC

I've have trolled this section of the forums section here and there for awhile now. I don't see much on supercharging. I am considering a low boost, for engine longevity, supercharger for my 79 SC. It doesn't seem that anyone is making a pre-designed kit any longer. Has anyone out there done this? What power gains could be expected compared to a cammed out 3.2 rebuild? My car is a 79 3.0 with stock internals, about 110,000 miles (a puppy in 911 world, hence my hesitance on ripping her apart) with cam chain tensioner update, SSI's into a 2 in 2 out M&K, and a nearly finished Bitz EFI set up.
Old 09-26-2012, 06:18 PM
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Sell your exhaust system, you will get good money for it, get some 930 headers and a turbo, no broken belts, no custom fabricating of brackets, no supercharger whine and all parts are off the shelf. The supercharger conversions I've seen look like too much messing around, turboing is so easy. Low boost on an SC should easily fetch you 300chp. Cammed out 3.2 would be lucky to make 250.
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Old 09-26-2012, 07:02 PM
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Quote:
Originally Posted by spence88mph View Post
Sell your exhaust system, you will get good money for it, get some 930 headers and a turbo, no broken belts, no custom fabricating of brackets, no supercharger whine and all parts are off the shelf. The supercharger conversions I've seen look like too much messing around, turboing is so easy. Low boost on an SC should easily fetch you 300chp. Cammed out 3.2 would be lucky to make 250.
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Old 09-26-2012, 10:08 PM
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Click on the link in my signature for a fairly detailed account of supercharging an air-cooled 911. From this experience I can say it is no harder or easier than turbocharging, but the difference is the amount of collective knowledge available to help design and troubleshoot the two approaches. There are many more experienced turbocharging posters than supercharged so if you need help along the way you are better off turboing.

In either case you need to sort out intake plenum, inter cooling, tuning, bypass/wastegate and bracketry.
Superchargers allow you to use a traditional exhaust, for cost, choice and complexity benefits. You also don't need to deal with oil plumbing which is necessary for most turbos.
You'll need to fabricate an output manifold for a supercharger, where turbos are usually a simple tube and hose arrangement.
Turbos can yield greater peak hp and torque results. The curves are typically different.

For the record my auto rotor with a gates pk6 belt does not whine. Observers are unanimously surprised when I tell them it's supercharged.
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Old 09-27-2012, 03:37 AM
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I also have a 79 which I supercharged. You can find it here: Rebuilding and Supercharging 3.0L

If you go low boost (about 6 psi) no intercooler is needed. It certainly makes the car a lot more fun to drive. I have a whipple and there isn't a significant whine. I actually like the sound it makes when it engages. It is driven by a serpentine belt.

With the EFI setup, you have a good way of controlling the engine so you are way ahead of the game for a boosting application, whether turbo or supercharged.
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Old 09-28-2012, 07:48 PM
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Thanks to all for your input. Nothing personal to the turbo guys but my heart leans to the supercharger. I understand that more power is obtainable via turbo but personally I don't mind the whine of a belt driven supercharger and since this is a street ride the instant boost. Also without sounding to simplistic the fabrication seems simpler. A low boost charger, intake tubing to the throttle body and fab up the mounts. Hardest part seems like the pulley set up and sizing. The main issue is keeping the boost low enough that my stock internals could handle it but high enough that it's worthwhile. I also like the idea since it's uncommon to have a supercharged 911. Seems to be different opinions. Some say with stock internals the car would be a bomb waiting to blow. Others say low boost would be Ok especially since the car has a relatively CR in stock form.
Old 09-29-2012, 05:56 AM
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Supercharging is more simple and easier to package than turbocharging. A mild 6psi whipple will yield 260WHP with instant boost. They drive like a V8 conversion. Best exhaust is none, they like big pipes and low restriction. The design of my medium length RSR Carrera headers is a good fit for this application.
Centrifugal is easier on the tranny, whipple is instant power.
Here is an old SOK Whipple that a fellow PCA member had a few years back.


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Old 09-29-2012, 08:08 AM
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Supercharging is harder on the engine and trans due to higher low-end torque and extra strain on the nose of the crank. Nothing to lose sleep over but just throwing that out there.

I'd say the 911 is probably easier to turbo versus supercharge unlike nearly every other car.
Old 09-29-2012, 08:49 AM
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Quote:
Originally Posted by des28h2 View Post
A low boost charger, intake tubing to the throttle body and fab up the mounts.

Just to be clear, every application I know of has the throttle body before the supercharger. I dont know if the TB after the charger will work, you'll need to get creative with bypass valves, etc. Corky Bell's book is a must read.

Mounting the charger can be a challenge, I came up with what I think is a pretty slick version. 3 rose-jointed turnbuckles off extended valve cover studs allow precise adjustment of the angle of the charger. A 2-layer bonded 6mm alu plate bolted to the engine in front. No slipped belts, rock-solid.

Good luck, and post lots of pics!
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Old 09-29-2012, 09:31 AM
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Here's mine. Beefed up engine and trans before we started.









Just about 300hp @ 5-6 lbs boost.

-e.
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Old 09-29-2012, 09:34 AM
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Old 09-29-2012, 09:47 AM
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I went down this road in my 996 days, the conclusion was you'd be dollars ahead just buying a factory 996tt. The resale on a supercharged franken car was in the toilet. The Ruf sc being the only exception.
So, I think you'd be better off just getting a 930. Jmo
Old 09-29-2012, 09:51 AM
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Resale of "Franken car" is irrelevant. If I were to sell my car, I'd simply unbolt the SC and sell the two items separately.
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Old 09-29-2012, 10:05 AM
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I was referring to sc'd 996 cars in general and my experiences, not yours in particular.
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Old 09-29-2012, 10:32 AM
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i supercharged a 993 C2 cabriolet using the TPC kit. BHP went from 272 to 354 hp and 300 ftlb torque. I t was great power and instantaneous. As previously mentioned i had drain pipes fitted as exhausts was loud and fast. No lag and power all the way to the red line at 7 psi dropping to 5 psi.
i removed the SC and sold the car and also sold the kit separately. One benefit its reversible
Would i do it again, yes but only to a car that wasn't original and perfect.
Costs are about 10k usd.

Cheers
Old 09-29-2012, 12:05 PM
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Boost falling off usually indicates belt slip.
Old 09-29-2012, 12:26 PM
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The 79 3.0L internals are very tough. You won't have to beef up anything in the engine. The tranny... well, treat the 915 nicely or pick the pieces off the ground. There are some tranny mods that can make it tougher, but that is another thread.

The supercharger makes torque even down low in the rpm band (at least the ones that aren't centrifugal), which means that you don't necessarily need high rpm (which is where engine internals need to be beefed up).

The 3.2's from the 80's had the high compression and the weak rod bolts. The 8.5 on the 79 is good; although with a supercharger, having a lower compression ratio and higher boost makes sense, since you have boost right away. When you do this on a turbo, a car at 7:1 or 6.5:1 off-boost is a dog.
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Last edited by Dr J; 09-29-2012 at 12:52 PM..
Old 09-29-2012, 12:49 PM
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Quote:
Originally Posted by esample View Post
Here's mine. Beefed up engine and trans before we started.









Just about 300hp @ 5-6 lbs boost.

-e.


Nice setup. Do you have a build thread of this conversion ?
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Old 09-29-2012, 03:32 PM
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Good for you!!!

I Super Charged my 911 15 years ago and have enjoyed every minute. Don't mind the comments against Super Charging. I have been on this forum for years and not many 930 owners support super charging 911's. "Franken Porsche" THAT REDICULOUS. Keep doing what you're doing. Have Fun. To each his own. You are no less a Porsche owner than anyone on this forum.

Mine is a Super Charging of Knoxville set-up with 5-7lbs of boost. It's enough for me.

Old 09-29-2012, 05:00 PM
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It has certainly never occurred to me that I may be less of a Porsche owner because I supercharged my car. But thanks for the encouragement Kdubb. It is fun to drive these cars, isn't it? I know I've pissed off more than one water pumper with mine.

-e.
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Old 09-29-2012, 05:37 PM
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