FRporscheman

Shawn's car is (correct me if I'm wrong Shawn) a 3.0L 968 engine with the 8v cylinder head from the 2.7 944. To further lower the compression he used custom pistons, and I believe he switched to 951 rods for more strength. But that's a different beast entirely. Turbo, with healthy amounts of boost. You can ask him about the pistons if you need specific info.

I've been doing a lot of research on turbo 968s. I plan on doing the conversion this summer, but I don't know what route I'm going so I've read about all these different possibilities, and I'm trying to understand and learn as much as I can about everything involved. Anyway, I hope this answers some of your questions.

With every turbo design, the compression must be lowered. With most aftermarket supercharger kits you don't need to lower compression (like with your kit), because of the way a supercharger makes boost (as opposed to a turbo). The supercharger makes boost proportional to the engine RPM. So there is like no boost at idle and full boost at redline. The engine breathing efficiency is worse at higher RPM so there is extra margin for added compression. The extra compression from the supercharger comes in as the engines natural compression ability fades out. So the system works out nicely and you end up "getting away" with not needing low-compression pistons. Remember there are always limits. Also remember to never trust what you read online... I'm still doing research and maybe what I just said is wrong, but that's what I understand.

Intercooling helps immensely with turbos because of the great heat associated with those systems. Superchargers still benefit from ICs and it can go a long way toward preventing detonation. It can also reduce thermal stress on your engine and especially the head gasket. I would recommend installing an IC even if you didn't want to raise the boost, just to keep the engine happy, and squeeze out a few horsepower at the same time.

Depending on your power goals and budget, if you do need to lower the compression, I've been told that thick head gaskets are an increasingly popular way. It's much easier than replacing pistons, much cheaper, and although it won't lower the CR by very much, it will be enough for a supercharger setup. But I think you'll be fine at 6psi with stock CR.

Anyway I hope some of what I wrote makes sense.

bleucamaro

Correct about the block & head. The rest is pretty much stock 951 stuff (intake manifold, etc.). I'm not sure if he used 951 rods or 968. With a change in stroke, I'm not sure if you can use the same length connecting rod

[QUOTE]I've been doing a lot of research on turbo 968s. I plan on doing the conversion this summer, but I don't know what route I'm going so I've read about all these different possibilities, and I'm trying to understand and learn as much as I can about everything involved. Anyway, I hope this answers some of your questions.[QUOTE] I personally like Shawn’s approach. He used 95% stock Porsche parts and everything was bolt-in (except the pistons).

Its not absolutely necessary to lower compression in ALL applications. However, a lot of times, it’s a pretty good idea. Its always important to ask yourself why you are doing something. The reason to lower compression isn’t because of the amount of boost you’re making, or weather you’re running a turbo or SC, its to fight pre-detonation. Many times there are other less expensive ways to do this, and its typically most economical to incorporate the biggest help for lowest dollar changes first .


[QUOTE]With most aftermarket supercharger kits you don't need to lower compression (like with your kit), because of the way a supercharger makes boost (as opposed to a turbo). The supercharger makes boost proportional to the engine RPM. So there is like no boost at idle and full boost at redline. The engine breathing efficiency is worse at higher RPM so there is extra margin for added compression. The extra compression from the supercharger comes in as the engines natural compression ability fades out. So the system works out nicely and you end up "getting away" with not needing low-compression pistons. Remember there are always limits. Also remember to never trust what you read online... I'm still doing research and maybe what I just said is wrong, but that's what I understand.[QUOTE] Most modern supercharger systems use a bypass valve, like a turbo so that there is no boost at partial throttle. Also, positive displacement superchargers (like the Eaton M90 being used by this thread starter) have pretty much flat boost/rpm curves because there is a fixed amount of air being forced into the engine, which is greater than the single cycle displacement of that engine. This is where calculating pressure ratios becomes important. Centrifugal superchargers (Vortech, Procharger, etc.) behave more in the manner of a belt driven turbo because of the way boost pressure increases with RPM, the fundamental difference being that the compressor speed is governed by a mechanical link to the engine speed, vs. a turbo is governed by the flow of exhaust gas and wastegate.

I don’t understand what you mean by this.

Good point. Most people will argue “adiabatic efficiency” when comparing turbos to superchargers, and when comparing roots to centrifugal supercharges. However, the compression of air is not the only source of heat in a turbo system, theres also that great big cast iron heatsink right next to the compressor housing with extra-hot exhaust gasses in it from all the backpressure.

Again, asking WHY you’re doing something, the reason to intercool, or water-inject is to reduce the intake charge temperature thereby reducing detonation. If you cool enough, you will be able to use less fuel (fuel is used as a charge cooler too) and more advance in the ignition timing.

I looked and looked and looked and couldn’t find a thicker head gasket. I even had a hard time finding a wide-fire head gasket. I think with intercooling, and tuning, 6psi is VERY conservative on this motor.

FRporscheman

Hey Dan, thanks for the clarifications. At this stage I'm just regurgitating a lot of what I've read online and you know that can sometimes lead to misinformation.

Many different, reliable sources have told me there are thick headgaskets available for the 3.0L motor. I don't know exactly where to get it but I've heard the word Cometic get thrown around. I need to find out more about this because this is an option I'm strongly considering.

And that part you didn't understand. Again it was just more regurgitation but what I was trying to say was, I read somewhere that the flow into the CC gets less efficient (less flow into) at higher rpm. Therefore adding boost at this point is safe (i.e. it kind of makes up for the lack of flow into the CC, and therefore you shouldn't cause detonation, keeping all other things equal). I don't know how theoretical/practical this truly is, it's just what I read.

Mikes3.0cabturbo

You can get a 3.2mm Cometic head gasket to lower the compression on your S2 it will drop it down to approx 9.2:1 if thats what you want. Available online.

If you are only after 300whp - I dont understand why you would bother reducing the compression, this would be around 7psi and talking from direct experience the engine is fine using this level of boost, with an intercooler, good AFR and some small ignition retard, I have about 4 degrees at 7psi.

Please PM me if you wish to talk on the process I went thru on my turbo S2 conversion some of the experiences may be useful to you.

rgds
mike

Lumbergs Lackey....MmmmKay

Man so much good info in this thread. Mike PM sent.

Also Bleu, do you remember if a strut brace would fit with the setup on the car? I wanted to buy the Racing Dynamics unit.

Thanks

blown 944

I just skimmed through this so please forgive me if something has been covered.

What I gather is that the IC and compression are the major concerns??

from what I have seen it is definately of great benefit to intercool over 5 psi. I have taken readings from both my 951 and the s/c car and the intake temps are very high if not intercooled. I personally had used methanol and e85 to keep my junk under control. But intercooling does bring about more power regardless plus the engine runs cooler. I ialso ran the car w/o and intercooler and with a small POS IC and it ran 3mph faster in the 1/4 with IC and it wasn't all that efficient.

heres my findings: on the blower car the intake temps run about 210deg f at around the boost levels you are talking about they get up to 280 at teh level I run at (15psi +). The 951 IC will drop that down to about 85 on a 70 degree day. Just imagine running around trying too hotrod a car on a 120 plus degree day and that's what you get.

$1000 is not bad at all to get it all plumbed. Just modifying the intake, tubing and assoc parts would run over 700 if I had to pay someone around here and I gaurantee there will be something that I am missing. If you can DIY minus the intake work you dould probably save some $$. One thing I would try to keep in mind when modding the Intake is that teh blower doesn't need that much area to be effective so you could keep a great amount of plenum area for the engine.

as for lowering the compression I am not as familiar withthe 16v stuff but from what I have read there is a thicker headgasket that has been used with success on one of the faster 951's (Markus)

One other thing you may want to check out is installing a knock counter.Do a search under the turbo forum and you will find a good thread. From what I understand your car has knock sensors so the install should be the same.

Bleu why'd you sell your setup??

Lumbergs Lackey....MmmmKay

^^^Thanks buddy. I'm picking so much great information. I'm just glad Bleu was willing to sell it to me as it lets me keep my A/C which is what was keeping me from doing it in the first place with somebody else's kit. Hopefully I can have a local shop do the manifold alteration for the intercooler. I will run a factory 951 intercooler as I cannot affort the SFR custom intercooler and work on both my Porsche and Crossfire hp projects.

blown by the way I'll be running an SMT7 Bleu was using.

bleucamaro

I didn't want to dump the money into going to the 'next step' which would be water/meth injection, intercooling, and lower compression. It was my feeling that this kit was best suited being non intercooled because of the manifold design. I actually have a couple new manifold designs I worked up in SolidWorks, but don't have the skillset or equipment to produce them. right now.


Wil, did you get it installed yet?

Lumbergs Lackey....MmmmKay

^^^No my friend I have not, my dog has been sick and I have spent quite a bit of money at the vet the last few weeks. But I love her so no biggie.

Your last comments are concerning me a bit about the manifold not being able to be IC. Is it possible or did your find its not possible? Want to know before I spend 1K and its gets destroyed.

Lumbergs Lackey....MmmmKay

bleu did you think that this manifold is not able to have an intercooler added? I'd like to find out before I take it to the mechanic and he destroys it.

thanks

hacker-pschorr

6psi I wouldn't worry about compression.
928 S4's and GT's are 9.5:1 or more (GT's are higher). We have guys running 12+psi with an air / water IC. Most of them are running colder than stock spark plugs & timing is turned down a bit under boost.

Jean-Louis was running 6psi, non intercooled on a 10.4:1 compression 928 race car. I say "was" only because he eventually added an air / air intercooler.

I would love to get my hands on one of these intakes for my 944S. Or borrow one so my local fabricator could copy it.

Raven951

Have Tim @ SFR do it. He's already done it on this 968.....

Lumbergs Lackey....MmmmKay

^^^Thats Tim's car???

Raven951

no, customer car.

toddk911

"Personally I would try water injection and intercooling first and see if you can meet your HP goals. If E85 is available in your area you could also run that (with larger injectors) and probably run 1 bar of boost safely."

Yes!