Alon

Hi Guys. I drive a 996 40 Jahre (no water-box "boo-ing" please) and I'm looking at buying a pre-'73 911 coupe with a freshly rebuilt 2.4e spec engine along with a 915 (7:31 ratio). My question is how do I extract more power form this engine? It has the E-spec MFI. I know that the obvious stuff like SSIs and Muffler make sense but the current owner mentioned that S-spec 2.2 pistons along with S-spec cams and revised MFI pump cam will create about 230 HP. Is this really possible? Prior to speaking with him, I had initial thoughts of taking it to 2.7 (with good studs) and porting the heads (possibly crank-fire for dual plug since the distributor setup costs almost the same) along with S or RS cams. This car is going to be a weekend/fun/lapping day car and I don't want to create an engine that will be sluggish and flat. I want the excitement of a high-revving engine that makes great power. Any suggestions would be greatly appreciated. I can't wait to be driving a raw, sub-2300 pound car with an equal power to weight ratio of my 996 40 Jahre. Ah, I can feel it already...

Thanks in advance.

GrantG

I think it's nearly impossible to get 230hp from a 2.4 unless you go to twin-plug heads and distributors and higher compression. My 2.7 makes almost 240hp and it's pretty highly tuned (but still single plug). If you really want power, try a 2.8RSR hi-comprssion style motor with RSR cams with twin plug and re-cammed mfi. These are good for around 300hp. These are pricey to build correctly though...

You might want to consult an expert like Steve from www.rennsportsystems.com

Alon

Yeah, I was skeptical as well to hear that you can safely get 100 HP per litre without going nuts. According to the car's current owner, this is spelled out in Bruce Anderson's 911 Porsche Performance Handbook (which I now have on order). My local mechanic/tuner is suggesting 2.7 RS spec pistons/cylinders, head work and the crank fire ignition and the recammed MFI for good results. If I can get 230 to 250 HP out of it and have it sing when it revs high, I'll be happier than the proverbial pig. Thanks for the link to Rennsport.

GrantG

Yes, I would agree with your mechanic - a 2.7RS is a great motor

Alon

You wouldn;t happen to be slightly biased now, would you?

GrantG

Well, maybe But, I've owned 6 Porsches now and the modded 2.7RS is by far my favorite. Nothing else I've owned has such great throttle response (if the MFI is rebuilt and properly tuned) and rips through 8k revs like it (upgraded valvetrain req'd). Better low-end than my 2.4S also...

L8 Apex

I also have a 2.7 MFI, RS Spec motor, built on a 2.4S case (5R). I didn't build it, but I do know it has 10.2:1 compression ratio, forged pistons, & S Cams. It made 196hp at the rear wheels (maybe 230 at the flywheel?) and 175 lb ft of torque. The torque band is nice and broad so the engine gives power on demand. Very nice, and a pretty common engine to build from what I've seen, so it might be a direction that you want to consider.

Alon

Yeah, I don't know if this car has a 5 or 7r case but either should work for what I want, right? Do you think that dual plug is that necessary? I understand the need for improved spark with higher compression/advanced ignition and all but wondering if it is in fact, that necessary. 10.2:1 doesn't seem very high by today's standards but today's iginition and fuel management systems are clearly superior to the older. What I'm happy about is the ability to retain the MFI with a simle space cam modification/swap because I don't want to run carbs. I assume that with the 2.7 cylinders and pistons, there would be a need for stronger studs since there is less material to hold everything together and really, that shouldn't be an issue since the existing cylinders would be removed. Does anyone know if machining to the crankcase needs to be done to accept the 2.7 setup? 230 at the flywheel and 200 at the rear wheels would be excellent for the weight of the car.

Ooh, I can't wait. I love my 996 but I doubt that I'll be anything but "all smiles" from this car...

GrantG

Alon - I think the only available Mahle (OEM) 2.7RS pistons are the 8.5:1 version. There was a high-compression racing version, but they're rare and pricey. The 2.8RSR's are available and are hi comp (I think close to 11:1, IIRC). You can also machine the heads to increase compression of the RS's a bit.

BTW, I think anything over 9.8:1 is well suited to twin-plug...\

My case is a 7R and it had quite a bit of machining done at Ollies in Calif. Not sure if this was req'd or just improves the case...

Alon

Thanks again for your responses.

Steve Weiner-Rennsport Systems

Alon:

You can build a real nice 2.7 with "S" cams, S-spec MFI pieces, and "S" spec ports for a very strong running engine in that light car.

If you have a bigger budget, a twin-plug 2.8 will just run away from the above version,....

Greg D.

>know that the obvious stuff like SSIs and Muffler make sense

Just checking here.. I thought the SSI was a repro of early 70s headers destined for the 80s cars which have more restricted flow - so what would be the point of SSIs on an early 911 as an enhancement ?

GrantG

They don't rust

Alon

The exhaust on the car now is the stock 1973 pieces and they don;t have an ounce of rust on them so if there is no power advantage to going with the SSI's, that will save me some cash. I don't know what muffler is on it but it is a dual in and single out type (Leistritz perhaps). I think that if budget allows, I might price out and go for the dual plug 2.8 over next winter but my mechanic has an early 70's car with a dual plug 2.5 (built on a 2.4) with mechanical injection and it pulls very hard right up to almost 8000 rpm. Sure, there isn't the torque that you'd get from more displacement but it revs very freely and I understand that it can be performed with no machining to the case (to accommodate potential piston deck to crankcase issues with larger pistons).

All I know is that this car will be fun no matter what. Now, how do I manage to build A/C into this thing...

Norske

I had 72E that I built to 2.7 RS specs. 2.7 RS Pistons, "S" cams, had the injection redone. S velocity stacks, oil fed tensioners, etc. It was a blast. Used to toy with 5 liter mustangs and really surprised a 944 Turbo "S' a few mornings on my way to work. He wwould pass when we hit about 75. Better low end than the 2.4S. I had my stock exhaust because ot was mostly a gutted mufler. When I put a different exhaust on I lost HP. Also the engine ran on regular gas because of teh 9.5 compression ratio.