horsepower available in 3.0/3.2 liter rebuild

Jim Gerecke · 09-26-2003, 09:58 PM

I've got plans for and a line on a 73 1/2 911T coupe with Carrera flares. I need a motor to rebuild for time trial and occasional street use (want to keep license plates and lights, maybe heat). Will a 3.0 SC or 3.2 Carrera get to 300 +/- h.p. on "S" cams, 9.8 compression, PMOs, lightened flywheel, and SSI type exhaust. I'll certainly consider other cams and/or bigger bore pistons, but I'd prefer not to need over 100 octane. From the "sample" engines in Wayne's book, this seems possible, but I'd appreciate any input, as I begin mapping out the project and budget. Thanks in advance.

dd74 · 09-27-2003, 09:17 AM

Hmmm...I think Bruce Anderson writes that a 3.0 short stroked to 3.2 with a setup like that will get you about 275 hp. Would be nice...

jluetjen · jluetjen's Garage

If you're getting a 3.0, you'll want a '78 or '79 unless you plan on porting heads. The heads from a 3.2 should be fine for use with an S cam.

cstreit · cstreit's Garage

I dunno...

3.2L shortstroke with 275 HP? I suppose if you opened up those 3.0L heads really good and spun the motor to 8000 RPM... ...and I think the power band would be pretty peaky with a cam that would be needed so you'd also need a close ratio gearbox... Meaning you're looking at replacing pistons and cylinders to accomodate the cams, porting heads, a lightweight valve train to accomodate the RPM's, and possibly twin-plugging because you'll have to run higher compression than 9.8 for that kind of HP.

In other words, probably easily a $15k build if you do the work yourself... More if you farm it out.

I don't want to sound like a pessemist, but my 3.0L with early heads, 10:1 compression, Webers, and a cam similar to an "S" makes about 240-250 horsepower at 7000 RPM... So you'll have to do more than this to get 275-300 out of it.

350HP930 · 09-28-2003, 07:33 AM

I concur.

300 HP is going to be nearly impossible and VERY expensive on a NA 3 Liter.

Now if it was turbocharged it would be easy as hell and cheaper.

dd74 · 09-28-2003, 09:10 AM

Would you guys turbo a N/A 3-liter, if given the choice?

CamB · CamB's Garage

Will a 3.0 SC or 3.2 Carrera get to 300 +/- h.p. on "S" cams, 9.8 compression, PMOs, lightened flywheel, and SSI type exhaust.

Nope, sorry. 230-240hp max would be my guess.

Porsche's own 3.0RS engine was pretty close to an S cammed, 9.8:1 SC engine (with MFI not carbs), and it had 230hp. Since MFI seems to add 10hp over carbs (I'm guessing this because that is what the change was from 1968 to 1969 for the S engine - from 160hp to 170hp). A sport muffler might get back another 10-15hp?

To give you an idea of what IS required, I've got:

- 3.2 short stroke (SC crank, 98mm pistons)
- S cam profile
- SSIs with standard exhaust (not sport)
- 10.5:1 Mahle pistons
- ported heads, etc with twin plug
- 40mm throttle bodies
- EFI (older MoTeC), mapping fuel and ignition based on throttle position and RPM only - it needed 330cc 944 Turbo injectors!

I have 245hp at the wheels (hubs - Dynapack dyno) at 6300-6400rpm. This is roughly 270-275hp at the flywheel. It works out around 85hp/litre, which is pretty much tops for an S cam, I think. It runs on premium gas (98RON).

I think I would get 300hp if I changed to RSR cams (and an upgraded valvetrain) and a sports exhaust. With full headers etc too, it might go 100hp/litre, although the intake is probably restrictive...

Obviously, this is expensive. I bought everything except the P&C set second hand, and got a really good deal on those anyway. It used to be my mechanics race engine (before the rebuild).

He has a 3.6 based 3.8 with 50mm throttle bodies, headers, GE80 cams and approx 340hp. It is awesome - with 964esque bumpers and a 993RS wing (on a '74) it can keep up with a GT3RS in a straight line.

Wayne 962 · Wayne 962's Garage

My engine that I'm building is almost the same as Camerons, except for a few minor details (Webers, Euro Carrera case). By all reasonable expectations, I expect about 275HP out of the flywheel, which would be in line with his 245 at the wheels. The Motec will be better than Webers, but I'm also running the mod 'S' cam - not entirely sure how much improvement that will give...

Cost for this engine is about $10K in parts alone. The pistons and cylinders are $3600 by themselves...

-Wayne