Which would be the better SC engine?
 

Which would be the better SC engine; my '79 Euro rebuilt with JE 9.5 pistons and a 964 (or 20 21) cam, or an '82 Euro that had a standard rebuild 10,000 miles ago?

'78 and '79SC have better intake manifolds and bigger intake valves. Both engines would SSIs.

the '79 of course..or is this a trick question?

Hee hee, I'm biased too.

hmmm .. . Porsche engineers were able to bump-up the CR after better mixing was achieved with smaller intake runners/higher intake velocity.

I suppose if you always run high octane fuel in the 79/w JE's, you'll be fine.

Bill would you retain the cis?
I run a spec 3.0 race car in nor-cal and from the dyno testing we did the best overall power and torque combination is cis euro compression pistons (rule mandates cis pistons) 46mm webers,sc cams (again rule mandated) and 1.625 headers or ssi
right around 250 hp @ 7k rpm (78-79 big head)
My engine last year had 40mm webers and 964 cams w/ 1.5 ssi's at 234 @6600
One thing to watch w/ the 964 cam is valve clearance.All my pistons (low comp cis) had been smacked pretty good by the exhaust valves.
So... If you can/want to run carbs there is a lot of hp to find without the 964 cam.

In short,if your P/C spec out and can be reused you have a good start to a great engine.
Best case is you can save the P/Cs, freshen the cam,add good rod bolts and valve springs, change the intake to carbs and run 1.625 ssi's ...bam 240-250 hp.

Good luck and best,
Thomas

Intake velocity is an interesting one, and being a street engine, maybe the better flow of the earlier heads would make any difference.

if peak HP is your goal, then go with the earlier motor.

if real-word performance and drivability are the goal, the Porsche engineers did a great job with the latter SC's. (esp the ROW)

side note: 911E's had less peak HP than the 911S's . . .. yet the E out accelerated the S. . ..and something like 1mph better top speed too. (don't under estimate the value of mid-range torque) Personally, I would prefer the E for drivability. . . .let someone else have the HP bragging rights of the S.

Dead on, Island. Glenn's correct about the later SC motor being the more friendly engine when it comes to anything other than WOT driving. The lack of throttle response people sometimes complain about with earlier SC motors was later attributed to the intake/cylinder head size, which was later reduced for the '81 through '83 3.0 engine. Thus the SC motor in this form was much more responsive from a lower level on the rev scale. In fact, Bruce Anderson stated in one of his last updates on the '78-'83 SC that the correct intake size for the 3.0 is 34mm and not the larger 36mm. Or is it 38mm?

Now, if you drive WOT more often than in city traffic, I'd definitely do the mods yet with the early heads and intake. That should give you the best of both 3.0 worlds - early and late.

Island,
While you are correct about the E,S analogy,Having owned an S spec car I would say not a very good daily driver.But haven driven a high spec SC on the street this is an apples and oranges comparison.The drivability issue all depends on where you drive(open road vs traffic) and at what rev range you play at,The engine I used as an example was compaired to a 78 SC (carbed low comp ssi) and the torque and hp were matched within 5 hp and 10 ft lb up until 3250 rpm then the higher spec motor took off like a shot and as a matter of fact the lower spec engines power and torque dropped of the map at 6200 rpm.
With an SC grind cam you just arent going to have "peaky" power delivery as you would with an S or even and E cam.
The cam is the main driver behind power delivery i.e. peaky or flat curves.
Anyway,the main point Im trying to stress is (with my limited research)the more you can get these engine to breath w/ intake,heads and exhaust the more fun you can have with them.But if its a daily driver sitting in traffic I would say without a doubt carbs are not the way to go.
Best,
Thomas

I wouldn't necessarily think the early and late SC motors are exactly apples to apples, either. One breathes, the other torques.

Supertec built me a similar engine and I am very happy. 78 heads and CIS, 83 block ith the JE 9.5s, 20/21s, and SSIs. Very fast and very divable.

Yup, I'd retain the CIS Thomas. Carbs seem fun, but a bit too committed for me. And thanks for the great input guys! Flintstone, please tell me more about your engine :)

Bill
Check out my profile:
http://www.pelicanparts.com/gallery/fintstone/
I asked the guys at Supertec to build me the best combination of SC engine for a daily driver. I wanted good throttle response, reasonably good mileage and it had to last at least 100k miles. I seem to have gotten all that. It is very fast without lag at any rpm. It is smooth as silk. It starts and runs like a Toyota....a very fast Toyota. I am not sure if it is just the engine combination or the great skill and experience at Supertec...Both I suspect.
I did not have any of the emissions equipment hooked up since my car was exempt in New Mexico.

Bill...details in this old post:
http://forums.pelicanparts.com/porsche-911-technical-forum/144332-rebuild-3-6-swap.html

Dave have you heard my dad's motor? Stock cis, ssi's, 2 in 2 out, 20/21 cams and it spins up like a champ! We even went for a fun drive today up angeles crest after work, my boss in his 98 993 s, me in my dad's car, a friend in his 83 sc, another guy in a crazy powerhaus turbo and a 928 v8 914. To be honest the 914 and I ran away, he was point and shoot mostly I guess the weight advantage we had and the shorter gearing paid off.

As far as 3.0 motors go with CIS still on top I think my dad's is hard to beat, I bet he will be even happier with the 3.4 I am building him without his knowledge though...

Ryder - why don't you build me a 3.4 after you finish up your dad's. Have any 3.2s lying around as well?

Re: Which would be the better SC engine?
 

I think the 964 cams would boost the 79 slightly over the 82, but you missed an important fact. From 1981 on the euro 911's had a 9.8:1 compression ratio, they still had the big ports and runners and the same cam timing as the earlier Carrera 3.0 and the 78-79 US motors. They were rated at 204 HP, DIN (maybe 195 HP SAE) and they were strong runners.

Porsche used the same valve sizes for all of the 3 liter engines (and I think the 3.2's).

Regards,

Jerry Kroeger

Flinstone, I barely reconised that as a SC engine, ya know, no oil lying around, not black and grimmy ;)

Yes this does sound like the sort of setup for me. I've got a spare parts car with only 10,000 miles on the engine since a rebuild, and the guys fitting up the engine say it's a really nice one, but it would be nice to get my origional engine sorted. And I could sell the '82 engine to offset some of the expenses.

I'd say the '79 engine. principally because of the cams. If it had driveability problems, it might be fun to experiment with just placing the later intake runners on the '79 engine. This, of course, would increase the intake air velocity.

I would imagine that wouldn't really give ya a desirabe end.

When the combustable gasses are pulled into the cylinder, the flow idea is to have a 'toroidal swirl' (like a smoke-ring, of sorts) (good mixing)

However, If the air flows from a smaller runner, to a larger diameter intake, the airflow will be tripped at the transition. . . likely counter to the desired swirl, as induced at the valve.

. . ..just conjecture. . . .that above, and manufacturing sure would have been easy if Porsche simply could get away with swapping in smaller runners (only).