Engine build advice for my 1967 911

[The Greek]

Im restoring a 1967 SWB to its original black color. And the dreaded time has come where I have to choose what engine setup I want to go with. The engine case is matching numbers but the 901 transmission is NOT original.

Im trying to find that balance of a great drivers car. Will only drive it for canyon runs and cruising. No racing. Plan is also to redo the gearing so its short geared with a long 5th.


The current motor now is a T motor that has S components installed. S pistons and rods, and S cam. Here are my 3 options:


- Keep original case. Keep it 2.0 or 2.2 retain the short 66mm crank. And just make the motor a fun little motor. New heads, twin plug, p/c, cam, etc. Probably will be 170-180hp

- Keep original case, but get a long stroke crank, and p/c's will get the motor to about 2.4 litres. Obviously heads, twin plug, can, etc. I think hp will be around 200ish.

- Shelve the original case, buy a spare 1967 case, and do a 2.5 short stroke motor. Shop says we can get around 210 hp. Ive always wanted to do a 2.5 short stroke build, but is it really worth it to spend the extra money.

[jutzsc]

i have a short stroke 2.5 with Webers in my 1967 targa (originally a 912). It's only built to about 170hp, but the response is amazing. Most of my driving is on the backroads of Northern California and it"s suited perfectly for that. It"s very quick revving and pulls hard through red line. I would definitely have it built the same way again.

[The Greek]

Thanks for the feedback.

Thats what I am kind of thinking. I had a 72 2.7 build that was about 230 hp. Was a riot dont get me wrong, but when I drove this 1967 with S internals, it was so balanced to drive. Full throttle fun. So thats why I like the idea of having the car in the 180 range with proper gearing.

[Jeff Higgins]

I guess I've never understood the attraction to short stroke motors. The difference in piston speed between 66mm and 70.4mm strokes is absolutely not any kind of a limiting factor regarding rev limits. The longer stroke, and the displacement that comes with it, always makes a more satisfying street motor. We are not constrained by any sort of racing class rules, so why not go with all of the stroke - and displacement - we can get? The added torque just makes them so much more pleasant on the street, in the rev ranges we normally drive.

[The Greek]

Jeff,

Thats the question that I seem to get different answers on. Does the longer stroke crank affect the character of the motor? I always read short stroke motors "rev more lively." But Ive never gotten a concrete answer.

[Jeff Higgins]

There are a myriad of other factors that weigh much more heavily on how "freely" a motor revs than 4.4mm of stroke. Probably the most significant factor would be flywheel weight.

I would venture to say that given two motors of identical displacement, all else being equal - flywheels, pistons, compression ratio, cams, ports, induction, exhaust, etc. - that no one could tell me which was which regarding the differences in bore and stroke. Their "personalities" would be identical. A great example would be the original 70.4mm stroke 2.8 (like the RSR) vs. the 66mm stroke 2.8 "short stroke" (the motor Porsche never built) - I would defy anyone to drive both and tell me which was which. I have, actually - I've driven examples of both. Their owners would have to tell me which one they had - I sure couldn't tell.

But we are not talking identical displacements. In the case of a street motor that does not have to meet some class displacement rule, the longer stroke offers more displacement. In that case, no one has to tell us which is which - the increase in power makes it obvious. And that increase in power absolutely makes it more "lively".

We are all drawn to the "character" of these motors. That is probably their single biggest attraction. We all know there are plenty of much, much cheaper ways to go a good deal faster, but we really don't care. Their "character" surmounts all of that. So, yes, it's important. I think there are a lot of other factors that affect that character far more than differences in stroke. Induction, compression, cams, exhaust, flywheel weight - stuff like that.