I think you mean short-stoke 3.2...

-Wayne

Wayne

I am probably going to use a 66mm crank.

Robert

Whoops - the original poster said he had the SC case, thought you had one too.

Okay, so you're going to make a big bore 2.8 (short-stroke 3.0). Yes, this will be a very high-reving, short-stroke 3.0L.

However, you will need to have custom pistons made for the engine from some place like JE. I am not aware of any 98mm pistons that have the correct piston-pin bore to run with the 66mm crank and rods.

I would assume that you're doing this for class restrictions? If not, I would just build the short-stroke 3.2 out of the engine (using a 2.7 crank).

-Wayne

Just weighing up all the options at the moment. I only get the motor next week - a 3.0 Carrera longblock with unknown history that has been standing a long time. If all is good with the crank and the cylinders are Nickasil then I will just rebuild it with 95mm 10.5 JE's. However from a cursory look at the motor I suspect it has Alusil cylinders and the crank will be no good. in that case I would get a 66mm counterweighted crank and rods and then must decide what P/C's to use.

Robert

You might be surprised. The last Euro Carrera 3.0L I bought in pieces had Nikasil cylinders. Also, these cranks are usually okay, unless the motor was severely abused...

-Wayne

Would be great if you are right Wayne, should know in about a weeks time. Counted the cooling fins last time I saw the motor and I am sure there were 11 so I could well be wrong.

Robert

That is not an accurate method of determing Nikasil or Alusil...

-Wayne

I believe all the 3.0 Carreras had Nickasil cylinders. Mine did. And I've read that they all did in a couple books, including Paul Frere's Porsche 911 Story. Unless someone swapped 'em, you very likely have Nicksil.

Sorry, sent before I was finished typing, try again ---

As I recall, the earlier 3.0 case has smaller mains than the later. If so, then Wayne's proposed short stroke 3.2 is dimensionally equivalent to the traditional short stroke 3.2 (as outlined in his book) but would have less friction due to smaller mains which may add to higher end output?

Nikasil or Alusil, that is the question
 

Hey guys, the easiest way to tell Nikasil from Alusil is with a magnet. Nikasil is magnetic.
As for piston pin location for short stroke (66 mm) crank, the pin location is the same for 2.0, 2.2, 2.4, 2.7, 3.0. and 98 mm 3.2. All these engines use a 32 mm wrist pin center to deck measurement . The difference will be the compression generated by similar domes. For example if you run a 3.0 RSR piston 10.4 to 1 on a 66 stroke crank the deck will be right but the compression will now be closer to 9.8 to 1. If you run a 10.4 to 1, 98 mm with 22 mm wrist pin on a 66 mm crank you will have a similar reduction on compression but the deck will be fine. Quick note: when building a custom engine like we're talking about, dimensioning the engine becomes all important.

REVVVVVVVVVV IT UP
 

Another thought:
If you run a 2.4/2.7 crank (70.4) you effectively limit your RPM to something like 7400-7600. Constantly revving a 2.4/2.7 crank over that is asking for trouble. That is why Porsche made the RSR crank. Too many failures from the stock crank. On the other hand the 66 mm crank loves 8000+.
and we all know how that sounds!!!
http://enginesounds.free.fr/porsche/911%202.0l%20-%20a%20bord.mp3

The difference between 2.2 and 2.4 pistons is the dome hieght not wrist pin location. In the early engines they shortened the connecting rod to make up the difference in stroke. I believe the measurement we are talking about is called compression distance and the compression distance on 2.0, 2.2, 2.4, 2.7, and 3.0 are all 1.335 in. or about 32 mm as I stated in the earlier response.
One of the problems with Porsche engine is that they keep changing the rod length to stroke ratio.
In the early cars it was almost 2 to 1. As the stroke grew the ratio got smaller causing some very bad rod angularity. I believe in the later engines the ratio is down to around 1.63 to 1.

Ummm, yes, I see your point. My proposed 3.2 is the same as a 911SC with 98mm pistons, but with a smaller crank journal.

I don't think it works like this. My guess is the frictional drag from smaller or larger main bearings would be negligible. It might even be higher on the smaller journal, because it's a smaller surface area? (think of the analogy of a woman wearing high heels - small surface area on the heel = harder to drag than than the same amount of weight in a big, flat box.

Again, I think the frictional forces between the two would be virtually the same, but that's just a guess.

-Wayne

Journal size counts
 

When talking about journal size there seem to be three factors.
Drag, load distribution and weight.
Small journal, less drag ( small surface area) , reduced load distribution, less weight.
Large journal, more drag ( larger surface area), better load distribution, more weight.
There is also an issue of strength but I believe that strength can be manipulated by corner radii of a given journal.
Given some of this is true:
Small journal with large radii should be, low drag, reduced load distribution (increase clearance, and oil pressure to correct) weigh less for easier rotation.
In the case Porsche engines, drag produces friction (heat) and in an oil cooled engine, heat is bad.

Can anyone confirm the viability of a set-up using the early turbo/3.0 Carrera case? I'm trying to build a CIS motor using these parts.

I am assuming the crank is same/similar in size as an SC crank, other than the small journals?

What about the rods that came with that engine? Same as SC's too?

Assuming I put in a 98mm MaxMoritz set, with a CIS-friendly cam, are there any benefits to be gained using 3.2 heads instead of the big port early SC heads?

thanks.

Re: REVVVVVVVVVV IT UP
 

WOW! I got chills listening to that sound clip! That's a high revving 2.0 with open tail pipes, yes?

No doubt, that clip is sweet!!

I think it's better to compare journal size with 'drilling'. I did a lot of drilling a few years ago and noticed that when using a large drill bit, the drill machine has to set at slow speed, otherwise the bit will overheat. With a small drill bit, it can be run at high speed. So, Henry's quote below is probably right.


Yoda, you kept saying that you're not an engineer, so where did you get that info from and how do you know if it's true?

25+ years of engine building and a life time of racing puts you in a place to pick up some knowledge.
Add that to a pretty good automotive library and then surround yourself with the best people and that's where my experience lies.

I don't necessarily state anything as the truth. If you read what I stated, you will find that almost everything is qualified.
Most of my conclusions are based in reason and observation.

Re: Journal size counts
 

This has been quantified by ford on their Windsor(351),429,460 engines. They all have a massive 3 inch main journal. The increased drag from such a large journal promotes severe local oil temps at higher rpms. Most of the Nascar Fords run with something less, around 2.75 inches so that they do not experience this problem.