2.8SS from 911SC case
 

Help,

I need to know whether it is possible to build a 2.8ss from a 911SC case.

I understand that i will need a custom/billet crankcase but are there any other reasons why this can't be done

Accepted that every one will say use a 3.0 Carrera case or 3.0 Turbo case as they use the same crank as a 2.7 motor and therefore i could then use a 2.0 or 2.2 crank.

Where would I buy a billet crank or can i have my SC crank custom offset ground and re hardened.

thanks in advance

Michael

I've made severely underbored cylinders to make 2.5 engines out of 3.0/3.2 and 3.0 out of 3.6 engines, so anything is possible.

As far as the crank work, billet or offset ground, http://www.racespecs.com/ can probably do it for you (they are in New Zealand). They are doing some billet four cylinder cranks for us and also are doing our type 4 billet heads for us as well.

if bigger is better, why reduce capacity?

is it to comply with racing regs and have rev-happy motor?

please enlighten me :)

bigger is not always better.


A mate and I are looking at building a 2.8RSR replica however the issues of pulled head studs etc with a mag case is a concern so the best bet is to use a alloy case and since a 3.0 carrera or 3.0 turbo are approaching stupid money we are looking at the SC case.

Michael

Right on the money, to comply with displacement limitations while allowing the use of later, more robust engines.

You could also source a 956 crank. It will work in the SC case. There are a few around. I was offered one about a year ago with Ti rods, it may still be available. Not cheap but neither is the other path. PM if interested.

Regards,
Bob

thanks mate!

Bob,

thanks for the thought on the 956 crank but i was thinking that if i get a custom/billet crank made then i will get the benefit of 20+ years advance in technology whilst still ending up with the displacement.

Charles as i get closer I will send you an email re pricing on nickies with a reduced bore.

So does anyone have any ideas where i can get a custom crank made?

Michael

Just to clarify what we are talking about here:

making a 66mm-stroke crank that is also a 9-bolt

the 2.0/2.2L crank, with its rev-happy 66mm stroke, was only made in a 6-bolt version, save for the 956. To run this in a case that has 3.0 heads and pistons/cylinders, you need a 3.0 Carrera or 930 case, which are pretty hard to find.

The idea is to use a standard, readily available 3.0 SC case or 3.2 Case with a 9-bolt, 66mm-stroke crankshaft. The standard bore of the 3.0/3.2 is 95mm, and that gives you exactly 2,807cc of displacement with a 66mm stroke. You do not need to underbore it, I don't know why you would unless you have to get under 2.8L. This compares extremely favorably with the factory 2.8RSR that was 92 borex70.4 stroke for a displacement of 2,808cc.

Michael-sent you a pm

Well, the idea would be to be able to use the 3.0 crank and not need a custom crank, with the 92 bore and 70.4 stroke - that is exactly what I have done before, or at least one example of an underbore cylinder. Doesn't cost any more to make it that way.

can a collar be made to hold the main seal for a 6 bolt (66mm) crank in an sc/carrera case? basically reducing the diameter of the bearing area for the early crank. are there other differences?

I understand that i can use the standard crank as per charle's comment but I would be seeking to have a stroke of 66mm to get a really high revving motor

If I undersatnd it correctly a 66mm stroke and a bore of 95 will give me 2.8ss

Or the other way i can go is a stroke of 70.4 and a bore of 92mm


I think the 2.8ss motor will be a better performance compared to the longer stroker smaller bore.
Michael

There is nothing saying you can't have a longer stroke while making an engine a revver, especially considering that a 70.4mm stroke isn't that much (Porsche 356/912 is 74mm and those engines rev freely, even with a 90mm bore and some a bit larger yet). Other considerations could be made to build either configuration into a revver - plan with cam timing (and cam itself), light flywheel, lighten wrist pins and pistons, etc. All things considered, the longer stroke will yield itself to higher piston velocity and with a smaller bore, should have better flame front. Not saying that one is better than the other, just the 2.8SS is the more common approach.

The 2.8SS is "2.8 Short Stroke". That means it has a shorter stroke~requires 956/custom crankshaft, to run 95x66, or a 3.0 930/Carrera ('75-77, typ #930/02 and 930/52) case.

Sure, you can make a 2.8 out of a 3.0SC, if you do 92x70.4. It's a 2.8, but it definitely isn't a 2.8SS.


Math (formula 6(pi)r^2h):

6(3.1416)(95/20)^2(6.6)= 2806.94 cc ;; 2.8 Short-Stroke, 95 x 66

6(3.1416)(92/20)^2(7.04)= 2807.95 cc ;; 1973 2.8 RSR, 92 x 70.4

I have built several 2.8SS engines. I hope this clarifies things.

Regards,
Scott