2.8SS from 911SC case

[Walko]

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

[cnavarro]

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.

[JV911SYDNEY]

Originally Posted by cnavarro

2.5 engines out of 3.0/3.2 and 3.0 out of 3.6 engines, so anything is possible.

if bigger is better, why reduce capacity?

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

please enlighten me

[Walko]

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

[cnavarro]

Originally Posted by JV911SYDNEY

if bigger is better, why reduce capacity?

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

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

[boba]

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

[JV911SYDNEY]

Originally Posted by cnavarro

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

thanks mate!

[Walko]

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

[YTNUKLR]

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

[cnavarro]

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.

[gestalt1]

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?

[Walko]

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

[cnavarro]

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.

[YTNUKLR]

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