Short stroke engine, proposed spec and considerations
Turbo Mini Forums

These South African 1100 cranks seem to provide a good option for creating a revvy engine, and for a car that will be doing mostly track work I like the idea of shifting at over 8k without worrying about whether I'm gonna break a 1275 crank or have to rebuild it twice a year.

How does this sound for an engine specification, and are there any other things that I may not have considered. If the whole thing produced 190bhp that would be fine as I'm not after massive power figures

1275gt block decked 225 thou, possibly a bit more depending on how far down the block the pistons still sit.

+20 accrilite forged pistons

70.2mm South African crank, wedged, bladed, cross drilled, and heat treated. Ground to bottom tolerance. Centre main strap.

A plus rods lightened and balanced

BMW k1100 head, with the LT cams.

GT1752 putting about 20 psi into the whole assembly.

Rev limit 8700.

Probably aim for about 9.0:1 compression


Cheers

James

Edited by minimole23 on 12th Nov, 2010.

Deck 250 thou with those pistons. Although someone will be able to comfirm how far those pistons sit down the bore on a standard stroke and block.

Id run the rs camshafts and fiddle about with them on the vernier to swings the cams away from each other.

Also!

Youll need 31cc unswept for the cc you want.

0.9cc for piston cut outs (Dont quote me!)
20cc head
4cc head gasket
0.8cc ring land.

Get a 5cc dish cut into the pistons also, offet to position under the spark plug.

Edited by Sam on 12th Nov, 2010.

If it helps I will have 6inch rods in stock very soon (S journal and large journal)- for these sorts of applications

If Carling made Mini engines
it would probably be like this one!

Sam, thanks for the info. Accrilite pistons seem to have a nice 6cc piston listed, so that could prove useful.

I've set the ball rolling to try to obtain those cranks.

John - By the time I have had a set of standard rods modified, and skimmed loads off an A-block it may work out similar to just buy some of your rods and use an a-plus block. I await the price!

We'll keep the price close to the std rod price - may even scrape a little TM discount in there.

Deck height is very important to keep a rigid gasket surface and sufficient thread depth for the head studs - ideally I'd like to see thicker than stock height for normal K applications.

If Carling made Mini engines
it would probably be like this one!

I agree John, as most of the K head studs hit outside the bosses for the original bosses the deck thickness is fairly thin, too thin to bolt the head to when the block has been skimmed a lot!

Longer rods is the way forward on an engine like this. I have a SA crank as well, but opted not to use it with my K conversion because of this.

It seems then that longer rods are the only way to do the job properly then in light of miniminors comments.

On the plus side I don't need to bother tracking down an a-series block now, skimming it loads, and modifiying the main bearing caps for the plain lower shell.

The quest for a crank steps up a gear!

Longer rod also reduce the angle the rod sees and I think it makes it more reliable with increasing revs and reduce bore friction.

That's even more bonus !

Rusty by nature