[bigahead]

The engine is the same apart from things like the pistons, ecu, so is it possible to bolt on the supercharger from the S, onto the cooper, as well as changing the other parts?

Is the 5 speed box up to the job?

Obviously they're original parts, but they're not going on the cooper S, would it technicaly effect the warrenty? Me thinks very likely!?

Wonder if the parts department at the BMW dealership has one in stock?

[Garfield]

For racing purposes, we're building a Cooper given to us from MINI. We couldn't get an "S". But, in Street Modified, I could bolt a Turbo or a Supercharger onto the Cooper. After some long discussions with our race mechanic, we ruled that not only would the engine not be up to it without the piston injectors, but the tranny would surely be toast. We will, however, run in Street Prepared with Air Induction, Headers, Exhaust, mill the head, bore to .0472, match ports, and chip it. Not too concerned with pumping another 20-25hp out of the engine.

[chiph]

Quote:

Originally posted by bigahead
The engine is the same apart from things like the pistons, ecu, so is it possible to bolt on the supercharger from the S, onto the cooper, as well as changing the other parts?

Is the 5 speed box up to the job?

Obviously they're original parts, but they're not going on the cooper S, would it technicaly effect the warrenty? Me thinks very likely!?

Wonder if the parts department at the BMW dealership has one in stock?

I think the parts will successfully mate up, but it'll be toast after the first rev - the normal Cooper has something like 10:1 compression, and the Cooper S uses much lower compression (8:1??).

Chip H.

[bigahead]

back to the drawing board!

[Wynn]

Um, call me dim, but I don't know what this whole engine compression thing is about... and I really cannot imagine why it's lower on the supercharged model than the normally aspirated engine. I'd have thought it was about how much air/fuel is compressed beneath the piston or something, and that value should be greater behind a turbo or SC. ...I'm rambling. Someone want to explain it for us in simple English for dumb Americans?

Thanks,
wynn

[chiph]

Wynn -
Take a look at:
http://www.howstuffworks.com/question395.htm

Basically, the compression ratio is how much the air/fuel mixture is compressed by the piston before being ignited by the sparkplug. On a normal (no turbo or supercharger) engine, the fuel/air mixture is more or less at normal atmospheric pressure when the compression cycle starts, so a 10:1 compression ratio works fine with premium gas.

On an engine with turbo or supercharger, the air that comes into the cylinder is already compressed above atmospheric pressure, and so the engine must not compress it as much before ignition, otherwise the fuel/air will burn early, and you have a diesel (as well as an engine-damaging knock from hell).

You change the compression ratio by swapping out one or more of these parts: crankshaft, connecting rods, and pistons. You can also resize the bore of the cylinder (making it larger will decrease compression ratio).

Chip H.

[jester]

as for the cooper tranny not being up to the job. a good friend of mine has a cooper running 150bhp + 100bhp nitrous, and it is very guick, beats a porsche boxter to 60. he has been running it for about 8 months with no probs. apart from the clutch wich is a racing item now. And his dealer has ok'd it, they said as long as he isnt blowing up gearbox's evry 6 months they'r ok with it!!


Go see http://www.mini-design.com

[Bilbo Baggins]

Quote:

Originally posted by chiph
Wynn -
.......You can also resize the bore of the cylinder (making it larger will decrease compression ratio).

Chip H.

This will have a very small effect on the compression ratio. But you could put in a thicker head gasket, that would lower it more significantly.

Increasing the volume of the cylinder by increasing the bore adds volume in the "squish area" of the combustion chamber where it is the thinnest, lowest volume, at full compression.

The compression ratio is determined by how much the piston crunches the air/fuel mixture. Approximately equal to the maximum volume of the cylinder divided by the minimum volume. Just as using a thicker head gasket will effectively increase the volume of the combustion chamber and lower the ratio. A thinner gasket or milling a couple of thousandths off the head will increase the ratio. The use of pistons with different deck heights(the distance from the wrist pin to the top of the piston) will also alter the ratio, taller/longer deck height=higher ratio, lower/shorter deck height=lower ratio.

[chiph]

Thanks, Bilbo.

You are correct. Increasing the bore will make the cylinder larger for the entire distance the piston moves, and so when the piston is at TDC, much of that space is pretty much wasted. By adding a thicker head gasket, you get more volume when the interior of the cylinder is at maximum "squish", lowering your compression ratio.

Of course, more displacement usually means more torque, and we all like that!

Chip H.