7 replies to this topic

[nobrakes]

I am building a 1310 supercharged engine and know the cc's of my pistons (6.4) and the cc's of the combustion chamber in the head (22.3), but want to know what the ideal cc's are for the supercharger so that I can get the right decompression plate for my engine.

All help much appreciated!

[Ouster]

Well, find out what the idea compression ratio for a supercharged engine is (8.5:1?), calculate your current compression ratio and then work out what decompression plate (which is a bodge IMO) you'll need to reduce the compression.

[Ethel]

The ideal compression is as high as you can get away with.

That will depend on the all sorts of stuff: the fuel grade, boost pressure, cam...

8.5:1 sounds reasonable for a typical road engine running maybe 10psi of boost. Better to create any extra cc's in the head and have only one head gasket to worry about failing.

[Rosslin Racing]

to answer the question between 28 and 30cc with 11cc pistons

Edited by Rosslin Racing, 26 October 2009 - 08:21 PM.

[richieg]

Probably a dumb Q but how do you calculate compression ratio?

[Sam Walters]

Compression ratio is swept volume against unswept.

[Turbo Phil]

You're really going to struggle to get it to a sensible level for supercharging with those small dish pistons.
Assuming the pistons come flush with the block & using a BK450 gasket, you've got 6.3cc in your pistons & 22.3 in the head, we'll assume 1cc for the ring land. This gives you a volume above the piston of 33.7cc. On a 1310 this will give 10.7-1 compression. Enlarging the chambers to 28cc only drops this to 9.3-1, still to high really ...........

[joe90]

i was told but jonspeed you need 44cc unswept volume. check out this sit to work out comp ratio http://www.csgnetwor...m/compcalc.html