compression calculation not working
Turbo Mini Forums

Hi all,

Ive been trying to work out what cc chamber size i would need for benross.
But something doesnt seem right.
Ive used alexs xls and done the calculation myself but it doesnt seem right still.
could someone work it out for me to see if my answers the same thanks.
I wanna run 8.4:1 cr

1275 with +20 thou bore
I have omega 10cc dish pistons,
81.3mm crank
the pistons sit 1mm down the bore.
i will be using a bk450 head gasket.

as i say im trying to work out the chamber volume required for this cr.

any help would be greatful

martin

EDIT:: no that would be right, 1mm it is...

Are you sure the Omegas are 1mm down the bore?? unless they are forged I did some research and omegas came up near 4cc


http://www.turbominis.co.uk/forums/index.php?p=vt&tid=121851

look towards the bottom..

Edited by Turbo Tel on 30th May, 2007.

website:- http://www.terryhunt.co.uk

yeah i phoned up med, and they said thats what it should be, so i went out and measured and it was 1mm,

I make 1mm down the bore on a 1293 bore 4cc

using your info and assuming another 1cc for the ringland vol i get

25 cc in the head= 8.54-1

26cc in the head= 8.37-1

yeah i got around that.

Bore 71.282
Stroke 81.3
Gasket Volume 2.80
Ring land Volume 1
Piston Volume 10.00
Head Chamber Volume 26.5
Deck Volume 4

This would give:

Compression Ratio 8.32:1

With this sort of compression ratio what would be the sorts of boost to run?

I have a +20 bore as 71.12mm

with that kind of CR boost = plenty!

seriously though it will depend on many things, but with a good intercooler you shouldn't have a problem. less so if you go megjajolt.

there are people running 10-12psi with 9-1 CR

I think benross runs about 8.4 and i reem to remember him posting that he had run 20psi

yeah i thought that was the bore of +20 but med said no its 71.282,

Yeah i got a 4x4 cosworth intercooler, and megajolt,

Just thinking before i get it all finished.

thanks for the help

no wories, always worth thinking ahead