Compression ratio

Post by **Onne** » Sat Dec 30, 2006 5:56 pm

How do I calculate my compression ratio?

standard 1098
175 psi compression
maybe a slight overbore

Onne

Post by **bmcecosse** » Sat Dec 30, 2006 6:08 pm

You can't calculate it from that figure - to do so would need the capacity of the combustion chamber. But if you have 175 psi compression readings - then it's in good condition. Nothing to worry about - and it's certainly not a 'low compression' engine.

Post by **Onne** » Sat Dec 30, 2006 6:12 pm

Just curious. How can I find out what CC my combustion chamber is then?

Onne

Post by **bmcecosse** » Sat Dec 30, 2006 6:19 pm

Remove head - invert on bench - fill chambers with thin oil mix from a burette! It's usual to have a piece of perspex with a small hole placed over the chamber - sealed with a thin smear of grease - this eliminates meniscus problems. The oil (or oil/paraffin mix) is run in through the small hole.

Post by **Onne** » Sat Dec 30, 2006 6:22 pm

ok. I'll give that a go when (read if) I remove the head.

Thanks BMC for the quick answer

Post by **bmcecosse** » Tue Jan 02, 2007 4:29 pm

No problem - happy to help! But with those comprssion readings (175 psi) there is absolutely nothing wrong - no need to worry !

Post by **Onne** » Tue Jan 02, 2007 11:23 pm

I don't, I was just curious how the ratio has been changed, if at all

Post by **bmcecosse** » Wed Jan 03, 2007 10:17 am

Why would it have changed - or this a different head that's been fitted ? I imagine JLH have the perspex and burette to measure the combustion chamber volume ??

Post by **Onne** » Wed Jan 03, 2007 7:56 pm

I am sure we do.

this engine just feels very powerful, hence my curiosity.

I might change some more bits to it now. Maybe get a recon skimmed 295 and a SW5 cam.

Get even more power

Post by **bmcecosse** » Wed Jan 03, 2007 8:44 pm

Better with MG Metro cam - and 12G940 head. But if the engine is good and goes well - maybe you should just be happy with it as it is !! Si fractum non sit, noli id reficere.

Post by **Onne** » Wed Jan 03, 2007 8:46 pm

I agree there!

It's just an idea that crossed my mind

Post by **bmcecosse** » Wed Jan 03, 2007 9:07 pm

Put these evil thoughts behind you for now. Rejoice that it's working well.

Post by **Onne** » Wed Jan 03, 2007 9:09 pm

Post by **Kevin** » Wed Jan 03, 2007 9:31 pm

this engine just feels very powerful,

Not suprising after the last Chesham special

Post by **Onne** » Thu Jan 04, 2007 12:30 am

Yes, I wonder why our Chesham special has been so very quiet

:D

Post by **Kevin** » Thu Jan 04, 2007 6:36 am

Yes, I wonder why our Chesham special has been so very quiet

Trade description act I expect