Compression ratio for UK pump fuels?

[DDave79]

Hi,

Considering a bbc engine build... Can anyone tell me what compression ratio you can get away with whilst ensuring ping free running on a classic yank tank?

Most of the U.S. Articles I read suggest around 10:1-10.5:1 for U.S pump fuel... But I'd have assumed that we can get away with higher given that std fuel over here is 95 octane and the overpriced stuff is 97?

Many thanks for responses.

Dave

[KevinCamaroSS]

IIRC the US pump fuel is near enough the same as UK. The US rating is in a different unit so comes as 91 and 95. These should be roughly the same as 95 and 99 in the UK. No doubt somebody can correct me if I am wrong.

[DDave79]

well... you learn something every day!

so; 10.5:1 is there or thereabouts for a non cranky; pump fuel american V8 in the UK.... can can anyone suggest any other environmental factors that might influence a UK engine build vs a US one?

[Total loss]

DDave79 said:

Hi,

Considering a bbc engine build... Can anyone tell me what compression ratio you can get away with whilst ensuring ping free running on a classic yank tank?


Dave

Would that be static or dynamic compression ratio ?

[minime68]

US uses the AKI scale and UK RON. 93 Octane US is equivalent to 98-99 on the RON scale. I had a 10:1 supercharged engine running 14psi. It is still running just fine.

[DDave79]

Total loss said:

Would that be static or dynamic compression ratio ?

Static.. The car currently has a 454 generating 10.25:1 from 118cc open chamber rectangular port heads. I'm contemplating 106.8cc aluminium L88 heads... But ideally would like to keep it pump fuel compatible!

[Total loss]

DDave79 said:

Total loss said:

Would that be static or dynamic compression ratio ?

Static.. The car currently has a 454 generating 10.25:1 from 118cc open chamber rectangular port heads. I'm contemplating 106.8cc aluminium L88 heads... But ideally would like to keep it pump fuel compatible!

Have you actually measured the CC ? Only published & actual can be quite different.

[DDave79]

Not yet... it feels like a lot of effort for the sake of confirming!

It's a rebuilt motor with aftermarket Pistons, ported heads and a hydraulic cam of unknown specs.... factory compression ratio for this casting (71 ls6 block and heads) was 9:1.

I'm TOLD it's a 10.25:1 engine.. But don't really know much aside from the fact that it pulls pretty hard.. Compared to the other cars I've owned or driven, I'd suggest it's >425 Bhp in current tune.

[ringram]

Static compression is irrelevant as its down to intake valve closing point and dynamic compression which can vary a lot with race/performance engines.
So depends on what application you have in mind.