driversdomainuk 8 Posted October 17, 2006 Hi When I finally get around to raising my CR on my 205 running twin 45s to 11.5:1 in preparation for the 288degree Catcam will I need to use Super unleaded/Optimax or will 95 unleaded do? Also, not that I could careless to be honest, but out of interest, will it sound/drive much differently at lower speeds? thanks Share this post Link to post Share on other sites
PUGugly 0 Posted October 17, 2006 Altering the compresion ratio will make no difference to the fuel you can use. You will find that the higher the octane rating of the fuel you use in general the better the performane but it all depends on the valve seats. If the seats arn't the right ones and not up to the job they will burn out meening head off and lots of repair work!! Seen burnt out valves and seats on so many engines and it's normally easier to replace the whole head. Will it run differnent at low revs with a performance cam?? Oh yes, Dependant on the cam it will vary from slightly lumpy on tickover to a complete bitch at low revs, Although once the revs start heading skywards you won't care to much!! Depends if you have to drive in the west end every day or out on the west country roads at night to how bearable this trade off is.!! Share this post Link to post Share on other sites
Ryan 99 Posted October 17, 2006 95RON is borderline on the standard engine unless you retard the timing and loose a bit of power. At 11.5:1 I'd say super unleaded is a must. Share this post Link to post Share on other sites
Rippthrough 98 Posted October 17, 2006 (edited) Altering the compresion ratio will make no difference to the fuel you can use. You will find that the higher the octane rating of the fuel you use in general the better the performane but it all depends on the valve seats. If the seats arn't the right ones and not up to the job they will burn out meening head off and lots of repair work!! Seen burnt out valves and seats on so many engines and it's normally easier to replace the whole head. I think you misread his question/mixed up your reply there?! Otherwise we'd all be running 20:1 compression ratios on 95 octane I'd say use super at the least, and you may have to retard the ignition a little until you get the cam in too, but perhaps you'll get away with it. Edited October 17, 2006 by Rippthrough Share this post Link to post Share on other sites
petert 554 Posted October 17, 2006 If using 98 octane, you can still run 30 deg. of total advance with that combination. Share this post Link to post Share on other sites
