Anthony Posted July 21, 2005 Share Posted July 21, 2005 Guys Apologies for the numpty question. What is the safe sensible level to run compression levels at, assuming pump petrol. Currently running 11.78:1 and looking to build a new head, just wondering about increasing compression ratio. Thanks Link to comment Share on other sites More sharing options...
BarryT Posted July 21, 2005 Share Posted July 21, 2005 Not so numpty a question, as there is no absolutely correct answer, but I'd say your already on the top limit for 97 RON fuel (assuming aluminium head). High speed race engines can go up to 13-14:1. Any higher and you won't get any more performance. More modest revving engines, particulalry those for the road, have to consider detonation. In general, but not exclusively, this is a low speed phenomenon so peak power may be OK. However, you may have to retard at lower speeds so throwing away the benefit of the higher compression. Its not worth pushing to the limit as the gains are small, unless you are trying to extract as much power as you can for a fixed capacity race formula. Barry Link to comment Share on other sites More sharing options...
Anthony Posted July 21, 2005 Author Share Posted July 21, 2005 Thanks Barry Much appreciated. I know the RST V8 is around 14;1 just trying to see if 12.5/13 is still OK Regards Link to comment Share on other sites More sharing options...
edmandsd Posted July 21, 2005 Share Posted July 21, 2005 Blimey 14 to 1 compared to my lowly 12.3 ❗ Can't be on pump fuel then surely 🤔 Home of BDR700 Link to comment Share on other sites More sharing options...
Swiss_Tony Posted July 21, 2005 Share Posted July 21, 2005 Anthony A friend has a vx engine with 12.7 comp. It runs with carbs and mapped ignition and he uses Optimax fuel. It was mapped by Steve G and it runs like a dream with no signs of det etc after a recent strip down of the head etc. As long as its mapped well as in this case it should be fine. James Su77on Se7ens Link to comment Share on other sites More sharing options...
oilyhands Posted July 22, 2005 Share Posted July 22, 2005 Static compression ratios tend to be higher on engines which have longer duration cams where the effective compression stroke is shorter. Depending on your cam choice, combustion chamber type and estimated power band I'd sat that you wouldnt gain too much by going higher than you curently have. Oily Link to comment Share on other sites More sharing options...
Anthony Posted July 22, 2005 Author Share Posted July 22, 2005 Thanks Guys Much appreciated ! Link to comment Share on other sites More sharing options...
EFA Posted July 22, 2005 Share Posted July 22, 2005 I run 12.7:1 no issues on Optimax Link to comment Share on other sites More sharing options...
edmandsd Posted July 22, 2005 Share Posted July 22, 2005 It surprises me how often CR is mis calculated and also how frequently the losses as a result of the necessary retarding of the ignition outweigh the gains from higher CR. Home of HTR700 Link to comment Share on other sites More sharing options...
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