MahomieFarmall Posted February 28, 2022 Share Posted February 28, 2022 At what compression ratio will 91 (Premium) start pinging if it’s in a built up SM with high compression? I’m hoping to use 91 for a 10:1 “SM” I’m planning to build this summer but not 100% sure that’s the right fuel to use in terms of possible detonation issues. Would higher octane race fuel be the best for this compression? Thanks for your time. Quote Link to comment Share on other sites More sharing options...
bitty Posted February 28, 2022 Share Posted February 28, 2022 @supermpuller Might have the wrong person. @superih Quote Link to comment Share on other sites More sharing options...
superih Posted February 28, 2022 Share Posted February 28, 2022 I'd say 10:1 is pushing it for pump gas, usually stay under 9:1, but you never know without trying it! Using flat top pistons and removing any sharp points that can get hot and cause preignition will make you more successful. I'm running 8.5 in a farm tractor on pump gas (91-93) running it hard for a couple hours and haven't had problems. 1 Quote Link to comment Share on other sites More sharing options...
Whats in the barn ? Posted February 28, 2022 Share Posted February 28, 2022 Differently 93 or higher.. Use to build race engines.. And 10.1 works best on 91 or better... Quote Link to comment Share on other sites More sharing options...
MahomieFarmall Posted February 28, 2022 Author Share Posted February 28, 2022 1 hour ago, superih said: I'd say 10:1 is pushing it for pump gas, usually stay under 9:1, but you never know without trying it! Using flat top pistons and removing any sharp points that can get hot and cause preignition will make you more successful. I'm running 8.5 in a farm tractor on pump gas (91-93) running it hard for a couple hours and haven't had problems. Yes I will be running flat tops for the LP Head and-in my opinion-for increased longevity. Thanks for the info👍 Quote Link to comment Share on other sites More sharing options...
bitty Posted February 28, 2022 Share Posted February 28, 2022 23 minutes ago, MahomieFarmall said: Yes I will be running flat tops for the LP Head and-in my opinion-for increased longevity. Thanks for the info👍 I have a 450 set up with a 450 LP head, 4 1/4" power domes , stock crankshaft and I am running 110. Pings like crazy on high test .. needs a good starter also Quote Link to comment Share on other sites More sharing options...
superih Posted February 28, 2022 Share Posted February 28, 2022 5 minutes ago, bitty said: I have a 450 set up with a 450 LP head, 4 1/4" power domes , stock crankshaft and I am running 110. Pings like crazy on high test .. needs a good starter also Does it have too much timing? Too hot of plugs? Quote Link to comment Share on other sites More sharing options...
bitty Posted February 28, 2022 Share Posted February 28, 2022 16 minutes ago, superih said: Does it have too much timing? Too hot of plugs? I can recheck the timing. Think I have 3116 auto light plugs if I remember correctly. 60k coil, electronic ignition Quote Link to comment Share on other sites More sharing options...
DWV Posted February 28, 2022 Share Posted February 28, 2022 Unless something different is done flat tops and LP head, 4.125 bore and stock stroke will only make slightly less than 9 to 1 CR. 1 Quote Link to comment Share on other sites More sharing options...
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