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What octane for 10:1 C.R?


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     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. 

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@supermpuller 

Might have the wrong person.  @superih  Screenshot_20220227-190907.thumb.png.bb44fbff83189e87b4d6083d39745b50.png

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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.

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Differently 93 or higher.. Use to build race engines.. And 10.1 works best on 91 or better... 

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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👍

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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

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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?

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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 

 

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