Compression Ratio

[n9mfk]

Hi all,
i have a question about Compression Ratio

let say i build a engine with these spec
Bore: 4.030
Stroke: 3.750
Cubic Inch: 383 @ 4.030
Compression Ratio: 10.5:1

it wood not run on 91 but it runs on 95 are the any tricks to stay at 10.5:1 an make it run on 91
thanks beau

[Eagledk]

Yes and no, you can make it run on 91, but you need to change to other carbs so you can get the fuel/air ratio to about 11-12:1, cam all the way op and retart the ignition a LOT

[Snowmen]

Just a quick tip in case you don't know. What compression and other factors do is modify the RON. Using 91 RON fuel means that you must keep the RON under 91. In this case, you would therefore need to reduce the RON to 91 in order to be able to use it without creating problems related to knock.