What psi before using race gas/blend

[mopar1rules]

IMO, the best/most accurate way is to find out what the UCCR (uncorrected compression ratio) is. You will need to find out the trapped volume (volume above the piston when at top dead center) and compare that cc volume reading to the volume above the piston when the piston is at bottom dead center. This will tell you exactly what's going on and the guessing game of what fuel to run is over.

[zach15]

OK, so I've got a basically stock ported engine with 65mm pistons and 21cc domes and just for shits and giggles, my cranking compression is 158psi. How then do I know what fuel I should be running? I'm using 93 octane pump gas and want to stay that way.

Its not the psi that changes the octane its your actul compression ratio. like a stoke banshee is 6.5:1 and 93 octane should be good up to 10:1 or so and im runing 15cc domes and im only at 8.5:1 so your good with 93.

[gotta_goatsfast]

OK, so I've got a basically stock ported engine with 65mm pistons and 21cc domes and just for shits and giggles, my cranking compression is 158psi. How then do I know what fuel I should be running? I'm using 93 octane pump gas and want to stay that way.

 

Is there any signs of detonation? Any pinging noises under load? Any pitting on the piston crown or dome? Any metal specs on the spark plug? If not, then there you are safe. Unless there are signs of destruction in your current setup, there is no need (and no benefit) to a different fuel.

[J-Madd]

I run a shaved head on my unported stocker that kicks 155 psi. I run +5 timing and 92 - 93 octane for years now. I couldn't tell you trapped volume or UCCR, but our motors should be very similar in that area.