please help..
if dynamic compresion ratio is :
4.2:1 what octane gasoline do I use ?
4.8:1 what octane gasoline do I use ?
5.4:1 what octane gasoline do I use ?
6.0:1 what octane gasoline do I use ?
6.6:1 what octane gasoline do I use ?
7.2:1 what octane gasoline do I use ?

 

Don't bother . . . With those DCR's, your car will be a "slug", if it even runs, at all !

 

General rule - multiply by 10.
So your 7.2:1 DCR needs 72 octane.

 

My homeboy Mike had a '67 street machine, complete with big-block, 4-speed on the floor and a ton of performance parts. I rode shotgun in that car alot and every single time it made me smile.





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Good for you for actually being concerned with dynamic compression ratio. IMO the dynamic compression ratio makes an engine. There are many factors when choosing a target dynamic compression ration. When I was building my 441ci LS7 for my Z06 I wanted to build it to be on the edge of what pump gas was capable of. My previous LS7 build in my C5 was very aggressive and required E85 which became very annoying. Through my research I found that around 8.5:1 was roughly the end of the cushion for 93 octane. I'm sure you could push it further on certain engine combinations with more efficient combustion chamber designs. But I was happy with sticking to 8.35:1 dynamic which ended up being 13.8:1 static. The engine runs exceptionally well. It made 655rwhp and 585ftlbs on 93 octane and took 26 degrees of timing with no issues at all. No signs of pre-detonation, no issues overheating. No issues at all honestly. I drove the car thousands of miles and many road trips. Even with only a 3.42 gear in the rear the car ended up running 9.90@143mph in the 1/4 NA and 8.90@160mph on a 300 shot.