What is the stock compression ratio on a SBO? I have read plenty of articles about rebuilt motors achieving a different CR but have not seen what it is from the factory.

And while on the topic, does the compression ratio change dramatically on an older motor (over 100,000 miles)?

d1

 

Don't get hung up on the mileage. The care that has been bestowed on an engine over it's lifetime will have a much greater effect on it that the odometer.

The compression ratio varied from about 7.8:1 to 10.5:1 and most anything else in between so just asking "what's the compression ration on a SBO" is a vague question. what year and what size engine? Did it come with a 2 or 4 bbl carb? What did it come out of? It all plays into how the engine was set up at the factory.

 

Good point. Motor is a 350 with factory 2BBL out of a 1970 Cutlass Holiday Coupe.

 

That will be a 9.0:1 ratio.

 

Thank you, sir.

 

What about the compression ration on a 1971 Cutlass Vert with a 4-barrel 350 single exhaust..

 

Advertised is 8.5:1, but if you take it apart and measure everything I'll bet it's closer to about 8.0:1. I did it on 3 72's, they were all right about 8.1:1.