New Engine Update and Question

[Gene Fiore]

I know it has been a long time coming, but my motor rebuild is about complete. Just a little more tuning with the camshaft degreeing to get it where I want it and just finish assembly of the head. I have been a little worried about my final compression ratio and would like someone to verify my numbers. I used a program from a website to calculate the compression based on these numbers.

Bore size 3.72
Stroke length 3.91
Head gasket bore diameter 3.80
Compressed head gasket thickness .053 ( Corteco gasket )
combustion chamber cc's 55 ( log head modified to accept Holley 2 bbl carb and some minor porting, plus 1.75/1.50 valves )
piston dish volume 1.5 ( these are 255 V8 pistons which according to the specs online the 4 tiny valve reliefs measure up to this volume )
Piston deck clearance .027 down in the hole

This is a 250 motor which has been bored .040 and will be running the Clay Smith 278 solid lifter cam.

I'm not going to say what compression ratio I came up with until I get some numbers from you all. Any help would be greatly appreciated. Thanks!

 

[falcon1963]

Gene, 10.7-10.8 area

 

[FalconSedanDelivery]

10.52-1 , is what I get

 

[64falconsix]

10.7 to 1

 

[Gene Fiore]

Thanks for the replies! I also came up with approx 10.78 to 1...I was hoping for more like 10 to 1 as this will be street driven. My machinest thinks the increase in quench due to using the 255 V8 pistons ( these pistons raise the piston in the bore by 85 thousands ) will help prevent detonation. I am planning to run just premium pump gas. Any thoughts on this? Is there a head gasket with a compressed thickness of more than .053?

 

[RacinNdrummin]

You should be able to run on premium, its just a matter of how much advance you can run before it starts detonating. The quench will help out a lot.

 

[Anonymous]

Gene, how are planning on keeping the engine cool next summer?

 

[Gene Fiore]

Aluminum radiator and electric fan...hope that does the trick!

 

[aahsac]

Gene What are you thinking about running for total advance? and what are you planning on fuel? I think you should be OK on the street if you drive conservatively but for racing pump gas isn't going to do it for a 10:1 motor.

 

[Gene Fiore]

Time will tell...I think with the improvement in quench and mods to the combustion chambers and the cam I am running that I may be ok. If not I'll have to put in some racing fuel when I go to the track!

 

[falcon1963]

Gene, to bleed off some of the compression, seeing that you are using a solid lifter cam, you can always set the intake valves @.016 instead of .018".

When you get the engine running do a cranking compression test using the recommended setting of .018" & then try it with a .016" setting.

That will increase your intake duration. That is the beauty of solid lifters. Falcon Man