Well a long time ago I cc'd my .400 Offy heads to check the chamber volume;wrote the numbers down;yep you guessed it ,now I can't find the damned paper! The engine is an 8BA,276 cubes,ran a compression check and the average is 145 lbs across the board.From what the gauge tells me it's about 8.0 to 1.There has been very little grinding to clearance the valves, a bit to unshroud the valves,and a bit to remove some metal around the plug holes.I was thinking about 8.5 to 1 or even 8.7 to 1.Yes I did do a search but nothing really definative. You guys have any thoughts on this? Thanks.
Here is a link to a copy of a page from Joe Abbin's Road Runner Engineering site that lists compression ratios of various heads and engine sizes: http://www.flatheadv8.org/compratio.htm Should give you a ball park figure.
29SX, I run Offy 400s on my 8BA and i found that combustion chamber cc's tend to be all over the place....at least, they were on mine. I did a comp test on mine and got an average of 155psi all around, but my 8BA is at 258ci with 3 5/16" x 3 3/4", so there will be a difference there too. I had to unshroud the area surrounding the plugs, unshroud the valves at least half way down the chamber and clearance the vavles so m Im guessing I addec a few ccs to the chamber volume. I remember when I sat the heads on tjhe block sans gaskets, a rotated the engine, the vlaves would lifet the heads at one end yet not lift the head at the other end. Valves were adjusted the same, so I had to surmise that chamber vols were not the same. Others have said that they've experienced the same....Offy quality control perhaps? Rat
Offy cast chambers need to be checked. 8.0:1 is good for a flatty - as you go up, you tend to reduce flow - hard to get much more than 8-8.5 on a 276 w/o reducing flow much....
Flat Ernie; Thanks for that info;looks like I'll be pulling the heads to recheck the chamber volume.Memory loss is a bitch!(who are you and why are we running?)LOL.
Instead of simply checking the chambers, check the clearance above the valve. To do this, use a ball of clay or rolled up tinfoil (use a dab of grease to keep it in place) & stick it on top of the valves. Bolt the heads down & rotate the crank two revolutions to ensure all the valves make it through their cycles. Pop the heads off & measure to see what kind of clearance you have. For improved flow, most folks like to see .100" over the intakes, but for clearance purposes (not flow), .050" is adequate for valves...
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