[ScumOne]

I'm getting some goofy readings on my 400 (still troubleshooting the carb situation) and I need some help.

The 400 was rebuilt with KB 346 pistons which are supposed to produce 9.7:1 compression with 72cc cylinder heads. I've switched to the KRE aluminum heads with the as cast 65cc combustion chambers, and had the heads milled .030 to get a lower cc volume, which should be around 63/62cc now.

The block was decked .010 to clean it up when it was rebuilt 12 years ago.

So it should have roughly a 10.634:1 compression ratio at 14.7 (sea level air pressure).

My mechanic tells me it's got 132/134 compression readings consistently at 5500 foot elevation. At 5500 feet the air pressure is 12, not 14.7.

My question is if it's a 10.6:1 compression ratio at sea level (100/200 feet above) with the same setup, is the lower AP at 5500 feet making the compression test read 132/134?

Because if I run the calculator it comes up with 132/12= 11:1 compression.

If I stick with 14.7 AP, then 132/14.7 comes up with 9:1 compression, which is way off from the UEM/KB piston calculator.

So what the hell am I doing wrong here?

Jim aka ScumOne