440 Compression

[Fastest1here]

I just started building my 440ex and I have read many of threads about checking your compression ratio with cc's of fluid in your combustion chamber. My head is still getting ported and a high flow valve job from trinity so I can put it together just yet. My Wiseco piston is supposed to be a 11:1 yet I hear that is over rated. So what I'm trying to find out is by experince can anyone tell me what I should expect with .020 off the deck height and .043 cometic gastket.

Thanks

Jim

Check out the thread below, it answered most of my questions.

There is just a lot more to it than most think and the answer is different with each individual engine etc.

decking set up (http://www.exriders.com/vbb/showthread.php?s=&threadid=48435&highlight=Have+you+decked+the+cylinder)


Hey Ben (or anyone else who knows) what do you need to make this old thread a sticky or something so it can stay up top etc.

[Steven]

I ran that same 89mm Wiseco on my first 440. It was rated at 11:1 and when I did the fluid test, it was really 9.6:1. What a bummer.

Anyway, how to fix it?

The piston should be about .040 on the hole at TDC. Add that .040 to the .043 head gasket (.040 compressed) you're talking about .080 clearance.

Ya need to get that clearance down to .040 or so. How? I would run a .012 base gasket (oem is .020), which will get you to .030 in the hole.

Then mill .015 off the cylinder and run the .025 head gasket. That should get your clearance down to about .040 and your desired 11:1 compression.

Get the idea? You can play with this stuff forever.

The above numbers are approximate. You really have to measure it.