Im upgrading to 103", but got a bit confused with the best compression ratio for 103" motors with Andrews 54H or 67H

High octane fuel is not a problem here. I want to go for 10.3 - 10.5, but im worried about reliability.

Any idea?

Im riding 07 Dyna.

 

Feedback that I got in going to the 54H was that 10:1 is ideal. You could go more, but then will need to pay more attention to the tuning. I live at high altitude so 10.5:1 is working well for me. Lower altitudes may introduce more sensitivity to pinging.

mark

 

I do ride mostly in sea level altitude, so I think I'll stick to 10:1

Which pistons are you running though? My build is mostly as yours, do you like the 54s or is it better to go for the 67s? do u have any dyno numbers?

Thanx.

 

I'm running the HD cast flat-tops. I like the 54H very much. Its got the power just where I want it. I'm sure I could get some more HP on the top end with headwork, but I don't ride there anyway.

Mark

 

So your static compression is about 10.3 & your corrected compression is about 9.4 is that right? I used BigBoyz calculater.

 

Correct. I think my static is closer to 10.5 if I use big boyz calculator, measure my CCP at 6500 ft, and then back into it.

Mark

 

Where you are you may want to use the 67 if your running 10:1. We use the 67 up here with 10.5 to 11 to 1 but can get away with it because of our latitude. Also the 67 works best with head work. The 54 with 9.6- 9.8 to 1 (without head work) may better suit you where you are.

 

Im sending my heads to BigBoyz, but I'll be using CP Pistons with 5.5 dome, so I think achieving 10:1 of corrected compression is impossible.

 

If you truly want reliability; leave it alone.

The 67 will move the power band to the right from the 54 and will probably make more HP. You can achieve 10:1 corrected but you would need to cut so much form the heads that you would most likely have valve to piston clearance issues. Static CR would be ove 11:1 and cranking compression well over 200psi; probably not a place you want to go. Keep your corrected compression to 9.3 or thereabouts and cranking compression under 200psi(the closer to 190psi, the better) and you will be fine. If you are sending the heads to BigBoyz, talk to Bean.

Flat top pistons will get the job done and make controlling squish and dealing with valve to piston clearance much easier; the dome pistons just complicate the build and are not necessary to achieve your goal. Mock up and measur and re-measure when assembling