I've got two sets of pistons for 95" build I'm getting ready to do!!
First set SE flat tops. Decking heads to 76 cc's. And 30 thou head gaskets. Gets me. 10.26 static. 9.34 corrected. And 191 ccp. With the mackie 575 cams at 460' above sea level...

The other set is the high comp SE pistons. 10.60 static, 9.54 corrected with a 30 thou gasket. And 199 ccp. With the mackie 575 cams.....
I have a set of Manley 600 lift springs and a set of comp releases to go in the heads...
Dave Mackie says the 10.60 comp is pushin it... I could run a 40 thou gasket to get back to 10.4 static...
HELP ME DECIDE...
I'm Leary about cuttin the heads so much to run the flat tops, and I think the high comp pistons will be to much compression...

 

Take a breath.

First, I don't get your numbers at 76cc; I get 9.24/189 which, IMHO, is good. No need to push for more; the gain just isn't there. Check your numbers again; are you allowing for deck height? Most early TCs are down in the hole .005"-.007".

In any event, I would go with the flat tops and the lower numbers. That cam has a TDC lift of .227"; pretty tall so checking valve to piston is critical. You have the cams, so check valve to piston with a .030" head gasket before you mill the heads to determine how much you can cut and maintain safe valve to piston clearance. Easy and quick to do if you have access to a Trock tool; if not, you will have to mock up a cylnder and do it that way.

The valve pockets on the flat tops are probaby deep enough but if running larger intake valves, there is the possibility that you may need to open them up toward the outside of the piston.

Consider the later OEM valve springs; they will handle the lift and be lighter on the seat. Heavy spring pressures just contribute to noisy valve trains and are not always necessary to control the valves in a street build.

JMHO

 

Im using the big boys calc, putting .005 in the deck height shows the 9.24 and 189. I did not allow for deck height..... I'm using 06 and newer heads to have the heads done so I can save my set for the next build... I'll take your advice on the springs.. A buddy is giving me a ton of parts off his old build. SE oil pump and cam plate, comp releases. And the stock 08 heads, I'm gonna have Big boys do the street port to em.... I'll relieve the piston valve pockets a bit..
I'm gonna tackle the build myself..... I just want to make it as easy and pain free as possible....
bit....

 

I am running those cams at 195psi. I know what Dave thinks and he knows what he is talking about. My guess is he will advise on the side of caution. He doesn't know if the person he is talking to knows what they are doing or can tune the bike properly. I am running the 10.5 SE pistons and as djl pointed out they were down in the hole, how much I can't remember but the numbers he gave sound about right. .030 hg gasket, ACR's installed. No problems at all of any kind.

 

I guess I'm trying to copy the Hippo build from a few years back.... Just not using the S&S 570's.

 

As long as you maintain a minimum of .180" dome thickness, you could always machine the dome, and cc it, in order to establish your needs/wants.
Wouldn't be the first time that was done.
Scott

 

Good advice. Even then if there is a casting flaw, the piston can crack; have seen it happen. Play it safe; stick with the flat tops.

 

With the 10.25:1 pistons,
0.005 deck height
85cc cyl head volume
0.030 HG
10.5 piston domes
460' above sea level
10.49 static
Mackie 575 with a 42 close
9.55:1 corrected
197.1 ccp