Deck height and compression

[AMXguy]

I'm not sure how to check my compression figuring in deck height. I have new KB237 pistons, Felpro 1009 head gaskets and my heads CC at 85cc. I put the first piston in and it comes .015 ABOVE the deck, I've never had this before, I know they decked the block but now I'm worried that the 10.16 compression KB's chart tells me I have isn't figuring the deck height I might have. I don't know if I have a problem or not, does .015 out of the hole with this piston seem abnormal to anyone who's used them? it's a pain in the rear end having the closest machine shop 150 miles away.

[Strawdawg]

what gasket thickness did they use?  The Felpros?  And did they use 85ccs?

[Strawdawg]

Looks like they used 85 cc with a .040" gasket...the fel pros are shown as .039"/  If your pistons are  +.015", then you need to recompute using .024" when you plug the numbers in and assume the piston is even with the deck...

[AMXguy]

I can't find anyplace to put the deck height in just the head CC, I think you're right it appears they are figuring flush with the deck.  where would you find out how much the .015 would raise the compression ratio? I'm thinking it shouldn't make a major difference but I want to be sure.

[Strawdawg]

deleted as compression ratio calculator did not take gasket volume into account

[moper]

What heads and cam are you using? I routinely spec them .010 above deck, .015 could be no problem but it will depend on what heads and what cam is going in with them. Also... what engine size is this?

[AMXguy]

It's a 440 .060 over, 906 heads that CC at 85.  the cam is an Ultradyne 288/296, duration at .05 is 231 IN / 239 EX gross lift is 485 IN / 239 EX.   

 
 

[AMXguy]

I got ahold of KB and they said the compression wouldn't be my problem but clearance would be too close. so I need a set of  .055 or .060 head gaskets. he told me to call Cometic and I will but is there anyone else who makes this gasket?

[Strawdawg]

What clearance?  Valve?  did you make a typo on the exhaust lift above?

[AMXguy]

He said the piston would be too close to the head, I don't think valves are the problem.

 If I did the calculator right it says 10.73, I think he came up with 10.52 so that's about as high as I want to go. I might even get a  thicker gasket I didn't really want to be over 10.1 in the first place.

[Strawdawg]

I must be missing something.  I thought 906 were open chamber heads.I thought they were close to 0.100" deep at the closest point which would put them .100 + .039 - .015"  = 0.124" clearance....but then I am assuming the pistons are flat tops

I guess that's the reason there is no substitute for being there and measuring it yourself

[AMXguy]

I used a dial indicator to get TDC and then a strait edge in top of the piston using feeler gauges. they are flat tops so I can't see a contact issue myself, but I need to lose some compression so it looks like I have to get gaskets anyway.

[Strawdawg]

Why do you need to lose compression.  You have a pretty good cam to kill the pressure.  Do you want to run lower grade gas?

Looks like the kb 184s are the ones to run with oc heads

[AMXguy]

I run a blend of about 30% Av gas and 70% super in my cars, but anything over 10.1 seems to be a pain. the cam might bleed off more than I'm accounting for though, I'm not sure on that.

[AMXguy]

I think the relief in the piston is 5CC. I have all new valves and the heads were trued so I'm guessing that's where they came up with 85 CC.