I'm thinking my compression is alittle higher than i should have. I'm running a z6 block with a y8 head with the thinner y8 headgasket. The head was resurfaced also. The pistons are 9.0:1 cp's. Anyone have an idea of what the compression #'s are with this combination?

 

not sure what your compression #'s should be, but i was told the y8 head combustion chamber is smaller then the z6. simliar to ls-vtec effect on c/r.
i was told that z6 block + y8 head+ 9.0 c/r pistons= a c/r of ~9.5 (with un milled head)
^^^^ told to me by Jeff (boosted hybrid)


maybe this will explain why your seein higher then normal numbers?

hope i helped.

 

10.245544451625258:1

per compression calculator

http://www.knology.net/~jediklc/D.htm

 

llewsirc is right... it should be somewhere around there.

to use that calculator right you need to get the dish volume of the 9:1 pistons (JE lists them on their site) and enter it as "other." if i remember right... 9:1 JE/SRP's for a Z6 have a dish of -11. also remember if u have an overbored motor the volume would be different.

 

I have 75mm cp's now my srp's melted. So is this c/r going to be too high for 15psi? I'm not sure how my srp's were destroyed. I dont want to melt my new ones. I never noticed any detination on the way to get it tuned or while it was being tuned so i'm really confused as to why they burned up. I only got on it twice on the way up and none on the way home b/c it was overheating on me. btw..compression #'s were 185-190 range before my trip to the dyno and then 135-140 when i got home.

 

overheating = not good

cant explain the drop in comrpression after your trip other than your eating those ones up too . whats your timing at? what kind of gas are you running? i melted a stock piston from bad gas

 

the overheating was another d-series head lifting issue but it was b/c a headstud stripped out. those pistons that were in the car at the time of the tune were my srps. I just bought new cp's this past week. My timing was at 7-9 btdc before going to get it tuned. We found out my engine builder set my timing off a tooth so we adjusted my cam gear to get it to 16 btdc. Im running 93 octance gas. There were no signs of knock or anything on the dyno and i did not notice anything on the drive up (no radio or anything so i sure i would have noticed it).

 

that timing sounds way retarded....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hella_JDM &raquo;</TD></TR><TR><TD CLASS="quote">that timing sounds way retarded....</TD></TR></TABLE>

lol...it sure was. the compression numbers stayed the same up until i took it to get tuned. I was running the hack for awhile going to the track a lot too. I didn't have any overheating problem before the drive up to get it tuned also

 

do you still have your spec sheet? can you scan it or take a pic for me?

 

i built my motor myself this time. A honda tech helped me build my motor last time. so i have no spec sheets for anything.