Compression ratio? help please!!
Compression ratio? help please!! I'm in the process of cam install, and i had my heads milled .060". I will be using a .040" Cometic head gasket and need help or direction in calculating the CR...i read it takes about .007" of milling to decrease 1cc chamber volume, so that gives me about 8.57 cc decrease i believe. i will also have to flycut quite a bit (MS4), and i dont know how much to account for the cuts. I dont know where to have my heads cc'd or have equipment to do it myself (unless there is an easy way to do it??), so i am just looking for a close estimate. I am guessing about 11.6-11.8:1, would this be about right?? thanks in advance for any help!
CC the heads to find out. I took a 60cc and 5cc syringe you can get a a pharmacy or veterinarian and built blank off with a CD case. I drilled a small hole in the CD case and sealed around the chamber with some Vasoline. ATF works best as a fluid, carefully fill the syringe with a measured amount of fluid and then fill your chamber. When it's full just add up how much fluid you used to fill it. It'll get you within a few cc.
These pictures are with clear mineral oil which works, but is harder to see.
These pictures are with clear mineral oil which works, but is harder to see.
Here's the ATF
When I took my stock heads off I cc'd them to see how accurate I was? I came out to right at 67cc so I'm fairly certain I'm +1cc or 2cc.
At least it will get you close enough to use the compression calculators to see where your DCR is.
When I took my stock heads off I cc'd them to see how accurate I was? I came out to right at 67cc so I'm fairly certain I'm +1cc or 2cc.
At least it will get you close enough to use the compression calculators to see where your DCR is.
I'm in the process of cam install, and i had my heads milled .060". I will be using a .040" Cometic head gasket and need help or direction in calculating the CR...i read it takes about .007" of milling to decrease 1cc chamber volume, so that gives me about 8.57 cc decrease i believe. i will also have to flycut quite a bit (MS4), and i dont know how much to account for the cuts. I dont know where to have my heads cc'd or have equipment to do it myself (unless there is an easy way to do it??), so i am just looking for a close estimate. I am guessing about 11.6-11.8:1, would this be about right?? thanks in advance for any help!
thanks guys, great idea ssheets...i never would have thought of that. i tried it, the first time i got 57cc before i noticed it was leaking out from the cd case, then i tried 3 more times and got 55cc consistently. so im pretty confident with that. so using the calculator thels1kid gave, it shows 11.5:1 CR. thanks a lot!!
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From: BFE
You are gonna have some intake alignement issues, you also reduced the head flow. Milling more than .035 starts hurting flow.
You need at least .090 cut on intake, I would say .100 to be safe.
If those heads are stock, IMO find yourself another set and start again. You can get 243s stock from Patriot for around $400.00 or so.
You need at least .090 cut on intake, I would say .100 to be safe.
If those heads are stock, IMO find yourself another set and start again. You can get 243s stock from Patriot for around $400.00 or so.
yhea i wanto know too.. why does milling .035 or more hurt flow.... Like if i wanted to swap from the stock gasket to a .030 (25 thousanths give or take) and then mill .010 or .020, i would be messing things up?...
i put the heads on today without head gaskets just to check intake alignment and even without the gaskets the intake bolted up no problem. I don't understand how milling that much will hurt flow...i have read of several people who have milled .060" with no problems. predator or jakson, could you please explain why this is???
All I know is the ovious. Milling .060" changes your valvetrain geometry and intake manifold alignment by .060" That's why I went with 5.3 heads to get the smaller chambers while leaving the other two issues alone. We had to re-valve and port them though to make good gains though. 5.3 heads are like like 241's milled .035"-.040" without the change in geometry other than valve drop.
If the heads were milled properly, (angle milled), then there should be no problem with valvetrain geometry or intake alignment! My LS6 heads were milled to 58cc, and I'm running 2.055" and 1.6" valves. Everything went back together nice and tight and I have had no problems with it in 14k miles of some pretty hard driving.
Not to dispute anyone's information in this thread but if milling heads this much hurts flow then how does ET Performance offer combustion chambers down to 35cc's and mantain the "stellar" flow? I doubt they have a tiny chamber which would shroud the valves.
http://www.etheads.com/mainpage.htm
follow that link and click on products and performance then 215's or 225's or any of them for that matter if You haven't seen what they offer it will be an eye opener!
http://www.etheads.com/mainpage.htm
follow that link and click on products and performance then 215's or 225's or any of them for that matter if You haven't seen what they offer it will be an eye opener!
