Cylinder heads milling

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drugster

drugster

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Hi:
Im gonna try to rise the compression ratio in my engine, the calculators say is 10.84 right now: 4.060X4.00, 73cc chamber, +5 cc piston, 0 deck, .039 gasket.
It suposse to need 60 cc chamber to get to 12.57, so the question is: how much milling you think is needed? On thousands.
Thanks
 
I got some questions for you?
...1) Are you absolutely sure you want 12.57cr?
...2) You want to cut 13cc out of your iron heads?
...3) How about buying the right pistons?
...4) Whats your idea for the higher compression?
....Back up the bus........You are starting down a slippery road. Ima thinkin its back to the drawing board........
 
To go from a 73cc chamber to a 60 cc chamber you will need about a .078" cut. Have at it.
 
You didn't say what heads you have ( last 3 digits of the casting number).......however rule of thumb for open chamber 340/360 cylinder heads for every .0048inch cut off the face of the head reduces the chamber volume 1cc. For every .010 cut from the chamber face, you will need to cut .0095 off the intake face to maintain correct intake manifold alignment.

Before you cut anything, have the chamber volume of your heads measured so you know where you are starting, so you will know where you will finish.

With the heads off measure where the pistons are at TDC, get a measurement of valve relief volume, figure out what head gasket you are gonna use; it all influences compression ratio. KNOW before you cut anything!!
 
The reason to try to rise the compression is that I have a big cam: mechanical flat tappet 254/[email protected], 640/656 lift, Indy single plane intake, Icon flat top pistons, and the heads are Hughes Bigmouth Edelbrock RPM's, originaly with 65 cc chambers, but with the cnc job they go to 73cc. When i talk with Dave i forget that detail :violent1:
 
what is wrong with 10.84 compression especially with a 4 inch stroke...?
 
Dave from Hughes engines told me that because of the thin air in my town (almost 5000 fts) is better to get some more compression
 
AJ/FormS said:
Better to get a turbo. lol
So how does it perform now, at the current compression? Or have you not run it yet?
Click to expand...

Not run yet. And yes, the next project is a turbo fuel injected, just need to finish with this engine and then try to decide between a la or a hemi Gen lll
 
Have you run the numbers through a Dcr calculator?
You may not want to hear this, or you may already have nixed it; a smaller cam will bring up the DCr as will a fast-rate-of-lift cam.And as a bonus this will fatten up the low rpm tq.

It might be cheaper and easier and more advantageous to switch to a fast-rate roller cam. The later opening intake will pump up the Dcr and require less Scr to get it and more off-the-line snap.
Dave at Hughes knows his stuff, so I imagine you guys have discussed these options?

I hate machining decks,heads and intakes. Here in Manitoba, nobody seems to get it right. So thats why the new piston comment. Then you can fit the pistons to the current chambers to get anything you want, almost.
 
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