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Milling heads for more compression?

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Old 05-27-2010, 02:17 AM   #1
0TheRadioFlyer97
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Default Milling heads for more compression?

A few guys on LS1 tech have suggested I mill the 243 heads i'm getting about .020" from the deck which should bring compression to 11:1.

a) has anyone tried this?
b) about how much $$$ does this job cost?
c) how does compression affect throttle response? Is is similar to that of a stroked engine?
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Old 05-27-2010, 07:22 AM   #2
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Compression is definitely a plus. What cam are you running? You need to also make sure the shop that does the milling can hit the flatness and surface roughness required for the gaskets you will be running. My compression is 11.3 but I am also running a thinner gasket to help with detonation. There are calculators you can use to figure it out.
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Old 05-27-2010, 07:58 AM   #3
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Quote:
Originally Posted by TheRadioFlyer View Post
A few guys on LS1 tech have suggested I mill the 243 heads i'm getting about .020" from the deck which should bring compression to 11:1.

a) has anyone tried this?
b) about how much $$$ does this job cost?
c) how does compression affect throttle response? Is is similar to that of a stroked engine?
I paid $110 plus tax to have my heads milled. Of course they were already off the engine and I delivered them to the shop.
I replaced my cam during the same tear down, so I cannot say how much of the added power was strictly due to the increased compression ratio.

Last edited by ipuig; 05-27-2010 at 08:01 AM.
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Old 05-27-2010, 08:45 AM   #4
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Quote:
Originally Posted by vettenuts View Post
Compression is definitely a plus. What cam are you running? You need to also make sure the shop that does the milling can hit the flatness and surface roughness required for the gaskets you will be running. My compression is 11.3 but I am also running a thinner gasket to help with detonation. There are calculators you can use to figure it out.
I plan on milling my 243's during my next mod project too. Am I correct in thinking all else being equal, .025 from heads would or should equate to 7.375 pushrods??

Also, Vettenuts, can you explain how running a thinner gasket would help with detonation ??

Sorry to the OP if this looks like a hi-jack.
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Old 05-27-2010, 09:49 AM   #5
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Quote:
Originally Posted by TheRadioFlyer View Post
A few guys on LS1 tech have suggested I mill the 243 heads i'm getting about .020" from the deck which should bring compression to 11:1.

a) has anyone tried this?
b) about how much $$$ does this job cost?
c) how does compression affect throttle response? Is is similar to that of a stroked engine?
As VN mentioned, there is a calculator that will help you figure how much material removed translates into how much compression boost.
The biggest improvement I notice when I bump compression is the throttle response. BIG difference!
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Old 05-27-2010, 11:06 AM   #6
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Quote:
Originally Posted by vettenuts View Post
Compression is definitely a plus. What cam are you running? You need to also make sure the shop that does the milling can hit the flatness and surface roughness required for the gaskets you will be running. My compression is 11.3 but I am also running a thinner gasket to help with detonation. There are calculators you can use to figure it out.
The Good news is that i'm stillin project planning/parts purchasing. I'm picking up the 243 heads tomorrow.

so far this is the cam i'm shooting for: 221/226 .565/.560 114
http://sdparts.com/details/scoggin-d...-center/sd0067
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Old 05-27-2010, 05:42 PM   #7
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I recommend calling TEA, and explain your setup/goals, and see how much they'd charge to do your 243s. I think you'd be happier with the results of a integrated design, than just milling the heads to bump CR. About the thinner gaskets to help reduce detonation..... thinner gaskets reduce "quench"; the gap remaining at the top of the cylinder/head interface can produce hot spots, which can induce detonation. It's not a problem unless your pushing the limits of timing/gas quality/CR. I went to 10.95 CR, with 8.55 DCR, and with the factory MLS gaskets, which I believe are about .055 compressed, got absolutely no knock retard with 92 octane gas. I don't know my timing numbers, though.
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Old 05-27-2010, 06:20 PM   #8
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I'm interested in this too. What gains can you expect from just milling the heads and a retune?
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Old 05-27-2010, 06:34 PM   #9
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The experts would tell you to check valve to piston clearance.
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Old 05-27-2010, 06:51 PM   #10
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The experts would tell you to check valve to piston clearance.
He'll be fine with the 221/226 cam he's running.
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Old 05-27-2010, 07:16 PM   #11
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Originally Posted by ctusser View Post
He'll be fine with the 221/226 cam he's running.
Well i plan to run 1.8 rockers with this cam:
221/226 .565/.560 114


I'm repalcing both lifters and pushrods as well so I can get custom lengths if requried.
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Old 05-27-2010, 09:02 PM   #12
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Quote:
Originally Posted by TheRadioFlyer View Post
Well i plan to run 1.8 rockers with this cam:
221/226 .565/.560 114


I'm repalcing both lifters and pushrods as well so I can get custom lengths if requried.
Its the duration and lsa more than the lift. By the time full lift is achieved the piston is inches down.
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Old 05-27-2010, 11:59 PM   #13
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Quote:
Originally Posted by ctusser View Post
Its the duration and lsa more than the lift. By the time full lift is achieved the piston is inches down.
Are you saying my setup should clear? I'm not familier with the total valve lift formula.
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Old 05-28-2010, 12:19 AM   #14
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Quote:
Originally Posted by TheRadioFlyer View Post
Are you saying my setup should clear? I'm not familier with the total valve lift formula.
It's not the total lift that gives you problems with piston to valve contact, because when the valve is all the way open the piston is near the bottom of its stroke and at the bottom of the cylinder. The large duration cams which keep the valves open longer when the piston is comming up is what causes the PTV issues. That is a small cam and you wont have problems with contact even if milling .020 to bump compression.
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Old 05-28-2010, 12:23 AM   #15
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Quote:
Originally Posted by ctusser View Post
It's not the total lift that gives you problems with piston to valve contact, because when the valve is all the way open the piston is near the bottom of its stroke and at the bottom of the cylinder. The large duration cams which keep the valves open longer when the piston is comming up is what causes the PTV issues. That is a small cam and you wont have problems with contact even if milling .020 to bump compression.
schweet
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Old 05-28-2010, 02:34 PM   #16
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Quote:
Originally Posted by TheRadioFlyer View Post
Well i plan to run 1.8 rockers with this cam:
221/226 .565/.560 114


I'm repalcing both lifters and pushrods as well so I can get custom lengths if requried.
with 1.8 rockers that will put the lift over .600, however that is dead bottom center.
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Old 05-28-2010, 03:14 PM   #17
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Quote:
Originally Posted by TheRadioFlyer View Post
Well i plan to run 1.8 rockers with this cam:
221/226 .565/.560 114


I'm repalcing both lifters and pushrods as well so I can get custom lengths if requried.
Make sure you talk to the cam manufacturer to make sure you can run 1.8s with their cam. Some will tell you not to
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Old 05-28-2010, 04:53 PM   #18
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On suggestion from my mechanic, i will not be milling my heads. My block has 130K miles on it and I'd prefer not to overstress it much. I think 10.5 compression will be just fine.
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