Question about block/head milling for streetable upgrade

[BTF/PTM]

Hi Everyone,

Been quite a while since my last post, hope everything is good. I have a question for the L-engine builders here, related to raising compression in a street L-engine to 10:1. I've read that, with flat-tops, roughly .080'' must be milled off the head. Here's my question:

Can anyone offer advice on whether it's better to mill that amount off both the block and head, or either the block or the head? My curiosity is in regard to excessive milling possibly (negatively) changing combustion chamber dynamics. Anyone have experience with this? Is there a best practice that should be...well...practiced? And I suppose a fair addendum could be, is the best solution to simply use pistons that raise the compression instead of milling?

Thanks all =)

[240260280z]

head only

[Diseazd]

Seek out a professional familiar with the process to build the head. There is so much more to it than just shaving .080 inches......there are shims, different valves and with a different cam, rocker geometry problems as well as spring heights.

[madkaw]

Which head??

[LeonV]

Keep in mind that shaving the block changes piston deck height...

[BTF/PTM]

Thanks guys, your replies are exactly why I wanted to ask.

As I understand it, in reference to deck and cam height, removing - for example - .040 from a block deck and .040 from a head surface would still warrant, in the case of an L-engine, using 0.080'' shims under the cam tower to retain crank/cam timing geometry. These numbers are simply examples in the interest of simple math. If this idea is not correct, please by all means correct me.

If this is correct, then it's why I'm curious about whether there's a limit of how much can be taken off the head before the combustion chamber shape becomes negatively affected. If material can be taken off the block in order to retain good CC dynamics, it makes sense to do it that way. That's what I was asking.

Again, please correct if I'm wrong.

Edited October 11, 2013 by BTF/PTM

[LeonV]

Thanks guys, your replies are exactly why I wanted to ask.

As I understand it, in reference to deck and cam height, removing - for example - .040 from a block deck and .040 from a head surface would still warrant, in the case of an L-engine, using 0.080'' shims under the cam tower to retain crank/cam timing geometry. These numbers are simply examples in the interest of simple math. If this idea is not correct, please by all means correct me.

If this is correct, then it's why I'm curious about whether there's a limit of how much can be taken off the head before the combustion chamber shape becomes negatively affected. If material can be taken off the block in order to retain good CC dynamics, it makes sense to do it that way. That's what I was asking.

Again, please correct if I'm wrong.

I don't understand what you mean by the "combustion chamber shape (being) negatively affected". Could you elaborate?

[jfa.series1]

Not having personal experience in this, it seems you will also want to pay attention to valve-piston clearances. Regular flat-top pistons are not dished for valve clearance.

[Zed Head]

Milling the block to raise CR would be essentially the same as installing pistons with a longer piston pin compression height (pushing the piston up above the deck). Much easier than milling the steel block. Maybe cheaper (I'm not familiar with machining or piston costs). Plus the fact that milling the block will change the relationship of the piston's top ring to the deck, which is important.

[BTF/PTM]

Thanks again, the feedback is great!

As for elaborating, an example of negatively changing a combustion chamber would be milling a head down so far that a quench zone is cut away or maybe a flow restriction around a valve opening is created. Like my example of the deck height/cam height math above, these ideas are not known factors, this is all conceptual. I am not a machinist or an engine builder, which is why I'm hoping to combine the tech stuff that I've read about with real-world experience that hopefully other folks have.

[LeonV]

As for elaborating, an example of negatively changing a combustion chamber would be milling a head down so far that a quench zone is cut away or maybe a flow restriction around a valve opening is created.

Both of these scenarios are impossible when milling the head deck. In fact, the opposite would be true in both cases.