Damian

iTrader: (89)

Lets say I wanted to mill an LS1 head to acheive 11:1 compression. How much would need to be hacked off? .060?

With 11:1, would a 7.3 pushrod be sufficient? Or would I need a shorter length? TIA


Josh

Jantzer98SS

iTrader: (54)

I believe .030 mill achieves 10.6:1 You need to remember that you can only mill the deck so much before you run into problems. And I've heard of as much as .035. Anything beyond that point and you have to worry about manifold alignment and valvetrain geometry etc. That's why so many people go with the truck heads.

WhiteDiamond

Is it better to offset a .030 mill with shorter pushrods or by shimming the rockers? At what point does shimming the rocker actually get it far enough out of geometry that you have problems?

What compresson ratio can you get with the truck heads with .xxx mill?

Sorry for the questions, just good research for an upcoming project.

Todd

Damian

iTrader: (89)

Well someone explain how people are getting 11:1 comp on a stock shortblock LS1. There are guys running as much as 11.5:1, how is this possible if milling over .030 is to much?

[ January 30, 2002: Message edited by: Damian ]</p>

WhiteDiamond

The information I have says that more than .030" of milling on the heads starts to get you into trouble. I have heard of a few guys going .035" and that might get them close to 11.0:1 compression. The normal .030" mill gets you ~10.8:1 compression. I think anyone going higher that this is most likely using the truck heads(5.3L). The LS6 head also has a smaller chamber, but I have no info on what compression ratios you get with such and such mill on those heads.

Todd

Ron@Vengeance

iTrader: (51)

<img src="gr_grin.gif" border="0"> <img src="images/icons/confused.gif" border="0"> <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" /> <img src="graemlins/gr_hail.gif" border="0" alt="[hail]" />

wizkid

iTrader: (3)

Here is a guess:

The aftermarket cams have a 0.030" smaller diameter (I beleive it is diameter and not radius) base circle. So, maybe the heads are milled 0.030" for that reason.

It seems that most people run stock pushrod lengths with that setup. Maybe that is why so they didn't have to figure out an acceptable pushrod length from factory spec's.

Eric

<small>[ March 15, 2002, 02:10 PM: Message edited by: wizkid ]</small>

Reckless

iTrader: (9)

We discussed this at length last week if you search for my post regarding CR.

The concensus was this (all empirical of course):

-Each .005 milled = 1cc loss to chambers
-Max mill for stock head is .050 (just had mine done)
-1cc loss = .13 increase in CR
-.050 mill = 10cc loss to chamber = 1.3 increase in CR

I have 12cc dished pistons, so this would bring me back to 10.0:1 CR with a zero deck height. A good sight to use for calculations is: http://www.prestage.com/carmath/

Using the following fifures in the calculator, you net an 11.5:1 CR:

Stock Bore = 3.9
Stock Stroke = 3.662
Stock Deck height = -.006
Stock gaskets = .054
Combustion chamber with .050 mill (or unmilled 5.3 truck head) = 57cc
Valve Relief = 2cc (I use this because it nets a 10.1:1 CR in the calculator)

Any other ideas?

CHRISPY

Great info Todd! <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Thanks,
Chris

VINCE

iTrader: (1)

I am going to give my 2 cents.. The more you mill you decrease your options in cams. Unless you have pistons with valve reliefs or fly cuts. I did not think about this when I had my 5.3L truck heads milled 42 thousandths.. Now a cam change would cost me more secondary to having to clay it and possible fly cutting.. Yes it might be worth it, but you are looking at over 1k just for a cam change and that is if you have the right pushrod lengths and the right springs..

Damian

iTrader: (89)

Sweet! I posted this like 3 months ago! LOL....