Few ?'s about milling, compression, & pushrod lengths
Few ?'s about milling, compression, & pushrod lengths 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
With 11:1, would a 7.3 pushrod be sufficient? Or would I need a shorter length? TIA
Josh
Re: Few ?'s about milling, compression, & pushrod lengths 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.
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Joined: Jan 2002
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From: Texas
Re: Few ?'s about milling, compression, & pushrod lengths 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
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
Re: Few ?'s about milling, compression, & pushrod lengths 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>
[ January 30, 2002: Message edited by: Damian ]</p>
TECH Apprentice
Joined: Jan 2002
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From: Texas
Re: Few ?'s about milling, compression, & pushrod lengths 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
Todd
Re: Few ?'s about milling, compression, & pushrod lengths <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]" />
Re: Few ?'s about milling, compression, & pushrod lengths 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>
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>
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Re: Few ?'s about milling, compression, & pushrod lengths 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?
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?
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Re: Few ?'s about milling, compression, & pushrod lengths 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..
