Milling 317 heads
07-27-2010, 09:46 PM
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Milling 317 heads
How much can I get away with with my cam and stock LQ4 shortblock. I pulled the heads to check everything out and the bores looks beautiful with the cross hatches still there. Cam is 585 lift. I am thinking I should be safe with PTV clearance with 20 off the heads? I know somebody said i can go 30 saftly but I dont know how that would be with the cam and a 54 gasket. Thoughts? Everybody says "go for the 243's" which is true but I'm on a budget and if it costs me 15HP staying with the 317's I'm not too worried. For 50 bucks to mill the heads it beats a couple hundred for used heads. I'll add more bolt-ons if need be.
07-27-2010, 09:53 PM
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Re: Milling 317 heads
Lift really doesn't matter, duration and lsa do. Personally i'd call whoever you got your cam from and talk to them.
07-28-2010, 08:07 PM
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07-28-2010, 09:31 PM
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Re: Milling 317 heads
sweet now flycut those pistons while the heads are off and mill the 243s about .040 and run a .040 head gasket and bam, you'd be 11.1:1
07-28-2010, 10:21 PM
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Re: Milling 317 heads
ALL stock LSx engines have the pistons at least 0.008" above the deck, so consider a 0.045" gasket to be the absolute minimum.
Any LSx head, stock or aftermarket, can safely be milled 0.040", but since you might someday do a rebuild, best to stop at 0.030" the first time, to leave 0.010" for the future rebuild.
Taking 0.030" of ANY LSx head is around 5 cc, which is about half a ratio of static compression, such as going from 10.2:1 to 10.7:1. On a 4.8L, it's a little less of a change, on a 400+ cube stroker, it's a little more.
Any LSx head, stock or aftermarket, can safely be milled 0.040", but since you might someday do a rebuild, best to stop at 0.030" the first time, to leave 0.010" for the future rebuild.
Taking 0.030" of ANY LSx head is around 5 cc, which is about half a ratio of static compression, such as going from 10.2:1 to 10.7:1. On a 4.8L, it's a little less of a change, on a 400+ cube stroker, it's a little more.
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07-28-2010, 11:45 PM
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Re: Milling 317 heads
Hey Zones, Have you run into any ptv issues with the trex? Or did you cut the stock pistons? I really don't want to cut them as i'm running some spray, although the max i;ll do is 200
07-29-2010, 07:59 AM
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Re: Milling 317 heads
Being as mine was a LQ4 with the dish pistons i had no issues, i had about .11 clearance if i remember correctly. 317s being a larger chamber helped out as well, i just hope when i go to a set of ported 243s that i will not have any issues, think i will be fine then too.
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