LS3 head milling...
10-30-2009, 04:24 PM
#1
LS3 head milling... I recently got a set of stock LS3 heads. I am going to have them cleaned up and have them milled to ensure flatness. I was wondering what should I have them by to bump up the compression a little while still running on 91 octane (all you can get regularly in CA) and without running into PTV clearance issues? I was thinking 10.5-11.5:1 would be fine...it's not going to be an all out drag car (~460rwhp), and I still want it to be safe.
I will be using stock valves and a 223/231 .610"/.617" 113+4 cam.
I have three options for the bottom end:
1) stock LQ4 shortblock (with stock dished pistons)
2) stock LQ9 short block
3) stock LS2 short block
What would you mill the heads down to in each of these situations?
Help is greatly appreciated, thanks.
I will be using stock valves and a 223/231 .610"/.617" 113+4 cam.
I have three options for the bottom end:
1) stock LQ4 shortblock (with stock dished pistons)
2) stock LQ9 short block
3) stock LS2 short block
What would you mill the heads down to in each of these situations?
Help is greatly appreciated, thanks.
10-30-2009, 04:40 PM
#2
when milling heads, always assume you will have ptv clearance issues and go ahead and cut in relievs while the heads are off. the scr will be diff. for each of these engines given the same milled head is used and also gasket used.
they will all also vary slightly on the + piston out of the bore. so gotta take that into account also. the valve relieves will affect SCR but will offer clearance and peace of mind.
as long as you dont cut any more than .030 off the oe heads, it will be alright. any more may cause heads to intake alignment issues.
they will all also vary slightly on the + piston out of the bore. so gotta take that into account also. the valve relieves will affect SCR but will offer clearance and peace of mind.
as long as you dont cut any more than .030 off the oe heads, it will be alright. any more may cause heads to intake alignment issues.
10-30-2009, 05:12 PM
#4
That's why I asked. I figured with the LS2/LQ9 I would bolt them up as-is with the stock MLS .054" gaskets. With the LQ4 I was thinking I'd get them milled .025". I don't want to flycut if I don't have to. I guess anything over 10.0:1 CR I'd be fine with.
10-30-2009, 05:23 PM
#5
Stock GM gaskets are .052 compressed thickness. I have mine milled .030 with the dished pistons. I had a 222/238 came with the heads milled and .045 head gasket, no clearance issues and it was about 10.8:1 CR.
I swapped cams to a little bigger and just put a stock 6.2L head gasket on and it is only down to 10.6 so no real difference.
I swapped cams to a little bigger and just put a stock 6.2L head gasket on and it is only down to 10.6 so no real difference.
10-30-2009, 06:25 PM
#6
I have an LQ9 with L92 heads, I milled them .030 and the biggest intake lobe I could fit was 219 @ .050(stock head gasket). I first tried a 223/231 cam and only had .045 PTV clearance. But there are many variables in everyone situation.
I dont think the LQ4s dished pistons will give you any more PTV with their valve reliefs. They are for 2.00" valves and your valve is now a 2.160"
I dont think the LQ4s dished pistons will give you any more PTV with their valve reliefs. They are for 2.00" valves and your valve is now a 2.160"
10-30-2009, 06:31 PM
#7
the relieves will serve as insurance for future revision. if decide to go with bigger cam, if you do they will offer added clearance and will not have to remove head again to cut them in. might as well take advantage of the compression and cam selection now, that everything is apart.
