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I have searched all over and have seen number that are all over the board

i am trying to get 10.5:1 out of my lq4

stock lq4 bottom end
243 heads milled .005
WHAT WILL MY COMPRESSION RATIO BE WITH STOCK GASKET AND .040 COMETIC GASKET?

other main question is will i have piston to valve issues

2007 chevy silverado classic 2500 hd
parts list include
220r .600 112 LSA TSP cam
ls2 timing chain
PAC 1218 springs
NNBS intake and throttle body
melling oil pump
TSP push rods
ls7 lifters

 

Lq4 has dished pistons, my calculations with either 799 or 243 heads unmilled should net you right at 10.5:1 compression since their combustion chambers are roughly 64cc, compared to the stock 71cc 317 heads have. If they're milled .005", you are loosing not quite 1 cc more, bumping compession even higher.

I don't have an exact answer but from what I've gathered (I'm literally doing the same build), you'll be right at 10.4-10.6:1 compression with a stock thickness gasket.

Also, the PAC 1218 springs are good to .600" lift, I'd find another spring rated higher, so you're not constantly running that spring to its maximum with that cam. I'm running PAC1219 springs, good for .625" of lift.

 

I am clearing a much larger cam with LS6 heads and 30 thou milled off them.

You should not have any issues with PTV unless you degree the cam. The TSP 220r has the advance already ground into it, so just install it dot to dot. The PAC 1218 springs are fine. They dont go into coil bind at .600 lift.

For a mild build I would run the following:
GM MLS 6.0/6.2 (12610046)
LS7 lifters are fine, but get new trays
Melling will be fine, just get the high pressure... NOT the high volume.
Personally I would recommend a pushrod length checker, however; the 7.400s will most likely be just fine

-Avery