Rochesterw

I am in the beginning stage of building my LQ4 its in an 01 2500hd. I have been looking around and originally wanted L92s but decided against it because of the extra $$ needed. I plan putting new rings in maybe pistons, mild cam, and possibly new heads. I have a budget of $2000 and I would like to do this right so I have a reliable motor. It will be DD for short trips I have an s10 for long drives.

Now my real question, I can get a set of 243s for ~$400 will it be worth the extra money to buy them with the limited build that I am doing? I run 93 octane already so I would like to mill the heads for a higher cr, around 11:1, and maybe some port work. So what are my pros and cons here?

1slowz71

iTrader: (6)

go 243's the floe better and they'll rise the CR! witch means more power! although you can mill the 317's if you want more CR you can mill the 243's to an even smaller cc !IMO! I BELIVE MY LQ4 ON 853'S ON 60CC is at about 10.89:1 in order to get to 11.0:1 you will have to go in to about 58cc or 57cc so IMO drop the 317's and try to get some 243's ! i belive you can safelly mill a head about .050 with no clearence issues! and if you make the math every .006 milled=1cc so make the math! this is what i was told from the fellows at wcch!

Rochesterw

Ok, that is kinda the direction I was leaning. Now at 11:1 will that be ok w/ 93 octane? Now on the piston issue should I stick with the dished or go to flat tops? Any recommendations?

1slowz71

iTrader: (6)

id say if your going to go dished get 243's if your going flat then stay with ur 317's ! the out come will be the same deppending on ur cc's! i was told i should be ok up to 11.1;1 on 91 so i am think if your going 93 then u should be fine ! but iam no expert ! this is just whatb ive learn through my build! but you can use the 243's on flat top pistons and you probably have perty high cr i just dont know how high!

Rochesterw

Thanks a lot. Anyone else know what my compression ratio would be with flat tops and 243s and if it would be safe on pump gas.

zero2sixT

iTrader: (4)

317s and 243s flow the same. I would find some used ported heads, or run what you have. You'd swap 317s for 243s b/c they have a smaller combustion chamber. Which gives you the bump in compression.

I'd run 11.1 CR on 93 all day long, every day.

How many miles does your LQ4 have? $1k more would get you in the price range of a used radix. Which will outperform a mild h/c 6.0 (which is pretty much what you're building), hands down.

1Bear

iTrader: (1)

An iron LQ4 6.0L fitted with 243 heads and flat-tops will be essentially the same thing as the aluminum LS2, which also uses the "243" casting heads. The compression of the LS2 is 10.9:1. A LQ9 fitted with stock cc 243 heads would be the same.

1slowz71

iTrader: (6)

Stock 6.0 Heads
Chamber 71.0 cc 0.100 0.200 0.300 0.400 0.500 0.550 0.600
Intake ??? 66 142 196 228 236 238 240
Exhaust ??? 59 104 137 155 167 173 177
Valve Diameter Intake 2.00 exhaust 1.55

Stock LS6 Heads
Chamber 64.45 cc 0.100 0.200 0.300 0.400 0.500 0.550 0.600
Intake 210 cc 62 126 184 224 251 256 257
Exhaust 75 cc 57 108 143 163 176 180 183
Valve Diameter Intake 2.00"
Valve Diameter Exhaust 1.55"
Part Number 12564243 (2001 +)
LS6 valves are 0.6mm or 0.023622" longer, hollow stem intake, and hollow stem sodium filled exhaust valves.




the diffrence between 317's and 243's

Bumpers

iTrader: (10)

Good info

zero2sixT

iTrader: (4)

you pick up an about 20 rwhp by swapping to stock 243s. I don't know your source, but if what you have is correct, not that big of a difference for the work.

I stand by what I said, I would stick with the 317s unless I had a cnc/hand ported set to replace them with. And about going FI over camming a 3/4 ton 6.0 with a stock converter 4l80e behind it. Just me tho.