317 heads questions...
Thread Starter
Joined: Jun 2008
Posts: 370
Likes: 0
From: Edinburg, Texas
317 heads questions... Ok well my question is how can I get my 317 heads to flow more like the LS6 heads... I have heard bout "milled down" but I am not sure what to do cause of my mods.
Engine Mods:
2005 LQ9 6.0
317 Heads
GM Hot Cam
LS6 Springs
Monster MotorSports Tune
LS6 Intake
LongTube Headers
And once off I will probably get them ported. How much do they need to get milled
Engine Mods:
2005 LQ9 6.0
317 Heads
GM Hot Cam
LS6 Springs
Monster MotorSports Tune
LS6 Intake
LongTube Headers
And once off I will probably get them ported. How much do they need to get milled
the 317 heads are very similar to the LS6 243 heads....only difference is the combustion chamber volume between the two. The 317s have a larger volume = lower compression ratio.
When people say to mill down the 317s, they just mean to have a machine shop shave/mill down the surface of the heads(combustion chamber) to decrease the volume of the combustion chamber = bump up compression ratio...
But if your engine is an LQ9, it already has a better compression ratio (because of the flat top pistons, the LQ4 had a slight dish piston which resulted in a 9.4:1 compression ratio for the LQ4, versus about 10:1 for the LQ9), so I wouldnt fuss with the heads...
When people say to mill down the 317s, they just mean to have a machine shop shave/mill down the surface of the heads(combustion chamber) to decrease the volume of the combustion chamber = bump up compression ratio...
But if your engine is an LQ9, it already has a better compression ratio (because of the flat top pistons, the LQ4 had a slight dish piston which resulted in a 9.4:1 compression ratio for the LQ4, versus about 10:1 for the LQ9), so I wouldnt fuss with the heads...
Thread Starter
Joined: Jun 2008
Posts: 370
Likes: 0
From: Edinburg, Texas
the 317 heads are very similar to the LS6 243 heads....only difference is the combustion chamber volume between the two. The 317s have a larger volume = lower compression ratio.
When people say to mill down the 317s, they just mean to have a machine shop shave/mill down the surface of the heads(combustion chamber) to decrease the volume of the combustion chamber = bump up compression ratio...
But if your engine is an LQ9, it already has a better compression ratio (because of the flat top pistons, the LQ4 had a slight dish piston which resulted in a 9.4:1 compression ratio for the LQ4, versus about 10:1 for the LQ9), so I wouldnt fuss with the heads...
When people say to mill down the 317s, they just mean to have a machine shop shave/mill down the surface of the heads(combustion chamber) to decrease the volume of the combustion chamber = bump up compression ratio...
But if your engine is an LQ9, it already has a better compression ratio (because of the flat top pistons, the LQ4 had a slight dish piston which resulted in a 9.4:1 compression ratio for the LQ4, versus about 10:1 for the LQ9), so I wouldnt fuss with the heads...
317 basically have the same intake and exhaust port as 243 heads
but with 71cc chamber, 243 has 65cc chamber
a good amount to mill is .035 = 10.15:1 scr from 9.4:11 stock
.040= 10.25:1
i personally do not like to remove anymore than .040 max on any ls head
my bad, this would be assuming the engine is a LQ4
I thought yours was LQ4,
for LQ9 stock SCR is 10:1
amount to mill equals
.021=10.5:1
.031= 10.75:1
.040= 11.0:1
but with 71cc chamber, 243 has 65cc chamber
a good amount to mill is .035 = 10.15:1 scr from 9.4:11 stock
.040= 10.25:1
i personally do not like to remove anymore than .040 max on any ls head
my bad, this would be assuming the engine is a LQ4
I thought yours was LQ4,
for LQ9 stock SCR is 10:1
amount to mill equals
.021=10.5:1
.031= 10.75:1
.040= 11.0:1
Last edited by NemeSS; Nov 6, 2008 at 12:56 PM.
