6.0 compression bump
6.0 compression bump im new to the ls motors, mustang guy really. im ditchin my mod motor and gonna do an ls swap. hopefully will be looking for an lq4 or an lq9 from the junkyard and was wondering what i could do to bump the compression as i plan on staying na (maybe a little juice). thinner headgaskets obviously, is there a decent price set of heads i could swap with smaller chambers, how much can i mill the heads? lookin for around 450 na.
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From: Frozen Tundra, WI
The LQ4/LQ9 should come with 317 heads. Putting on a set of 243 heads will take you from 71 cc chambers to about 65 cc chambers. This would probably be the cheapest and quickest way to bump compression a significant amount. From what I have read on here...at .030+ mill you start running into problems with intake fit. I will be milling my 317's .015 to .021 which should add around .35 to .5, on the CR.
Last edited by Paul57; Oct 17, 2009 at 11:01 AM.
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From: Frozen Tundra, WI
Id get #243s from an LS6 Vette, which has leightweight hollow stem intake valves and sodium filled exhaust valves. Depending on your budget, Id just go ahead and get a new set of CNC #243s, just make sure you get the lightweight valves, not all #243s have them.
If you get an LQ9 it will have more compression, with its flat top pistons, than the LQ4 (dished pistons).
I had an LQ9 with #799 heads(same as #243, cheaper, but only comes with heavy valves) and it ran really well. Ive since swapped to CNC ported L92/LS3 heads.
I went from 10.9:1 to 10.5:1 with my head swap, but my new heads flow 340-350cfm, so I willing to give up a little compression for a lot of flow, which is WAY more important to me.
If you get an LQ9 it will have more compression, with its flat top pistons, than the LQ4 (dished pistons).
I had an LQ9 with #799 heads(same as #243, cheaper, but only comes with heavy valves) and it ran really well. Ive since swapped to CNC ported L92/LS3 heads.
I went from 10.9:1 to 10.5:1 with my head swap, but my new heads flow 340-350cfm, so I willing to give up a little compression for a lot of flow, which is WAY more important to me.
Last edited by SweetS10V8; Oct 17, 2009 at 11:03 AM.
gotcha, how bout the 241s? i see them going very cheap even with comp valve springs. i could get bigger valves installed on the cheap as my shop does alot of work for the machine shop across the street. i can also do a decent hand porting myself.
and this might be a retarded question but i'm new at ls motors. i will be running a carbureted aluminum manifold (haven't chosen one yet). when i have the heads milled should i have the intake milled as well to compensate?
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From: Frozen Tundra, WI
From the info I have...Stock 241's have the same valves as the 243's (2" & 1.55") but slightly smaller ports (200 vs. 210 int, 70 vs. 75 exh.). Also, the 243's have about a 2 cc smaller combustion chamber.
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ok so it seems i could bolt the 243 on with no work and be in a good spot or purchase a set of 241s and work them a little bit and still be in a good spot. hmmm decisions decisions. how bout the milling the intake thing?
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From: Frozen Tundra, WI
The 241's may provide a little more low RPM torque than the 243's because of the smaller (higher velocity) ports but your upper RPM HP will suffer a bit.
Last edited by Paul57; Oct 17, 2009 at 12:39 PM.
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From: Frozen Tundra, WI
Run the compression numbers in a calculator to be certain...but, from the numbers I've seen on here a .025 mill, on a 317, should get you about the same CR as a 241...which should be around + .6 CR . Don't forget about pushrod length if you're milling this much and I would take a good look at intake fit, just to be sure, with this much mill...but that is just me.
Last edited by Paul57; Oct 17, 2009 at 12:07 PM.
The #241s are cheap for a reason, they are the common everyday head. The #243s and #799s have proven about 20-25hp over #241s. If your going to change, get the better heads.
Ive seen #799 heads go for $200! $243s still have a little bit more of a premium and its hit or miss if you get the good valves or not.
If your going to spin this thing to 7000+ get the light valves. Pushrods are also a very weak point of these engines. Get an aftermarket set, prefeably with a thicker wall. Personally I went with Comps newer .105" wall pushrods instead of the typical aftermarket .080" wall.
Cylinder head flow is key to your engines ability to make power!! You can have all the compression in the world or the greatest cam, but wtihout a set of heads that flow well your going to leaving power on the table because you cant move enough air through the engine. (see sig)
Ive seen #799 heads go for $200! $243s still have a little bit more of a premium and its hit or miss if you get the good valves or not.
If your going to spin this thing to 7000+ get the light valves. Pushrods are also a very weak point of these engines. Get an aftermarket set, prefeably with a thicker wall. Personally I went with Comps newer .105" wall pushrods instead of the typical aftermarket .080" wall.
Cylinder head flow is key to your engines ability to make power!! You can have all the compression in the world or the greatest cam, but wtihout a set of heads that flow well your going to leaving power on the table because you cant move enough air through the engine. (see sig)
believe me i come from the modular 2v world i know flow is the key to power as the heads for those engines blow unless you go to an expensive 4v swap but even then a factory ls head blows that out the water pretty much. the engine will most likely never see over 6500 rpm as this is my street car with a little bit of strip use. i was only considering the 241s factoring in i would port them myself.
If you get a set of 799s go to http://www.rockauto.com they have the sodium filled and hollow intake valves dirt cheap. All gm factory equipment cheaper than any one else. Those valves are considered factory equipment.
