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Hey guys, ive googled and searched but only came out with old threads and unanswered questions. I have a 2000 LQ4 with iron heads in my Sierra. Im wanting more compression as i run dirt drags and run E85 in my truck so octane wont be a problem with the rise in compression. A little about my setup; 2004 Sierra RCSB 4x4, lq4/4l80e, TBSS intake manifold, 87mm tb, 214/224 on a 115LSA, .625 springs, pushrods, stock manis, with y pipe and no cats, exhaust is a 4" magnaflow with the y pipe cut at the merge for a uncorked exhaust, 36lb injectors, Walbro 450 e85 pump, my truck runs really good right now but i want more power and i have some LM7 heads laying around. My questions are, has anyone ever done this and did they feel a difference? Will it feel the same if i dont install a bigger intake valve? Ive heard it feel slower since the valve is smaller. But i honestly think the bump in compression will help more.
rear fender flares are being painted.
Last edited by Venomous281; 01-05-2018 at 11:43 AM.
i know they are, but im asking about 706/862's. The main reason i want LM7's is so when i pop the hood they see 706/862 and they continue thinking its stock. If i put a set of 799/243's ill get bumped to the modified class. My buddies run the modified class and are way faster than me.
Basically what i was asking if i will feel a loss in power if i dont install 2" valves. sorry if i made it hard to understand
What are the rules for this class ? You can run oversized valves , you can port them I take it . Yes you having a 4" bore you would benefit from the 2" but you need to do chamber work .
The compression increase, specially if you mill them .030" (and I would) will more than offset the minor flow lacking from the 1.89" intake valve. Personally I would have a local shop do a valve job for the 2" valve and some minor bowl blending, but if you're on the "cheap"; mill, lap the current valves, and install
That cam will LOVE the compression hike
What are the rules for this class ? You can run oversized valves , you can port them I take it . Yes you having a 4" bore you would benefit from the 2" but you need to do chamber work .
Class rules for stock class are; no headers, exhaust ok, cold air intake, tune. All other mods will throw you in modified. But my cam isnt noticeable, and the intake manifold hides under the stock intkae cover.
The compression increase, specially if you mill them .030" (and I would) will more than offset the minor flow lacking from the 1.89" intake valve. Personally I would have a local shop do a valve job for the 2" valve and some minor bowl blending, but if you're on the "cheap"; mill, lap the current valves, and install
That cam will LOVE the compression hike
I really want to do a set of 2" valves and have them milled but the guy that does my head work is booked for a while. So I'm thinking they're going to go on with the small valved and unmilled.
I really want to do a set of 2" valves and have them milled but the guy that does my head work is booked for a while. So I'm thinking they're going to go on with the small valved and unmilled.
Well the LS2 head gaskets are quite cheap but at .051" they are thicker than needed
You can cheat a tad by running .040" Cometic gaskets which are more expensive but about the same as paying a local shop to mill.
Well the LS2 head gaskets are quite cheap but at .051" they are thicker than needed
You can cheat a tad by running .040" Cometic gaskets which are more expensive but about the same as paying a local shop to mill.
I think i have one ls2 gasket in my toolbox. i need to check what i have. Some cometic .040's would be nice though. But i think ill do cometics when i get a nicer set of heads.
I think i have one ls2 gasket in my toolbox. i need to check what i have. Some cometic .040's would be nice though. But i think ill do cometics when i get a nicer set of heads.
Compression will be 11.36:1 with the factory LS2 gaskets and the 61.5cc heads
Otherwise 11.70:1 is possible with the Cometics
Both of these will work great and love the E85 plus since manifold vacuum will increase, that cam will sound even smoother
Also wonder if LS7 manifolds would fit or even C5 Tri-Ys from 01-04 are better flowing than the log stuff....those are meant to be mounted backwards and running into one of those spinning muffler thingys....
Also wonder if LS7 manifolds would fit or even C5 Tri-Ys from 01-04 are better flowing than the log stuff....those are meant to be mounted backwards and running into one of those spinning muffler thingys....
I was going to turbo it, but i'm looking for another truck that isn't so nice to turbo again. Thanks for your input, i appreciate it.
Compression will be 11.36:1 with the factory LS2 gaskets and the 61.5cc heads
Otherwise 11.70:1 is possible with the Cometics
Both of these will work great and love the E85 plus since manifold vacuum will increase, that cam will sound even smoother
Correct me if I'm wrong but an lq4 with 59 cc heads and .051 gaskets should be around 10.7 :1. Where is that 11 side coming From?
I finally got around to swapping the heads. I still havent gotten it retuned but i plan on it this week. But i just got some livernois motorsports stage 3 243's and a 235/244 cam ill be swapping in once i get a stall converter next month.
01-05-2018, 10:36 AM
LQ4 with LM7 cylinder heads 
