LM7 head upgrade

[Yukonjoe2001]

Im looking at making my cammed lm7 breathe better, but my brain hurts trying to understand cylinder head politics.. Can some one please explain, why i can run 5.7 243 heads on an lm7 hassle free..or machine my 862s to fit a 2 inch intake valve.. Yet, according to summit..these heads pictured wont work. I want these aftermarket heads, because they are cheap, have 202 intake valves, and have smaller cc combustion chambers.. I feel running 64cc chambers with 2 inch valves will hurt compression.

 

[Chrisw_2003]

https://www.motortrend.com/how-to/1712-surprising-hp-numbers-from-our-stock-ls-cylinder-head-test/ Also check out https://www.youtube.com/@richardholdener1727 he probably has everything you want to know on how to make a 5.3 a monster in his videos. Same guy who wrote the article on the ls heads

 

[Mudsport96]

706/862 heads will make 500+ hp NA.
What cam are you running?

 

[Mudsport96]

Remembered your other thread. BTR 3 cam. Just use the heads that are on the engine. Every other heads is going to trade a decent amount of torque for a minimal gain in hp where you will rarely use it. And in the end your rig will be slower because it weighs so much that the few extra ponies that you get are offset by the minimum 15 lbft you lost.
Even the 799/243 heads on the aluminum 5.3 in the Silverado lose 12lb ft of torque over the 706/862 casting in a back to back test.
Here is a dyno graph from Richard holdener. Engine is a 6.0 with the comp 54-459-11. That cam is BIGGER than the BTR stage 4 TURBO cam, and in cam terms vastly larger than your BTR 3 truck cam.

The 799 casting is the same as the 243 without the lighter valves for the Corvette.
If I get time later I may see if I can find a graph from the truck cam line. But I think this should point you in the correct direction.

 

[Marky Dissod]

243 — '04-up LS6 / LS2 aluminum center bolt 5.7L; also some '05-up trucks: 64.45cc
799 — '05-up 4.8L / 5.3L truck heads; basically, 243 heads (L33): 64.45cc

706 / 852 / 862 — '99-up 4.8L / 5.3L truck heads: 61.15cc

The above is correct, so far as I can tell.
Those are the heads most of us are better off using.
If the combustion chambers are OVER 65cc, the compression LOSS effectively costs torque production under 3000RpM, which costs MpGs.

The vast majority of our engines spend the vast majority of their run time UNDER 3000RpM.
Choose heads and cam and roller rockers and valvesprings with that understanding.

The above makes even more sense given that most of us are using insufficient axle gears:
Those with 4L60Es should use either 4.10 or 4.30.
Anything less wastes power (and city MpGs!)

Those with 6L80Es should use either 3.42 or 3.73.
Anything less wastes power (and city MpGs!)

Keep in mind that many of us drive on taller tires that weaken the effective axle gear ratio.

 

[Yukonjoe2001]

Remembered your other thread. BTR 3 cam. Just use the heads that are on the engine. Every other heads is going to trade a decent amount of torque for a minimal gain in hp where you will rarely use it. And in the end your rig will be slower because it weighs so much that the few extra ponies that you get are offset by the minimum 15 lbft you lost.
Even the 799/243 heads on the aluminum 5.3 in the Silverado lose 12lb ft of torque over the 706/862 casting in a back to back test.
Here is a dyno graph from Richard holdener. Engine is a 6.0 with the comp 54-459-11. That cam is BIGGER than the BTR stage 4 TURBO cam, and in cam terms vastly larger than your BTR 3 truck cam.
View attachment 417718
The 799 casting is the same as the 243 without the lighter valves for the Corvette.
If I get time later I may see if I can find a graph from the truck cam line. But I think this should point you in the correct direction.

Sorry late, but i went 243 heads.. But 6.0. Project under construction..lol

 

[5x10]

Remembered your other thread. BTR 3 cam. Just use the heads that are on the engine. Every other heads is going to trade a decent amount of torque for a minimal gain in hp where you will rarely use it. And in the end your rig will be slower because it weighs so much that the few extra ponies that you get are offset by the minimum 15 lbft you lost.
Even the 799/243 heads on the aluminum 5.3 in the Silverado lose 12lb ft of torque over the 706/862 casting in a back to back test.
Here is a dyno graph from Richard holdener. Engine is a 6.0 with the comp 54-459-11. That cam is BIGGER than the BTR stage 4 TURBO cam, and in cam terms vastly larger than your BTR 3 truck cam.
View attachment 417718
The 799 casting is the same as the 243 without the lighter valves for the Corvette.
If I get time later I may see if I can find a graph from the truck cam line. But I think this should point you in the correct direction.

I’ve been watching his videos and saw where he said the stock heads are fine

so if I am wanting some easy adds to hp on my stock lq9, it’s cam, springs, and headers/exhaust?

thanks for help, new to this
just want some more power at a reasonable cost
my Escalade feels like a bus, mainly looking for low speed power and tourque gains and it’s mostly stop and go

 

[Mudsport96]

I’ve been watching his videos and saw where he said the stock heads are fine

so if I am wanting some easy adds to hp on my stock lq9, it’s cam, springs, and headers/exhaust?

thanks for help, new to this
just want some more power at a reasonable cost
my Escalade feels like a bus, mainly looking for low speed power and tourque gains and it’s mostly stop and go

Biggest bang for the buck will ALMOST always be better gears. What gear ratio does your Escalade currently have in the differential?

 

[5x10]

Biggest bang for the buck will ALMOST always be better gears. What gear ratio does your Escalade currently have in the differential?

It’s stock as far as I know, I just looked it up and

First:
3.06

Second:
1.63

Third:
1.00

Fourth:
0.70

Reverse:
2.29

Final drive ratio:
3.73

 

[Marky Dissod]

OE heads, as in OE LQ9 heads?
I'd use the OE heads from any 4.8L or 5.3L engine on an LQ9, without blinking.

12559862 / 12561706 heads came on '99-up 4.8L / 5.3L heads:
61.15cc combustion chambers, 200cc holy intake runners, 70cc oval exhaust runners, 1.890" intake valves, 1.550" exhaust valves

OR

12564243 / 799 heads came on '01-up LS6 5.7L, '05-up LS2 6.0L ... and '05-up 4.8L & 5.3L:
64.45cc combustion chambers, 210cc holy intake runners, 75cc D-port exhaust runners, 2.000" intake valves, 1.550" exhaust valves

If you're more concerned with more power ABOVE 3500RpM, use the 243 / 799 heads.
If you're more concerned with more power UNDER 3500RpM, use the 862 / 706 heads.
The 862 / 706 heads may also get better MpGs.

Your Escalade's axle gear ratio looks like 3.73.
You should consider 4.10, unless highway MpG is more important to you than city MpG.