So I'm fixing to swap in a LQ9 out of a 03 Escalade into my 03 Tahoe... I have a set of 799 heads that I'm thinking about throwing on that LQ9 before putting it in the truck... Any major modifications needed for that or just a simple head swap?
Lq9 swap
- Thread starter Mrwick_02
- Start date
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Marky Dissod
Full Access Member
Apart from a pcm tune to take maximum advantage, no NEED.
Use whichever injectors are larger.
(Mind that an LS2 is a 6.0L with 10.9:1 scr and fancy flyweight valves in 243-799 heads.)
If you want to be able to spin it past 5800RpM often, upgrade the valvesprings.
Choose the headgasket to keep scr under 11-to-1 (10.9:1 is FINE).
If that's not enough for you, upgrade the cam WISELY.
If you do not tune the pcm, either use 91 octane, or drive like you're afraid of detonation ...
Use whichever injectors are larger.
(Mind that an LS2 is a 6.0L with 10.9:1 scr and fancy flyweight valves in 243-799 heads.)
If you want to be able to spin it past 5800RpM often, upgrade the valvesprings.
Choose the headgasket to keep scr under 11-to-1 (10.9:1 is FINE).
If that's not enough for you, upgrade the cam WISELY.
If you do not tune the pcm, either use 91 octane, or drive like you're afraid of detonation ...
I'm gonna be running my tahoes stock flex fuel injectors(l59). Would those work? Are ls6 valvesprings acceptable for 6500-7k rpm?
Also would stock LQ9 head gaskets be good?
Marky Dissod
Full Access Member
Not a 'yes' or 'no' question.
33lb / hr injectors can safely support about 500 horses at the crank, or 400 at the wheels.
LS6? No. Think you want LS7 valvesprings, or better.
More importantly, OE solid stem valves are only safe to 6000RpM.
You really want lightweight hollow valves over 6000RpM.
Although I don't definitively know the answer to this one, my guess is you'll want something better.
I guess I'll be keeping it 6k and under... Not really going for anything crazy, just wanna build a relatively reliable LQ9 to throw in the hoe... It's gonna be used as a dd with some racing/donuts/burnouts here and there.
Trey Hardy
8” fabtech icon coilovers uniballs 24x14on35/15.50
You can do a mild build on my last setup I had a stock 5.3 bottom end with ported milled 243 heads with a valve job and new ls7 springs
Hardened pushrods
Ls7 lifters
And ls7 head gaskets
Matched with a stage 4 cam that crewcab truck cut doughnuts as tight as a corvette would and would just naturally smoke them 35/12.50s off of her!
Don’t forget gears is the biggest bang for the buck on these things too as far as waking them up
My next project will be swapping the stock 3.73s out in my Silverado for some 4.56s
Mudsport96
Full Access Member
Ok, so 317 heads will be fine you will see minimal gains for the almost 11:1 compression the 799s will give for the same cfm flow that the lower compression 317s have. In a heavy suv the stock LQ9 compression will be fine. Use a Truck Norris cam for maximum torque and the power under 6k where a Tahoe needs it. Unless you upgrade the G80 goveloc, you are going to explode your diff.... so don't plan on too many doughnuts before that happens. I would also recommend saving up for a new 4L60E as it will also die with enough races and doughnuts.
LQ4 truck norris dyno
You could probably add 15hp to these numbers for a LQ9. Also remember this is turning big HEAVY offroad tires so rotating mass is eating up a good percentage of power as well. So for stock size tires I would say add another 15hp. AND these are rear wheel numbers. A stock LQ4 with an optimal tune and long tubes and no accessories makes like 400 at the crank. A 5.3 with the same stuff makes 350 at the crank. So you are already bolting in AT LEAST 50hp with just the engine swap. BTR claims a 60hp gain from the cam in a 5.3 so for simple math we will say a 6.0 will also see 60hp. So that would be at minimum 110hp over the stock 5.3 because the stock tune is not optimal it would probably be closer to 125hp gain. All in a usable rpm range...not in the 7k range....
Also the flex injectors SHOULD be okay. They are the same ones used in the stock 8.1 I believe.
Marky Dissod
Full Access Member
4.10 at a minimum.
I probably should've said this earlier... I thought ahead when I first purchased the Tahoe, all the "supporting mods" have been done. Fully built 4l60e with a truck cool 40k, 4.10 gears with a Eaton trutrac, fully rebuilt front diff, new transfer case. Motor is the last thing left and since my 5.3 has a crack in the block and a few failed lifters, I figured it's the perfect time to throw in this LQ9. My original plan was to buy a LQ9 short block and throw the 799s on it which is why I had bought them in the first place. Still really wanting to do that.
