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
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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
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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.
Mudsport96
Full Access Member
4.10s will help immensely, but 799s are still going to give you compression in the neighborhood of 10.9:1..... We are talking 93 octane and a DEAD nuts tune. Or you will have unique powdered pistons. An fbody or vette, or hot rod swap that is light could get by with that. But a heavy pig suv or truck is going to end up with detonation. And then the knock sensors will pull timing, and you will lose power. If you stay with a more sensible compression that the 317 will give, you will be able to avoid that. Or you can tune for and run e85. But then you will need bigger injectors and a flex sensor just in case you ever end up in a place without e85. Also because e85 varies from station to station. One can be e85 and the one down the street is e65 because of how it is mixed.
The 799 heads flow the same as the 317s. The ports are identical, just the chamber is different. Smaller on the 799s and larger on the 317s.
Even a built 60e is going to need a good tuner to set everything up correctly or it will die.
Marky Dissod
Full Access Member
LS2 is a 6.0L with 243-799 heads yielding 10.9:1 static compression.
TrailBlazers SS weighed over 4000lb.
That he will REQUIRE a smart tuner to do a good job is one thing.
Quite another to advise against the 243-799 heads, or to prefer the LQ4/LQ9 heads over 243-799 heads.
For lower compression with 243-799 heads that will still outperform LQ heads, he can use a thicker gasket.
TOTALLY agree regarding the 4L60E though.
TrailBlazers SS show 4L60Es very little mercy.
TrailBlazers SS weighed over 4000lb.
That he will REQUIRE a smart tuner to do a good job is one thing.
Quite another to advise against the 243-799 heads, or to prefer the LQ4/LQ9 heads over 243-799 heads.
For lower compression with 243-799 heads that will still outperform LQ heads, he can use a thicker gasket.
TOTALLY agree regarding the 4L60E though.
TrailBlazers SS show 4L60Es very little mercy.
Mudsport96
Full Access Member
Thicker gasket is a horrible idea. Sure it drops the compression..... so now you are back closer to 317 head compression. But, it also opens up the quench distance. Which raises the requirement on octane because it lowers knock resistance. So you have to back off timing also lowering fuel efficiency so mpg suffers. The TBSS also used an E38 computer with more processing power than the P59 his Tahoe has.
I'm not knocking high compression, I had a 12.5:1 small block chevy. In a relatively "light" car with a 4.56 and shorter tires compared to even TBSS. And 93 octane was the minimum I could run without issues. He has to take in account of availability of the fuel he will be required to run. It would suck to visit somewhere and the best fuel they have is 89.
I'm just trying to put out there he would be better off with the lower compression in a heavy suv and perhaps offset it with a 300 rpm higher stall converter.
As for the weight, I can't find a definitive answer on tahoe weights just somewhere between 4500 and 6500, but luckily the SS guys are obsessed with weight. And they weigh anywhere from 4200 to 5000 depending on options. Maybe I'll weigh my tahoe this week so I have a number.
I'm not knocking high compression, I had a 12.5:1 small block chevy. In a relatively "light" car with a 4.56 and shorter tires compared to even TBSS. And 93 octane was the minimum I could run without issues. He has to take in account of availability of the fuel he will be required to run. It would suck to visit somewhere and the best fuel they have is 89.
I'm just trying to put out there he would be better off with the lower compression in a heavy suv and perhaps offset it with a 300 rpm higher stall converter.
As for the weight, I can't find a definitive answer on tahoe weights just somewhere between 4500 and 6500, but luckily the SS guys are obsessed with weight. And they weigh anywhere from 4200 to 5000 depending on options. Maybe I'll weigh my tahoe this week so I have a number.
Just finished my LQ9 swap in an 04 Tahoe. I kept the 317 heads with just a touch of cleanup polishing. Cam, springs, rocker trunnions, MLS gaskets and half the ARP catalog. HP Tuners custom tune on 91 octane and it's kind of rowdy. I cant imagine another point of CR.
Collinmcballin
Member
I'm next in line and quite excited!
~300k on my 05's LM7. trying to find a decent LQ9, but dang they're hard to come by. looking for an 05/06 i don't want to fight EGR and different fuel rails etc. ideally i just need a solid short block, all the goodies on my 5.3 are dialed and can be transferred.
-right now i have fresh 243 heads with ls7 springs and my Melling truck/tow cam (mtc-7) which has treated me well. still passes smog
(243 comp okay?)
-I think Blackbear can do the tuning for me right? just tell them what i have and get a PCM on the way? i don't want engine codes and still need to use my obd2 scanner when needed haha
-Trans is first of course, saving for an L4 FLT 4L60E with all those Sonnax goodies, seriously almost rebuilt it myself, but its my DD i cant afford the downtime.
-no budget for gears, just gonna leave the factory 3.43's and factory stall TC. trying to keep things OEM-ish. its AWD so no burnouts lol. 33'' tires. currently 1750rpm @ 70mph old engine just cant pull OD
-also planning on re-routing PCV w/ catch can through valley cover to prevent driver side valvetrain from turning black
anyway...
~300k on my 05's LM7. trying to find a decent LQ9, but dang they're hard to come by. looking for an 05/06 i don't want to fight EGR and different fuel rails etc. ideally i just need a solid short block, all the goodies on my 5.3 are dialed and can be transferred.
-right now i have fresh 243 heads with ls7 springs and my Melling truck/tow cam (mtc-7) which has treated me well. still passes smog
(243 comp okay?)-I think Blackbear can do the tuning for me right? just tell them what i have and get a PCM on the way? i don't want engine codes and still need to use my obd2 scanner when needed haha
-Trans is first of course, saving for an L4 FLT 4L60E with all those Sonnax goodies, seriously almost rebuilt it myself, but its my DD i cant afford the downtime.
-no budget for gears, just gonna leave the factory 3.43's and factory stall TC. trying to keep things OEM-ish. its AWD so no burnouts lol. 33'' tires. currently 1750rpm @ 70mph old engine just cant pull OD
-also planning on re-routing PCV w/ catch can through valley cover to prevent driver side valvetrain from turning black
anyway...
Marky Dissod
Full Access Member
Good idea to lighten up on the budget for the 4L60E,
so that you can upgrade to 3.73 or even 4.10.
Going from 3.42 to 4.10, from the stopwatch's POV, is like 30ftlb to the wheels at EVERY RpM.
Collinmcballin
Member
hmm.. I was really debating that too. but changing ratios in front 8.5 diff to 4.10 is rocket science that I'm not interested in. although I could buy a front diff from wrecked escalade that had 3.73 from fact. (the AWD diff's are different than the 4wd w/ actuator...) then i guess tow to shop for the rear gears.. blegh sounds like a mission
what's fwy rpm like? I'm thinking the LQ9 can push low rpm cruising no prob. currently @ 17.8-18.2 mpg fwy
factory TC fine you reckon?
thanks,
what's fwy rpm like? I'm thinking the LQ9 can push low rpm cruising no prob. currently @ 17.8-18.2 mpg fwy
factory TC fine you reckon?
thanks,
Marky Dissod
Full Access Member
3.73 & 4L60's 4th & 33" tall tires = 1862RpM @ 70MpH
4.10 & 4L60's 4th & 33" tall tires = 2047RpM @ 70MpH
3.73 & 4.10 were also GM OE, depending on which version of which GMT800.
4.10 more likely in Suburbans, more likely in 4WD, more likely in 4WD 'bubbas.
Think about how much less often you'd be downshifting with more gear.
4L60's longevity / durability is proportional to the number of shifts over its lifetime,
even moreso if it works or plays hard for a living.
Bet you'd spend more time in 4th & less in 3rd & 2nd with 3.73 or 4.10.
I've got 3.73, and can BARELY break all 4 tires loose for a split second,
only in very bad weather or very loose earth or both. 4.10 would make me VERY happy.
GM OE torque converter should be ok if you're not a leadfoot / towing heavy / both.
4.10 & 4L60's 4th & 33" tall tires = 2047RpM @ 70MpH
3.73 & 4.10 were also GM OE, depending on which version of which GMT800.
4.10 more likely in Suburbans, more likely in 4WD, more likely in 4WD 'bubbas.
Think about how much less often you'd be downshifting with more gear.
4L60's longevity / durability is proportional to the number of shifts over its lifetime,
even moreso if it works or plays hard for a living.
Bet you'd spend more time in 4th & less in 3rd & 2nd with 3.73 or 4.10.
I've got 3.73, and can BARELY break all 4 tires loose for a split second,
only in very bad weather or very loose earth or both. 4.10 would make me VERY happy.
GM OE torque converter should be ok if you're not a leadfoot / towing heavy / both.
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