Lq9 swap

[Mudsport96]

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.

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]

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.

 

[Mudsport96]

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.

 

[jeffg]

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.