The aftermarket torque converter won't change your highway MPG. It will greatly improve your 0-60mph though. It also makes the car a lot more "fun" to drive.

You can find "base-model" converters for about $500-$600. For better durability/reliability, I upgraded to a"billet" converter model for an extra $200. Mine came out to $799 shipped. I went with a Circle-D HP 3000-3200 stall "billet" option, and wouldn't recommend anything with a lower stall speed.

 

Hey guys been a while since I posted anything but I've been doing some more searching and I need some input on a change I'm looking at doing. I'd like to run 87 octane fuel in this build and I'm willing to sacrifice on my hp for that. So I was looking at just doing a 224r cam 112 lsa, stock LQ9 with ls6 intake, and I'm gonna change up to a t56 with a 3.73 gears. So my question is will my fuel economy still be in the 20s?

 

One reason you maintain fuel mileage with a stall converter; LOCKUP.

 

I agree 100% I was just thinking on boosting my economy numbers is all. that's why I wanna t56 swap it.

 

Depending on your driving habits you should have no problem achieving the 20mpg target. Using either transmission will get you there as both have O.D. With your combo the Camaro should cruise 70mph @ slightly under 2000 rpm. I think you could see 24 mpg
I am doing a LQ9 transplant as well. Mine is a 1971 RS Camaro. 243 heads ported and cut by TEA ,cr11.3 (premium pump gas) , 228/232 112+2 (Martin Smallwood)cam. Yank PA3400 converter (spec'd by Dave)and a 4l60e that I am re-doing now. The rear gear is 3.42:1 I expect over 20mpg's with this combo and decent 1/4 mile et's as well

 

Sorry , I missed your post saying you were going with 3.73 years. That will change things quite a bit. You will have a hard time knocking down 20's if cruising interstate speeds. imo

 

well 3.73s is only if I put a t56 in it. I'm running 3.25 now with an automatic and it performs decent with my TPI engine but I'm just tossing ideas around to get even better. T56 with a 3.73 in 6th gear will tach right around 2200 at 70. So that pretty close to what my auto puts down.

 

Yeah. You probably won't be able to run 87 octane with 243 heads on an lq9. That is 11:1 and I wouldn't run anything under 91 octane and 93 if possible. That said you are building this engine for power. Let go of the idea of getting good mileage and 87 octane and just enjoy the horsepower. Or find a 5.3 with AFM and get good mileage.