Not so good, but I still have a lot of tuning to do with my modded up TBI. I think the best tank with the 383 is around 11 or 12, but I've had some single digit tanks, too. but again, it's been very little highway driving, with a lot of idling, tuning runs, Home Depot runs, dump runs with utility trailer, etc. I'm hopeful I can get it up to 13-14 on the highway, of course not towing anything.
Did you check out my
post from a few days ago? I go into a lot of detail about what I did in my swap. (I went through a lot of similar questions as you're asking now. And I'm still not sure I would have done everything the same, sometimes I wish I had gone BBC). You are right to be asking these questions, especially about what trans goes behind which engine, but in your other post I didn't see much info about fuel system choices, for either of your engine choices (LS and 383)? I'm not the guy to talk to regarding LS, but for the 383 you have basically three choices: 1) modified TBI, 2) aftermarket FI, or 3) carb. If you go with 4L80e or another "e" tranny, you'll have to have some way to control the trans. My post talks about how to do it with TBI and stock GM stuff, for #2 and #3 you have to control the trans with an aftermarket device. with aftermarket FI you may be able to have an all in one computer that controls both fuel and trans. They all have their ups and downs, all require a fair amount of work and cost. I may be jaded, but I think #1 is the most work, but hopefully it will be worth it!
