LT1-LT4 Modifications - Need some input on what how these mods will affect the engines gas mileage..

I don't have a Camaro, but I'm looking to put a 350 vortec in my S10 Blazer and no one on any of the forums seems to be able to answer my question so I figured I'd come here. Current owner says that in his Blazer he was getting 24-26mpg with 4.10 gears and a T56.

Here's what I'm looking at:
350 vortec, bored .030 over and was taken down to a zero deck. With the head gasket im running it should be right at 9.8:1 compression ratio. It has an Lt4 hot cam, comp cams 1.6 ratio full roller rockers, Comp cams beehive springs and retainers....Black Bear Performance custom tuned PCM


I'd be keeping it fuel injected and tuned with a 411 computer. So I'm wondering if this engine would get terrible gas mileage or good (for a V8). I'd be wanting at least 20+

Or...... I have an idea what mpg it would get with a stock 350 vortec, could you tell me how all the custom stuff with the tune will affect the mpg?

That's not bad!
My bolt on Lt1 w/4.10s gets 26 on the highway when it had the 3.42s it got 27-29 on the highway.

Im doin a stockish LT1 build with a 4L60E in my S10 ext cab Itll have dana 44s front & rear on 35x12.50s with 4.10 posi front & rear It should get 24 or 25mpg hwy Youve gotta figure for awhile youll be rompin on it lol since you just added a lot more power :) If your usin a 4.3 trans it might need some Upgrades