Sad about good MPG

[cosmick]

So the 4-cylinder has an internal knock.
I have ordered the correct oilpan and mounts for the 4.8L LSx V8 swap, then I scored the known-to-work exhaust manifolds off Ebay.
I know my '89 S-10 4.3 / 4L60 / 3.42:1 did 28 MPG HWY, so I expect this to be similar with 3.08:1.
I'm probably installing a 70 mm turbo right away, since I have to fabricate a new custom exhaust anyway.
I already have mandrel-bent 2.25"-OD tubing to get to a Flowmaster Y-pipe, then I'm planning a 3" ULEV cat before the T70.
So the current goal is 30 MPG with 500 HP.
I'll probably swap the 3" rear lowering blocks for 2", or none, and fabricate my own copies of the Cal-tracs bars for traction, and fit 275/35s onto some 19" x 10" wheels I have. I'll definitely swap in a Traction-Lock differential.
Lastly for now, a new set of Z06 valvesprings, and hopefully raise the WOT upshift point from 5800 to 6500 RPM. Shifter for the "new" automatic will be "borrowed" from my '86 Camaro, since the S-10 was manual-shift until now.

[cosmick]

I ordered some 2.733:1 gears for this rear axle, and that would give it 1500 RPM at 65 MPH, which it should pull, assuming 27.7" rear tires, such as 215/75R15s. But I just went out and did a test fit of my 19" x 10" Corvette wheels, as the turbo may need more traction than 225/60R16s, so I'm considering 275/40R19s, which is why I calculated at 27.7" tires.
But while I hope that will give me over 30 MPG, I'm having to consider a stronger transmission. I have an unbreakable SM465 that'd fit cheaply and easily, but has no OD. It does have a granny gear, and with it I could tow trailers up mountains at normal car speeds without any worry of anything failing, even with a turbo whistling at full song.
I found a T70 turbo, 0.81 A/R, new, $255 from CXRacing. Chinese, but a decent reputation these days.
So I'm adding pics of test-fitting the 19x10s.

[cosmick]

[cosmick]

[cosmick]

[cosmick]

Did some tire shopping, then some spreadsheets. I'm still torn between MPG VS reliability.

[cosmick]

Spreadsheets are showing no way to have the 4.8 at a useful RPM for towing with a 2.73:1 or even 3.08:1 axle, I'm considering selling my SM465 and my 4L60E to get a NV3500 with the 3.49 / 2.16 / 1.40 / 1.00 / 0.73 gearset. SM465 is 6.55 / 3.58 / 1.70 / 1.00

[cosmick]

I got the "correct" exhaust manifolds, they need a little porting. Yep, like what cylinder heads get, and for the same reason, unrestricting the airflow.
I ordered a set of new injectors, 50 lb/hr, should support 581 HP at 80% duty cycle.
I guess I'll run the 4L60E with the 2.73:1 axle gears for a MPG number, hopefully I won't kill the 60E with turbo boosted torque before I get a good number.
Oh, I'm considering as much as a 285/45R19 back there.

[bentring]

With all the changes you are planning, you might find this link useful for comparing possible setups. It won't let me post links, but wwwdotgrimmjeeper.com/gears.html

[Xist]

Originally Posted by bentring

With all the changes you are planning, you might find this link useful for comparing possible setups. It won't let me post links, but wwwdotgrimmjeeper.com/gears.html

Gear Ratio Calculator