For the LT1 Swap owners...

What kind of a of gas mileage are you seeing?

Easy day to day driving and race to each light driving?

Thank you
JM

As you may know, the LT1 is a high horsepower performance not an economy engine. Only a few Fiero owners have this swap but from what I can find online , the combined gas mileage of an LT1 in a Corvette runs from 16 to 21 mpg (data from actual users). I would figure 10% more in the lighter Fiero but gearing will have a huge effect.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

I get 14-18mpg, but I don't drive it gently enough to get better. Then again, I didn't swap in the Lt-1 for the iron Duke because I was interested in fuel economy.

Depends on the transmission. The upper limit on the getrags is about 23 mpg at 75 mph due the pumping losses of pulling heavy vacuum at 2700+ rpm.
F40 should be able to get in the 28 mpg range due to the lower cruise rpm which also drops the vacuum at cruise.
4 speed auto should be able to get 26+ mpg depending on the gearing and cruise rpm.

For the V8s, cruise fuel economy is all about getting the rpms down and the throttle blades more open to lower the vacuum (pumping losses).

quote Originally posted by fieroguru: Depends on the transmission. The upper limit on the getrags is about 23 mpg at 75 mph due the pumping losses of pulling heavy vacuum at 2700+ rpm. F40 should be able to get in the 28 mpg range due to the lower cruise rpm which also drops the vacuum at cruise. 4 speed auto should be able to get 26+ mpg depending on the gearing and cruise rpm. For the V8s, cruise fuel economy is all about getting the rpms down and the throttle blades more open to lower the vacuum (pumping losses).

Do you happen to have an example with typical numbers?

For instance, vacuum at 75 mph in 3rd, 4th, 5th, 6th with your LS4/F40?

Edit: I found this cute picture on Quora. Not a V8, but similar shapes I suppose?

[This message has been edited by pmbrunelle (edited 06-22-2022).]

I estimate I'm getting around 12-14 MPG. Driving it like I stole it. So that appears to be within range.


Thank you all.

That LT1 I built into a 377ci just got bought by the original owner after 7 years! I went to get the car appraised to get bought back and as soon as I heard the motor start and Idle I said: Buy it back!!!!!! It sounded like the first day I built it. I'll get back to you on the gas mileage. it is a a 6 speed manual. It Dynoed at 431WHP(504BHP) and 497WTQ(582BTQ) Thats's 1.54 LBS per Cube!!. With a catalog cam and stroker kit and I did all the head porting. Gas milleage is not the norm here, performance is.

[This message has been edited by La fiera (edited 06-24-2022).]