We've seen a lot of different swaps and various dyno sheets and time slips. We have a good idea of what kind of power can be had from the different swaps.
With gas prices on the climb, it might be good to compare the gas mileage, too.

So, what swap do you have and what kind of gas mileage do you get? Even if you didn't build it for mileage, let us know what you get and what you've done with your swap.
A 300 HP swap that gets 30 mpg highway might be more tempting to some than a 150 HP swap that gets 40 mpg, but let's hear about them all.

LS3/F40 with the hot cam got 27.2 MPG on the freeway for 300 miles running between 70 and 80 MPH (RPM s under 2000 with the six speed) on it's shakedown cruize to Carlisle last June. I need to do a mileage check now that the engine has some miles on it

Jim

333cu with a 4barrel carb, cam and 4spd manual. I don't even want to think about it

2007 GXP LS4 with factory Auto and tap shift...

Originally 30 Hwy and 24 around town... (first 400 miles after swap) Now that I have learned to enjoy the package.... about 27.5 and 18.... LOL

Jeff

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N* 275 and 300 engines. Easily getting 30+MPG. Due to the tires (275/30/20) matching the original tire size-at 70MPH the rpms are under 2,000. Late last night I saw a Chevron gas station listing premuim at $4.99.9 Last week it was $4.29 or so.

This is/was my daily driver - 97 Park Avenue Ultra (Da Boat) SC 3800 Series II
It averaged 27 mpg in mixed driving - 60 miles a day - calculated at each fill up
Only minor mods at first which should increase mpg
CAI and a much less restrictive exhaust

I certainly hope it gets better when it goes in the Fiero

Second round of mods will be head work and 3.3 pulley (prolly not beneficial)

[This message has been edited by Pappy (edited 03-05-2011).]

Mileage is a mathematical equation that is directly related to the variable called FOOT, or foot=(mpg-gp)+grin which is also directly related to the phenomenon of moths leaving a wallet.

My old setups:
SBC/Getrag: 22-23 on the interstate at 75-80, and 17 for my daily commute
4.3/4T60: 30-32 on the interstate at 70-75, and 25-28 for my daily commute
2.8/Isuzu: 30-33 on the interstate at 75-80, and 25-28 for my daily commute

The current LS4/F40 swap in progress might hit up to 35 mpg on the interstate and I am hoping it could get 22 on my daily commute... but it all depends on how I drive it!

quote Originally posted by Jim88GT: LS3/F40 with the hot cam got 27.2 MPG on the freeway for 300 miles running between 70 and 80 MPH (RPM s under 2000 with the six speed) on it's shakedown cruize to Carlisle last June. I need to do a mileage check now that the engine has some miles on it Jim

I call quasi-BS on that. Because the F40-MT2 is the tallest-geared possible version of the F40, and even with 26.1" tires, you're doing 1991 rpm at 70 mph. Before showing the math that proves this, let me point out that a 26.1" tire is a 205/75R14, a 235/60R15, or a 255/45R17.
The formula for finding RPM is gears times the constant 336, times mph, then divide by new, unloaded tire diameter in inches.
3.5454545 x 0.6230 x 336 x 70, / 26.1 = 1990.5

quote Originally posted by Isolde: I call quasi-BS on that. Because the F40-MT2 is the tallest-geared possible version of the F40, and even with 26.1" tires, you're doing 1991 rpm at 70 mph. Before showing the math that proves this, let me point out that a 26.1" tire is a 205/75R14, a 235/60R15, or a 255/45R17. The formula for finding RPM is gears times the constant 336, times mph, then divide by new, unloaded tire diameter in inches. 3.5454545 x 0.6230 x 336 x 70, / 26.1 = 1990.5

Feel free to call quasi-BS all you like - there is a picture of my dash during the trip showing 70MPH at well under 2,000 RPMs on page 3 of the CT#10 update thread. I verified the miles driven with 2 other Fieros I was traveling with, and the mileage was as stated. I'm running 18" rears. Since you seem to be so mathematically astute, maybe you can enlighten all of us less educated folks on how the drag coefficient of a choptop vs a regular GT would preclude getting the stated mileage.

Have a nice day

quote Originally posted by Isolde: I call quasi-BS on that. Because the F40-MT2 is the tallest-geared possible version of the F40, and even with 26.1" tires, you're doing 1991 rpm at 70 mph. Before showing the math that proves this, let me point out that a 26.1" tire is a 205/75R14, a 235/60R15, or a 255/45R17. The formula for finding RPM is gears times the constant 336, times mph, then divide by new, unloaded tire diameter in inches. 3.5454545 x 0.6230 x 336 x 70, / 26.1 = 1990.5

Uhm. What BS? 1990 is less than 2000 last I checked. And how is the MT2 the tallest-geared possible version? There are only two versions. The MT2 and MU9, and the MU9's 6th gear is 0.71:1 instead of 0.62:1, with the same FD of 3.55:1. With the MU9 it would be at almost 2300 RPM.

quote Originally posted by Dogcreek: 2007 GXP LS4 with factory Auto and tap shift... Originally 30 Hwy and 24 around town... (first 400 miles after swap) Now that I have learned to enjoy the package.... about 27.5 and 18.... LOL Jeff

Did you keep the Displacement On Demand?

quote Originally posted by Jim88GT: Feel free to call quasi-BS all you like - there is a picture of my dash during the trip showing 70MPH at well under 2,000 RPMs on page 3 of the CT#10 update thread. I verified the miles driven with 2 other Fieros I was traveling with, and the mileage was as stated. I'm running 18" rears. Since you seem to be so mathematically astute, maybe you can enlighten all of us less educated folks on how the drag coefficient of a choptop vs a regular GT would preclude getting the stated mileage. Have a nice day

To be fair, where the tach needle is pointing exactly is covered up by the ignition/column in the pic. But based on the angle it's at, from the 1500 mark, I would guess that it's between 1850-1900. And that would put your rear tires somewhere in the 27-28" range (since I don't remember white size you're running, and I can't read the tire in the pics to calculate it).

There are also some other factors involved. Like the fact that going up to Carlisle, probably the last 1/3 of the trip is coming down off the mountain, and probably 2/3 of the trip back is all headed down to sea level from the mountains. There's a lot more to the MPG calculation than simple gear ratios, indeed.

I wouldn't get too worked up on the exact cruise RPM since most fiero tachs in stock form are less than precise... and that is before they are altered for engine swaps. One of my V6 cars the factory tach read about 300 rpm higher than what my scan tool showed, so trying to be precise with a stock tach is a waste of time. Besides, this thread is about MPG, not cruise RPM.

Hi Formula88,

The internals are in it but it is shut off electronically with HP Tuners.

Jeff

I've posted about it before, but I wish more people would sign up and use www.fuelly.com to track their gas mileage. It would be nice to see a larger sample of Fieros to see what kind of real-life mileage people get.

Here's a link to my Fiero's page (I only have a few fill-ups on it but will probably be adding more soon).

http://www.fuelly.com/driver/akursedx/fiero

Prior to using fuelly, I got 28.7 mpg tank on a highway trip. That was with my 3800-turbo and a 4t65eHD with a 3.29 gearset.

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'88 GT- 3800 Turbo 11.367@121.03mph
FOR SALE
GM Tuners

88 formula 3400SFI turbo
15MPG highway right now (running on a very sh*tty tune)

[This message has been edited by pontiackid86 (edited 03-06-2011).]

88 Mera with 3800 SC Series III engine, N* TV, XP cam, intercooler, and Getrag 282 transmission. Running the A/C at around 74 mph I get 24-25 mpg. Similar results on an 87 Mera with a turbo and five speed getrag.

Nelson

[This message has been edited by hnthomps (edited 03-06-2011).]

I was driving 177km round trip to work. on about 20l each day. That's about 20.8 mpg. its a stock series 2 supercharged. It was a mix of highway and downtown crawling. that's worse than my Buick...

quote Originally posted by madcurl: N* 275 and 300 engines. Easily getting 30+MPG. Due to the tires (275/30/20) matching the original tire size-at 70MPH the rpms are under 2,000. Late last night I saw a Chevron gas station listing premuim at $4.99.9 Last week it was $4.29 or so.

dunno about you guys, but the best ive ever gotten in my entire 28 year association with my 84 is about 27mpg. i have the 4.10 final drive in my muncie 4 speed and the tallest tires i can get on the rear - 215 55 16's. anyway we are paying 1.30$C/liter or about $5.15/galUS for regular - and thats at the cheapest station that i can find.

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I'm the original owner of a white ' 84 2M4 purchased Dec 10, 1983 from Pontiac. Always garaged, no rust, 4-wheel drifts are fun!