Hey guys, hows it going. Well I just finished my swap to a 3.8 SC III on my 88 5spd trany. Im only getting about 13 mpg. Does anyone know what I could do to improve. I am also not driving Hard, Im only just cruising. I cant afford to drive hard with this MPG. Please if anyone knows of anything let me know what to do.


Thanks
Fieroman10

You are doing better than me. I just finished my 3.4 swap and I am getting 9MPG. Good luck!

that may be average mileage for the 3.8.

I don't have one in my fiero, but my wife as one in her Regal.

On average (keep in mind, this is a 4000 lb car) she gets about 15 mpg. But she does very little highway driving.
Its real fun to get on it, watch the boost rise, and the mileage fall. I can get the gauge to read 2 MPG. Braggin rights there!

Check the plugs, and see what color they are. You may have to go with a hotter plug, or regap the plug.

Do you know the mileage of the car the 3800 came out of?

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[This message has been edited by 85FieroGT3.4 (edited 10-26-2007).]

well I got the engine in mid 2004.. It was from a reck and it took out the driver side of the car so they were un able to get the miles. So Im guessing max like 12,000 and ive drove already like 6,000 miles so its still a fairly new engine. I just thought it would be getting better MPG, for being such a light car

You should. Most people get around 30 MPG. Have you searched the forums? Do you do alot of stop and go driving? Alot of speed changes? That will mess up your gas mileage.

Good grief, something is definitely wrong if a 3800 (supercharged or not) is getting 13 mpg. I'm not sure about city figures, but 3800 SC S2 cars usually get at least 28 mpg highway with the getrag, perhaps a bit more. With the 4t65, they can get more like 31, 32 mpg highway.

I do most of my driving in the city but I dont get much traffic. I havent done any upgrades to the engine yet... its still stock at a rock.... What are the average fuel pressure the 3800 are running at? Could that play a role with the fuel consumption? What else plays a big part of MPG?

I have a 87 GT with 2006 GP 3800SC III with auto trans that came with the motor with about 10,000 miles on it, With (ETC drive by wire) Around town I get anywhere between 14 to 17 mpg. When the swap was first done I thought damm this thing should be getting better mileage, Even driving like granny, was still only clocking 17, stick your foot into it a little and BAM 14, So I had to go to Plant City a months ago and thought let see what kind of mileage this thang will get on I-4 at 70 mph. BTW this thang is not even breathing hard at 70, It's only clocking 1800 rpm. Well gas this sucker up in Daytona Bch and took off for Plant City. Gas up again in Plant City and Lo and Behold this badboy clock in at 29 mpg there and back