tell me your gas milage increase or loss since converting to efi

[chpr1972]

Im going to be driving my Pontiac [bbc] as often as possible and wondering if converting to efi will actually be worth it. I know that motor size, ods, and gear ratios, tire size will make a different as how you drive. But I think that a lot of us who will drive their car what to know if it will make a difference enough to pay for it. How much did it increase in city driving and on highway? I will be taking a trip from Florida to the west coast up into washing and back thru South Dakota and would like to do power tour and maybee woodward cruise if I dont run out of money Im going to have to change my manifold and to a bigger carb is why Im considering an efi system.

[rickpaw]

I had a Pontiac 400 with a T400, 3.55 gear, Holley 750 carb in my Firebird. My best mileage was 11 mpg. I put in a Gearvendor overdrive, mainly wanting to drop the engine rpm at freeway speed. Mileage after the swap jumped up 20% (just as GV claims), to around 13 mpg. I recently completed a 5.3/4l60e swap, kept the rear end. I've had only 120 miles since the swap, and my OBD II app has been showing 28-30 mpg.

One guy in our Firebird club has a 400 with Powerjection EFI/200-4r transmission, and he says he's getting 17 mpg.

[69cutlassrkt]

Tu Ho, the 28-30mpg you have been getting is that all highway, city, or both? And do you have a stock torque converter in the 4l60e?

[rickpaw]

It's a combined mpg. 50/50 mix driving. Realistically, i'm thinking the real mpg will be in the mid 20's. Bone stock drivetrain out of a 2001 Silverado.

[69cutlassrkt]

wow, that's pretty good. When mine was on a stock tune it would get 24mpg combined city/hwy. And that's with 2.78 gears and a 2500 stall lock-up torque converter at the time.

[69cutlassrkt]

chpr1972, one of the magazines did a comparison of carb, tbi and mpfi, maybe someone here remembers it. So are you looking to do throttle body injection, or some sort of multi point setup?

[Hammered]

For driveability and mileage, my first investment would be an overdrive transmission. EFI will never pay for itself in saved gas, but I do love never having any trouble starting it in any weather or at any engine temperature. I just replaced my seven year old Optima which had lost 80% of it's cold cranking amps and it had no trouble starting the car as long as it had a full charge. Leave a courtesy light on for half hour and it had some trouble though.

[rickpaw]

Agreed with the above. If you don't have OD trans in the car now, I'd say's it's best to put your money toward an OD swap. I swapped an LS engine/OD combo so it's not even a close comparison, but the guys in my firebird club who put throttle body FI on top of Pontiac engine get around 17 mpg, with an OD transmission.

[Jim Nilsen]

With EFI it all depends on your tune at cruising speeds more than anything.
With a 383 and an Accel gen7 unit I can get 18 to 20mpg on the highway at good cruising speed and will get 15 + all the time in the city and over 10mpg when I am full throttle at the track.

If you don't get better mileage it is because you aren't trying hard enough or you had the perfect carb.

I run a .76 OD with a 3:07 rear and a 25.5 to 26" tire.

For only twice the money of a really good ($750 +)carb these days you can have self tuning EFI.

Have fun it will stump you somewhere before you get it running REAL good. But it is worth every penny and problem to get there.