ad356

how does gas millage compare between a 350 TBI in a camaro and a 305 TBI in a third gen compare? 305 currently in the car is a stock l03 and the canidate for a possible future swap would be the 350 GM crate engine off of summit, 250 HP 350 ft/lbs of torque that sells for 1,500 8.5:1 compression. i want to eventually do a 350 swap. however at 2.95/gal an rising fuel price, gas prices are at the forefront again. i am very pleased with the fuel millage the 305 delivers, i think 25 MPG is great when you are getting a fun drive. i could care less about 40 MPG, what good is 40 MPG if the car you are driving is completely void of any fun driving experiance. in order for me to get the most of a gal of gas it has to be fun to drive, not just good on gas. gas millage isnt everything but it needs to be good enough to be affordable. i would probably stay with the stock rear gears 2.73's, i think(its a 5.0 RS). i would like to make it a limited slip rear end though. one wheel peals suck. in order for a car to be afforable to drive it should deliver 16city/23highway, is that a realistic goal for that kind of combo. transmission would remain a 700R4. is that a realistic goal? how does TPI/TBI/LT1 compare in regards to fuel economy?

GOY

Two opinions here:

First is that TBI can deliver the same fuel economy as MPFI (TPI/LT1 in your question). The second if that MPFI will ultimately deliver better fuel economy. I'm a guy that goes with the second. *I feel* the closer you can get the injector to the combustion chamber, the better. There's less room for the fuel to puddle in the intake or condensate on the walls (loss of economy). I'm probably going to stay TBI however - less parts that move = less parts to break down on you.

As far as 305 vs 350 in an Fbody.... have no clue, I would expect a 3MPG loss if tunes were equal. My LO5 in a much larger, more wind resistant vehicle gets 15MPG average. Fast355 has posted some great F/E numbers however in a vehicle which may even be larger then mine, with lower (higher numerical) gears. Of course, I'm not sure if his flying bookshelf is more aerodynamic than my flying bookshelf, given that my flying bookself has this entire long "Wind Capture Device" attached to the rear....

Anyways... I would expect 2-4 MPG loss.

adambros

iTrader: (2)

It really depends on what components you use for your swap (heads, cam, manifold, etc and how good the tune is) -- but I did that exact swap, albeit with a slightly hotter cam, performance heads, headers, and intake and I'm getting about 16/22 after dialing the tune.

UnderCover89TBI

iTrader: (25)

im getting around 20 mpg in my 350tbi 89 camaro. has a camshaft, headers, free flowing exhaust and a couple other thangs..

86LG4T56

I'm getting 11/23mpg in my carbureted 305, so I'd say don't go with a carb if you want mileage. But you probably already knew that...

Jproz1167

iTrader: (3)

My car averages mid 18's to high 19's this is based on everday driving and fillups. I've never done a pure highway MPG test because there is so much traffic out here can't really expect my car to do well. This mid 18 to high 19 is basically a average in the commuting world with gridlock and all.

My engine is a L-98 with LO-3 injection. Your 2.73's would help alot I would think my car has 3.73's but even so my fuel mileage increased a bit from the old LG-4/automatic with 3.08 gears. With the LG-4 I got maybe high 18's but that was on a good day but it did have it's bad days of 15mpg.

If you stay with 2.73's I doubt you will notice more than a 3mpg drop may even stay the same. Hard to say but life is a gamble LOL take the good with the bad and make the best best out of it ...... You certainly won't miss the 305 I can tell you that. My LG-4 was probably equal to the anemic LO-3 maybe a bit worse.

Good luck

beatercoprice

4200lbs 92 caprice cop car with 3.42 posi and stock L05 150K. I get 20 mpg average.

V8Astro Captain

iTrader: (1)

I've been in a few "what mpg do you get?" threads. I would say the going MPG is mid to low 20's. Generally speaking

I didn't notice a MPG difference from 305 to 350. I've had a couple of the same vehicles where I did alot of switching around.

My current combo gets 19.8 MPG combined...consistantly. Read the sig tho...