i dont kno where to post this question but this looks like a good place. i just turned 16 and im bout to start driving my 5.7 TPI and i was wondering what kind of gas mielage you guys get. cause im gonna be goin from home to school to work then to home. any body even keep up with what kind of gas mileage your cars get? well let me kno thanks

 

If I baby it, I can get 19 mpg, but I goose it up long hills and stuff and usually get about 15-16. My bad 02 sensor isn't helping that at all.

 

In good weather keeping my foot out of it I can get around 17mpg in the city and 22+ on the highway.

 

14mpg in town, 19mpg highway. My hotcam doesn't help much.

 

If i rod on it a lot 16mpg seem to be what I get out of it but I can pull 20mpg if I take it easy.

 

I guess I'm about average 14 to 15 in town and 20 to 21 highway. Of course I'm running 389 cubes.

 

I got 19mpg on a 300-mile trip with my 355ci/5.8L with 10.5:1 compression and a decent sized cam 224*/230* and 3.23 gears out back. This included a little bit of topping my car out on the open freeway and sitting in traffic for a while before getting on the freeway.

Keep in mind I don't have a working speedometer and thus don't have the highway mode for spark/fuel and also no torque converter clutch lock-up. The combination of those two would probably give another 20% highway gas mileage. My front right tire is out of alignment after I replaced my struts to the point where I can see the steel bands on the inside shoulder of the tire. Not to mention my car is really out of tune as well. Running a stock '89 Corvette tune with my mildly ported heads, LT1 intake, moderate cam, and large-tube headers.

I'd bet I could pull mid-upper 20s for highway MPG once I get all of that stuff fixed and tuned. I'm also installing an MSD 6AL ignition next weekend which should help a bit to make a more efficient burn as well.

 

you will never get good gas milage..you'll be too busy burning rubber and smokin' the imports

 

I usually average 22-24 and if I stay around 70mph on the highway I can get 26-28 out of her.

 

the last time i got 18.5, but i had two relays switched. this time i filled up and switched the relays back, ill let you know what i get this tank.

 

My buddy's 87 GTA was getting about 18-19 in town, and 22-23 highway. It s 9:1 355 w/ a 220/230, 497/502 cam. Stock chip/tune, mildly ported heads/plenum, 700R4, 3.27 gear. - He's stealthramed now, so not sure about current town but I know its still pulling 22-23 highway...

later, justin...

 

I pull 15 - 16 in town and then 25-27 on the freeway, even through the mountains. I'm happy. I don't have an economy car by any means but it does very well for what it is.

 

I only get about 12 mpg, granted I play with it a lot. But I should be getting a lot better.
This is City, and I haven't gone on any long highway trips in a while to tell ya that number yet.

 

I got 26.9 mpg with the T56 and 3.42's with my rebuilt low compression L98 going through the mountains in traffic with low tire pressure and extra weight while slightly untuned.

I think it could hit 30 in 'perfect' conditions.

 

what do STOCK 5.7 TPIs get?

my 3.1mpfi 4-speed/3.23s got 27-28 consistently... 85mph highway.

I got less than 19 in the city though... isn't that a huge difference?

I am planning on getting the 1990 5.7 TPI... I was really hoping I'd get somewhere near 25+ for highway...

 

I got 313 miles to the tank cruising at 70mph (80% highway driving) in my 350.

 

I got 313 miles to the tank cruising at 70mph (80% highway driving) in my 350.

 

yeah, but what mileage? I don't know exactly how many gallons are in your tank.

 

22 MPG city including 4 passes using 150 shot of nitrous.

The secret lies in the little piece of silicon in the dash.

 

Do thirdgens have any other tank than 15.5 gallons?

 

I thought some had different tanks

 

i think theres something seriously wrong with my car then cause i havent really done anything to it and i havent been goin hard on it all teh time and im gettin 11.8 miles to a gallon. thats crazy there has to be something wrong like that little skip thats in the motor must be causing bad gas mileage.

 

maybe you need some ignition work.

 

I'm getting over 24.6 now combinded city/hwy. When I first bought the car it was getting low 13's. A total TPI tune up is what it needed.

 

hey halfinchwinch what all did u do during the tune up? cause my gas mileage is like yours was so what all did u do?

 

https://www.thirdgen.org/techbb2/sho...hreadid=327219

More detailed approach to what I consider a total TPI tune up.

 

Man too bad you couldn't get the L98 with a six speed it'd probably do better than the LT1. Some of you are getting 25 mpg with autos In stock trim I got my best mileage on a run from okc to tulsa at about 85 or 90 mph getting about 30 mpg. That massive 6th gear helps a ton on the highway.

If mileage is a real priority I'd look at doing a 6 speed swap, not only will you pickup serious mileage the car will be more fun to drive and you can really keep it in the TPI power band. I've been in a couple L98 cars with 6 speeds and WOW...

 

I have an 18.x gallon tank in my IROC. Came from a 1992 Formula 350 car.

best I have gotten is 418 miles on 16.8 gallons, that was pretty much all highway cruising at 80 mph

 

When my engine was bone stock with no modifications to the eprom, I got about 23-25 US mpg. With the engine bone stock but tuning the eprom to optimize for fuel economy, I got 29-30 US mpg.

 

a lot of the late 4thgen trans ams with the m6 and 3.23 get 30mpg in 6th gear, cruising at 70-80mph... you can't go any slower in 6th

 

You can its just got no real acceleration below about 70 in 6th. I switched to 3.73's and it made a HUGE difference on 6th gear. Even though I'm only turning a couple hundred rpm more it made a big difference in 6th gear throttle response.

 

I have 3.27s in my car right now, and i pretty much hate it. I don't shift to 6th till 70. It's pretty useless below that even for light throttle cruising.. it's like trying to start from a stop in 3rd, even 5th is annoying at 50 mph it's not quite enough, but 4th is too much

Spring will be better, that's when the 4.11 dana44 goes in

 

Ohhh my...3.27 gears and a T56? Thats gotta be unbearable in 6th gear. 3.42s with my LT1 in 6th was rough especially if it was more than about a 5% grade. 3.73's woke it up quite a bit 4.11s = but you'll see a mileage drop, probably a significant one

 

I think the new trans ams have 3.42 gear ratio... if you can hardly maintain speed in 6th, would it be better to shift down to 5th to climb hills, or to put in taller gears and stay in 6th gear?

 

When I had 3.42's I had to downshift to 5th to make it up steep hills at 65 or 70mph, otherwise I'd lose speed. Sometimes on the back roads heading to the lakehouse even with 3.73's I give her a downshift just so she doesn'thave to work as hard up steep grades.

 

Damn, I couldn't imagine how fast those new WS6's would be with say, 4.11 rear end gears... it might be too annoying to shift... don't you shift pretty early in a 6-speed? like 20mph for 1st gear?

 

I can run first to 41 or 42 mph but remember with an LT1 I'm shifting at 5700 rpm.

 

not too worried there, since the car isn't a daily driver. It's pretty much just for fun.

 

out of curiosity, what is the MAXIMUM gas mileage you can get out of these v8s (3rd or 4th gen?)

like, what if you put in 2.73s or something? Can you get over 35mpg on the highway, or will the engine be at too low of an RPM to even function in 6th gear?

 

2.73's make 6th gear useless literally, its just too tall at that point. Then you beat up your bearings using 6th gear and your mileage wouldn't be too good because you'd be deep in the throttle with very small changes in elevation. I got about 30mpg peak in my car, LS1 cars can get 32 to 33 mpg with 3.42 gears.

 

3.42 is stock... that's promising, because that's more than I got with my 3.1... what a difference technology makes!