Ashton89iroc

Hey guys, I've been noticing people saying "i have an '87 5.0 TPI and i get 18 HWY" or " i have a '90 5.7 TPI and i get 21 HWY"....and its not just on here, but everywhere! i did a google search for IROC-Z MPG and this is what i come up with. I guess what I'm trying to say is it confuses me how they're all getting such horrible gas mileage! I own an '89 IROC with a 5.7 TPI and auto trans...and i get 27 HWY and 18-ish CITY, how on earth are people getting 18-22 MPG with practically the same set up?

People badmouth our cars for their shitty MPG and i turn around and say i get 27 with a 350 and they flat out call me a liar. Am i the only person that finds that strange? Give me your thoughts on this....oh! I'm wanting to toss a T-56 in my car, manuals generally get better MPG...how much do you think this would help my fuel economy?

LilSki

iTrader: (1)

I'm sure this kind of thread has been covered before but I'll bite. My car may not be the best example as I am not running a stock motor and I'm also not running a stock computer. I run a 350 vortec with a 96 Fbody LT1 cam with no EGR or cat and a T56. I average around 17 around town and that is not driving nicely either. On the highway I hang around 25 MPG. Now I'm sure I could squeeze some more MPG out of my setup by messing with the timing tables and fuel mapping some more but I'm happy with what I am currently getting.

Guest

1992 Camaro Z28 L98 350 bone stock:16-17 city(casual driving), 26-27 highway.

Ashton89iroc

I hope I'm not being "that guy" who just posted a thread thats been covered 12 other times beforehand, haha. i tried searching, but didn't come up with much (hate the search engine on this site, its my only beef here)

but yea, you probably lay some weight on that gas pedal of yours and you still get arguably decent gas mileage. it just baffles me how i get called a liar and that i don't know anything about cars just because my fuel injected 350 gets better gas mileage then their carb'd 383! hell...even their fuel injected 305, haha

Ashton89iroc

thats TPI then eh? did the later end models even come out carb'd?

gta_knight

i done the test on mine a couple of years ago and i was getting 16.7 MPG around town, and when im in the Trans Am i dont just tootle around, i like to pull away from lights and junctions with enthusiasm, lol

on the motorway i got 24.7 MPG so i just thought that was normal.

since then ive had a stainless exhaust fitted, no CAT, all emissions removed, hooker headers fitted so i would imagine im getting less now

lonestar7

iTrader: (1)

Only done 4 fill-ups so far, getting around 16MPG with almost all in town driving.

http://www.fuelly.com/car/pontiac/firebird/1988

Ashton89iroc

does higher air flow really kill your MPG? I was always told the opposite, if your engine can breathe better it actually HELPS it. i understand the combustion process, but just because an engine is pulling more air in, doesn't mean its burning more...look at people who have turbos on their cars...turbos don't hurt gas mileage at al from what i understand. am i wrong on this?

Camaro86IrocZ

iTrader: (1)

Rear End Ratios will make the difference, 2.77 vs 3.23 vs 3.42 ect....

Thirdgen89GTA

iTrader: (5)

Pure 160 mile highway trip, avg speed was probably 60mph or so, I kept it close to speed limit most of the way.

32mpg.

B-body LT1, CAI, Tune, !EGR, full exhaust, cruising in 6th with a M28 T56.

Ashton89iroc

wow! thats really good. I've been wanting to put a t56 in my iroc (currently automatic) think this would add a few mpg?

85 roc it

Must be nice. My 383 6sp get about 14-15, thats driving nicely also

Thirdgen89GTA

iTrader: (5)

B-body LT1's have ridiculously small camshaft profiles. Max HP was about 5100rpm, max TQ was about 2800rpm.

I was using some hypermileing techniques on that trip, using Semi's to draft, keeping the engine speed as low as possible, coasting as much as possible.

I did the same thing on the trip back using Wisconsin's better gas with less ethanol content and eeked 34mpg. Though the Wind might have been in my favor on the trip back too.

50/50 mix was about 24mpg or so.

Same engine/mods with a broken 4L60E (wouldn't go into OD, and no TCC Lockup) netted about 17mpg highway with an average RPM of 3000rpm or so as shown in this video:


Before anyone yells at me for driving on a broken trans, it was a PCM/harness issue I never cared to track down. I drove the car for about 17,000 miles like that and it was decently happy. Every video of it at the strip is on that broken trans.

The T56 was sitting in a garage pending some swap parts for a long while, all freshly rebuilt and such.

88FormulaF_Bomb

iTrader: (1)

88 l98 2.77 gears 17-18 city 25-27 ooorrrr 14-17 highway depending on my mood ; )


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Podium

iTrader: (2)

I average about 22-26 a tank city/highway combined. 89 t5 lb9 3.08 rear

LostX

iTrader: (1)

88 l98 350 converted to a 670 vacuum secondary carb. .480 lift cam and headers. 3.42 rear gears. mid to low 12's in quarter mile. 87 octane gas. 13 city - 26 highway. spark plugs gaped to .042. Engine has well over 100,000 miles on it from what ive been told. it puts out alot of smoke out the valve cover breather. And puts out alot of black sut when you hit the gas hard

with the new t5 i put in it just idles on the highway. 81 mph = 2000 rpm. 70 mph is about 1600 rpm . with 3.42 rear gears

it could easily get close to 30 highway when i replace my cheapo chinese ebay coil and module with a correct one. and fix my horribly bent axle shaft. i know the highway vibrations are killing effiecincy

car weighs about 3000 pounds which helps

fireburdluvr85

lately 17.5 highway, was 27 highway with my last engine. city seems to be about the same lately.

L695speed

Been averaging 15 making runs around town with a shift kit and 3000RPM stall 700r4 L98 GTA that has an LT1 cam in it and 3.70 gears. Its been consistent. If I do the heads and have it tuned I may get better than that.

dieseldog

Same here average about 15 mpg with L98.

insomniac

iTrader: (3)

13 ugh

erik69&85

iTrader: (1)

92Z, 5.0 TPI, T-5 manual, Bone stock driveline - started at 19mpg on the highway after the car had been sittingfor 6 years with the previous owner....

swapped in some Bosch Fuel injectors from Southbay - upped to 26 mpg highway, 20 city

No joke....... getting good fuel atomization goes a LONG way!

Ashton89iroc

how much did those bosch injectors cost you? probably a pretty penny id bet.

Buggy Disaster

iTrader: (1)

I get around 13mpg with a mostly stock 305 TPI.

theBIRD2445

a solid 14 on winter gas and a heavy foot.

me420

87 iroc 5spd 3.42 gears 19 city 25-28 highway

seafire

I have a crate 350 i am currently getting 14/10 highway/city how to fix do i?

LostX

iTrader: (1)

first thing to check is to make sure you have no fuel leaks. i found 2 leaking lines under my car and a leak out the top of my gas tank that im currently fixing

seafire

i have the carpet out above the gas tank and there is a hole were the metal is cut out so the fuel pump could be replaced. i replaced all the lines about 5yrs ago so they should be fine but ive always got that kinda mileage since i put the new motor in in 2007. i dont know but i feel like the carb is really rich, if i am idling and smash the petal in first, it just floods...should i do something to the carb?

LostX

iTrader: (1)

well my 350 has well over 100,000 miles and its got a 670 carb getting about 28 on the highway now so something is wrong with your setup. Try tuning the carb or adjusting the timing. adjust the floats too. what kind of ignition system do you have and what are your plugs gaped to?

seafire

Well that's an eye opener. Ill have to look into that, thank you LostX.

LostX

iTrader: (1)

ive also got 3.42 gears too so don't blame your poor mileage on the rear end ratio

Sean O'Hara

1988 Trans Am GTA L98 Auto Bone Stock
16 mpg/24mpg and I drive the **** out of it.

cuisinartvette

40 mpg with heads stroker nitrous blower and turbo and Im on it all the time.

camarofvr

5.7 tpi with 204/214 edelbrock cam and 700r4. Got 20 mpg on the highway last time I checked but it would have probably been better if I hadn't got it up to 102 mph a few times.