305 TBI gas mileage? - Third Generation F-Body Message Boards


TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

305 TBI gas mileage?

Reply
 
Thread Tools Search this Thread
Old 10-09-2017, 06:38 PM   #1
Junior Member
Thread Starter
 
Join Date: Dec 2015
Location: Boyertown, Pennsylvania
Posts: 77
Car: Firebird
Engine: 305 tbi
Transmission: 700r4

305 TBI gas mileage?

So Iím hearing a lot of people say theyíre getting mid to high 20s mpg, in their 305 tbi cars. Mines a 1991 firebird with a 305 tbi, it has 145k miles on it and has brand new injectors, fuel filter, completely rebuilt tbi, spark plugs, ignition wires, ICM, distributor cap & rotor. Mine gets consistently 14-16 mpg. Iíve never gotten more than 16 and never got less than 14, so how are people getting these higher numbers? The majority of my driving is high way driving too.
Mattkovitch is offline   Reply With Quote
Old 10-10-2017, 06:46 AM   #2
Junior Member
 
Join Date: Nov 2016
Location: Connecticut
Posts: 54
Car: 1991 Camaro RS
Engine: Hot 355ci
Transmission: Beefed TH350
Axle/Gears: 4:10

Re: 305 TBI gas mileage?

Got 2.73s with overdrive doing 55 on highway? I don't know what my car got stock, when it got to empty I filled it I'm sure some inflate numbers too.
Jacobaxeman is offline   Reply With Quote
Old 10-10-2017, 09:10 AM   #3
Senior Member
 
Join Date: Feb 2011
Posts: 856

Re: 305 TBI gas mileage?

Quote:
Originally Posted by Mattkovitch View Post
So I’m hearing a lot of people say they’re getting mid to high 20s mpg, in their 305 tbi cars. Mines a 1991 firebird with a 305 tbi, it has 145k miles on it and has brand new injectors, fuel filter, completely rebuilt tbi, spark plugs, ignition wires, ICM, distributor cap & rotor. Mine gets consistently 14-16 mpg. I’ve never gotten more than 16 and never got less than 14, so how are people getting these higher numbers? The majority of my driving is high way driving too.
That's not far off from what I get with my 350 K1500. I'd expect better from an F-body. The F is lighter, smaller engine, and more aerodynamic.

1. What is the cranking compression of all eight cylinders?
2. Restricted exhaust (Plugged catalyst, crushed pipes, damaged inner pipe wall, etc.)
3. Brakes dragging? (Stuck caliper pistons, seized emergency brake parts, etc?)
4. Ignition timing set properly?
5. Hilly terrain? Hills will kill fuel economy.
6. Cruise control working properly?
7. Tires inflated?
8. Transmission has four gears + converter lock-up? Or five manual gears?
9. O2 sensor failed?
10. What does the scan tool show for short- and long-term fuel trim?
11. Knock sensor retarding timing?
12. Coolant temp sensor failed?
Schurkey is offline   Reply With Quote
Old 10-10-2017, 09:43 AM   #4
Supreme Member
 
dmccain's Avatar
 
Join Date: Mar 2014
Location: Ms
Posts: 1,798
Car: 89 Trans Am clone
Engine: L03
Transmission: 700R4
Axle/Gears: 3.73 posi

Re: 305 TBI gas mileage?

Even with 3.73 gears I'm getting over 25mpg out of mine. Is the car running sound?
dmccain is offline   Reply With Quote
Old 10-10-2017, 11:58 AM   #5
Senior Member
 
Ghettobird52's Avatar
 
Join Date: Apr 2010
Location: Modesto, California
Posts: 976
Car: 88 Firebird Formula
Engine: LO5 5.7 TBI/Ebl Flash
Transmission: 700R4
Axle/Gears: 2.73 stock rear end

Re: 305 TBI gas mileage?

Everyone is going to have different values, relating to your driving conditions. If i purely drove freeway, my 350 with EBL can get 28mpg cruising at 60mph. Yet if i drove at 85mph same car, it would dip VERY fast.



If im WOT every street light i get 6mpg...

My Average for 90% city 10% freeway i get 11-12mpg. (350 TBI that is)
Ghettobird52 is offline   Reply With Quote
Old 10-14-2017, 03:47 PM   #6
Supreme Member
iTrader: (2)
 
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 7,925
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears


Re: 305 TBI gas mileage?

Quote:
Originally Posted by Ghettobird52 View Post
Everyone is going to have different values, relating to your driving conditions. If i purely drove freeway, my 350 with EBL can get 28mpg cruising at 60mph. Yet if i drove at 85mph same car, it would dip VERY fast.



If im WOT every street light i get 6mpg...

My Average for 90% city 10% freeway i get 11-12mpg. (350 TBI that is)
I could put my 5,300# G20 van to the floor out of every stop sign and traffic light and on every ramp when it still had a mostly stock 305 and still average close to 14 mpg. Running 75 mph down the highway it would get 17-18 mpg consistently. That was with a 1983 carb 305, 601 heads, 204/214 @ .050 cam with TBI conversion, doug Thorley tri-y headers, exhaust, and some chip tuning. I later rebuilt the same engine, changed the intake manifold, changed the camshaft to a stock 350 camshaft, and it would get 22-23 mpg running 70-75 mph with lean cruise enabled at 16:1 a/fr

Last edited by Fast355; 10-14-2017 at 03:57 PM.
Fast355 is offline   Reply With Quote
Old 10-16-2017, 09:16 PM   #7
Supreme Member
iTrader: (6)
 
DynoDave43's Avatar
 
Join Date: Aug 2013
Location: MICHIGAN
Posts: 2,305
Car: 1988 Trans Am
Engine: L03
Transmission: 700R4
Axle/Gears: 10 Bolt 2.73 Open

Re: 305 TBI gas mileage?

Interesting subject, and some interesting results.

I'm one of those nuts that keep track of every gallon of gas he buys. No, I don't always fill up at exactly the same pump...there are some MINOR variable. This is mostly in town, a few highway miles in there. And it's almost always driving a little faster, and accelerating a little harder from every stop than I ought to. There are NO economy runs on this page...no all highway, cruise control set, getting the best mileage I can runs.



So of the lowest averages are from a trip to the drag strip, or the Woodward Dream Cruise (4 hours of idling through traffic), or short fill-ups, and the next one is unusually high. Let me save you the trouble...that's an average of 18.1 for all of those.
DynoDave43 is offline   Reply With Quote
Old 10-18-2017, 12:47 PM   #8
Supreme Member
iTrader: (2)
 
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 7,925
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears


Re: 305 TBI gas mileage?

Quote:
Originally Posted by DynoDave43 View Post
Interesting subject, and some interesting results.

I'm one of those nuts that keep track of every gallon of gas he buys. No, I don't always fill up at exactly the same pump...there are some MINOR variable. This is mostly in town, a few highway miles in there. And it's almost always driving a little faster, and accelerating a little harder from every stop than I ought to. There are NO economy runs on this page...no all highway, cruise control set, getting the best mileage I can runs.



So of the lowest averages are from a trip to the drag strip, or the Woodward Dream Cruise (4 hours of idling through traffic), or short fill-ups, and the next one is unusually high. Let me save you the trouble...that's an average of 18.1 for all of those.
Definitely interesting results! It is also interesting to see how the march of technology has helped power and mpg. You can have much more powerful engines getting better mileage in heavier vehicles now days.

I actually kept a log on Fuelly.com for my 2012 Titan when I owned it. Logged more than 15,000 miles worth of driving. That included everything from towing heavy trailers, often loaded to near payload capacity, to driving into the mountains, to daily stop and go traffic. My highway speeds are higher than most as well, ranging from 75-90+ mph.

http://www.fuelly.com/car/nissan/tit...titansv/134758

I have not kept a log on my current car, but the car has its own log and I have stayed at an ECM calculated 19.6 MPG for the past 24K miles, since I reset the total accumulative. The ECM was accurate enough that I have not kept a log outside of what the car shows because it was accurate within +/-0.2 mpg the times I checked. 2011 M56S weighing 4,400 lbs empty making close to 500 HP at the crank. With myself and 2-3 passengers I am often rolling down the road at over 5,000 lbs.
Fast355 is offline   Reply With Quote
Old 10-18-2017, 07:18 PM   #9
Supreme Member
 
dmccain's Avatar
 
Join Date: Mar 2014
Location: Ms
Posts: 1,798
Car: 89 Trans Am clone
Engine: L03
Transmission: 700R4
Axle/Gears: 3.73 posi

Re: 305 TBI gas mileage?

My carbed, cammed, vortec350 in my last trans am avg 16-18 mpg and the torque converter wasn't even locking up.
dmccain is offline   Reply With Quote
Old 10-19-2017, 07:59 PM   #10
Senior Member
 
Arctic White 91 RS's Avatar
 
Join Date: Apr 2000
Location: Terre Haute, IN & Gastonia NC
Posts: 557
Car: 91 RS/99 T/A/72 vette
Engine: L03/LS1/Dart400
Transmission: A4/M6/TH400
Axle/Gears: 2.73 / 4.10 /3.08


Re: 305 TBI gas mileage?

When my white 91RS was a 305 TBI 700r4 w/2.73 gears 30+ was easy on the highway. Car was in ideal state of tune, good tires properly inflated, good alignment, all maintenance meticulously done. Friend of mine didn't believe it was possible to get 30 mpg in the car. He was with me when I filled the gas tank at the same pump and the whole 440 mile round trip. It was almost all interstate. He was with me when I refilled the gas tank with ~14.4x gallons of gas. The RS odometer was within 1 mile of GPS on mileage covered.

Made a believer out of him that my white RS could get 30+ mpg.

The white RS could get 32-33 mpg consistently. Some of it is driving style. Easy on the gas

My 91 RS Convertible can only hit 28.5 mpg, same maintenance etc. I suspect the transmission in the convertible slips just a hair.
Arctic White 91 RS is offline   Reply With Quote
Reply


Go Back   Third Generation F-Body Message Boards >

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Advertising
Featured Sponsors
Vendor Directory

1982 Camaro '82 || 1983 Camaro '83 || 1984 Camaro '84 || 1985 Camaro '85 || 1986 Camaro '86 || 1987 Camaro '87 || 1988 Camaro '88 || 1989 Camaro '89 || 1990 Camaro '90 || 1991 Camaro '91 || 1992 Camaro '92


All times are GMT -5. The time now is 04:55 AM.


All content copyright © 1997 - 2014 ThirdGen.org. All rights reserved. No part of this website may be reproduced without the expressed, documented, and written consent of ThirdGen.org's Administrators.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: