Search



Go Back   Third Generation F-Body Message Boards > Tech Boards > Transmissions and Drivetrain
Register Forgot Password?

Transmissions and Drivetrain Need help with your trans? Problems with your axle?
Sponsored by Hughes Performance
Click Here

Welcome to ThirdGen.org!
Welcome to ThirdGen.org.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join the ThirdGen.org community today!


Reply
 
Thread Tools Search this Thread
Old 12-11-2009, 01:15 PM   #1
Member
 
Join Date: Sep 2006
Location: JSS Soto, Tallil IRAQ
Posts: 184
Car: 87 IROC-Z28
Engine: 414ci Twin Turbo
Transmission: T56
Axle/Gears: Ford 9"

Classifieds Rating: (0)
TH400 gas mileage

to make a long story short, I have a slipping 700r4 and I need to replace the tranny, I will be replacing it with a TH400.

With my 700r4 I was getting around 30mpg with a Holley Stealth Ram on an otherwise stock 350 with a good Megasquirt tune.

My question is how much will losing an overdrive gear affect my MPG?

If it makes an difference (and i know it will) I will be upgrading to a 427sbc, 210cc alum heads and a medium duration solid roller turbo cam.

Like i said before I have a Megasquirt with a Wideband O2 sensor, so I can run it fairly lean for improved mileage.

Mileage is very important to me because I NEED to drive it 2000 miles to get it to my new home. After I get it there, MPG is no longer important.

Thanks.

EDIT: I should mention that for the trip I am going to run a really tight convertor. Summit has a 1700-2100 stall Convertor for $99, hughes makes a "Fuel Mizer" TQ for $189, but I dont think that TQ will save me $89 worth of fuel compared to the summit.

http://www.summitracing.com/parts/HUP-GM5FUEL/
__________________
When I get back from Iraq:
Twin T70 Turbo'ed Solid Roller 414ci 4 Bolt Splayed Main Bowtie Block with Callies Crank and Callies I-Beam Rods.
B&G Megasquirt II, 120lb Injectors, Electronic Boost Control
T56, Ford 9"
Deep Dish Vette Z06 Wheels 18x9.5 front, 19x10 Rear

Last edited by IROC-You; 12-11-2009 at 01:28 PM.
IROC-You is offline vBGarage Page   Reply With Quote
Old 12-11-2009, 01:25 PM   #2
Supreme Member
 
Orr89RocZ's Avatar
 
Join Date: Sep 2003
Location: Pittsburgh PA
Posts: 20,073
Car: 89 Iroc-z
Engine: Twin Turbo 401
Transmission: TH400
Axle/Gears: 4th gen 12 bolt 3.42

Classifieds Rating: (20)

Send a message via AIM to Orr89RocZ
Re: TH400 gas mileage

depends on the gearing. My turbo car has 2.73s currently and with 26" tire it drives around very nicely... but overdrive would be great to have. If you have steeper gears like 3.42's or more, which are common for n/a motors, then you will be turning lots of rpm at 55-65 mph cruising speeds and its gonna suck on mileage.

motor combo also will determine mileage
__________________
1989 Twin Turbo IROC-Z
"Twin Turbo 401 Buildup Pics "
Photobucket 401 Twin Turbo
1009 whp / 844 wtq 24.5 psi pump gas only
Orr89RocZ is offline vBGarage Page   Reply With Quote
Old 12-11-2009, 01:27 PM   #3
Supreme Member
 
Orr89RocZ's Avatar
 
Join Date: Sep 2003
Location: Pittsburgh PA
Posts: 20,073
Car: 89 Iroc-z
Engine: Twin Turbo 401
Transmission: TH400
Axle/Gears: 4th gen 12 bolt 3.42

Classifieds Rating: (20)

Send a message via AIM to Orr89RocZ
Re: TH400 gas mileage

dbl post...

Last edited by Orr89RocZ; 12-11-2009 at 01:30 PM. Reason: dbl post
Orr89RocZ is offline vBGarage Page   Reply With Quote
Old 12-11-2009, 01:43 PM   #4
Member
 
Join Date: Sep 2006
Location: JSS Soto, Tallil IRAQ
Posts: 184
Car: 87 IROC-Z28
Engine: 414ci Twin Turbo
Transmission: T56
Axle/Gears: Ford 9"

Classifieds Rating: (0)
Re: TH400 gas mileage

Quote:
Originally Posted by Orr89RocZ View Post
depends on the gearing. My turbo car has 2.73s currently and with 26" tire it drives around very nicely... but overdrive would be great to have. If you have steeper gears like 3.42's or more, which are common for n/a motors, then you will be turning lots of rpm at 55-65 mph cruising speeds and its gonna suck on mileage.

motor combo also will determine mileage
I think it has 3.23's in it right now, i could throw in some different gears in the rear end just for the trip, but would it make enough difference to justify buying new gears?

I am looking at some Trip cost things on the internet, and getting 20mpg would only be $250 based on current gas prices. 15mpg would be $333, but I have a feeling I can squeeze 20mpg out of it with a good tune.
IROC-You is offline vBGarage Page   Reply With Quote
Old 12-11-2009, 01:43 PM
ThirdGen
1992 Camaro




Paid Advertisement


Reply

Go Back   Third Generation F-Body Message Boards > Tech Boards > Transmissions and Drivetrain

Tags
350, 400, 4th, combo, firebird, gas, gen, gm5fuel, good, hughes, mileage, th400, transmission, turbo, work
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

 


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 07:40 AM.


Powered by vBulletin® Version 3.7.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
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.

Emails & Contact Details