I was wondering if someone could clarify the correct ratio for highest fuel economy? is it better to have 2.84 or 3.33? also, on the 4t60 if anyone had the tag codes to identify what the ratio is? I plan on going to the salvage yard soon and want to be able to get the correct one. this will be put in a plain 2.8 fiero, nothing fancy just want more mpg..

The lowest gearing will get you the best fuel economy which should be the 2.84 ratio.

Here is a partial list of ratios: http://lesabret.com/phpBB/v...opic.php?f=13&t=7237

Theres another site with a full list though, I'll see if I can find it.

the 2.84 should get better millage than 3.33 you will turn less rpm on the highway

If it in the car then check RPO code. Fiero's RPO code list is left inner fender.

Auto tranny has 2 code. 1 is tranny. 1 is tranny ratio.
See cave. gear ratio.

code:

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LOCATION OF RPO LABEL
To find the location of the RPO label, you can look at the Carline chart below.
 Locations of RPO labels vary by "Carline." To determine the
"Carline" refer to the 4th and 5th digits of the VIN label on 1985 to present automobiles, 
5th digit for 1982 to 1985 automobiles and 6th digit for
all trucks. See: Vehicle Identification Number (VIN)
TYPICAL RPO LABEL
A typical RPO label is shown in the accompanying image.
CARLINE LOCATION
A ......... On spare tire cover or RH rear wheel well.
B35 ...... On spare tire cover (85-91).
B35 ...... On rear quarter panel (92).
B19-69... On deck lid.
C ......... (Oldsmobile & Buick), On deck lid, on spare tire cover, underbody, or jack storage container.
C ......... (Cadillac), On spare tire cover, underbody, or jack storage container.
D ......... On deck lid.
E ......... On deck lid (85-90).
E ......... On underbody spare tire well (91-92).
F ......... On console door (85-90).
F ......... On inside of rear quarter trim panel door.
G ......... On deck lid.
H ......... On deck lid, underbody, or jack storage container.
J ......... On spare tire cover.
K ......... On LH rear door or on deck lid (85-90).
K ......... On underbody spare tire will (91-94).
L ......... On spare tire cover.
M ......... On spare tire cover.
N ......... On deck lid (85-87).
N ......... On spare tire cover (88-94).
P ......... On front compartment LH fender well.
R ......... On spare tire cover.
S ......... On spare tire cover or deck lid.
T ......... On spare tire cover.
U ......... Inside of glove box door.
V ......... In spare tire wheel well.
W ......... On spare tire panel cover.
X ......... On spare tire cover.
Y ......... Under rear floor panel compartment (84-85).
Y ......... On front floor console door (86-94).

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Carline: VIN character position 4

No need in/under car to check id tag.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

[This message has been edited by theogre (edited 10-04-2009).]

https://www.fiero.nl/forum/Forum2/HTML/102795.html

Awesome information.. thank you guys a ton! hey lemme ask though.. if my fiero th125 is 3.33 and i'm doing 3500 rpms ar 60, with a 4 speed 3.33 will it still be 3500 rpms at 60? i know the 333 is the lower gear box, just using it for an example.. I want the 2.84 for mileage..

If your turning 3500 rpms @60 with a 3.33 Th125, then with a 4t60 3.33 you'd be turning 2450 rpms. I presently have a 4t60 in my 85 GT with a highy modded 3.4 with a 3.42 ratio and get about 30 mpg on the highway. I think I'm turning 2400 at 65-70mph. If you go too high of a gear it could hurt your mpg. Also with my 3.42 gear my ratio changes to a 2.39 in OD (4th gear), 3.33=2.33, 2.84=1.98. I personally would go with the 3.33 since you only have a 2.8, you have less torque that my 3.4. I'm after performance and your after MPG

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85 GT 3.4
14.9 @ 90 1.9 60' Old TH125/3.06
Unknown New 4T60/3.42

I turn 2400 rpm at 70 mph with a 3.33 ratio and 275/40 17 rear tires. My trans is a 89 4T60 out of a Cadillac. It is powered by a 96 LT1. I don't have an accurate mileage figures yet, only have about 1000 miles on the setup and I just keep adding gas when I need it... My build is located at www.v8-fiero.us

Actually there are 12 different combinations for gear ratios with this trans. 3 finals to choose from 3.33, 3.06, 2.84. There are 4 different chain ratios also 33/37, 35/35, 37/33, 38/32. Final can range from 3.73 to 2.39 depending on how you set it up. This site is a good read if you have the time...
http://spacecoastfieros.com/tech/440-4T60/

There is also a stronger F7 version if you can find it. They were in the cadillac Allante only. When looking for the lowest ratio look at 90 and older 4.5 cadillacs. 91 and up went electronic shift. Cadillacs had the lower ratios to start with because of the V8 engines. Best of luck.

EDIT: Just an FYI. Be careful going too low on the final drive. You need your alternator to turn fast enough to keep from killing the battery on long drives.

[This message has been edited by Fieroseverywhere (edited 10-05-2009).]

quote Originally posted by Fieroseverywhere:...Be careful going too low on the final drive...

Can you really go too low using one of the GM transmissions? I could see some aftermarket mod letting you go too low but I would think that none of the GM options would make this an issue.

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RickN
White 88GT 5spd
White 85GT Auto
White 99 F250SD 7.3PSD 6spd
1956 Ford 860 Tractor w/ Freeman Loader
20Ft Tilt Bed Trailer

Too low/high ratio deepens on application. Can you wreak the tranny? Maybe. Sticky Tires and/or Big Engine....

4T60 trany ratio can use 3 chain and 3 Final gear. (TH125c/3T40 uses 4 chain and 3 final.)
4T60 The highest possible is 2.53:1 (RPO F16) and lowest is 3.73:1 (RPO F77)
You want 2.84? Check RPO Code or Trans ID... 3.18:1 trans ratio but with 2.84 final.

Again... See Cave. Gear Ratio. It covers all of this.
And option & project, aod convert. see math.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

[This message has been edited by theogre (edited 10-05-2009).]

thanks again everyone. i did some printouts of the transmission charts and where to find the rpo tags ( that was a major help ) I think for my high mileage 2.8L i'll try to stick with a 3.33 non electronic overdrive. I just hate the sound of 3500 rpms rolling down the highway, and at 70 mph I just keep waiting for something to blow.. I doubt it will but i'm very use to the pontiac's running so quiet and smooth that it just worries me. a little gas mileage will go along way and also less rpms might save the engine for a while longer too. its got 151k on it now, and i'd like to see it achieve 175k before pulling this engine.. or at least till I finish up the 1985 gt with the 3800 swap.. one hurdle at a time.. I bought a 3.33 for the supercharged one thinking it was the higher mileage tranny. my bad but I can live with it. for now though i jsut want to get this tranny in the car before snow flies here in Pa. then finish up the 3800 one... so many things to do... so little time.