MPG difference between 2:73s and 3:73s

Hawaii-50 · Aug 19, 2005

I am about to buy a house that is twice the distance from work than my current apartment. I'm looking at 72 miles round trip and I currently get 17-18 hwy. She's my daily driver/only car and I need to give her the longest legs possible since gas is going through the roof. Buying another car is out of the question now that I have a mortgage, so I figured this would help. Any ideas/thoughts?

Thanks-
Ted

tjm73 · Aug 19, 2005

a significant drop in acceratablity.

You'd probably gain 3-5 mpg probably a bit more.

I recently got 22 mpg (I think, can't remember for sure) with my 90 GT with a B303 and 3.73's on a 200 mile round trip.

So I think you should be able to get at least that with 2.73's.

Grn92LX · Aug 19, 2005

You probably won't notice a difference except at first when your having fun with your new 3.73's. Driving normal on the highway, I garantee you won't notice much if any mpg drop.

5spd GT · Aug 19, 2005

I would drop it down to around a 3:27 gear ratio to keep you at a more effiecent rpm on the highway where the power you have at that particular rpm can sustain you against the wind resistence.

Personally I would just keep the gears. It won't outway the cost for a very long time with the cost of gears/install.

I get 24mpg with my 373's and h/c/i and that is 70/30 highway/city.

Hawaii-50 · Aug 19, 2005

Sorry if I wasn't clear. I currently have 3:73s and may swap them for 2:73s.
Oops.

tjm73 · Aug 19, 2005

Hawaii-50 said:
Sorry if I wasn't clear. I currently have 3:73s and may swap them for 2:73s.
Oops.

My post was in the terms of you have 3.73's and want to go to the 2.73's.

5spd GT · Aug 19, 2005

So was mine...

crazypete · Aug 19, 2005

I got my absolute best highway milage to date with 3.73's. The 2.73's impose too much load and less torque multiplication so you end up having to power through everything instead of letting the gears do the work....if that makes any sense.

Chances are, you'll gain back 2 maybe 3 mpg but the cost of the install will far outweigh the benefits and your car will be much slower and less fun.

stang1986GT · Aug 19, 2005

crazypete said:
I got my absolute best highway milage to date with 3.73's. The 2.73's impose too much load and less torque multiplication so you end up having to power through everything instead of letting the gears do the work....if that makes any sense.

Chances are, you'll gain back 2 maybe 3 mpg but the cost of the install will far outweigh the benefits and your car will be much slower and less fun.

This is interesting. Why do some people say that 3.55 is the best of both worlds due to gas mileage then? Don't get me wrong, I'm not disputing you...just trying to learn. I never in my wildest dreams thought that any 5.0 with 3.73s could get in the 24 mpg range, as 5spd GT stated. If this is true, what would be the advantage of 3.55s?

(Sorry for the thread highjack)

crazypete · Aug 19, 2005

You end up with better gas milage with steeper gears through the operating range of your highest "gear" on the transmission after that point, you will lose milage.

A lot of folks report better city milage with higher gears. This is because the motor doesnt have to work as hard to push the car around. It's torque is being multiplied better. At higher speeds, you run out of transmission gearing and then wind up but still, the motor has extra torque multiplication so you're burning less gas at 3000 rpms with 3.73's than 3000 rpms with 2.73s from the reduced load.

If you learn to drive the car "on gears" rather than through power, just letting it roll through its gears and shifting at the right point, barely feathering the throttle the whole time, you can get really really good milage. Helps to install a vacuum guage and drive by it. Then you can really see what actual effects your input is having on engine load.

DW5.0L · Aug 19, 2005

My car originally came with 2.73's. I used to get anywhere from 22-28MPG's over the course of the life of the original engine. I now have 3.73's waiting to go in once the rebuild is over. I never got more than 16 in the city.

crazypete · Aug 19, 2005

Install a vacuum guage and drive by it. Then you can see which of your driving habits are the culprit for low milage. Any time the guage dips, you're loading up the engine.

Hawaii-50 · Aug 19, 2005

Crazypete-

Specifically, what kind of vacuum gauge, and where do you attach/mount it? For optimum mileage, what kind reading should one aim for? I try not to shift above 2K rpms.

Thanks-
Ted

Daniel50 · Aug 19, 2005

i personally got better mpg with 373's sine you dont bog the car so much to highway speed

luckythirteen13 · Aug 19, 2005

i get 20mpg at 100mph on the freeway with my 3.73's. i say dont bother switching the gears

93 teal terror · Aug 19, 2005

I get 26mpg with 2:73s on the highway and used to get 28 before I added the t body. Around town I get 21 or 22.

txstang84 · Aug 19, 2005

man, i can't wait to get the FI swap on my car...i used to get 22-24 highway, 12-16 city with 308's, when swapped to 373's, new numbers were 16 highway, 10-12 city...

355's weren't much better...

Dtowncats · Aug 19, 2005

How are you guys managing these numbers with 2:73s? The most I ever got was 21 mpg on my way down to OC, Maryland. I routinely get 17 mpg now with new 02 sensors but that is about 70% of my driving on the highway. I don't mean to jack the thread but what can I change or check besides my driving habits to get better gas mileage? The engine is all stock and I have a full exhaust. Thanks guys.

Hawaii-50 · Aug 19, 2005

Dtowncats-

Don't worry about jacking the thread. I think we could all benefit from some mileage gaining tips.

crazypete · Aug 21, 2005

Actually you want to shift more like 2500 or so. But dont race to get up there...just let the gears slowly run out to 2500. If you shift at 2000, you'll be bogging in the next gear right away then using engine load to muscle through it.

Actually this is how most people drive which is why everyone complains about getting awful gas milage.

The vacuum guage is the basic summit/autozone $10 vacuum guage with a long rubbber vacuum hose run out and plugged into ...the intake optimally...or the vacuum tree. Your car idles at 21 hg vacuum. You dont want to dip much past 16 hg. Drive your way and you'll probably see yourself down near 13-14 hg then do it my way and see that you can drive around 17-18 hg, motor barely breaking a sweat. This works better with high gearing....the 2.73s will bog down the car almost always

MPG difference between 2:73s and 3:73s

Hawaii-50

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