the difference of gas milage between gears

[chefster]

with all the talk of 373s..I am tempted..what difference is the rpms at 80 between the 373 and my 308s....94 Cobra

 

[Joe 5.0]

My mpg is the same with 3.73's as it was with 3.08's. The highway rpms are higher, but the car doesnt have to fight to get off the line. At 80mph I am turning ~ 2700 rpm. 4.10's would probably be about 3k rpm.

 

[CManT1914]

With 3.73's, I'm turning 2250 at 70 mph, about 2600 at 80 mph, and 3000 at 90 mph. My gas mileage actually improved with the 3.73's. In town I'm getting at least 17.5 mpg, and on the highway, around 25 or so. Get em, you won't be disappointed.

 

[greg@berkeley]

i got about 16 w/my 2.73s, and i got about 17-18 w/my 3.73s before the h/c swap. i got 19.5 after the swap but before i started tweecing. now i get about 18.5. i need to make a gas mileage tune...

 

[Black95GTS]

I don't see how you can get better gas mileage with steeper gearing. If you go from cruising 80 at 2000 rpms to cruising 80 at 2700 rpms, wouldn't gas mileage be worse?

 

[igotyofire]

I don't see how you can get better gas mileage with steeper gearing. If you go from cruising 80 at 2000 rpms to cruising 80 at 2700 rpms, wouldn't gas mileage be worse?

thats what i belive, also i dont see how up above i just asked the same question but how would H/C change help out the gas mileage, i thought better flow means more air, and more air = more fuel, = more power is exactly what someone said the other day, so less gas,heh.....but also belive the engine is working harder to breath in some instances....

 

[greg@berkeley]

bigger heads make the engine more efficient. more efficiency=better mileage because the engine doesn't have to work as hard to get to a certain rpm/speed. also, there is no reason high-power efi cars can't be fuel efficient. it's kind of a myth that carried over from the inefficient carb days, i think.

i have no scientific evidence to back this up, but this is what i have learned. someone please correct me if i'm wrong!

 

[swingline]

If you keep your foot out of it, there is no reason a H/C/I car can't get just as good gas mileage as a stocker.

 

[Joe 5.0]

My gas mileage IMPROVED when I went from 3.08's to 3.73's, believe it or not.

My attempt at reasoning for this? I say that since the engine doesnt have to work as hard all the time to overcome the tall gearing it is under load less, thus uses less fuel. I dont have to downshift into 4th to pass on the expressway because 5th now has some passing power, whereas with the 3.08's it was an absolute dog. Plus, off the line the engine would bog if you didnt slip the clutch off the line but now it is almost difficult to bog it even if you let the clutch out entirely right off idle.

My last tank of gas I got 18.5mpg. This was with a trip to the track and 1/2 tank of gas driving in 4th @ 75mph. I did this because I wanted to burn some gas before I got to the dragstrip. I usually get 20-21mpg even with pretty aggressively driving and LOTS of WOT and 5k rpm shifts.

 

[ARed1995GT]

we dont buy these cars for gas mileage, hehe

 

[Joe 5.0]

Very true, but it's nice to know you arent schitting out $$$ because OPEC decides they are gonna be arseholes.

 

[Mrgreen94gt]

I noticed no change in mileage with 4.10s. Nothing that I've done to my car has effected the mileage any.

 

[CManT1914]

I dont have to downshift into 4th to pass on the expressway because 5th now has some passing power, whereas with the 3.08's it was an absolute dog.

You thought 3.08's were bad, try some 2.73's! Now those were some horrible gears.

 

[Black95GTS]

alright, I'll buy that it MAY help you out in a stop and go situation. But in the situation that I proposed above, there is no way that an engine revving higher consistently will have better gas mileage then one that is revving lower. I'll put 10 bucks down and say this: Get two of the same cars side by side, full tanks of gas, one with 273s and one with 373s, and have them both drive at 65 miles per hour for 1 hour. The one with 273s will get better gas mileage as it is not revving as hard, thus the engine is not working as hard to sustain the 65mph.

I can definately understand how an H/I setup will affect gas mileage positively. However, when those of us that get Cams get these radical setups that crank open the intake stroke of the piston and shove more fuel in there, that will negatively affect mileage.

 

[gcomfx.com]

You thought 3.08's were bad, try some 2.73's! Now those were some horrible gears.

I had 2.73 in an AODE... so I don't want to hear it.

I went to the 3.73s and found a small drop in gas mileage - that's based on daily driving in distance only... cause my speedo is off.

I have a problem though... I rarely drive for gas mileage... as someone said, I didn't buy this rig to save money, I bought it to hot rod around in. What sucks is my other vehicle is an 85 S-10 Blazer 4x4 with a crappy 2.8L in it. Driving fast to work, I get better gas mileage with the stang... go figure.

 

[CManT1914]

I had 2.73 in an AODE... so I don't want to hear it.

Man... that sucks worse than a chinese immigrant...