4.10 diff swap...seems like same mpg

[bimmer630]

I went from 3.73 to 4.10 recently.. the car is a blast to drive now. I am running 4k rpm at 75mph cruising the highway, so I was worried I'd be sucking massive amounts of fuel down.. but coming back from jersey Saturday I got about the same range as usual. As long as I don't hammer on it, cruising at high Rpm doesn't seem to make a huge difference.
What are everybody else's experiences?

[ANDRÜ]

I put a 4.10 in my eta, from a 2.93. I didnt notice a huge drop either. I figured b/c cruising youre not really on the petal as if you were driving aggressively. It takes little fuel to maintain rpm, much more to increase it.

[mr ilia]

As long as load on the engine remained the same as with old diff, the fuel consumption will chnge little if any. Higher rpm with less load and downhill will be definately a fuel saver.

The same principal applies as if a car is doing 30 in 5th gear the fuel economy will be worse than travelling at the same speed in the 4th gear.

[nando]

The same principal applies as if a car is doing 30 in 5th gear the fuel economy will be worse than travelling at the same speed in the 4th gear.

no, it won't. watch your econo gauge. I get better mileage at 25mph in 5th gear than I do in 4th, except the trans doesn't like being lugged along at ~1300rpm. :p

but, on the highway, the % difference in RPM is small, and you're still pretty much right in the engine's peak efficiency zone (torque curve), which is why there's not much of a difference in fuel economy.

[mr ilia]

no, it won't. watch your econo gauge. I get better mileage at 25mph in 5th gear than I do in 4th, except the trans doesn't like being lugged along at ~1300rpm. :p

but, on the highway, the % difference in RPM is small, and you're still pretty much right in the engine's peak efficiency zone (torque curve), which is why there's not much of a difference in fuel economy.

lol you might be right for m20.... I was speaking of my m42 and was converting from metric to imperial units and night have screwed up the speed number.....but the general idea is stil there, be in the most efficient power band for the best fuel economy.

An because I like these dancing dudes, here we go:

[Oly_Schmidt]

It's all about the power band.
Last fall I took the 4.10 open diff out of my automatic and put in a 3.73 LSD for winter driving.
Was surprised when the mpg went DOWN slightly. Mostly it was because the car became such a slug that I was accelerating harder to try to match the old performance. After I adjusted my driving style I got the mileage back where it had been.
Now that we appear to be done with the snow, I can't wait to put the 4.10 back in.

[TobyB]

Now that we appear to be done with the snow

oh, now, you've gone and done it...

t

[SynSyx]

kept the 4.10 in my vert went i went from auto to 5spd, def sweet for acceleration but i worry at speeds of 75/80+ that im straining the engine. just feels like there should be another gear up there for cruising

mpg-wise i still get a solid 23, which is pretty good considering im running a 2.7 with boltons and a 93 octane chip, and i only baby the engine when its cold. pretty much every time i drive it, i DRIVE it

[dothadance]

pretty much every time i drive it, i DRIVE it

words we should all live by.

[JinormusJ]

Pretty much every time i drive it, i DRIVE it

YOUR DOING IT RIGHT

I just swapped in a 3.73 LSD cause I destroyed my 4.10 open in my automagic. I love it cause I hated turning over higher revs when cruising highway. Feels like such a slug-mobile now though. I did notice a small boost on the highway though, but on streets, it dropped big time. I'm getting a solid 22 right now, but I took a road trip last fillup and I got a solid 24 total with about 90% highway. I know driving back from Sac the first day I bought this thing that I was getting 22 with the 4.10 with the same conditions, so here's a slight difference, but not much..

Hoping to get 25+ with a 5-speed though :-D

[Mystikal]

S54 MZ3: Went from stock 3.15 to 3.73
M42 Ti: Went from installed 3.73 to 3.15

Noticed no change in economy with either. Acceleration, yes.