740iL m62 to m52 swap?

[Kershaw]

a friends dad is selling his e38 incredibly cheap. 150k. and i love them. they are gorgeous cars. but if i bought it, i would use it as a 70 mile a day DDer. so gas mileage is kind of important. the difference between 18mpg on premium (rx8) and 27mpg on regular (eta) is $50/week. so i need to keep that eta gas mileage. i can sell my eta to cover the cost of buying this e38, thats how cheap it is. but i cant do 22mpg on premium or whatever the m62 will get. and i think i can sell the v8 to cover the cost of a straight six.

so... 728i anyone? i'd keep the auto trans. just swap motors. obd2 everything. should be fairly straight forward, right? i dont care about how much slower this will make this 2 ton beast. if i can get this rolling leather sofa to do 27-28mpg, i will go for it. i love e30s, but e38s are soooo much comfier. especially for DD duty.

what are your thoughts?

[george graves]

Never mind - my bad

[M-technik-3]

MPG is gonna suffer around town. Big car for a smaller engine coupled with an automatic. 728i's in EU were stick correct? Most smaller engine'd cars in big chassis's were. How much city driving will you be doing?

[e30e]

528i's don't get 27-28mpg why do you think an even heavier car would get that? Hell even e28 528e's didn't get that.

[Kershaw]

MPG is gonna suffer around town. Big car for a smaller engine coupled with an automatic. 728i's in EU were stick correct? Most smaller engine'd cars in big chassis's were. How much city driving will you be doing?

they were stick yes.

it would be 80/20 highway/city.

[Kershaw]

http://www.autoevolution.com/engine/bmw-7-series-e38-1998-728i.html

just so i dont leave this thread unresolved.

i will do this if i get the car. 29.7mpg in an e38? hell yes. and yes i will granny drive it. so thats ok.

[M-technik-3]

Then by all means do it since M52 is less hassle to work on than the big M62. Why not go S52 to have the extra torque and then granny drive it?

[Jean]

He mad

[gearheadE30]

I think that kind of mileage is wishful thinking, at least with an auto. Heavier car + auto = more throttle opening to get the car moving. At least a stick would let you use more revs with less throttle to get the job done. That's only worth a few mpg though, probly. Sounds like a cool idea, I just don't know if it would be a practical one.

[Kershaw]

its practical from a maintenance stand point too.

no valley pan to worry about.

[Jean]

Valley pan will take less time/effort to do than swap.

[Kershaw]

sure. but fixing the valley pan wont give me better mpg.

[Jean]

putting a smaller engine in heavy car, might not do it either.

[Stephen]

Also on the flip side, e38s do better than 18mpg. Nowhere near 27, but i think you should just put down the e38 dream if you're trying to be that frugal. Itll eat up the money elsewhere regardless.

[Mossman]

Yeah I think this is a bad idea. 528i 5 speed is basically the car you need and you can find them for 5-6k. If your dad is giving away the E38 buy it, get it up to date maintenance wise, detail it and sell it for 6k, and buy an e39 5 speed. I just checked and the e39 528i/manuals came with 2.93's already, was gonna suggest swapping diffs but I don't think anything taller is available.

omg I actually just solved it. 6 speed swap the e38. I think e38 stock diff is 2.93 as well, while 540i/6's are 3.15's IIRC. And diameter of 7 tires is bigger, essentially knocking the gearing up a bit there. Get something with super high tread life, low rolling resistance, maybe even a tiny bit skinnier and taller than stock, and you should be able to equal e39 540i/6 highway mileage, which is about 30mpg's if you drive like a prius owner.

To top it off you will have made your car better and worth more rather than a piece of shit.