What engine swap for improved fuel economy?

[nando]

Think about what your fuel savings will be (25-30mpg isnt really a big improvement, and 30 will be tough to reach) to what it would cost for a swap. I bet you can buy a lot of fuel for your M20 with what it would take to break even.

I agree that a diff swap makes the most sense.

[estoguy]

My Eta has also been a consistent fuel user... my three year average is 7.8L/100 km (just over 30MPG US for those south of the border).

On some long drives, I have gotten as low as 6.3L/100km (37 MPG US).

During the warmer months, I can get her to average between 7.7 and 7.1 ... 30.5-33 MPG.

I agree that a 2.93 or 2.79 diff would be cost effective as well.

[jeffnhiscars]

My M10 which was a 5 spd never got more highway mpg than my m20s w auto trans. Add my vote to a diff swap and possibly detune to run on regular fuel.

[bataangpinoy]

I can't believe no one has suggested the use of a ZF 6 spd. With a 2.93 or 3.15 R&P, you'd still get great acceleration in gears 1-5 and have 6th for highway economy.

I wouldn't pull your existing driveline out just for that, but if you decide to do a 24v swap down the road.. Look into the 6 speed option.

[nando]

that's going to cost a lot, if you're doing it for fuel economy, it would take years to break even.

[Ether-D]

I bet it's half for the fuel economy and half because he wants another project to smash. Amirite, AndyB? Doit.

[Ether-D]

Double post ninja edit fail...

[Swanny]

Exactlly! M50 cuz bored

[Andy.B]

I bet it's half for the fuel economy and half because he wants another project to smash. Amirite, AndyB? Doit.

Yeah, this is honestly part of it.

I could detune and swap diffs, and lose power to slightly improve fuel economy... Perfectly valid suggestions.

I could also sell the e30 and but a used Chevy Cobalt HF for less money, and get great fuel economy.

Or.....

I could sell off my current go fast goodies to recoup some money, slam in an m50, and gain power AND fuel economy.

It isn't the most practical option, but neither is daily driving an e30. I'm not looking for the best good decision, but the least terrible bad decision.

[stonea]

M54, but it can get costly if you're not good at wiring. Plus I don't know how much it costs to flash the ECU.

[nando]

Somebody posted the files to delete ews - it could be nearly free.

[stonea]

Somebody posted the files to delete ews - it could be nearly free.

Don't tell me that... I'm already struggling between a M54 swap and a M30 and a possible turbo for it down the line. (I know,weird to be stuck between those two engines.)

[whitebulat22]

For the diff choice, my squid tuned 2.7i with the 2.93 indicated 25 mpg in 4th gear and 26 in 5th on the freeway. 65 ish, 4 people in the car, repeated both gears a couple times for a couple minutes to verify results. OBC usually about 3 mpg pessimistic. So going all the way down to a 2.93 isn't necessary IMO because below the higher freeway speeds it only helps so much.

Plus second gear starts coming out of a slow turn or near stop don't really work with the 2.93.