What's Your M50 or S50 E30 Mpg??

[nando]

Aerodynamics KILL E30 MPG at 70+ MPH. On a modern car, the difference between 65 MPH and 80 MPH is a 15%~ reduction in fuel economy. Now imagine what it is for the E30 with its awful co-efficient of drag (0.38+). E30 M3 body style doesn't have this problem with aero CoD of 0.32~.

Things to improve E30 aero:

Lower car ride height
Front valence/spoiler
Underbody panelings to reduce drag

Unfortunately E30 aero is like a brick. :\ And it doesn't help that S50/S52 are high compression engines which means that they engine brake rapidly and can't coast at all at freeway speeds.

The ironic thing is that an E30 with a turbo M50/S50 etc with lowered compression would actually get better MPG due to the turbo increasing fuel efficiency (especially while cruising) and the ability to coast further/longer thanks to lowered compression.

where'd you get .38? is that for a non-sport model? diving board eta?

I've seen anywhere from .34-.35 for a 325is (late body). the trunk spoiler actually decreases drag by about 2% according to BMW.

you can laugh but BMW did actually wind tunnel test the later E30s.

[avery0829]

M52 OBD1 + ZF + 2.93lsd with a mix of freeway and city driving 25mpg

[BBDirtbiking]

I can't believe people are running a 2.93 with a G240 or a G260... Haha.

[nando]

I dunno, it's a wierd obsession with overly tall gears IMO. what's the point of being able to do 75-85mph in 2nd gear? I don't *want* to downshift to pass people. :p

[dude8383]

The size of the tank does not affect gas mileage. Unless you count the negligible factor of both having a full tank and the larger tank carrying slightly more weight. Things like driving style, mods, and what people consider to be city/mixed/highway and other factors are what account for the differences.
So why would it matter if it was previously a 318is in terms of gas mileage?

I guess I'm curious to see how much mileage you can squeeze outta the tank.

[golde30]

S52 obd1, 21.5lb inj, 3.5MAF, eBay SS header, UUC 8.5lb flywheel, getrag260 w/3.73. Got 26mpg on my last 1600mi road trip@ 75mph.

[SHunter]

Update:
I took a road trip a couple of weeks ago, Portland->San Francisco, SF->Trinity Lakes, and back home. The car was pretty loaded with camping gear plus the two of us but nothing on the roof. Best tank 33mpg and worst 31mpg. That includes a little bit of driving in the city too! I was seeing 350-380miles between fill ups. We drove 70-75mph most of the time including over the passes. Last time I did this trip was with the m20 and I would have to downshift a lot in the mountains, not an issue anymore. More power and better mileage is tough to beat.

-SH

[Fusion]

22mpg / highway, city, and 30mins of full throttle at the track

[DisgustipatedAP1]

where'd you get .38? is that for a non-sport model? diving board eta?

I've seen anywhere from .34-.35 for a 325is (late body). the trunk spoiler actually decreases drag by about 2% according to BMW.

you can laugh but BMW did actually wind tunnel test the later E30s.

Check this post out: http://forums.bimmerforums.com/forum...4&postcount=35

Apparently older ones had horrible aero, the late bodies were really good, and the M3 was phenomenal. So I guess my E30 isn't as bad as I think it is.

[VinniE30]

Check this post out: http://forums.bimmerforums.com/forum...4&postcount=35

Apparently older ones had horrible aero, the late bodies were really good, and the M3 was phenomenal. So I guess my E30 isn't as bad as I think it is.

Actually, E30 aerodynamics are pretty good.
Drag area is a better way to measure how aerodynamic a car is because it takes into account both the drag coefficient and the a car's frontal area. This is what Car and Driver uses to compare cars aerodynamics.

http://en.wikipedia.org/wiki/Automobile_drag_coefficient#Drag_area

The late model e30 has a drag area of 6.63 sqft. Early models are a little worse. E30M3 is in between.

http://www.mayfco.com/bmw.htm

So the E30 actually has a good drag area. Better than e36 or the e90!

[Cyrix2k]

bumping this

I can't believe people are running a 2.93 with a G240 or a G260... Haha.

I want the tall gearing for when I go turbo. My '85 was fantastic with a turbo M20B27, G260, and 2.79 LSD. I later swapped to an M50NV & G250 - once again, it has plenty of power. Unfortunately, the '91 is a total dog with the NA M50NV :(

I dunno, it's a wierd obsession with overly tall gears IMO. what's the point of being able to do 75-85mph in 2nd gear? I don't *want* to downshift to pass people. :p

M50NV + G240 + 2.79 LSD here. I didn't realize the G240 had an overdriven 5th gear when I swapped in the 2.79... Anyway, mileage is coming in around 26-29 mpg combined cycle. Last fillup average 26.6 mpg (245 miles / 9.2 gallons) with a lot of stop & go in the mix.

The G240 will be leaving the car once I get to the turbo stage of the project, but I'm thinking about going with a six speed now because that OD is nice on the highway.

[MR E30 325is]

S52, ZF, 2.93

Drove to Monterey Bay last month, averaged 32mpg over the whole 1600 miles.

Car just received an entire assortment of new parts, plus the alignment is spot on.

I was very impressed.

[hwy84]

91 325i sedan - full weight - S50B30 - 3.73

Average MPG over last 1200 miles...

...20

Poor!

But due to where I live I have to drive at least 10 miles down a twisty canyon road before I can even get to a freeway, and at least 10 miles back up whenever I come home.

And, I also have to drive as hard as possible in those 10 miles, because, I mean, who wants tires to last more than 3500 miles? The could get stale, or moldy, or something if you leave them on too long. ;)

So, you know, that probably doesn't help on the ol' fuel economy tip.

[e30rapidic]

S50 with pink top injectors, 3.5 intake, headers, TRM tune, zf and 2.93 = 27.9 mpg @75

with the 3.46 I was getting like 15. Which is still better than my F150!

[Bimmian89]

S52B32 OBD1 2:93 LSD

Highway is ~27
City is ~ 24-26