Author Topic: "optimal"cruising speed (Read 4825 times)

///m42 sport · « **on:** April 08, 2010, 11:27:59 PM »

Thought this was interesting. I did a 600mile roundtrip. Had my tires inflated to 37psi. First half of the trip my avg speed was 55mph. I calculated my mpg by fillups and got 27.8.

second half of the trip. Everything was the same, except avg speed was 70mph. and avged 33.8mpg!

BlueBMW · « **Reply #1 on:** April 09, 2010, 12:50:16 AM »

I experienced similar. It seemed like I got better mileage around 70mph than I did around 55. Must be something to do with volumetric efficiency or some fancy term like that.

tjts1 · « **Reply #2 on:** April 09, 2010, 08:25:09 AM »

The gearing is way too short on these cars, especially verts. On our 890 mile move, I did 31mpg with the car packed and another 200lb of knock down wood furniture on the roof rack. I don't know what my average speed was but MOST cars get their best FE at the lowest possible speed in 5th gear. The speed limit varied between 70mph and 60mph (fucking oregon!) and I didn't want to speed because the car was so heavily loaded. This is with a 3.64 differential, Efan, no PS and EV6 injectors.

lqbanotxano · « **Reply #3 on:** April 09, 2010, 08:58:37 AM »

If there was a strong head & tail wind your numbers could be off.

jeff_b · « **Reply #4 on:** April 09, 2010, 08:59:24 AM »

Quote from: tjts1;90620

The gearing is way too short on these cars, especially verts. .....

I have a 4.27 open diff in my cabrio M42. It really bakes that one tire!!

1991 E30 M42 · « **Reply #5 on:** April 09, 2010, 04:49:47 PM »

With a 2.0 liter engine w/mark d, mustang injectors, cop, custom intake/exhaust, 3.73 rear diff and many other mods made 36mpg on a 5 hour trip 80mph with about an hour going through the mountains

BlueBMW · « **Reply #6 on:** April 09, 2010, 06:45:25 PM »

I did about 26mpg average hauling that M20 motor in the trunk back over the mountain from North Carolina.

flyinglizard · « **Reply #7 on:** April 09, 2010, 07:47:50 PM »

Should be around 3400to 3600, max torque.
Other than about 72+-4mph. it will improve at about 45mph in 5th . If it will pull gear..
wimpy little thing that it is..

bmwconnect · « **Reply #8 on:** April 09, 2010, 08:28:48 PM »

This should help a little . m42 Low load spark map in Degs(used when cruising) between 2500-4000rpm is optimal with the m42.

tjts1 · « **Reply #9 on:** April 09, 2010, 10:02:48 PM »

Quote from: flyinglizard;90645

Should be around 3400to 3600, max torque.
Other than about 72+-4mph. it will improve at about 45mph in 5th . If it will pull gear..
wimpy little thing that it is..

I'm sorry but best MPG is not going to happen at 72mph. M42 torque peaks at 4600rpm and nobody drives like that. Its also ignoring other factors such as internal friction and aerodynamic drag.

Quote from: bmwconnect;90646

This should help a little . m42 Low load spark map in Degs(used when cruising) between 2500-4000rpm is optimal with the m42.

This is very cool. Does motronic 1.7 switch spark maps based on throttle angle? How many spark maps does it store?
thanks
Justin

flyinglizard · « **Reply #10 on:** April 14, 2010, 08:54:24 AM »

I cruise at 3400-3600, get 28-30 mpg. If i could cruise at 2800, maybe it would be 30,Due to aero drag value, but who cares what it is at 60? 3400-3700, seems to be this engine's happy rpm. It is all working well through this range.
My Merkur got about 28 at 3100rpm, but it had 200hp and and weighed 3000#. Nice car, nice third gear for passing. Very good computer, E 4, ran over 250K easy.

strad · « **Reply #11 on:** April 17, 2010, 07:43:05 PM »

I only did one long trip in my E30 M42 318i -- 2000 miles or so. I did not experiment much with cruise speed (the intent was getting to the destination at a certain time lol) so at 75-80 mph I saw about 29-30 mpg. Interestingly, my 328 does only about 1 mpg less, but with 60+ more horsepower lol. What a difference aerodynamics and technological advancement make.

Romrog318is · « **Reply #12 on:** April 17, 2010, 08:37:59 PM »

i need to check my MPGs... its kinda hard to get an accurate reading considering i cant even tell when im doin over 100 anymore lol

DesktopDave · « **Reply #13 on:** April 17, 2010, 08:52:51 PM »

Most important is not having alcohol in the fuel mix. Our normal winter fuel, idling, longer warm ups and traffic patterns up here in PA can cut mileage significantly. You'll get better fuel mileage with the factory TB heater plate in place. High humidity and moderate air temps should also help.

My best mileage seems to be at around 70degF, I'd guess 75% humidity. I still have my TB heater and I tend to draft semis. About 100ft back seems to work well.