Driving 55mph? (Is it the most efficient speed?)

[jwxr7]

Originally Posted by tasdrouille

There's a real fuzzy one in there for the 1.0 GEO SI engine

Thanks, Wow that is fuzzy and it looks like a small peak efficiency island compared to the saturn 1.9l's.

[MetroMPG]

Thanks for finding/posting that! First map I've seen for the 1.0 .

That's interesting - the best case island is higher up the RPM scale than I've been aiming for during P&G.

Though, having said that, the XFi cam shifts the peak island to a lower RPM...

[jwxr7]

For those with a vortech 4.3l GM engine. I found info for my truck engine here http://www.bucksengines.com/Data/24.pdf. All the way down on page 71 it has a BSFC chart. There is a wealth of other neat info there too, like % power loss vs intake air temp and intake air restriction.

sorry bbb3108 if this is taking over your thread .

[optiwatch]

My mazdaspeed3 has 6 gears, but the gearing is target at 0-60 acceleration. I can shift into 6th at 45-50 mph, but driving at 80 mph leaves me wanting for a 7th gear. Can I avoid changing out the gears by installing larger tires?

[MetroMPG]

Yes, though you'll also raise the vehicle, which may increase drag (e.g. Lexus claims a Cd .01 decrease for a 1 inch drop).

Your car and mine are vastly different, but note that by lowering my RPM 20%, my steady state fuel economy improved by about 5%. You could use that as a starting point for some rough calcs. There are many tire size calculators out there for figuring out how a circumference change affects diameter & RPM.

[DifferentPointofView]

On all the car audio-video forums they refer ICE as In Car Entertainment.

Your engine is generally most efficient at 70-80% throttle, but you then run into the aero problem again.

Ever try to run against 45 mile per hour winds during a storm? you don't get very far, and you get tired pretty quickly. A car at 70mph is having to push through all that air, which is also pushing you back. you go slow, you have an easier time. So most vehicles (autos specifically) have a sweet-spot between 45-55 range. Generally, that spot is around 45-52ish. Also, cars usually have a hard drop in FE for every 60mph, especially in trucks and SUV's. Mostly from the wall-like windshield.

I can go a lot farther on a tank going 50, but I rarely get to do that cause I'm usually carting around a lot of impatient people. they don't mind me doing 55.

[LostCause]

As all cars will vary, the easiest and most accurate route will be to do some experiments with FE instrumentation at different speeds.

I know automatics will drop off once the torque converter opens up, so 45mph (or whenever the TC kicks on) tends to be the best spot for those cars. My car has such low gearing that at 45mph I'd be running 1000-1200rpm, which is only 400-600rpm above idle. When I drive 55mph, my engine rpm is ~1550-1600, so I do take a pretty significant hit...but I wouldn't stay legal otherwise.

Modifying your engine for low-gearing/low-end torque might spell disaster if it is overdone. I imagine massive forces are going into a drivetrain at loads experienced at such slow speeds. This is mitigated w/ aerodynamics and LRR tires, though.

- LostCause

[DifferentPointofView]

45mph I'd be running 1000-1200rpm, which is only 400-600rpm above idle. When I drive 55mph, my engine rpm is ~1550-1600, so I do take a pretty significant hit...but I wouldn't stay legal otherwise.

Huh, same here. What do you run doing 70mph? I go almost 2000rpm, not quite on the line, but close enough. I do about 1200 at 47. TC opens at 45.

[Peter7307]

Originally Posted by jwxr7

For those with a vortech 4.3l GM engine. I found info for my truck engine here http://www.bucksengines.com/Data/24.pdf. All the way down on page 71 it has a BSFC chart. There is a wealth of other neat info there too, like % power loss vs intake air temp and intake air restriction.

sorry bbb3108 if this is taking over your thread .

Great link there. Thanks for posting.

Pete.

[jwxr7]

Great link there. Thanks for posting.

Pete

No problem. Too bad it's hard to find comprehensive stuff like that for other engines.