Full Throttle at low RPM, or High RPM and low throttle

[theholycow]

You could also skip figuring time and go straight to figuring distance, except that there's no data for that.

Making more power would mean that you've used more fuel and gone further. However, if you're making more power then you're doing it wrong. You're supposed to shift low to limit the amount of power you make.

So now you're making the same power and the only differences are:
- lower RPM with less reciprocating loss, less engine friction loss, more work done per power stroke (and fewer powerless intake/compression/exhaust strokes)
- less energy wasted pulling a vacuum ("throttling" "pumping" loss)

You're making the same energy from the fuel but wasting less of that energy, putting more of it to the road.

Of course, if you get to open loop enrichment then that changes things. Therefore it is wise to know how much you can open the throttle before you hit enrichment.

Too bad that BSFC map isn't plotted for throttle position instead of torque, that would be really great for us.

[pgfpro]

Originally Posted by theholycow

You could also skip figuring time and go straight to figuring distance, except that there's no data for that.

Making more power would mean that you've used more fuel and gone further. However, if you're making more power then you're doing it wrong. You're supposed to shift low to limit the amount of power you make.

So now you're making the same power and the only differences are:
- lower RPM with less reciprocating loss, less engine friction loss, more work done per power stroke (and fewer powerless intake/compression/exhaust strokes)
- less energy wasted pulling a vacuum ("throttling" "pumping" loss)

You're making the same energy from the fuel but wasting less of that energy, putting more of it to the road.

Of course, if you get to open loop enrichment then that changes things. Therefore it is wise to know how much you can open the throttle before you hit enrichment.

Too bad that BSFC map isn't plotted for throttle position instead of torque, that would be really great for us.

theholycow

Whats the vacuum at when you do this?

[Project84]

So, walk me through reading and understanding this BSFC map for the Saturn if you don't mind. I really want to know and understand more about this.

Would the BSFC map change for automatic vs. manual? Slightly I'd guess?

[theholycow]

Originally Posted by pgfpro

theholycow

Whats the vacuum at when you do this?

I'll have to check, it's been a long time since I've looked at that...but vacuum is significantly reduced, as I remember.

Originally Posted by Project84

So, walk me through reading and understanding this BSFC map for the Saturn if you don't mind. I really want to know and understand more about this.

Would the BSFC map change for automatic vs. manual? Slightly I'd guess?

No, it's for the engine, not for the vehicle as a whole. The wiki explains it pretty decently:
http://en.wikipedia.org/wiki/Brake_s...el_consumption
Just consider it a matter of how much fuel is used to do a given amount of work.

[GasSavers_Erik]

Unless the ECU for manual vs auto had different pre programmed fuel maps, then no.

Here's my interpretation of that graph:

The 250 grams of fuel per Kw/hr "island" is the lowest fuel consumption seen on that engine per unit of power it produces. This occurs between 1500-3500 rpms at the higher torque values (above 93 Newton meters).

This suggests that using heavy throttle application in that rpm range would be best for fuel economy. The lower torque values (toward the bottom of the graph) would represent a light throttle approach (less load= higher vacuum) and the lines show that the fuel consumption per amount of power produced by the engine is greater (more fuel consumption per mile if you drive this way).

[pgfpro]

I will try to explain myself a little better using the map above.

In the above map can someone explain why the blue mark @ a BSFC of 275g/kwhr uses 0.436lbs/min of fuel based on the 122ft/lbs of torque and the red mark @ a BSFC of 325g/kwhr uses 0.144lbs/min of fuel based on the 34ft/lbs of torque????

Both marks are at a A/F ratio of 14.7 @ 2500rpm with a IAT of 60*F The blue mark is at 100% TPS with a vacuum reading of 0 inch/hg and 100VE. The red mark is at 35% TPS with a vaccum reading of -10.18inch/hg and 50%VE.

So...

Blue mark equals 0.436lbs/min useage of fuel at a BSFC of 275g/kwhr making 122 ft/lbs.

Red mark equals 0.144lbs/min useage of fuel at a BSFC of 325g/kwhr making 34 ft/lbs.

conversion 1 Lb-Ft = 1.35582 Nm.

[spotaneagle]

wow that last response totally confused me, I'm sure it means something..

I've been doing some experimenting lately with lower rpm shifts, and I'm finding that 1800-1900 works well and keeps fuel usage down, the only thing I am finding is i have to give it a little extra kick at the end of each gear like that so it shifts correctly into the next gear, this is accelerating though, I do not feel that on a saturn accelerating to 2400 rpms is efficient moreso at all, in fact its is risky business to shift as low as 1800 but it can be done and you make the most of the time, by giving the boost at the end of each gear so like I said there's no time wasted in low rpm clutch/gear land... But I also do have a 99 and the pistons/cams in my car were made better in 99+ versions for better low end torque, so I think that is why I am getting away with this.. and honestly I have the lightest saturn you can buy from what Ive gathered a 99 sl2 is lighter than sc2 by 40 lbs and ive stripped 80lbs + out of this car so im at 2270 I'm assuming.. I dont need those extra 200 rpms to get me going... But cruising at 58 mph is a 2400rpm cruise, so that's the distinction on what we're talking about here is that 2400 is the best cruising speed, that vs wot or not I guess is lost somewhere in the graph..

[Little REDZED]

check the f ookfilter

[JanGeo]

What you are looking at is at light throttle and low burn rates (red) you burn more Grams of fuel to get a KWH of energy output 325 Grams per Kilowatthour. At wide open throttle burning fuel at a high rate (blue) you burn less Grams of fuel to get a KWH or energy output 275 Grams per Kilowatthour (50 grams per KWH less fuel). And the center of the graph is the "sweet spot" to operate the engine however it is also where the engine is producing a lot of torque - centered around 124 Nm of torque in the 1500-3500 RPM range which is probably when you are climbing a hill if you don't have proper gearing to travel at the speed of the road you are on. Keep in mind that this may be the power level needed to go 80 mph which although you end up operating the engine at peak efficiency it is also where there is really high air drag off setting this efficient engine operation with higher than normal speed air drag.

[fowljesse]

So, in the simplest terms, are you saying that it's generally most efficient to stay at about 75% throttle, shifting early, until @ cruising speed?
My car's powerband is from about 4K to 7,400K rpm, but I usually shift at about 2,500rpm.