Shift timing/patterns

[MetroMPG]

Hey extragoode - you should post your vehicle in the garage, so people don't have to go searching around to know what your referring to in future threads: http://ecomodder.com/forum/emgarage.php?do=add

Straight-3 welcome to the forum. I was surprised to discover this week that even 2400 RPM may not be in the best BSFC area for our engines. Tasdrouille found a Geo 1.0L map, and it suggests 3k rpm may be the middle of our (very narrow) best BSFC island.

[extragoode]

Done. I'd been meaning to, but I hadn't quite had time to figure it out yet. Is there someplace you guys have found to look up cDs and frontal areas, cause I couldn't find anything on any of my vehicles?

[s2man]

While googling a BSFC map for my engine I found this document, Technical Options for Improving the Fuel Economy
of U.S. Cars and Light Trucks by 2010–2015, written in 2001. Of course, they recommend things we all know about, and practice, like reducing load due to Cd, Crr, mass and accessories. Another thing they recommend is 5 or 6 speed electronic transmissions and CVT's, programmed to keep the engine running in it's most efficient rpm range during acceleration. Though they mention this would keep rpm's down, which reduces friction, their focus seems to be on keeping rpm's at optimum efficiency (BSFC) for FE gains. Looks like we're on top of that too.

Other recommendations like Variable Valve Control, direct-injection, and Integrated Starter-Generators are beyond our ability to mod. So we'll have to wait for them to hit the market.

Originally Posted by Daox

At WOT plus at peak torque is going to be where your optimal BSFC is.

Google also found where I had asked that question in this forum: "Does peak torque equal optimum BSFC?". I had assumed that was the case. Got verification on that, Daox? The document listed above has maps showing a standard engine reaching peak torque well above the optimum BSFC island (while a VVC engine can extend that island to nearly peak torque).

[Straight-3]

Originally Posted by Daox

If you can get a dyno graph for your car (search online, use gtech or similar device, or dyno) you should be able to tell when you achieve maximum torque. At WOT plus at peak torque is going to be where your optimal BSFC is. With the dynometer graph of torque you can see what rpms you should be keeping the engine in for peak efficiency (still in WOT). I did this with the Paseo recently and it seemed to return roughly 4% increase in fuel economy (48 to 50 mpg). In my case I actually had to increase the rpm range in which I had been driving.

Originally Posted by MetroMPG

Straight-3 welcome to the forum. I was surprised to discover this
week that even 2400 RPM may not be in the best BSFC area for our engines. Tasdrouille found a Geo 1.0L map, and it suggests 3k rpm may be the middle of our (very narrow) best BSFC island.

Thanks for the welcome.
I was never able to find any torque/power curves or BSFC info published for the suzuki3. If 3000 rpm should be my target I may not ever even use 5th gear! Now I'll have to figure out where to shift again.

[MetroMPG]

Originally Posted by Straight-3

I may not ever even use 5th gear!

For acceleration, that probably makes sense. But you still want 5th for cruising.

Remember - a BSFC chart shows fuel consumption of a significantly LOADED engine. Under light loads (ie. level road cruising), lowest RPM is generally the most efficient:



http://metrompg.com/posts/rpm-mpg.htm

[Daox]

Originally Posted by s2man

Google also found where I had asked that question in this forum: "Does peak torque equal optimum BSFC?". I had assumed that was the case. Got verification on that, Daox? The document listed above has maps showing a standard engine reaching peak torque well above the optimum BSFC island (while a VVC engine can extend that island to nearly peak torque).

I can't remember exactly what I had searched for, but it was on wikipedia. I should mention that it said 'in most cases' the lowest BSFC occurs at peak torque. There are, as always, exceptions to the 'rule'.

The curve ball gets thrown in by altering air/fuel ratios and/or altering ignition timing. Therefore, I accelerate as hard as I can without kicking the engine out of closed loop mode so I know my air/fuel ratio is near 14.7:1. I can't really control ignition timing, so I just keep rpms as low as I can.

[s2man]

[QUOTE=MetroMPG;14524]Remember - a BSFC chart shows fuel consumption of a significantly LOADED engine.[/IMG]

I'm gonna have to disagree there. The Y axis on a BSFC map shows the load, in torque or engine pressure, from 0 to max for each rpm on the X axis. Though the max torque is at WOT, those low-torque consumption values must be measured at lower loads to create the entire map.
********
I've just spent a geeky afternoon looking at every BSFC map I can find online. After isolating the maps for gasoline engines, I've got a few observations:

A - The peak efficiency islands, measured at the top, bottom, left and right extremes vary from 50 to 90% of peak torque for that rpm. The center point of the islands ranges from 62 to 79% of peak torque for that rpm, with an average of 72%.

B - Though peak efficiency islands' load is within a narrow band, their rpm width varies greatly between engines.

C - BSFC goes way up at low loads.

D - In general, the BSFC goes up after reaching peak torque.

My general conclusions and questions:

A - Can we infer % of max torque from TPS or LOD? (I would hope LOD is just that)

B - No conclusion, actually. Some engines may stay in their peak island with three gears, some may need more.

C - Besides higher BSFC during acceleration, it takes longer to get into top gears

D - I had assumed shifting to keep rpm's averaged at peak torque was optimum. I now think shifting *at* peak torque will result better FE.

[Straight-3]

Originally Posted by metrompg

For acceleration, that probably makes sense.

Yeah I was just thinking about full throttle operation, not cruise. Nice graph. Do you actually own a Firefly? I've never seen one, or seen one advertised on craigslist, a true rarity.

[MetroMPG]

Yeah, it's a Firefly - I just call it a Metro to minimize the confusion .

The Canadian market had both the Metro and this rebadged Pontiac, for those who aren't familiar. We get a bunch of rebadged Pontiacs that for some reason the US doesn't market. "Pontiac Wave" = Chev Aveo; "Pursuit" = Cobalt.