View Full Version : FAS calculation and an idea
03-24-2006, 01:53 PM
I did a quick calculation to see what I gain by FASing and thought I would share the results. My commute this morning was 9 miles, and let's say I normally achieve 32mpg if I coast NICE-on instead of FAS. But this time there were two spots where I performed a FAS for about 1/4 mile each. Here's how the math works out:
NICE-on coasting instead of FAS: 9 miles on 0.28125gal = 32mpg avg
Each 1/4 mile FAS at an average 30mpg saves 0.0025gal since I'm turning the engine off for about 30 seconds, whereas it would otherwise be burning fuel at a rate of 0.3GPH.
One FAS replacing one NICE-on coast: 9 miles on 0.27875gal = 32.3mpg avg
Replace both NICE-on coasts with FAS: 9 miles on 0.27625gal = 32.6mpg avg
So the gains are significant but not enormous. But thinking about it, that's pretty darn good for so little distance travelled with the engine off. Just imagine what would happen if I were able to shut off the fuel every single time I didn't need power from the engine! I suppose that's exactly what you would get if you had a hybrid with no electric assist. It makes sense when you consider that P&G and "EV glide" seem to work best when the driver stays out of the assist, minimizing the need to go into regen. How else would the "mild hybrid" Civic be capable of nearly as impressive numbers as the "full hybrid" Prius?
This brings up an interesting idea. What if you built an "ultra-mild" hybrid that can coast without injecting fuel, like current hybrids, but only has an aux motor and HV battery big enough to quickly spin up the engine when resuming travel from a stop? Manufacturers could realize a large portion of the hybrid FE gains without adding as much money to the cost of the vehicle.
I wager that regular vehicle could be modified to behave in a similar manner if one wanted to make the effort. I smell a potential white paper...
03-24-2006, 04:10 PM
I think that is basicaly what GM's BAS system is.
03-24-2006, 04:59 PM
Interesting. To Google I go...
Haha. Yep, that's pretty much what I had in mind. If they were to implement that system properly and on the right car (that didn't suck) it would be a hypermiler's dream. It would be great to see GM rise from the ashes with a few appealing, highly efficient vehicles. They clearly have the technology.
03-24-2006, 06:26 PM
truck (pun?!) on back over to GH for a bit and look up martinjlm's threads. He works for GM and has added a LOT to the discussion particularly re: why GM is making the choices it has/is on what models to hit up with hybrid, BAS, and their 2nd gen system. Whether or not you think its the right way, he is pretty knowledgeable about what they're doing and why, and has some good rebuttals to the "Toyota is king of all that is green" argument.
Their Silverado thingy this model year is exactly what you talk of (is it BAS too? I thought it was only on the VUE).
Slipping offtopic a bit...
The GM philosophy in a nutshell is that a smallish gain by shutting injectors and idlestop in their largest volume vehicles nets the largest overall gain- hence their focus on the truck side. They will trickle the hybrid stuff 'down' to the cars later. Right? Wrong? Wayne and everyone has their opinion...
Their claim is that they are taking longer to get fullon hybrids to market becasue they are tackling the work truck problem head-on first: how to keep the tow/haul capacity that requires a V8 no matter what, but get compact SUV-like FE. Even Toyota has had to go back to the drawing board to figure that one out. Again- right? wrong? Doesn't matter- the decision was made 5ish years ago and they have to stick with it and make it work. To them, the soccer mom in her Tahoe is a pleasant, moneymaking distraction- they see their 100% core constituency as the contractor who lives and dies by his truck. (And of course, Delta's candid camera targets would fall into the 'distraction' category- they're certainly more into lookng good than working good ;) )
Can you tell I'm cheering for Detroit to come roaring back? Jeez I pray they can do it...
03-24-2006, 07:21 PM
I think the silverado is using their 2-mode hybrid system.
03-24-2006, 09:19 PM
ya lets hope gm doesn't BOCH it and things go haywire when you try to FAS
if you read about the guy who tried to FAS a crystler 300 C haha he couldn't even control his car!!! he had to lucky pull over until the car stopped completely, put it into P and then turn the key... go figure...
GM don't boch the VUE now...
___In my FAS to NICE-On experiments for GoNavy, a FAS was worth a heck of a lot more then a NICE-On. Let me repost …
Reset FCD w/ 2.1 miles total. 52 mph - 28.4 mpg initial when FAS performed at overpass sign just before a high speed off-ramp and coast into a gas station. Final = 50.0 mpg.
Reset FCD w/ 2.1 miles total. 54 mph - 29.9 mpg initial when a NICE-On was performed at overpass sign just before a high speed off-ramp and coast into a gas station. Final = 41.2 mpg.
___Not as scientific as I would have liked like, it was good enough to show a rather large increase in FE using a FAS vs. NICE-On at those speeds in this driving scenario. Because this test was performed with a Reset aFCD while the ICE was running, the numbers are as close to dead on vs. ICE-On to ICE-Off to ICE-On again in the Accord which can skew the results displayed mightily.
___GoNavy, Martins intentions are as honorable as one could imagine given his managerial position in GM’s hybrid group. When GM is pushing SUV sales at a point in history when we are approaching or have possibly breached peak oil, where do you think this will place GM’s competitive position in the longer term? It was not 3 years ago Christmas I paid just $1.37 for a gallon of fuel. The other day it was $2.69! Will GM have achieved an almost doubling of their EPA FE ratings between the Tahoe of 2003 and the upcoming Dual-Mode Tahoe to be released in late 07/early 08? Not a chance. Did you, I, or the average worker here in the states see our average hourly wage double between 12/03 and 03/06? Not a chance. This is the real problem. GM and Ford keep downsizing due to a product mix that is not selling well let alone being profitable. Unless they get their FE numbers up far higher then what we have seen to date, they are whistling past the graveyard let alone the many undesirable products they are currently producing today. I hate saying this again and again but the honest truth needs to be told or the US auto industry as we know it is doomed. With Honda and Toyota offering a multitude of HQ - 40 + mpg solutions, at what gasoline price does the US auto industry collapse due to a lack of high FE alternatives?
___I am cheering mightily for Ford and GM but a relatively simple change like an Atkinson intake and taller fourth and fifth gears in the manual tranny based Focus, Cobalt, and Aveo would improve those models FE to Yaris/Corolla/Civic like numbers. Because of Ford’s and GM’s shortsightedness however, these models are allowed to languish as more buyers grab the 40 + mpg highway rated Japanese offerings. This landslide can only get worse as our real world fuel prices continue to climb.
___Tom, the Silverado uses a relatively simple Start/Stop with regen capability only. The Saturn Vue and Malibu will get the upgraded IMA like BAS setup. The next gen Tahoe and Yukon will receive the Dual-Mode.
03-24-2006, 11:09 PM
Shows how much I was paying attention at the autoshow ;)
03-25-2006, 07:17 AM
preachin' to the choir, Wayne. There is no excuse for not doing those simple things you mentioned on the low-end models- especially gearing the OD properly. And why the hell GM is still mucking with 3 and 4ATs when 5 and 6s are everywhere...
03-25-2006, 11:44 AM
The cool thing about transmisions is you realy haven't heard of any massive failures in the CVTs from either company. Once they prove their reliability I think that will go a long way in helping bring up mpgs. It killed me in the rental where I had to drive at nearly 2500 rpm just to cruse along at 35. It wouldn't shift into the next gear until 45. Then when it shifted I had the choice of staying at 10+ over the speed limit or having it downshift again when I dropped to 35. It was a bit frustrating. I totaly missed being able to be able to hold on to 1200 - 1500 rpm driving around. I will never go back to a regular auto if I can help it. Its either MT or CVT from now on.
03-31-2006, 01:24 AM
there was a gm guy over at GH, the 4speed AT is tried and true to GM roots. They think its the most reliable AT they have... and sadly its true lol anything else and its untrustable. But their numbers are almost (in some cases) better than most 5AT these days, so they just stuck with what worked best.
But what's interesting me these days is volkswagon Direct Sequential Gearbox or DSG for short. Basically its a manual transmission system with two clutches, and electronically controlled. Some folks say its like driving with the "best manual transmission" driver in the world. Shifting into the next gear faster than any left foot and right hand can ever do and to impress us all it does it very smoothly. Not only that in some cases if driven right the DSG beats a regular 5spd with ease in terms of power and efficency, truly the next wave of automatics.
Now if we can only bump start on a DSG... ONE PLEASE :D
backing it up with facts http://www.greencarcongress.com/2005/04/vw_golf_diesel_.html
03-31-2006, 06:55 PM
Don't all vehicles on the GMT900 (2007 Tahoe, Suburban, Escalade, Silverado, etc.) get the 5-speed automatic?
03-31-2006, 08:59 PM
Interesting input from everyone on this. I have been using this "FAS" ever since "Xcel" was here. He stopped by on his way to Florida and gave some brief, but notable example of "FAS" while on the way to Dinner (Supper) and Xcel did the driving on the way back to our home. Fas does work. :)
___GM and Ford co-developed a 6-speed Auto as reported in the following thread: Ford’s new 6 speed transmission for the upcoming Edge ( http://www.cleanmpg.com/forums/showthread.php?t=81). Another good article on its capability can be seen at the following: New Hydra-Matic 6T70 Six-Speed Automatic Delivers Performance and Fuel Economy (http://www.theautochannel.com/news/2005/08/25/141299.html).
___Whether GM will use it in anything but the upcoming Saturn Aura is anyone’s guess? I think they will have to but again, GM has been known to do some very strange things with its best technologies?
___As a side note, I FAS the GM ½ and ¾ ton trucks at work and those GM tranny’s are a dream to re-engage at speed. Ford gained mightily from the 6-speed in this partnership because their current Auto’s are the closest thing to junk under that same condition.
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