Unintended Consequences of 54.5 M.P.G. Fuel Economy Standard

[38P]

btw I had a nice trip to the HAMB drags, neat stuff there.

It looks like you had a fun race with Billetproof.

[38P]

@ TC

Assume it takes 25 h.p. to run a steady 60 m.p.h. Assume an incredible BSFC of .364. Assume that the m.p.g. target is 1.5 g.p.h. (9.1095 lbs/hr fuel = 40 m.p.g. @ 60 m.p.h.)

Even at 22:1 AFR, you'd have to get the engine to make sufficient power on ~ 48 SCFM (3.34 lbs/min) of air. Now consider that a 350 theoretically "pumps" about ~ 101 SCFM at a tractor-like 1,000 r.p.m. (100%VE), and it should be clear that you'd have to reduce air density by over half through breathing restrictions without losing BSFC to even have a shot at hitting 40 m.p.g.

That's simply not possible using known technology while meeting currrent emissions standards. Moreover, any acceleration would totally blow average fuel consumption. The "US06 Supplemental FTP Driving Schedule" and "UDDS" are much more aggressive than a steady-state 60 m.p.h. test. See e.g. http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

Now a 90 CID engine theoretically "pumps"~ 52 SCFM at 2,000 r.p.m. (100% VE), so the breathing reductions, AFR, and BSFC required wouldn't be nearly as severe to hit 40 m.p.g. That in a nutshell is why engineers most often (but not always) cut cubes first when going for big m.p.g.

Note these are rough, oversimplified, "back of the envelope" calculations that probably won't satisfy any true engineering types, but they do illustrate the difficulty of the problem.

[TC]

Assume it takes 25 h.p. to run a steady 60 m.p.h. Assume an incredible BSFC of .364. Assume that the m.p.g. target is 1.5 g.p.h. (9.1095 lbs/hr fuel = 40 m.p.g. @ 60 m.p.h.)

Even at 22:1 AFR, you'd have to get the engine to make sufficient power on ~ 48 SCFM (3.34 lbs/min) of air. Now consider that a 350 theoretically "pumps" about ~ 101 SCFM at a tractor-like 1,000 r.p.m. (100%VE), and it should be clear that you'd have to reduce air density by over half through breathing restrictions without losing BSFC to even have a shot at hitting 40 m.p.g.

That's simply not possible using known technology while meeting currrent emissions standards. Moreover, any acceleration would totally blow average fuel consumption. The "US06 Supplemental FTP Driving Schedule" and "UDDS" are much more aggressive than a steady-state 60 m.p.h. test. See e.g. http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

Now a 90 CID engine theoretically "pumps"~ 52 SCFM at 2,000 r.p.m. (100% VE), so the breathing reductions, AFR, and BSFC required wouldn't be nearly as severe to hit 40 m.p.g. That in a nutshell is why engineers most often (but not always) cut cubes first when going for big m.p.g.

Note these are rough, oversimplified, "back of the envelope" calculations that probably won't satisfy any true engineering types, but they do illustrate the difficulty of the problem.

You need to add select fire into that, where only four of the cylinders are receiving fuel while at cruise.......Effectively cutting the BSFC in 1/2.........

They could also get rid of catalytic converters and make better tuned exhaust systems, since the efficiency of the exhaust system has a direct effect of how efficient the motor runs......... IMO factory exhaust systems leave a lot on the table.......

But then my dad's Diesel Jetta is getting a consistent 52mpg....... 4 cylinders and 90hp in a 4000+lb car.................

[Beagle]

Factory exhausts are pretty damn good compared to 1975, and for the intended operational range are hard to beat. The exhaust on my Escape is actually damn impressive for a stocker. I was suprised, but then again, in 74 the Vega made 85 hp out of 2300 cc, and current crops of pedestrian low end 2.3's are well over 150hp. They aren't leaving a lot on the table.

Mom and Dad who rarely see over 2500 rpm will get better mileage with crappy small manifolds than they will with long tube large diameter headers. You don't start seeing the difference until 2250 or so, and shorties win up to there. For the averages, 750-2250 rpm torque improvements over longer primaries will pay off for CAFE in cars that run v8 style gears and 2500 or less on the highway. The Escape example again, has fairly long tube primaries, but it runs 3000 at 75-80, and the long tubes start paying back money at that point.

When the magazines show you 15 hp improvements with exhaust, they don't show you what happens below 3000. It sounds better, so it "feels" better. In most cases, it's not. We're not the kind of drivers that get all worked up about what's going on under 3500 though... and HP numbers sell parts.

Hypermiling sites will generally say to leave the exhuast alone and free up the intake as much as you can, but that's a "generalization" as well. The OEM's have an interesting challenge trying to keep everyone happy and make a sh*t pile of money. Their economy stuff is not a money maker compared to a 45,000.00 pickup truck, but they are probably the most highly tuned stuff on the lot. You can't intentionally leave anything on the table and compete with someone like Honda or Toyota's four bangers.

For all of the bitching about no V8's, I have to say I wish I had researched more myself when buying a new car. Mine was an impulse purchase and it was a good decision at the time. Now that things are more like when I was a kid (no kids at home) I can get back to cars more like when I was a kid. I like the current crop of Duratec 4 cylinders and was sad to see the Ranger go. If I had known they had the Duratec in there and not the old Pinto motor, I might have bought one. 10:1 motors that run on regular just interest the hell out of me.

Focus make some v8 like numbers with small boost. In something light, say a Cobra kit car, a turbo'd four would be a great economy car. If / when we ever run out of V8's, there is plenty of other stuff that will interest me. I get tickled with this because I'm over at my Dad's a lot lately, and there are books and junk from 1985 in there talking about the future of hot rodding and praising the biggest pile of stink I can think of, the 2.8 Chevy. BDS blowers on a 2.8? lmao. Yeah, we're doomed. 25-30 years after the predicted death of the V8, where are we now? 400 plus HP pony cars again.

TC, I see you are on a Vizard kick right now. Go read "How to rebuild your small block Chevy" from HP Books, around the 82 time frame edition. Take a look at the clean room conditions and get back to me on me being a hack, okay? lol.

with a gasoline based economy, I don't see this stuff going away. I don't believe there were ever any 300mpg carburetors who's inventors were killed, but I do believe we compromise everything and the OEMs know how to manipulate CAFE numbers. The unintentional consequence of CAFE for me is MUCH higher HP, much more efficient mills than anything I had available when I was a kid.