Last post on Jul 31, 2010 at 10:48 PM
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Performance Mods, Engine, Fuel Efficiency (MPG)
#1 of 4019 Power to Mileage ratio
Jun 07, 2006 (3:34 pm)
How much power are you willing to give up for that last bit of fuel economy?
I get the impression that while there's a lot of attention on mileage in absolute terms and ensuing discussion on the cost of the more fuel effecient cars, there seems to be very little discussion if any, about fuel mileage in relation to power.
- production cars
- aftermarket cars and parts
- power band
(remember, unit-wise: hprpm = torque x rpm)
- highway vs city
- cruising vs WOT
#2 of 4019 Re: Power to Mileage ratio [jimveta]
Jun 07, 2006 (4:11 pm)
I think every car should have a ridiculously high 6th gear like the Corvette. In the weakest cars you can't go too far; you need enough power to beat aerodynamic resistance at 90mph, imo.
Driving a Corvette in 6th must pretty similar to driving a 9,000rpm engine at 3,000rpm. You can have speed or mileage, but not at the same time.
Jun 07, 2006 (4:38 pm)
power-to-weight ratio? With the range of performance parameters that gearing would provide, I think 1 hp for every 20 pounds of car is plenty. That and a combined EPA rating of 35 mpg or more suit me just fine.
The newest subcompact cars (Fit, Yaris, '06 Accent) don't quite make this mark, and so they sacrifice a bit of fuel economy to keep the performance up, and fall slightly below the 35 combined mpg threshold as a result. It's hard to think of too many cars (or trucks) with a ratio worse than 1:20. Perhaps there is an SUV or two struggling out there with a small engine that gets below 1:20.
Cars like the Corvette are just so OBSCENELY over this ratio, it's funny. The Vette gets about what, 1 hp for every 8 pounds of car? And yet I can applaud GM for not making the Corvette a pig - the weight is still around 3200 pounds, right? For a car that can do the speeds it can, I could see wanting a good ton and a half of metal around you. The Corvette represents VAST overkill for all but track use, but excess is what we like to spend our dollars on, and so GM is never wanting for Vette customers.
Now, I know the speed hounds will have a thing or two to say about the 1:20 thing, so have at it!
#4 of 4019 That works out...
Jun 08, 2006 (9:05 am)
...to about 175HP for an average mid-size sedan. So not too bad - it's about what my wife's Alero has and it has decent acceleration. But something is the range of 1:15 or even 1:13 is pretty fun.
#5 of 4019 One of the worst power-to-weight ratios...
Jun 08, 2006 (9:25 am)
I've ever had was my '82 Cutlass. It weighed about 3200 lb I guess, and had 110 hp. That comes out to about 29 pounds per horsepower!
I'd guess about the best power-to-weight ratio I've had is about 17 pounds per hp. My Intrepid has 200 hp, and weighs about 3400-3500 lb, giving it about 17 lb/hp. My '67 Catalina has about the same ratio I'm guessing. It weighs about 4200 lb I'd guess, and when you account for the gross-to-net hp transition, I'd guess it has about 250 hp. It had a 290 hp 400-2bbl originally, but has a 4-bbl on it now which I think put it up to around 325 hp. To get net hp I just took 3/4 of that figure.
#6 of 4019 Re: what about [nippononly]
Jun 08, 2006 (10:43 am)
The various Corvettes range in Lb to HP from about 9.3 to 6.2 for the newest Z06, from the C5 Coupe I drive at 350hp and 3250lbs. With the very tall 6th gear as noted I can get 35mpg if I stay just under 65mph on the flat and level. Wind resistance above that brings down results quickly. My last trip from Fernley NV, to the bay area came in on the trip mileage average at 30.2mpg and I wasn't doing close to 65 most of the time and included one gas stop. BTW, my former daily drive was an '87 Pulsar for 15 years and just over 100k miles, I've been on the other end of the ratio.
From my POV the real issue is weight and aerodynamics, keep the one down and improve the other and you get good mileage no matter how much HP you have. I doubt the many Prius I see doing over 85mph are getting good mileage. Speed kills mileage in everything.
Jun 08, 2006 (10:44 am)
that has the 1:20 ratio almost nailed dead-on is the 4-cyl Accord, and my friends and I went on a vacation to Yosemite in theirs last weekend. Five people (two were in car seats) and all their gear not only fit in there, but fully loaded it never strained to climb the hills to the 6000-feet-plus pass you have to go over to get there. And was able to do 80 mph with ease on the highway, and to pass slow trucks on the highway-speed grades you hit early on the Yosemite road once you leave the freeway.
And still managed better than 30 mpg over 15 gallons or so! With the A/C running most of the time. To me, that is the definition of the sweet spot in power-to-weight.
#8 of 4019 power to mileage ratios
Jun 08, 2006 (12:45 pm)
Prius: 1.8:1 (using 110hp and 60mpg, both of which are arguable)
2006 Civic: 3.5:1 (40mpg highway, right?)
Accord 4cyl: 6.9:1 city, 4.9:1 highway
Accord V6: 12.2:1 city, 8.4:1 highway
Corvette: 22:1 city, 14.3:1 highway
Bugatti Veyron is at 125:1 city, 66.7:1 highway
That's with EPA figures; real world numbers would be lower. Unfortunately I didn't learn much from any of this.
#9 of 4019 Re: power to mileage ratios [carlisimo]
Jun 13, 2006 (11:48 am)
Theres three issues with this.
First issue here is that we're not using the right numbers.
A car that has 10HP at 10MPG (very bad) and a car that has 100HP at 100MPG (very good) are both 1:1 if your measuring this way.
What you should be doing for HP to mileage is take the inverse of the mileage (or...gallons per mile, not miles per gallon). This will measure horsepower generated per gallon of gas consumed each mile, which is a (very rough) measure of power efficiency from gasoline consumed.
The 10HP at 10GPM car would score a 100 HP/G/M, and the 100HP at 100GPM would get 10000 HP/G/M.
Another issue is that max HP is only generated at peak RPMs when these mileage numbers mean nothing, since this measure compares fuel consumption going a mile while cruising (hwy) or stop an go (city) driving, not measuing power at peak usage. If you could get real mileage numbers at wide-open throttle for a mile, then that number would be meaningful here.
Third is that its not linear in reality. Its easier to double HP than to double MPG, yet both would be rated the same if these measurements are linear. You would need to give some kind of higher weight to the MPG to make this number meaningful. Unfortunately, the weight is going to depend on each person and how they value fuel economy over power, or vice versa.
Anyways...heres a few numbers using the inverse.
Prius should be 110HP 1/60 gpm = 6600 HP/G/M
Camry V6 (Hwy) is 268HP 1/31gpm = 8308 HP/G/M.
RS4 (Hwy) 420 1/20gpm = 8400 HP/G/M
M5 (hwy) 500 1/18gpm = 9000 HP/G/M
Bugatti (hwy) 1000HP 1/12gpm = 12000 HP/G/M
Corvette Z06 (hwy) 505 1/26gpm = 13130 HP/G/M