Bus Conversions dot Com Bulletin Board
October 02, 2014, 03:21:17 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
News: New ownership began September 1st 2012!  Please send any comments to info@busconversions.com
   Home   Help Forum Rules Search Calendar Login Register BCM Home Page Contact BCM  
Pages: 1 [2] 3  All   Go Down
  Print  
Author Topic: Engine HP v. mileage  (Read 4091 times)
bevans6
Hero Member
*****
Offline Offline

Posts: 4677


1980 MCI MC-5C




Ignore
« Reply #15 on: June 15, 2010, 06:01:48 AM »

I thought I posted this yesterday, but obviously I neglected to hit "post"...   Anyway, watching Top Gear and they are doing fuel mileage comparisons.  Of the supercars, the Ferrari lost with 1.8 mpg (at full chat on a race track) and the Audi R8 won with 5 mpg.  Then they had to do a comparo relevant to the common man...so they compared a Toyota Prius to a BMW M3 with a 400 hp V8 engine.  They went around the race track as fast as the Prius could go, all out.  But a walk in the park for the BMW to keep up.  Prius got 17 mpg and the 400 hp BMW got 19 mpg, proving for all time that the BMW M3 is a more ecologically sound choice than the Prius... Grin

Brian
Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
belfert
Hero Member
*****
Offline Offline

Posts: 5446




Ignore
« Reply #16 on: June 15, 2010, 06:50:34 AM »

Most engines when run flat out will get fairly lousy mileage compared to regular highway speeds.  The BMW was not maxed out as the Prius was.  I bet the BMW running flat out would get worse mileage than the Prius.  The BMW can presumably go a lot faster than the Prius.

The original Dodge Dakota crew cab was available with a V6 or the 4.7L V8.  The V8 actually got better mileage as the V6 was pretty maxed out with the extra weight of the crew cab.  My Dina has the smaller 11.1L Series 60.  The newer Dinas with the 12.7L Series 60 seem to get slightly better mileage because the smaller engine is probably working pretty hard.
Logged

Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
BG6
Hero Member
*****
Offline Offline

Posts: 642




Ignore
« Reply #17 on: June 15, 2010, 08:59:30 AM »

But what busnut is installing a large engine and not dipping into it?

Blows it all out the window, for he with 500 HP will surely use more of it than is necessary for efficient movement down the road.

Give this some thought.

You come out of the hole at a stoplight, put your foot in it, then go up through the gears.  When you get to highway speed, you come off the pedal to get the right speed.

How will you burn more fuel if you get through the gears in 30 seconds than if it takes a minute and a half?

How will you burn more fuel at 65MPH using 50 HP from a 500 HP engine than using 50 HP from a 400 HP engine?

Logged
Jeremy
Hero Member
*****
Offline Offline

Posts: 1890


1987 Bedford Plaxton


WWW

Ignore
« Reply #18 on: June 15, 2010, 09:58:15 AM »

Give this some thought.

You come out of the hole at a stoplight, put your foot in it, then go up through the gears.  When you get to highway speed, you come off the pedal to get the right speed.

How will you burn more fuel if you get through the gears in 30 seconds than if it takes a minute and a half?

I have a book produced by Porsche on 'Advanced Driving Techniques' which I think they gave away to their customers in the 1980s. It says unequivocally that accelerating quickly to a given speed uses no more fuel than accelerating slowly to the same speed. I do not believe this is correct though, because it's wrong to consider the 'time' aspect in that way (ie. "going through the gears in 30 seconds rather than a minute and a half" etc). You might just as well say driving quickly uses less fuel than driving slowly because if you drive quickly you reach your destination sooner, and therefore run the engine for less time.

Jeremy
Logged

A shameless plug for my business - visit www.magazineexchange.co.uk for back issue magazines - thousands of titles covering cars, motorbikes, aircraft, railways, boats, modelling etc. You'll find lots of interest, although not much covering American buses sadly.
Len Silva
Hero Member
*****
Offline Offline

Posts: 4086


Angle Parked in a Parallel Universe


WWW

Ignore
« Reply #19 on: June 15, 2010, 10:14:34 AM »

I think the only way that can work is if you are computing miles per gallon per hour.
Thus if you valued your time at $50.00 per hour and saved an hour by using $20.00 more fuel, it would be worthwhile.  Most of us are not in that position.
Logged


Hand Made Gifts

Ignorance is only bliss to the ignorant.
RoyJ
Full Member
***
Offline Offline

Posts: 177





Ignore
« Reply #20 on: June 15, 2010, 12:06:48 PM »


How will you burn more fuel if you get through the gears in 30 seconds than if it takes a minute and a half?

How will you burn more fuel at 65MPH using 50 HP from a 500 HP engine than using 50 HP from a 400 HP engine?




Like Jeremy mentioned above, you can't simply use a time factor to judge fuel usage. If that was the case, top fuel dragsters at 1 gal/second would be the most fuel efficient car on earth.

It comes down to engine efficiency at converting fuel to work. If you run an engine to its redline, it's inefficient. It may be doing 500hp of work, but consuming 2500hp worth of fuel. Back it off a bit, and efficiency recovers. At 250hp, engine uses lower than 1/2 the amount of fuel, while vehicle does not, generally, take twice as long to gain speed.

At 50hp, a 400 and 500hp engine will likely have the same efficiency (crappy). But, a 300hp engine making 200 hp would be a lot more efficient than a 500hp engine making 200hp.
Logged
TomC
Hero Member
*****
Offline Offline

Posts: 6815





Ignore
« Reply #21 on: June 15, 2010, 01:24:49 PM »

The biggest factor in engine fuel mileage (and this has been proven with big truck fleets) is the loose nut behind the steering wheel and how much lead is in his shoes.  A bus cruising at a leisurely 55mph @ say 1400rpm is going to get a whole lot better fuel mileage then the same bus cruising at 75mph @ 1900rpm. Big horsepower engines use lots of fuel when you ask them to work-like uphill, into the wind, etc.

This discussion has been played over and over with owner/operator truck drivers for years.  Personally-I like to have big power loafing down the road, then a small engine screaming all the time.  Then if you need sudden power for passing, etc, the big engine can do it.  Just like my now turbocharged 8V-71-I can actually pass vehicles (even with my car in tow) now when before would just have to wait-much nicer.  Good Luck, TomC
Logged

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Kenny
Full Member
***
Offline Offline

Posts: 223





Ignore
« Reply #22 on: June 15, 2010, 05:53:50 PM »

Relating to passenger car engine efficiencies (miles per gallon) and engine emissions, the federal gov has set the bar rather high for the car companies. The car companies, to achieve this, are producing engines that have their optimum efficiencies and lowest emissions in a rather narrow rpm range. To utilize the narrow rpm range, they are coupling the engines up with 5 and 6 speed automatic transmissions which under acceleration and at cruising speeds the additional transmission ratios attempt to keep the engine in this rpm range. All engines have their sweet spot when it come efficiency and as Tom said the driver has the most impact over this.
Kenny
Logged

1941 and 1945 Flxible - South Lyon, Michigan
mikelutestanski
Sr. Member
****
Offline Offline

Posts: 381


Mikes Metal Mistress




Ignore
« Reply #23 on: June 16, 2010, 06:07:19 AM »

HEllo:     DOnt forget the effects of windage on the flat front of a bus.   ie the same or very similar to a truck.  The effect is to decrease fuel mileage by .1 mpg for every 1 mile increase over 55.   In other words at 65 mph you lose 1 mpg for wind resistance. THat is just to push the bus through the air in front of it.   Thats why usual practice is based on 55 mph because most studies were based on that number.  If you look up mileage and the trucking industry you can find all sorts of facts and figures about driving and mileage
    Regards and happpy bussin   mike



Logged

Mike Lutestanski   Dunnellon Florida
  1972 MCI 7
  L10 Cummins  B400R  4.625R
belfert
Hero Member
*****
Offline Offline

Posts: 5446




Ignore
« Reply #24 on: June 16, 2010, 07:09:10 AM »

Certainly the nut behind the wheel has a huge effect on MPG, but I still want a vehicle that gets the best overall MPG.  I would certainly rather get say 9 MPG at 55 MPH instead of 7 MPG with a different engine and bus.

If I had a goal in mind of getting say 8 MPG I would personally rather be able to go 65 MPH instead of 55 MPH to attain that goal.  My style of driving is interstates for long distances and others may be fine with 55 MPH if they take the back roads.  The extra 10 MPH can cut hours off of a long trip.
Logged

Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Len Silva
Hero Member
*****
Offline Offline

Posts: 4086


Angle Parked in a Parallel Universe


WWW

Ignore
« Reply #25 on: June 16, 2010, 12:35:52 PM »

It all depends on how you use your bus and what your priorities are.  If you make your living in the bus and getting there on time matters, then that is a major consideration.

Consider a bus that gets 5.5 MPG at 65 MPH and 7.5 MPG at 55 MPH. (Is that a reasonable assumption)?

If you drive 400 miles in a day at 55 MPH and fuel is $3.00/gallon, you will arrive in 7 hrs and 16 minutes at a cost of $160.00.

The same trip at 65 MPH will take only 6 hours and 9 minutes and cost $218.00

So, if my math is correct, you saved 1 hour and 7 minutes at a cost of $58.00
Logged


Hand Made Gifts

Ignorance is only bliss to the ignorant.
Kenny
Full Member
***
Offline Offline

Posts: 223





Ignore
« Reply #26 on: June 16, 2010, 04:34:24 PM »

Quote
If I had a goal in mind of getting say 8 MPG I would personally rather be able to go 65 MPH instead of 55 MPH to attain that goal.

Brian, You need my MC9, last trip 2400 miles, 20 ft enclosed trailer, approx 34,00lbs, 65 mph, got exactly 8 mpg (6V92)
Kenny
Logged

1941 and 1945 Flxible - South Lyon, Michigan
belfert
Hero Member
*****
Offline Offline

Posts: 5446




Ignore
« Reply #27 on: June 16, 2010, 04:43:15 PM »

I'm not really sure, but I don't think my bus has nearly a 2 MPG difference between 55 MPH and 65 MPH.  The main issue for me is time.  I have different bus use than many.  We drive straight through for 2,000 miles with five to six drivers.  An extra 5 hours on a trip that is already 31 hours before stops is a big deal.

55 MPH would be a safety hazard on interstates with posted speed limits mostly 75 MPH with some 70 MPH sections.  Yes, I could take 2 lane roads, but I can't stand them if I have a choice.  They generally are more taxing to drive with less margin for any errors.  The guys on the trip don't mind an extra $10 to $20 each to save 10 hours overall.

Kenny, I get almost exactly 8 MPG with my bus at 65 MPH.  I am doubting a little bit your numbers.  Most with a 6V92 report at least 1 MPG less  at 65 MPH without a 20 foot trailer.
Logged

Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Kenny
Full Member
***
Offline Offline

Posts: 223





Ignore
« Reply #28 on: June 16, 2010, 04:50:47 PM »

Brian I was shocked and didn't believe either but every fill up I did the math and even combined all the millage and fuel used at the end of the trip and it was exactly 8mpg. Maybe that's the reason my buddies call it the Magic Bus.
Kenny
Logged

1941 and 1945 Flxible - South Lyon, Michigan
kyle4501
Hero Member
*****
Offline Offline

Posts: 3135


PD4501 South Carolina




Ignore
« Reply #29 on: June 17, 2010, 10:29:18 AM »

Tis a complicated thing this HP vs. MPG
If it was simple . . . . .

My two cents -

Fuel mileage is a result of the efficiency of the engine as it is being used. Some setups are inherently poor for efficiency while others are better. More available HP will allow you to accelerate back to an efficient rpm range when a low HP engine can't. In this case, if the driver of the low HP engine will usually have to drop a gear & then will ride the governor to maximize speed up the grade. In this case, if a little more speed was dropped, the engine would be in a more efficient rpm range & use less fuel.

I like having the choice of using more power or not - I don't much like feeling strapped.

If you look at the fuel curve of a given engine, you will see the rpm range that provides the most HP for a given amount of fuel. The higher HP engines will allow you to spend more time in this rpm band. You can also get there by having more gear ratios available in the transmission - but few of us are interested in constantly changing gears.

If your driving style is to wait until the bus looses speed on a hill then accelerate back up to desired cruise speed, then you are gonna have to feed those extra horses you used. However, if you 'float' your speed a little on hills, your mileage will be better.

I've used 2 suburbans to drag my 32' tin turd down the road. The 350ci would barely do 65mph on the flats & got only 9 mpg. The 454ci will accelerate up any hill I've encountered & gets about the same mileage, maybe a little better - but still in the single digits when the tin turd is attached.   Shocked

The 454 is so much easier to drive & it is amazing how much less frustrating traffic is when you can keep up if you want to.


If I get the chance, I'll install as much HP as I can - in the mean time I'll have to play the cards in my hand (hard to justify buying another engine when you have several running ones . . . . Sad )
Logged

I know you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant. (R.M. Nixon)
Pages: 1 [2] 3  All   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.18 | SMF © 2013, Simple Machines Valid XHTML 1.0! Valid CSS!