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Author Topic: Engine HP v. mileage  (Read 4119 times)
akroyaleagle
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« Reply #30 on: June 17, 2010, 11:48:23 AM »

There are many good replies to this post and some which are in my opinion baseless.

I don't know much about birthing babies.

I do know that in my Eagle I had a 8-71N (318 hp) and replaced it with a Canadian Grizzly 8V92TA. (525 hp). I made several trips from Alaska to Key West, Mazatlan, Yuma and other winter destinations with both engines. I keep a mileage record of every time I fuel the coach (15 years and a LOT of miles). There is negligible difference in the fuel mileage. I use the same driving principals with the 92 that I did the 71. I also pulled the same trailer with both engines. The difference is I no longer have to endure 15mph climbs over 3000 miles of Rockies nor insulting remarks from the truckers over the CB like "You shoulda spent more on power and less on paint". Now they say "Bring my doors back".

If you install a hot rod engine and use that engine like a hot rod, fuel mileage will be your smallest problem. how much worse than 6.5mpg can you get?

If you install a big horse motor and use it when big horses are called for while considering the rest of your drive train you can never have too much hp and will be much happier.

You do not in most cases need more hp for speed, only climbs. Most coaches are designed to run hwy speeds. If you need more speed, change gearing.

You do not get an accurate estimate of mpg by taking a trip. You get a better picture after use of your coach over time and different conditions. I understand the principals of speed/drag/hp etc.

Most of us are different. The coach is a different brand, design, height, width, weight, rearend, transmission, is driven under different conditions (I now live in SD. Everywhere is uphill and against the wind), etc.

Some of us are compelled by nature to stretch the truth about mpg claims. That doesn't matter, one need only be concerned about their own.

In my opinion, if a mile or 2 of mpg is a great concern, The coach should be sold and a VW should be used.

Fleets of buses or trucks or any other vehicle need be concerned about these small differences due to the amount of fuel consumed spread across the fleet. That is one of the reasons you see generators in most trucks now that power the a/c and heat.

As someone on the boards says, "Your mileage may vary".
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Joe Laird
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unclewilly
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« Reply #31 on: June 17, 2010, 01:41:45 PM »

    Horse power doesn't mount to a hill of beans if the torque is not there thats what moves the mass.
Two engines with the same horse power and diffrent ft lbs of torque is going to effect the fuel milage
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kyle4501
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« Reply #32 on: June 17, 2010, 02:07:39 PM »

Unclewilly is right.
To further expand;

Torque is a measure of twisting effort independent of time - A pound-foot is the moment created by a force of 1 pound applied to the end of a lever arm 1 foot long.

HP is a measure of work - 1HP is the rate of work required to raise 33,000 pounds 1 foot in 1 minute.

HP can be related to torque if time is considered :
HP = (torque lb-ft) x rpm / 5252


So . . .
Torque moves the vehicle up the hill.
HP tells you how fast you make it to the top. (& gear ratios required)

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Len Silva
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« Reply #33 on: June 17, 2010, 02:15:13 PM »

That was the nice thing about owning a 4104.  I never had to worry about such foolishness as how fast I was going to drive.  I simply drove as fast as it would go.  A lot like driving an old VW Beetle.
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philiptompkjns
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« Reply #34 on: June 17, 2010, 04:05:03 PM »

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

Jeremy, as others have said; efficiency in acceleration versus cruise are 2 totally different games.  One depends more on weight and the other depends on drag (as I see it anyway). Power required for given speeds goes up exponentially because of drag.
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« Reply #35 on: June 17, 2010, 04:18:16 PM »

Jeremy, as others have said; efficiency in acceleration versus cruise are 2 totally different games.  One depends more on weight and the other depends on drag (as I see it anyway). Power required for given speeds goes up exponentially because of drag.

You might have meant to make this reply to someone else...I haven't said anything about this...

Jeremy
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