2 Big Broncos Forums
lee Alessi
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• Denham Springs, LA, USA |
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• Registered on 6/3/2003 |
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• 192 posts |
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 Posted:3/7/2004 22:27 |
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Power-to-weight ratio is a measure commonly used when comparing various vehicles (or engine), including automobiles, motorcycles and aircraft. It is, simply, the power the engine develops, divided by the vehicle's or (or engine) weight.
In road vehicles the power-to-weight ratio is often used as an indication of likely accelerative performance. Vehicle weights have relatively little impact on top speed, which is mostly dependant on aerodynamic drag, which is proportional to the square of the vehicle speed (see drag equation). Acceleration, on the other hand, is dominated by the Newtonian acceleration term, P = ma, so more power (P) will deliver more acceleration (a) for any given vehicle weight (m).
In any vehicle the engine power-to-weight ratio is essential for vehicle power-to-weight ratio. But in an aircraft it's more critical than in any other vehicle because any additional weight requires more lift to be generated by the wings in order to lift it. More lift from the wings automatically means more drag, through a process known as induced drag, slowing the plane down. Thus if any two engines deliver the same power, the lighter one will result in a better plane. Power-to-weight ratio therefore has a much more important impact on overall performance in aircraft, including top speed.
In this usage the power-to-weight ratio is typically used to refer to the weight of the engine alone, as a useful way of comparing various aircraft engines. The term applying to the aircraft as a whole is power loading. |
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Bowtie Blazer
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• Baton Rouge, LA, USA |
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• Registered on 5/27/2003 |
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• 1,220 posts |
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Posted:3/7/2004 22:46 |
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I definately agree 800hp small block would be fun and make my truck go real fast but once I hit about 70-75 the HP it takes to beat the areodynamics of a flying brick that my truck represents is huge, so that also plays a big factor...as that article states its proportional the the vehicle speed squared which "should" be a climbing straight line which I allow to plateau at the safer speeds my vehicle can operate, brake and that my tires can handle.
In your situation, lacking such few MPH and having such low HP i think the weight to power ratio is considerable, being that such a small peice of this drag curve is being examined(taking the derivative of a larger section), if that makes sense.........your higher accreleration ability will get you that extra sustained speed.
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lee Alessi
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• Denham Springs, LA, USA |
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• Registered on 6/3/2003 |
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• 192 posts |
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Posted:3/7/2004 23:14 |
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hunh?????
go here....
http://www.geocities.com/z_design_studio/transmission.html
type in
5.61 3.04 1.67 1.00 and .73 for the gear ratios.
300 96/16 tires for my tires
you can drag your mouse over the chart to see speed vs rpm
so i dont think changing gears would have as much top speed effect,as getting say more hp and tq.hp is 105 @2500 and torque is 265 ft lbs @ 1500. i can get the truck in 4th to 63, shift into 5th and get to 67. assuming its aerodynamic drag, im more interested in fuel economy...... opinions?
| Quote: | this guy in a scout is using 3.73:1 gears with the NV4500 5 speed with 33/10:50 BFG MT's. Its running 2000 rpm @ 65mph and getting 25 mpg. 28mpg if he drives 60.
The Scout weights 4300 lbs with a full tank of #2 |
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Bowtie Blazer
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• Baton Rouge, LA, USA |
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• Registered on 5/27/2003 |
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• 1,220 posts |
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Posted:3/8/2004 00:46 |
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thats what I was talking about, deeper or higher gears will only increase and decrease torque....
Taking your mass as constant(although increasing with the addition of your winch and bumper) your coef of drag increases lets almost say linearly(in a straight line) with speed
power is equal to mass times acceleration.....considering mass constant your power made is directly proportional to the torque you make......UNTIL you consider drag...
This is when at lower speeds the torque you make is much more noticable from gearing do to lower drag.....
Power = Mass x acceleration
P=ma
Acceleration = Velocity x time
a=v(t)
Power = mass x velocity x time
P=mv(t)
sqrt = squart root
d = coef of drag
considering drag P =mv(t)sqrt(d)
Think of the = sign as a divider between two completely different animals yet equal
@ low speeds say drag is negligable and mass is constant
mass = 1
P=a
p=v(t)
so your power made at the engine is directly proportional to your velocity or the distance you cover in a certain amount of time make lots of power at the block get places fast, make little power at the block but have gears that make you move fast and it will make up for that power they are always 1:1 increase one or the other and they follow each other
Consider a much much higher velcity in this case highway speeds
mass is still constant but drag is considered
mass = 1
saying velocity is the square of drag
v x v = d
v = sqrt(d)
p=sqrt(d)(t)
at this point d becomes considerable because velocity is so large.....so lets assume you can make more power to begin with from the motor, if Power is already large, it takes a much higher velocity to equal out that power to drag ratio of 1:1 and give you the same feeling of feeling slowed down.....(think about it and pick a few numbers)
not considering drag
100 = 10(unit of speed) x (1 unit of time) => 100 = 10 => 100/10 = 10
considering drag
100 = 10 x 10 x (1 unit of time) => 100 = 100 => 100/100 = 1 (drag sucks)
considering you make more power at the motor and move at the same speed
800 = 10 x 10 x (1 unit of time) => 800 = 100 => 800/100 => 8 800/400 = 2
it takes 8 the original power considered for you to double in speed
granted all kinds of other factors including road surfaces (coef of friction), engine braking, etc etc etc play parts as vehicles vary
you don't need a double in speed you need a minor increase in speed, so a small gain in HP(turning up injectors) may get you there with a change in fuel economy( Home much? I couldn't tell you) this is where comfortable engine RPMS, running temp, etc are etc etc all play parts (on a diesel I doubt this change will be much)
consider these situations:
I had an 82 chebby with 4.11's p235's and a decent 350 and I could kill near anything including newer v-8 camaros stop light to stop light, because our speeds never got that high where drag would set in that much....
Also consider how people say crotch rockets have no power because of lack of torque......or off the line acceleration versus say a harley, because a harley has much more HP yet when speed and drag set in the mass of the harley looses severly to a crotch rocket, making the HP to a point then it falls not to mention the crotch rocket gains HP with speed...
Does your brain hurt yet?
I think turning up the injectors will hurt very little and increase your top speed a bit
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schmuck
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• nola, XX, USA |
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• Registered on 5/21/2003 |
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• 1,187 posts |
• 1 Vehicle
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Posted:3/8/2004 17:03 |
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you should have just left it at power to weight ratio
too much bull shit just to say your truck is too fat and you need more motor
nucking futs
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Donzi
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• New Orleans, LA, USA |
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• Registered on 6/7/2003 |
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• 259 posts |
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Posted:3/8/2004 18:29 |
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| Quote: | you should have just left it at power to rate ratio
too much bull shit just to say your truck is too fat and you need more motor |
Well said  |
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LOCKED UP
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• Baton Rouge, LA, USA |
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• Registered on 9/29/2001 |
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• 1,256 posts |
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