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big_torque
Dodge Dakota
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11/13/2002
16:59:57
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 Subject: BHP and RWHP
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I think I may have posted this before :
I see alot of people say 18%, 20 % , 22% loss through the drive train. I think you can say a percentage but its not always the same if you "free up" HP. I think its a constant # and not a %.
Example : 5.9L magnums rated @ 250 BHP and I`ve seen many dynos come up about 195 RWHP. Ok thats 22% loss or 55 HP loss.
Now free up 100 HP. (heads , cam , intake , etc.) -stuff that doesnt require anymore power to turn.
350 BHP - 22 % loss = 273 RWHP
350 BHP - 55 HP loss= 295 RWHP
MY QUESTION :Which one is correct?
I think you`ll always lose 55 HP ( in this example) unless you have a SC pulley to turn , different gears , different dia. tires , AC on , etc.
Heres another question : Same truck , same 55 HP loss. If the motor only made 40 HP , would the truck even move ?
All replys welcome
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Roger Dodger
Dodge Dakota
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11/13/2002
17:03:53
| RE: BHP and RWHP
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Good question. I'll bet if you presented dodge with that question that the R/T drive train might mysteriously improve. :P
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.alex.
Dodge Dakota
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11/13/2002
17:09:29
| RE: BHP and RWHP
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The driveline is causing you to lose a percentage of your power. Not a fixed amount of power.
As you increase horsepower at the crank (or what's also known as BHP), you also increase the rear wheel horsepower proportionally. The accessories and transmission and other components cause you to lose that percentage.
If you start with your 250bhp example, and add a 200 shot of nitrous, you will have 450 bhp (theoretically) at the crank. Once that power is transferred through the accessories and transmission to the rear end, you have lost 22% of the original 450 bhp. And thus you have 450bhp-99hp leaving you with 351 hp at the rear wheels........ versus your original 195 rwhp form the factory. That's pretty healthy, I'd say.
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Rodger Dodger
Dodge Dakota
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11/13/2002
17:19:43
| RE: BHP and RWHP
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Whats concidered the typical power loss through the drive train for most performance vehicles? (if there is a typical percentage)
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Bob Ross
Dodge Dakota
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11/13/2002
17:23:05
|  RE: BHP and RWHP
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Man 40 horsepower at the fly on the Dak R/T drive train... a wopping 8.8 RWHP! :)
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hello
Dodge Dakota
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11/13/2002
17:34:43
|  RE: BHP and RWHP
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sure 40hp would not need the big trans, driveshaft, or fly wheel. if you have a dyno who cares? most of the time people jugde rwhp to see what goes to the pavement. then take that number to see percentance of loss of flywheel hp. 40 hp would move it but not like 250hp. the word wench mean anything to you? most of the time people dyno their cars or trucks in third gear.
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big_torque
Dodge Dakota
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11/13/2002
18:03:29
| RE: BHP and RWHP
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.alex. ,
I talked about a 55 HP loss( approx.) Add the 200 shot and now you are losing 99 HP ? Wheres the added 44 HP loss come from ? The power from the engine (BHP)goes through :
Torque converter
Transmission
Drive shaft
Differential
Axles
and then to the wheels.
Of course the pulleys on the front of the engine takes away power too.
--- All those power robbing things havent changed----. They all of a sudden DONT provide more resistance or friction. See what I mean ?
Dyno before and after a 200 shot is added. I bet it puts another 200 right to the wheels.
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Canucker
Dodge Dakota
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11/13/2002
18:19:04
| RE: BHP and RWHP
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big_torque, not more friction .. more rotational resistance to being accelerated faster (by more TQ) ....
for instance .. try spinning a bike tire on a stationary bike (the ones in the gym) with one hand ... go as fast as you can, then use both hands ... can't spin it twice as fast can you? I doubt it.
it takes TQ to accelerate all those internal and external components (crank, pulleys, gears, clutch, driveshaft, ring&pinion, tires etc etc etc), if you increase the TQ applied to them, they're going to use some of that torque to get them selves moving before it passes the leftovers on to the next component.
So Friction is a constant load (xx.x hp) but as you start getting more hp your drivetrain inertial loss will increase proportionatly (sp?)
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.alex.
Dodge Dakota
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11/13/2002
18:20:49
| RE: BHP and RWHP
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So, if I buy a 200 shot kit and I was already making 250 at the crank. I was making 195 rwhp to begin with. Now i hit the button and all 200 hp go to the rear wheels. So I am making 395 at the rear wheels..... but if you account for 22% driveline loss, I am making 506hp at the crank. So my 250 hp motor is now making 256 hp more? Why don't they call it a 250 shot?
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.alex.
Dodge Dakota
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11/13/2002
18:26:00
| RE: BHP and RWHP
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Dude, Canucker.... whew. I jsut spent 17 minutes trying to type out what you just wrote.... and I kept erasing and trying to explain it a different way and all this shyte....
My brain hurts. But you're exactly right. It's not friction, it's resistance to motion or inertia. A body at rest tends to stay at rest, etc......
sheesh.
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hello
Dodge Dakota
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11/13/2002
18:28:40
| RE: BHP and RWHP
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200hp shot BY BY MOTOR on nitrous kits they`re not as accurate as you think, with power levels over 100hp. how are you going to get 200hp on a kit plate, fogger, cause a single nozzle won`t flow that much!! plus your percent of loss will go down because extra hp out of the same stuff. 10-15% loss let me know if that helps you?
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Jon
Dodge Dakota
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11/13/2002
19:16:50
| RE: BHP and RWHP
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A lot of nitrous kits advertise 100hp at the rear wheels. So does that mean they are actually adding about 120hp to the motor?
-Jon
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hello
Dodge Dakota
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11/13/2002
19:25:23
| RE: BHP and RWHP
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good question put one on your truck and tell us? so many different variables, now you are just getting silly. PS run your bottle pressure at about 2000 psi and see if you grenade your truck!!!
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big_torque
Dodge Dakota
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11/13/2002
20:09:02
| RE: BHP and RWHP
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I saw a show on TV where they dynoed a newer Vette before and after a 100 shot. 296 RWHP before , 405 RWHP after.
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KRC Tech
Dodge Dakota
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11/13/2002
22:13:21
| RE: BHP and RWHP
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That's why you do a negative dyno pull, you see the loss of HP/TQ when doing this. It is usually 22% on a stock R/T and the VIper converter drop's it to 18%. When I spray a 100 shot, I usually get 90-98 rear wheel, when I spray 150, I only get around 120. The percentage is linear as verified by the negative dyno pull. 22% at stock and 22% above stock.
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Shane
Dodge Dakota
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11/14/2002
06:50:43
| RE: BHP and RWHP
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drive train power loss is constant ex. a factory CC r/t had 86 hp loss to wheels (acording to motor trend) you add 100 hp to the engine you still lose 86 hp you dont lose more power for power gained most of the loss cannot be gained back though with light weight wheels,light drive shaft and trans mods you could probly reduce loss by mabie 30 hp but its not a cost effective gain.
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OneFast 4X4
GenII
11/14/2002
07:09:16
| RE: BHP and RWHP
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Yall are talking some serious SH!T on this post...Whew, that made me tired and my brain hurt from even reading it. But kudos for all the guys that have the technical knowledge out there!!
125 hp Nitrous, 5.5 Inch Lift, 33x12.50's .........etc. etc. etc.
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Demon Dakota
DakotaEnthusiast
11/14/2002
09:15:12
| RE: BHP and RWHP
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It's really simple. If your truck loses 20% through the driveline without NO2, then it will lose 20% with the NO2, but the NO2 will give you some number of HP at the rear wheels. Don't let the NO2 kit HP numbers distract you, because they are not exact. They are an approximate amount based on their testing. The same kit on different trucks/cars doesn't even produce the same rear wheel HP gains because every car, even if it's the same model, have their own unique power losses. It's almost like a signature. Say you use all synthetic lubricants in your truck, while the exact duplicate model your buddy has is running dinosaur products. I guarantee the one running the synthetic stuff has a better gain out of the add on power. All in all, there are so many variables that's it's impossible to just say "my truck loses 20% exactly, so I must have 400 HP at the crank". Take it to a dyno (before and after mods), and take from that what you will. Then figure in your crank HP (by dividing your RWHP by a numer, say .85 for a manual, and .8 for an automatic). I know you guys/gals know all the formulas and such, but it seems that some of you are putting way too much thought into this. A percentage loss is a constant in all your equations. The variables are the add on power makers.
K&N Drop in AF
True Dual exhaust and removed third cat
HO Cams & HO Intake
Modified TB
Autolite 3923 Plugs
TPS @ .76 VDC
IAT Adjuster Mod
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.alex.
Dodge Dakota
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11/14/2002
09:29:37
|  RE: BHP and RWHP
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Okay Okay Okay. The damn nitrous was a bad example. Of course there's no way anybody would put a 200-shot on a truck. It was just an example.
If everybody is so damn torn up about driveline loss, then dyno your truck on a chassis dyno first. Then strip the motor out of the truck and put it on a motor dyno and get that number.
Then divide the two numbers and you will see how much horsepower you lose through the drivetrain.
But you will have to do that same process everytime you modify anything to understand how much power it gave you.
Jeez.
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Canucker
Dodge Dakota
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11/14/2002
11:04:29
| RE: BHP and RWHP
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Shane: what are you trying to say?? could you clarify a bit please?
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004.7sltxtra
Dodge Dakota
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11/14/2002
19:33:22
| RE: BHP and RWHP
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I dyno'ed my 2000 4.7 slt extra cab at school (uti) also by magnaflow performance it pulled 191 hp and and 243 ft/lbs of tq My truck was what magnaflow used to make there 3 inch cat back system 11 hp increase and 38 ft/lbs of tq at the wheels
If you increase torque you can turn your driveline parts easyer thats why the math does not always work
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BlkDak
Dodge Dakota
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11/14/2002
20:28:44
| RE: BHP and RWHP
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demon dakota laid it out the simplest way of looking at it. that's all there is too it !
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GSMarquis
Dodge Dakota
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11/14/2002
20:37:10
| RE: BHP and RWHP
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When you get a tranny kit like trans-go....does this inprove just shifting or also power transfer?
21% off all GASOLINE @ any station!
email me marquisdurango@aol.com
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KenDawg
Dodge Dakota
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11/14/2002
21:49:55
| RE: BHP and RWHP
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Ok hope this clears some things up. You have people asking if I have 250 BHP and end up with 197 RWHP thats a 53 HP loss to the Rear wheels. So if I modify it and get 270 BHP does that mean I will still lose 53 HP. OF COURSE YOU WILL, you didn't change the resistance in the drivetrain so you will still lose 53 HP to the rear wheels, plus with a dyno the weather and tire pressure affect your outcome, so don't base it on only 2 runs. The only way to reduce your drivetrain loss is a diff tranny, axle, tires, and a carbon fiber drive shaft. Plus I don't think anyone here could actually give you a accurate BHP unless they pulled the motor and dynoed it.
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Shane
Dodge Dakota
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11/14/2002
22:27:33
| RE: BHP and RWHP
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Canucker: What he said! ^ . Basicaly im trying to say that drivetrain loss is a fixed figure. if you have 250BHP and 200RWHP Your losing 50HP to the drive train, If you Work some magic And get 300BHP you would have 250RWHP (numbers are purely example)
It would not make any sence for the drive train to take anymore power Then what it requires. alot are saying 20% loss across the board but its not as you increase BHP, the % of loss is less
250 BHP with 50 hp loss we will say is 20%
500 BHP would become 10% loss because you have doubled BHP but still have a 50HP loss in the drivetrain. Hope that makes sence.
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Duner
Dodge Dakota
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11/15/2002
02:11:50
| Resistance to Acceleration = Driveline Loss
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Try pushing your truck......
You can probably lean against the tailgate and get it rolling. After it's moving it doesn't take all that much effort to keep it rolling. What happens if you try and get it rolling quickly all at once? It takes MUCH more effort to accelerate the truck from a dead stop quickly. The faster you try and accelerate that weight the more energy it takes. Did the truck get heavier? Did it develop more rolling resistance? Nope! You just tried to accelerate it faster. The principals work the same regardless of where the power is coming from. The driveline loss isn't really a loss - it's a number difference based upon resistance to acceleration.
In the acceleration process - the driveline components and accessories have that resistance to acceleration. The amount of resistance is largly based upon how quickly you try and accelerate them. The dyno measures how quickly you can drive the rear wheels to speed. The more power you have the quicker they get to speed. This quicker acceleration is realized as more horsepower. The quicker you accelerate all of the driveline components and accessories - the more they resist that acceleration. That resistance is our driveline loss. The driveline loss goes hand in hand with the greater power/acceleration of the whole system. That's why it's always a PERCENTAGE of the power put into the system.
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litlpunisher
GenIII
11/15/2002
10:14:01
| RE: BHP and RWHP
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when i spray nitrous i go faster in the quarter mile. Does the hp matter or is it how it performs that matters. What does the % matter when all hp is a calculation. where running fast times is a rush. someone can have 300hp more than another person and still lose a race.
98 Dakota
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Texas Todd
Dodge Dakota
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11/15/2002
10:45:48
|  RE: BHP and RWHP
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I tend to agree with 'Duners' explanation of this concept.
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.alex.
Dodge Dakota
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11/15/2002
10:51:31
| RE: BHP and RWHP
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Centuries of scientists and especially physicists all agree with Duner's explanation, too. They've written whole books about it.
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Duner
Dodge Dakota
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11/15/2002
11:01:59
|  Physics books?
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It's difficult to explain some concepts without using any of the "book" type terminology.
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Texas Todd
Dodge Dakota
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11/15/2002
11:05:11
|  RE: BHP and RWHP
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Alex, Duner,
"WE'RE NOT WORTHY"
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