what do you believe to be accurate?

[bimmertech]

ok, lets duke this out. what do you feel is more accurate when converting RWHP numbers to flywheel numbers?

i personally feel that a drivetrain will lose a certain amount of hp and not a percentage.

many a dyno operator i have talked to feel the same way.

the consensus for a 5.0 w/ a 5spd is a 32hp drivetrain loss.

go ahead and feel free to call me dumb, but you better have hard evedince to back that up.

engine dyno numbers are usually way higher due to electric water pump, dyno specific exhaust systems,no accersories, etc..

if you where to eliminate those variables i feel you would find a 32hp difference.

keep this applicable to dynojet chassis dyno's for arguments sake.

 

[CManT1914]

Well everybody says 15%, but really, the drivetrain only takes so much power to move right? Anymore power and that's just extra. So say it takes 30hp to move the drivetrain, well it's not gonna sap more power from a 500hp motor than a 200hp motor I would think. But what do I know? I've never been to the dyno, lol.

 

[loudpedal99]

I think the problem with that is you aren't just moving the drivetrain, you're accelerating it. A more powerful motor is going to rev quicker, but to do that it has to accelerate the drivetrain quicker. So I could see the drivetrain claiming more power at a higher engine output (just guessing).

Whether or not the power loss would increase linearly enough with respect to increasing engine output to make a reference as easy as a percentage, I don't know. I don't even know if the power loss would even increase enough over a range of power outputs to even need to be taken into consideration. Say you dyno a car with a 300hp engine, and you lose 30hp through the drivetrain. Then, say you dyno the same car only at 500hp and you may lose 32hp (close enough for a set number), or you may lose 50hp (more like a percentage). No way to know w/o direct testing, or some real formulas.

Again, I have no "hard evidence", just my .02

 

[Numbles]

I personally would say percentage. The faster you try to turn over the drivetrain the more it pushes back.

For example. Grab a 10lb weight and hold it straight out. Now spin it slowly. The weight doesn't push back on you that hard. Now try and spin that same weight at a faster rate and it takes more muscle from yo to do it. Same principles with drivetrain coupled with vehicle weight.

 

[HISSIN50]

I say it is closer to a given number, not a percent. Not that it is a given number and that this number does not change, but it is not large in comparison to the initial parasitic loss value.

I would even venture to say that one could come up with a loose value that for every XX additional HP a given combo makes, add "A %" to its baseline.

 

[Numbles]

Hissin50. With your logic. And im not trying to be a smartass here. Wouldn't taking a "loose value" and adding a % to the baseline for "XX amount of power."

Be the same as just using a loose percentage.

And I agree with you on it being a loose figure. Too many factors.

 

[DarkProphet]

I beleive it should be a exponentially decaying percentage bassed on RPM's. But im a nerd. It takes a certian amount of power to make the drive train spin, but to make it spin faster, it takes more power, so Im going with the percentage. By using 13% or 15% or whatever, your taking an average, but I think it should be based on the %loss at the max HP RPM's and that would be the most accurate, but overly complex. By using the average number, you might be off at the max hp or torque's rpm rating, and this could skew the results a bit. Not sure.. just ideas.

 

[HISSIN50]

Hissin50. With your logic. And im not trying to be a smartass here. Wouldn't taking a "loose value" and adding a % to the baseline for "XX amount of power."

Be the same as just using a loose percentage.

And I agree with you on it being a loose figure. Too many factors.

It would be two different numbers in the calculation though. Like if someone makes 250 RWHP and has 15% driveline loss. If they do future mods to make 500 RWHP (double previous power) but retain the same driveline (same basic intrinsic parasitic loss there), there would be additional parasitic loss, but not double the value of what it was before. Two different factors at work (one %for baseline and one % for additional power added). And the latter percentage would be relatively nominal compared to the first. It is a percent, like you said, but not a straight percent per HP (doubling the power would not double the driveline loss).

Hmm, that cleared up what I was trying to say not one bit.

 

[CManT1914]

Hmm, that cleared up what I was trying to say not one bit.

I think I am MORE confused now! j/k

 

[wytstang]

Sound like your applying Newtons 2nd law JT or trying to explain it (may be wrong) Newton's Second Law of Motion:
II. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors in this law the direction of the force vector is the same as the direction of the acceleration vector.

 

[final5-0]

It would be two different numbers in the calculation though. Like if someone makes 250 RWHP and has 15% driveline loss. If they do future mods to make 500 RWHP (double previous power) but retain the same driveline (same basic intrinsic parasitic loss there), there would be additional parasitic loss, but not double the value of what it was before. Two different factors at work (one %for baseline and one % for additional power added). And the latter percentage would be relatively nominal compared to the first. It is a percent, like you said, but not a straight percent per HP (doubling the power would not double the driveline loss).

Hmm, that cleared up what I was trying to say not one bit.

Makes sense to me JT ...... and I agree with you

Don't focus on the first 90% of your post and key in on the last sentence.

If you double the total power ...... why in the would would it take double the amount of power from before to turn the exact same drive train

I think this is one of those things that you can't really know for sure!

Like ... does the light really go out when you close the fridge door

Grady

 

[nmcgrawj]

Like ... does the light really go out when you close the fridge door

Grady

SURE it does...close the door really really slowly and u can see it go out But i get what u are saying. I also think it would be some sort of complicated combination....its obvious it would take more to spin faster....but it wouldnt take as much as the original amount would. Its kind like saying, like was said above, take your base of XXhp off for accessories...then take away 1% for ever 10hp added or something crazy like that.

Someone who is bored and has resources should do this one day

 

[Joes95GT]

the consensus for a 5.0 w/ a 5spd is a 32hp drivetrain loss.

go ahead and feel free to call me dumb, but you better have hard evedince to back that up.

You made the claim. YOU need to bring the "hard evidence" to back it up.

I've browsed through a few of the posts, and I'm finding a few people who believe what I do. There is no way that a specific value can be assigned to what a 5.0 is losing through a 5-speed.

There is absolutely no way in hell that a blown H/C/I 302 is getting the same power sucked up as a completely stock 302, or as a 300 RWHP 5.0. Naturally, I would think (and remember, I know next to nothing) that each of those engines accelerate differently. Because of the different rates of accelerations, the parasitic loses would vary. As you turn something faster and faster, there comes a point where it becomes MORE difficult to turn it faster (i.e. parasitic loses).

I really hope I'm making sense. I have a hard time conveying my point sometimes.

Also, I think different clutch set-ups would affect rear wheel output slightly...

Joe

 

[nmcgrawj]

You made the claim. YOU need to bring the "hard evidence" to back it up.

I've browsed through a few of the posts, and I'm finding a few people who believe what I do. There is no way that a specific value can be assigned to what a 5.0 is losing through a 5-speed.

There is absolutely no way in hell that a blown H/C/I 302 is getting the same power sucked up as a completely stock 302, or as a 300 RWHP 5.0. Naturally, I would think (and remember, I know next to nothing) that each of those engines accelerate differently. Because of the different rates of accelerations, the parasitic loses would vary. As you turn something faster and faster, there comes a point where it becomes MORE difficult to turn it faster (i.e. parasitic loses).

I really hope I'm making sense. I have a hard time conveying my point sometimes.

Also, I think different clutch set-ups would affect rear wheel output slightly...

Joe

Its pretty simple i think....u turn something...it gives resistance....what we are discussing is the amount of resistance right? Well turn it faster, its GOTTA give more resistance...how much more? Hmmmmmmmm

 

[SQUEEZE&STROKE]

Me thinks..."Who cares about flywheel Hp...what does it make to the ground?!?"

 

[strokedandblown]

If your on an engine dyno then you know what is made at the flywheel

If your on a chasis dyno then you know what is at the wheels.
obviously

IMO, unless your selling the engines i really dont care what it makes at the flywheel i want to know what it puts on the ground.

but this is very intersting to read

 

[Zero Signal]

An inversly decreasing percentage with RPM. Like rolling resistance, drivetrain loss as a percentage will decrease with power and rpm. So you are increasing the actual loss, but decreasing the percentage untill, in theory, it flatlines. That will get you the most accurate model. But what's the point. When nobody here actually uses an engine dyno.

 

[Joes95GT]

Me thinks..."Who cares about flywheel Hp...what does it make to the ground?!?"

Sort of out of the realm of discussion, but wait until you put a big horsepower, high RPM motor with a HUGE converter on it. RWHP numbers will become VERY deceiving...

Joe

 

[YEAHLOH95]

i think thats how the dynos work by measuring how fast they are accelerated they don't care whats between them and the engine. the percentage is just a guess at how much you are using to turn the drivetrain by itself . and you use a different % for an auto as they aren't as effiecient. i have heard of just changing wheels makes the numbers vary between pulls IE lighter wheels = more power . i agree with f = ma but you also have an ineritia force going against the dirrection you are turing everything.just as a alum fly wheel and drivshaft help in that department .less mass

 

[DarkProphet]

An inversly decreasing percentage with RPM. Like rolling resistance, drivetrain loss as a percentage will decrease with power and rpm. So you are increasing the actual loss, but decreasing the percentage untill, in theory, it flatlines. That will get you the most accurate model. But what's the point. When nobody here actually uses an engine dyno.

Exactly, thats what i kinda tried to say. But it was late and I was drunk...