Topic: Drivetrain loss on a dyno

[Arabas]

on each dyno run, we get a result of whp.
i have been reading that to calculate the hp at the cranck, we also calculate an X% drivetrain loss, different percentage for each car model.

on our LNF, we have a stable 18% IIRC that we calculate on the whp to get hp at the crank.

my reasoning is that if we get a dyno run for a certain LNF kappa (stock) we add a 18% to get crank hp. we tune the very same car (everything else remains the same) and on the whp we also add a 18% to get crank hp.

to my understanding, the drivetrain loss on a car is the same regardless of the whp, so my guess is that it is somewhat wrong to calculate an X% of drivetrain loss. i suppose the more reasonable is to calculate a certain amount of hp that the car "consumes" for the drivetrain function. (hope i explained it right, given that it is a bit compplicated to explain myself in english)

i was wondering what is the correct way to calculate the crank hp, percentage of whp or a fixed amount of hp?

[Brazen17]

If we used a fixed amount and "built" the engine to make less hp than this number would we be making negative hp? Perhaps the real way to calculate hp loss is somewhere in between. Just something to think about.

[miller11386]

Crank HP is calculated on an engine dyno.

Wheel HP is calculated on a chassis dyno.

If you want a crank HP number, pull the motor and put it on a engine dyno. Everything else is just a "guess"

IMO crank HP is a useless number anyway. IE: a C6 Z06 has 505hp!!! that's great for GM bragging rights, but only about 440-460rwhp gets to the wheels.

[snaponbob]

1) "Conventional wisdom" seems to be 15-18% on rear drive cars. As for "calculate a certain amount of hp that the car 'consumes' for the drivetrain function", that is basically driveline loss. That said, there are lots of variables. Drive line component lube viscosity and temps are a couple.
2) "Horsepower" is only a mathematical calculation based on torque. And that is all it is.
3) The only TRUE method (for a given car) to KNOW the drivetrain loss is to pull the engine and dyno IT.
4) Lyndon Wester has explained that a dyno can be used to generate a "reverse" power curve by graphing drag as the drum slows down. (Bad wording, but that is the general idea.)
5) And lastly, I will throw out the standard cliche - all that matters is the change at the wheels after tuning (with conditions as similar as possible and on the same dyno).

[Critterman]

If it goes faster after tuning and won't stay pointed in one direction you know you are getting there.

[TomatoSoup]

If it goes faster after tuning and won't stay pointed in one direction you know you are getting there.

Yahooooooooooo!!! (and/or scream of terror from your passenger)

[Arabas]

If we used a fixed amount and "built" the engine to make less hp than this number would we be making negative hp? Perhaps the real way to calculate hp loss is somewhere in between. Just something to think about.

Brazen17, i would say  that in the case u describe, the motor would not even have the power to spin the axle, so we would consider it as 0 whp + the hp "consumed" by the axle.

thank u all  for your answers. from what i understand it seems that hp on a dyno is actually some way to calculate estimated hp (as in point 2 of sob)

[snaponbob]

If it goes faster after tuning and won't stay pointed in one direction you know you are getting there.

"Butt dynos" are cheap, aren't they? And, NO WAITING !!!!!!!!!!!!!!!!!!!!!!!

[DeepBlueGXP]

"Butt dynos" are cheap, aren't they? And, NO WAITING !!!!!!!!!!!!!!!!!!!!!!!

I don't know, $399 doesn't seem cheap
http://kalecoauto.com/index.php?main_page=product_info&products_id=41

[Arabas]

I don't know, $399 doesn't seem cheap
http://kalecoauto.com/index.php?main_page=product_info&products_id=41

 

anyone seen the part number on this one??


Model: ARSE411 

[GXPinKC]

Arabas, that is so funny!  Kind of fits!

[miller11386]

The reviews are better

I pasted them below:

Reviews:
by Billy Joe Jim-Bob    Date Added: 07/10/2006
I added a big tri-level wing and some stickers to my car (Geo Metro).
I knew that I felt a difference but my friends all laughed. That is until I showed them the results of the butt dyno.
Now they're all laughing with me, not at me.

by Ajaxus Titties    Date Added: 05/16/2006
One set of 10 yo used spark plugs and 5 bean and cheese burrito's later I've got gains of up to 150whp and thanks to this lil baby I can prove it. Thanks guys for yet another great product!


by dave wray    Date Added: 01/09/2007
This thing is junk, I added a electric supercharger (that kinda looked like a computer fan) and it said I only added 8hp. My car now pulls like crazy. I blew the doors off a dsm, and a mustang in my accord in the same night. Although they where in the turning lane.....

by dysolve dredd    Date Added: 01/28/2007
Guys come on when does the 4wd version get released? I have to put my skyline on bricks to use this... First i take the rear tyres off the car and put the axels on bricks and run the front wheels , Then i do the same process with the back wheels.

by Daniel Jenk    Date Added: 05/29/2007
I'm returning this piece of junk...I bought it to accurately gauge how much horsepower I gained from the 2" lift and 32" tires I put on my Wrangler, but it doesn't work. I installed it on my seat, just like the instructions said, but in all my excitement while flooring it, I farted (a little squirty, I admit) and the thing shorted out and gave me a nasty little shock on my posterior. WTF? A little butt gravy and the thing goes FUBAR? There should be some kind of warning on it! I want my money back!

[SKY888]

thats funny shiiiit guys!!! lol

[SKY888]

now I need to get their email address/contact info........so I can submit a sponsorship proposal.........so I don't have to pay $399   

[kennysabarese]

If this post is still serious, There are two school's of thought on drivetrain loss. And it's been debated a billion times on every car forum ever.

One is that the loss is a constant percentage, so for example if you had 50% drivetrain loss, a 100bhp car would give you 50whp and a 500bhp car would give you 250whp.

The other school of thought is that it's NOT the first example aka, not a linear loss, but a certain amount chopped off depending on the car. So say if there is 50hp drivetrain loss, if you have 100bhp car you have 50hp, and if you have 500bhp car you get 450whp.

I don't know the answer. Honestly I don't care. Dyno you car stock, then dyno it on the same dyno in similar conditions if possible after mods to see the gain. DONE.

[Arabas]

If this post is still serious, There are two school's of thought on drivetrain loss. And it's been debated a billion times on every car forum ever.

One is that the loss is a constant percentage, so for example if you had 50% drivetrain loss, a 100bhp car would give you 50whp and a 500bhp car would give you 250whp.

The other school of thought is that it's NOT the first example aka, not a linear loss, but a certain amount chopped off depending on the car. So say if there is 50hp drivetrain loss, if you have 100bhp car you have 50hp, and if you have 500bhp car you get 450whp.

I don't know the answer. Honestly I don't care. Dyno you car stock, then dyno it on the same dyno in similar conditions if possible after mods to see the gain. DONE.

second theory is what i initially asked about. maybe i didn;t put it that straightforward as you, language barrier, but it seemed to me as the correct approach.
not a fan of dyno numbers, i just wanted to see what people think/know is true about this

[Gentleman Jack]

How is it that this is even still a question?  Surely someone somewhere with too much money has done the tests required to find the answers.  Dyno engine, install in car, dyno car.  Remove engine, make changes, dyno engine.  Install in car, dyno car.

It's not very complicated.  It is very expensive. 

The same question can be asked about air conditioning. That is said to use 10% of a cars horse power.  So when I tune my engine, with no mechanical changes what so ever, my ac all of a sudden required more power too?  Bone stock my ac into would need 26hp.  But now that my car is tuned to the hilt it all of a sudden requires 38.76 hp? 

Kenny- I think you should tell Miller to do the test.  He seems to have spare change lying around since he can't find a block to buy, so he is a perfect candidate. 

GJ

[kennysabarese]

The same question can be asked about air conditioning. That is said to use 10% of a cars horse power.  So when I tune my engine, with no mechanical changes what so ever, my ac all of a sudden required more power too?  Bone stock my ac into would need 26hp.  But now that my car is tuned to the hilt it all of a sudden requires 38.76 hp? 

"They" say similar things about superchargers. I've never researched enough to get to the bottom of it.

Any money Miller doesn't spend on his Kappa he will surely spend to buy yet another car, then complain about money

[miller11386]

Sorry GJ I dont have my car to do that with at the moment. its all tied up for the winter.

However you would be a great candidate for this project as well! Cali has tons of tuner shops and engine dynos  & chassis dynos to use!

[miller11386]

"They" say similar things about superchargers. I've never researched enough to get to the bottom of it.

Any money Miller doesn't spend on his Kappa he will surely spend to buy yet another car, then complain about money

Sorry kids! It's hard to play in Ohio when you have all these cars running around. The king of the streets in Cleveland has a nasty Supra in the 800hp range. (still have yet to see it) That car plus a few Evos that are running around are kings on the street @ ~500-600hp

Unfortunately it makes ppl when they see the sky's little baby turbo and measly 350whp

[Dave@DDMworks]

"They" say similar things about superchargers. I've never researched enough to get to the bottom of it.

Any money Miller doesn't spend on his Kappa he will surely spend to buy yet another car, then complain about money

On modern cars, when you go full throttle the A/C compressor is turned off, so it takes 0 horsepower to run at full throttle.

AS for superchargers, the load that they exert is dependent on the pressure and speed of the engine, so it is not a fixed percentage.