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Old 02-02-2003, 01:39 PM   #1
Cyberdemon
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Default WRX Drivetrain loss

Just out of curiousity and for arguements sake. If a WRX was dyno'ed at around 350WHP, what would be a fairly close approximation at the crank? My understanding of drivetrain loss was that it was always fairly constant, because generating more power wouldn't cause the drivetrain to magically become heavier and drain more force.

I was talking to someone who said their friends WRX dyno'ed 350 at the wheels, which means hed be at around 500 at the crank, his logic being that since a stock WRX dynos at around 160WHP, and is crank rated at ~225, that means that when the WHP is doubled, so is the drivetrain loss.

150hp worth of power loss seems completely wrong to me, but he seemed to be sure he was right, so thats why I'm asking you guys.

Anyone want to clear this up?
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Old 02-02-2003, 02:28 PM   #2
dookiebob
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No one knows the exact answer for sure, but it's generally accepted that the loss is not a linear percentage. Most people (including myself) think that as you go up in hp #s, the drivetrain loss is a smaller percentage. How much that percentage actually is remains uncertain.

That said, 350whp is nothing to scoff about. I hope he's got rails, tranny upgrades, and internal modifications on top of the usual mods...
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Old 02-02-2003, 02:28 PM   #3
CoreyRED02
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Default

Drivetrain loss is typically a percentage. And that is a topic of much debate especailly AWD cars. Each dyno house uses a "correction factor" when quoting crank HP. A fairly standard drivetrain loss for an AWD car is 20%. If that is true for the WRX is another question. I highly doubt that your friends car has 500 crank HP. If it does than it is most likely somebody on this board.

My $0.02

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soon to be CoreySTi04
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Old 02-03-2003, 12:45 AM   #4
amelnikov
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Drivetrain loss is almost constant with a very small percentage increase as more power is applied and friction becomes higher. This does not mean that at some point you're losing 150 hp through the tranny. Just think how much heat that would generate!!!! Most RWD tranny's as an average loose about 20hp worth. FWD is more efficient. AWD is the hog of them all. But the most I would venture to say is 40-50 hp. It has become popular to the extreme to "assume" a fixed percentage loss, which makes really nice numbers at the crank...Well you get the point.

Alex...
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Old 02-03-2003, 03:01 AM   #5
RED WORKS(WRX)
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Here plug in the numbers.....

http://www.vishnutuning.com/How%20Bi...Horsepower.xls

should give u some what, what you need....
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Old 02-04-2003, 01:52 PM   #6
dug-e-fresh
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There are two majpr schools of thought regarding drivetrain loss.

1) fixed loss

2) percentage loss

1) Fixed loss says that no matter how much power is being made, the drivetrain will only absorb soo much. In the WRXs case... its about 62 hp.

2) assumes that the intial ratio of crank horsepower vs wheel horsepower remains unchanged. In the WRXs case using the 62 hp number from above that equals 27.3% power loss (62/227).

So given a car that makes 350 WHEEL horsepower... method 1 says that its making 412 hp @ the crank (350+62). But with method 2, a car making 350 WHEEL horsepower would be making 481.4 crank horsepower.

So what do ya do? Is it 412 or is it 481?

Well, I say its neither.... what I do is average the two... makes me feel as if I am not inflating, yet not selling myself short...

481+412=893
893/2= 446.5

sound good?

def
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Old 02-04-2003, 02:10 PM   #7
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dug-e-fresh That is a very good concept you have thought of. I'm with you on that.
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Old 02-04-2003, 02:13 PM   #8
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dug-e-fresh, I think I like your approach better than either school of thought..
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Old 08-03-2013, 07:31 PM   #9
teethandnails
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I go with a solid 50% drivetrain less. Makes me feel better about spending crap tons of money!
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Old 08-04-2013, 10:18 AM   #10
03Sonicywrx
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Holy 10 year old thread.
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Old 08-05-2013, 11:50 PM   #11
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Bump from the dead? haha.
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Old 08-06-2013, 01:04 AM   #12
xandi911
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Quote:
Originally Posted by dookiebob View Post
No one knows the exact answer for sure, but it's generally accepted that the loss is not a linear percentage. Most people (including myself) think that as you go up in hp #s, the drivetrain loss is a smaller percentage. How much that percentage actually is remains uncertain.
Thats exactly what happen.
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Old 08-09-2013, 07:59 PM   #13
my2000apb
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you really need to do a wheel dyno and back it up vs an engine dyno
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Old 08-09-2013, 11:55 PM   #14
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My cobb AP says I have 600 hp and 867 ft/lbs, and I believe it! My WRX is a BEAST!
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Old 12-03-2015, 03:43 PM   #15
Cfarb72
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Default At Least You Believe It..!!

Well at least u believe it..!!? Lol.. There's NO WAY that u have 600+whp & almost 900lbft of Torque..!! 1st of all in order 2 get that kind of power besides that it probably would cost u over 20k 2 do so.! U don't get that kind of power by bolting on a bigger turbo/intercooler ect.! That kind of power would require major fuel system upgrades, internal Trans/Engine upgrades & Chassis/Suspension upgrades as well in order 2 do it right.! What makes me laugh about 2days younger generation is that 4 the most part they have no clue in regards 2 what "Real Power Is..!" It's not a matter of simply bolting on parts & adding up the amount of HP that the company says that it will increase, which btw IS NEVER EVEN CLOSE 2 BEING CORRECT & IT'S NOT "WHP" they are talking about either.!! With all of that been said lets 4get about the 600whp that "U Think" that u have & move on 2 the almost 900lbft of Torque that your "Computer Tuner" estimated u have.! Let's pretend 4 just a moment that it was true.!? I doubt but also hope that u know what exactly what Torque is & what function that it lends 2 a vehicle's performance.!!? Anyway if u had that amount of Torque in an AWD car without "Major Drivetrain/Suspension Modifications" it most likely wouldn't be a pretty site as far as your car goes after a few hard good traction launches.!! So your "Cobb Computer Tuner" says that u have 600+whp & almost 900lbft of Torque..!? Without knowing anything about what your car has in it but going by the fact that it's obvious that u have no idea of what "In Reality & Not Cobb Computer Fantasy Land.!" What it takes both "Knowledge & $$..!" Wise what it would take 2 actually generate those numbers I will almost guarantee that your "Self-Proclaimed Beast" makes no more than & I'm being generous 375whp & about the same or less in Torque.!?

Quote:
Originally Posted by Anubis80 View Post
My cobb AP says I have 600 hp and 867 ft/lbs, and I believe it! My WRX is a BEAST!
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Old 12-03-2015, 04:44 PM   #16
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Old 08-21-2023, 10:06 PM   #17
JP06_Bullitbullit
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Holy 10 year old thread once again
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Old 09-02-2023, 01:11 PM   #18
coalslaw
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my center diff bearings in my 5 speed dccd are going, its def causing drivetrain power loss.
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