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Old 04-27-2013, 08:16 PM   #476
Phatron
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^ who measured it? and with what?
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Old 04-27-2013, 08:41 PM   #477
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Quote:
Originally Posted by vicious_fishes View Post
drivetrain loss is 25% guys. this has been measured/verified in the past. obviously this will change if you have a light flyhweel, crank pulley, driveshaft or whatever. but stock...
So a wrx loses more hp to the drivetrain than a rs/2.5i just because it makes more power at the crank?

Last edited by RaceFaceXC; 04-27-2013 at 09:02 PM.
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Old 04-28-2013, 06:22 PM   #478
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Originally Posted by RaceFaceXC View Post
Drivetrains loss is more a constant HP than percent of power. For example A 500 WHP car does not make 750 at the crank.
I wouldn't say it's a constant horsepower, that doesn't make sense. That would be saying that your car has negative power at idle. More accurately, it is a percentage of the power but it doesn't apply as a linear function.
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Old 04-28-2013, 06:27 PM   #479
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should of just bought an older wrx?
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Old 04-28-2013, 06:49 PM   #480
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Originally Posted by Rudgers73 View Post

I wouldn't say it's a constant horsepower, that doesn't make sense. That would be saying that your car has negative power at idle. More accurately, it is a percentage of the power but it doesn't apply as a linear function.
Logic. Get some
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Old 04-28-2013, 09:26 PM   #481
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Originally Posted by RaceFaceXC View Post

Logic. Get some
Don't understand. You were wrong and I was just offering a more rational answer. The percentage of loss in a mechanical system is a function of the sum off all of the parts that contribute to the inefficiency. When you add up a bunch of mechanical inefficiencies that have different modes of loss (torsional displacement, gearing inefficiency, contact resistance, all different types of inertial forces acting together and against each other) than the total percentage lost is going to vary infinitely. Each part of the system becomes less efficient at different rates for different reasons. You could generalize, but that wouldn't be very logical
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Old 04-28-2013, 09:45 PM   #482
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Originally Posted by RaceFaceXC View Post

So a wrx loses more hp to the drivetrain than a rs/2.5i just because it makes more power at the crank?
Yes. If a wrx has 200 HP and loses 25% it transfers 150 to the wheels. If an RS makes 170 HP and has the same 25% loss it will transfer about 131 to the wheels.

Look at what we have: wrx - 50 HP loss, RS - 42 HP loss
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Old 04-29-2013, 02:02 AM   #483
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Don't understand. You were wrong and I was just offering a more rational answer. The percentage of loss in a mechanical system is a function of the sum off all of the parts that contribute to the inefficiency. When you add up a bunch of mechanical inefficiencies that have different modes of loss (torsional displacement, gearing inefficiency, contact resistance, all different types of inertial forces acting together and against each other) than the total percentage lost is going to vary infinitely. Each part of the system becomes less efficient at different rates for different reasons. You could generalize, but that wouldn't be very logical
Quote:
Originally Posted by Rudgers73 View Post

Yes. If a wrx has 200 HP and loses 25% it transfers 150 to the wheels. If an RS makes 170 HP and has the same 25% loss it will transfer about 131 to the wheels.

Look at what we have: wrx - 50 HP loss, RS - 42 HP loss
They have identical parts, why would they have different parasitic losses?

If one did a wrx engine swap into ones rs would the drivetrain become less efficient because the Engine bolted to it had changed?
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Old 04-29-2013, 03:10 AM   #484
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There's a big techy thread about this deep within the bowels of the drivetrain forum.
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Old 04-29-2013, 06:07 AM   #485
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Originally Posted by RaceFaceXC View Post

They have identical parts, why would they have different parasitic losses?

If one did a wrx engine swap into ones rs would the drivetrain become less efficient because the Engine bolted to it had changed?
The efficiency would be the same on the drivetrain. The loss is always a percent of the total power. More power, more loss. 25% of a big number is always going to be more than 25% of a small number. You'll always have more power with an engine that makes more power, but the actual number of horses lost will go up as the total power increases.

Sucks, right?
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Old 04-30-2013, 08:59 AM   #486
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Quote:
Originally Posted by Rudgers73 View Post
The efficiency would be the same on the drivetrain. The loss is always a percent of the total power. More power, more loss. 25% of a big number is always going to be more than 25% of a small number. You'll always have more power with an engine that makes more power, but the actual number of horses lost will go up as the total power increases.

Sucks, right?
Your math sucks.

It takes X ft/lbs of torque to twist the input shaft of the tranny (and thereby the rest of the drivetrain). Multiply that times RPMs and divide by 5252 to get the horsepower required. The number you come up with is the drivetrain loss. If it's 50 hp, that'll be 25% of a 200 hp motor, but only 12.5% of a 400 hp motor. The drivetrain torque requirement is static with regards to the motor spinning it; changing that motor only changes the percentage.

If it was always a fixed percentage, regardless of what was spinning it, you'd be able to make your car go by twisting the input shaft by hand, using only 25% of your available hand torque. Try that and get back to us to let us know how it goes. Hint: it won't.

J
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Old 04-30-2013, 10:02 AM   #487
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Quote:
Originally Posted by Special J View Post

Your math sucks.

It takes X ft/lbs of torque to twist the input shaft of the tranny (and thereby the rest of the drivetrain). Multiply that times RPMs and divide by 5252 to get the horsepower required. The number you come up with is the drivetrain loss. If it's 50 hp, that'll be 25% of a 200 hp motor, but only 12.5% of a 400 hp motor. The drivetrain torque requirement is static with regards to the motor spinning it; changing that motor only changes the percentage.

If it was always a fixed percentage, regardless of what was spinning it, you'd be able to make your car go by twisting the input shaft by hand, using only 25% of your available hand torque. Try that and get back to us to let us know how it goes. Hint: it won't.

J
Holy ****, someone with common sense.

I will say that as engine tq increases, shaft deflection increases, presumably increasing parasitic drag through the drivetrain. I would guess that this amount of increased loss to friction is small relative to the overall drivetrain loss.
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Old 04-30-2013, 12:07 PM   #488
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Quote:
Originally Posted by Special J View Post

Your math sucks.

It takes X ft/lbs of torque to twist the input shaft of the tranny (and thereby the rest of the drivetrain). Multiply that times RPMs and divide by 5252 to get the horsepower required. The number you come up with is the drivetrain loss. If it's 50 hp, that'll be 25% of a 200 hp motor, but only 12.5% of a 400 hp motor. The drivetrain torque requirement is static with regards to the motor spinning it; changing that motor only changes the percentage.

If it was always a fixed percentage, regardless of what was spinning it, you'd be able to make your car go by twisting the input shaft by hand, using only 25% of your available hand torque. Try that and get back to us to let us know how it goes. Hint: it won't.

J
I stand corrected. That makes sense. I knew something was going to be almost a constant. Turns out it was power required to compensate for the loss, not the percent lost
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Old 04-30-2013, 11:23 PM   #489
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Originally Posted by RaceFaceXC View Post
Holy ****, someone with common sense.
S'not so common these days.

Quote:
Originally Posted by Rudgers73 View Post
I stand corrected. That makes sense. I knew something was going to be almost a constant. Turns out it was power required to compensate for the loss, not the percent lost
If only everybody else out there were willing to listen to reason. Good on ya, Rudge.
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Old 05-01-2013, 01:56 AM   #490
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Did an argument just end peacefully on nasioc?
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Old 05-01-2013, 02:34 AM   #491
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Did an argument just end peacefully on nasioc?
No! That's not true! THAT'S IMPOSSIBLE!
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Old 05-01-2013, 09:32 AM   #492
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Did an argument just end peacefully on nasioc?
Quote:
Originally Posted by Counterfit View Post
No! That's not true! THAT'S IMPOSSIBLE!
And, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood; and the stars of heaven fell unto the earth...

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Old 05-01-2013, 11:22 AM   #493
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I guess we could get into an argument about who is gay or who is a total noob, but as long as the right answer comes out of it I am happy haha
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Old 05-01-2013, 02:33 PM   #494
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I guess we could get into an argument about who is gay or who is a total noob, but as long as the right answer comes out of it I am happy haha
Yup, you're the noob.
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Old 06-01-2013, 11:22 AM   #495
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Figured I'd bump up this thread to give some feedback. Finally got around to getting Mike to tune my car this year! kept talking about it, but never had the time. I've got the Rallisport v2 UEL headers, Tsudo N1 catback, and a Cosmo SRI. Mike was awesome with the tune and super quick, got everything wrapped up in about two weeks. Final tune feels GREAT. Pulls hard (for what it is) from 1.5k-redline now, used to bog down a lot under 2k and didn't really get power until about 3k-4k. Highly recommend you guys with mods to go get a tune. Makes the car feel MUCH better.
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Old 06-14-2013, 10:31 AM   #496
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Is anyone familiar with the guy on here who got his 2007 impreza 2.5i tuned and made like 189whp/187wtq? I know I saw it somewhere, but I can't find it and there's guys on the legacy forum who are calling BS on this.
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Old 06-14-2013, 10:39 AM   #497
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Those numbers would require a lot of work.
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Old 06-14-2013, 12:23 PM   #498
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^^^The guy had like a header back exhaust, intake, and LWCP. I've seen it somewhere, but where?
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