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Discussion Starter · #1 ·
TurboXS claims that a stock WRX has 168.4 whp at a chp of 227. That is a 26% loss. Now the Evo has pulls 233 whp at a chp of 271. That us a 14% loss.

Can anyone explain?

TurboXS did state that the 168.4 hp is at 5731 rpm, but at 12.1 psi, which is lower than stock max psi. Or does the max psi come after the max whp? So then max whp comes at a lower psi than max...doesnt seem efficient. Are my numbers off?

Evo chp maxes at 6500 rpm, reaches max boost of 18.8 psi at 4100 rpm, slowly coming down to 16.1 by redline, which is 7000 rpm. This makes more since, because at 6500 rpm the boost is still upthere. Makes sense, because of the bigger turbo.
 

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Discussion Starter · #2 ·
sorry i did not use the search button... :p

it seems like the consensus is that the factory rated hp of the Evo and Sti are lower than actual...

Assuming the same drivetrain loss as the WRX, which is 26% the Evo hp crank hp should be approx:

317 hp

and that of the Sti, approx:

362 hp
:confused:

Does that seem right?
 

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I'm no expert but i'd assume that the sti and maybe the evo also have better driveline bits that reduce drivetrain loss. So it would be safe to assume they probably are near 20% or maybe even less. The case flexes on 5mt's, the transmission mounts are not as hard allowing a little torque to be lost i think. There are certainly other bits that cause loss where the STI will not have as much loss.

I doubt they drop their HP figures too much. They don't want to claim the razor edge of what some STI's or evo's will do(like mazda did with the rx8) But still they need to say the cars are powerful.
 

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I have always figured around 15% drivetrain loss on my EVO (or the AWD DSM's from the 90's) and around 10% loss on the FWD DSM's.

The difference is that the EVO is basicly a FWD setup (very compact and efficient) with a trasfer case, drive shaft, and rear diff added in. The Scoobies are more of a traditional RWD setup with the FWD components added arn't they? My GF just got hers and I havn't had a chance to put it up on a lift and look at it :)

I always figured anyone claiming huge power train losses was trying to make excuses why their dyno numbers sucked, and on the EVO's I still feel this way. I think that the scoobies may actually have this much lose though :(

Keith
 

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No, the Subaru system is designed from the start as an AWD system. The FWD cars they used to have were an adaptation of the AWD system, not the other way around.

It's a bit of a mystery to me. The Evos aren't nearly as much faster percentage wise compared to the dyno power percentage difference. According to the dyno, the Evo is putting out 35% more power at the wheels, yet it's only what, 1/2 second quicker in the quarter and like .3 0-60? With similar weight? That's a pretty small difference compared to 35% more power. Of course more goes into a time than HP, but the WRXs gearing is certainly not ideal. And if you tune a WRX to put out the extra 60hp, it's considerably quicker. Likewise, a Neon SRT-4 puts up huge numbers on the dyno yet is slower than either car.

C
 

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Discussion Starter · #6 ·
Ok then another thing. The TXS Stage 1 Claims 275 crank hp while the Evo has 271 hp. TXS Stg 1 runs at around 15.1 psi while the Evo runs at 18.5 psi, so I guess the only conclusion is that the Evo actually has more, since they both have 2.0 liter engines, and 4G63 is more power potent.

Also TXS Stage 2 claims 309 crank hp, which is 'supposedly' higher than both Sti and Evo, yet that is still insufficient for the car to keep up...Could that be maybe due to different power curves, in that the Stage 2 actually reaches 309 hp, but takes longer and drops down quicker?
 

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GV27 said:
No, the Subaru system is designed from the start as an AWD system. The FWD cars they used to have were an adaptation of the AWD system, not the other way around.

C
I do not believe in % loss. I think its closer to an absolute value. Regardless of how much HP you are making, you will lose the same amount of power to friction. So, it the car loses 62HP to the powertrain, it will ALWAYS lose 62HP to the powertrain, even if it have 400WHP. If this is not true, then my WRX was making a truly absurd crank HP number, because she trapped at 103.9mph in the 1/4 at full weight.

Anybody agree with me on this?

-Jim
 

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Discussion Starter · #8 ·
I think the more power you make the more you lose to friction. The equation for the force of friction requires the coefficient of friction (which is material dependent) and the magnitude of the applied force. So if the applied force is stronger, friction icreases proportionally. Power is work over time, and work is force applied over time, so from this I must say that I disagree....
 

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I agree with Jimbo on this one, but add one little thing. Because of the properties of drag, as the liquid in the differential spins faster and faster, drag increases exponentially. That means that it's an absolute value of loss, plus a very very small exponential factor of additional loss due to drag.

Anyway, most chp claims are over rated from the factory for marketing purposes, as has been proven by just about every well renound tuner out there.
 

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eulerfx said:
I think the more power you make the more you lose to friction. The equation for the force of friction requires the coefficient of friction (which is material dependent) and the magnitude of the applied force. So if the applied force is stronger, friction icreases proportionally. Power is work over time, and work is force applied over time, so from this I must say that I disagree....
But giving it a single PERCENTAGE is completely inaccurate as well. Fluid friction increases with the square of rotational velocity. The engine isn't spinning any faster.

-Jim
 

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Discussion Starter · #11 ·
I also think a single percentage is inaccurate. And I was not talking about the differential fluid, I was just talking about the gears in the tranny. Also, the engine may not be spinning faster but its making more torque at the same RPM so that causes the tranny gears to spin faster, so that must mean that fluid in the differential is too...doesnt it? I don't really know anything about cars, just trying to be logical...
 

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eulerfx said:
I also think a single percentage is inaccurate. And I was not talking about the differential fluid, I was just talking about the gears in the tranny. Also, the engine may not be spinning faster but its making more torque at the same RPM so that causes the tranny gears to spin faster, so that must mean that fluid in the differential is too...doesnt it? I don't really know anything about cars, just trying to be logical...
That makes no sense. At a given engine speed/road speed in a given gear, the gears MUST travel at the same speed regardless of torque. These are simple machine design principles.

-Jim
 

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Discussion Starter · #13 ·
oh well :wiggles:

so how come the car goes faster then? what does that extra torque at say 4000 rpm do? Must make somethin go fast, because the car does?

or am I wrong again?

:confused: :confused:
 

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eulerfx said:
oh well :wiggles:

so how come the car goes faster then? what does that extra torque at say 4000 rpm do? Must make somethin go fast, because the car does?

or am I wrong again?

:confused: :confused:
The engine accelerates the input shaft faster due to morw torque, allowing you to go thru the gears faster.

-Jim
 

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Discussion Starter · #16 ·
PPMotorsports said:
The engine accelerates the input shaft faster due to morw torque, allowing you to go thru the gears faster.

-Jim
but don't you get higher speed at the same rpms in the same gear?
 

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eulerfx said:
Ok then another thing. The TXS Stage 1 Claims 275 crank hp while the Evo has 271 hp. TXS Stg 1 runs at around 15.1 psi while the Evo runs at 18.5 psi, so I guess the only conclusion is that the Evo actually has more, since they both have 2.0 liter engines, and 4G63 is more power potent.

Also TXS Stage 2 claims 309 crank hp, which is 'supposedly' higher than both Sti and Evo, yet that is still insufficient for the car to keep up...Could that be maybe due to different power curves, in that the Stage 2 actually reaches 309 hp, but takes longer and drops down quicker?
Or it could just be that thier power claims are a load of $hit! I don't know myself, I am new to the Subaru world and don't know if TXS is a well known and proven to be honest type of place or not. I never trust anyones "at the crank" claims.

Any shop wanting to make HP claims needs to get some at the wheels dyno figures and compare them to a stock STi on the SAME dyno. If they want to claim 300 HP at the crank and show on the chassis dyno that it makes the same or more HP at the wheels as a stock STi then I say great! If they are claiming they are putting out 270 HP at the crank and it makes as much or more power on the chassis dyno than a stock EVO then great! Otherwise don't go making "at the crank" claims. All I have to do to inflate at the crank numbers is use an outrageously high drivetrain loss percentage.

Keith
 

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eulerfx said:
but don't you get higher speed at the same rpms in the same gear?
Nope. You get from 1000 RPM to 7000 RPM in a shorter amount of time because the force applied to the gears is greater....but the wheels will be spinning at the same speed at 4000 RPM in 3rd gear weather you have 100 HP or 1000 HP driving the wheels. Now getting from 4000 RPM to 7000 RPM will take a LOT less time in a car making 1000 HP than it does in a car making 100 HP :D

Does this help you out?

Keith
 

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Discussion Starter · #20 ·
PPMotorsports said:
No. Unless you go to a higher engine speed, a higher road speed cannot be obtained in each gear.

-Jim
so then your car's top speed will not increase with upgrades unless you upgrade the engine so it can go to higher rpms in top gear?
 
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