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Old 01-18-2012, 01:21 PM   #85
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Is drivetrain loss a constant percentage of power made by the engine? It seems more likely to me that it's a constant value such as 25chp loss to drivetrain friction. If it was a constant percentage that would indicate that friction (drivetrain loss) increases with increased power. I could be way off base here, just speculating.
No. Driveline loss is a function of RPM, Temperature, Material deformation, fluid vsicosity (another function of temperature), rotational momentum, and physical mechanical properties between joint connections and gearing teeth.

Basically, sitting still at idle will be less than that of WOT at redline.
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Old 01-18-2012, 01:37 PM   #86
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Quote:
Originally Posted by grambles423 View Post
No. Driveline loss is a function of RPM, Temperature, Material deformation, fluid vsicosity (another function of temperature), rotational momentum, and physical mechanical properties between joint connections and gearing teeth.

Basically, sitting still at idle will be less than that of WOT at redline.
off topic, but....when designing/engineering for an auto manufacturer, do they actually take that into consideration...so say when subaru says the imprezza makes 170hp they know its only going to put out a whopping 120awhp?
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Old 01-18-2012, 01:42 PM   #87
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off topic, but....when designing/engineering for an auto manufacturer, do they actually take that into consideration...so say when subaru says the imprezza makes 170hp they know its only going to put out a whopping 120awhp?
No, they normally design the engine first and throw it into a vehicle and design the rest around it. Good example...massive SUVs with 4cyl engines and DCTs to propel it forward enough to even make it comparable. But by God they're getting 28MPG while they are a dog in traffic.

Doesnt make since, I know, but why else has VW continued to offer their 2.0T in almost EVERY single vehicle. Cost and profit. Some engines are given better tunes and slightly better hardware to compensate. (IE: Ridgeline with V6 VTEC for more low end torque or the new 2.4L Civic SI)
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Old 01-18-2012, 02:09 PM   #88
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at rai?....anyways its not the point that numbers on dynos matter...just comparing dynos of the same car stage 2 vs k04 show 60-75whp difference
ok, i see your stage 2 dynos. I think that's fair then. WHP verse brake hp is obviously different. Originally i was referring to brake hp.
I also have only seen k04 dynos on 91 octane. Have you seen any on 93 with the version 2 tune? The only thing i can find on youtube is 313 whp on the version 1 tune.

I think we're splitting hairs here. If you take 80 brake horsepower, with 15% drivetrain loss, you are looking at 68 whp. If you did it with 90 brake horsepower, you are at 76.5 whp. If you take APR's number of 366 hp minus stage 2 of 274, you are at 92 horsepower. So it's pretty close.
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Old 01-18-2012, 02:26 PM   #89
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Quote:
Originally Posted by grambles423 View Post
No. Driveline loss is a function of RPM, Temperature, Material deformation, fluid vsicosity (another function of temperature), rotational momentum, and physical mechanical properties between joint connections and gearing teeth.

Basically, sitting still at idle will be less than that of WOT at redline.
Right, but what I was really getting at was the question about whether drivetrain loss is a constant percentage across all power levels (how everyone treats it) or if it is more of a certain amount of power, regardless of how much power the engine is making.

I still don't know if that makes any sense. does in my mind...
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Old 01-18-2012, 02:39 PM   #90
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.........or if it is more of a certain amount of power, regardless of how much power the engine is making.
I dont get the second portion or your comparison.

You have constant percentage (pretty much what EVERYONE does) and....????
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Old 01-18-2012, 02:44 PM   #91
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sorry... I meant a constant amount of power lost regardless of how much horsepower or torque the engine makes. Example: a constant 25hp lost whether the engine is making 200 or 300 hp. But I suppose that point is moot because more power usually means higher temps which would increase drivetrain loss.

I really should stay away from these technical questions...
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Old 01-18-2012, 03:10 PM   #92
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Originally Posted by Banshee View Post
sorry... I meant a constant amount of power lost regardless of how much horsepower or torque the engine makes. Example: a constant 25hp lost whether the engine is making 200 or 300 hp. But I suppose that point is moot because more power usually means higher temps which would increase drivetrain loss.

I really should stay away from these technical questions...
No no, I see what you mean. I think I have a fair answer for you.

In regards to the question, both instances you described are roughly the same thing, except one is a percentage function of the power provide which would increase with power increases and the other is just a constant 25HP off.

200 HP at assumed 10% loss = 180WHP
150 HP at assumed 10% loss = 135WHP
200 HP at 25HP constant assumed loss = 175WHP (12.5%)
150 HP at 25HP constant assumed loss = 125WHP (17%)

However, lets get technical with it:

What makes the power? The force pushing down on the piston which turns the crank. This force is generated by a number of things (Cylinder Pressure, Temperature, Fuel Heating value, Bore, Stroke, etc. etc.)

The engine power is roughly described, in theory, like this. Taken from another thread I did this in:

Quote:
Brake Horsepower (Watts) = N*Displacement(in cubic Meters)* (RPM/2)* nc*nm*nth*nv*Qhv*(F/A)*Air Density

N = Number of cylinders
Displacement = Bore*Stroke*pi/4
RPM/2 = Must be placed in Revs/Second = RPM/2 * (1/60 {s/min})
nc = Combustion efficiency = about .98-.99 on newer cars (can be calculated further, but these estimations are fine)
nm = mechanical efficiency = Function of RPM/heat/etc range of about .8-.93 (can be calculated further, but these estimations are fine)
nv = volumetric efficiency (what percentage is your TB open?)= 100% at WOT (Possibly a little more depending on the flow. Most I've seen is 108%)
nth = thermal efficiency = 0.8*(1-[compression ratio^(-.35)])
Qhv = Heating value of the fuel = 43,000,000 J/kg

Air Density = Pressure Entering / (287.2 J/kg-K * Intake Temperature)
Pressure Entering = Atmospheric Pressure * Pressure Ratio (This is a function of RPM) - J/m^3
Now that you have the power the engine makes you can determine how much force can be placed on the crankshaft to provide the neccessary torque at the flywheel. This is a function of material properties and mechanical efficiencies which decrease/increase throughout the rev band due to fluids heating up and metal expanding when hot.

Nevertheless........what an automaker displays as their "specific output" is what it has been measured at on the engine dyno and calculated through various equations and testing.

NOW...onto Driveline loss

Now that you know what your engine makes how do you quantify it through the wheels?

Easy: Power = Difference in Kinetic Energy over the amount of time it takes

Easiest way to do that is to dyno it in a controlled enviorment. Normally, this "constant" weight and constant air temp and etc. etc. is propelled by your wheels. This is a great indication of the power through your wheels...but it doesnt really coorelate to what your engine is making because of the weight of the driveshafts, gears, wheels, tires, hubs, etc. etc.

You could do a velocity run with a certain scan rate in VAGCOM but that accounts for drag forces which will make your power output significantly lower.

So how can you relate wheel HP to crank then? Well....you can theorhetically calculate it, but that leaves room for error (Plus it gets really confusing quick. Fluids dynamics + thermodynamics + variating degrees of freedom, frictional factors, stress analysis, plastic yielding effects with respect to temp), or you can do a very long process:

1) Dyno your engine
2) Using the same dyno, dyno your engine + Trans (1 for every gear since the mass changes for different gears
3) Using the same dyno, dyno your engine + trans + driveshafts
4) Using the same dyno, dyno your E + T + DS + Hubs
5) Using same dyno, dyno your E + T + DS + Hub + Wheels

This will take various fixtures to mount the dyno to...but would be one of the most accurate ways to relate your efficiencies together and finally provide a coorelation between brake and wheel horesepower.

Whats easier? Assuming constant percentage difference calculated from factory dyno and vendor dyno? or the process described above? Remember, no dyno is the same. All calibrations are different for various altitudes and temperatures and etc. etc.

1/4 Mile times are a good indication of power. Its as simple as how long did it take to propel this 3000lb vehicle in a 1/4 mile and what was its final speed?
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Old 01-18-2012, 03:30 PM   #93
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Can anyone tell me why I have so much hp lost when I did my dyno at dyno dynamic machine? My ride is only 4 months old, stock gti mk6 dsg, and 18 inch wheel with toyo R1R.
Whp: 171
Wtq: 180

I thought this car should have 210hp and 260 torque. I sent my car to vw service center, they said everything is all right, the reason I got such low hp is cause by the wheel (18 inch so is heavier) and the tyre and dyno dynamic will show lesser whp compare to other dyno machine like dynojet.. Also they told me the torque I'm getting is exactly 260 torque (manufacture number), apparently they said theres a format for them to refer. this is like 20% lost in hp and 30% lost in torque..

Somehow I feel something doesn't make sense here..
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Old 01-18-2012, 03:36 PM   #94
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Your technical knowledge is immensely superior!

Most of it makes sense. Thanks dood
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Old 01-18-2012, 03:40 PM   #95
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Your technical knowledge is immensely superior!

Most of it makes sense. Thanks dood
I hope it did man. I felt I got lost in a sea of physics there for a second.

Back on Topic: Apologies gregprep
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Old 01-18-2012, 06:15 PM   #96
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ok, i see your stage 2 dynos. I think that's fair then. WHP verse brake hp is obviously different. Originally i was referring to brake hp.
I also have only seen k04 dynos on 91 octane. Have you seen any on 93 with the version 2 tune? The only thing i can find on youtube is 313 whp on the version 1 tune.

I think we're splitting hairs here. If you take 80 brake horsepower, with 15% drivetrain loss, you are looking at 68 whp. If you did it with 90 brake horsepower, you are at 76.5 whp. If you take APR's number of 366 hp minus stage 2 of 274, you are at 92 horsepower. So it's pretty close.
Greg.... I know it's not 93, but there's some solid APR K04 dyno info from CA in this thread: http://forums.vwvortex.com/showthrea...1#post75230311

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Old 01-18-2012, 08:21 PM   #97
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cool, thanks Evan. 313 whp on 91 with the s3 intercooler is pretty nice. That's right at 360 brake hp. I know USP is having their party coming up in February which is half off dyno services, maybe i'll dyno on 93 and see if I come up with anything different. I know with the stage 1 tune there's only 4 hp difference, but maybe with k04, it's a little more.
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Old 01-18-2012, 08:30 PM   #98
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cool, thanks Evan. 313 whp on 91 with the s3 intercooler is pretty nice. That's right at 360 brake hp. I know USP is having their party coming up in February which is half off dyno services, maybe i'll dyno on 93 and see if I come up with anything different. I know with the stage 1 tune there's only 4 hp difference, but maybe with k04, it's a little more.
Found a dyno vid USP motorsport put up with the k04 v2 software. I'm sure this is with 93 octane

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