168 Whp, 25%drivetrain loss?

SlideWRX · 08-01-2001, 12:16 PM

in one of the latest magazines, someone dynoed a WRX and got 168 wheel hp, which is about 25% drivetrain loss. I was wondering if anyone else has done this, with a wrx or rs, and can confirm the 25% thing for our AWD drive train. Considering 2wd manuals run 15-18%, the 25% still seems high.

mbiker97 · 08-01-2001, 12:32 PM

Yeah that seems about right. I've also seen around 180 WHP. Think about it. There are the extra set of axle/parts that all need to turn also. There is alot of parasitic drag in all AWD/4WD vehicles. As for those particular dyno results, remember dyno for the most part are somewhat inaccurate. The daily variables like temp, humidity, engine heat soak all play a huge role in the dyno results. Plus if it was a load based dyno instead of a dynojet the results could be different also. Hope this helps.

Seth

JGard · 08-01-2001, 12:35 PM

word...

also can't forget we have 3 differentials compared to one for 2WD cars. Those eat up power easily

ITR&RSGUY · 08-01-2001, 12:47 PM

be sure also to see if they used a proper 4 wheel dyno , I know on a 4 wheel dyno a RS will show 100 hp to the wheels which is 65 hp down form the flywheel at that ratio the WRX would show about 138 at the wheels on a 4 wheels dyno, this is the way I look at it, the WRX is very fast, the RS is quick for a NA sub 20K so who cares how much your putting down stock, fact is HP is MUCH easier to make than traction and we have all the traction we can use so be happy :-)

jk147 · 08-01-2001, 01:04 PM

yeah I read that article as well.
Remeber, we get 168 hp from all 4 wheels, not just front or just back. We lose more horsepower, but gain a lot more tranction. actually, twice as much traction as fwd or rwd cars

Julian · 08-01-2001, 01:19 PM

FWD cars have less parasitic loss than either FWD or AWD. RWD cars used to run about 22% loss. I expect that's less now, with modern manufacturing techniques. I seriously doubt 25% of the engine's output is soaked up by the various drivetrain bits.

Subaru used to claim that a FWD version of one of their AWD cars would not get statistically better mileage.

Julian

Besides, each dyno is different.

XT6Wagon · 08-01-2001, 01:54 PM

Um, guys, stop using a dynojet to create "facts". A dynojet will show a HP "loss" when you add larger heavier brakes. Yet some how I doubt that a larger brake rotor has ANYTHING to do with the output of the engine.

A FWD, RWD, and AWD will ALL PUT DOWN THE SAME HP!!!!!!!!!
Now it might be that the FWD will take less HP to acclerate for that given aceleration rate, and the FWD, and RWD will both need less than the AWD. This is due to rotating mass. Many people including myself at times have gotten lazy and refered to reducing the rotating mass as a way to make HP, when in fact it most likely doesn't. You can get some HP gains by reducing the wieght of the crank pulley and flywheel if they are causing frictional losses at the bearings.

Also modern differentials are so effecient that its likely that a glob of mud on the driveshaft would be a greater HP loss (flexing of the shaft due to unbalance) than the Diff itself. This isn't the 50's anymore and they are cars besides so they don't need heavy gears, rugged bearings and the other added things that 4wd trucks use to have a rugged 4wd system. Recall that a huge percentage of the 4wd/awd myths come from the early 4wd pickups.

ITR&RSGUY · 08-01-2001, 02:07 PM

A FWD, RWD, and AWD will ALL PUT DOWN THE SAME HP!!!!!!!!!

Uh no. Friction losses, heat generated, and Noise, yes noise.....these all are generated by HP going through the drive system, the less power leaches you have on said vehicle the more power to the wheels. an AWD car with a 2.5L 165 HP H4 will dnyo with less HP to the wheels than a RW or FF car with the same engine. FACT, doesnt matter if the differential is effecient, it is still not 100% effecient, and NEVER will be it sucks power plain and simple. But it is a GOOD trade off, POWER can be made EASy and relatively cheap, hell 3000 will but you 100hp on a Turbo RS, but trust me it will cost you more than 3000 to make a say integra AWD.

WRX1 · 08-01-2001, 07:26 PM

On a awd car, there at many more bearings that are spinning(transfer case, 2 sets of diff bearings, 2 sets of wheel bearings, etc), so threre is going to be drivetrain loss. You can't spin all the extra parts on not have less wheel HP, but at the same point and time, you are also gaining a ton of traction.

Russ

krzyss · 08-01-2001, 09:10 PM

there is no free lunch.
So as many others said spinning 4 wheels instead of 2 needs more effort.

Krzys

PS If You have Subaru check how far can You coast.

shirokuma · 08-01-2001, 10:10 PM

I've gone and done a dyno test for my Legacy B4, and after observation of the testing, came away with some questions to the overall validity of the testing, especially for Subaru's.

The first thing I noted right away is that they open the hood to attach instrumentation, and leave it that way for the test. Now, this raises some problems for the intercooler - as in, there is no air being fed to the intercooler, as it would under speed. In fact, the test is run in 4th gear, which means at the top end, air would be being forced over the intercooler at around 110mph. This has a rather beneficial effect on power - on the road. So right there, you have to scratch out most of the power from the intercooler.

The other problem is that ambient temperature makes a large difference in turbo power output - for the same reason the intercooler does. So, for instance, I could have up to a 20hp varience in hp output depending on if I did testing in the middle of winter vs. mid summer.

So, take any measurements with a grain of salt - there will be no definitive answer from a dyno test, the only real answer will be from acceleration tests.

Paul

Zahnster · 08-01-2001, 10:42 PM

shirokuma makes some very good points.

As he says the intercooler is going to start heat soaking rather quickly. Since people testing their car rarely do just one run and call it a day. Normally two or 3 runs are done. I would think the first run would be signifigantly better than the third run. Which one did they print?

What kind of dyno did they use?
What was the ambiant tempature?
What was the barometer?
What was the elevation?

Did they do anything to help keep the car on the rollers?(I've read about the like making a difference before, i.e. full of passengers)

Too many variables.

jk147 · 08-02-2001, 12:23 AM

turbox has 180hp to the wheels on their site, so who knows.

SoobATV · 08-02-2001, 02:23 AM

hmm, I know this may be a little late, but your experience with Dynojets showing a hp loss with larger brakes... isn't that accurate? Larger brakes=more unsprung weigh, yes? And it takes little pissed off Sube horses turn that higher wiegh, correct? So it isn't that you're losing power due to the higher unsprung weigh, it's just that fewer pissed off Sube horses are making it to the ground. Do respond if I'm incorrect; just wanted to bring that topic to mind a little.

XT6Wagon · 08-02-2001, 06:08 AM

Ok, for the people who think that AWD has more losses due to the extra bearings and stuff. Well guess what, on the road a car has to spin up the non-powered wheels. It simply uses the ground to get the power to the non-powered tires, instead of a driveshaft. Also look at the fact that the AWD puts less HP into each diff. So if you are putting 50HP into 2 diffs, how is that different than putting 100HP into one diff that is just as efficent?

The problem with dynojets and how they measure power, is the assumption that they now the rotating mass being acclerated. However this is not the case as the entire driveline of the car is an unkown mass, and in the case of the 2wd cars a portion of the rotating mass is not accounted for. The mass of the Drum used is also of importance, as a car that dyno's on a 4,000 lb drum will make a different HP reading than one on a 3,500lb drum in most cases. Also a car that is a mere 2K lbs will react far different in the real world as compared to the dyno on the heavy roller. Same with a heavy car dynoed on a light roller. This is why most real engine builders tune on a engine dyno, then go test the motor in a car on the drag strip. Afterall its $20 for all the dynopulls you might want.

On the rotor issue, yes heavier rotors will slow a car down, BUT they don't decrease HP to the wheels. They simply use up more HP than the smaller ones. This is one reason I thnk disks are going to be replaced as soon as a low inertia setup is developed that can equal the performance of the disks. Nothing like free HP and MPG. I should also mention like everything this is a generalization, it could possibly be that the added rotating mass does have an affect on the engine/tranny combo. Its like the fact that many Twin turbo setups are designed and mapped for the stock wieght. So you monkey with the weight and the ECU can't deal with the change in boost curves (turbos respond to load on the engine for some reason). My SHO also puts a bit more down do to heavy rotors for brief time, as the added flywheel effect prevents the auto tranny from hitting the tires too hard, then doing a mini-bog. I will say that it is very minor, and in no way compensates for slowing of the car due to the added mass.

Ed_RS · 08-02-2001, 11:28 AM

Hey guys,
I have a good question that might settle this.

A 00 Prelude puts around 168 to the wheel, and weights around 3000lbs. WRX 163 at the wheel and around 3100 lbs.

Has anyone ran into one? Should the WRX be afraid of the lude?
If so then we really do loose that much hp, if not it would prove that the numbers arn't compairable.

-Ed

Ed_RS · 08-02-2001, 03:03 PM

ttt

Xio · 08-02-2001, 05:01 PM

You are forgetting about torque. The WRX generates much more, IIRC.
I don't think the WRX has anything to fear from a Prelude, stock vs. stock, unless you are racing from 120mph+. WRX should be able to walk away from a Prelude at any other speed, esp. at a stoplight drag.

garface · 08-02-2001, 06:04 PM

When racing against a car with the same power/weight, you must also remember gear ratios. XT6wagon is right about most of what he says. But bigger brakes soak up power just like big heavy wheels, so does an AWD system or any heavy rotating mass. When a 2WD car is dyno'd, the other 2 wheels are sitting nice and pretty without moving, but on the street, those wheels have to be pulled or pushed along with the two driven wheels. There is no way to get a real comparison to the wheels that I can think of between AWD and 2WD.

08-01-2001, 12:16 PM	#1
SlideWRX Scooby Specialist Member#: 3803 Join Date: Jan 2001 Chapter/Region: MWSOC Location: Soon to be Indy Vehicle: 07 Mustang GT Learn2Spinout noob!	168 Whp, 25%drivetrain loss? in one of the latest magazines, someone dynoed a WRX and got 168 wheel hp, which is about 25% drivetrain loss. I was wondering if anyone else has done this, with a wrx or rs, and can confirm the 25% thing for our AWD drive train. Considering 2wd manuals run 15-18%, the 25% still seems high.

08-01-2001, 09:10 PM	#10
krzyss Scooby Specialist Member#: 8365 Join Date: Jul 2001 Location: Massachusetts Vehicle: 2005 Legacy GT Ltd Atlantic Blue	first rule of life there is no free lunch. So as many others said spinning 4 wheels instead of 2 needs more effort. Krzys PS If You have Subaru check how far can You coast.

08-02-2001, 02:23 AM	#14
SoobATV Scooby Specialist Member#: 6883 Join Date: May 2001 Location: newenglandsubarus.com Vehicle: 2004 Forester XS 1993 Legacy wagon	Dynojet... brakes... hmm, I know this may be a little late, but your experience with Dynojets showing a hp loss with larger brakes... isn't that accurate? Larger brakes=more unsprung weigh, yes? And it takes little pissed off Sube horses turn that higher wiegh, correct? So it isn't that you're losing power due to the higher unsprung weigh, it's just that fewer pissed off Sube horses are making it to the ground. Do respond if I'm incorrect; just wanted to bring that topic to mind a little. Last edited by SoobATV; 08-02-2001 at 02:25 AM.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

08-01-2001, 12:32 PM	#2
mbiker97 Scooby Guru Member#: 7922 Join Date: Jun 2001 Chapter/Region: MWSOC Location: Tucson Vehicle: 04 CTS-V b/b/b 99 GMC Highrider	Yeah that seems about right. I've also seen around 180 WHP. Think about it. There are the extra set of axle/parts that all need to turn also. There is alot of parasitic drag in all AWD/4WD vehicles. As for those particular dyno results, remember dyno for the most part are somewhat inaccurate. The daily variables like temp, humidity, engine heat soak all play a huge role in the dyno results. Plus if it was a load based dyno instead of a dynojet the results could be different also. Hope this helps. Seth

08-01-2001, 12:35 PM	#3
JGard Pooptastic Member#: 1904 Join Date: Jul 2000 Chapter/Region: NESIC Location: Salem, MA Vehicle: 2009 WRX Premium 5dr 1991 Mazda Miata	word... also can't forget we have 3 differentials compared to one for 2WD cars. Those eat up power easily

08-01-2001, 12:47 PM	#4
ITR&RSGUY Scooby Newbie Member#: 8455 Join Date: Jul 2001 Chapter/Region: AKIC Location: Anchorage AK Vehicle: 2006 WRX CTSV Viper Silver Black Red	be sure also to see if they used a proper 4 wheel dyno , I know on a 4 wheel dyno a RS will show 100 hp to the wheels which is 65 hp down form the flywheel at that ratio the WRX would show about 138 at the wheels on a 4 wheels dyno, this is the way I look at it, the WRX is very fast, the RS is quick for a NA sub 20K so who cares how much your putting down stock, fact is HP is MUCH easier to make than traction and we have all the traction we can use so be happy :-)

08-01-2001, 01:04 PM	#5
jk147 Scooby Specialist Member#: 7621 Join Date: Jun 2001	yeah I read that article as well. Remeber, we get 168 hp from all 4 wheels, not just front or just back. We lose more horsepower, but gain a lot more tranction. actually, twice as much traction as fwd or rwd cars

08-01-2001, 01:19 PM	#6
Julian Scooby Specialist Member#: 1182 Join Date: Mar 2000 Location: Ventura, CA Vehicle: MY00 RS BRP	FWD cars have less parasitic loss than either FWD or AWD. RWD cars used to run about 22% loss. I expect that's less now, with modern manufacturing techniques. I seriously doubt 25% of the engine's output is soaked up by the various drivetrain bits. Subaru used to claim that a FWD version of one of their AWD cars would not get statistically better mileage. Julian Besides, each dyno is different.

08-01-2001, 01:54 PM	#7
XT6Wagon Scooby Specialist Member#: 524 Join Date: Nov 1999 Location: WA Vehicle: 04 STi White	Um, guys, stop using a dynojet to create "facts". A dynojet will show a HP "loss" when you add larger heavier brakes. Yet some how I doubt that a larger brake rotor has ANYTHING to do with the output of the engine. A FWD, RWD, and AWD will ALL PUT DOWN THE SAME HP!!!!!!!!! Now it might be that the FWD will take less HP to acclerate for that given aceleration rate, and the FWD, and RWD will both need less than the AWD. This is due to rotating mass. Many people including myself at times have gotten lazy and refered to reducing the rotating mass as a way to make HP, when in fact it most likely doesn't. You can get some HP gains by reducing the wieght of the crank pulley and flywheel if they are causing frictional losses at the bearings. Also modern differentials are so effecient that its likely that a glob of mud on the driveshaft would be a greater HP loss (flexing of the shaft due to unbalance) than the Diff itself. This isn't the 50's anymore and they are cars besides so they don't need heavy gears, rugged bearings and the other added things that 4wd trucks use to have a rugged 4wd system. Recall that a huge percentage of the 4wd/awd myths come from the early 4wd pickups.

08-01-2001, 02:07 PM	#8
ITR&RSGUY Scooby Newbie Member#: 8455 Join Date: Jul 2001 Chapter/Region: AKIC Location: Anchorage AK Vehicle: 2006 WRX CTSV Viper Silver Black Red	A FWD, RWD, and AWD will ALL PUT DOWN THE SAME HP!!!!!!!!! Uh no. Friction losses, heat generated, and Noise, yes noise.....these all are generated by HP going through the drive system, the less power leaches you have on said vehicle the more power to the wheels. an AWD car with a 2.5L 165 HP H4 will dnyo with less HP to the wheels than a RW or FF car with the same engine. FACT, doesnt matter if the differential is effecient, it is still not 100% effecient, and NEVER will be it sucks power plain and simple. But it is a GOOD trade off, POWER can be made EASy and relatively cheap, hell 3000 will but you 100hp on a Turbo RS, but trust me it will cost you more than 3000 to make a say integra AWD.

08-01-2001, 07:26 PM	#9
WRX1 Scooby Specialist Member#: 3533 Join Date: Jan 2001 Chapter/Region: MWSOC Location: St. Paul MN, USA Vehicle: 2002 Impreza WRX WR Blue	On a awd car, there at many more bearings that are spinning(transfer case, 2 sets of diff bearings, 2 sets of wheel bearings, etc), so threre is going to be drivetrain loss. You can't spin all the extra parts on not have less wheel HP, but at the same point and time, you are also gaining a ton of traction. Russ

08-01-2001, 10:10 PM	#11
shirokuma Scooby Specialist Member#: 5489 Join Date: Apr 2001 Chapter/Region: NWIC Location: The Empire of Seattle Vehicle: 1995 Eurotrash 4.0 Oxfordgrud	I've gone and done a dyno test for my Legacy B4, and after observation of the testing, came away with some questions to the overall validity of the testing, especially for Subaru's. The first thing I noted right away is that they open the hood to attach instrumentation, and leave it that way for the test. Now, this raises some problems for the intercooler - as in, there is no air being fed to the intercooler, as it would under speed. In fact, the test is run in 4th gear, which means at the top end, air would be being forced over the intercooler at around 110mph. This has a rather beneficial effect on power - on the road. So right there, you have to scratch out most of the power from the intercooler. The other problem is that ambient temperature makes a large difference in turbo power output - for the same reason the intercooler does. So, for instance, I could have up to a 20hp varience in hp output depending on if I did testing in the middle of winter vs. mid summer. So, take any measurements with a grain of salt - there will be no definitive answer from a dyno test, the only real answer will be from acceleration tests. Paul

08-01-2001, 10:42 PM	#12
Zahnster Scooby Specialist Member#: 2918 Join Date: Nov 2000 Location: Simi Valley, CA, USA Vehicle: 2002 Impreza WRX Silver Sedan	shirokuma makes some very good points. As he says the intercooler is going to start heat soaking rather quickly. Since people testing their car rarely do just one run and call it a day. Normally two or 3 runs are done. I would think the first run would be signifigantly better than the third run. Which one did they print? What kind of dyno did they use? What was the ambiant tempature? What was the barometer? What was the elevation? Did they do anything to help keep the car on the rollers?(I've read about the like making a difference before, i.e. full of passengers) Too many variables.

08-02-2001, 12:23 AM	#13
jk147 Scooby Specialist Member#: 7621 Join Date: Jun 2001	turbox has 180hp to the wheels on their site, so who knows.

08-02-2001, 06:08 AM	#15
XT6Wagon Scooby Specialist Member#: 524 Join Date: Nov 1999 Location: WA Vehicle: 04 STi White	Ok, for the people who think that AWD has more losses due to the extra bearings and stuff. Well guess what, on the road a car has to spin up the non-powered wheels. It simply uses the ground to get the power to the non-powered tires, instead of a driveshaft. Also look at the fact that the AWD puts less HP into each diff. So if you are putting 50HP into 2 diffs, how is that different than putting 100HP into one diff that is just as efficent? The problem with dynojets and how they measure power, is the assumption that they now the rotating mass being acclerated. However this is not the case as the entire driveline of the car is an unkown mass, and in the case of the 2wd cars a portion of the rotating mass is not accounted for. The mass of the Drum used is also of importance, as a car that dyno's on a 4,000 lb drum will make a different HP reading than one on a 3,500lb drum in most cases. Also a car that is a mere 2K lbs will react far different in the real world as compared to the dyno on the heavy roller. Same with a heavy car dynoed on a light roller. This is why most real engine builders tune on a engine dyno, then go test the motor in a car on the drag strip. Afterall its $20 for all the dynopulls you might want. On the rotor issue, yes heavier rotors will slow a car down, BUT they don't decrease HP to the wheels. They simply use up more HP than the smaller ones. This is one reason I thnk disks are going to be replaced as soon as a low inertia setup is developed that can equal the performance of the disks. Nothing like free HP and MPG. I should also mention like everything this is a generalization, it could possibly be that the added rotating mass does have an affect on the engine/tranny combo. Its like the fact that many Twin turbo setups are designed and mapped for the stock wieght. So you monkey with the weight and the ECU can't deal with the change in boost curves (turbos respond to load on the engine for some reason). My SHO also puts a bit more down do to heavy rotors for brief time, as the added flywheel effect prevents the auto tranny from hitting the tires too hard, then doing a mini-bog. I will say that it is very minor, and in no way compensates for slowing of the car due to the added mass.

08-02-2001, 11:28 AM	#16
Ed_RS Scooby Newbie Member#: 2082 Join Date: Aug 2000 Vehicle: 2002 WRX	Hey guys, I have a good question that might settle this. A 00 Prelude puts around 168 to the wheel, and weights around 3000lbs. WRX 163 at the wheel and around 3100 lbs. Has anyone ran into one? Should the WRX be afraid of the lude? If so then we really do loose that much hp, if not it would prove that the numbers arn't compairable. -Ed

08-02-2001, 03:03 PM	#17
Ed_RS Scooby Newbie Member#: 2082 Join Date: Aug 2000 Vehicle: 2002 WRX	ttt

08-02-2001, 05:01 PM	#18
Xio Scooby Specialist Member#: 3805 Join Date: Jan 2001 Chapter/Region: International Location: Paris, FRANCE	You are forgetting about torque. The WRX generates much more, IIRC. I don't think the WRX has anything to fear from a Prelude, stock vs. stock, unless you are racing from 120mph+. WRX should be able to walk away from a Prelude at any other speed, esp. at a stoplight drag.

08-02-2001, 06:04 PM	#19
garface Scooby Guru Member#: 1581 Join Date: Jun 2000 Chapter/Region: Tri-State Location: yonkers, ny Vehicle: MY00 RS/STi7 MY01 RS Both Silverthorne	When racing against a car with the same power/weight, you must also remember gear ratios. XT6wagon is right about most of what he says. But bigger brakes soak up power just like big heavy wheels, so does an AWD system or any heavy rotating mass. When a 2WD car is dyno'd, the other 2 wheels are sitting nice and pretty without moving, but on the street, those wheels have to be pulled or pushed along with the two driven wheels. There is no way to get a real comparison to the wheels that I can think of between AWD and 2WD.