bhp at wheels
02 December 2003, 11:25 AM
#1
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Got mine dyno'd at the weekend and got 217bhp at the wheels. Does anyone no what that would be at the flywheel. Am guessing between 280 and 300ish bhp?
Also how much bhp for a 3psi increase on a standard (except downpipe and B box) Version 5 type r?
Cheers
Also how much bhp for a 3psi increase on a standard (except downpipe and B box) Version 5 type r?
Cheers
02 December 2003, 12:17 PM
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Depends on transmission loss which I think may be a bit lower on a type R, but my WRX (classic) made 235bhp at the wheels,309bhp at the flywheel at Power Engineering, so I would think 285 - 295 bhp.
Len.
Len.
03 December 2003, 12:09 PM
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I have been on 3 different rolling roads and the one thing that has been consistant is the drivetrain losses:- Tuning Japanese 79.5 bhp,Powerstation 79 bhp and PowerEngineering 74 bhp. I don't know where your getting your fiqures from as it has been said on here many times before that this is a typical fiqure of the drivetrain loss,some of the more knowledgeable people on here have stated that the type RA models have lower losses of around 65 bhp.I'd like to hear from anybody who has only lost 45 bhp through the drivetrain.
Len.
Len.
05 December 2003, 09:31 PM
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How about some common sense? Or some reseach boastman?
22% loss which you claim is enough kinetic energy to heat conversion to boil the transmission fluids and damage the casings.
If you made 500 HP, and lost 22% to drive the wheels, you seriously think it takes 110 HP to get the wheels moving?
Your car is just running bad, and the guys running the rolling road are using b.s correction numbers to give you a false flywheel figure. If I were you, I have my engine checked out.
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05 December 2003, 10:15 PM
#8
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Well Cosworth 427, your obviously a man who knows a lot more about transmission losses then three tuning organisations! who mentioned 22% loss? I think what obvious to most is that my (and probably other Imprezas) lose approx 75bhp, so according to my maths a Scooby with 500bhp (-75 bhp) =425bhp, still, I'm at Tuning Japanese tomorrow and I'll put your point to them and suggest that they throw the calibration certificate for their rollers away and ask them to give you a call for you "estimate" instead which by the sound of it will be much more accurate.
Boastman.
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05 December 2003, 10:58 PM
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At 400 BHP flywheel I reckon my car is only losing about 40-50 BHP through losses.
Accelerometer testing gives considerably higher power at wheels than most chassis dynos which are subject to IMHO artificially higher losses. My car has shown over 100 BHP losses on some rollers!
There is a double contact patch per roller and the car is tied down onto it.
If a standard Impreza really made only 140-150 WHP they would be even slower than they already are.
Accelerometer testing gives considerably higher power at wheels than most chassis dynos which are subject to IMHO artificially higher losses. My car has shown over 100 BHP losses on some rollers!
There is a double contact patch per roller and the car is tied down onto it.
If a standard Impreza really made only 140-150 WHP they would be even slower than they already are.
06 December 2003, 10:02 AM
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The Type R will have lower losses than a UK or WRX car due to the diff.
The figure quoted at 258bhp at the fly sounds about right to me though, ive seen a few of these cars on Rolling Roads and the losses have been around the 40-50bhp mark but on higher powered cars (280bhp@wheels, 327@fly for one that i saw).
Tony
The figure quoted at 258bhp at the fly sounds about right to me though, ive seen a few of these cars on Rolling Roads and the losses have been around the 40-50bhp mark but on higher powered cars (280bhp@wheels, 327@fly for one that i saw).
Tony
06 December 2003, 10:08 AM
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Mine is not a Type R though.
The road speed reached in gear seems to be the main reason to me that the short geared imports show fewer losses. Note AndyF's car with fancy diffs but a UK gearbox showed very similar losses to my UK on the same rollers back to back (apart from a little glitch at the top end which is irrelevant here).
If I run with similar gearing to his Type RA gearbox (ie I run in 3rd he runs in 4th) then the losses are similar and far more realistic.
The road speed reached in gear seems to be the main reason to me that the short geared imports show fewer losses. Note AndyF's car with fancy diffs but a UK gearbox showed very similar losses to my UK on the same rollers back to back (apart from a little glitch at the top end which is irrelevant here).
If I run with similar gearing to his Type RA gearbox (ie I run in 3rd he runs in 4th) then the losses are similar and far more realistic.
06 December 2003, 11:56 AM
#12
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Boostman, you said:
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"my WRX (classic) made 235bhp at the wheels,309bhp at the flywheel at Power Engineering"
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309 HP - 22% = 241 WHP
309 HP - 23% = 237 WHP
So you only making 235 HP at the wheels assuming a flywheel HP of 309 is actually atleat 23%!!!
I said before, if you lost that much power through heat and friction, it would almost certainly destroy your transmission and differential.
Still not convinced?
john banks also made a valid point, if you were to lose THAT much power to the wheels, then all Imprezas will have different (far worse) performance figures compared to others cars of similar weight and power.
I'm sorry, Boostman, you should check your ignition timing and for boost leaks. Don't blame it on your transmission.
----------------------------------------------------------
"my WRX (classic) made 235bhp at the wheels,309bhp at the flywheel at Power Engineering"
----------------------------------------------------------
309 HP - 22% = 241 WHP
309 HP - 23% = 237 WHP
So you only making 235 HP at the wheels assuming a flywheel HP of 309 is actually atleat 23%!!!
I said before, if you lost that much power through heat and friction, it would almost certainly destroy your transmission and differential.
Still not convinced?
john banks also made a valid point, if you were to lose THAT much power to the wheels, then all Imprezas will have different (far worse) performance figures compared to others cars of similar weight and power.
I'm sorry, Boostman, you should check your ignition timing and for boost leaks. Don't blame it on your transmission.
06 December 2003, 05:29 PM
#14
Cosworth,
The problem is that the rolling road measure the power at the wheels in the state that it sits on the rollers.
If you put a 2wd cossy on the rollers, the coastdown test doesn't add the tyre and shaft losses of the front wheels, although it exists on the road.
In the case of most rolling roads, like PE for instance, you will see around 90hp losses on a UK car run in 4th gear. I am not suggesting that a standard UK car runs 130hp at the wheels on the road, but it's very possibly (probable) that that's the figure that the rollers see.
John has done much testing in the area with rolling roads, accelerometer and datalog results. Rollers do give higher than real life losses, about 50% too high.
Ultimately if you were to get 217hp at the wheels on a 4wd MAHA (SUN) rolling road, then you will be pushing 300hp at the flywheel on a Type R (which will measure lower losses than UK car). But in reality you are putting more down on the road than 217hp.
Paul
The problem is that the rolling road measure the power at the wheels in the state that it sits on the rollers.
If you put a 2wd cossy on the rollers, the coastdown test doesn't add the tyre and shaft losses of the front wheels, although it exists on the road.
In the case of most rolling roads, like PE for instance, you will see around 90hp losses on a UK car run in 4th gear. I am not suggesting that a standard UK car runs 130hp at the wheels on the road, but it's very possibly (probable) that that's the figure that the rollers see.
John has done much testing in the area with rolling roads, accelerometer and datalog results. Rollers do give higher than real life losses, about 50% too high.
Ultimately if you were to get 217hp at the wheels on a 4wd MAHA (SUN) rolling road, then you will be pushing 300hp at the flywheel on a Type R (which will measure lower losses than UK car). But in reality you are putting more down on the road than 217hp.
Paul
06 December 2003, 05:31 PM
#15
Oh yeah, forgot to add, much of that power (and transmission loss on general) is lost at the tyres, the heat is easily shed to the air and the road surface.
Subaru gearbox does get very warm with quick driving.
Paul
Subaru gearbox does get very warm with quick driving.
Paul
08 December 2003, 01:28 PM
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------------------------------------------------------------------
Cosworth,
The problem is that the rolling road measure the power at the wheels in the state that it sits on the rollers.
If you put a 2wd cossy on the rollers, the coastdown test doesn't add the tyre and shaft losses of the front wheels, although it exists on the road.
In the case of most rolling roads, like PE for instance, you will see around 90hp losses on a UK car run in 4th gear. I am not suggesting that a standard UK car runs 130hp at the wheels on the road, but it's very possibly (probable) that that's the figure that the rollers see.
John has done much testing in the area with rolling roads, accelerometer and datalog results. Rollers do give higher than real life losses, about 50% too high.
Ultimately if you were to get 217hp at the wheels on a 4wd MAHA (SUN) rolling road, then you will be pushing 300hp at the flywheel on a Type R (which will measure lower losses than UK car). But in reality you are putting more down on the road than 217hp.
Paul
------------------------------------------------------------------
There's some slight contradiction there. You said that rolling road dynos only measure the wheels in the state that they are on the dyno, yet you then say "in reality" you are putting more power on the road? You're saying that on the dyno rollers, the wheels put down less HP than they do on tarmac??!
Where is this assumption derived from? Factory rated HP from the manufacturer are attained from set conditions, this means altitude is at sea level, ambient air temperature is around 60 - 70 degrees F, humidity levels must be consistent too.
One day some Joe Schmoe (Mr Boostman) gets his car dynoed, finds out that the power at the wheels when considering that realistic sensible transmission losses still do not add up to manufacturer flywheel ratings, so in comes fabricated estimates of 23-25% losses to make it appear that its spot on with factory ratings, without even considering the conditions the car was tested in.
Tranmission losses are not even a fixed percentage. It's independent on the amount of power you make, otherwise you'd need 100 HP to drive the wheels in a 400 HP car!
I wish people would consider the conditions of where their car is tested, and the condition of the CAR ITSELF. People dont realise with turbocharged cars is that maximum factory boost is not always acheived in the real world, on a hot day you will loss a few psi and not make maximum rated power.
[Edited by Cosworth427 - 12/8/2003 1:29:38 PM]
Cosworth,
The problem is that the rolling road measure the power at the wheels in the state that it sits on the rollers.
If you put a 2wd cossy on the rollers, the coastdown test doesn't add the tyre and shaft losses of the front wheels, although it exists on the road.
In the case of most rolling roads, like PE for instance, you will see around 90hp losses on a UK car run in 4th gear. I am not suggesting that a standard UK car runs 130hp at the wheels on the road, but it's very possibly (probable) that that's the figure that the rollers see.
John has done much testing in the area with rolling roads, accelerometer and datalog results. Rollers do give higher than real life losses, about 50% too high.
Ultimately if you were to get 217hp at the wheels on a 4wd MAHA (SUN) rolling road, then you will be pushing 300hp at the flywheel on a Type R (which will measure lower losses than UK car). But in reality you are putting more down on the road than 217hp.
Paul
------------------------------------------------------------------
There's some slight contradiction there. You said that rolling road dynos only measure the wheels in the state that they are on the dyno, yet you then say "in reality" you are putting more power on the road? You're saying that on the dyno rollers, the wheels put down less HP than they do on tarmac??!
Where is this assumption derived from? Factory rated HP from the manufacturer are attained from set conditions, this means altitude is at sea level, ambient air temperature is around 60 - 70 degrees F, humidity levels must be consistent too.
One day some Joe Schmoe (Mr Boostman) gets his car dynoed, finds out that the power at the wheels when considering that realistic sensible transmission losses still do not add up to manufacturer flywheel ratings, so in comes fabricated estimates of 23-25% losses to make it appear that its spot on with factory ratings, without even considering the conditions the car was tested in.
Tranmission losses are not even a fixed percentage. It's independent on the amount of power you make, otherwise you'd need 100 HP to drive the wheels in a 400 HP car!
I wish people would consider the conditions of where their car is tested, and the condition of the CAR ITSELF. People dont realise with turbocharged cars is that maximum factory boost is not always acheived in the real world, on a hot day you will loss a few psi and not make maximum rated power.
[Edited by Cosworth427 - 12/8/2003 1:29:38 PM]
08 December 2003, 04:12 PM
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I can see what you are saying Cos, I suspect Boostman's car is not actually underperforming though compared with its peers of similar spec, as most rolling roads with multiple published Subaru results show similarly high (and it seems we all agree they are unrealistic) losses. Can the double contact patch per tyre and the way they are tied down not explain this, plus the fact that 2WD cars are at an unfair advantage because the losses for the undriven axle are not accounted for?
08 December 2003, 06:05 PM
#22
There's some slight contradiction there. You said that rolling road dynos only measure the wheels in the state that they are on the dyno, yet you then say "in reality" you are putting more power on the road? You're saying that on the dyno rollers, the wheels put down less HP than they do on tarmac??!
On the road, the car sits on the flat, and has a certain amount of rolling resistance from the tyres.
On a rolling road, the situation is not the same, and the additional tyre deflection will sap power that the rollers will not see.
It's a shame I don't have any direct comparison figures, but there is a considerable difference between the power figures you get at the hubs from a Dynapak (hubs bolted directly to dyno input shafts) and a rolling road such as the MAHA setup that uses a pair of smallish rollers for each wheel.
Paul
09 December 2003, 09:00 AM
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quote:
--------------------------------------------------------------------------------
There's some slight contradiction there. You said that rolling road dynos only measure the wheels in the state that they are on the dyno, yet you then say "in reality" you are putting more power on the road? You're saying that on the dyno rollers, the wheels put down less HP than they do on tarmac??!
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
There's some slight contradiction there. You said that rolling road dynos only measure the wheels in the state that they are on the dyno, yet you then say "in reality" you are putting more power on the road? You're saying that on the dyno rollers, the wheels put down less HP than they do on tarmac??!
--------------------------------------------------------------------------------
[Edited by AvalancheS8 - 12/9/2003 9:01:06 AM]
09 December 2003, 07:52 PM
#24
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For the transmission (and everything aft of the flywheel) to lose power there has to be power fed into it for it to lose. This is why rolling roads cannot measure transmission loss.
Transmission losses will increase as power increases. They are not fixed.
What happened to common sense?
Transmission losses will increase as power increases. They are not fixed.
What happened to common sense?
09 December 2003, 08:00 PM
#25
Hypoluxa,
The flywheel figures are calculated fom power at the rollers and measured transmission loss.
Transmission loss is "calculated" by doing a coast down with engine in gear and clutch dipped. During this period the innertia of the rollers is used to drive the wheels, and entire drive train in the gear used for the run.
It's not perfect, but should be quite accurate as by far the greatest losses are viscous and non torque specific friction (bearings, seals etc), tyre deflection. Actual gears are relatively efficient so sap relatively little torque.
System is open to abuse (ie feather brakes on coast down to increase losses and flyhweel figure) and doesn't measure front wheel losses on 2wd cars, but it's close enough for most people.
Paul
The flywheel figures are calculated fom power at the rollers and measured transmission loss.
Transmission loss is "calculated" by doing a coast down with engine in gear and clutch dipped. During this period the innertia of the rollers is used to drive the wheels, and entire drive train in the gear used for the run.
It's not perfect, but should be quite accurate as by far the greatest losses are viscous and non torque specific friction (bearings, seals etc), tyre deflection. Actual gears are relatively efficient so sap relatively little torque.
System is open to abuse (ie feather brakes on coast down to increase losses and flyhweel figure) and doesn't measure front wheel losses on 2wd cars, but it's close enough for most people.
Paul
10 December 2003, 12:54 PM
#26
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Paul
That is coastdown drag, not transmission loss.
Coastdown loss will be the same (for a given rpm/gearing) as it has nothing to do with the proportion of the flywheel power that gets lost as friction in the gearbox, diffs, bearings and tyres etc.
During the coastdown run the engine is no longer powering the drivetrain, so you could have a 250hp or 500hp engine - it wouldn't matter.
That is coastdown drag, not transmission loss.
Coastdown loss will be the same (for a given rpm/gearing) as it has nothing to do with the proportion of the flywheel power that gets lost as friction in the gearbox, diffs, bearings and tyres etc.
During the coastdown run the engine is no longer powering the drivetrain, so you could have a 250hp or 500hp engine - it wouldn't matter.
11 December 2003, 04:22 PM
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I've got an STI Type UK, standard, except panel filter and back box. Should be 261 PS / 265 bhp, right?
It got 192bhp at the wheels with road dyno yesterday.
Very similar losses to the results of the above.
It got 192bhp at the wheels with road dyno yesterday.
Very similar losses to the results of the above.
11 December 2003, 04:28 PM
#29
During the coastdown run the engine is no longer powering the drivetrain, so you could have a 250hp or 500hp engine - it wouldn't matter.
Like I already mentioned, very little of the overall drivetrain loss (flywheel to road surface) is to do with the friction between loaded surfaces. The losses are massively dominated by speed related losses, not torque related losses.
Also, there is torque being transmitted through the drivetrain during coastdown test, just in reverse, if there wasn't, there wouldn't be any losses at all.
Paul
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