Power loss over age.
Discussion
Hello people
Not so long ago i traded my car with a member of my family for her 2001 206 GTI 138 with 35,000 on the clock.
it got me thinking would the 206 still produce the same bhp as it allways did?
what causes an engine to lose bhp? I would of thought with modern cars being controled with computers that the management system would make changes so that the engine would still produce the power it should be?
Not so long ago i traded my car with a member of my family for her 2001 206 GTI 138 with 35,000 on the clock.
it got me thinking would the 206 still produce the same bhp as it allways did?
what causes an engine to lose bhp? I would of thought with modern cars being controled with computers that the management system would make changes so that the engine would still produce the power it should be?
Mick23 said:
Hello people
Not so long ago i traded my car with a member of my family for her 2001 206 GTI 138 with 35,000 on the clock.
it got me thinking would the 206 still produce the same bhp as it allways did?
what causes an engine to lose bhp? I would of thought with modern cars being controled with computers that the management system would make changes so that the engine would still produce the power it should be?
It's mainly down to piston rings, valve seats, big ends and so on. There's room for perhaps 10bhp, but The failure curve is pretty steep. If it's down on power by much more than that, and you're actually noticing that it's down by that much, it's going to die within the next month!Not so long ago i traded my car with a member of my family for her 2001 206 GTI 138 with 35,000 on the clock.
it got me thinking would the 206 still produce the same bhp as it allways did?
what causes an engine to lose bhp? I would of thought with modern cars being controled with computers that the management system would make changes so that the engine would still produce the power it should be?
Other less severe and more temporal causes might be things like a collapsed catalytic converter a knackered carb, a clogged air filter, dead sparkplugs or distributor.
Edited by dilbert on Thursday 16th October 22:36
I was wondering much the same thing, so when some colleagues recently booked a day on a rolling road, I took my car down to see what it had. My car is 18 years old and coming up to 250,000 miles. I've never done anything to the engine apart from routine servicing and it burns a fair amount of oil these days (about 400 miles to the pint). It is supposed to have (according to the brochure) about 190bhp at the flywheel and it gave 154bhp at the wheels on the rollers. It's a front wheel drive and I guess that a bit over 20% transmission loss isn't unreasonable. If that's the case, it was still producing pretty much the same power as it did when it was new!
30% is an average transmission loss, piston rings and leaking valves are the main area where power can be lost, but its also down to servicing, if a service has been missed or neglected then it could be something like an injector spray pattern, Breaking down plug, causing a minute misfire which is very hard to diagnose, Compression test is a good idea for Cylinder leakage, get a full service done and then give it a run on the rollers, bear in mind that all rolling roads are different and bhp readings will vary
Dave
Dave
Cleary then you are quick to make judgements of people before actually knowing them then?, i was going on what i was told was an AVERAGE Transmission loss for FWD Cars, i admit i dont have much experience in rr losses and calculations, Considering they all vary slightly anyhow? looking at my last power graph my transmission losses are around 15-20% but i have seen FWD cars loosing slightly more than that
I must admit, I don't understand that. I'd have thought a front whel drive transmission would loose LESS power as there are fewer bits in the system. Surely the main difference is that it doesn't need to turn the drive through 90 degrees to get it to the wheels, so no big bevel gear loss in the diff?
davebell1984 said:
Cleary then you are quick to make judgements of people before actually knowing them then?, i was going on what i was told was an AVERAGE Transmission loss for FWD Cars, i admit i dont have much experience in rr losses and calculations, Considering they all vary slightly anyhow? looking at my last power graph my transmission losses are around 15-20% but i have seen FWD cars loosing slightly more than that
Surely unless you are actually measuring your flywheel output (which I guess you're not unless you have an engine test cell kicking around) then all you're doing is assuming that the manufacturers' figures for the various engines are actually correct and then adjusting for any differences at the wheel by calling them "transmission losses"?In order to estimate engine output, RRs have to measure what's at the wheels and then simply apply a "one size fits all" fudge factor to work back to the flywheel figure. The accuracy of this factor can't be verified on an individual basis, so the numbers are effectively meaningless.
The only thing that would have any meaning is to take your car back to the same RR on a regular basis (preferably with similar weather conditions each time) and compare the readings over time to see if the engine & transmission package is losing power with age.
No i dont have a test cell to hand, Flywheel power is like you say only properly measured on one, power at the wheels is what counts anyhow, its going to be estimated on a rolling road as there are going to be resistances after the flywheel, i.e. Gearbox, driveshafts, Wheel bearings could be tired etc i dont know how they calculate the "flywheel" power, apparently its something to do with coast down, but its "calculated" and people get a little annoyed when they have a car rr'd and it looks like its down on power when really it might not be,
Avocet said:
I was wondering much the same thing, so when some colleagues recently booked a day on a rolling road, I took my car down to see what it had. My car is 18 years old and coming up to 250,000 miles. I've never done anything to the engine apart from routine servicing and it burns a fair amount of oil these days (about 400 miles to the pint). It is supposed to have (according to the brochure) about 190bhp at the flywheel and it gave 154bhp at the wheels on the rollers. It's a front wheel drive and I guess that a bit over 20% transmission loss isn't unreasonable. If that's the case, it was still producing pretty much the same power as it did when it was new!
20% seems a lot to me.Most reckon 15% for manuals and 18% for auto's. Although these are still only guesses.
Some use 12% + 10bhp, but on a low powered car I think this would be misleading.
Personally I suspect that drivetrain loss consists of a fixed amount + a diminishing percentage.
Using a common formula gives an estimated flywheel figure of 181.2bhp from 154bhp at the wheels.
But without knowing other key factors the wheel readings are fairly meaningless. Things to know are:
-Dyno type, is it an inertia or eddy current dyno?
-Graph smoothing
-Metric or imperial HP
-Were any correction standards used (SAE/DIN)
-If so, were they used correctly
-If not, what where the local conditions (temp, humidity, pressure, etc.) and altitude or DA
-What gear was the car dyno'd in
As I'm sure you're aware the X% x 10 bhp formula is my own which was devised to give a simple best fit curve which accounted for the fact that transmission losses are a greater percentage of flywheel power in low powered cars than high powered ones.
Transmission losses are more properly split into actual transmission losses and tyre losses. The former are fairly simple to evaluate and with the recent advent of hub dynos there is now a lot of data about to work from in which the tyre losses are excluded from the results.
What we find is that with hub dynos the transmission loss is very much a fixed percentage of the engine power output, which is exactly what you would predict from long established gear efficiency data. It's about 7% for fwd cars, a bit more on rwd ones because the drive has to be turned through 90 degrees so about 8% to 9% and obviously more on 4wd or autos which to be honest don't concern me much in the performance world.
The tyre losses are the big enigma. They vary obviously depending on power input to them, tyre size, tread pattern, carcass construction, vehicle weight, tyre pressure and road speed. These can never be estimated with precision because two similar powered cars could have wildly different tyres fitted.
The two biggest tyre variables, power input and road speed obviously both go up with increasing engine power. If we look at very low powered, low speed vehicles like say a 34 bhp 850 Mini which could easily have the identical transmission and tyres to a 90 bhp Metro turbo then any simple formula is unlikely to fit it. The way we can proceed with that is to estimate the actual power delivered to the road from the top speed and drag data. We find that to achieve its measured top speed of 72 mph it needs about 26 to 27 bhp delivered to the road. That means total losses are about 7 to 8 bhp or 20% to 23%. For a 2wd car that's going to be at the very extreme of the percentage power losses.
For more normal cars in the 90 bhp and above range my formula of deducting 10% plus 10 bhp for fwd and 12% plus 10 bhp for rwd from the flywheel bhp gives a very good fit to the data.
In reverse to estimate flywheel bhp from wheel bhp we add 10 bhp then divide by 0.9 (fwd) or 0.88 (rwd).
One of the cars I had a great amount of input from was the Fiesta XR2 when I was building engines for the Challenge series. The standard 94 bhp engine would deliver an average 75 bhp to the wheels on a wide range of rolling roads i.e losses of 20% of flywheel bhp. 75 bhp + 10 bhp = 85 bhp / 0.9 = 94. Right on the money.
For more powerful cars like the 2wd rwd Cossie we'd see 165 to 170 bhp at the wheels for the nominal 202 std bhp. At an average of 167.5 we get 167.5 + 10 = 177.5 / 0.88 = 202 bhp. The percentage loss has dropped to 17% of flywheel power but the equation still fits.
The equation allows for a very good fit even when you get to extremely powerful cars with several hundred or more bhp. The total percentage losses drop considerably but as always they're going to be about the same percentage at the hub as lower powered cars plus whatever the tyres lose. So for rwd it's still going to be about 9% plus the tyre portion. If that tyre portion was very high the tyres would melt and clearly they don't. Using my equation the fixed 10 bhp part becomes steadily less important as engine power rises so we gradually approach a limit where just the 10% or 12% portion of the equation is significant. Again this approaches a similar amount as the hub dynos show plus a bit for tyres so not surprisingly it stays fairly accurate.
Anyway, all of this is discussed in much more detail on my website.
Dave Baker
Puma Race Engines
Transmission losses are more properly split into actual transmission losses and tyre losses. The former are fairly simple to evaluate and with the recent advent of hub dynos there is now a lot of data about to work from in which the tyre losses are excluded from the results.
What we find is that with hub dynos the transmission loss is very much a fixed percentage of the engine power output, which is exactly what you would predict from long established gear efficiency data. It's about 7% for fwd cars, a bit more on rwd ones because the drive has to be turned through 90 degrees so about 8% to 9% and obviously more on 4wd or autos which to be honest don't concern me much in the performance world.
The tyre losses are the big enigma. They vary obviously depending on power input to them, tyre size, tread pattern, carcass construction, vehicle weight, tyre pressure and road speed. These can never be estimated with precision because two similar powered cars could have wildly different tyres fitted.
The two biggest tyre variables, power input and road speed obviously both go up with increasing engine power. If we look at very low powered, low speed vehicles like say a 34 bhp 850 Mini which could easily have the identical transmission and tyres to a 90 bhp Metro turbo then any simple formula is unlikely to fit it. The way we can proceed with that is to estimate the actual power delivered to the road from the top speed and drag data. We find that to achieve its measured top speed of 72 mph it needs about 26 to 27 bhp delivered to the road. That means total losses are about 7 to 8 bhp or 20% to 23%. For a 2wd car that's going to be at the very extreme of the percentage power losses.
For more normal cars in the 90 bhp and above range my formula of deducting 10% plus 10 bhp for fwd and 12% plus 10 bhp for rwd from the flywheel bhp gives a very good fit to the data.
In reverse to estimate flywheel bhp from wheel bhp we add 10 bhp then divide by 0.9 (fwd) or 0.88 (rwd).
One of the cars I had a great amount of input from was the Fiesta XR2 when I was building engines for the Challenge series. The standard 94 bhp engine would deliver an average 75 bhp to the wheels on a wide range of rolling roads i.e losses of 20% of flywheel bhp. 75 bhp + 10 bhp = 85 bhp / 0.9 = 94. Right on the money.
For more powerful cars like the 2wd rwd Cossie we'd see 165 to 170 bhp at the wheels for the nominal 202 std bhp. At an average of 167.5 we get 167.5 + 10 = 177.5 / 0.88 = 202 bhp. The percentage loss has dropped to 17% of flywheel power but the equation still fits.
The equation allows for a very good fit even when you get to extremely powerful cars with several hundred or more bhp. The total percentage losses drop considerably but as always they're going to be about the same percentage at the hub as lower powered cars plus whatever the tyres lose. So for rwd it's still going to be about 9% plus the tyre portion. If that tyre portion was very high the tyres would melt and clearly they don't. Using my equation the fixed 10 bhp part becomes steadily less important as engine power rises so we gradually approach a limit where just the 10% or 12% portion of the equation is significant. Again this approaches a similar amount as the hub dynos show plus a bit for tyres so not surprisingly it stays fairly accurate.
Anyway, all of this is discussed in much more detail on my website.
Dave Baker
Puma Race Engines
% loss is all arse anyway...
There will be a torque requirement relative to components of drivetrain speeds, which we could 'generalise' to a bhp loss vs rpm, for a particular gear...
Give or take, my car looses about 22-24bhp at 4000rpm in 3rd... if I double my wheel power (as I have), I don't double my losses (as a % method would do)
As much as I generally agree with Pumaracing's figures, they are only a guide on a standard car. Take a 200bhp Golf V GTi with 197 bhp and you get ~ 30bhp losses. Tune it to be 400bhp, while leaving all else the same, and it doesn't now have 50bhp loses...
However, a standard car with about 400bhp will probably have such heavy duty components that it might well loose much more... and so get closer to that 50bhp losses.
Dave
There will be a torque requirement relative to components of drivetrain speeds, which we could 'generalise' to a bhp loss vs rpm, for a particular gear...
Give or take, my car looses about 22-24bhp at 4000rpm in 3rd... if I double my wheel power (as I have), I don't double my losses (as a % method would do)
As much as I generally agree with Pumaracing's figures, they are only a guide on a standard car. Take a 200bhp Golf V GTi with 197 bhp and you get ~ 30bhp losses. Tune it to be 400bhp, while leaving all else the same, and it doesn't now have 50bhp loses...
However, a standard car with about 400bhp will probably have such heavy duty components that it might well loose much more... and so get closer to that 50bhp losses.
Dave
Edited by Mr Whippy on Friday 24th October 16:54 because I'm a looser
Edited by Mr Whippy on Friday 24th October 17:21
pdV6 said:
Surely, though, all of the above involves taking the manufacturers flywheel figures as gospel and all the calculations thereafter simply juggle the numbers to make it fit?
I suggest you read the relevant articles first.http://www.pumaracing.co.uk/POWER3.htm
http://www.pumaracing.co.uk/coastdwn.htm
http://www.pumaracing.co.uk/setup01.htm
http://www.pumaracing.co.uk/trans.htm
I've used many methods including engine dyno data, computer simulations of vehicle performance and top speed calculations to work out what the flywheel bhp must have been for a given wheel bhp and vice-versa.
However certainly it's not correct to just assume OE flywheel figures are accurate for a given individual car and I cover this in detail in my articles. Over many many car tests though we can derive reasonable averages and frankly as no one else is going to test engines in as much detail as the OE manufacturers do we are hard pushed to find a more definitive baseline to work our wheel bhp figures from. Even if you take an engine out of the car and put it on an engine dyno you can't be certain it will now produce the same power as it did when it was installed inside an engine bay. Temperatures, airflows and ancilliary component drive losses might all vary.
Pumaracing said:
pdV6 said:
Surely, though, all of the above involves taking the manufacturers flywheel figures as gospel and all the calculations thereafter simply juggle the numbers to make it fit?
I suggest you read the relevant articles first.http://www.pumaracing.co.uk/POWER3.htm
http://www.pumaracing.co.uk/coastdwn.htm
http://www.pumaracing.co.uk/setup01.htm
http://www.pumaracing.co.uk/trans.htm
I've used many methods including engine dyno data, computer simulations of vehicle performance and top speed calculations to work out what the flywheel bhp must have been for a given wheel bhp and vice-versa.
However certainly it's not correct to just assume OE flywheel figures are accurate for a given individual car and I cover this in detail in my articles. Over many many car tests though we can derive reasonable averages and frankly as no one else is going to test engines in as much detail as the OE manufacturers do we are hard pushed to find a more definitive baseline to work our wheel bhp figures from. Even if you take an engine out of the car and put it on an engine dyno you can't be certain it will now produce the same power as it did when it was installed inside an engine bay. Temperatures, airflows and ancilliary component drive losses might all vary.
I've currently tuned my car, but am having serious difficulty calculating anything from my figures, being a diesel with peak power from ~ 3000-4000rpm is clearly distorting matters...
Current spec... recorded with G-tech Pro RR, and weighed on my quarries local weighbridge (within 4kg of book weight)
2/3rd tank, 1130kg car, and a driver of 95kg, and some 5kg of extras maybe... so 1255kg all up.
1/4m data (please note rollout was not included)
60ft 2.827s
330ft 7.053s
1/8mi 10.521@71.85mph
1000ft 13.511s
1/4m 16.035s@89.04mph
0-100mph
0-30 2.947s
0-40 4.085s
0-50 5.771s
0-60 7.460s
0-70 9.864s
0-80 12.462s
0-90 16.907s
0-100 21.372s
I've got figures ranging from 130bhp to 150bhp with the various 1/4m sums.
Cd is apparently 0.32 or 0.34 and Cx is about 1.86m.sq, 195/50R15 tyres, nothing fancy, but same brand/pressures since I got the car...
Dyno'd standard at 93bhp/74bhp (flywheel/wheels) on Dyno Dynamics
Dyno'd again at 122bhp/101bhp (as above) on Dyno Dynamics
Dyno'd again at 119bhp/99bhp (as above) Dyno Dynamics
Lastly, my G-tech gave me a reading of 122bhp peak at about 55mph in 3rd at 3750rpm or so...
(ps, those figures were not ideal, I've had 0.2s quicker to 60mph with similar weight, but I'm starting to feel sorry for my gearbox
)Edited by Mr Whippy on Friday 24th October 17:09
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