So just when will this stop? (rant mode on)
01 August 2007, 11:31 AM
#31
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Cut and paste me old deary. Although it didn't C&P properly (SN doesn't allow more than 3 spaces in a row 
) So I may as well typed the whole lot myself.
Next time I'll put a link to it
I would put it in the ScoobyWiki thing, but thats such and **** to sort the spacing right in the editor, I just cannot be bothered, PLus OllyK will re-edit it 1000 times anyway, so he may as well do it
) So I may as well typed the whole lot myself.Next time I'll put a link to it
I would put it in the ScoobyWiki thing, but thats such and **** to sort the spacing right in the editor, I just cannot be bothered, PLus OllyK will re-edit it 1000 times anyway, so he may as well do it
Last edited by Shark Man; 01 August 2007 at 11:34 AM.
01 August 2007, 01:45 PM
#35
As many people know I generally use PowerStation's rolling road as my reference point for BHP & TORQUE claims. I have previously (last year) did comparisons with a Dyno Dynamics RR and the figures attained at both were within an acceptable limit ( a couple of % ) with the flywheel power. Generally I would never suggest to compare RR readouts from different types as you can imagine they can (and do) work differently.
During my recent round of modifications for Stage 3, at a given point (very early on):
PowerStation (MAHA) - 465bhp 460lbft FLYWHEEL
WRC Technologies (DD) - 450bhp 475lbft FLYWHEEL
To try and get another comparison I put the car on a Hub Dyno for power (at the hubs) at the same PS power level stated above:
AET Turbos (HD) - 392bhp AT THE HUBS
All in all as expected and certainly within reason on all three types of dyno.
Car (as I type this) is now 510bhp / 500lbft on PowerStation's rollers, but I have yet to compare again as work is still left to do, so I doubt these will be the final figures. Based on these figures now I would expect a DD RR to give circa 495bhp / 525lbft.
During my recent round of modifications for Stage 3, at a given point (very early on):
PowerStation (MAHA) - 465bhp 460lbft FLYWHEEL
WRC Technologies (DD) - 450bhp 475lbft FLYWHEEL
To try and get another comparison I put the car on a Hub Dyno for power (at the hubs) at the same PS power level stated above:
AET Turbos (HD) - 392bhp AT THE HUBS
All in all as expected and certainly within reason on all three types of dyno.
Car (as I type this) is now 510bhp / 500lbft on PowerStation's rollers, but I have yet to compare again as work is still left to do, so I doubt these will be the final figures. Based on these figures now I would expect a DD RR to give circa 495bhp / 525lbft.
01 August 2007, 04:47 PM
#37
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i showed my dad this thread and he had this to say (retired a few years ago but 30+ years as an automotive engineer for a global car manufacturer);
"Normal losses I think are something like:
Tyres: 1.45% this is on a road but the figure for rollers depends on the radius so may be higher.
Transmission: depends on the gear. In the old days top gear (usually 4th) was a direct gear (no torque transmitted through any meshing gears; the layshaft merely idles)so efficiency was about 97% however most transmission these days have an indirect top gear where the transmission path goes from the main shaft to the lay shaft and back to the main shaft so there are 2 sets of messing gears. Each gear set is about 93% efficient. so that .93x.93x.97 = 84%
next you have the centre dif. Don't know the details but I think the diff is a 'unequal torque splitting' device, again 2 sets of gears meshing (.93x.93 = 0.86)
Now the biggies hypoid differentials. Lots of sliding tooth contact in diffs with lots of side force I would estimate about 0.85. Although there are 2 diffs (f&r) they are in parallel so are not cumulative.
So what number do I get?
0.84x0.86x0.85x.955xdynoloss=0.67xdynoloss i.e 33% loss between the flywheel and the road.
So 44% sounds very high and 25% might be alright for a 2 wheel drive; I told you 4x4 are terrible!!
I don't know how the centre diff works, but is there is any viscous coupling element in it there will be a further loss. The only true way to work out the torque at the road is to measure the instantaneous acceleration and apply good old Mr. Newton's equation P=mf which says the force to accelerate (tractive effort at the road/tyre interface) = the mass of the bodyxthe acceleration. Unfortunately you also need to know the aerodynamic losses as well and for that you need a rather good wind tunnel.
All the efficiencies I have assumed are at 'working' temperature variation of which can make very big differences which is why fuel economy is always better in the summer and on long runs.
The only way to measure flywheel output in on an engine dynamomteter
You know my thoughts on all these power increase claims of these bolt on bits - never trust a salesman!!"
makes sense to me anyway
"Normal losses I think are something like:
Tyres: 1.45% this is on a road but the figure for rollers depends on the radius so may be higher.
Transmission: depends on the gear. In the old days top gear (usually 4th) was a direct gear (no torque transmitted through any meshing gears; the layshaft merely idles)so efficiency was about 97% however most transmission these days have an indirect top gear where the transmission path goes from the main shaft to the lay shaft and back to the main shaft so there are 2 sets of messing gears. Each gear set is about 93% efficient. so that .93x.93x.97 = 84%
next you have the centre dif. Don't know the details but I think the diff is a 'unequal torque splitting' device, again 2 sets of gears meshing (.93x.93 = 0.86)
Now the biggies hypoid differentials. Lots of sliding tooth contact in diffs with lots of side force I would estimate about 0.85. Although there are 2 diffs (f&r) they are in parallel so are not cumulative.
So what number do I get?
0.84x0.86x0.85x.955xdynoloss=0.67xdynoloss i.e 33% loss between the flywheel and the road.
So 44% sounds very high and 25% might be alright for a 2 wheel drive; I told you 4x4 are terrible!!
I don't know how the centre diff works, but is there is any viscous coupling element in it there will be a further loss. The only true way to work out the torque at the road is to measure the instantaneous acceleration and apply good old Mr. Newton's equation P=mf which says the force to accelerate (tractive effort at the road/tyre interface) = the mass of the bodyxthe acceleration. Unfortunately you also need to know the aerodynamic losses as well and for that you need a rather good wind tunnel.
All the efficiencies I have assumed are at 'working' temperature variation of which can make very big differences which is why fuel economy is always better in the summer and on long runs.
The only way to measure flywheel output in on an engine dynamomteter
You know my thoughts on all these power increase claims of these bolt on bits - never trust a salesman!!"
makes sense to me anyway
Last edited by trails; 01 August 2007 at 04:49 PM.
01 August 2007, 05:24 PM
#38
i showed my dad this thread and he had this to say (retired a few years ago but 30+ years as an automotive engineer for a global car manufacturer);
"Normal losses I think are something like:
Tyres: 1.45% this is on a road but the figure for rollers depends on the radius so may be higher.
Transmission: depends on the gear. In the old days top gear (usually 4th) was a direct gear (no torque transmitted through any meshing gears; the layshaft merely idles)so efficiency was about 97% however most transmission these days have an indirect top gear where the transmission path goes from the main shaft to the lay shaft and back to the main shaft so there are 2 sets of messing gears. Each gear set is about 93% efficient. so that .93x.93x.97 = 84%
next you have the centre dif. Don't know the details but I think the diff is a 'unequal torque splitting' device, again 2 sets of gears meshing (.93x.93 = 0.86)
Now the biggies hypoid differentials. Lots of sliding tooth contact in diffs with lots of side force I would estimate about 0.85. Although there are 2 diffs (f&r) they are in parallel so are not cumulative.
So what number do I get?
0.84x0.86x0.85x.955xdynoloss=0.67xdynoloss i.e 33% loss between the flywheel and the road.
So 44% sounds very high and 25% might be alright for a 2 wheel drive; I told you 4x4 are terrible!!
I don't know how the centre diff works, but is there is any viscous coupling element in it there will be a further loss. The only true way to work out the torque at the road is to measure the instantaneous acceleration and apply good old Mr. Newton's equation P=mf which says the force to accelerate (tractive effort at the road/tyre interface) = the mass of the bodyxthe acceleration. Unfortunately you also need to know the aerodynamic losses as well and for that you need a rather good wind tunnel.
All the efficiencies I have assumed are at 'working' temperature variation of which can make very big differences which is why fuel economy is always better in the summer and on long runs.
The only way to measure flywheel output in on an engine dynamomteter
You know my thoughts on all these power increase claims of these bolt on bits - never trust a salesman!!"
makes sense to me anyway
"Normal losses I think are something like:
Tyres: 1.45% this is on a road but the figure for rollers depends on the radius so may be higher.
Transmission: depends on the gear. In the old days top gear (usually 4th) was a direct gear (no torque transmitted through any meshing gears; the layshaft merely idles)so efficiency was about 97% however most transmission these days have an indirect top gear where the transmission path goes from the main shaft to the lay shaft and back to the main shaft so there are 2 sets of messing gears. Each gear set is about 93% efficient. so that .93x.93x.97 = 84%
next you have the centre dif. Don't know the details but I think the diff is a 'unequal torque splitting' device, again 2 sets of gears meshing (.93x.93 = 0.86)
Now the biggies hypoid differentials. Lots of sliding tooth contact in diffs with lots of side force I would estimate about 0.85. Although there are 2 diffs (f&r) they are in parallel so are not cumulative.
So what number do I get?
0.84x0.86x0.85x.955xdynoloss=0.67xdynoloss i.e 33% loss between the flywheel and the road.
So 44% sounds very high and 25% might be alright for a 2 wheel drive; I told you 4x4 are terrible!!
I don't know how the centre diff works, but is there is any viscous coupling element in it there will be a further loss. The only true way to work out the torque at the road is to measure the instantaneous acceleration and apply good old Mr. Newton's equation P=mf which says the force to accelerate (tractive effort at the road/tyre interface) = the mass of the bodyxthe acceleration. Unfortunately you also need to know the aerodynamic losses as well and for that you need a rather good wind tunnel.
All the efficiencies I have assumed are at 'working' temperature variation of which can make very big differences which is why fuel economy is always better in the summer and on long runs.
The only way to measure flywheel output in on an engine dynamomteter
You know my thoughts on all these power increase claims of these bolt on bits - never trust a salesman!!"
makes sense to me anyway
01 August 2007, 05:33 PM
#39
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not quite boil
that loss only occurs during WOT so you would have to drive for prolonged periods with WOT.
that loss only occurs during WOT so you would have to drive for prolonged periods with WOT.
Last edited by trails; 01 August 2007 at 05:36 PM. Reason: terrible grammar
01 August 2007, 09:30 PM
#43
A percentage is just that, losses vary absolutely but rarely in percentage terms (across the rpm range).
The opening post was made from an assumption that all rolling road designs are going to produce a comparable power at wheels figure for a given car, not true as the differeing designs all measure losses in differeing ways and also all measure power at the wheels using different methods.
Maha do it very differently to Dyno Dynamics, Power Stations Maha genetrates much lower paw figs but measures losses as huge, DSA/WRC (that was) and other Dyno Dynamics users are stuck with a design that doesn't actually measure loss at all but "calculates" an allowance, the DD shoot44 mode is usually 21.8% loss added. I have seen a couple of graphs purporting to be that with higher though which strictly shouldn't happen.
As most know I use Deltadash to benchmark the cars I map or a GTech Pro where that isn't possible, both give results that allow for drag etc and, of course, being run on the road true wind resistance and tyre drag is experienced across the speed range of the run. I then have to decide on how much loss factor to add, so I tend to stick to 22% being, in my view, a mean average. For me it doesn't matter as consistency is what its about. I experimented for a long time to arrive at that conclusion re losses, 25% is allowed for a 5 speed box by some (including me initially) but I felt this was a bit high, the six speed box was allowed 21% typically.
BTW a Dastek rolling road would allow far lower losses than either of the above mentioned yet still come up with a power at the flywheel in the same ballpark.
Rolling roads are the bane of a tuners life, they should either all be made to use the same system or banned completely, excellant diagnostic tool though but pants for true absolute mapping. (loosened the lid but not opening it!!)
my two penneth (btw I do map on the rollers when I have a car to do that has absolutely no basis to work off, can rough cut something to get it drivable first)
cheers
bob
The opening post was made from an assumption that all rolling road designs are going to produce a comparable power at wheels figure for a given car, not true as the differeing designs all measure losses in differeing ways and also all measure power at the wheels using different methods.
Maha do it very differently to Dyno Dynamics, Power Stations Maha genetrates much lower paw figs but measures losses as huge, DSA/WRC (that was) and other Dyno Dynamics users are stuck with a design that doesn't actually measure loss at all but "calculates" an allowance, the DD shoot44 mode is usually 21.8% loss added. I have seen a couple of graphs purporting to be that with higher though which strictly shouldn't happen.
As most know I use Deltadash to benchmark the cars I map or a GTech Pro where that isn't possible, both give results that allow for drag etc and, of course, being run on the road true wind resistance and tyre drag is experienced across the speed range of the run. I then have to decide on how much loss factor to add, so I tend to stick to 22% being, in my view, a mean average. For me it doesn't matter as consistency is what its about. I experimented for a long time to arrive at that conclusion re losses, 25% is allowed for a 5 speed box by some (including me initially) but I felt this was a bit high, the six speed box was allowed 21% typically.
BTW a Dastek rolling road would allow far lower losses than either of the above mentioned yet still come up with a power at the flywheel in the same ballpark.
Rolling roads are the bane of a tuners life, they should either all be made to use the same system or banned completely, excellant diagnostic tool though but pants for true absolute mapping. (loosened the lid but not opening it!!)
my two penneth (btw I do map on the rollers when I have a car to do that has absolutely no basis to work off, can rough cut something to get it drivable first)
cheers
bob
01 August 2007, 10:23 PM
#44
Lets face it most (don't want to tie all with the same brush) companies that do RR's for the public want to make money and they aren't going to do that if there RR give apparently poor figure (even though they may be more accurate).
the funniest RR i have ever seen was a standard astra GSI (mk4 turbo) get 230 BHP at the wheels both myself and the owner pissed our selves at how a car with only circa 200BHPat the fly when it left the factory can make 230 BHP at the wheels.
just goes to show how inaccurate RR's can be.
The trouble to many people want high figures from the mods and tuning and seem possesed with chasing these peak figures that they forget its not just peak figures that count
Untill the other 90% reailse this RR's will keep making figures up to get bussiness.
the funniest RR i have ever seen was a standard astra GSI (mk4 turbo) get 230 BHP at the wheels both myself and the owner pissed our selves at how a car with only circa 200BHPat the fly when it left the factory can make 230 BHP at the wheels.
just goes to show how inaccurate RR's can be.
The trouble to many people want high figures from the mods and tuning and seem possesed with chasing these peak figures that they forget its not just peak figures that count
Untill the other 90% reailse this RR's will keep making figures up to get bussiness.
01 August 2007, 10:25 PM
#45
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bugger 
what is that saying again? "A little knowledge is..."
There are a few nicely written posts here that have enhanced my knowledge. Thanks ppl
My initial concept was that all rr should be able to measure whp equally well. That to my mind was what they were all about, trying to determine how much power your wheels actually put down on the road. My assumption was the better the rr, the more accurate the whp figure. Measuring losses to my mind was purely optional.
It seems that rrs have been developed in different ways. It does seem strange to use an rr that shows higher losses than would be expected on the road, even if that does lead to an accurate flywheel figure.
Still, at least Bob has summed it all up, and offered a nice tip. All remaps should be finished on the road, not the rollers
what is that saying again? "A little knowledge is..." There are a few nicely written posts here that have enhanced my knowledge. Thanks ppl
My initial concept was that all rr should be able to measure whp equally well. That to my mind was what they were all about, trying to determine how much power your wheels actually put down on the road. My assumption was the better the rr, the more accurate the whp figure. Measuring losses to my mind was purely optional.
It seems that rrs have been developed in different ways. It does seem strange to use an rr that shows higher losses than would be expected on the road, even if that does lead to an accurate flywheel figure.
Still, at least Bob has summed it all up, and offered a nice tip. All remaps should be finished on the road, not the rollers
01 August 2007, 11:47 PM
#46
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My two points, with little slip between F & R diffs, a sticky centre diff shouldn't be too lossy. IMHO !!
Mine was mapped on the road 'cos I use it on the road..... No ***** waving numbers available, sorry.
Thanks to Mr. Richard Bulmer for a ballistic missile that's soooo smooth, it's
deceptively fast. Massive torque hit as the boost comes in, lovely.
Dunx
P.S. My old Golf 16v put out about 138 (atw) bhp back in 1994....
Mine was mapped on the road 'cos I use it on the road..... No ***** waving numbers available, sorry.
Thanks to Mr. Richard Bulmer for a ballistic missile that's soooo smooth, it's
deceptively fast. Massive torque hit as the boost comes in, lovely.
Dunx
P.S. My old Golf 16v put out about 138 (atw) bhp back in 1994....
02 August 2007, 08:50 AM
#47
Is it not possible to calculate an Impreza's transmission loss (& indeed any car's) from a few bits of data, like vmax, bhp (fly) weight (kerb) & Cd ...as all these bits of info are readily available, assuming manufacturer's 'claimed' numbers are correct?
02 August 2007, 11:29 AM
#48
i showed my dad this thread and he had this to say (retired a few years ago but 30+ years as an automotive engineer for a global car manufacturer);
"Normal losses I think are something like:
Tyres: 1.45% this is on a road but the figure for rollers depends on the radius so may be higher.
Transmission: depends on the gear. In the old days top gear (usually 4th) was a direct gear (no torque transmitted through any meshing gears; the layshaft merely idles)so efficiency was about 97% however most transmission these days have an indirect top gear where the transmission path goes from the main shaft to the lay shaft and back to the main shaft so there are 2 sets of messing gears. Each gear set is about 93% efficient. so that .93x.93x.97 = 84%
next you have the centre dif. Don't know the details but I think the diff is a 'unequal torque splitting' device, again 2 sets of gears meshing (.93x.93 = 0.86)
Now the biggies hypoid differentials. Lots of sliding tooth contact in diffs with lots of side force I would estimate about 0.85. Although there are 2 diffs (f&r) they are in parallel so are not cumulative.
So what number do I get?
0.84x0.86x0.85x.955xdynoloss=0.67xdynoloss i.e 33% loss between the flywheel and the road.
So 44% sounds very high and 25% might be alright for a 2 wheel drive; I told you 4x4 are terrible!!
I don't know how the centre diff works, but is there is any viscous coupling element in it there will be a further loss. The only true way to work out the torque at the road is to measure the instantaneous acceleration and apply good old Mr. Newton's equation P=mf which says the force to accelerate (tractive effort at the road/tyre interface) = the mass of the bodyxthe acceleration. Unfortunately you also need to know the aerodynamic losses as well and for that you need a rather good wind tunnel.
All the efficiencies I have assumed are at 'working' temperature variation of which can make very big differences which is why fuel economy is always better in the summer and on long runs.
The only way to measure flywheel output in on an engine dynamomteter
You know my thoughts on all these power increase claims of these bolt on bits - never trust a salesman!!"
makes sense to me anyway
"Normal losses I think are something like:
Tyres: 1.45% this is on a road but the figure for rollers depends on the radius so may be higher.
Transmission: depends on the gear. In the old days top gear (usually 4th) was a direct gear (no torque transmitted through any meshing gears; the layshaft merely idles)so efficiency was about 97% however most transmission these days have an indirect top gear where the transmission path goes from the main shaft to the lay shaft and back to the main shaft so there are 2 sets of messing gears. Each gear set is about 93% efficient. so that .93x.93x.97 = 84%
next you have the centre dif. Don't know the details but I think the diff is a 'unequal torque splitting' device, again 2 sets of gears meshing (.93x.93 = 0.86)
Now the biggies hypoid differentials. Lots of sliding tooth contact in diffs with lots of side force I would estimate about 0.85. Although there are 2 diffs (f&r) they are in parallel so are not cumulative.
So what number do I get?
0.84x0.86x0.85x.955xdynoloss=0.67xdynoloss i.e 33% loss between the flywheel and the road.
So 44% sounds very high and 25% might be alright for a 2 wheel drive; I told you 4x4 are terrible!!
I don't know how the centre diff works, but is there is any viscous coupling element in it there will be a further loss. The only true way to work out the torque at the road is to measure the instantaneous acceleration and apply good old Mr. Newton's equation P=mf which says the force to accelerate (tractive effort at the road/tyre interface) = the mass of the bodyxthe acceleration. Unfortunately you also need to know the aerodynamic losses as well and for that you need a rather good wind tunnel.
All the efficiencies I have assumed are at 'working' temperature variation of which can make very big differences which is why fuel economy is always better in the summer and on long runs.
The only way to measure flywheel output in on an engine dynamomteter
You know my thoughts on all these power increase claims of these bolt on bits - never trust a salesman!!"
makes sense to me anyway
using an my98 UK Impreza, 215 bhp (fly) that has a top speed of 144 mph ...ive used 1235kg for weight (for calc'ing rolling resistence) a drag co. of 0.32 & a frontal area of 22ft.
Im getting a rolling resistence of 35lbs ...& air resistence of 373lbs, so 408lbs in total
to get 408lbs of total resistence upto 144 mph takes 157 bhp @ the wheels ...so ive lost 58 bhp (215-157) ...or 27%
please feel free to pick holes in my math ...but if anyone disagrees with anything, take it up with the author of this
:Puma Race Engines Technical Guide - How engine power and top speed are related
Last edited by DazW; 02 August 2007 at 11:31 AM. Reason: .
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