Dyno Dynamics rolling road, accurate?
#162
PassionFord Post Troll
I propose a new PF standard.
All power figures to be quoted at the wheels unless taken on an engine dyno.
For me the fact that DD rollers use a GUESSED correction factor is confirmation that quoting flywheel figures from them is pointless.
All power figures to be quoted at the wheels unless taken on an engine dyno.
For me the fact that DD rollers use a GUESSED correction factor is confirmation that quoting flywheel figures from them is pointless.
#164
Doug, I think describing it as an "observed typical value" rather than a "GUESS" would be far more fair.
Personally I would sooner do it that way then any of the run down nonsense which IMHO is simply not accurate as it doesnt change with power anyway, so a 50bhp engine and a 500bhp engine on the same box will get the same rundown losses, but cogs under more pressure exert more resistance so the losses will in fact be greater on the 500bhp instance.
So I think of the two options the DD one is the better one personally!
I do agree that wheels figures are what counts though!
Personally I would sooner do it that way then any of the run down nonsense which IMHO is simply not accurate as it doesnt change with power anyway, so a 50bhp engine and a 500bhp engine on the same box will get the same rundown losses, but cogs under more pressure exert more resistance so the losses will in fact be greater on the 500bhp instance.
So I think of the two options the DD one is the better one personally!
I do agree that wheels figures are what counts though!
#165
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i agree too chip
with a car ran on a dyno with 500bhp @fly and coast down lose of 100bhp giving 400@wheels does that mean that a 100bhp engine wouldnt turn the wheels???
dd might have a best guess but thats exactly how the manual on dyno suggests and wheel bhp is king
another graph thats always interesting is our dyno graph is same shape curve with wheel bhp and fly figure have a look at a dyno that uses coast down does......
with a car ran on a dyno with 500bhp @fly and coast down lose of 100bhp giving 400@wheels does that mean that a 100bhp engine wouldnt turn the wheels???
dd might have a best guess but thats exactly how the manual on dyno suggests and wheel bhp is king
another graph thats always interesting is our dyno graph is same shape curve with wheel bhp and fly figure have a look at a dyno that uses coast down does......
#168
After all, Ive seen LOTS of posts on here "how do I get 400bhp from my cossie engine"
But Ive seen none asking "how do i get 340 RWHP from my cossie engine"
which is the same question.
Everyone wants a 400bhp cossie engien, no one wants a 340ATW cossie engine
#170
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Any device designed to measure something that uses any kind of "guess" factor in my mind is no use as a reference to anything but itself...LOL
I dont aim that specifically at the DD RR.
I dont aim that specifically at the DD RR.
#171
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OK, so PAW is a better figure to rely on.
#172
The problem is that mankind hasnt yet invented a way to measure transmission losses accurately.
What DD have done, is rather than use the horrific "rundown" method, they have accepted that it CANT be measured (and it really cant, they are right!) and instead just used a realistic estimate, rather than an inaccurate psedo measurement.
#173
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Another reason people want @Fly BHP is to compare with manufacturers figures which I find are mostly quoted @Fly.
For example, stock RS Turbo is 132bhp@fly (or whatever it actualy is), you do your mods and your tuner says well done mate you've got 155BHP @wheels and your face drops as you were expecting 180-190bhp and then he tells you your @Fly 183BHP and things seem are a whole lot better!
But I agree 100% that ATW BHP is what counts!
For example, stock RS Turbo is 132bhp@fly (or whatever it actualy is), you do your mods and your tuner says well done mate you've got 155BHP @wheels and your face drops as you were expecting 180-190bhp and then he tells you your @Fly 183BHP and things seem are a whole lot better!
But I agree 100% that ATW BHP is what counts!
Last edited by Karlos G; 01-04-2009 at 05:52 PM.
#174
What have u all concluded after this? That the car registers more BHP in a lower gear? That is what I read from all the posts, anyone come up with a reason why yet?
Chip u are right that the software "should be able to account for it". It clearly doesn't.
The rr should just measure the effort it takes to stabilise the engine (or in DD shoot out mode 44, what effort it takes to stabilise the engine to 10 kmh per second accel).
The answer (as far as I can see) to christian is that a map made on a quick accel run (10 kmh per second) could be overly risky, especially if you stick 5 people in your car, point it up a steep hill in 5th on a hot summers day and nail it.
Simulating the worst scenario would ensure you have a map that is safe for all conditions and I personally (not being at the cutting edge of motorsport) would always prefer a reasonable safety margin. Especially as I don't drive in a "point and squirt" fashion, instead spend large amounts of time at WOT, generating higher temps.
Interesting topic but I am not sure we are really getting to the bottom of WHY the rr in this case is measuring less bhp in the lower gear.
If 125mph is the limit of the rr speed, can you measure a 600bhp at the rear wheels car? I ask as I guess it might try and wheelspin on the rollers in lower gears and that might mean u need to run a higher gear at a speed beyond 125mph?
I would also be interested to understand what the rr measures? I guess it can only measure the effort put in by the retarder to control the revs of the car under load and apply a calculation to that figure to come back to a useful BHP figure that people would recognise?
I don't personally think you can compare figures from rr to rr. Not wheels figures or flywheels figures, only chance might be if the rrs were both of the same manufacture to try and remove different figures generated by different build styles.
Still interested as to the theory as to WHY a rr registers a lower figure in a higher gear. Anyone got any thoughts?
RW
Chip u are right that the software "should be able to account for it". It clearly doesn't.
The rr should just measure the effort it takes to stabilise the engine (or in DD shoot out mode 44, what effort it takes to stabilise the engine to 10 kmh per second accel).
The answer (as far as I can see) to christian is that a map made on a quick accel run (10 kmh per second) could be overly risky, especially if you stick 5 people in your car, point it up a steep hill in 5th on a hot summers day and nail it.
Simulating the worst scenario would ensure you have a map that is safe for all conditions and I personally (not being at the cutting edge of motorsport) would always prefer a reasonable safety margin. Especially as I don't drive in a "point and squirt" fashion, instead spend large amounts of time at WOT, generating higher temps.
Interesting topic but I am not sure we are really getting to the bottom of WHY the rr in this case is measuring less bhp in the lower gear.
If 125mph is the limit of the rr speed, can you measure a 600bhp at the rear wheels car? I ask as I guess it might try and wheelspin on the rollers in lower gears and that might mean u need to run a higher gear at a speed beyond 125mph?
I would also be interested to understand what the rr measures? I guess it can only measure the effort put in by the retarder to control the revs of the car under load and apply a calculation to that figure to come back to a useful BHP figure that people would recognise?
I don't personally think you can compare figures from rr to rr. Not wheels figures or flywheels figures, only chance might be if the rrs were both of the same manufacture to try and remove different figures generated by different build styles.
Still interested as to the theory as to WHY a rr registers a lower figure in a higher gear. Anyone got any thoughts?
RW
#175
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I might be missing something here as this seems a bit too obvious but BHP comes from this equation:
Horsepower = Torque x rpm / 5252.
So surely 3rd gear will transfer more torque to the rollers than 4th gear (certainly does on the real road, and is why most average cars wheelspin in 1st, 2nd, but not 3rd, 4th, or 5th the lowers gears put down more torque), and that is why a lower gear will make more BHP (assuming the engine reaches peek output before the rev limit)?
Horsepower = Torque x rpm / 5252.
So surely 3rd gear will transfer more torque to the rollers than 4th gear (certainly does on the real road, and is why most average cars wheelspin in 1st, 2nd, but not 3rd, 4th, or 5th the lowers gears put down more torque), and that is why a lower gear will make more BHP (assuming the engine reaches peek output before the rev limit)?
Last edited by Karlos G; 01-04-2009 at 06:45 PM.
#178
Testing the future
#181
I might be missing something here as this seems a bit too obvious but BHP comes from this equation:
Horsepower = Torque x rpm / 5252.
So surely 3rd gear will transfer more torque to the rollers than 4th gear (certainly does on the real road, and is why most average cars wheelspin in 1st, 2nd, but not 3rd, 4th, or 5th the lowers gears put down more torque), and that is why a lower gear will make more BHP (assuming the engine reaches peek output before the rev limit)?
Horsepower = Torque x rpm / 5252.
So surely 3rd gear will transfer more torque to the rollers than 4th gear (certainly does on the real road, and is why most average cars wheelspin in 1st, 2nd, but not 3rd, 4th, or 5th the lowers gears put down more torque), and that is why a lower gear will make more BHP (assuming the engine reaches peek output before the rev limit)?
FPMSL!
Most retarded reply ever
Think about it!
You just said yourself what BHP equals.
So if measuing it at the wheels, whats it going to be?
Torque @ Wheels * RPM @ Wheels
So as your torque at the wheels is magically going up by being in a lower gear, tell me please sir, what is happening to your RPM at the wheels because of the same lower gear
#182
Originally Posted by Steven_RW
Still interested as to the theory as to WHY a rr registers a lower figure in a higher gear. Anyone got any thoughts?
RW
RW
Not saying you are wrong, just saying that 1 isnt an ideal sample size generally when looking for trends
#183
Professional Waffler
#184
Gareth.
Take a sample point, say 4000rpm
Take measurement in 4th gear at wheels for BHP
Which will consist of 2 elements, wheel rpm, and wheel torque
Now take a measure at the same RPM in 3rd gear
He is saying the BHP will go up because the torque is increased by the lower gearing.
But what of the rpm, what happens to that?
And by what ratio? EXACTLY the same decrease in rpm % wise as the increase in torque % wise
Net effect : Zero
Take a sample point, say 4000rpm
Take measurement in 4th gear at wheels for BHP
Which will consist of 2 elements, wheel rpm, and wheel torque
Now take a measure at the same RPM in 3rd gear
He is saying the BHP will go up because the torque is increased by the lower gearing.
But what of the rpm, what happens to that?
And by what ratio? EXACTLY the same decrease in rpm % wise as the increase in torque % wise
Net effect : Zero
#185
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i agree too chip
with a car ran on a dyno with 500bhp @fly and coast down lose of 100bhp giving 400@wheels does that mean that a 100bhp engine wouldnt turn the wheels???
dd might have a best guess but thats exactly how the manual on dyno suggests and wheel bhp is king
another graph thats always interesting is our dyno graph is same shape curve with wheel bhp and fly figure have a look at a dyno that uses coast down does......
with a car ran on a dyno with 500bhp @fly and coast down lose of 100bhp giving 400@wheels does that mean that a 100bhp engine wouldnt turn the wheels???
dd might have a best guess but thats exactly how the manual on dyno suggests and wheel bhp is king
another graph thats always interesting is our dyno graph is same shape curve with wheel bhp and fly figure have a look at a dyno that uses coast down does......
Of cause a 100bhp engine would still turn the wheels, but as you've pointed out, i wonder what the power would be like at the wheels at 110mph in a 4wd cossy.
As for the differences between gears.
I'd say the biggest difference would be down to load, boost levels/control, mapping/timing advance and wheel speed, most of the car's "transmission loss" is probably from tyres and wheels (weight) and friction which of cause would be higher in the taller gear.
Last edited by RickyLee53; 01-04-2009 at 11:13 PM. Reason: spelling
#186
Professional Waffler
Gareth.
Take a sample point, say 4000rpm
Take measurement in 4th gear at wheels for BHP
Which will consist of 2 elements, wheel rpm, and wheel torque
Now take a measure at the same RPM in 3rd gear
He is saying the BHP will go up because the torque is increased by the lower gearing.
But what of the rpm, what happens to that?
And by what ratio? EXACTLY the same decrease in rpm % wise as the increase in torque % wise
Net effect : Zero
Take a sample point, say 4000rpm
Take measurement in 4th gear at wheels for BHP
Which will consist of 2 elements, wheel rpm, and wheel torque
Now take a measure at the same RPM in 3rd gear
He is saying the BHP will go up because the torque is increased by the lower gearing.
But what of the rpm, what happens to that?
And by what ratio? EXACTLY the same decrease in rpm % wise as the increase in torque % wise
Net effect : Zero
#187
Lol, no mate, of course I know a fucking gearbox is a torque mutliplier, but I also knows its an RPM divider at the same time.
I wish whoever said "give me a long enough lever and I'll move the world" had added onto the end "but fuck me it wont go far"
I wish whoever said "give me a long enough lever and I'll move the world" had added onto the end "but fuck me it wont go far"
Last edited by Chip; 01-04-2009 at 11:54 PM.
#188
Professional Waffler
#189
Chip - seriously... You don't hang about with the AVA guys since 1995 and rely on some data that gary has put up to know that the power at the wheels goes down as you use a higher gear.
RW
#191
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(no disrespect intended !)
Last edited by ECU Monitor Enthusiast; 02-04-2009 at 08:04 AM.
#192
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do it martin we found that first customer we came to after saying we would only give atw figure had toys out pram
everyone is only interested in a fly firgure for bragging and im just as guilty!!!
everyone is only interested in a fly firgure for bragging and im just as guilty!!!
#193
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Btw, anyone that has only had a flywheel graph can simply call and I will print off an ATW graph FOC (its all stored in the computer)
Last edited by Martin-Hadland; 02-04-2009 at 08:11 AM.
#199
Colossal Pervert
I wonder what it is that makes amateurs spend considerable time on the internet going round and round in circles on subjects like this? It happens on every forum, site, club, bulletin board - and this topic is a favourite!!!
#200
GaryEvo can I ask a genuine question, on the 2 graphs posted why does on both in 3rd gear towards end of the graph why it makes more power but less torque? Similarly why in 4th gear it makes less power and more torque at higher revs?