Fresh GTS engine with GT cams, dyno
06-08-2019, 04:38 AM
#31
Addict
Rennlist Member
Rennlist Member
Join Date: Feb 2004
Location: Monterey Peninsula, CA
Posts: 2,374
Likes: 0
Received 16 Likes
on
12 Posts
I'm not an engineer but I'm curious about the physics and how it's calculated to represent the engine's resultant output.
I can definitely understand the engine on a test stand in a dynamometer cell being rated and correct for atmospheric conditions etc. by the factory's engineers as they're doing their analysis in a lab and recording the results. Consistent for the most part except if they cheat... That would address the rated engine output or engine HP/TQ etc..
With RWHP/TQ numbers, I'm always suspicious of claims made to interpolate a resultant "engine" output number when the method assumes a constant driveline loss across the board and rpm range....
It seems to me that the driveline loss would be static irrespective of what improvements are done to just the engine. It doesn't seem possible that if a power train was rated with an engine at 300HP at 15% driveline loss or 45hp that the driveline would be losing more power from the friction losses of an increased nominal amount of the engine produced 500hp so the resultant loss was now 75 HP...
What would account for the increase in drivetrain loss of 45hp to 75hp when nothing on the driveline was changed. That always seems impossible to me....
I myself many years ago also believed that reading several magazines that used that 10% or 15% or whatever % was correct. However I thought about it one day and it has never made sense to me since....
Now, comparing a resultant change measured on the same vehicle on the same dyno on a before and after as RWHP/TQ would seem to be apples to apples, assuming no cheating in the machine or vehicle calibration.
My question that keeps coming back is that if the driveline loss was 45 hp to start and after engine only modification the driveline used 30 more HP than before, it made no sense whatsoever. As, how can the same driveline at 6,000 or whatever rpm be different from another measurement when nothing changes in the driveline...... that seems physically impossible.
If it takes 45hp to spin the driveline at 6k rpm, then it should take the same 45hp to spin the same driveline on one day vs the other day.
The only variance would be for wear and frictional losses associated with temperature, lubricants in the driveline etc. which shouldn't vary much if done in similar environments.
So again, what is accounting for the extra 30hp of resultant work (hp) being used by a driveline when no change was made to the driveline. If I use a change from original 300hp before to 800hp after and the 15% number, then my variance goes from 45hp to 120hp or 75hp in additional work being used for the same driveline with no change. It makes absolutely no sense to me whatsoever...
Again, I'm not an engineer, but I can not believe that the work magically increased to do the same thing that was done prior with less work....
If someone can explain this, I would love to learn!!!
I can definitely understand the engine on a test stand in a dynamometer cell being rated and correct for atmospheric conditions etc. by the factory's engineers as they're doing their analysis in a lab and recording the results. Consistent for the most part except if they cheat... That would address the rated engine output or engine HP/TQ etc..
With RWHP/TQ numbers, I'm always suspicious of claims made to interpolate a resultant "engine" output number when the method assumes a constant driveline loss across the board and rpm range....
It seems to me that the driveline loss would be static irrespective of what improvements are done to just the engine. It doesn't seem possible that if a power train was rated with an engine at 300HP at 15% driveline loss or 45hp that the driveline would be losing more power from the friction losses of an increased nominal amount of the engine produced 500hp so the resultant loss was now 75 HP...
What would account for the increase in drivetrain loss of 45hp to 75hp when nothing on the driveline was changed. That always seems impossible to me....
I myself many years ago also believed that reading several magazines that used that 10% or 15% or whatever % was correct. However I thought about it one day and it has never made sense to me since....
Now, comparing a resultant change measured on the same vehicle on the same dyno on a before and after as RWHP/TQ would seem to be apples to apples, assuming no cheating in the machine or vehicle calibration.
My question that keeps coming back is that if the driveline loss was 45 hp to start and after engine only modification the driveline used 30 more HP than before, it made no sense whatsoever. As, how can the same driveline at 6,000 or whatever rpm be different from another measurement when nothing changes in the driveline...... that seems physically impossible.
If it takes 45hp to spin the driveline at 6k rpm, then it should take the same 45hp to spin the same driveline on one day vs the other day.
The only variance would be for wear and frictional losses associated with temperature, lubricants in the driveline etc. which shouldn't vary much if done in similar environments.
So again, what is accounting for the extra 30hp of resultant work (hp) being used by a driveline when no change was made to the driveline. If I use a change from original 300hp before to 800hp after and the 15% number, then my variance goes from 45hp to 120hp or 75hp in additional work being used for the same driveline with no change. It makes absolutely no sense to me whatsoever...
Again, I'm not an engineer, but I can not believe that the work magically increased to do the same thing that was done prior with less work....
If someone can explain this, I would love to learn!!!
06-08-2019, 07:10 AM
#32
Nordschleife Master
I'm not an engineer but I'm curious about the physics and how it's calculated to represent the engine's resultant output.
I can definitely understand the engine on a test stand in a dynamometer cell being rated and correct for atmospheric conditions etc. by the factory's engineers as they're doing their analysis in a lab and recording the results. Consistent for the most part except if they cheat... That would address the rated engine output or engine HP/TQ etc..
With RWHP/TQ numbers, I'm always suspicious of claims made to interpolate a resultant "engine" output number when the method assumes a constant driveline loss across the board and rpm range....
It seems to me that the driveline loss would be static irrespective of what improvements are done to just the engine. It doesn't seem possible that if a power train was rated with an engine at 300HP at 15% driveline loss or 45hp that the driveline would be losing more power from the friction losses of an increased nominal amount of the engine produced 500hp so the resultant loss was now 75 HP...
What would account for the increase in drivetrain loss of 45hp to 75hp when nothing on the driveline was changed. That always seems impossible to me....
I myself many years ago also believed that reading several magazines that used that 10% or 15% or whatever % was correct. However I thought about it one day and it has never made sense to me since....
Now, comparing a resultant change measured on the same vehicle on the same dyno on a before and after as RWHP/TQ would seem to be apples to apples, assuming no cheating in the machine or vehicle calibration.
My question that keeps coming back is that if the driveline loss was 45 hp to start and after engine only modification the driveline used 30 more HP than before, it made no sense whatsoever. As, how can the same driveline at 6,000 or whatever rpm be different from another measurement when nothing changes in the driveline...... that seems physically impossible.
If it takes 45hp to spin the driveline at 6k rpm, then it should take the same 45hp to spin the same driveline on one day vs the other day.
The only variance would be for wear and frictional losses associated with temperature, lubricants in the driveline etc. which shouldn't vary much if done in similar environments.
So again, what is accounting for the extra 30hp of resultant work (hp) being used by a driveline when no change was made to the driveline. If I use a change from original 300hp before to 800hp after and the 15% number, then my variance goes from 45hp to 120hp or 75hp in additional work being used for the same driveline with no change. It makes absolutely no sense to me whatsoever...
Again, I'm not an engineer, but I can not believe that the work magically increased to do the same thing that was done prior with less work....
If someone can explain this, I would love to learn!!!
I can definitely understand the engine on a test stand in a dynamometer cell being rated and correct for atmospheric conditions etc. by the factory's engineers as they're doing their analysis in a lab and recording the results. Consistent for the most part except if they cheat... That would address the rated engine output or engine HP/TQ etc..
With RWHP/TQ numbers, I'm always suspicious of claims made to interpolate a resultant "engine" output number when the method assumes a constant driveline loss across the board and rpm range....
It seems to me that the driveline loss would be static irrespective of what improvements are done to just the engine. It doesn't seem possible that if a power train was rated with an engine at 300HP at 15% driveline loss or 45hp that the driveline would be losing more power from the friction losses of an increased nominal amount of the engine produced 500hp so the resultant loss was now 75 HP...
What would account for the increase in drivetrain loss of 45hp to 75hp when nothing on the driveline was changed. That always seems impossible to me....
I myself many years ago also believed that reading several magazines that used that 10% or 15% or whatever % was correct. However I thought about it one day and it has never made sense to me since....
Now, comparing a resultant change measured on the same vehicle on the same dyno on a before and after as RWHP/TQ would seem to be apples to apples, assuming no cheating in the machine or vehicle calibration.
My question that keeps coming back is that if the driveline loss was 45 hp to start and after engine only modification the driveline used 30 more HP than before, it made no sense whatsoever. As, how can the same driveline at 6,000 or whatever rpm be different from another measurement when nothing changes in the driveline...... that seems physically impossible.
If it takes 45hp to spin the driveline at 6k rpm, then it should take the same 45hp to spin the same driveline on one day vs the other day.
The only variance would be for wear and frictional losses associated with temperature, lubricants in the driveline etc. which shouldn't vary much if done in similar environments.
So again, what is accounting for the extra 30hp of resultant work (hp) being used by a driveline when no change was made to the driveline. If I use a change from original 300hp before to 800hp after and the 15% number, then my variance goes from 45hp to 120hp or 75hp in additional work being used for the same driveline with no change. It makes absolutely no sense to me whatsoever...
Again, I'm not an engineer, but I can not believe that the work magically increased to do the same thing that was done prior with less work....
If someone can explain this, I would love to learn!!!
06-08-2019, 10:55 AM
#35
Nordschleife Master
I don’t know. Our data say it’s almost proportional for the 928 5-speed. Some losses are of course just proportional to rpm, like windage losses. Our formula gives those about 10hp at the typical peak power rpm. But it’s just a SWAG, not the truth.
06-08-2019, 11:41 AM
#36
Drifting
06-08-2019, 01:11 PM
#37
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Compensating for atmospheric conditions is always fun. For automobile piston engines, Carl's corrections are pretty close. The zero-correction temperature is approximately 77ºF per SAE J1349, and there are easily-accessible online correction calculators that will help folks do their own estimates. The corrections for air pressure (barometer) and the effects of moisture content (relative humidity) on actual air density and available oxygen content make seat-of-the-pants correction estimates a bit tougher. Further, the SAE standard does not include actual manifold or charge temperatures, only the ambient air.
928 Five-speed dyno pulls should be done in gear five, which is one-to-one and lowest gearbox losses. On some chassis dynos, this can exceed the speed capability of the dyno itself. In that case, gear four should be used, and a friction loss correction made based on lower-RPM samples taken at both ratios.
The 15% friction loss estimate is a standard that auto manufacturer's agreed to use when actual friction loss numbers are not available. Besides the driveline losses that we all know, this factor also includes the engine accessories like alternator, water pump, power steering and air pumps when installed. The 15% number is used only when actual numbers are not available. Engine accessory number are easily determined by spinning an individual accessory with an electric motor, and measuring the power needed to spin them at an engine-equivalent 5252 RPM.
---
Interesting tangent: I get to work on some pretty good sized stationary gas turbine engines. The performance calculations are very similar, but the standard test conditions are around 62ºF, sea level, with about 25% RH. Contrast with the automotive piston-engine standard test condition under discussion that is at about 77ºF, sea level, and 0% RH. The effect of RH on air density is most interesting and by far the biggest "negotiating point" in a performance calculation. The engine manufacturers actually guarantee a certain electrical output under corrected ambient conditions, and will detune a new engine to barely make that guarantee value. A fraction of a percent difference in test correction is $$$millions, and all parties know that. Fun stuff!
928 Five-speed dyno pulls should be done in gear five, which is one-to-one and lowest gearbox losses. On some chassis dynos, this can exceed the speed capability of the dyno itself. In that case, gear four should be used, and a friction loss correction made based on lower-RPM samples taken at both ratios.
The 15% friction loss estimate is a standard that auto manufacturer's agreed to use when actual friction loss numbers are not available. Besides the driveline losses that we all know, this factor also includes the engine accessories like alternator, water pump, power steering and air pumps when installed. The 15% number is used only when actual numbers are not available. Engine accessory number are easily determined by spinning an individual accessory with an electric motor, and measuring the power needed to spin them at an engine-equivalent 5252 RPM.
---
Interesting tangent: I get to work on some pretty good sized stationary gas turbine engines. The performance calculations are very similar, but the standard test conditions are around 62ºF, sea level, with about 25% RH. Contrast with the automotive piston-engine standard test condition under discussion that is at about 77ºF, sea level, and 0% RH. The effect of RH on air density is most interesting and by far the biggest "negotiating point" in a performance calculation. The engine manufacturers actually guarantee a certain electrical output under corrected ambient conditions, and will detune a new engine to barely make that guarantee value. A fraction of a percent difference in test correction is $$$millions, and all parties know that. Fun stuff!
06-08-2019, 05:10 PM
#38
Rennlist
Basic Site Sponsor
Basic Site Sponsor
I'm not an engineer but I'm curious about the physics and how it's calculated to represent the engine's resultant output.
I can definitely understand the engine on a test stand in a dynamometer cell being rated and correct for atmospheric conditions etc. by the factory's engineers as they're doing their analysis in a lab and recording the results. Consistent for the most part except if they cheat... That would address the rated engine output or engine HP/TQ etc..
With RWHP/TQ numbers, I'm always suspicious of claims made to interpolate a resultant "engine" output number when the method assumes a constant driveline loss across the board and rpm range....
It seems to me that the driveline loss would be static irrespective of what improvements are done to just the engine. It doesn't seem possible that if a power train was rated with an engine at 300HP at 15% driveline loss or 45hp that the driveline would be losing more power from the friction losses of an increased nominal amount of the engine produced 500hp so the resultant loss was now 75 HP...
What would account for the increase in drivetrain loss of 45hp to 75hp when nothing on the driveline was changed. That always seems impossible to me....
I myself many years ago also believed that reading several magazines that used that 10% or 15% or whatever % was correct. However I thought about it one day and it has never made sense to me since....
Now, comparing a resultant change measured on the same vehicle on the same dyno on a before and after as RWHP/TQ would seem to be apples to apples, assuming no cheating in the machine or vehicle calibration.
My question that keeps coming back is that if the driveline loss was 45 hp to start and after engine only modification the driveline used 30 more HP than before, it made no sense whatsoever. As, how can the same driveline at 6,000 or whatever rpm be different from another measurement when nothing changes in the driveline...... that seems physically impossible.
If it takes 45hp to spin the driveline at 6k rpm, then it should take the same 45hp to spin the same driveline on one day vs the other day.
The only variance would be for wear and frictional losses associated with temperature, lubricants in the driveline etc. which shouldn't vary much if done in similar environments.
So again, what is accounting for the extra 30hp of resultant work (hp) being used by a driveline when no change was made to the driveline. If I use a change from original 300hp before to 800hp after and the 15% number, then my variance goes from 45hp to 120hp or 75hp in additional work being used for the same driveline with no change. It makes absolutely no sense to me whatsoever...
Again, I'm not an engineer, but I can not believe that the work magically increased to do the same thing that was done prior with less work....
If someone can explain this, I would love to learn!!!
I can definitely understand the engine on a test stand in a dynamometer cell being rated and correct for atmospheric conditions etc. by the factory's engineers as they're doing their analysis in a lab and recording the results. Consistent for the most part except if they cheat... That would address the rated engine output or engine HP/TQ etc..
With RWHP/TQ numbers, I'm always suspicious of claims made to interpolate a resultant "engine" output number when the method assumes a constant driveline loss across the board and rpm range....
It seems to me that the driveline loss would be static irrespective of what improvements are done to just the engine. It doesn't seem possible that if a power train was rated with an engine at 300HP at 15% driveline loss or 45hp that the driveline would be losing more power from the friction losses of an increased nominal amount of the engine produced 500hp so the resultant loss was now 75 HP...
What would account for the increase in drivetrain loss of 45hp to 75hp when nothing on the driveline was changed. That always seems impossible to me....
I myself many years ago also believed that reading several magazines that used that 10% or 15% or whatever % was correct. However I thought about it one day and it has never made sense to me since....
Now, comparing a resultant change measured on the same vehicle on the same dyno on a before and after as RWHP/TQ would seem to be apples to apples, assuming no cheating in the machine or vehicle calibration.
My question that keeps coming back is that if the driveline loss was 45 hp to start and after engine only modification the driveline used 30 more HP than before, it made no sense whatsoever. As, how can the same driveline at 6,000 or whatever rpm be different from another measurement when nothing changes in the driveline...... that seems physically impossible.
If it takes 45hp to spin the driveline at 6k rpm, then it should take the same 45hp to spin the same driveline on one day vs the other day.
The only variance would be for wear and frictional losses associated with temperature, lubricants in the driveline etc. which shouldn't vary much if done in similar environments.
So again, what is accounting for the extra 30hp of resultant work (hp) being used by a driveline when no change was made to the driveline. If I use a change from original 300hp before to 800hp after and the 15% number, then my variance goes from 45hp to 120hp or 75hp in additional work being used for the same driveline with no change. It makes absolutely no sense to me whatsoever...
Again, I'm not an engineer, but I can not believe that the work magically increased to do the same thing that was done prior with less work....
If someone can explain this, I would love to learn!!!
I can see frictional losses increasing, but are they a straight percentage?
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
06-08-2019, 05:28 PM
#39
Nordschleife Master
Studying piston design in 2018 told me taught me the following. A piston manufacturer will not accidentally not drill the holes thru.
There are two alternative, intentional designs. The first is drilling them thru and the second is not drilling them thru. The choice comes from the piston designers estimate of whether the bore walls have too much or too little oil. Too much oil, drill thru. Too little oil, don’t drill thru and instead create oil reservoirs. I don’t think crankcase gas flows or pressures are related.
My opinion (not a fact) is that they’ve misdiagnosed the oiling conditions in the 928 engine. I believe that there’s too much oil on the bore walls and therefore one should drill the holes thru. Furthermore, one should do whatever one can to reduce the amount of oil on the bore walls.
06-08-2019, 05:31 PM
#40
Nordschleife Master
Years ago, dumped a bunch of data in a spreadsheet and estimated 10hp due to windage etc torque independent losses and 12% due to losses that scale one for one with torque for 928 S4 five speed. This I consider a reasonable approximation for 928 engines making peak power at low 6000s of rpms. It’s an approximation.
06-09-2019, 02:10 AM
#41
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Friction losses go up directly with change in pressure (load) and at the square of increase in speed. The 15% estimate is interesting, as there are some engine parasitic accessory losses that don't change with load. The water pump, for example, carse very little about how many horsepower spill out the opposite end of the crank. Ditto alternator and steering pump load. All of those loads atay the same so long as RPM's are constant. Driveline inertia makes a difference on a Dynojet, not on a brake dyno. And that's why most manufacturErs actually measure the parasitic numbers, calclate the driveline numbers. The 15% "standard" is the agreed-upon default when you don't know the actual values.
06-10-2019, 01:51 AM
#42
Addict
Rennlist Member
Rennlist Member
Join Date: Feb 2004
Location: Monterey Peninsula, CA
Posts: 2,374
Likes: 0
Received 16 Likes
on
12 Posts
Originally Posted by GregBBRD
You've got a very valid point.
I can see frictional losses increasing, but are they a straight percentage?
I can see frictional losses increasing, but are they a straight percentage?
If I remember correctly it's about 742 watts per HP so I can see increased cooling and heat load management. I can also see some frictional losses in the engine increasing a little.
I didn't see the driveline increasing at all, nor did I see the accessories increasing either as they are just being spun by the motor and should not take more work (HP) to spin than they did prior to engine output increase...
06-10-2019, 03:21 AM
#43
Rennlist
Basic Site Sponsor
Basic Site Sponsor
This is what I was trying to understand, would the losses scale in a linear manner with the increase in engine output.
If I remember correctly it's about 742 watts per HP so I can see increased cooling and heat load management. I can also see some frictional losses in the engine increasing a little.
I didn't see the driveline increasing at all, nor did I see the accessories increasing either as they are just being spun by the motor and should not take more work (HP) to spin than they did prior to engine output increase...
If I remember correctly it's about 742 watts per HP so I can see increased cooling and heat load management. I can also see some frictional losses in the engine increasing a little.
I didn't see the driveline increasing at all, nor did I see the accessories increasing either as they are just being spun by the motor and should not take more work (HP) to spin than they did prior to engine output increase...
Chevy built a 427 Big Block (L88). Aluminum heads, huge ports, huge valves, lots of compression, big *** camshaft, huge Holley carb, crazy strong valve train, etc. It made 425hp (probably a bit conservatively rated.) Today, if you can't assemble those same parts and make 600 hp, you should sell your tools.
What's the difference?
Dyno inflation.
The odds of a 100,000 mile stock GTS that hasn't been tuned, probably isn't getting full throttle (super common for the throttle cables to stretch and for 928's be getting 3/4 throttle), and has 1.5mm of carbon on the pistons (which makes the knock sensors retard the timing) making 350hp are....less than zero. They probably struggle to make 300hp, in all honesty.
Dyno testing a tired engine and assuming it makes "as new" power and using that number as your conversion basis is one of the sources of "dyno inflation".
Your point about drivetrain losses not being linear is, obviously, a second source of "dyno inflation".
True story......
Rob Rossitto, God rest his soul, had one of my first 6.5 liter strokers with an automatic (Rob was a paraplegic, without use of his legs.) It made 360 hp at the rear wheels.
He met this guy with a supercharged 928 that had just finished his car.....dynoed at just over 500 rear wheel horsepower.
Just for giggles, the two arranged to meet one evening at the drag strip up near Palmdale (has altitude, BTW.)
Rob spanked this guy, multiple times...they did standing starts, slow rolling starts, faster rolling starts. Spanked hIm everytime.
Rob loved this! This had to be the "highlight" of his life after he broke his back! The "cripple" with hand controls and 360 horsepower spanked the 500 hp supercharged monster.
(I like to think that Rob smiled, thinking about this, as he took his last breath....)
Dyno inflation.....
The point is, let's agree on a conversion factor and all use it. (I vote for conservative.)
06-10-2019, 03:37 AM
#44
Addict
Rennlist Member
Rennlist Member
Join Date: Feb 2004
Location: Monterey Peninsula, CA
Posts: 2,374
Likes: 0
Received 16 Likes
on
12 Posts
Originally Posted by GregBBRD
I really dislike "dyno inflation" and always choose to error on the conservative side, hoping people are smart enough to figure out that most numbers are inflated.
Chevy built a 427 Big Block (L88). Aluminum heads, huge ports, huge valves, lots of compression, big *** camshaft, huge Holley carb, crazy strong valve train, etc. It made 425hp (probably a bit conservatively rated.) Today, if you can't assemble those same parts and make 600 hp, you should sell your tools.
What's the difference?
Dyno inflation.
The odds of a 100,000 mile stock GTS that hasn't been tuned, probably isn't getting full throttle (super common for the throttle cables to stretch and for 928's be getting 3/4 throttle), and has 1.5mm of carbon on the pistons (which makes the knock sensors retard the timing) making 350hp are....less than zero. They probably struggle to make 300hp, in all honesty.
Dyno testing a tired engine and assuming it makes "as new" power and using that number as your conversion basis is one of the sources of "dyno inflation".
Your point about drivetrain losses not being linear is, obviously, a second source of "dyno inflation".
True story......
Rob Rossitto, God rest his soul, had one of my first 6.5 liter strokers with an automatic (Rob was a paraplegic, without use of his legs.) It made 360 hp at the rear wheels.
He met this guy with a supercharged 928 that had just finished his car.....dynoed at just over 500 rear wheel horsepower.
Just for giggles, the two arranged to meet one day at the drag strip up near Palmdale (has altitude, BTW.)
Rob spanked this guy, multiple times...they did standing starts, slow rolling starts, faster rolling starts. Spanked hIm everytime.
Rob loved this! This had to be the "highlight" of his life after he broke his back! The "cripple" with hand controls and 360 horsepower spanked the 500 hp monster.
I like to think that Rob smiled, thinking about this, as he took his last breath....
Dyno inflation.....
The point is, let's agree on a conversion factor and all use it. (I vote for conservative.)
Chevy built a 427 Big Block (L88). Aluminum heads, huge ports, huge valves, lots of compression, big *** camshaft, huge Holley carb, crazy strong valve train, etc. It made 425hp (probably a bit conservatively rated.) Today, if you can't assemble those same parts and make 600 hp, you should sell your tools.
What's the difference?
Dyno inflation.
The odds of a 100,000 mile stock GTS that hasn't been tuned, probably isn't getting full throttle (super common for the throttle cables to stretch and for 928's be getting 3/4 throttle), and has 1.5mm of carbon on the pistons (which makes the knock sensors retard the timing) making 350hp are....less than zero. They probably struggle to make 300hp, in all honesty.
Dyno testing a tired engine and assuming it makes "as new" power and using that number as your conversion basis is one of the sources of "dyno inflation".
Your point about drivetrain losses not being linear is, obviously, a second source of "dyno inflation".
True story......
Rob Rossitto, God rest his soul, had one of my first 6.5 liter strokers with an automatic (Rob was a paraplegic, without use of his legs.) It made 360 hp at the rear wheels.
He met this guy with a supercharged 928 that had just finished his car.....dynoed at just over 500 rear wheel horsepower.
Just for giggles, the two arranged to meet one day at the drag strip up near Palmdale (has altitude, BTW.)
Rob spanked this guy, multiple times...they did standing starts, slow rolling starts, faster rolling starts. Spanked hIm everytime.
Rob loved this! This had to be the "highlight" of his life after he broke his back! The "cripple" with hand controls and 360 horsepower spanked the 500 hp monster.
I like to think that Rob smiled, thinking about this, as he took his last breath....
Dyno inflation.....
The point is, let's agree on a conversion factor and all use it. (I vote for conservative.)
You've gone and said what I was secretly thinking
Inflation.....
06-10-2019, 06:12 AM
#45
I like the crux of the issue raised by blau928.
If I spin a slave unit with an engine of a given hp and torque and at a given slave unit speed speed I will lose drive power due to friction in the slave unit. I could measure the heat produced by the slave unit as a proxy for friction as a further proxy for transmission loss.
If I were to then spin that same slave unit with a hugely more powerful engine (vastly more HP, vastly more torque) but at the same given slave unit speed I would wager that the slave unit would produce the same heat = i.e the same friction i.e. the same transmission loss.
In other words, gearbox transmission loss is - I believe - independent of engine power (for a any given nominated rotational speed). Every force (slave unit friction) is met by an equal and opposite force (engine power loss). Wasn't that Newton's 3rd law of motion?).
Now - to labour the point - why would the alternator or water pump or other peripherals differ from my hypothetical slave unit discussed above (for a given rotational speed etc)? [Note - I am not suggesting that these units do not consume power - I am only suggesting that the amount of power they consume is independent of the inherent power of the motor driving them (at a given rotational speed).
Rather than agreeing on some arbitrary power consumption / drive line loss / engine peripheral loss I would suggest a better approach would be to test it (I assume you guys Greg & Carl have the opportunity to do so) - access to engines, access to dynoes and indeed a professional interest in this stuff.
My suggestion:-
1. Determine crank HP & torque on a nominated engine with no engine peripherals attached ( no alternator, power steering pump, etc);
2. In same weather conditions, do the same with peripherals attached; and
3. In the same weather conditions, measure rwhp and rwtq with the same engine in car and all peripherals attached.
4. Publish results
5. Publish conversion factors at different rpm
That is way beyond my resources to do, but surely not too hard to establish the truth by those with access to the required 'stuff'
Regards
DaveO
If I spin a slave unit with an engine of a given hp and torque and at a given slave unit speed speed I will lose drive power due to friction in the slave unit. I could measure the heat produced by the slave unit as a proxy for friction as a further proxy for transmission loss.
If I were to then spin that same slave unit with a hugely more powerful engine (vastly more HP, vastly more torque) but at the same given slave unit speed I would wager that the slave unit would produce the same heat = i.e the same friction i.e. the same transmission loss.
In other words, gearbox transmission loss is - I believe - independent of engine power (for a any given nominated rotational speed). Every force (slave unit friction) is met by an equal and opposite force (engine power loss). Wasn't that Newton's 3rd law of motion?).
Now - to labour the point - why would the alternator or water pump or other peripherals differ from my hypothetical slave unit discussed above (for a given rotational speed etc)? [Note - I am not suggesting that these units do not consume power - I am only suggesting that the amount of power they consume is independent of the inherent power of the motor driving them (at a given rotational speed).
Rather than agreeing on some arbitrary power consumption / drive line loss / engine peripheral loss I would suggest a better approach would be to test it (I assume you guys Greg & Carl have the opportunity to do so) - access to engines, access to dynoes and indeed a professional interest in this stuff.
My suggestion:-
1. Determine crank HP & torque on a nominated engine with no engine peripherals attached ( no alternator, power steering pump, etc);
2. In same weather conditions, do the same with peripherals attached; and
3. In the same weather conditions, measure rwhp and rwtq with the same engine in car and all peripherals attached.
4. Publish results
5. Publish conversion factors at different rpm
That is way beyond my resources to do, but surely not too hard to establish the truth by those with access to the required 'stuff'
Regards
DaveO