thinking to dyno my new ride
- Thread starter peckhs
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Re: thinking to dyno my new ride
SAE (Society of Automotive Engineers) dyno numbers are corrected for barometric pressure, relative humidity, and air temp... These three conditions (and subsequently engine output) are "corrected" to a standard value using those environmental parameters in an attempt to factor out atmospheric conditions when comparing engine output. SAE assumes 15% frictional loss within the engine, which is probably close for a piston engine. This 15% loss of power is not drivetrain loss from crankshaft to the rear wheels.
So what's the correction factor? It will depend on the actual air temperature, pressure and humidity with respect the standard values. Example: you go to the dyno in a cool day when the air is dry and high barometric pressure. You get a dyno graph with STD (Standard) numbers and corrected numbers. Then few months later you go back to the same dyno (assuming it is calibrated and well maintained and you haven't changed anything), the weather is raining (high humidity, low barometric pressure, moderate temp). The corrected SAE numbers "should" be the same while your STD (Standard) numbers will be a little lower.
SAE (Society of Automotive Engineers) dyno numbers are corrected for barometric pressure, relative humidity, and air temp... These three conditions (and subsequently engine output) are "corrected" to a standard value using those environmental parameters in an attempt to factor out atmospheric conditions when comparing engine output. SAE assumes 15% frictional loss within the engine, which is probably close for a piston engine. This 15% loss of power is not drivetrain loss from crankshaft to the rear wheels.
So what's the correction factor? It will depend on the actual air temperature, pressure and humidity with respect the standard values. Example: you go to the dyno in a cool day when the air is dry and high barometric pressure. You get a dyno graph with STD (Standard) numbers and corrected numbers. Then few months later you go back to the same dyno (assuming it is calibrated and well maintained and you haven't changed anything), the weather is raining (high humidity, low barometric pressure, moderate temp). The corrected SAE numbers "should" be the same while your STD (Standard) numbers will be a little lower.
Re: thinking to dyno my new ride
Hi Ken, 15% relative to what, and how is this figure used with chassis dynos since what you get at the crank or wheels, is what you get at that location anyway? Conversion of fuel energy to crank energy is very inefficient for just about all current gasoline engines at roughly 65-70% loss.
kenntona;374763 said:
Hi Ken, 15% relative to what, and how is this figure used with chassis dynos since what you get at the crank or wheels, is what you get at that location anyway? Conversion of fuel energy to crank energy is very inefficient for just about all current gasoline engines at roughly 65-70% loss.
futron.sim
Well-Known Member
Re: thinking to dyno my new ride
I am just curious, is it E30 or E36? Cause the engine is different. E30 using M20 while E36 using M50
I am just curious, is it E30 or E36? Cause the engine is different. E30 using M20 while E36 using M50
Re: thinking to dyno my new ride
My impression is that the range of friction loss is wider? Say 60% - 85%? How could anyone generalises the friction loss from say lubrication conditions change (changes in viscosity and clearances between rubbing surfaces) at diff temp? I would have thought that at diff temp range, each component's friction contribution to total engine losses varies?
Shaun, the 15% loss is relative to rated engine power (and I suspect) at hypothetically highest range of the torque curve. But this number was perhaps a gauge in steady-state experiments if not simulation? I do not think they could extract stats from transient experiments.Shaun said:
My impression is that the range of friction loss is wider? Say 60% - 85%? How could anyone generalises the friction loss from say lubrication conditions change (changes in viscosity and clearances between rubbing surfaces) at diff temp? I would have thought that at diff temp range, each component's friction contribution to total engine losses varies?
Crufty Dusty
Well-Known Member
Re: thinking to dyno my new ride
Is there link to a paper or publication where this was info was obtained?kenntona;375477 said:
Er... I don't think it was generalized.... the subject is SAE correction factor applied to measured torque, nothing to do with tribology although that can also be measured scientifically.kenntona;375477 said:
Crufty Dusty
Well-Known Member
Re: thinking to dyno my new ride
Thank God I do not own any Land & Sea dynos. The link you supplied is a marketing page disguised as technical information to deceive the layman.
Thank God I do not own any Land & Sea dynos. The link you supplied is a marketing page disguised as technical information to deceive the layman.
Re: thinking to dyno my new ride
"The older J607 standard considers that the engine was run on a 60°F day with 0% humidity and a barometric pressure of 29.92 in-Hg or the newer SAE J1349 standard of 77°F (25°C) day with 0% humidity and a barometric pressure of 29.234 in-Hg (99 KPa)."
And J1349, which rates the complete engine with all standard intake and exhaust systems, measures horsepower at the flywheel and excludes all transmission and drivetrain losses. Without even looking into its replacement standard J2723, how could any "generalisation" of a 65-70% friction loss stands its argument? The diff standards used for correction factors are already an indication of wider margin of error. Am I missing something here?
kenntona said:
Refer to same article:Crufty Dusty said:
"The older J607 standard considers that the engine was run on a 60°F day with 0% humidity and a barometric pressure of 29.92 in-Hg or the newer SAE J1349 standard of 77°F (25°C) day with 0% humidity and a barometric pressure of 29.234 in-Hg (99 KPa)."
And J1349, which rates the complete engine with all standard intake and exhaust systems, measures horsepower at the flywheel and excludes all transmission and drivetrain losses. Without even looking into its replacement standard J2723, how could any "generalisation" of a 65-70% friction loss stands its argument? The diff standards used for correction factors are already an indication of wider margin of error. Am I missing something here?
Re: thinking to dyno my new ride
It can't be because torque peak varies widely and depending on where it is on the engine speed scale, actual friction will vary a tremendous amount since it grows as a square of engine speed.
For every 100 hp you have at the crank, you're wasting roughly another 200 hp through the exhaust and cooling system losses. Friction makes up a very small portion of this.
For reference, in friction testing racing V8s making around 850-1400hp, with everything exactly the same as on a live engine, full install except closed off non-live cylinders to minimize pumping losses and leave only friction, the motors that turn the engine over are rated for anywhere from 25-75 hp only. Some of these less crazy engines even leave ports open and take on the pumping losses. Take that into account and realize that anywhere from 1600 - 2600 hp in those engines is suffered from thermal losses and pumping losses, and raw friction as a % is very small. Smaller still when on road car low redline engines.
For all road car purposes, what you have at the crank is what you have at the crank, you have a drivetrain loss, and what you have at the wheels is what you have at the wheels. There's really no need to go any deeper than that because it takes too much to find out exactly.
kenntona;375477 said:
It can't be because torque peak varies widely and depending on where it is on the engine speed scale, actual friction will vary a tremendous amount since it grows as a square of engine speed.
Whether steady state or transient, by running a few separate tests, it is possible to arrive at pretty accurate separate figures for friction losses, pumping losses, and thermal losses. What is for sure is that friction can't be pegged at 15%, and even if very roughly done, requires much more qualification like, relative to what, and assumed conditions.
Again, 60 - 85% of what? I'm not sure why anyone except very high level race engine developers would be concerned at all with actual proportion of power loss attributed to friction losses, when pumping and thermal losses far eclipse friction losses. Pumping losses are sometimes lumped with friction, but in the context of this thread, they are separate.
For every 100 hp you have at the crank, you're wasting roughly another 200 hp through the exhaust and cooling system losses. Friction makes up a very small portion of this.
For reference, in friction testing racing V8s making around 850-1400hp, with everything exactly the same as on a live engine, full install except closed off non-live cylinders to minimize pumping losses and leave only friction, the motors that turn the engine over are rated for anywhere from 25-75 hp only. Some of these less crazy engines even leave ports open and take on the pumping losses. Take that into account and realize that anywhere from 1600 - 2600 hp in those engines is suffered from thermal losses and pumping losses, and raw friction as a % is very small. Smaller still when on road car low redline engines.
For all road car purposes, what you have at the crank is what you have at the crank, you have a drivetrain loss, and what you have at the wheels is what you have at the wheels. There's really no need to go any deeper than that because it takes too much to find out exactly.
Re: thinking to dyno my new ride
Ken, you should not have deleted that post I was going to reply to it
The loss I mentioned is not pulled from thin air.. it is a known loss. For every unit of energy contained in the fuel mass, the amount transferred to the crankshaft is only roughly around 30%. That's where the 65-70% loss came from. It's not in reference to friction, but overall loss, mainly thermal and pumping losses.
Ken, you should not have deleted that post I was going to reply to it
The loss I mentioned is not pulled from thin air.. it is a known loss. For every unit of energy contained in the fuel mass, the amount transferred to the crankshaft is only roughly around 30%. That's where the 65-70% loss came from. It's not in reference to friction, but overall loss, mainly thermal and pumping losses.
Re: thinking to dyno my new ride
I have to delete it because the arguments presented in that article is presumed fallacious.Shaun said:
Wait. Lemme digest. Say my car is "rated" 306 bhp at crank, and dyno figures show 276 thereabout. That's pure drivetrain loss of 30 horses. It is only 10% loss. How do you intepret this 276 bhp reading?Shaun said:
Re: thinking to dyno my new ride
There is, but it is splitting hairs IMO. The type of dyno, and the variance in setting the car up on the chassis dyno, the lack of logging air and all in-car fluid temps, process control like time between runs to let hot spots dissipate, etc. all are as large or larger than the difference in the corrections. The diff between those corrections is usually within 2%.
Just go with whatever correction everyone else has done their cars, or the one that you did when you did your baseline, etc. We're talking road cars.. no big deal.
kenntona;375606 said:
There is, but it is splitting hairs IMO. The type of dyno, and the variance in setting the car up on the chassis dyno, the lack of logging air and all in-car fluid temps, process control like time between runs to let hot spots dissipate, etc. all are as large or larger than the difference in the corrections. The diff between those corrections is usually within 2%.
Just go with whatever correction everyone else has done their cars, or the one that you did when you did your baseline, etc. We're talking road cars.. no big deal.
Re: thinking to dyno my new ride
dynojet correction factor - Bimmerforums - The Ultimate BMW Forum
autoweek drives G37, 335i, IS350 - bimmerfest - BMW Forums
Yep, that's what I read in bimmerfest too.Shaun said:
dynojet correction factor - Bimmerforums - The Ultimate BMW Forum
autoweek drives G37, 335i, IS350 - bimmerfest - BMW Forums
Re: thinking to dyno my new ride
I take it as 276 wheel hp at that particular dyno on that day with that correction - nothing more nothing less.
To measure crank power, put it on an engine dyno, which again requires corrections applied, but in a dyno cell you can control cell air temp, pressure, coolant temp, oil temp, to the point you don't need any correction.
kenntona;375614 said:
I take it as 276 wheel hp at that particular dyno on that day with that correction - nothing more nothing less.
To measure crank power, put it on an engine dyno, which again requires corrections applied, but in a dyno cell you can control cell air temp, pressure, coolant temp, oil temp, to the point you don't need any correction.
Re: thinking to dyno my new ride
If I take 276 at the wheels, and that's after a 65-70% loss, how does that reconcile with a rated 306 bhp (supposedly) at the crank? That BMW understated the rating horsepower by 90?
Shaun said:
This is the part I could not reconcile.Shaun said:
If I take 276 at the wheels, and that's after a 65-70% loss, how does that reconcile with a rated 306 bhp (supposedly) at the crank? That BMW understated the rating horsepower by 90?
