Let's discuss dyno calibration and consistancy
12-21-2007, 10:44 PM
#41
The Superflow can function as an inertia dyno or a load dyno, as can most load dynos. This dyno will do inertia acceleration, timed acceleration, %torque acceleration (absorber power%) or a steady state acceleration, where the speed is held at x for y time before proceeding to the next step. The acceleration run can also be done 'backwards' where the run is started at the top and the absorber pulls the vehicle's speed down. The absorber can also be controlled manually by percentage, vehicle speed can be held to x, normal driving can be simulated.
All these BS numbers that are way off just stir **** up and it's mainly people who fudge their dynos to try to bring business. Dynojet ought to lock their software so tuners cant **** with the calibration.
Scott
12-22-2007, 09:50 AM
#42
That's funny, when I used CAM exclusivly my dyno numbers were always lower that what my car ran at the track by about 20rwhp. Every one said to go to RPM to get higher numbers. Now I go to other shops for convienence and my numbers are higher. Heck, even the MD I just used gave me like peak numbers to Jeffs DJ. Are you saying his numbers are inflated? Just curious, not defending.
12-29-2007, 06:14 PM
#44
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[QUOTE=70Stang;8345209]A dyno dynamics dyno is in a CONSTANT recalibration loop...it is ALWAYS adjusting for temp and metal growth, everything. On a DD you can pull up the load cell and look at it re-calibrating for 0. QUOTE]
It may be adjusting for 0 but how about checking the load cell/strain guage for calibrated torque at a specific value like we do with an engine dyno water brake (where we install a torque arm and hang a calibrated weight from it to check the torque reading at values of 300 - 500 - 700 ft/lbs, etc.).
Yes, a big problem in this business is that everyone WANTS a big number.... and that can drive operators to overlook accurate testing procedures to give the customer what he/she wants.
Yes, the best procedure is to test a car before and after modification to quantify results of said modifications. I wrote an article on our website that explains much of this for those who are interested. http://htmperformance.com/showthread.php?t=11
I personally use a DJ 248 for it's simplicity and repeatability... about the only thing that can mess with the numbers is the weather station (which we cannot alter in the field) - which is not very consistent from unit to unit but we constantly check the correction factor against known weather data, and the built in clock which runs on an internal battery and needs to be replaced about every 5 years I'm told by Dynojet. The only other issue I can see with them is that the correction factor doesn't compensate for the fact that weather has almost no effect on the frictional losses in the drivetrain (unlike a Superflow engine dyno where it tries to estimate the friction in the engine and not compensate for that).
The bottom line is that you have to take into consideration alot of variables in a shops HP claims/results when you try to compare results from one shop to another.
It may be adjusting for 0 but how about checking the load cell/strain guage for calibrated torque at a specific value like we do with an engine dyno water brake (where we install a torque arm and hang a calibrated weight from it to check the torque reading at values of 300 - 500 - 700 ft/lbs, etc.).
Yes, a big problem in this business is that everyone WANTS a big number.... and that can drive operators to overlook accurate testing procedures to give the customer what he/she wants.
Yes, the best procedure is to test a car before and after modification to quantify results of said modifications. I wrote an article on our website that explains much of this for those who are interested. http://htmperformance.com/showthread.php?t=11
I personally use a DJ 248 for it's simplicity and repeatability... about the only thing that can mess with the numbers is the weather station (which we cannot alter in the field) - which is not very consistent from unit to unit but we constantly check the correction factor against known weather data, and the built in clock which runs on an internal battery and needs to be replaced about every 5 years I'm told by Dynojet. The only other issue I can see with them is that the correction factor doesn't compensate for the fact that weather has almost no effect on the frictional losses in the drivetrain (unlike a Superflow engine dyno where it tries to estimate the friction in the engine and not compensate for that).
The bottom line is that you have to take into consideration alot of variables in a shops HP claims/results when you try to compare results from one shop to another.
12-30-2007, 04:37 PM
#45
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Just to give you an example of what others are trying to say. My car does not dyno well. It put down 486rwhp but ran 9.65 at close to 140. I use the dyno to tune and not to sell products.
Last edited by mikey; 12-30-2007 at 05:03 PM.
12-30-2007, 04:57 PM
#46
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This is true for a Dynojet. With the built in weather station, you are locked into what it says. On a Mustang dyno you can enter in your own values and make the numbers come out to whatever you want. We actually looked at a Mustang a few years back and decided against it for this reason. I'm offering 3 free dyno pulls to any local who is questioning their Mustang dyno numbers. *PM me for details on the offer.* Our Dynojet here is very repeatable and lines up with others accross the country.
Mikey, PM sent on the 3 pulls...does this include tuning to correct those cars too?
12-30-2007, 05:08 PM
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I've tuned on a Mustang, a Dyno Dynamics, a Bosch dyno (in Germany) and my own DJ 248.
Let me start by saying people that say you cant properly load an inertia dyno havent spent any significant time on a DJ with proportional air control. In addition to using that, and just the weight of the drum to lug down a motor in the lower rpms, you can hit most of the cells in the VE table, and end up with a VE table thats very, very close on the street.
All that being said, the DD and mustang dynos, with all of their operator entered correction factors, never have seemed to be consistent from car to car, and run to run. They may be great for loading, and steady state tuning, but for repeatable numbers, whether favorable or not, not exactly what I want to run a car on over and over and over.
We ran 3 cars that had been run on my DJ, on a Dyno Dynamics dyno, on the same day. One car was right on, within a couple HP. One car was high, and one car was low. Both of them by a significant amount. One by 30 HP plus (low). We in turn ran them again on my dyno to check the accuracy of them. They were all with 1 or 2 HP of their previous numbers on the same dyno (mine).
I've had numerous cars on my dyno that have previously been on a local Dyno Dynamics, and have had mixed results from them as well. One was 60 HP LESS on mine, than on the local D.D. So much for DJs reading high, eh?
We dont fudge or weather station. We print the weather specs on the printout. Our dyno computer in online and I check the local weather daily to make sure we're close. The only thing thats of by more that a couple % is the humidity, and thats usually within 10%.
I'd also like to note, that consistency and repeatability of a car on a dyno has as much to do with the accuracy of the tune as it does the dyno. I've tuned cars that come back 6 months later (after a tune) for a dyno day, and make within 1 hp of what they did when I tuned them. And thats on cars well over 500 hp.
In closing, I'd like to say, I like the steady state tuning capability with an eddy current dyno. But I wouldnt trade my DJ for one. EVER.
Let me start by saying people that say you cant properly load an inertia dyno havent spent any significant time on a DJ with proportional air control. In addition to using that, and just the weight of the drum to lug down a motor in the lower rpms, you can hit most of the cells in the VE table, and end up with a VE table thats very, very close on the street.
All that being said, the DD and mustang dynos, with all of their operator entered correction factors, never have seemed to be consistent from car to car, and run to run. They may be great for loading, and steady state tuning, but for repeatable numbers, whether favorable or not, not exactly what I want to run a car on over and over and over.
We ran 3 cars that had been run on my DJ, on a Dyno Dynamics dyno, on the same day. One car was right on, within a couple HP. One car was high, and one car was low. Both of them by a significant amount. One by 30 HP plus (low). We in turn ran them again on my dyno to check the accuracy of them. They were all with 1 or 2 HP of their previous numbers on the same dyno (mine).
I've had numerous cars on my dyno that have previously been on a local Dyno Dynamics, and have had mixed results from them as well. One was 60 HP LESS on mine, than on the local D.D. So much for DJs reading high, eh?
We dont fudge or weather station. We print the weather specs on the printout. Our dyno computer in online and I check the local weather daily to make sure we're close. The only thing thats of by more that a couple % is the humidity, and thats usually within 10%.
I'd also like to note, that consistency and repeatability of a car on a dyno has as much to do with the accuracy of the tune as it does the dyno. I've tuned cars that come back 6 months later (after a tune) for a dyno day, and make within 1 hp of what they did when I tuned them. And thats on cars well over 500 hp.
In closing, I'd like to say, I like the steady state tuning capability with an eddy current dyno. But I wouldnt trade my DJ for one. EVER.
Great post Ed. You've summarized exactly what I've seen as well.
12-31-2007, 11:47 AM
#48
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Very interesting thread. I've learned a lot.
And to the original poster Brian, thanks for letting this thread explore the more intricate points of dyno calibration.
After reading a number of responses, I am slowly becoming more of a convert to the principle of "net horsepower", A.K.A. G-tech.. using rolling resistance and the factor of increasing air resistance with greater speed. I guess this is what the track guys have been getting at when they say "it's the track that matters".
Yes, I know weight of the car, gearing, weather effect E.T., but perhaps trap speed to a lesser effect.
Since a number of top-rated dyno experts have commented, my questions are as follows:
1). Would you agree dyno's are best for tuning purposes instead of absolute HP numbers?
2). What type of dyno would give one the most realistic ability to tune a car, WOT and part throttle?
3). Can a dyno's HP numbers be manipulated by entering a different car weight or final drive gear ratio?
While I have used a G-tech a number of times, finding an open and safe road is not easy. Other than weather factors, do you consider 1/4 Trap speed (known car weight) a fairly accurate way to correlate HP/HP gains.
It's an interesting point to ponder, as I have found 1/4 trap Speeds to be within 3-4 mph throughout the track season.
Thanks. I know this discussion has become more advanced, but a number of us have learned quite a bit. Thanks again, Brianc for letting us expand your thread.
..WeathermanShawn..
And to the original poster Brian, thanks for letting this thread explore the more intricate points of dyno calibration.
After reading a number of responses, I am slowly becoming more of a convert to the principle of "net horsepower", A.K.A. G-tech.. using rolling resistance and the factor of increasing air resistance with greater speed. I guess this is what the track guys have been getting at when they say "it's the track that matters".
Yes, I know weight of the car, gearing, weather effect E.T., but perhaps trap speed to a lesser effect.
Since a number of top-rated dyno experts have commented, my questions are as follows:
1). Would you agree dyno's are best for tuning purposes instead of absolute HP numbers?
2). What type of dyno would give one the most realistic ability to tune a car, WOT and part throttle?
3). Can a dyno's HP numbers be manipulated by entering a different car weight or final drive gear ratio?
While I have used a G-tech a number of times, finding an open and safe road is not easy. Other than weather factors, do you consider 1/4 Trap speed (known car weight) a fairly accurate way to correlate HP/HP gains.
It's an interesting point to ponder, as I have found 1/4 trap Speeds to be within 3-4 mph throughout the track season.
Thanks. I know this discussion has become more advanced, but a number of us have learned quite a bit. Thanks again, Brianc for letting us expand your thread.
..WeathermanShawn..
12-31-2007, 07:10 PM
#51
I'll try this one.
I would say they are for both. Tuning, as well as measuring power. You have to be able to quantify changes made.
An eddy current dyno gives the best ability to load a car, and hit the most cells, and hold it there. Inertia dynos are much harder to do the same. But, using one continuously, you learn "tricks" to make them do what eddy current owners say inertia dynos cant do. 
Yes. This is my biggest issue with Mustangs, and Dyno Dynamics. They can be purposely skewed.
I think the problem with trying to correlate HP gains with trap speeds is the lack of consistency of most drivers. Not all car owners are experienced drag racers.
I hear people tell me all the time "I'll probably take it to the track just once to see what it will do". My response is, "If you only take it once, you will be disappointed". Why? Because you cannot drive your car to its potential in just a few passes. Even if you're just going to see what MPH you can get.
Using a dyno on the other hand, gives a repeatable verification. It much easier to be consistent on a dyno.
Very interesting thread. I've learned a lot.
And to the original poster Brian, thanks for letting this thread explore the more intricate points of dyno calibration.
After reading a number of responses, I am slowly becoming more of a convert to the principle of "net horsepower", A.K.A. G-tech.. using rolling resistance and the factor of increasing air resistance with greater speed. I guess this is what the track guys have been getting at when they say "it's the track that matters".
Yes, I know weight of the car, gearing, weather effect E.T., but perhaps trap speed to a lesser effect.
Since a number of top-rated dyno experts have commented, my questions are as follows:
1). Would you agree dyno's are best for tuning purposes instead of absolute HP numbers?
And to the original poster Brian, thanks for letting this thread explore the more intricate points of dyno calibration.
After reading a number of responses, I am slowly becoming more of a convert to the principle of "net horsepower", A.K.A. G-tech.. using rolling resistance and the factor of increasing air resistance with greater speed. I guess this is what the track guys have been getting at when they say "it's the track that matters".
Yes, I know weight of the car, gearing, weather effect E.T., but perhaps trap speed to a lesser effect.
Since a number of top-rated dyno experts have commented, my questions are as follows:
1). Would you agree dyno's are best for tuning purposes instead of absolute HP numbers?
While I have used a G-tech a number of times, finding an open and safe road is not easy. Other than weather factors, do you consider 1/4 Trap speed (known car weight) a fairly accurate way to correlate HP/HP gains.
It's an interesting point to ponder, as I have found 1/4 trap Speeds to be within 3-4 mph throughout the track season.
Thanks. I know this discussion has become more advanced, but a number of us have learned quite a bit. Thanks again, Brianc for letting us expand your thread.
..WeathermanShawn..
It's an interesting point to ponder, as I have found 1/4 trap Speeds to be within 3-4 mph throughout the track season.
Thanks. I know this discussion has become more advanced, but a number of us have learned quite a bit. Thanks again, Brianc for letting us expand your thread.
..WeathermanShawn..
I hear people tell me all the time "I'll probably take it to the track just once to see what it will do". My response is, "If you only take it once, you will be disappointed". Why? Because you cannot drive your car to its potential in just a few passes. Even if you're just going to see what MPH you can get.
Using a dyno on the other hand, gives a repeatable verification. It much easier to be consistent on a dyno.
12-31-2007, 10:36 PM
#52
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This thread interests me as I just had a raw baseline pull done on my car and it was about 1.5points rich and we didnt get to finish it yet, so next weekend I will be back on the rollers to trim the fuel and iron it out. But for what its worth, mods in sig running real rich put down only 320 on a *Brand New* Mustang Dyno....It was assembled, calibrated and tested less than a month ago by Mustang reps. So..the numbers may hurt but as long as I run good when I hit the track I'll still be smiling.
12-31-2007, 11:03 PM
#53
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Good explanation Ed..
Thanks for the summary.
Just like there is a purpose and need for pure engine dyno output and RWHP, it's just the concept of net horsepower that is intriguing [..value of the measurement of all the horsepower that is available to accelerate your vehicle after all power losses have been subtracted..drive train loss, rolling resistance, aerodynamic drag etc..].
Just noting that is the intent of a 1/4 Trap Speed given a known weight and final drive gear ratio.
Your right, in the real world it is not a very practical or reliable test. Hence the dyno.
On a side note.. have played around with both G-Tech and GPS technology to calculate net horsepower..WOT in the same gear it is pretty easy to calculate acceleration and hence HP. I then compare to the dyno. The comparison has worked fairly well for me.
Thanks for the dyno information.
It's nice to get a honest answer.
Happy New Year to All..WeathermanShawn..
Thanks for the summary.
Just like there is a purpose and need for pure engine dyno output and RWHP, it's just the concept of net horsepower that is intriguing [..value of the measurement of all the horsepower that is available to accelerate your vehicle after all power losses have been subtracted..drive train loss, rolling resistance, aerodynamic drag etc..].
Just noting that is the intent of a 1/4 Trap Speed given a known weight and final drive gear ratio.
Your right, in the real world it is not a very practical or reliable test. Hence the dyno.
On a side note.. have played around with both G-Tech and GPS technology to calculate net horsepower..WOT in the same gear it is pretty easy to calculate acceleration and hence HP. I then compare to the dyno. The comparison has worked fairly well for me.
Thanks for the dyno information.
It's nice to get a honest answer.
Happy New Year to All..WeathermanShawn..
01-03-2008, 01:04 PM
#55
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Dyno info Great thread as I have read most of it, pretty closely. One thing you have to consider is the state of tune of the car, as most are tuned by ECU to conditions, fuel density, oil viscosity and a number of other variables. 95% of our chassis dyno work has been on CUP type cars and they are old school but still very complex.
For consistency we warm engines, oils and use the same drum of fuel for all of our in house testing and prior to making any data pulls we run the car at 3 runs from 30 to 180 mph to make sure everything is consistent. We also let the weather correct for itself on the internal Superflow weather program ( I have a Superflow Inertia Dyno ).
We are able to change air correction jets in a Holley by .001" and it will change power approx. 2hp and change them back and overlay curves almost identically ( A-B-A ). We try to utilize A-B-A testing for all of our development work as a change should go back to original numbers if your test procedures are accurate.
I am willing to bet that the cars ECU is adjusting for changes in air quality, temperature and 02 levels and conditions in your testing facility. We have a 7500 sq.ft shop and find that the air becomes significantly contaminated after 8-10 800hp pulls and we allow a 10 minute dwell time to exchange the air in the shop with 2 - 4' Air movers.
I have dyno'd a few 500hp street cars on my dyno and they usually pull 350-400hp on my dyno. As a reference an 830HP Cup Car will hit about 750-800HP at the rear depending on the drivetrain development done on the car.
Hope this helps, mail me if you have any additional???
Thanks,
Mark
For consistency we warm engines, oils and use the same drum of fuel for all of our in house testing and prior to making any data pulls we run the car at 3 runs from 30 to 180 mph to make sure everything is consistent. We also let the weather correct for itself on the internal Superflow weather program ( I have a Superflow Inertia Dyno ).
We are able to change air correction jets in a Holley by .001" and it will change power approx. 2hp and change them back and overlay curves almost identically ( A-B-A ). We try to utilize A-B-A testing for all of our development work as a change should go back to original numbers if your test procedures are accurate.
I am willing to bet that the cars ECU is adjusting for changes in air quality, temperature and 02 levels and conditions in your testing facility. We have a 7500 sq.ft shop and find that the air becomes significantly contaminated after 8-10 800hp pulls and we allow a 10 minute dwell time to exchange the air in the shop with 2 - 4' Air movers.
I have dyno'd a few 500hp street cars on my dyno and they usually pull 350-400hp on my dyno. As a reference an 830HP Cup Car will hit about 750-800HP at the rear depending on the drivetrain development done on the car.
Hope this helps, mail me if you have any additional???
Thanks,
Mark
01-03-2008, 01:31 PM
#56
Great thread as I have read most of it, pretty closely. One thing you have to consider is the state of tune of the car, as most are tuned by ECU to conditions, fuel density, oil viscosity and a number of other variables. 95% of our chassis dyno work has been on CUP type cars and they are old school but still very complex.
For consistency we warm engines, oils and use the same drum of fuel for all of our in house testing and prior to making any data pulls we run the car at 3 runs from 30 to 180 mph to make sure everything is consistent. We also let the weather correct for itself on the internal Superflow weather program ( I have a Superflow Inertia Dyno ).
We are able to change air correction jets in a Holley by .001" and it will change power approx. 2hp and change them back and overlay curves almost identically ( A-B-A ). We try to utilize A-B-A testing for all of our development work as a change should go back to original numbers if your test procedures are accurate.
I am willing to bet that the cars ECU is adjusting for changes in air quality, temperature and 02 levels and conditions in your testing facility. We have a 7500 sq.ft shop and find that the air becomes significantly contaminated after 8-10 800hp pulls and we allow a 10 minute dwell time to exchange the air in the shop with 2 - 4' Air movers.
I have dyno'd a few 500hp street cars on my dyno and they usually pull 350-400hp on my dyno. As a reference an 830HP Cup Car will hit about 750-800HP at the rear depending on the drivetrain development done on the car.
Hope this helps, mail me if you have any additional???
Thanks,
Mark
For consistency we warm engines, oils and use the same drum of fuel for all of our in house testing and prior to making any data pulls we run the car at 3 runs from 30 to 180 mph to make sure everything is consistent. We also let the weather correct for itself on the internal Superflow weather program ( I have a Superflow Inertia Dyno ).
We are able to change air correction jets in a Holley by .001" and it will change power approx. 2hp and change them back and overlay curves almost identically ( A-B-A ). We try to utilize A-B-A testing for all of our development work as a change should go back to original numbers if your test procedures are accurate.
I am willing to bet that the cars ECU is adjusting for changes in air quality, temperature and 02 levels and conditions in your testing facility. We have a 7500 sq.ft shop and find that the air becomes significantly contaminated after 8-10 800hp pulls and we allow a 10 minute dwell time to exchange the air in the shop with 2 - 4' Air movers.
I have dyno'd a few 500hp street cars on my dyno and they usually pull 350-400hp on my dyno. As a reference an 830HP Cup Car will hit about 750-800HP at the rear depending on the drivetrain development done on the car.
Hope this helps, mail me if you have any additional???
Thanks,
Mark
Sometimes when I have results that I think are questionable, I do the a-b-a thingy. Make a change, see the result, change it back, see if its what you started with.
I would imagine dynoing cup cars is a blast. Most car guys dream job.
01-04-2008, 11:27 PM
#58
See, what bothers me is this -
You CAN skew the numbers on a Dyno Dynamics or a Mustang dyno, but what does that have to do with anything? They are a better dyno. They perform better then a DynoJet and allow tuners to hold a car in any situation for any amount of time.
We can take a 600hp turbo car and bring it to near IDLE with our DD - at wide open throttle we can load a car to a dead stop....that allows load cell tuning that you can not get on a DynoJet without the LC.
My point of all this is - The ability to skew a number means nothing. HONEST dyno operators can tune a car with better control on a better dyno. This should be easy to understand....why do you think DynoJet is adding the load control to the new models? Certainly not because they just feel like it? THe smaller knurled rollers on a DD dyno allow much smaller changes to be seen in tq and hp. A 2000lb roller spinning at 6000 engine rpm is not going to see a 5ft/lb difference in a tuning change, nor will it be able to hold a car in that load cell for 30 seconds to a minute to make timing changes and watch the results in real time.
That is the difference, not the dyno operator.
At our shop, we offer anyone access to any file on our dyno at any time. We have saved every run for the last 3 years and can show any and every factor involved in the run....this is the difference between a good and bad shop, imo.
Also, the new DDs have a built in weather station.
You CAN skew the numbers on a Dyno Dynamics or a Mustang dyno, but what does that have to do with anything? They are a better dyno. They perform better then a DynoJet and allow tuners to hold a car in any situation for any amount of time.
We can take a 600hp turbo car and bring it to near IDLE with our DD - at wide open throttle we can load a car to a dead stop....that allows load cell tuning that you can not get on a DynoJet without the LC.
My point of all this is - The ability to skew a number means nothing. HONEST dyno operators can tune a car with better control on a better dyno. This should be easy to understand....why do you think DynoJet is adding the load control to the new models? Certainly not because they just feel like it? THe smaller knurled rollers on a DD dyno allow much smaller changes to be seen in tq and hp. A 2000lb roller spinning at 6000 engine rpm is not going to see a 5ft/lb difference in a tuning change, nor will it be able to hold a car in that load cell for 30 seconds to a minute to make timing changes and watch the results in real time.
That is the difference, not the dyno operator.
At our shop, we offer anyone access to any file on our dyno at any time. We have saved every run for the last 3 years and can show any and every factor involved in the run....this is the difference between a good and bad shop, imo.
Also, the new DDs have a built in weather station.
01-04-2008, 11:33 PM
#59
1). Would you agree dyno's are best for tuning purposes instead of absolute HP numbers?
No. Dynos are capable of reporting gains and losses but also can accurately tell absolute HP numbers for a given day and setting.
2). What type of dyno would give one the most realistic ability to tune a car, WOT and part throttle?
Any dyno with load control is best.
3). Can a dyno's HP numbers be manipulated by entering a different car weight or final drive gear ratio?
Yes. On a DD, there is no input for either weight or final drive ratio, altho drivetrain inertia is a factor that can be altered.
No. Dynos are capable of reporting gains and losses but also can accurately tell absolute HP numbers for a given day and setting.
2). What type of dyno would give one the most realistic ability to tune a car, WOT and part throttle?
Any dyno with load control is best.
3). Can a dyno's HP numbers be manipulated by entering a different car weight or final drive gear ratio?
Yes. On a DD, there is no input for either weight or final drive ratio, altho drivetrain inertia is a factor that can be altered.
Hope that answers some of them
01-05-2008, 01:58 AM
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Dyno results... I don't mean to be a drag on the thread, but my response was to the variance in the results on the individual dyno runs on different days with the same car and the same tune.
Unless I am mistaken cars with O2 sensors send info back to the ECU to keep the engine in a certain range. 99% of those sensors are +/- 5-10% on the range and capabilities of the sensor thru a wide temperature band. Other cars with airspeed / density programming can be more accurate but are sensitive to the dimensions of their tuning capabilities, Throttle position, rpm, temperature etc.
As I am not an expert on this stuff I did sleep in Holiday Inn a couple months ago and I think that helps. I own one of the first 10 DFI programmers for 1988 Chevrolets and the deal was a laptop plug in from DFI which ended up being the Accel deal and sprouted a bunch of others.
My point was this :
From the dyno results given I was guessing the car was tuning itself to either weather or shop conditions and the dyno was recording the proper output. As far as dyno correction factors, unless you have a significant correction database for you dyno and shop surroundings the STP correction factors are not the best for all situations.
Example, if you drive a car to the dyno shop in ATL on 90 degree day, what is the temperature of the fuel in the gas tank. If you let the same car sit overnight in your shop and then re-dyno it what is the fuel temp then. Fuel density can change by 5-10% easily and most cars do not adjust for that as the fuel systems are usually volume/pressure systems as are the injectors.
That is why some cars run great at Daytona on a hot day and some suck...restrictor plates are hell on a hot day. Same thing with a 10 second grocery getter.
As far as dynos with load cells, I think they are great & probably good for finding steady state tuning info, and other stuff I really have not come across yet.
All I do know is the faster you can accelerate up the big wheel the faster the car will be on the street, strip and oval track. On my dyno, I tend to concentrate on thrust curves and instantaneous acceleration in the RPM band that is most common for the application, and I try and get the fuel delivery right to make the most power per gallon that the fuel is capable of.
Unless I am mistaken cars with O2 sensors send info back to the ECU to keep the engine in a certain range. 99% of those sensors are +/- 5-10% on the range and capabilities of the sensor thru a wide temperature band. Other cars with airspeed / density programming can be more accurate but are sensitive to the dimensions of their tuning capabilities, Throttle position, rpm, temperature etc.
As I am not an expert on this stuff I did sleep in Holiday Inn a couple months ago and I think that helps. I own one of the first 10 DFI programmers for 1988 Chevrolets and the deal was a laptop plug in from DFI which ended up being the Accel deal and sprouted a bunch of others.
My point was this :
From the dyno results given I was guessing the car was tuning itself to either weather or shop conditions and the dyno was recording the proper output. As far as dyno correction factors, unless you have a significant correction database for you dyno and shop surroundings the STP correction factors are not the best for all situations.
Example, if you drive a car to the dyno shop in ATL on 90 degree day, what is the temperature of the fuel in the gas tank. If you let the same car sit overnight in your shop and then re-dyno it what is the fuel temp then. Fuel density can change by 5-10% easily and most cars do not adjust for that as the fuel systems are usually volume/pressure systems as are the injectors.
That is why some cars run great at Daytona on a hot day and some suck...restrictor plates are hell on a hot day. Same thing with a 10 second grocery getter.
As far as dynos with load cells, I think they are great & probably good for finding steady state tuning info, and other stuff I really have not come across yet.
All I do know is the faster you can accelerate up the big wheel the faster the car will be on the street, strip and oval track. On my dyno, I tend to concentrate on thrust curves and instantaneous acceleration in the RPM band that is most common for the application, and I try and get the fuel delivery right to make the most power per gallon that the fuel is capable of.