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Old 03-24-2008, 01:40 PM   #1
sponaugle
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Default Dyno runs in a 1:1 gear ratio?

This post is inspired by a couple of comments on another thread (a GT40 PPB thread):

Quote:
Originally Posted by tino View Post
Yeh it was dynoed in 5th gear as for stis that is the closest 1:1 ratio... for wrxs with 5 speeds dynos should be done in 4th gear to get 1:1 ratio
Quote:
Originally Posted by modaddict View Post
I wish more people would realize this.

Somehow in the last couple years, it's switched to 4th gear in the sti and 3rd in the wrx

I was pondering these two statements. Why would the gear ratio have any effect on the measured power? What is special about 1:1? How does the rear diff ratio come into play?

I did some research, and as far as I can tell, this is bunk when it comes to manual transmission cars. The primary reason for this ‘wives tale’ must be the large change in transmission efficiency with a 1:1 ratio when compared to the lower ratio gears that use the planetary members. As far as I can tell, the power efficiency in an automatic transmission can vary by more than 15% based on the gear.

However, in a modern helical gear manual transmission this does not appear to be true. Gear efficiency in a two gear helical setup, running from .5:1 to 5:1 seems to be around 98-99%. It does not appear to be heavily biased towards the change in ratio.

Take a look at: http://www.roymech.co.uk/Useful_Tabl...fficiency.html

As you dyno in higher and higher gears, you increase the energy loss due to velocity of the gears, so reads of horsepower usually drop a bit. On the Mustang dyno at PDX, a 5th gear pull is usually a few hp less than a 4th gear pull.

The final drive ratio (3.9 in the STI) is of course not 1:1, so how would this effect the power output? I believe the answer is only in as much as the efficiency of the differential. As far as I can tell, the overall efficiency of the differential itself is far lower than the efficiency of the 3.9:1 gear transfer.

So, perhaps someone else can correct me on this. Before undertaking this task however:

(1) Don’t post back linking to a page from a shop that says “1:1” is the way to go. I have found hundreds of such examples, none with any backing.
(2) Don’t post back empirical results for an automatic.
(3) For any discussion about resulting numbers, be sure to know how the dyno corrects for speed based losses. Remember that some dynos, like the dynapak, used time based loading. They keep the time to ramp at a constant, which means in higher gears (larger speed ranges), the angular acceleration of the wheels, diffs, etc, will be higher. This should results in lower hp in higher gears.
(4) Yes, as you change the gears you change the resulting wheel torque, which the dyno recorrects back to engine torque via RPM. No need to explain that.

Comments?

Jeff Sponaugle
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Old 03-24-2008, 02:23 PM   #2
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Very good post, I concur with all your findings. For example over here in a Dynojet we actually see a wider powerbands (due to the extra load) in 4th (or 5th) than in 3rd gear. But peak numbers are very close. For the people that don't believe me... go do it yourself... you will see!
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Old 03-24-2008, 04:41 PM   #3
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Jeff - the reason for the dyno in the 1:1 gear ratio is due to the Dynojet. Dynojet mathematically creates a horsepower number based on mass (which is the known weight of the rollers) and accleration (how fast the car is accelerating the known weight).

F=ma

From force (F), we can calculate horsepower.

Dyno the car in 2nd gear, and acceleration (a) goes way up, causing force (F) to go way up.

So by dynoing the car in the gear closest to the 1:1 gear ratio, we eliminate any acceleration advantage or disadvantage caused by the transmission, which gives us unskewed whp numbers (even though Dynojet has a fudge factor in there which makes them skewed anyways and read high).

As for other dynos out there (i.e. Mustang and Dyno Dynamics) - they use a load cell to measure roll force (the amount of force the tire is placing on the roller). Based on roll force and the radius arm going to the load cell, we get roll torque. Based on roll torque and roll speed, we can get vehicle horsepower. Vehicle horsepower and vehicle RPM gives vehicle torque. It doesn't matter what gear you run in on load cell style dynos as they are measuring force, not acceleration. Force does not change from gear to gear.

wow...haven't had to give that speech for a while.
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Old 03-24-2008, 04:47 PM   #4
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Yeah, like at SEMA...to me
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Old 03-24-2008, 04:52 PM   #5
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Quote:
Originally Posted by SloRice View Post
Jeff - the reason for the dyno in the 1:1 gear ratio is due to the Dynojet. Dynojet mathematically creates a horsepower number based on mass (which is the known weight of the rollers) and accleration (how fast the car is accelerating the known weight).

F=ma

From force (F), we can calculate horsepower.

Dyno the car in 2nd gear, and acceleration (a) goes way up, causing force (F) to go way up.

So by dynoing the car in the gear closest to the 1:1 gear ratio, we eliminate any acceleration advantage or disadvantage caused by the transmission, which gives us unskewed whp numbers (even though Dynojet has a fudge factor in there which makes them skewed anyways and read high).

As for other dynos out there (i.e. Mustang and Dyno Dynamics) - they use a load cell to measure roll force (the amount of force the tire is placing on the roller). Based on roll force and the radius arm going to the load cell, we get roll torque. Based on roll torque and roll speed, we can get vehicle horsepower. Vehicle horsepower and vehicle RPM gives vehicle torque. It doesn't matter what gear you run in on load cell style dynos as they are measuring force, not acceleration. Force does not change from gear to gear.

wow...haven't had to give that speech for a while.

Awesome, thanks! Man I love good information, my head feels fatter now
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Old 03-24-2008, 04:59 PM   #6
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Quote:
Originally Posted by DoctorNick View Post
Yeah, like at SEMA...to me
probably one of the last times I gave that speech.


I miss the industry....but at the same time I don't.
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Old 03-24-2008, 05:58 PM   #7
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Quote:
Originally Posted by SloRice View Post
I miss the industry....but at the same time I don't.
Hmmm...kinda like the STi, huh?
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Old 03-24-2008, 06:26 PM   #8
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Quote:
Originally Posted by SloRice View Post
Jeff - the reason for the dyno in the 1:1 gear ratio is due to the Dynojet. Dynojet mathematically creates a horsepower number based on mass (which is the known weight of the rollers) and accleration (how fast the car is accelerating the known weight).

F=ma

From force (F), we can calculate horsepower.

Dyno the car in 2nd gear, and acceleration (a) goes way up, causing force (F) to go way up.

So by dynoing the car in the gear closest to the 1:1 gear ratio, we eliminate any acceleration advantage or disadvantage caused by the transmission, which gives us unskewed whp numbers (even though Dynojet has a fudge factor in there which makes them skewed anyways and read high).
Force goes up but the angular speed of the drum, which is part of the power calculation, goes down in lower gears.
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Old 03-24-2008, 06:51 PM   #9
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Quote:
Originally Posted by sponaugle View Post
(3) For any discussion about resulting numbers, be sure to know how the dyno corrects for speed based losses. Remember that some dynos, like the dynapak, used time based loading. They keep the time to ramp at a constant, which means in higher gears (larger speed ranges), the angular acceleration of the wheels, diffs, etc, will be higher. This should results in lower hp in higher gears.
(4) Yes, as you change the gears you change the resulting wheel torque, which the dyno recorrects back to engine torque via RPM. No need to explain that.

Comments?

Jeff Sponaugle
Jeff, you'll notice that my comments were made on a thread that had a car dyno'd on a dynapak

Also, flycaster, Ozer (a customer of yours, PDXtuning), and I had some conversations about why all 3 of us had perrin 30r kits, and Ozer's PDXtuning dyno "numbers" were signficantly higher than even flycasters 'built block'. (mine is stock). It raised some questions, we had good dialog and *I* deemed it to be the fact that whoever tuned Ozer's car at PDX, dyno'd it in 4th gear, and flycaster and I had dyno'd in 5th. I was tuned by Jarrad, flycaster by Tim, and Ozer ???
http://www.iwsti.com/forums/engine-p...ater-meth.html


By Tim the mustang dyno guy's explaination on a dynojet if you put it in 2nd or 3rd you can get a different tq/hp calculation....resulting in higher numbers.

Can anyone say 500+whp out of an fp green on pump gas?



Quote:
Originally Posted by PERRINJeff View Post
A little history on the Dynapack and how it is setup. Many people run the cars in 4th gear, at for 12 seconds. Because of our big plans with this car, we started in 5th gear, and run it for 14 seconds. Both of these factors play into the actual HP and TQ numbers by lowering them. We could have made the dyno read a bit higher, by changing to 4th gear, or making the run shorter, but for tuning purposes, and future part comparos, this is what we decided on.
Quote:
Originally Posted by Crawford / I-Speed USA
Hi Everyone,

There have been quite a few people that ask the question, why does one tuning shop perform baselines/dyno tuning in gear X while another tuning shop uses gear Y? We recently had a a 2003 US EVO (5 Speed Manual) drop by for baseline pulls in 4th gear and 3rd gear.

If dyno tuning or baselines are performed it is very important to run vehicles close to a 1:1 final drive ratio as specified by various dyno companies (ex. Dynapack). As seen in the charts below if testing is not performed in the gear ratio close to a final drive of 1:1, the transmission will have a larger mechanical advantage over the dyno. In turn the numbers will read higher and give false numbers.

Chart Key:
- Bold Lines - 4th Gear Pulls
- Thin Lines - 3rd Gear Pulls


Dyno Run Set 1: Average Difference 15-20 horsepower, 5-7%


Dyno Run Set 2: Average Difference 10-15 horsepower, 4-6%

Cheers,
I-Speed USA

The only variable in this test was gear selection, and all other features were kept constant between baselines.
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Old 03-24-2008, 06:52 PM   #10
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Quote:
Originally Posted by SloRice View Post
Jeff - the reason for the dyno in the 1:1 gear ratio is due to the Dynojet. Dynojet mathematically creates a horsepower number based on mass (which is the known weight of the rollers) and accleration (how fast the car is accelerating the known weight).

F=ma

From force (F), we can calculate horsepower.

Dyno the car in 2nd gear, and acceleration (a) goes way up, causing force (F) to go way up.

So by dynoing the car in the gear closest to the 1:1 gear ratio, we eliminate any acceleration advantage or disadvantage caused by the transmission, which gives us unskewed whp numbers (even though Dynojet has a fudge factor in there which makes them skewed anyways and read high).

As for other dynos out there (i.e. Mustang and Dyno Dynamics) - they use a load cell to measure roll force (the amount of force the tire is placing on the roller). Based on roll force and the radius arm going to the load cell, we get roll torque. Based on roll torque and roll speed, we can get vehicle horsepower. Vehicle horsepower and vehicle RPM gives vehicle torque. It doesn't matter what gear you run in on load cell style dynos as they are measuring force, not acceleration. Force does not change from gear to gear.

wow...haven't had to give that speech for a while.
I don't follow how being at 1:1 or not makes any difference. The calculated HP, which is derived from the rate of acceleration, must always take into account the gearing.

Are you suggesting that a car that has a .971:1 gear vs a .890:1 gear will always ready a lower power even though it makes the same power. I find it very hard to believe the dyno could not take that into account.

You could argue, however, that at a higher gear you accelerate the drum slower, giving much greater resoltion to the pickup, and thus the graphs.

On top of that, the car does not have a 1:1 ratio ever! A stock STI in 5th gear has a primary gear ratio of .971:1, plus a secondary gear ratio of 3.9:1. So even in 5th gear the ratio from engine to wheel is 3.7:1. Consider that if the car had a real engine to wheel ratio of 1:1, at 8000 RPM that would be (8000 R/min * 78 in/rev / 12 in/ft / 5280 ft/mile * 60 mins/hr) = 590MPH.

Even in 5th gear, there is significant mechanical advantage.

This explanation does not account for the 1:1 suggestion.

Quote:
Originally Posted by Airboy View Post
Force goes up but the angular speed of the drum, which is part of the power calculation, goes down in lower gears.
If you make a run in 1st gear, it will accelerate to a lower speed, but in less time. If you run in a higher gear, it will accelerate to a higher speed, but in more time. While the raw torque at the rollers will change, the fundemental power output will not change (ignoring efficiency loss).

Either I am missing something here, or this 1:1 is bogus.

Jeff Sponaugle
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Old 03-24-2008, 06:58 PM   #11
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Quote:
Originally Posted by modaddict View Post
Jeff, you'll notice that my comments were made on a thread that had a car dyno'd on a dynapak

Also, flycaster, Ozer (a customer of yours, PDXtuning), and I had some conversations about why all 3 of us had perrin 30r kits, and Ozer's PDXtuning dyno "numbers" were signficantly higher than even flycasters 'built block'. (mine is stock). It raised some questions, we had good dialog and *I* deemed it to be the fact that whoever tuned Ozer's car at PDX, dyno'd it in 4th gear, and flycaster and I had dyno'd in 5th. I was tuned by Jarrad, flycaster by Tim, and Ozer ???

By Tim the mustang dyno guy's explaination on a dynojet if you put it in 2nd or 3rd you can get a different tq/hp calculation....resulting in higher numbers.

Can anyone say 500+whp out of an fp green on pump gas?
I follow you, and I remember those tunes. While we had the Dynapak (which is now at Perrin's shop), I spent some time playing around. I generally found that 5th gear pulls resulted in less peak hp then the 4th gear pulls, however (only on low powered cars), the 3rd gear pulls were less then 4th.

The Dynapak uses a very strange method of controlling pull rate, and it is very unnatural. It biases the load to maintain a fixed rate of acceleration. The harder the car pushed, the harder it pushed back. The causes some very strange and interesting behavior. The Mustang has a more elegant method that is based on weight and drag.

Neither of these ideas explain the 'mechanical advantage' referenced above. The car ALWAYS has mechanical advantage. Even in a 1:1 main gear, the rear diff is a 3.9:1. Mechanical advantage does not change hp, only torque. By all account if you have a gear box that can change output power with 'mechanical advantage', patent it. Quickly.

Jeff
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Old 03-24-2008, 07:12 PM   #12
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I think that this 1:1 deal is interesting.

when you have a trans that's rwd and say 4th gear is 1:1 (truely) the power goes straight from the inputshaft to the output shaft and theoretically less drivetrain loss. If you break an individual drivetrain component down, you have a percentage of how efficient that component is.

for example, I was told in college, a ford 9" rear end (very very common all over) is only about 90% efficient. (my instructor at Ford, was a Huge Ford racing guru. I wish I knew half of what he has forgotten)

Do we know what the sti trans is in efficiency if you were to rate it like that? I don't even know how they came up with the number, or what they compared it to.

I believe this is one reason Crawford does the 20% calculation from whp to HP. Their stock sti dyno's at 250whp in 5th gear. Is the 20% loss is the same throughout how much power you make...weather it be 300whp, or 600whp? I'll leave that up to your own opinion. Is it really right or wrong? It doesn't matter to me, I have my whp dyno charts...that's what I wanted. Some people want to know how much HP they make. Afterall, it's just us forum nuts who say that. the average joe doesn't know whp from hp.
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Old 03-24-2008, 07:15 PM   #13
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Quote:
Originally Posted by sponaugle View Post

Quote:
Originally Posted by Airboy View Post
Force goes up but the angular speed of the drum, which is part of the power calculation, goes down in lower gears.
If you make a run in 1st gear, it will accelerate to a lower speed, but in less time. If you run in a higher gear, it will accelerate to a higher speed, but in more time. While the raw torque at the rollers will change, the fundemental power output will not change (ignoring efficiency loss).

Jeff Sponaugle
That's what I was getting at, in my reply to SloRice
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Old 03-24-2008, 07:38 PM   #14
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Quote:
Originally Posted by sponaugle View Post
I don't follow how being at 1:1 or not makes any difference. The calculated HP, which is derived from the rate of acceleration, must always take into account the gearing.

Are you suggesting that a car that has a .971:1 gear vs a .890:1 gear will always ready a lower power even though it makes the same power. I find it very hard to believe the dyno could not take that into account.
That's exactly what I'm saying!! Have you ever entered the gear ratio into the Dynojet software?? They do not take gear ratio into account.

Gears less than 1:1 on a Dynojet = lower power
Gears higher than 1:1 on a Dynojet = higher power


Load cell style dynos don't care about the gear. I've dynoed my car in 2nd, 3rd, 4th and 5th gear on a Mustang Dyno....all within 10whp.
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Old 03-24-2008, 08:05 PM   #15
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Quote:
Originally Posted by sponaugle View Post
...The Dynapak uses a very strange method of controlling pull rate, and it is very unnatural. It biases the load to maintain a fixed rate of acceleration. The harder the car pushed, the harder it pushed back. The causes some very strange and interesting behavior. The Mustang has a more elegant method that is based on weight and drag.
Jeff
I thought I would add a bit to the discussion here...

The dynapak dyno controls the rate of acceleration, trying to act like an engine dyno does... Engine dyno's are usually set at a fixed rpm increase of 300 rpm a second...

Roller dyno's use the acceleration rate/force applied to a drum...

There are many debates on which way is the "best way" to "tune" a car...

The best answer is "neither of them"....

Now ask yourself "why"................

The reason is that the engine will probably never see either acceleration rate in the real world...

What many people tend to forget, is that the acceleration rate of an engine has a direct effect on the timing of the waves in the intake and the exhaust system...

The best way to tune something is, at the rate of acceleration it sees the most, or the rate it can take advantage of most...

High level road racing cars are tuned differently at different tracks, to take advantage of this very fact...

Go watch this video of Renault doing exactly what I am talking about...
They are tuning/testing it for a specific track... Renault 3.0L V10
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Old 03-24-2008, 08:13 PM   #16
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Maybe Mythbusters can do a special on this!
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Old 03-24-2008, 08:13 PM   #17
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Thanks jeff for using my quote

I made that comment as ive had real life experience for differences of gear selection on a dyno dynamics dyno in australia (ill try find the dyno graphs).

On a dyno day that we had a few yrs back my fpgreen 2.0ltr sti made 252 kw atw in 4th gear and 235 kw atw in 5th gear..

The same sort of discrepencies have been shown from other ppl dynoing stis in 4th rather than 5th. And visa versa for wrxs that have a 5-speed. This is the only experience ive got to base my opinon as i dont know the theories behind how a dyno works..

Imagine a car with a large turbo like a 40R the variation would be much greater and u could see 30-50 kw atw difference just by changing gears. When the car is completely sorted i will put it on the dyno dynamics dyno and show u the differences that it produces..

Last edited by tino; 03-24-2008 at 08:28 PM.
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Old 03-24-2008, 09:03 PM   #18
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Quote:
Originally Posted by SloRice View Post
That's exactly what I'm saying!! Have you ever entered the gear ratio into the Dynojet software?? They do not take gear ratio into account.
Gears less than 1:1 on a Dynojet = lower power
Gears higher than 1:1 on a Dynojet = higher power
Load cell style dynos don't care about the gear. I've dynoed my car in 2nd, 3rd, 4th and 5th gear on a Mustang Dyno....all within 10whp.
The dynojet does not need the gear ratio to determine power because the gear ratio does not directly change the output power (there are some indirect changes). The dynojet can estimate the power because power is a measurement of work over time. The engines power output DOES NOT change directly as a result of gearing. If you change the rear diff in your car, does the power of the engine change? No. (again ignoring some interesting side effects).

A properly calibrated non loading dyno should be able to show the same power out (Assuming the engine in fact has the same power output) regardless of gear.

Also: What about my comment about the 3.9:1 rear diff? As I mentioned, no car has a 1:1 ratio for engine to wheels. There is nothing special about 1:1 in a manual gear box, especially when compared to .89:1 or 1.1:1. I am more convinced then ever that the origin of the 1:1 is due to the way an automatic transmission works.

Quote:
Originally Posted by modaddict View Post
I think that this 1:1 deal is interesting.

when you have a trans that's rwd and say 4th gear is 1:1 (truely) the power goes straight from the inputshaft to the output shaft and theoretically less drivetrain loss. If you break an individual drivetrain component down, you have a percentage of how efficient that component is.

for example, I was told in college, a ford 9" rear end (very very common all over) is only about 90% efficient. (my instructor at Ford, was a Huge Ford racing guru. I wish I knew half of what he has forgotten)

Do we know what the sti trans is in efficiency if you were to rate it like that? I don't even know how they came up with the number, or what they compared it to.

I believe this is one reason Crawford does the 20% calculation from whp to HP. Their stock sti dyno's at 250whp in 5th gear. Is the 20% loss is the same throughout how much power you make...weather it be 300whp, or 600whp? I'll leave that up to your own opinion. Is it really right or wrong? It doesn't matter to me, I have my whp dyno charts...that's what I wanted. Some people want to know how much HP they make. Afterall, it's just us forum nuts who say that. the average joe doesn't know whp from hp.
As far as I can tell, the efficiency (power loss) in a 2 gear helical setup does not change when going from .65:1 to 1:1. The fact that there is no reduction has no impact on the power efficiency. As mentioned above, the car still has a rear diff with a 3.9:1 ratio. The output efficiency of this rear diff my infact be 90%, but that is a constant 90% loss, regardless of the ratio.

My comments are not related to the driveline loss as an absolute…. But as it related to the gear selection. Interesting.

Quote:
Originally Posted by shvrdavid View Post
I thought I would add a bit to the discussion here...
The dynapak dyno controls the rate of acceleration, trying to act like an engine dyno does... Engine dyno's are usually set at a fixed rpm increase of 300 rpm a second...
Roller dyno's use the acceleration rate/force applied to a drum...

There are many debates on which way is the "best way" to "tune" a car...
The best answer is "neither of them"....
Now ask yourself "why"................
The reason is that the engine will probably never see either acceleration rate in the real world...
What many people tend to forget, is that the acceleration rate of an engine has a direct effect on the timing of the waves in the intake and the exhaust system...
The best way to tune something is, at the rate of acceleration it sees the most, or the rate it can take advantage of most...
High level road racing cars are tuned differently at different tracks, to take advantage of this very fact...
A couple of corrections:

(1) The Mustang dyno can do all three varieties of loading. It can do a controller ramp (just like the dynapak), it can do an open loop acceleration (like the dynojet), and it can do a ‘road simulation’ which more correctly simulates the load you see on the road. This road simulation is exactly what you describe, and is why I prefer the Mustang dyno over the others.

(2) As you indicate, the best way to tune is the ‘simulation mode’. Indeed the Mustang does this, and does it well. In fact you can even program in different test loops to simulate a road course.


Agreed that the rate of acceleration does in fact have an indirect effect on the power output as a secondary feedback. Changes in load can make certain conditions (timing, fueling, etc) sustainable that might otherwise not be.

Jeff Sponaugle
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Old 03-24-2008, 09:13 PM   #19
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^^^^ Jeff but arent most dyno runs done in "shootout" like mode so maybe it dosent take into account such variables??

I know that any power run is always done in this mode in australia..
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Old 03-24-2008, 09:16 PM   #20
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Sort of related...RPM vs Time data that I collected for the Dynapak, Mustang, and the road.
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Old 03-24-2008, 09:37 PM   #21
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Quote:
Originally Posted by sponaugle
...
...The Mustang dyno can do all three varieties of loading. It can do a controller ramp (just like the dynapak), it can do an open loop acceleration (like the dynojet), and it can do a ‘road simulation’ which more correctly simulates the load you see on the road...
I did not know that the Mustang could do all 3 types of loading...
Goes to show that you learn something new every day...
I'll be looking for a Mustang when I tune mine..........
Quote:
Originally Posted by sponaugle
...Agreed that the rate of acceleration does in fact have an indirect effect on the power output as a secondary feedback. Changes in load can make certain conditions (timing, fueling, etc) sustainable that might otherwise not be.

Jeff Sponaugle
At high rpm like in F1, it has a huge impact...
I'll let everyone in on a little known secret, on how they get around it...
F1 engines have 2 injectors per runner, one of them is close to the valves, and the other is well above the runner opening...
Now, can you guess why.... It has to do with a fuel delta load offset, but it is different than the normal delta we think of...
The engine doesn't need 2 injectors per runner to run, one of them will supply all of the fuel it needs to run... But not optimally...
The fuel delta offset on that type of setup is used to alter the effective length of the runner, you can see it change in the halo height of gas, in the open plenium...
The fuel delta offset in F1 modifies which injector (upper or lower) is injecting the most fuel to modify the speed of sound within the runner, making more effective use of the orders in the intake runner...

This technique can be used in any setup that has 2 injectors per runner, if they are mounted at different ends of the runner...
Food for thought...........
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Old 03-24-2008, 09:46 PM   #22
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Quote:
Originally Posted by tino View Post
^^^^ Jeff but arent most dyno runs done in "shootout" like mode so maybe it dosent take into account such variables??

I know that any power run is always done in this mode in australia..
A shootout mode typically means no corrections, or corrections of some fixed kind. With or without such a mode, the dyno should be able to read power the same regardless of gear.

Of course the dyno can only read what is there. If the dynojet loading (or lack there of) causes a change in power output, the reading should be different if it is accurate.


Quote:
Originally Posted by Airboy View Post
Sort of related...RPM vs Time data that I collected for the Dynapak, Mustang, and the road.
Very cool! That shows the simulation mode working pretty darn well. I assume you used the correct weight and hp@50?

Quote:
Originally Posted by shvrdavid View Post
I did not know that the Mustang could do all 3 types of loading...
Goes to show that you learn something new every day...
I'll be looking for a Mustang when I tune mine..........
Yea, it works great.

As for the F1., that is indeed very interesting. I'll have to think about that for a bit.
Jeff
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Old 03-24-2008, 10:00 PM   #23
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Quote:
Originally Posted by sponaugle View Post
Very cool! That shows the simulation mode working pretty darn well. I assume you used the correct weight and hp@50?

Jeff
I didn't operate the dyno, I was just data logging with my laptop during a dyno day. The dyno operator selected the car from a list, if that means anything. It didn't to me, at the time. I didn't know the Mustang had different loading "profiles".
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Old 03-24-2008, 10:03 PM   #24
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Jeff,

I'm really glad you posted this up. Every time I see someone mention 1:1 I cringe and roll my eyes a bit. I never really posted about it because I imagined exactly this kind of confused discussion would result.

Anyway, the main issue here is that in order to properly measure/estimate power, any dyno needs to look at the rate of acceleration of the wheels (or hubs), the force being overcome by the wheels, and finally a clean engine RPM reading. The RPM reading is what most people seem to be missing in their assumptions. As long as the dyno knows the wheel speed AND the engine RPM, it can calculate the gearing that got it there. Now as long as these values are recorded properly, the dyno should not show any significant power differences between gears (aside from external factors). Just because in 2nd gear, the torque actually applied to the wheels is greater than in 3rd or 4th gear, doesn't mean the dyno will read higher. It simply looks at the wheel speed versus engine RPM, calculates the correct gearing and displays the correct power output.

Now that being said, I've seen many dyno operators who do not use any sort of direct RPM pickup and instead set up a locked wheel speed to RPM ratio from a single sample (say 3000 RPM at 25miles in 3rd gear). This is very common practice and it does pose some potential problems. The main one is that as wheel speed increases, tire deflection varies and will actually throw off the locked in ratio. There is really no way around this without a direct RPM signal. Note that Dynapaks shouldn't have this issue since there are no tires used .

I'll note a couple findings from my heavy use of road dyno software. I've actually found that all things being equal, most cars will actually read slightly higher numbers in higher gears on my road dyno software. Note that this is assuming that there is no additional heat soak, the same timing, boost, and fuel curve throughout the pull in either gear. After thinking this over and discussing with a couple mechanical engineering friends, there is a very simple explanation. During a pull in a higher gear, the mechanical gears in the transmission and diff are actually being accelerated at a slower rate. The slower rate of acceleration of the mass of the gears actually results in less inertial loss than it would in a lower gear and faster rate of acceleration. So technically you have the most parasitic losses in 1st gear, and the least in 6th gear .

To conclude, I believe that most of the time when people claim lower numbers in higher gears, this is due to other factors such as lack of airflow for a longer sustained pull resulting in heat soak, pulled timing, etc. Its just been greatly confused and too many people have concluded this false statement that IN GENERAL higher gears produce lower numbers.



BTW, I absolutely hate the way Dynapaks and DynoDynamics dyno's load up the car. They try to maintain a constant rate of acceleration throughout the entire pull and this really holds no merit in the real world. On a real road, more torque means faster acceleration, less torque means slower acceleration. This is an oversimplification of course since you must account for weight, aerodynmic drag, and vehicle inertia, but the Mustang dyno does come the closest to a real world load curve. I find the grossly simplified load curves applied by the other two dynos to be nearly useless for accurate tuning for real world applications.

Thanks
-- Ed
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Old 03-24-2008, 10:38 PM   #25
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I have no real technical contribution to this thread, but i thought the general rule of thumb was that 5 speeds (dyno in 3rd gear) and 6 speed (dyno in 4th gear). Is this correct?
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