Proposed Rule Change - Dyno Allowance as a Percentage

[ianacole]

Propsed rule/change: Change the wording of the dyno allowance from a static number (4) to a percentage (4%)

Background: Dyno variance can be quite significant, this change would for variable differences based on the HP of the car.

Status: Open for debate

[ianacole]

Is a percentage approach to allowance fair/reasonable? For a 100HP car, this allows for +/- 4HP...for a 500HP car this allows for +/-20HP. I don't know how dynos work in this manner...the greater the HP the greater the amount of variance potential from machine to machine or region to region?

[Enzo]

Where do we submit proposed rule changes?

[ianacole]

Ah...great question. You can PM me, or start a thread (a la the Grand-Am slick rule debate).

[RSCoupe]

I vote for a percentage rule. 4hp is barely over 1% for me.

[cosm3os]

I have no idea about this other than I know dyno's can vary on a given dyno/day etc. How about a % per hp (eg. 1% per 100 hp) or what about different percentages for the different classes commensurate to the kind of hp each class makes?

 

I agree 4hp is too small. It would be nice not to have to account for significant error in BOTH classification criteria (I have to keep an extra 60 lbs in case the scales are off and x lbs in case the dyno is off and xx lbs in case both are off!).

[Brad Waite]

I think we have to be careful here and really understand what we are doing before changing the exception. 4 HP is not really that small. In most GTS2 cars that would amount to nearly a 2% variance. I think we need to understand the dynamics behind this decision including whether there is a linear relationship to variance as Hp increases. Let's not take this one lightly without the correct research.

 

Brad

[maxxfish]

A percentage is much more fair than a hard HP number. But of course now drivers that are right on the power-to-weight bubble can fudge their HP numbers down by a few HP so that they can run lighter. It just becomes a numbers game, but if they're dynoe'd at the track, they have to be within tolerance, and the're now NO excuse of dyno/weather/BS variables.

[dillehayd]

Has anyone asked Dynojet? I just fired off an email to their tech support. I included a link to this thread but if I get an email reply I'll post it up here.

[Eric W.]

I think we have to be careful here and really understand what we are doing before changing the exception. 4 HP is not really that small. In most GTS2 cars that would amount to nearly a 2% variance. I think we need to understand the dynamics behind this decision including whether there is a linear relationship to variance as Hp increases. Let's not take this one lightly without the correct research.

 

Brad

 

Ok, maybe a % isnt as good an idea. Maybe a # depending on class? All I know is... before a MidO event, I dyno'd locally at 251rwhp. I goto MidOhio and I get 263rwhp. Then I come home and redyno and got 256rwhp. Then goto another dyno and read 253rwhp. A couple events later at Summit Point, I get 264rwhp. And then at another Summit event, I get 266rwhp.

 

That was with NO changes to the car at all. I saw a 12rwhp swing depending on dyno. If I had prepped even within 4rwhp or hell, even to be safe 8rwhp, I still would have been DQd. One could prep their car to be legal, but on any given day and on any given dyno, you could see a swing of anywhere up to or over 15rwhp (or 165lbs for GTS3)! That's just crazy!

 

Then, lets not even get into scale variance. For this last NJMP event, I put my metal trunk/hood back on and somehow I weighed in less than when I had the light CF parts in!

 

And THEN... what are the rules regarding impound dyno? At NJMP I was told if impounded, we had to PAY for our dyno?? Somehow I find that to be not right.

[Enzo]

Ian, thanks for starting the rules change threads and listening to our feedback - good discussion here.

 

I agree with Brad on this one. We need to be real careful on this. I think percent is a good way of doing it, but 4% seems too much to me. If our allowable hp cushion suddenly doubles inevitably people are going to come to depend on that, and possibly use it as a competitive advantage as opposed to an "allowance". Every time I've dynoed my car its been within 2hp, even on different machines. (Maybe I've just been lucky on this, not sure...)

 

I'm guessing Dynojet states its accuracy in %, which also would support using percent instead of a fixed number (however I havent been able to confirm that so dont quote me on that).

 

If we're doing % I'd vote for 2-3%, make it 5hp across the board, or just leave the rules alone. You have to draw the line somewhere...

 

How many people have been DQ'ed because their post-race dyno numbers have been more than 4hp over? Just wondering - how big of a problem are we talking here?

 

Eric -as far as your dyno numbers, sounds like your local dyno is off. All the numbers you reported at NASA events were within 3hp... those are the numbers I would use...

 

 

 

Thanks,

[Eric W.]

Enzo, that's what I thought too. So I brought it to a different one and got the 256 number. Still quite a bit off from 262-266.

[Enzo]

I didnt realize that Eric. I havent run into that yet so I'm guess I dont have a good feel for how much variability really exists between dynomometers. Sounds like you have some experience with this and I can understand your frustration.

 

Anyhow, I guess the only dyno that really matters is the one at the track so I would use those numbers otherwise you will just increase the risk of DQ'ing yourself (unfortunately).

 

I'm still for percent, so cars with more HP get more variance. I just think 4% might be a little high...

[dillehayd]

Well, the time required to get a response from Dynojet wasn't much. I recieved the following:

 

Hello Dave,

 

 

 

I have talked to a number of guys in NASA, American Iron Series and other various forms of Spec class racing over the years about this same question and it is a very valid question when trying to make sure the playing field is as level as possible. One of the best things about using Dynojet dynamometers is the fact that they are not only repeatable but extremely consistent from one dyno to the next. Because of our manufacturing techniques and minimum amount of mathematical variables, Dynojet dynamometers will typically be within ½ hp of each other which is an industry standard. Almost always, the noted “difference” between one dyno and the next isn’t the dyno, but a host of other factors that must be carefully noted when comparability is paramount. We need to look at the correction factor with each dyno run and make sure it is similar to other runs we are comparing to. Also, we must look at the single largest factor as far as repeatability goes which is….THE CAR. Does power fall off as it gets hotter? Is the cooling system adequate? Are the runs being done in the same manner each time? Have there been gearing changes? All of these things can and will affect your numbers yet sometimes they go on forgotten.

 

I could literally go on for pages going over all the possibilities etc. however I will attach a document for you that explains it much better. Feel free to check it out and share with other racers and let us know if you still have any questions.

 

 

 

Thanks,

 

 

 

Christopher Olson

 

Dynojet Research Inc.

 

 

I uploaded the document he attached. Please right click, save as: http://fmjmotorsports.com/link/Truth_Lies_Dyno%20Runs_Final.pdf

[dillehayd]

Enzo, that's what I thought too. So I brought it to a different one and got the 256 number. Still quite a bit off from 262-266.

 

Using the same type of tires for each dyno? Not picking, just asking because I've seen tires smoke on dyno drums before.

[Eric W.]

Enzo, that's what I thought too. So I brought it to a different one and got the 256 number. Still quite a bit off from 262-266.

 

Using the same type of tires for each dyno? Not picking, just asking because I've seen tires smoke on dyno drums before.

 

Dont remember... but you bring up another good point. Tire pressures also play a fairly important role.

 

Ive learned not to trust my dyno sheet. If it is a big event like nationals, Ill either carry extra weight or get dyno'd that weekend.

[scottbm3]

Some may not understand how it actually works. First you must meet your minimum weight at scales. Then you go to the dyno. Let say you dyno 10hp over your declared hp. You then deduct the 4hp from the 10 and your actual weight must be legal for the extra 6hp. In the rules it suggests that you don't run your car to the exact minimums just in case this happens. I'm for whatever seems fair, but as Enzo said, you'll have guys that start to rely on the allowance as a performance edge.

 

Only once in 4 years has my car not dyno'd within a few hp of my previous runs on different Dynojet dyno's. Then it was 9hp before the 4hp allowance and I was still over in weight.

 

 

-Scott B.

[Enzo]

Dynojet also brings up a good point about test conditions. Temperature, humidity, and barometric pressure will all have an effect on the results. I think there is a rule of thumb on temp - something like 1hp loss for every 10 degrees increase in ambient temp. These things are not the dynos fault, but definetely will affect the numbers... Unfortunately, these variables are something that we can not easily control...

[ianacole]

Dynojet also brings up a good point about test conditions. Temperature, humidity, and barometric pressure will all have an effect on the results.

 

Isn't that what the correction factor supposed to account for, to include altitude?

[Enzo]

Dynojet also brings up a good point about test conditions. Temperature, humidity, and barometric pressure will all have an effect on the results.

 

Isn't that what the correction factor supposed to account for, to include altitude?

 

Yes, thanks for correcting me. After looking into it I see that the SAE correction factor is used to compensate for differences in ambient test conditions so that dyno runs can be compared directly even if the ambient test conditions were not the same.

 

Our Dynojet’s software will use this formula to accurately display the horsepower and torque of dyno runs made on different days (regardless of weather conditions). These corrected horsepower and torque numbers are referred to as “SAE” and allow you to compare runs of similar vehicles tested on other Dynojet dynamometers across the country.

[dillehayd]

As a tangent to this discussion: Was the dyno available to racers prior to the first on-track session? If it were, that would help us all ensure our own compliance. I'd be willing to cough up $75 bucks for a couple pulls on Friday night just to make sure I wasn't going to have a problem on Saturday morning. The idea is to prove compliance, not play gotcha, right? Just a thought.

[scottbm3]

As a tangent to this discussion: Was the dyno available to racers prior to the first on-track session? If it were, that would help us all ensure our own compliance. I'd be willing to cough up $75 bucks for a couple pulls on Friday night just to make sure I wasn't going to have a problem on Saturday morning. The idea is to prove compliance, not play gotcha, right? Just a thought.

 

 

In the Great Lakes region, when the dyno was present, it was usually available before hand so you could check your numbers before your first official timed session. It was usually $85.00 for three pulls. Heck after qualifying one weekend at Mid-Ohio, Sean Tillinghast(pole) paid to re-check his numbers after a motor swap and was over the limit. He DQ'd himself and added weight to be legal and started at the back. Now that's pretty stand up and what the series is all about.

 

-Scott B.

[Michael G.]

Eric, I am surprised to hear, that you were told to pay for the dyno at the impound at NJMP. Next time let me know please - I agree - that is not right. Regarding difference in scales - that is not the first time I came across the difference on different scales. The last time it was at Nationals, where my car became lighter, even though I have my own Longacre scales at home and know what the real weight is. Michael G.

[dillehayd]

My car was on 4 different sets of scales last year and the weight varied by ~40lbs between them. Fuel was some of that variation, but not all of it. If I can't get on the scales on Friday night, I have to run a little extra weight until I do get on the scales. I've seen this happen in other series as well.

[dillehayd]

As a tangent to this discussion: Was the dyno available to racers prior to the first on-track session? If it were, that would help us all ensure our own compliance. I'd be willing to cough up $75 bucks for a couple pulls on Friday night just to make sure I wasn't going to have a problem on Saturday morning. The idea is to prove compliance, not play gotcha, right? Just a thought.

 

 

In the Great Lakes region, when the dyno was present, it was usually available before hand so you could check your numbers before your first official timed session. It was usually $85.00 for three pulls. Heck after qualifying one weekend at Mid-Ohio, Sean Tillinghast(pole) paid to re-check his numbers after a motor swap and was over the limit. He DQ'd himself and added weight to be legal and started at the back. Now that's pretty stand up and what the series is all about.

 

-Scott B.

 

It's probably not something that could be required, but having the trackside dyno available for people to check their cars certainly seems like a desirable policy.

 

Considering the feedback from Dynojet, and taking it with a healthy grain of salt, it looks to me like the 4hp allowance is a reasonable number. We need to pay attention to details setting up for the dyno like we do setting up for a race. If we do, we'll find less variability and fewer surprises. We also need to try to make sure we use competent dyno operators who take good care of their equipment both at home and at the track since small variations in the mass of the dynojet drum can have adverse effects on the numbers.

 

Some racers are always going to push their cars to the edge of legality regardless of where the edge is. The larger the allowance is, the greater the advantage of pushing to the edge which will simply encourage people to do it. Given such a simple rule set I think it's appropriate to keep the tightest reasonable tolerances on those rules we do have.

 

I don't know Sean personally, but do respect him. If I remember correctly, he had a tech issue w/ BMWCCA that he could easily have hidden but freely admitted instead. He seems to be a stand up guy.