2005 rules - Dyno Variability

[mwilson7]

Jim,

 

Let me throw this out there to see how you would deal with this.

 

I dyno my car Saturday morning before the race and come up with 315 hp. I add/remove ballast so that I have a 50lbs cushion. I change nothing that would affect hp or tq. After the race I am dynoed and come in at 321 and am disqualified for being 1 hp over. What have I done wrong? So the next day I add another another 10 lbs to compensate for the extra 1 hp I gained the day before. I get dynoed again and come in at 305 hp so now I'm 152 lbs over weight. Definitely an amount that would affect my performance that day.

 

You keep saying that this is all for fun which I agree with but what is the fun of trying to do the right thing and then being DQ'ed because of dyno variation?

 

Asking everyone to carry around an extra 75lbs is EXACTLY the same thing as adding a fudge factor in the 9.5:1 number. The difference is that you are asking people to carry the weight instead of allowing them the hp.

 

P.S. I like that the GTS guys at least acknowledge that this happens and are trying to address it.

Edited September 21, 2004 by Guest

[Jim P.]

Jim, the last time I had my car tuned it varied as much as 8 RWHP. 8rwhp=76lbs, see why the question has come up.

 

You were still under the 9.5:1 limit weren't you?

That wasn't so hard to do...was it?

 

 

 

 

Posted as the SE Regional Fun Director and a Racer who is having fun at NASA Events

[Jim P.]

Jim,

 

Let me throw this out there to see how you would deal with this.

 

I dyno my car Saturday morning before the race and come up with 315 hp. I add/remove ballast so that I have a 50lbs cushion. I change nothing that would affect hp or tq. After the race I am dynoed and come in at 321 and am disqualified for being 1 hp over. What have I done wrong? So the next day I add another another 10 lbs to compensate for the extra 1 hp I gained the day before. I get dynoed again and come in at 305 hp so now I'm 152 lbs over weight. Definitely an amount that would affect my performance that day.

 

You keep saying that this is all for fun which I agree with but what is the fun of trying to do the right thing and then being DQ'ed because of dyno variation?

 

Asking everyone to carry around an extra 75lbs is EXACTLY the same thing as adding a fudge factor in the 9.5:1 number. The difference is that you are asking people to carry the weight instead of allowing them the hp.

 

A) You did nothing to reduce the HP of that car Saturday nite

B) You did you do too much to reduce the HP of that car Saturday nite

C) You went out drinking Saturday nite

D) All of the above

 

 

I think what most of us are saying is that anyone that is that close to the 9.5:1 ratio risks being DQ'd. If you don't want to be DQ'd then reduce your margin for variability - or run AI/X. Either way you'll have fun racing with the same group of great racers.

 

 

Posted as Fun Director and a Fun Racer - who's caught in the middle because he likes to race

[mwilson7]

Why should we even being concerned about being over hp? If it's just for fun who cares where the dyno numbers come out then!

 

Apparently you don't think this is an issue Jim but some of us in AI do. We can all put our hands around weight very easy as it is an absolute. If HP was an absolute I wouldn't have any problem but it's not so we have to look at ways to address it.

 

The way I see it we can do one of two things:

 

1. Ignore it (reduces fun and increases stress)

2. Address is (maintains or increases fun and reduces stress)

 

Which one do you prefer?

 

P.S. Jim - I wouldn't recommend implying that people are cheating even if it is a joke. That's a good way to really p1ss people off.

[Jim P.]

P.S. Jim - I wouldn't recommend implying that people are cheating even if it is a joke. That's a good way to really p1ss people off.

 

Mark,

I apologize if you took that the wrong way - I wasn't implying that you were cheating - if I was in your shoes and my car was over the limit I would do whatever was necessary to get it under the limit - even if it meant that I didn't go out drinking saturday nite!

 

The fact that your car had vastly different #'s between Saturday and Sunday led me to believe that maybe, just maybe, you and/or Brian adjusted something to make sure you weren't over on Sunday. Am I correct in assuming that? If you truly did nothing to the car between Saturday and Sunday then I deeply apologize for my assumptions.

 

 

 

As a footnote - I am going to run a CMC prepped car this weekend in AIX - just because I am racing purely for the fun of it.

[Guest]

P.S. Jim - I wouldn't recommend implying that people are cheating even if it is a joke. That's a good way to really p1ss people off.

 

Mark,

I apologize if you took that the wrong way - I wasn't implying that you were cheating - if I was in your shoes and my car was over the limit I would do whatever was necessary to get it under the limit - even if it meant that I didn't go out drinking saturday nite!

 

The fact that your car had vastly different #'s between Saturday and Sunday led me to believe that maybe, just maybe, you and/or Brian adjusted something to make sure you weren't over on Sunday. Am I correct in assuming that? If you truly did nothing to the car between Saturday and Sunday then I deeply apologize for my assumptions.

 

 

 

As a footnote - I am going to run a CMC prepped car this weekend in AIX - just because I am racing purely for the fun of it.

 

The car had ZERO changes, not even additional fuel. it rolled off the dyno on saturday night or sunday morning. We qualified the car on Sunday morning the exact way it was on sat night and when we dynoed after qualifying we discovered the 'lost' hp.

 

For the record we were not over on Saturday night. We were not weighed (scales non functional) so there was no way to determine the HP:WT ratio. When the scales were functional for a short period of time on sunday before qualifying it showed that even at the escelated power level we had on Sat we were legal based on the weight of the car after the race on saturday.

 

Jim- we all understand that this racing thing is fun. Some of us have more 'fun' when we win. The point of a race is to win. If I were out there to just have 'fun' i would be running HPDE 4 and not actually racing. I understand that some people are entered in the races just for fun while others are in it to win. You as a regional director seem to forget that it's okay for the racers to actually want to WIN. We don't want to simply lap around the track we want to race for an actual victory against competition. This is the reason that the issues being discussed in this and all the rules threads are so important the folks that actually want to race to win.

 

You keep repeating yourself about just having fun, but you are not out there making a serious attempt to win a championship or to race for an AI victory. Your mindset is different. You want to have a good time, I want to have a good time by winning.

 

This idea may seem foreign to you but getting barraged by your reminders of 'fun' is getting out of hand. I am not the only one that is on the track to win, there are plenty of others with my same feelings.

 

Do you understand?

[trackboss]

Nick brings up some good points. However I don’t agree with not allowing changes from race to race or even day to day. In particular, carbureted cars. As he mentioned, the variability is mostly in the motor itself as well as the environment, not the dyno. On a mass air meter equipped car that is not radically altered it can probably compensate for these types of things, but a carburetor cannot. It is not fair to restrict such a motor to only using one particular tune as far as jets and such. For example, not being allowed to do so can actually damage a motor if it has to run jetting that is too lean for that particular day. That would drive up costs even more and really piss off competitors. I also don’t agree with the average power numbers over 3 different water temp ranges. I would prefer a single temp that everyone can reasonably use such as 200. Otherwise there are too many combinations.

[gbrown8439]

My car was on the dyno 3 times at BR. Other than problems with the car running right on Sat. we got very repeatable numbers the other two sessions. I'm not sure who you talked to at Dynojet but we were told that there is a 2% error factor in there dyno.

As far as using uncorected numbers let me ask this. Lets say you get to the track friday afternoon and its hot. You pay for a run just to make sure you are legal. A big storm rolls thru that night and it cools off. You get put on the dyno in the morning after qualifing and its 20 degrees cooler than it was friday. You are going to get a much bigger variable in hp from the temp change than you would if you were using corrected numbers.

I think we must use the correction factors and we all live with the same variatons in the dyno.

 

Greg Brown

OH/IN AI #7

[mwilson7]

P.S. Jim - I wouldn't recommend implying that people are cheating even if it is a joke. That's a good way to really p1ss people off.

 

Mark,

I apologize if you took that the wrong way - I wasn't implying that you were cheating - if I was in your shoes and my car was over the limit I would do whatever was necessary to get it under the limit - even if it meant that I didn't go out drinking saturday nite!

 

The fact that your car had vastly different #'s between Saturday and Sunday led me to believe that maybe, just maybe, you and/or Brian adjusted something to make sure you weren't over on Sunday. Am I correct in assuming that? If you truly did nothing to the car between Saturday and Sunday then I deeply apologize for my assumptions.

 

 

Jim,

 

Anyone would do anything to get under the limit but if it's after the race you get DQ'ed anyway so the point is moot.

 

If you read my post I stated that we didn't do anything that affected hp or tq. If we changed something then it wouldn't be a big deal because I could understand the variation and there is no discussion. Point is we did nothing but check the oil level and our CORRECTED hp changed by 11 hp.

 

Of the three cars dynoed both days two of them experienced the fluxuation from day to day. The Third (Greg B's car) experienced some running issues on the dyno and I believe that Greg's car had the spark plugs and ignition box changed between runs which may have affected his readings which could have compensated for the loss that Robin and we experienced. I could be wrong about that. It should also be noted that one car that experienced the variation was FI and the other carbed.

 

My point to all this is that there is variation in the dyno. If your feel the solution is to have everyone carry around an extra 75 lbs then you have effectively changed the hp to weight ratio. There needs to be a fair, viable solution that doesn't leave those of us running near the 9.5:1 number wondering if we are going to get DQ'ed because of something out of our control.

[Guest]

My car was on the dyno 3 times at BR. Other than problems with the car running right on Sat. we got very repeatable numbers the other two sessions. I'm not sure who you talked to at Dynojet but we were told that there is a 2% error factor in there dyno.

As far as using uncorected numbers let me ask this. Lets say you get to the track friday afternoon and its hot. You pay for a run just to make sure you are legal. A big storm rolls thru that night and it cools off. You get put on the dyno in the morning after qualifing and its 20 degrees cooler than it was friday. You are going to get a much bigger variable in hp from the temp change than you would if you were using corrected numbers.

I think we must use the correction factors and we all live with the same variatons in the dyno.

 

Greg Brown

OH/IN AI #7

 

My issue with correction factors is that the atmoshperic module plays a large role in determining the corrected value. Also that corrected number is supposed to be a consistent and repeatible number. I know that both Robin and mark/me lost hp from the corrected value on Sunday morning. That is my main concern. When we gain/lose phantom power it becomes very difficult to get the car to an acceptale weight. we lost 11hp, that is approx. 100lbs that can be dropped with fuel load, but if after the race the phantom hp returns we are up the creek.

 

That is my major concern. Also, that 10hp at our power level is approx. 3%.

[mwilson7]

After discussing dyno variability with a couple people I also wanted to add in a couple of other variables which should be considered and called out under the dyno rules:

 

1. A smoothing factor should be specified. Going from min to max smoothing can affect the peak hp and tq numbers by as much as 3%.

 

2. Correction factors should be paid attention to. If the correction factor is over 1.1 there is probably something wrong with the dyno's equipment.

 

3. Dynos do vary by as much as 2%. Next months Mustang Enthusiast has the results from having the same car visit 3 dyno's on the same day and the results are definitely interesting. They also visit the same dyno with the same car on different days with mixed results as well.

 

4. Current rules don't specify whether a correction factor needs to be used.

[Black Horse]

Spending some time looking at the exisiting rules I see where the Dynomometer Certification Rule 8.1 spells out that "Dynomometer tests must be conductedon a DynoJet Model 248 in a commercial facility...."

 

I could take this to mean that Dyno Tests performed at the track on a Mobile Dyno are not valid.

[mwilson7]

Has anyone ever read 17.8 of the CCR? Interesting.......

[RichardC]

Mark,

 

Right or wrong I read that as applying to the AI class minimum of 2800lbs not a weight derived from power output.

 

Richard.

[Keith]

To get back to the main topic, has anyone ever studied the variance between runs on a given DynoJet 248 on different days with the identical car? Has anyone every studied the variance from dyno to dyno on an identical car?

 

I will have a car near the limit next year and I would like to know what sort of safety I need to build in...

[mwilson7]

Yes Keith they have. There is a great article is the most current issue of Mustang Enthusiast where they do two things. They first dyno the same car on three different dynos on the same day with a variation of 10 hp on a roughly 300 hp motor.

 

Then they dyno the same car on the same dyno on different days and the difference is about 4 hp (I believe). It then goes into factors that could cause the dyno to vary and what not. It's a good article which would help out our cause.

 

I really don't think this whole dyno thing is an going to be an issue until more people start running close to the limit and reach the same frustration level that we have.

[Keith]

So a magazine did a test of three dynos. That's a good start. I am hoping for a larger sample size but this may be less practical than I originally thought.

 

I wonder if the manufacturer knows the variance that can occur and whether their marketing department will let that information out to the public? They obviously have to have a standardized testing procedure for preshipment v&v of dynos. This would be valuable data to obtain. Anyone here have any contacts at Dynojet?

 

10hp variance at 300hp is 3.3%. 4hp variance at 300hp is 1.3%

 

I am going CMC next year and the max hp for CMC is lower than than a stock LT1 will produce. I need to detune the motor (within the rules) to get lower than the max hp numbers for the series. I plan on targeting a "safe" hp number. I do not want to get DQ-ed... Ever. I *do* like the gray area in the CMC rules that will let you slide with more weight if you are a little over on power. It can work in CMC because the hp and weight are both hard limits, not ratios like AI has. My car will always be a pig as long as it remains street-legal.

[Jeff F]

Keith, the thing that we are missing when you talk about dyno variability is that it's not just the dyno itself, a lot of the variation is the car-- which is the car owners responsibility. Some cars are very repeatable while others aren't. I've seen AI cars being dyno'd where they were all over the map with no changes, and others are dead consistent.

 

In my case I did my dyno cert in Detroit about a month before the event. The car was fully warmed up, as it had been driven to the dyno and was put right on when I arrived. I ran a few different timing settings, and when I was done returned to the setting I wanted (which was run #2) and re-dyno'd. The final numbers (run #6, about 20 minutes later) were +1.8HP and +0.5TQ compared to run #2. Some of the difference might be that I didn't get the timing exactly back where it was, but still very close.

 

When I got to BeaveRun, I paid to have my car dyno'd on Saturday morning after practice, just to confirm my numbers from home. The only difference from home is that it had the race tires on it instead of street tires (245/45/17's on 17x8s) The car was warmed up from practice, but it had sat for a while (dyno'd at 10:40AM, practice ended at 9:30). I had three runs in a row, with a spread of 1.4HP (from -1.1 to -2.5 compared to home) and 2.2ft-lb (equal to -2.2 compared to home).

 

From my experience, I have confidence that I have a car that will dyno consistently and repeatably. Even so, I give myself a buffer of around 7 to be safe, which should have me more than covered.

 

I'd like to hear the results from other cars, especially you guys that are getting dyno'd on a regular basis.

[mwilson7]

Keith - Dynojet claims up to a 3% variation from dyno to dyno.

 

Jeff - If all of us had engines that were as repeatable as yours then we wouldn't have an issue, problem is that for whatever reason they aren't.

[Jeff F]

Jeff - If all of us had engines that were as repeatable as yours then we wouldn't have an issue, problem is that for whatever reason they aren't.

 

Well then, is that NASA's problem or your problem? If the engine you built varies by 15HP and mine varies by 5HP, then I get a 95lb advantage for building a better engine package.

[mwilson7]

Obviously Jeff you have either chosen to ignore the fact that Dynojet says they expect up to a 3% variation from dyno to dyno or you have decided that you are somehow immune. Obviously you don't feel you are immune because you stated above that you carry a 7 hp "reserve".

 

The biggest problem is that there is not a set procedure for dynoing the cars. They are put up on the dyno whenever and once they are strapped down they let them rip. No regard to engine or driveline temp.

 

Why don't you entertain me and explain how one builds an engine that varies from dyno run to dyno run.

[Jeff F]

I realize that the dyno procedures are far from ideal, but on the other hand I don't think that the problems you guys have had can all be blamed on the dyno. I've seen your car run on the dyno, and I've seen consecutive runs that had a lot of variance. On several ocassions I've had my car on a dyno for back-to-back runs, and every time they were all very close.

 

3% x 300ish = 9HP, which is about what I account for. If you guys were within 9HP from day-to-day and dyno-to-dyno I don't think you'd be as concerned as you are. I'm guessing you're way more than that.

 

I'm not the expert at building an engine that has a lot of variability, you are. But if I had to guess, first I'd spec out a bunch of parts (heads, intake, cam) that are way more than needed to make the power I need. Then I'd have it calibrated so that it never ran closed loop, which would keep it from adjusting the fuel trims based on the O2 sensors. Then I'd choke off the air filter in a way that makes the flow to the MAF so unpredictable that the transfer function is probably way off of what I think it is-- which would work great with my closed-loop only cal that was done without the tape on the filter. Seems like a good start.

[mwilson7]

Unfortunately Jeff I don't think we will agree on this. You are ok with a 9 hp variation? That's almost 90 lbs of weight which is definitely noticeable on the track. I'm not because I can feel the difference that 90 lbs makes to the performance of a vehicle.

 

What I find ironic is that the CCR allows for a variance in total vehicle weight because someone obviously understands there is variation from scale to scale or they are giving the benefit of the doubt. For some reason with the dyno (which Dynojet is very clear in stating there is variation from dyno to dyno and day to day) we don't seem to care.

[Keith]

Unfortunately Jeff I don't think we will agree on this. You are ok with a 9 hp variation? That's almost 90 lbs of weight which is definitely noticeable on the track. I'm not because I can feel the difference that 90 lbs makes to the performance of a vehicle.

 

What I find ironic is that the CCR allows for a variance in total vehicle weight because someone obviously understands there is variation from scale to scale or they are giving the benefit of the doubt. For some reason with the dyno (which Dynojet is very clear in stating there is variation from dyno to dyno and day to day) we don't seem to care.

 

I understand you point, Mark. However, I think that the way the rules are written in this situation (AI rules), instead of trying to "hit" a limit on the rules, you have to look at it that you need to "under" this limit. With this in mind, we all just need to pick a safe number based on some sort of assumed variance.

 

My attitude is that if it's 9hp for the dyno variation then so be it and we all have to live with it equally. If there is an additional issue in the motor itself that causes a signficant variance, you can either increase the safety margin some more to account for the variance, or try to address the variance in the motor to decrease it (which is what I think Jeff is suggesting).

[RichardC]

This is making AI too much of a headache for me.

 

I'm okay with trusting that no-one is cheating and letting NASA do a spot check on every car at one or two race weekends not just the top 4 finishers.

 

If we all build our cars to be able to easily add 100lbs of ballast if need be then when NASA dyno's all of us we can add weight as neccessary.

 

I want to have fun racing, I don't want to continuously be worrying if so and so has 9 HP more than me.

 

Richard.