all_bark

iTrader: (5)

i was wondering why the HP on the cats went up with the sae correction and the HP oon the plenum went down with the sae correction then in the end it yielded the same results!

FLY BY Z

Yeah thats what i was referring to. A couple of posts ago I said that SAE correction doesn't always add HP. Apparentley, the correction brought one day down and the other day up. The HP stayed the same as opposed to going up even more if both days had increased (or conversley, gone down even further). One of these two scenarios would have only been possible if conditions were identical on the two days, or more importantly, had they been done on the same day at almost the same time.

D'oh

In the other Kinetix plenum thread Z1 Performance posted an excerpt from an SCC article that discusses this very issue. It explains things pretty well, and also gives some instances in which the correction factor makes things less accurate (especially in boosted applications when wastegates are involved). That doesn't apply to this, but it is a pretty good read.

-D'oh!

350zdanny

Where did you find the correction numbers you listed? Z1 Performance listed some different numbers in the other thread.

FLY BY Z

He didn't list any correction numbers in the other thread. These are standard correction numbers for SAE (Society of Automotive Engineers). The only time you will use different numbers is when you are in another country standardizing to a different groups numbers. Z1 only listed theoretical variable differences to illustrate some examples.

350zdanny

So the ones you listed are the real correction numbers that dynos correct to all over the country? Are the other 3 or 4 dynojet correction factors also useful for something even though SAE is the standard?

FLY BY Z

I don't know what you are talking about. It doesn't matter what dyno you use, these are the standard correction numbers. I suppose you can use any number you want, but unless you are using these, your correction is skewed. Actually, the link I provided on the other page has a lot of useful info. Check it out.

FLY BY Z

Another:
http://wahiduddin.net/calc/calc_cf.htm

Another:
http://www.yzf-r1forum.com/Dyno.html

350zdanny

Thanks. I found what I was looking for in that second link. It compares the different correction factors for SAE and STD. The differences aren't as pronouned in my dynos as they say they should be but it still makes some difference.

I also found out that my SAE correction factor is 1.133 inside an oven.

phile

Ohh, thanks for the exlpanations. I honestly know nothing about dynos, or how hp/tq is affected and manipulated. That's why I was confused why some people put an emphasis on smoothing. I thought smoothing the graph would generally yield lower results at any arbitrary point on the graph. I was confused in general and am by no means an expert in statistics :P I just have books and what little knowledge I retained for some reference on the topic. I appreciate the input

350zdanny

You're right. The smoothing eliminates the outliers, but in most cases, the dyno take so many data points that the difference is actually a matter of much less than 1 whp and a much more accurate depiction of the actual power you are making.

Dan

phile

I just wish there were a way to produce concrete, foolproof results. Too bad the environment is such a factor! If only engines didn't rely on the enviroment and rather were self-contained untis...then dynos would be pretty concrete.

dr_gallup

Actually, the SAE correction factors quite effectively eliminate the environmental effects. That is why it is so important to always use SAE corrected results. Otherwise you are just pissing in the wind.

What most people on this board choose to ignore are all the other variables involved in chassis dyno testing. Testing in a different gear makes for completely incomparable data because dynojet dynos do not measure torque (there is no load cell), they just infer it from how fast the drum accelerates. Also, there is always slip taking place between the tires and the dyno drum. This is affected by how accurately the car is aligned to the dyno, how tightly it is tied down, tire pressure, etc.

Fuel makes a big difference and I guarantee you the fuel you can by this time of year is very different from what the same station will be selling in July. The very best anyone can hope for is +/- 1% repeatability (~+/-2.5 HP in the Z's case). This is why I just laugh at all the people who claim 2-3 HP gains for CAI or grounding kits. They make three runs, pick the highest number and say "See, it works!".

I'm not puting down anyone who has spent money and time doing dyno testing, I'm just saying you have to use proper experimental technique if you want to be able to draw valid conclusions.

350zdanny

Well what is the proper experimental technique in your opinion?

And I know you're not putting people down, but talk is cheap. It might be more instrumental if some of the people talking about "proper experimental technique" and how the people doing the dynos are ignoring things actually put up some money and showed some of the ignorant how it's done. I'm not singling you out or putting you down in any way. I'm just quoting your words because they're right in front of me. I think that there are alot of people on this board who are quick to criticize the methods of others, but are not so quick to take up their time to actually produce results (and once again I'm not saying that you are one of these people as I have no proof of that whatsoever, but after the "dyno wars" that just went on I think everyone will agree that there is a very critical attitude toward anyone that posts up a dyno). What do you think?

Dan

D'oh

Well, it certainly doesn't hurt to be a skeptic, but at the same time using a little consideration and tact is a good idea.

I believe that as long as people explain their dyno procedure, and try to indicate how they accounted for different conditions (or clearly state how they weren't able to account for them) then the more data we have the better.

Because the dyno's can vary so much, it really does no good to get all wound up because one run (or set of runs) doesn't show what you want. And of course, no one should get too excited just because one dyno shows something very positive.

On this site I typically see a few posts that are extremely harsh, which causes a the original poster to start getting defensive, which then makes that original poster start getting upset at anyone else that poses even legitimate questions. Most of the regulars on this site are able to separate themselves from the arguments and keep thigs civil, but occasionally people get pissed and go a little overboard. That's just the nature of life. Just gotta try and remain calm and realize that most of the time the guy at the other end of the keyboard isn't trying to be a jerk, but is simply not understanding what you are trying to say and vice versa.

Anyhow, maybe one of these days I'll get my stock car dyno'd. Until then, I'll just sit back and rip apart the hard work of other's (but I'll try to do it as nicely as possible).



-D'oh!

FLY BY Z

Lack of communication is the cause of all wars. What better way to communicate than this?

Anyways, with all this dyno talk and how important it is to everyone, people should remember that a dyno is NOT that important in the scheme of things. Just because a car dynos 5 HP more than another car doesn't mean it is faster. After all, that is why we mod cars, at least through this forum, right? We don't just sit and rev our Z's in the parking lot or driveway do we? No, we put them in gear and go. Around corners, down the road, etc. There is a lot more to the driving experience than just how much horsepower you have. In fact, a better driver can overcome 50 HP. Even more than that sometimes. I don't think everyone should get so caught up in what a part might dyno. It really doesn't matter. You put together a package to make some more power based on avg gains the parts have made before. It isn't going to make the same power on your car. But even so, if your suspension or tires can't handle it, it makes no difference. Or if YOU can't it could mean a lot more trouble than losing a race. For instance, if the Kinetix or Crawford make within 5 HP of each other, which they undoubtedly do, get the one that you think looks, sounds, fits better. There is more to the Z than the last 4 horsepower. We aren't building NASCARs here. We aren't building Indy cars. We aren't building Formula One cars. Everyone here has a street car and even the FI Z's are pretty mild in comparison to what exists in the world. It is important not to stress too much about a dyno. It is really silly.

350zdanny

You guys are absolutely right. Doh, I don't think there's any way around people getting defensive because over the internet, on a forum, you can't hear a person's tone or inflection and almost every time, something will be taken as insulting. I've done it. Everyone has at one time or another.

FlyByZ, I think the obsession with dynos, or the reason why they are over-emphasized is just the product of people wanting to squeeze out every last bit of value from the X amount of dollars they spend. It almost always won't matter in the real world, but a person would want to say that they are making 257 to the wheels with the Kinetix rather than saying they are making 255 to the wheels with the Crawford. That is within the error of the dyno, but people just want that extra "value".

I guess there's also the mentality that these little bits of HP are going to add up in the end (I don't mean mods adding up, I mean that scraping a little extra here and there will eventually mean something). It's just human nature. Any intelligent person wants to get the most bang for their buck. In most cases, though, these huge arguments are spurred over symantecs or a marginal amount of HP. This is the reality of the internet I guess. I won't lie. I love comparisons, and I'll always buy the part that makes more power, regardless of whether it's 1 or 2 ponies.

Dan

FLY BY Z

But that is what I am trying to emphasize. People want to place value on the 1 or 2 HP when there is absolutley NO value in that 1 or 2 HP. They may spend more for 1 or 2 HP and give up some tangent benefit worth much more than the 1 or 2 HP that will be nullified by any of a million variables. That is just a bad decision.

Road Warrior

iTrader: (16)

it really doesn't matter how much power you have compared to the other guy....its what you can do with it that counts. there is more to a car than how much it puts down on a dyno, otherwise we wouldn't be racing every sunday. people around here get too wigged about dyno numbers....so i can see where others would get discouraged about posting up their results. i am thankful of those who share their information and time cuz if it wasn't for them we would not have this performance forum

ujmot

This is great stuff. Thanks fellas for the edumacation. I wish all threads here were like this....