This question is for everyone who has a chassis dyno or has had their car chassis dyno'd. I am wondering what correction factor that is used by everyone. The reason I ask is if we all come to one standard, it will end alot of the talk about how much power everone is really making. If you are using the standard SAE J607, also reffered to as STP, these are going to be bigger numbers than the SAE J1349 correction.

What I am proposing is that we as a community decide unanimously on a correction and stick to it. This is going to help everyone when we are deciding on what products are best for us. There is to much talk of these huge power gains, when really all they are is a falsley generated number.

What this will do for us as a community is it will force our suppliers to be truthful to what they are advertising. If they say we are going to see 20 RWHP, then damn it, I better see that number.

Believe it or not, the suppliers listen to what we have to say. Remember, they have to, we pay their bills. So if they aren't producing what they said they would, you can bet that they are going to here about it.

So what is it going to be, SAE J607, or SAE J1349. One thing to note is that GM and the rest of the OEMs use J1349 as a correction. So when you take your stock car to a chassis shop and see 300 RWHP from a 320 HP car, you can know that something is not adding up and you can quiz them if they entered in the correction data for the day and if it is SAE J1349. If they have no idea what you are talking about, tell them they need to look into it because all they are is generating a number that means nothing in the real world.

Sorry for rambling on, and sorry if this has already been brought up, but it is time to do something. Thanks so much for any input

My vote is for J1349 so we can compare with the factory specs.

 

THis is going to change our world.

 

Sorry, but I am of the school that the correction factors are pretty much junk anyways.

Both corrections are a blanket attempt by SAE to provide an inkling as to what power the car should make for correct conditions. They are good for a ballpark comparison, but if you are trying to get within +/- 20 HP you will have to look for a more accurate correction.

Addtionally, all corrections reley on a wheather station at the dyno. As I'm sure you are aware with all computer formula's........ JUNK IN = JUNK OUT. As long as the wheather station is not reading the proper ambient conditions for the dyno, then it doesn't matter what correction you use.

And last but not least, it is a dyno, and thats it. As will all measuring equipment there are variences between each. Most dyno shops aren't interested in scientific accuracy, so they won't regularly calibrate their dyno, or make usual checks to ensure accuracy. It is not uncommon for 2 different dyno's to differ by more than 20 HP.

If setups want to be compared within 20HP +/-, both people are going to have to show up on the same day and dyno on the same dyno back to back.

Dynos are a tool. They should be used more to measure the dPower rather than the absolute power.

JMO

 

The SAE correction factor used by Dynojet is built into the software. I have no idea which one it is. If we didn't use correction factors, us shops down here in Texas would be screwed on days in Augsut when the dyno air is 105*F

If we all use SAE (at least Dynojet guys), we will all be comparing apples to apples. Let's face it, it can't be 70 degrees, 29.92hg, and 35%RH everywhere.

 

sure, I'll bite.

If you run the correction for a 105 deg day it is only going to move your HP around approximately 3%. For a stock car that would be the difference between 300 HP and 309 HP. I don't know if I would necessarily call that screwed?

None the less, it doesn't solve the problem that correction factors aren't all that accurate.

 

I'm new here, thus the late response. Sorry NoGo but I could not disagree more with your statements. Due to atmospheric correction factors, elevation, baro pr, temp and humidity, our dyno numbers get corrected over a 10% spread throughout a year. Due to that most modern dyno's repeatability is very accurate. Many customers are amazed at how they can come in many months later and still get less then a 1% repeatable pull. During the course of an all day custom tune on an engine management system, we may see near a 5% correction factor as the shop warms up and the baro pr dramatically changes due to a storm front coming or going. We could not provide the very accurate testing, comparing and tuning services without this. Also, consider a dyno located it TX at sea level and another one located in CO. These correction factors, if done correctly, set a very good standard for comparative testing. As far as what standard is used, J607 Vs J1349, just ask what standard is being used. If they are using the J607, common on all engine dynos today or chassis dynos installed prior to 1990, J607 reads approx 5% higher then SAE 1349 Rev 90. If they don't know, find another shop. Ask to see these inputted numbers because this is the area where some shops fudge to make customers happy payers.

Like any fast growing profession, we now have a lot of new inexperianced, unknowledgeble or unscrupules dyno operators. We are also getting some very sophisticated, high tech, load bearing chassis dynos into this field. These, especially combined with the above operators, can really negatively taint this profession. Also, many are buying used dynos and not being guided by the manufacturer as to their proper installation, calibration and operation proceedures. Example, many installs do not know that they are supposed to use "station pressure" for barometric pressure. This can be much different then the baro pr we normally read on a gauge or get from the weatherman because it compensates for installation elevation. Having worked with engine or chassis dynos for over 20 years now, I think that they are the most valuable and accurate way to gather many engine vitals in the least amount of time, if done by a competant operator and a good dyno. We have hundreds of customers, many race shops, that would agree with that statement and usually a 2-3 week backlog waiting to get on it. This is not a self promotion because, as you can see, we don't need the advertising and if it was I would have gone back and tried to correct my grammer and spelling.

EJ

 

Correction factors for high altitude applied to forced induction engines can lead to some very inflated numbers. Especially on a turbocharged engine with a wastegate referenced to absolute pressure.

 

Good point, I agree, we usually inform boost customers of that. We and most other dyno shops use the same correction factor for everything but yet many of us know it is not correct for boost applications, they make their own atmosphere. But something has to be used because atmoshperic conditions do affect them also but not as much. Unlike N/A engines, a true correction factor would be different for each application. Getting consistant back to back runs on boost applications is already difficult because the engines vary so much do to induction heat soak etc., same problems at the track even without regards to atmosphere. Not using any correction factor for such applications would make some sense but like usual, arguable.

Thanks, EJ

EJ