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Music to my ears

 

To clarify things since some don't seem to understand how dynos work:

1) This dyno was done an a Dynojet

2) You cannot compare the results of any different dyno machine because they are calibrated differently, even if its the same type

3) You definately cannot compared the results of a dynojet to a dynopack.

280 HP seems to be the range for the VQ35HR on a dynopack, and 260 HP seems to be the range for the VQ35HR on a dynojet.

These results seem about right for.

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Also, why are these numbers uncorrected?

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I work in the powertrain testing industry. If people really understood dynos and how to use them, then you should certainly be able to compare results from different dynos. If someone told me some line of crap like "this is a low reading dyno" I'd want my money back from the test. Calibrating a dynamometer is not rocket science. If it's a well designed unit, calibrated, and with good software, the readings should be spot on.. However, I suspect that in many of the testing shops anywhere from one to all of the above statements are not true.

 

Your numbers look to be right on when you factor in 20% driveline loss..

 

I've had my car on 4 different dynojets, and one dyno dynamics. The DD dyno is a load based dyno instead of an intertial dyno.

Two of the local dynojets are comparable. When one run from each shop is overlayed, they are almost identical, except for a couple of ecu timing/fuel hiccups.

The other local dynojet reads about 5hp lower throughout the powerband.

The fourth dynojet is at Z1 outside Atlanta. On it, I dyno'd 252 peak, versus 265 peak at the two local shops. All four dynojets are the same model number.

The DD dyno uses STD corrections. It's by far more accurate than a dynojet, though the dynojet is the industry norm, so it's considered to be the "currency" of dynos.

One reason I say the DD is more accurate is because it's weather station is more sophisticated and robust, so the corrections are more accurate. For example, the DD comes with an air intake sensor that is mounted inside the filter media, so it gets to monitor intake temps that are very close to what the car's MAF will see.

Another reason the dynojet is less accurate is that it uses an internal factor that is a "magic number". Basically when dynojet started out making motorcycle dynos, the numbers were consistently off, and no amount of tweaking to the software's horsepower mathematical models produced accurate numbers. So the dynojet software retained it's models, then applies a correction to a magic number to achieve a horsepower figure that is more realistic. To my knowledge, this magic number is still in use today even in its automotive dynos.

And one more thing about dynos in general. A/F metering from the tailpipe is not very accurate. Most people tend to think that the measurements read leaner after the cats, but when I consulted the owner/operator of my preferred local dynojet, he stated that is not the case. Rather, the measurements are delayed by a few hundred rpms for most cars. For example, the a/f reading on his dyno at 3500rpms is actually the rpm reading from 4k rpms. As one can imagine, this makes tuning difficult, especially because the exhaust velocity and displacement of the engine affect the margin by which the measurements are delayed. He told me that he's observed delays ranging from 1200rpms to 300rpms, when compared to widebands installed before the cats.

 

You make valid points Trey. My comments are meant to be a sort of general indictment of the tuning industry. It just kind of irritates me that they are all over the map in how they setup and use their equipment and the results they produce. I say in theory you _should_ be able to compare results from systems, but sadly that is not the reality.

The type of dyno used, (single roll, double roll, eddy current, high mechanical inertia, electrical inertia, etc) certainly impacts what sort of testing it is suitable for. Different setups are better for certain applications, (steady state tuning, transient testing, power mapping, etc.) Also, how the test is run and the "corrections" that the software does can make a big difference. Any corrections should be fully documented, no magic number funny business. Also, proper testing methods should be used, such as have an adequately sized fan, preconditioning the engine, transmission, monitoring combustion air temp.

If you have a properly setup system, you should be able to very accurately and repeatably measure the torque and speed of your vehicle, and you should be able to correlate with results from other systems.

If I tried telling some of my customers BS like "oh, but this is a low reading dyno" we would promptly be shown the door. Our test systems are used to do product development, so the quality of the results are a lot more important.

 

Here is a good article I found online related to Dyno tuning:

http://dinancars.com/whitepapersFile.asp?ID=9

They may be considered "the enemy", but it seems like they have very good test practices.

 

Mike, I work for MagnaFlow Performance Exhaust and we like to say that dyno numbers are only as good as the people operating them-

Unfortunately as you said, there are way too many people out there who are buying dynos and not taking the time to learn how to properly use them completely-

Its amazing how you can skew dyno numbers with the same car on the same dyno if you want to by changing the parameters-

 

So you're the one that can get the group buy together for people that just want to swap the mufflers on their 07s?

 

I just need to figure out what mufflers to swap too- Ive had the car for a month now, and Im still trying to decided which ones to try first-

I like more of the clean look, not a lot of bling on my own cars- so Im still trying to figure it out as on these cars the mufflers are very visable- so Im thinking a non polished muffler might look nice-

 

I like the dual setup for looks... I loved that in my Maxima. Don't want the "grapefruit launcher / sewer pipe" look either, so... what do you have in that department that fits?

Do it... DO IT!

 

Sorry mike, I misunderstood your post. I agree that dynos should be more repeatable, in theory. But I've learned that's not usually the case.

Any dyno that maintains contact with the tires is going to vary, even the dyno dynamics. On a dynojet, one can experience different numbers depending on the arc of the roller making contact with the tires. If the rear axle is placed dead center on top the the rollers, the numbers will be different than if the tires are 30 degrees aft of center.

Even on a dyno dynamics, where the car is "rolled" on the dyno to let it settle between the two rollers, the numbers can vary. I discussed this very topic with Sharif@Forged recently. He said the same car, with the same operator and techs, can be rolled onto his dyno 10 times in the same day and produce different numbers. Having said that, the delta amongst the runs is going to be smaller on the DD than on a dynojet.

That's one thing I like about dynapaks. By mounting to the hubs, the entire tire interface becomes moot. There are no effects due to tire pressure or even tire deformation. That's one reason the dynapaks are so repeatable between runs. On the down side, they are so rare that the numbers are almost meaningless in the world of dynojets for internet racers like most of us.

What I find interesting about the tire argument is that many dyno operators refuse to dyno in any gear that exceeds ~140mph(different per guy). Even if say 5th is the true 1:1, many shops will only dyno in 4th because of fears of spinning the rollers so fast.

Oh, here's a tidbit for you: back in November of 2005 I dyno'd my car with kinetix cats. 6 weeks later I dyno'd again, this time with crawford cats on the samy dyno. Conditions were nearly identical, but my tires in December were 6 tenths of an inch shorter than stock, or roughly 2.5% shorter.

I lost between 5 and 6hp everywhere throughout the power band. I highly doubt the crawford cats perform any worse than the kinetix, particularly 5 to 6hp everywhere. They certainly didn't affect my trap speeds very much.

If you look at the two dyno charts, they are near duplicates of one another, except the second one is shifted down a wee bit. The shorter tires were the culprit IMO.

 

Oh, that is an excellent piece. I don't care which automotive manufacturer they target, that whitepaper should serve as an authoritative source on dynos.

Did you notice the power differences when they ran without the fan? Or how meticulous they were about simulating airflow of the car at speed? And how diligent they were about recording operating variables?

Fascinating article for the geeks amongst us.