Z1 Performance

iTrader: (564)

I just igired I would post this little excerpt from SCC a number of years ago.

everyone is always quick to "want" the SAE numbers, when in reality it makes no real difference. There is nothing to say either result is the "right" result, thogh it is nice to have both to look at. Anyway, enjoy:

Corrected or Uncorrected
Dynojets can read corrected or uncorrected horsepower. Because different weather conditions can result in different air densities and different oxygen concentrations, the weather can have a significant effect on power output. The SAE has a standard set of correction factors that can be used to normalize all power outputs to what they would be at sea level, on a 60 degree day, with 0 percent humidity. Every Dynojet has a small weather station built in to feed the appropriate temperature and barometric pressure readings to the computer so it can calculate this factor. The difference between 0 percent and 100 percent humidity is about a seven percent correction. A temperature change from 60 to 90 degrees, on the other hand, will have an effect of about a 2.8 percent. A difference in elevation from sea level to 5000 feet is worth a whopping 20 percent!

If you use uncorrected data, the changes in power output due to weather conditions could be misconstrued as being a result of something else. For example, if you have a dyno sheet showing that a header made a 15-hp gain, but the runs were done on different days and the plot was made with uncorrected data, you can't be sure if that is really a 15-hp header, or an 8-hp header and a 7-hp weather change.

Corrected numbers, on the other hand, can be suspect in certain cases as well. Turbocharged cars running at high altitude, for example, might be more accurately represented by uncorrected numbers. Say you are testing an FD3S RX-7 in Denver, where the elevation is approximately 5,000 feet. Shiv Pathak, master of our FD3S RX-7 project, reports that he always sees higher boost levels at high altitude. The reason is simple. The wastegate opens when boost is 12 psi higher than the normal sea-level reference air behind the wastegate actuator diaphragm (air that has been stuck in there ever since the diaphragm was sealed somewhere in Hiroshima). As the air density drops at high altitude, the actual pressure in the boosted intake manifold remains constant. The boost gauge, though, reads pounds of boost over ambient pressure. If the ambient air pressure in Hiroshima was 14.5 psi when that diaphragm was sealed, but it is only 13.5 psi when Shiv drives through the mountains, his boost gauge will read 1 psi higher than normal.

The SAE correction factor used by Dynojet assumes that lower air pressure at the sensor box means lower air pressure in the intake manifold, though, so at 5,000 feet the dyno is applying a 20-percent correction factor to compensate for a loss of air density that the engine never sees. This is fine if you are doing all your tests in Denver, but if you do one test in Denver and one test in New Orleans (the highest mountain in New Orleans is 12 feet above sea level) uncorrected numbers will be more accurate.

The SAE correction factors are only accurate over a relatively limited range, and the Dynojet software is smart enough to warn you when two runs with wildly different correction factors are being compared. The software in New Orleans can't check your glovebox for that last dyno printout from Denver, though, so you'll have to warn yourself.

Courtesy of Dave Coleman

geeman49

I would mod my G sedan with it whether it has the dip or not if it provides the performance advertised. The dyno curve looks great.

Would a redesign of the plenum for a non-STB G yield greater gains? I recall the plenum thickness was less beneath the STB. Even if the plenum was made thicker and smoothed out the inside flow properties might not be improved significantly.

It may come down to looks for G owners who don't like the dent. I'm more interested in the performance enhancing apsects of the piece. For an under the hood device it is not that big a deal vs the other benefits.

Just come up with something cool to put there. Personalized skins?

ChrisMCagle

Very interesting read! Thanks for the info, but now I don't know what to read my dyno results as. Either I'm making 232 hp, or 241 hp!!! I like the later, but don't want skewed results in the end after modding.

-Chrismcagle

350zdanny

The results won't be skewed as long as you used the same correction factor across all the dyno plots. Besides, RunViewer doesn't allow you to plot one run in SAE over another run uncorrected or anything like that.


dan

jak

My thought is it is the difference that matters. So if you dyno the SAME way all the time the differences will be accurate.

The only reason I can see for wanting to know exactly how much horespower you have is for some kind of bragging rights. In that case you would be better off and more accurate doing an engine dyno.

To much emphisis is put on these dynos. Dynos by there very nature are inacurate and should be used as a guide only.

Jeff

phile

Acceleration performance is better measured (IMO) using the 1/4 mile run on flat ground, at sea level, on a 60 degree day with zero humidity. Oh, and a professional driver running the car 5 times

So, lets erect a large climate controlled building we can race in at sea level at any time of the year! I got 5 bucks, anyone wanna chip in?

Gsedan35

iTrader: (10)

When LSDunique say's we want's to know who would be interested in a front strut tower bar for the G35, he wants to see how many people are interested. He knows, the G35 does not have the special welded on mounts that the Z has that are REQUIRED to mount such a bar at all and that Infinti put some things in the way were those mounts would go. He's looking into the issue. IF and that's a big IF, he can make the mounts without too much trouble, he will offer the bars for the G35. If he can do the mounts, I'm in.

D_Nyholm

Now, that sounds more like it with the bar. If it is possible and cost effective (for him and us), I would be willing to take a look at it. Stiffness sure does help at the autocross!!

roark

iTrader: (2)

The SAME way must include the exact same enviromentals of course.

If you perform a base pull at 80 degrees, 28 inches of mercury and 90 percent humidity, then perform some mods and repull at 40 degrees, 30 inches of mercury and no humidity, then your gains are skewed by more favorable environment of the second run.

If you can't repeat the environment, then you need to compare using SAE or other correction scale.

ericinmiami

If the Stab. bar comes out good, (works well & price).

I'm in for the combo of plenum & stab.

-Eric