Nissan 370Z Forum - View Single Post

370Z JT · 03-23-2012, 01:15 AM

Here is an email received from Shawn Church in regards to the delta gain discrepancies from the two dynos.

Quote:

Hi Jason,

How would you like the files? The standard dynapack files are not readable without the dyno (older versions are, but they changed the format a couple years ago). I can either give you exports to .CSV files that you can use in excel,or I can send you screenshots of each set of run files?

BTW, sorry for the delay in responding. I just received a call from Tony asking me if I had read your thread. Didn't realize there was any sort of controversy going on.

Just so you know, with all due respect to the tuner at SZ, there are ways to increase timing on the VQ37VHRs. I have spent a ton of time working on my G37 to do just that. It's a bit of a bandaid to get there and I'd much rather have full control like the older VQ engines, but until then.....

As for the differences, or lack thereof, you might want to consider a couple of things. First of all, when we did the baseline runs on the SZ tune, the car did lean out substantially at higher rpms. This may be due to some AFR learning taking place over time as you drive the car. It would probably not have shown up during the original dyno tuning or right after a reflash as it takes for the learned fuel trims to adjust (they mainly change at part throttle). Seeing as how the AFR curve on your retest was flat, and I doubt that the guys at SV targeted anything _but_ a near flat AFR curve under load, that would suggest that any AFR learning had not taken place yet during your retest.

In fact, I would surmise that this is a big part of the difference. If you'll note, your baseline here at CAT showed the SZ tune was near identical to our tune between 2500 and 4500 rpm. The lines literally crossed back and forth many times. But once the car went lean at 5000 rpm, the SZ tune showed dips.

Finally, please note that a dynojet, especially at a smoothing factor of 5, hides small differences. Between the substantial mass of the dyno rollers and heavy smoothing factor, small differences can easily be lost. A Dynapack does not use any sort of smoothing factor at all, and does not have any inertia, allowing us much greater resolution for tuning. It is very hard to resolve differences of 1% or less on a dynojet, and your gains were just outside that range. As we stated when we tuned your car, the tune that was on there was pretty decent to begin with.

I of course have no comment about which exhaust might be better or worse. That I will leave to the exhaust makers.

SC

Is it typical for the AF to change like what Shawn is describing?