I thought this might be of interest. Pull out your dynojet graphs and look at the a/f plot. Notice how nice and straight it is, that is not reality. Did you ever wonder why a fuel adjustment with the VEC does not change the a/f as planned. The following (opinion) is the reason.
I installed the Innovate a/f meter two years ago and have had a good chance to compare the Innovate with the changes in fuel input via the VEC. They correlate almost exactly, if you pull 5% of the pulse width (fuel), you will see a fairly close change in a/f. In my experience this is not always true on a dynojet, especially when the dyno operator also uses the dynojet brand a/f meter.
I did some pulls this weekend and compared the changes in a/f for a given change from the VEC. I noticed a little earlier in the year that the dyno a/f didn't seem to correlate with the Innovate numbers. Here is what I found:
1. The Innovate readings were very close to what you would expect for a specific change from the VEC.
2. The Innovate and the dyno a/f were drastically different up to approximately 4000 rpm, thereafter, they were close or identical.
3. For a given change from the VEC, the dyno's change in a/f didn't correlate, especially from 2750 to 4000.
If you think about the shape of the dyno's a/f plot, it is too straight and pretty, there is a drastic amount of smoothing taking place. If I do curve fitting it looks like the dynojet plot has between 1 and 2 seconds of smoothing. The reason that the first part of the pull has incorrect a/f is that the 14 or 15:1 a/f prior to wot throttle is being averaged into the first 1 or 2 seconds of the pull. This is also why you do not get a corresponding change with the VEC, expecially below 4000 rpm.
Even when the operator selects no-smoothing, the factory software still seems to insert smoothing. As I said previously, real a/f curves do not look like the dyno plot. Just to lend credance to my theory, one of the best dynojet techs in our area will not run the dynojet a/f system, he claims it is over a point off. I ran the numbers, and they verify a huge amount of smoothing or just a plain error in the front end of the the dyno run.
Some of this might not matter, if you drag race the car is typically not run under 4000 rpms, but, if you road race, it is possible that if you dyno tuned you could be be running very rich up to 4000 rpm's.
This inherent inaccuracy can be verified, the next time on the dynojet, keep track of the VEC changes you input below 4000 rpms, I don't think you will get corresponding changes in a/f. The nearer you are to the beginning of a run, the more variation you will see.
I installed the Innovate a/f meter two years ago and have had a good chance to compare the Innovate with the changes in fuel input via the VEC. They correlate almost exactly, if you pull 5% of the pulse width (fuel), you will see a fairly close change in a/f. In my experience this is not always true on a dynojet, especially when the dyno operator also uses the dynojet brand a/f meter.
I did some pulls this weekend and compared the changes in a/f for a given change from the VEC. I noticed a little earlier in the year that the dyno a/f didn't seem to correlate with the Innovate numbers. Here is what I found:
1. The Innovate readings were very close to what you would expect for a specific change from the VEC.
2. The Innovate and the dyno a/f were drastically different up to approximately 4000 rpm, thereafter, they were close or identical.
3. For a given change from the VEC, the dyno's change in a/f didn't correlate, especially from 2750 to 4000.
If you think about the shape of the dyno's a/f plot, it is too straight and pretty, there is a drastic amount of smoothing taking place. If I do curve fitting it looks like the dynojet plot has between 1 and 2 seconds of smoothing. The reason that the first part of the pull has incorrect a/f is that the 14 or 15:1 a/f prior to wot throttle is being averaged into the first 1 or 2 seconds of the pull. This is also why you do not get a corresponding change with the VEC, expecially below 4000 rpm.
Even when the operator selects no-smoothing, the factory software still seems to insert smoothing. As I said previously, real a/f curves do not look like the dyno plot. Just to lend credance to my theory, one of the best dynojet techs in our area will not run the dynojet a/f system, he claims it is over a point off. I ran the numbers, and they verify a huge amount of smoothing or just a plain error in the front end of the the dyno run.
Some of this might not matter, if you drag race the car is typically not run under 4000 rpms, but, if you road race, it is possible that if you dyno tuned you could be be running very rich up to 4000 rpm's.
This inherent inaccuracy can be verified, the next time on the dynojet, keep track of the VEC changes you input below 4000 rpms, I don't think you will get corresponding changes in a/f. The nearer you are to the beginning of a run, the more variation you will see.
