Dyno Confusion

[logan]

Whilst I understand that no two dynos (even if the same make) will read the same and weather conditions (hot/cold) do impact on results, can anybody explain the following:

After having my Smalt System fitted, I had the bike set up with a custom map on my PCiii by Southern Cross on their Fuchs Dyno. Results showed a healthy 7 rwhp rise from 128 to 135 (over the slip on Akras, custom map and evo airbox) at the top end and between 5 and 7 rwhp across the rev range. Torque was up about 3ft pounds from 70.5 to 73.8 as well across the rev range.

Southern Cross tune for maximum power and do not measure or adjust Air/fuel ratios.

Concerned that the new larger bore system might cause the engine to run a little lean, I thought I'd take the Factory to another Dyno centre that could optimise the air/fuel ratio. On Steve Jordan's Dyna Pro Dyno (which is the Dyno used for the UK "Mini Twins" race series). She was measured on the first run at 123 rwhp and 67ft/lbs of torque (having been measured at 135 rwhp and 73.8ft/lbs of torque on the Fuchs) and after remapping for a better air/fuel ratio ended up with 129 rwhp and 69ft/lbs of torque. I was not so much concerned by the difference in numbers, as Steve said the Dyna Pro would read lower than the Fuchs or Dyno Jet and seat of the pants, she certainly felt stronger, although he did say he had to re do all the part throttle openings.

Here comes the strange bit. Last week whilst back down at Southern Cross for some non related stuff, I had them put it back on their Fuchs Dyno and was expecting to see and increase over and above their original 135 rwhp reading, given the gains made on the Dyna Pro dyno. However, their Fuchs dyno recorded a maximum of 128 rwhp. Somehow despite a 5 rwhp plus gain on the Dyna Pro dyno after custom mapping the air/fuel ratio, the bike had lost 8rwhp on the measurement obtained on the Fuchs.

Knowing that Fuchs dynos are known for being pretty accurate as between themselves, last Saturday, I took it to another Fuchs Dyno centre for a power run and that one too measured a maximum 128 rwhp.

Has anybody come across anything similar to this or is able to provide an explanation? I'm totally confused.

Thanks

[dougan]

how often do you actually ride.....? stay away from the dynos once you've got a smooth map you're happy with. Fuch numbers.

[live2ride]

Hi did you tell the dyno operator what spockets size the bike has. I use the dyno from southerncross as well, they always ask the spockets size before dyno runs. Can someone please explain why?

I don't think you have to worry too much about the number differences. As long as the before and after comparisons are measured on the same dyno.

Beside all those dyno graphs are measured at full throttle, and I don't think any of us hardly reach 100% throttle or stay there much longer. So its not a true representation of how the bike behaves on the road.
If you got dyno graphs of say 25%; 50% and 75% of throttle opening. Then that will be quite interesting to see how much power and toque has increased.

[Italijet]

Do you have the before and after AF readings from the second session ?

It maybe that the custom map from Southern cross was running a higher AF ratio giving a bigger torque hit to the dyno. Where as the later map may have have lowered the amount of fuel to air in the ratio, giving a weaker burn (slightly lean engines spin up better, but give less torque power).

Post the original and after AF Ratios.