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Is it normal that AFR measurements vary between Dynojet benches?


Dutchy

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That HP measurements vary bench to bench I know and accept.

 

What puzzels me is AFR... I thouhgt this this is NOT a calculation but a "true" measurement....

 Here the measurements a few weeks ago

Black line prior to PCV

Green line after pcv instal/setup

The PAIR air hose was clamped shut

AFR.thumb.JPG.4a54ae075d58409b57aece2e12bc3004.JPG

 

 

And this today on a different bench where a simple run was done; the PAIR hose was not clamped

PSX_20190405_160926.thumb.jpg.64e2ba535d719dddfe791de95048be75.jpg

The operator today was a bit reluctant at 1st (to put is mildly) to do the run "I donot want to compare benches" "the dyno bench is not a toy"... 

I was there because a pal wanted his special cams tested/setup on his SP1 and merely wanted to see what mine did "standard"compared to his on the same bench...

He was glad to take my money though......  (miauw!!!)

 

Opinions?

 

 

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a few observations:

 

1. Dynojet dynos are toys. At least compared to the bigger, more expensive dynos.  They're inertial, which is the simplest way of doing what you do. They do vary. They tend to rate power higher than other dynos. Whatever.  They serve a purpose and you learn to work with them. They have some compromises, but dynos are not a perfect tool. They're just way better than trying to do it without a dyno.

 

2.  Your PAIR absolutely will make a difference. They do leak a little air when not new and you can't compare any readings with and without them plugged.

 

3. I don't know  for sure, but when I put a PCIII in my bike it went from running rich enough to backfire on decel to not backfire on decel. That's with a zero map. I am not convinced that the zero map is genuinely completely zero to stock, though by all accounts it should be.  This is totally anecdotal, and the plural of anecdote is NOT data, but I am personally not surprised a slightly smoother and less rich cuve shows up on your zero map.

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I was told that the tolerance Dynojet allow is 6% between their dynos. Different day, different place, different setup, different dyno.

 

Only meaningful comparison is on the same machine.

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Cheers Moose Eggs!!! :tongue:

 

The max HP did (as expected) differ, 133 now vs 138 then.   

 

On the AFR question I believe now that here it must be a calibration delta/error, combined with the PAIR leaking.  I have very very little backfire on decell.  I'll be on the Assen WSBK/MotoGP track again on the 15th and she is running strong. If only my riding skills were at a level to match... 😀

 

 

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The AFR should not vary from dyno to dyno, because it’s measured using an O2 sensor sniffer. That said depending on how that system is maintained will impact the readings it produces, plus your bike will change its fuelling based on atmospheric pressure, mass air flow sensor, temperature etc. 

 

Thats is why PC + auto-air or RBR with MTB are a better option than a fixed dyno custom tune, which is only perfect for that day with those atmospheric conditions. 

 

 

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