Dyno Figures and Variations

[Luders]

After a few discussions on dyno variations and such like, I decided to post this to clear and dispel any myths around dynos and what they read.

In my opinion, the figure given out by a dyno operator is arbitrary, unless it is compared with other bikes being ran up on that same dyno.

The second point which is not my opinion, but rather fact, is that different dynos read different results, given different variables, one of which is the make of dyno used. Which brings me back to my first point and the importance of consistency and having something to bench mark your results to.

To prove my point, I came across some old information on Mark Jordan's site, back from when he was developing his race bike engines and noticed a dyno chart comparison done of a dynojet dyno.
His bike was making 71.57bhp back then, which was probably before the data shown on the Dynapro dyno from a standard KR-1S, his LSR Bonnie and his race engines.
Comparing the curves and looking at where they are making peak power I would say that the 71.57bhp would be comparable to the Rbike06 data putting out 61.87bhp on the DynaPro.

To conclude the DynoJet is reading nearly 10bhp (roughly 16%) higher than the Dynapro reading, making MJ's engine still the most powerful I've seen and to quote a friend, "when the green flag drops, the bullshit stops"




Data taken from http://myweb.tiscali.co.uk/teamsparrow/kr1stune2.htm and http://www.krazy-katt.com/16may09/EvoKR1S.JPG

[mj43]

I had forgotten about those runs. Done on a dyno I used to use in Worksop. From memory the 03 engine is the 06. The 04 evolution mentioned in the webpage was the best I ever did. Unfortunately I never dynoed the engine before the barrels tore themselves to pieces. I have had barrels crack but these had been braced and after 2 meetings both barrels cracked front and back. Was gutted as they had taken months to port. Got another set but have never finished them. 03/06 engine had a little more work which with a set of Lomas pipes is the 08 engine. One day I will finish the 04 second set of barrels off. Will have to go back to Krazy-Kat and see what that engine would have done. Still as Ben says don't get carried away with comparing figures from different makes of dyno as they give allsorts of answers. When developing stick with one then you know where you are going. James at Krazy-Kat is a good one to use if you want to compare as he has tested a vast range of two strokes and I know the dyno pro is consistent. Didn't know the old web pages could still be accessed

[Hawk]

Spot on Ludders

Dyno figures are, IMO, worthless unless they are direct comparisons - best used for back to back runs following changes. But people are obsessed with numbers rather than getting a smooth curve / spending the money on getting the AF right.

I was told that, many moons ago, a dyno operator used to do the first run with the choke on, charge the punter for some work and then run as normal so he could show gains! And I've had a bike on a dyno that showed I had more power at the wheel than at the crank from a previous dyno!

[jarno]

X2

[Luders]

Yeah I hope it clears up a few things and when I talk bhp figures, I always quote and reffer to DynaPro figures as they are most accurate.

I mentioned the other day I had not seen a 65bhp KR-1S and MJ's is the most powerful I have ever seen, I still stand by that statement based on the above data.

Anyone got any DynaPro results they would like to share with us?

[maccas]

Here are the results from my KR1 the first time i had it on the dyno 2 and a half years ago. The top curve is versus MJ's Bonny bike and the stock KR1S





As you can see mine was crap even compared to a stocker. On a dynojet dyno my bike might have shown 53-4 bhp or even more.

This isn't a KR but my 3xv from a couple of years ago also. Really shows how crap my KR was



Dan

[Luders]

You've actually got a respectable curve from the KR-1 there Dan. It was brick walling there below 10 grand, so if it kept revving, it would probably be close and comparable to Mark's Bonneville engine. Do you know what was stopping it from revving?

[maccas]

There was allsorts wrong with it Ben, tired pistons, too high compression ratio, kips ports too small etc.

To say it has lomas pipes, 35mm carbs, zeeltronic and flowed cases it was crap haha. Goes much better now, need to get it back on the dyno.

Dan

[TwoStroke Institute]

You actualy can compare brands of dynos,it all comes down to the correction factor. The dynojet I use pretty much within 1-2hp of the dynapro figures with RGV's. Using "STD/DIN" correction on a Dynojet is what gives the inflated figures. Placement of the weather station seems to have an effect on the reading as well though I dunno why. I used a Dyno dynamics and figures off that were very accurate as well.

[mj43]

Wondered how long before somebody commented on that. Conditions on the day were exceptional and I never put any value on the numbers. Just served to show you can generate numbers over a wide range

[Luders]

Which is kind of my point

[TwoStroke Institute]

Have also seen a huge variation same bike same dyno just different weather which just showed the jetting was off. Gone in at night in the winter and seen very good numbers.
Older dynojets seem to be optimistic, Japanese figures are always converted beck to crank as are most but not all German figures.
Would love to take the same bike to different dynos on the same day and see the result

I was told that, many moons ago, a dyno operator used to do the first run with the choke on, charge the punter for some work and then run as normal so he could show gains! And I've had a bike on a dyno that showed I had more power at the wheel than at the crank from a previous dyno!

One other swifty is to say the cold case figure(first power run) is the "after" and the hot case figure the "before"

[mj43]

It was a cold winter morning