I'll share some thoughts based on observations and add to this post as I find time. Musings on dyno stuff I guess.
I have access to four dynos on my side of town. The dyno operators specialise in various bike designs, one with in line four bikes for street and track, one with performance big twins and two are expert race engineers on the verge of retirement.
I hope the two older guys write books or give lectures before their incredible knowledge base is lost.
I'm not a dyno expert and don't get to operate them myself. I do tuning work using the data from accessing dyno services and communicate my objectives and tuning "recipes" with the dyno operator. Having a trusting and respectful relationship with the dyno operator is crucial. I test ride the bikes and give feedback as the bike may need follow up testing and tuning. EFI tuning is usually conducted by the dyno operator with the software relevant to the selected tuning devices in light of the customer's objectives. I take care of the carby tuning.
A few topics I'd like to cover are:
1. Dynos don't lie, or do they?
2. Dyno charts for marketing VS Tuning and Performance
3. Dyno readings and calibrations.
4. Dynos and your Objectives.
5. Post dyno road or track testing.
The above topics will give me a bit of structure.
1. Dynos are good for testing people's claims. JD Hord called them a "bullshit meter". You don't know for sure unless you measure.
But if you try hard enough under some circumstances you can manipulate the dyno software parameters. Two dynos I access have weather stations that are automatic and cant be tampered with. The correction factor is what it is. Not perfect but designed to allow hp comparisons on different days.
But what if you can manually overide the inputs? I have heard of the correction factor being manipulated to give a bigger hp number. Test the bike on a cold day with low humidity and high atmospheric pressure, but punch in unfavorable weather conditions (high temps, very humid) that make the correction software add hp.
2. A dyno operator told me that he provides a simple WOT before and after power run to satisfy customers, but that there are charts they wouldn't understand or show interest in. The other charts may give more information but aren't as pretty. They could be messy looking part throttle charts with AFR traces all over the place more resembling a Richter Scale. A recent dyno tune of a Ducati Scrambler focused entirely on over riding the closed loop portion of the mapping and tuning it for more low and mid range torque at part throttle inputs. Although this made no difference to the WOT hp chart and peak hp numbers it gave the strongest improvement for the riders seat of the pants experience.
3.There has been quite a bit of discussion about different dynos giving different readings from the same bike. Then there's different versions of software used for the same dyno machine. A software update has shown about 10% lower numbers on two dynos that I have accessed. The only change was the software. Different model dynos from the same mfr and dynos from different mfrs are more obvious explanations for varying figures.
On the same Dynojet 250i dyno, the different software gives an M900ie for example both 71hp (newer) and 78hp (older). I take this into account looking at charts in my folder. I have heard of another 250i dyno in my city reading even higher and I suspect it's because the operator wants to keep a better comparison of historical data.
4. The results for objectives like more peak power or more mid range torque, a smoother power delivery, etc can be tested. Dyno tests with an exhaust gas analyser can be useful when you want to know why a bike is behaving in an atypical manner. I'm going have a Honda RVF400/NC35 dyno tested that I suspect has race porting. The bike feels different to the others. An ex race bike out of Japan i suspect.I want to know what's going on. The bike feels like it has big ports for peak horsepower and some dyno tests should give me an idea before pulling things apart.
Dyno testing can tell you if your motor recipe worked and is vital to peak hp tuning without track testing or going to jail.
The plan is to spend some money to save money, to avoid chasing my tail.
5. I road test bikes after dyno tuning because dynos don't tell the whole story. I remember a 500cc single cylinder bobber needing more fuel even though the AFR numbers were "correct". The motor needed an extra dollop of fuel to be happy. Full cream rather than diet milk. Another case was a YZF750 that was easier to ride with 118hp vs 122. The best looking dyno chart never felt as good and the expert dyno tuner warned me to test the bike with each tune. He was right.
On the other hand a bike tuned with more mid range torque might not have the "whoosh" sensation compared to the tune with a hole in the mid range. The Scrambler previously mentioned is also a good case in point where the rider felt a significant improvement in torque exiting slow corners on the track despite the WOT power runs appearing identical.
Thanks for your patience. This post is an indulgence in preparation for a presentation I'm making to a classic english mc club. I hope it promotes some discussion on the forum.
[popcorn]
G'day Howie [beer]
Hope this promotes some discussion.
I'll just add another update to the main post. For points 2, 3 and 5.