Brad The Bike Boy: Another dyno debacle with Minnie the 400

Monday, July 11, 2016

Another dyno debacle with Minnie the 400 - Ducati Monster 400 dyno runs

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So, I had some time today to return to Dynobike with Minnie. Last time, some weird stuff went down with dyno interference. This time, I had some different Kokusan ignition units fitted and took along a couple of Ignitechs - my old one with the last curve I ran, and a new one just in case. I checked them all with the timing light before hand and all the units (2 pairs of original Kokusan and 2 Ignitechs) had the same idle and full advance, with my old Ignitech taking longer to get there.

My old Ignitech and the Exactfit ignition coils have been on this bike with the 750 engine on this dyno before, so I figured that, if required, that set up should ultimately rule out any issues.

Bup bow. Wrong again. I forgot the Ignitechs would have had the rev limit set at a normal-ish 9,000 rpm. The 400 goes to 11. Plus they seemed to have a misfire of sorts.

Anyway, eventually some runs without rpm or air/fuel (the bike shuts both of those dyno functions down) were made, comparing cam timing settings and std vs the all conquering Megacycle mufflers. As below. 46 mph = 5,500 rpm. 80 mph = 9,500 rpm, 93 mph = 11,000 rpm. Ish.

Megacycle mufflers fitted. Comparison of 108 degree inlet centreline cam timing in red, 120 degree cam timing in blue.

Same as above, but with std mufflers. The interesting thing here is is the angle of the power curve right at the end of the 120 degree run. You could hear it on the dyno too.

Clearly, no matter what else you're running, 108 degree inlet centreline is the go. I had the pullies drilled for 112 and 116 too, but I wasn't going to waste anymore time with what seemed like pointless experimentation.

Next, std mufflers in blue versus Megacycle in red with cam timing at 108 degrees. Odd linear straight line bit between 25 and 45 mph, hole between 50 and 60 mph.

With the cam timing at 120 degrees, it's pretty much the same thing with a bit less everywhere.

For a bit of a starting point to final comparison, std mufflers and 120 degree cam timing in blue, Megacycle and 108 degree in red. Up to 15% better in places, but then again, 15% of not much is quite a bit less. The red curve power goes flat at 9,000 rpm and peaks around 9,500 rpm, so you can shift earlier too.

Finally, a sample of the frustration. Blue is the run from the first session two and a half months ago. Red is the same set up from today's session. The only change is the ignition control units, one pair of original Kokusan units replaced with another pair. But even more confusing is the green curve. That's from today as well, with the Ignitech unit fitted (the new one from memory). It had a bit of a misfire through the rpm range, but it's about 20% stronger than the runs with the original control units that followed minutes later. If someone can explain that to me I'd be very happy.

Lastly, what timing belts look like going to 11,000 rpm.

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The 851

The 400SS

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The Mighty KR1S 250

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