Wednesday, December 22, 2010

Power Valve Testing

Yesterday as I wrote about what the Jolly Moto pipes did and did not do for the TZR I thought it would be nice to include a dyno chart.  Well I did have one, but it has less data points than the other charts I have.  Not so worried about that as I am not trying to make any significant comparisons - just show it as reference to where I was (and am never going back to).  More important is the shape of the Jolly Moto curve.  I will say that the only other thing I had done concurrent to the addition of the Jolly Moto's was conversion to the FIII carb spec as per Yamaha engineering notes.  The first generation TZR does not like to have its airbox stripped off unless the carbs are carefully re-jetted.  The RZ350 is the same way.  So did I loose some of the midrange as a result of the airbox-ectomy alone?  Maybe - but I think not.  I can't parse those two changes to be sure.  The chart doesn't show it, but the Jolly's allowed for a lot of over-rev - to 12,000 if I was of a mind - bordering on abuse with stock crankshaft components!  I guess the Jollys are an OK pipe if you're not bashful about high RPM.  Still - I think they are best suited to a track bike and then _only_ if the crankshaft is built to an appropriate spec.  Might as well get out the grinder and widen the exhaust port while your at it.  I think maybe high 50's would be the best you'd get as the standard transfers are pretty modest by 250 race-rep standards.

I need to give Krazy Katt and BDK Race Engineering a big shout out here because they have been a good source of race-rep info.  It has been a while since I've been to the KK website and it seems the dyno charts they had detailing the change to power valve timing _only_ are no longer available.  I believe they still offer a ride in service that swaps out only the standard Yamaha power valve controller (for a Zeeltronic controller).  That chart is what I based my initial setting for the TZR389.  The stock tune 2MA engine likes to have the PV openning "window" shifted down the RPM range.  According to BDK Race Engineering the standard 1KT pv starts to open at 5850 RPM and is not fully open until 10,500.  Look back at the chart above and you will see that the standard 250 engine is _done_ at 9500 RPM.  What were Yamaha thinking?  Just indexing the fully open state to 8550 RPM nets big gains from 6500 to 9500 RPM.  See chart below.

So!  That is the initial logic I decided to go with at the dyno.

To test the logic with _this_ engine, I decided to do a couple of runs to proof theory.  One run with the valves left in the closed position and one with the valves in the open position.  Easy enough to do with the Zeeltronic pv controller.

A few things seem to speak out here:

You might look at the above comparison chart and say "Simple - open the valves at 7912 RPM." and you'd be kind of right.  While indeed the torque curves do cross at approximately that point, there are other things to think about.  First - the electronics / pv motor can't react instantaneously (over a single RPM?!).  Second: and while opening the valves as quickly as possible is likely an appropriate logic for say ........ an RG500 engine it likely isn't for the Yamaha spool type power valves.

It was a mistake to start opening the valves at 5500 RPM.  Look at how the torque curve for the pv closed run (blue) is above the base line run (black) until about 7300 RPM.  That says leave the valves closed until about 7300.

I was closer on having the valves fully open at 8500.  We'll say 8300.

For the rest of the testing the valves were programmed to start opening at 7300 and be fully open by 8300.

Note:  There is an anomaly on this chart.  Why does the pv open run measurably stronger (almost 3 HP) above 8300 RPM when all other conditions were as much the same as I could make them?  Hmmmmm.

next post ....... Ignition Curve Testing

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