Combat Wombat max HP or torque

[DGardner]

Ed this is close to the hole we put in it.

[Bullfrog]

Considering previous activity on this thread . . . are you willing to put your right hand on a chrome tank and swear (or affirm) that the photo/diagram just provided is indeed a close representation of the piston actually running in the engine?

Ed

[DGardner]

Sorry about the other photos! Yes my right hand is on the chrome tank and i swear that is very close.

[hodakamax]

DG, quit apologizing for the "other photos" Max still giggles when he thinks about it!

[DGardner]

Okay I found a photo of the piston.

[DGardner]

Okay the last one is a joke.

[Kels]

Okay I found a photo of the piston.

Doug you left out the "Doug" part of the piston.. I have corrected it for you

[DGardner]

Keep it up and I'm going to punch you in the throat!

[Kels]

Keep it up and I'm going to punch you in the throat!

Pic from your Maico Years..

[thirdstone]

I'm curious as to why you put the vertical slot where you did. It seems to me that it would align with the 03 vertical liner web and that the subsequent mixture transfer would suffer from excessive turbulence.
Kev

This new wombat Wiseco piston with added slots would be more efficient

[hodakamax]

Okay the last one is a joke.

OK Doug, you win, the funniest Forum post of the month!

Maxie

[DGardner]

Kev....I'm testing some intake ideas to see what works and doesn't......

[Zyx]

There you go. A real photo of a real piston. I agree. One large central slot is not as likely to work well as the two slots, and it isn't going to last with one large hole as shown.

[Zyx]

Kev....I'm testing some intake ideas to see what works and doesn't......

With that caveat, I concur. Experiment as you will. Only way to find out.

[Zyx]

Discrediting any dyno report without data to substantiate the dis-creditation Or simply because you do not like the results..... is simply unfair.

I am not discrediting the dyno report, only doubting its accuracy, and I do have data on which to base such a doubt. It was stated that engine speed was calculated based on gear ratios. This is so easy to screw up it isn't worth going into. Which is why I suggested revisiting the computation. You want to post your calculation in full, fine. Otherwise, it wasn't me who introduced doubt into the report.

Never said anyone was dishonest. That suggests an intent you would know more about than I do. I was suggesting that science based on assumptions is not science.

[DGardner]

Arizona.....I'm doing the best I can and if it is off a little I'm sorry! I still think it is very close. I debated even posting the dyno runs just for this reason.....I was afraid that I would have to defend myself from someone but then there's the people out there that would like to see what we find out. If someone other than me was doing the dyno runs and posting them I would be all over it and thankful that they would take the time to do it! Again I'm sorry for the wood piston photo and the one with the holes in the side....that's just my sense of humor and was never intended to make someone mad. Remember we do this for fun! DG

[taber hodaka]

Hey lets get real the hodaka started with a wooden gas tank seems like a wooden piston would be fitting. I am one that likes dry humor during these drought years. And not to offend anyone we must not be consumed by assuming assumptions. Signed SMOKEY in the west. I wish I could test my ace 90 as I am sure it would outdo a wombat. No I do not want to run for office as all sides would be mad at me.Clarence

[hodakamax]

Lots of "seat of the pants" tuning going on in the early Hodaka days. Clarence, Bill and Max could have made good use of a that Dyno! One of our old methods was to drag race the two racers in the shop (which were almost always equal) and then try a new mod on one and go after again. The down side of this method was annoying all the neighbors. What can I say? Actual races at a track also sorted out inflated claims of performance. Just a little ramble to start the day.

Max

PS---Clarence, wouldn't it be fun to drag race our Wombat beating 90s of the day? Just dreamin'.

[DGardner]

I was talking to Tim the dyno owner last night and ask him what he thought the power loss was on a motorcycle. He told me that the dyno can tell you how much loss you get. I guess when you shut off at the end of the run but keep the dyno going it will calculate the power loss. Tim said a modern 450 mx bike is about 5 hp and he thinks the hodaka would be about 3 hp. So I will find out next time exactly how much it is.

[hodakamax]

Comparing bikes with actual HP reaching the ground is the way to go. Driveline losses can be quite a factor in racing particularly with small engines. 200 HP GP bikes probably have no more driveline loss than a 450 MXer but on a 10 HP bike small changes in lubricant and their level, tire sizes and pressures, chain friction losses, gear width and type, mass and other things add up quickly. It would be interesting to see the results of that test. Obviously mass is a factor and all the factors listed above would be downsized somewhat for the Hodaka. Three HP sounds reasonable which is still a 30% loss for a 10 HP bike compared to a 200 HP GP bike which would only be a 2.5% loss. All speculation of course, that's what machines are for, to measure. OK, still ramblin'.

Max again

[racerclam]

Just a coment on the one large hole in the piston, I tried that back in 1975 and it didnt work any better than the four hole design , and piston durability would be lost.

Rich

[Zyx]

Max is largely correct regarding things that can affect the result. I did suggest there were too many variables involved to rely on the raw numbers produced. I disagree on the disparate percentages of parasitic loss in the drive system. As far as I know, mass of moving parts is not an issue since it affects the time it takes to change speed more than the effort it takes to do so, and the dyno tracks effort, not elapsed time.

I asked Ed if Hodaka or Pabatco ever identified the loss through the transmission, and the answer was no. Perhaps the engineers did during the development of the patent on the design, but I haven't found any patent records, and at this point no one seems to know. I would expect the Hodaka style of gear set to have more drag than a slider and dog style of transmission as used in other Japanese bikes. The Hodaka design is intended to be inexpensive and simple, not efficient.

However, the differences in drag between constant mesh and slider transmission is not 27% of the whole. The best way I know of to determine drag percentage would be to compare crankshaft to rear wheel results on the same engine on the same day. Not going to happen.

The old drag race or race day results are fun but not science. Too many human error factors. An expert on a Hodaka can beat a novice on a Penton. I drag raced a machine back in the mid 70's and almost never had the same elapsed time from heat to heat on any given night. Too many variables, which is why most amateur drag races are done using ET brackets.

I also doubt that a rear wheel dyno can compute drag loss simply by tracking the back down after a power run. You would have to know a great deal about mass of parts, and just as an MX bike with a rotor CDI will rev faster than one with a flywheel magneto, so too will it back down faster, even though the transmissions in several various Hodaka models is virtually identical. I suppose it is possible to compute work applied both in power up and power down modes, but without a comparable baseline of data, the result would just be raw numbers that meant nothing much. The rear wheel dyno already knows the mass and drag of its own roller equipment, but unless you tell it what you have, it would not know how to compute a relative loss, because there is nothing to relate it to.

As a matter of perspective, the two machines reported here are very similar in design, whether or not they have the same gear ratios. The driveline from crank to rear tire is much the same for both bikes with the possible exception of helical versus spur primaries. If you want to assume something, assume that the parasitic loss between these two machines is very similar. For the 94, it has been speculated that loss is something like 30%. If so, the loss for the other bike is also on the order of 30%, and since it produced something like 15 hp at the rear wheel, one might then extrapolate the crank power to be around 22 to 23 hp. While I would love to think this is possible, I don't. Point is that percentage of loss doesn't change based on total hp produced. It is a product of mechanical design and mechanical impact: oil viscosity, gear tooth design, total frictional surface contact, and so on. It is easiest to understand by thinking of what we often do, which is to swap top ends on the same engine in search of more power. The bottom end doesn't change, so why would parasitic loss change?

All of this is why I suggested that of the two bikes tested, one was either too high or the other too low, unless something is wrong with the second bike, or something was different in the computation of power between the two. I don't know if there are mechanical issues with the 94, but we do know there is a significant difference in data collection between the two because it was not possible to track ignition sequence with the non-electronic bike. It was necessary to back into rpm based on a computation of how fast the engine was turning versus how fast the dyno rollers were turning. A difference of 500 rpm would be enough to skew the results, but because I don't run a dyno, I don't know how much of a skew could be introduced.

I would just take the second bikes results with a grain of salt because they were based on an estimation of engine speed. That's all I am getting at. I am not angry with anyone, just trying to interject some sense into the discussion. At the end of the day it may well be that the original Wombat made only 8 hp at the rear wheel. I think the only way to know is to take the assumptions out of the test. This may be as simple as devising a way to get a better ignition pulse so the dyno can read it.

[DGardner]

Did you get beat up a lot as a kid?

[RichardMott]

Ouch!

[Zyx]

Nope.