Wombat Dyno

[DGardner]

I was able to get the wombat on the dyno yesterday. Okay first off this thing was designed for torque not H.P. and second we changed the porting after the pipe was made, so now we need to change the pipe again to match the porting. The new motor is in red and last years motor is in blue. For seat of the pants riding WOW! this thing has a lot torque and for what I use it for it is so easy to ride, it will just stay at 55MPH at 6000RPM. It has so much torque that I think I could gear it up two (47 to 45) teeth on the rear.

[Bullfrog]

Oooooo . . .
Soooo many questions. Can you give us a quick narrative about this comparison? Which Wombat? (Iron barrel, piston port? Alloy cylinder, reed valve?)

Was last years engine "stock"? Carb, porting, pipe?

This year's power curve sort of falls off a cliff after 6,000 - but is pretty muscular up till then. Seems like it would be a fun powerplant to ride. Pipe re-work may change the "cliff" part of the power curve substantially?(!)

Before Bob chimes in - any chance of a Resonator Revisited article in the future?

Ed

[DGardner]

I just got back from a 120 mile ride on the wombat and all I can say is WOW! this thing is a blast to ride. The problem that I have had in the past is with the tall gearing (16F 47R) when you shift you would have to rev it to the moon just to pull the next gear and if your on a hill or have a head wind it may not be able to pull it and it back to the lower gear and just rev it. This motor you shift at about 5900-6000 RPM and it falls back to about 5000-5100 RPM and that is right at the peak of the torque, then it just starts to pull. I don't think I will change a thing. The carb is 28mm PWK with thunder products divider. Last year I had Rich's reed, this year I pulled them out and put a set of duel stage Boyesen reeds with a 03 manifold with the suffer. last year I had a circle F pipe and this year I had Tim from TTR performance dyno make the pipe and it has a adjustable stinger. We found it made more torque and HP with the stinger at 19mm, we started at 23mm. The head is a custom RK Tek head that Kels made and all the porting is his work also. Last year we was trying to run the stock 97 piston with the dykes ring with bad results. This year we have a yamaha piston in it....still up in the air but I think it will work good. Ed.....when I fist rode this bike I thought to myself "now this is the type of power Ed would like" You need to take it for a ride at Hodaka days. DG

[dirty_rat]

Inquiring minds want to know!!! What Yamaha piston did you use and was it for an iron barrel cylinder or an aluminum cylinder?

Thanks

[DGardner]

The piston we used was for a 1978 - 1981 DT125.....Oh and the hodaka cylinder started out as a model 03 aluminum cylinder.

[racerclam]

Why the Yamaha piston ?

Rich

[---]

What I see is that it used to give you linear power throughout the band, and now it is lumpy from low to midrange with a couple of significant flat spots, and to say it falls off a cliff understates the problem. Clearly nothing you have done so far has helped unless you are building a trials bike. I would start with the new pipe. Toss it. And frankly it isn't the stinger. If the rest of the pipe isn't tuned for your system, the stinger won't fix that. That is neither old nor new school thought, just math. Put the circle F back on and see if your new porting is aided in any way. Hopefully you can still get usable torque and also get some revs out of it. Limited to 6,000 rpm I can't see how you get up to 55. I would have to do the math on your total gearing, including tire sizes.

Torque is a wonderful thing. Most John Deere tractors have it, and they are sexy and a hoot to drive.

[Bullfrog]

Let's keep in mind it IS a development project and a new pipe is already part of the near future plans - so lets see how it all develops.

It would be interesting to see how close these two engine specs might be on a twisty track with an old coot at the throttle (translation - a guy who uses the clutch for starts and shifts . . . but who does not fan/slip the clutch on the track).

With a Combat Wombat transmission, shifting from 3rd to 4th at 6,000 RPM would drop the engine speed to 4,400rpm. Which is a slightly more muscular spot on the power curve than the 5,353rpm the "old" engine would have seen when shifted from 3rd to 4th at 7,300rpm.

To be sure, for outright "go fast" riding, considerably more revs are needed before power starts to fall off. But right now, the "new" engine looks like it would be a hoot out in the woods.

Waiting with interest to see what develops (and hoping to throw a leg over it in a few days!!!)

Ed

[DGardner]

Like Ed said "it IS a development project" I had a dyno time scheduled for 11.30AM and I got the bike put togeather at 9.30AM, then rode it 35 miles to Tim's to put it on the dyno. So this is about as new and untested as a bike can be. We know the dyno sheet is not the best looking and the the bike could use some over rev, but it is still a very fun bike to ride! See you all at hodaka day. DG

[Bill2001]

Agreed, this is an R&D project and sometimes you have to break some eggs...

--Bill

[Kels]

I am hoping with some pipe modifications that we can get the curve to look more like this one (Green)

But for the 1st attempt "build it" from scratch.. Tim at TTR did an excellent job..

[---]

For what it's worth, since this is a developmental experiment, change only one parameter at a time. Doing the head, the porting, a completely different piston, and a one-off pipe all at once, you have no way to determine what works and what doesn't, or which part of this has increased torque and which has cut off the ability to rev more freely.

The pipe should be built around the porting, rather than the other way around, so if the pipe was based on stock porting, and then you changed that porting, it's a crap shoot if the pipe will work.

In any experiment, limit variables to one at a time. If you have a stock head, put it back on and see if something changes. Put a stock pipe or the Circle F back on and see if things change. Can't change the porting at this point, but you can reduce the variable count.

My guess is that the pipe isn't complimenting the other things you did. I can't see the fluted head being an issue, and unless the Yamaha piston is very different and is part of a complete port timing and compression shift, I don't see the piston being an issue either. The porting, who knows? Depends on what was done. But since it ran okay with the old pipe, that's an easy try. You can even verify your ignition timing. Make sure that isn't way off.

[Kels]

Shorty...

With all due respect.. We do not need/require your advice (as poor as it is), I do this for a living and have a VERY good handle on how to mod/design an engine and the order of operations...

This is NOT an experiment... It is a methodical "Process" that is common place in the 2 stroke engine building world.

We have PLENTY of methods to determine how each component effects the other.

[---]

Bull.

[dirty_rat]

WOW,

And all this time I thought this was a nice friendly chat group. Then, along comes KELS and he starts treating people as if they are dirt and not worthy of an opinion (especially if it seems to him to threaten his self esteem). KELS, if you don't want to get along with others, or can't, why don't you just stop posting on this site.

[---]

Dirty rat,

Not to worry. Kaptain Kels clearly has the situation in hand. I should never had cared to offer an observation so the fault is mine. Here we have a process that has so far taken a bike from 14 hp to about 11 (inspirationally close to an Ace 100), inserted what looks like four flat spots into a curve that previously had none, and caused the engine to sign off at 6,100 rpm instead of 7,400. Seen in its correct perspective, this is progress, is it not?

My intention was to help if possible in getting doug's engine to perform a bit better through simple comparison and control of variables, and to encourage in that process. Seems I insulted instead. My bad.

So we will simply wait for the whole thing to play out, so that we may be instructed and informed in the end. What's wrong with that?

[hodakamax]

Love it AZ, keep after em!

Maxie

[Bullfrog]

Encouragement might sound something like, "Hey - the "new" engine is producing 63% more power at 5,200rpm than the "old" engine did at that engine speed. Cool! Let us know how the engine performance changes as the development process continues."

Ed

[---]

Except it isn't. The 11 that it makes at 5200 is 57% "more than" the 7 it made before, not 67%. If that were the intention, fine. As I said, if trials is the target, it's getting there. One might also say it now makes only 35% of the power it used to at 7300. Cherry pick all you want. What is shown is, hopefully, not the final product. Even Doug and Kels have agreed that it isn't done yet or where they want it to be. I was trying to identify why it is what it is.

[Bullfrog]

Interesting. We don't even read a graph the same way. (6.8 VS 11.1)
Ed

[Kels]

As stated earlier, you are NOT offering any encouragement, just condescending remarks which is the "norm" for you and this forum.

For your information ,the GOAL of this engine is to WIDEN the effective power band.. Yes, create MUCH more LOW END POWER and give little to no top end power change ..

We all know how much low end power these engines have in stock form.. right??

The low end power of this engine is where Doug wants it..

Getting the over-rev will be fairly easy with some simple pipe modifications. This will happen when Doug returns..

Looking at the peak power vs the area UNDER the curve is a common mistake made by people who do not understand what it takes to make an 85 octane STREET-BIKE Engine.... Not a race BIKE Engine.

Like previously mentioned.. The order of operations for this build has been carefully planned out and is progressing very nicely.. The pipe is "1-off" and is 10" (inches) LONGER than the previous pipe.. put that in your calculator.

Once completed the dyno graph will , hopefully, resemble the one I mocked up and will be an engine that is made for street running but would also dominate on a moto cross track... The piston will last longer, the engine will rid itself of heat more efficiently, and it is able to "lug" (something Wombats are not known for) and still run 70MPH on the highway.

The Bike will be at Hodaka Days this week.. Throw a leg over it and then tell us how poor it runs. AGAIN--> Area under the curve!!!

Time ran out.. the bike was finally fitted with its new components just last Friday.

Work will continue once time permits.

As it sits now, it is a nice improvement over the previous set up .. which, the previous set up was a nice improvement over stock (about 75% power increase improvement over stock power)

Feel free to post your dyno graph.. Would love to see it..

[dcooke007]

As stated earlier, you are NOT offering any encouragement, just condescending remarks which is the "norm" for you and this forum.

Feel free to post your dyno graph.. Would love to see it..

Kels,
Condescending remarks have not been the norm on this forum ......as a whole. This was a nice place to share ideas and get encouragement for your Hodaka projects and have some fun. Until GMC arrived.

Danny Cooke

[hodakamax]

Love it AZ, keep after em!

Maxie

Hey Doug, that was a comment on clashing personalities, not your cool project. It just struck me funny. Keep up the good work.

Max

PS-- And did you see those cool Maicos I posted for you the other day?

[Modracer70]

How will the piston last longer? The Yamaha piston? And how will the engine remove heat more efficiently?
Thanks, Dave

[Kels]

Piston can rid itself of heat fast and more efficient..

This allows the cylinder to run cooler, the piston to run cooler which will make the piston last longer and the engine will produce more power..

Running 70's technology in a 70's engine is fine.. but running a more modern designed piston will allow for improvements..

Hence, the reason why any modern bike does not resemble any bike produced in the 70's or 80's