Texas Two Step Taco

That head should be a significant improvement. It should be possible to lose a little metal around the outside and maybe groove it to lose a few grams, but don't thin it too much and have it distort.

Did you determine why the ring snapped? It's hard to see from the video but with a wide port, it's important to have sufficient curvature of the roof and a suitable chamfer to ease ring back in after it bulges into the port. A square top makes a little more power by creating more time area and because the pressure wave is stronger but it kills rings. That higher pressure wave also creates a sharper exhaust note. So once again it's a case of finding the optimum. Raise the center of the port which will add even more exhaust time area and be easier on the rings.

14:1 CR sounds fine for an air cooled machine. If you go much higher, the combustion chamber gets to be too flat and that can hurt flame propagation, pressure rise and power. More optimization decisions. :)
 
teazer said:
That head should be a significant improvement. It should be possible to lose a little metal around the outside and maybe groove it to lose a few grams, but don't thin it too much and have it distort.

Did you determine why the ring snapped? It's hard to see from the video but with a wide port, it's important to have sufficient curvature of the roof and a suitable chamfer to ease ring back in after it bulges into the port. A square top makes a little more power by creating more time area and because the pressure wave is stronger but it kills rings. That higher pressure wave also creates a sharper exhaust note. So once again it's a case of finding the optimum. Raise the center of the port which will add even more exhaust time area and be easier on the rings.

14:1 CR sounds fine for an air cooled machine. If you go much higher, the combustion chamber gets to be too flat and that can hurt flame propagation, pressure rise and power. More optimization decisions. :)
Why did the ring fail? This piston has an L shapes upper ring which seems strange. BB said he hasn’t seen those since the 70’s. Someone took a hack saw to the intake side of the piston to increase the duration will post a picture later.

Thank you for the information on the porting.

Are you watching the Man Cup Finals this weekend?


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Texasstar said:
Why did the ring fail? This piston has an L shapes upper ring which seems strange.

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Oooh dyke rings, someone was worried about high rpm ring flutter...


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https://youtu.be/CpsrSNJugmI

This is amazing....we have been watching James FUSION weld up these titanium expansion chambers. Titanium is a reactive alloy and attracts things into the weld puddle like no other metal we have welded. Just a speck of dust causes the arc to wander. It also needs to have low amperage spark initiation. James is using our Lincoln Electric Precision TIG 225 which has micro-Start TIG TM technology and is “capable of independently welding off of its electronic power supply when the amperage is down to the minimum rated 2 amps. As the operator depresses the foot Amptrol to increase the current, the main welding circuit (i.e. transformer and SCR bridge) turns on and provides amperage. The technology assists the transformer SCR choke circuit with its special electronic welding circuit instead of completely relying on chokes to smooth the arc as do conventional machines. The result is a very stable and smooth output at low amperage levels.” Our friend had an older conventional machine that did not have this technology and it was almost impossible to weld the thin titanium. However, James’s welder is programmable for less than 1 amp for his day job welding Porsche titanium roll cages...and I bet it is a dust free environment.


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Beautiful welds. Not at all like mine.....

Dykes rings are the bees knees but like most things in life have some issues. Check you exhaust port shape and chamfer when you get a chance.
 
teazer said:
Beautiful welds. Not at all like mine.....

Dykes rings are the bees knees but like most things in life have some issues. Check you exhaust port shape and chamfer when you get a chance.
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this is the exhaust port there is a chamfer at the top of the port. Take a look how ported out the floor is...



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Hmm. That floor is like most Yamaha twins with a big step. Admittedly, by the time the port is fully open, there's typically not a lot of pressure or flow over that step, so it's not quite as bad as it looks. Most of the pressure should have been dissipated by the time the transfer ports open. If not we get reverse flow. And that does happen.

The top leaves a lot to be desired and is almost flat, so the ring will be hitting that almost straight edge and that can't have helped. Check your port map and see if you can raise the center to give the rings an easier time and then get that exhaust port a better (more consistent) chamfer.

You may also want to think about relieving the exhaust bridge a little so that when it expands into the barrel, it won't put as much pressure on the rings or piston.

There is room for improvement there for sure.
 
Bultaco Femsa electronic ignition rotor
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one brass pole or copper
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two non magnetic
 
Zeke has been walking around taunting me with the L sign on his forehead but I learned a lot racing the Bultaco. Fuel changes made a huge difference. Going 93 octane to 108 c12 causes the bike to start in reverse and kicks the crap out of your leg. So the first thing I am working on is making a reductor for the Zeeltronic BB gave us...we will have to add a few coils and waste some spark but we will then be able to see what the bike wants instead of guessing.
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I plan on mounting the reductor on the back of the flywheel shaft.

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Zeel should make things a lot easier for sure. That's the DC CDI unit. Very nice.
 
This is why you want a programmable ignition for a two stroke. This is the Zeeltronic and Skip to 1:10 to start and watch the ignition degrees as the Aprilia RS250 revs.

https://youtu.be/gcYwvqEfNIE


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If we had engines that revved to 12k with powervalves etc which made around 240hp/liter, we'd all need programmable ignitions. Unfortunately, our old clunkers are not so responsive to ignition timing - except when it's too advanced on the day that air is dense and we are jetted lean......

The higher teh state of tune, the more that we need to get timing spot on to get the most out of a motor. At low revs with zero to negative pipe effects, we can light the fire much earlier. On the pipe at higher revs compression and temperature are higher and we need less advance to get peak pressure at the right time (14-16 ATDC).

What's really nice with programmable ignition on our old bikes is that you can set timing quite late at startup to reduce the chance of kickback and reverse running. On a low state of tune drag bike that only runs at wide open throttle and in the powerband, there's probably not as much need for a complex ignition curve, but it all helps.

Sleds are interesting. Some Polaris 2 strokes had peak advance as low as 3000 and retarded slowly from there. Others don't reach peak advance until 6000 (19 degrees) and drops off to around 11 degrees at 8,000. What Sled guys spend a lot of time on is setting up the clutching to get the most out of what power it makes.

I see lots of dyno time in your future.
 
teazer said:
If we had engines that revved to 12k with powervalves etc which made around 240hp/liter, we'd all need programmable ignitions. Unfortunately, our old clunkers are not so responsive to ignition timing - except when it's too advanced on the day that air is dense and we are jetted lean......

The higher teh state of tune, the more that we need to get timing spot on to get the most out of a motor. At low revs with zero to negative pipe effects, we can light the fire much earlier. On the pipe at higher revs compression and temperature are higher and we need less advance to get peak pressure at the right time (14-16 ATDC).

What's really nice with programmable ignition on our old bikes is that you can set timing quite late at startup to reduce the chance of kickback and reverse running. On a low state of tune drag bike that only runs at wide open throttle and in the powerband, there's probably not as much need for a complex ignition curve, but it all helps.

Sleds are interesting. Some Polaris 2 strokes had peak advance as low as 3000 and retarded slowly from there. Others don't reach peak advance until 6000 (19 degrees) and drops off to around 11 degrees at 8,000. What Sled guys spend a lot of time on is setting up the clutching to get the most out of what power it makes.

I see lots of dyno time in your future.
There is always nitrous....;)


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teazer said:
Now you're talking..... :)
Parts on the way
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new head is finished and on its way. Zeke has a broken stud bolt on his 900ss but got a job as a tech for Ducati this summer. So we are back to our little competition. So the next step is finding a way to start this on the line with 14:1 compression.


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