Texas Two Step Taco

First 60’ is killing me I am 52 left


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Better with heavier flywheel
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left sometime on the strip with the second reaction time
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Kicked by a Bull. 108 octane c12 has a slower flame propagation LOL started in reverse.
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Zeke on his Ducati 900ss https://youtu.be/pJtle6xXUk0


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Second day of The Twist Off. Had some challenges the first day. Bike started in reverse because of the C12 race fuel higher octane. Had to push start the Bultaco for both days. Magneto was shorting to the smaller flywheel at higher revs. Changed to the heavier flywheel for the second day and 13/54 gearing from 15/54. Removed the wheelie bars. 93 octane 32:1 with semi synthetic oil. Feathering the clutch was a challenge and you realize why these guys had popeye forearms. Ran a 10.41 and bettered our best of 10.81 the day before. We lowered our our previous years ETA time by 2 seconds. Engine is old and tired and so am I. Engine only has 95psi compression and we have seized it twice do to overheating. We had a blast!

https://youtu.be/nd9eoBfsXFk




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pidjones said:
Rubbed wires are a pain.
Yes...Had two runs after the flywheel change and no stutter on the upper end...then headed back to the staging area and it died. Checked the plug and had no spark, checked woodruff key a usual suspect and it was ok, checked points and they were grounded. Those two wires come together under the points.

Easy fix and now we can test the other pipes.




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1fasgsxr said:
heavier one is where it seems to work best. What did you settle on for gearing?
13/54 this past weekend. Changing to a lighter Honda rear wheel and will try 13/56 next time out on the 1/8.


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Getting there. Progress can be frustrating.

Just for giggles I looked at some recent numbers from a stock RZ350 ridden by my wife who is a little cautious because she would refer not to loop it. She has enough metal in her leg and wrists already. She is doing around 9.7 at 82 or so in the 1/8th. A mate of ours was doing 9.5 at 72 on a stock GT550 that weighs a ton and he's not light either. With ported barrels he's doing a touch faster but with 1/2 second better 1320 times and already 15 MPH better than stock at the top end.

The Bultaco is much lighter than either of those bikes and should make slightly more than the 37 or so stock rwhp of the stock GT550.

For next time, maybe consider a lock up clutch that will allow the motor to sustain its revs as you get off the line. And for the pipe, focus on torque across the mid to top end rather than absolute peak HP. That will let it pull harder.
 
teazer said:
Getting there. Progress can be frustrating.

Just for giggles I looked at some recent numbers from a stock RZ350 ridden by my wife who is a little cautious because she would refer not to loop it. She has enough metal in her leg and wrists already. She is doing around 9.7 at 82 or so in the 1/8th. A mate of ours was doing 9.5 at 72 on a stock GT550 that weighs a ton and he's not light either. With ported barrels he's doing a touch faster but with 1/2 second better 1320 times and already 15 MPH better than stock at the top end.

The Bultaco is much lighter than either of those bikes and should make slightly more than the 37 or so stock rwhp of the stock GT550.

For next time, maybe consider a lock up clutch that will allow the motor to sustain its revs as you get off the line. And for the pipe, focus on torque across the mid to top end rather than absolute peak HP. That will let it pull harder.
Zeke learned something
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torque matters and he shifted at 7500 into fourth instead of holding 3rd out to redline and significantly dropped his ETA. You can see where he figured that out. His bike has more torque than HP.


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lock out clutch...I like that idea! Also going to drop some more pounds off the rear wheel.

Going to refresh this engine eventually. But would like to see what we can do with the other pipe first. The slick on the grass was a blast... https://youtu.be/j8RmXHEpqrc


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That looks insane. 95psi is a little low to be expecting stump pulling power, but as compression rises, so does combustion chamber temperature. I run 150-165 on the street on a 70mm bore 65mm stroke but the timing is dialed back a little from stock depending on fuel. That's watercooled, so easier to control temps. Did I hear you were thinking about machining a multi port barrel and head from billet?
 
teazer said:
That looks insane. 95psi is a little low to be expecting stump pulling power, but as compression rises, so does combustion chamber temperature. I run 150-165 on the street on a 70mm bore 65mm stroke but the timing is dialed back a little from stock depending on fuel. That's watercooled, so easier to control temps. Did I hear you were thinking about machining a multi port barrel and head from billet?
well this design won’t work...this is Zeke’s M70 Bultaco with two plugs. Is this what happens when you have no squish? What was Bultaco thinking? https://youtu.be/2yVF0kgK9Ik


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Bloody mice got in the barn again? Get a better cat :)

Interesting. That head has two squish bands with a bathtub chamber and twin plugs to fire it up in that long tub. That means it has two flame fronts and a high probability of detonation when they collide. Much better to have a concentric squish band and make sure that the thickness is right.

You can see either contact in the squish or no burning because it was tight compared to the rest of the crown - especially at the exhaust port. It looks like it has been detonating for a while. See the carbon on top of the holes?

OK so it detonated. The question is why.

Was the exhaust too restrictive causing a heat soak effect?

Was the fuel too low octane level and could not resist detontation?

Was compression too high?

Were transfer flows not balanced to provide sufficient turbulence?

Did the cast barrel heat soak raising temperatures past critical?

Too much ignition timing?

Was the bike hot when that run started? It needs to be cool

Mixture too lean perhaps? There is no wash pattern to see, suggesting that the mix is lean, but the crown also shows little sign of overheating which we would expect to see with that amount of detonation. Usually the crown will be a dull gray color from molten aluminum that one is not.

That suggests perhaps the thing didn't so much overheat as have a fuel problem. That could also be because it was ridden at lower speed after all that damage had occurred.

EDIT: I had another look at the video - larger this time and it looks more like a broken ring than detonation. Deto usually looks like sand blasting with coarse medium. That appears to have sharp indentations. That might be from ingesting a foreign object or a broken ring . You can see a chunk of the Dykes ring is missing from the exhaust side and probably from insufficient chamfer or the top of the port is too square.
 
teazer said:
Bloody mice got in the barn again? Get a better cat :)

Interesting. That head has two squish bands with a bathtub chamber and twin plugs to fire it up in that long tub. That means it has two flame fronts and a high probability of detonation when they collide. Much better to have a concentric squish band and make sure that the thickness is right.

You can see either contact in the squish or no burning because it was tight compared to the rest of the crown - especially at the exhaust port. It looks like it has been detonating for a while. See the carbon on top of the holes?

OK so it detonated. The question is why.

Was the exhaust too restrictive causing a heat soak effect?

Was the fuel too low octane level and could not resist detontation?

Was compression too high?

Were transfer flows not balanced to provide sufficient turbulence?

Did the cast barrel heat soak raising temperatures past critical?

Too much ignition timing?

Was the bike hot when that run started? It needs to be cool

Mixture too lean perhaps? There is no wash pattern to see, suggesting that the mix is lean, but the crown also shows little sign of overheating which we would expect to see with that amount of detonation. Usually the crown will be a dull gray color from molten aluminum that one is not.

That suggests perhaps the thing didn't so much overheat as have a fuel problem. That could also be because it was ridden at lower speed after all that damage had occurred.

EDIT: I had another look at the video - larger this time and it looks more like a broken ring than detonation. Deto usually looks like sand blasting with coarse medium. That appears to have sharp indentations. That might be from ingesting a foreign object or a broken ring . You can see a chunk of the Dykes ring is missing from the exhaust side and probably from insufficient chamfer or the top of the port is too square.
Bingo ring broke
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Some of us want to go faster on a slow motorcycle. Then there are those who want to go faster on a fast motorcycle. Ralf Schipmann has been going faster and faster on his H2 Kawasaki for years now. In fact if you google his name you will see everything to make a Kawasaki H2 better. Behind his kind demeanor there is a fire to improve. He has made his own patented lock up clutch, he sandcasts a modern H2 Heads, and he flies to Texas to help others go faster on their slow motorcycles. Here he designed a head with a toroidal combustion chamber for our Bultaco Drag Bike Project. 14:1 compression. 1.4 mm squish. https://youtu.be/5aM8RolC9Jo
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