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Author Topic: Texas Two Step Taco  (Read 6509 times)

Offline 1fasgsxr

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Re: Texas Two Step Taco
« Reply #210 on: Nov 08, 2018, 13:21:33 »
heavier one is where it seems to work best.  What did you settle on for gearing?
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Offline Texasstar

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Re: Texas Two Step Taco
« Reply #211 on: Nov 08, 2018, 14:08:14 »
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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Offline teazer

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Re: Texas Two Step Taco
« Reply #212 on: Nov 08, 2018, 16:56:33 »
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.

Offline Texasstar

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Re: Texas Two Step Taco
« Reply #213 on: Nov 08, 2018, 17:16:36 »
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 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.   


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...


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Offline teazer

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Re: Texas Two Step Taco
« Reply #214 on: Nov 08, 2018, 20:16:23 »
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?   

Offline Texasstar

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Re: Texas Two Step Taco
« Reply #215 on: Nov 11, 2018, 10:14:09 »
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?


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Offline teazer

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Re: Texas Two Step Taco
« Reply #216 on: Nov 11, 2018, 12:56:10 »
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.

« Last Edit: Nov 11, 2018, 13:07:49 by teazer »

Offline Texasstar

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Re: Texas Two Step Taco
« Reply #217 on: Nov 11, 2018, 15:00:02 »
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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Online der_nanno

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Re: Texas Two Step Taco
« Reply #218 on: Nov 11, 2018, 16:24:31 »
So...  how tight was the squish?
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Offline Texasstar

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Texas Two Step Taco
« Reply #219 on: Nov 13, 2018, 08:42:51 »
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.


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It's an optimization exercise and not a maximization trip.-Teazer


And though she be but little, she is fierce - WS
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Third Times a Charm cb175
http://www.dotheton.com/forum/index.php?topic=66169.0

Honda Cb175 Victoria!

www.dotheton.com/forum/index.php?topic=52299.0

Honda Cb200 Lucky!
http://www.dotheton.com/forum/index.php?topic=45872.0

Bultaco El Montadero 360

http://www.dotheton.com/forum/index.php?topic=64349.0