Texas Two Step Taco

Texasstar

Can't is a four letter dirty word
Sonreir said:
That always confused me about two stroke timing as well. It seems a lot of them use a distance measurement rather than degrees. I never did figure out why.
Matt I chose this category because we didn’t have a Drag bike category on DTT. Will all pictures posted on DTT through tapatalk stay on DTT’s servers?


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teazer

Over 10,000 Posts
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And yet a Hitachi has a flat "curve" that retards slightly because of the delay ie the time it takes for the electrons to get to their destination. They travel at the same speed, but as motor speed increases, they have less time to get there, so they arrive later and later.

That video is neat but doesn't show us what happens above the speed of that drill which is probably around 1200 rpm. What happens at say 6,000 or 10,000?

If you want more mental exercise, https://www.hindawi.com/journals/jc/2011/678719/

Yamaha published papers back in the sixties about the elements that change the timing curve in an old style analogue ignition with high and low speed coils.

New topic. Mm down or degrees. Good question and easy to answer. With a small degree wheel, it's hard to be accurate to +/- 1 degree. On say a Yamaha twin with 110mm con rod and 54mm stroke let's look at teh numbers
19 degrees = 1.82mm
20 = 2.02
21 = 2.22
.
.
45 = 9.57
46 = 9.96

With say a 65mm stroke and 130mm rod, the numbers follow the same trend
19 = 2.20mm
20 = 2.43
21 = 2.68
22 = 2.94
Close to tdc, the mm difference is also small but the larger the degrees, the larger is the difference in mm so it is much easier to set accurately in mm than it is in degrees - as long as you use a TDI (dial gauge) and not a plunger rod.

Unlike a 4 stroke at "normal' revs that needs more advance as revs rise because there is less time to burn, a high performance 2 stroke has rising cylinder pressure and temperature and needs progressively less advance as revs rise.

Try 32 or 30:1 or even down to 25:1 for better cylinder cooling and more power. Jennings liked 16:1 and would have been even lower numerically if he could. It would be nice to see how those tests come out with modern oils.

A single cylinder 'taco has a long stroke and large piston and huge combustion chamber surface area to absorb heat and cause issues - but you will only run for about 30 seconds all up, so let's start pushing the technology. You could also machine a billet head and play with different combustion chamber shapes. See BB for details.

Maybe it's time to cast up a new cylinder with 5 or more transfers and auxiliary exhaust ports like say a CPI Cub motor and water cool it like a late model TSS like the one I had to sort for a client a few decades ago. What did AJR do with their Bultaco TSS air cooled replica ports and head design? https://ajrmotocicletas.es/epages/c3bd36bc-2950-45ce-8ec9-2ca023feb311.sf/en_GB/?ObjectPath=/Shops/c3bd36bc-2950-45ce-8ec9-2ca023feb311/Products/M09-200

Does that look like yours? The head is a more modern design too.

https://ajrmotocicletas.es/epages/c3bd36bc-2950-45ce-8ec9-2ca023feb311.sf/en_GB/?ObjectPath=/Shops/c3bd36bc-2950-45ce-8ec9-2ca023feb311/Products/M09-150
 

Texasstar

Can't is a four letter dirty word
Old worn out Bultaco

Cylinder pressure: 95psi

1 and 2 expansion chamber 26 whp
3 expansion chamber reduced stinger ID 26.2 whp
4 stock pipe 22 whp

Bultaco Montadero Dyno run

“The engine was the centerpiece, securely bolted into the frame, aesthetically a beautiful piece of work with oval cases and a squat nine-finned cylinder. Horsepower, with its 10:1 compression ratio, was rated between 32 and 33 at 6,000 rpm, but more importantly peak torque was at a nominal 5,000 rpm. Do not forget that up until the mid-1960s, big British, low-revving thumpers were considered the bike of choice for off-road.”
https://ridermagazine.com/2014/01/29/retrospective-bultaco-montadero-360-1968-1972/




Well we have a starting place.
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teazer

Over 10,000 Posts
DTT BOTM WINNER
And from there it's onwards and upwards....

Those are a little better than our 180cc CB175 sloper but not by much. ::)
I suspect the 'taco makes a lot more torque though.

What is your target? For a drag motor maybe 40 to 44. ;)
 

Texasstar

Can't is a four letter dirty word
teazer said:
And from there it's onwards and upwards....


I suspect the 'taco makes a lot more torque though.
“Those are a little better than our 180cc CB175 sloper but not by much. ::)

Yea I am just happy now that I have empirical evidence that my smaller stinger makes more HP

What is your target? For a drag motor maybe 40 to 44. ;)

Well our friend with the Pursang 360 says he is making mid 50’s
Nitrous? Lol

Zeke has been trash talking me so I am highly motivated. However he is helping me make a stretched swing arm
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Texasstar

Can't is a four letter dirty word
Here is a race where Zeke beat me. I was on Lucky our Cb200 (left) going up against Zeke on the Bultaco (right) at the drag strip.
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the cb200 in its state of tune at 18 whp was very much a contender for the Taco. I am 217 lbs and Zeke was 150 ish You would think the Bultaco even as a dirt bike would have whooped Lucky. Lucky was 5/6 against the taco on the grass sprints and on the strip. Zeke was handicapped with the faulty shifter. I was short shifting... Zeke doesn’t know how to do that...shhhh. Oh Coker says we are good to 100-110 mph on the tires.


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Texasstar

Can't is a four letter dirty word
teazer said:
What is your target? For a drag motor maybe 40 to 44.
the Bultaco Bandido made 42 bhp so that is maybe 35 whp? And at 7500 rpms the piston speed was only 3175 ft./min.

Cycle World has the Bandido at 8.23 seconds in the 1/8th mile at around 80 mph. So I would think 40-44 whp would be a good goal.

The only differences I can find between the Bandido and the Montadero is the expansion chamber, ignition timing, and the weight of the flywheel. Everything else seems to be the same.

“ I am beginning to believe the engine is ancillary to the Pipe” ~from the Man Down Under. So does BB with his titanium expansion chambers that our friend is welding up.

The problem with my head is the single spark plug and cooling. Zeke’s has twin plugs. Cycle world said that the reason why Bultaco went to two plugs is to help cool the head by increasing flame propagation.

The man from down under had the same problem with heat in his Pursang build and he went to a Husky Head and that took care of the detonation problem.


We pegged the Teazer tach plus 15000 Rpms yesterday (7500 Rpms )actually and the bike didn’t mind it at all. Of course it really didn’t help the HP at all.

The Chinese CRF magneto will take care of the flywheel weight. I would like to get Bandido pipe for testing. I wonder if that was built using Jennings data? I have just started looking at Blair. So much to learn.

I will be reacting on the third Yellow...so will Zeke.





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Texasstar

Can't is a four letter dirty word
Video from our Bultaco Dyno Test https://youtu.be/eoGcWHOMqNk


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teazer

Over 10,000 Posts
DTT BOTM WINNER
Couple of thoughts in no particular order.

Reaction time: .6 vs 0.6. Hmm. Zeke won before you started rolling. All your times - 60 foot to 1/8th are better than the taco so practice the launch timing. He is much younger and his reactions should be significantly better than yours, so you need to be consistent.

Ports or pipes: I have run so many sims through MOTA that show that the pipe is really really important - bigly. I created a modified Kart pipe for a customer some years ago and after about 100 or so runs, managed to fine tune it to get an extra HP and that was worth a second a lap. I ran a bunch of sims on a GT380 with stock ports and a good pipe versus well ported and an OK pipe and the optimized pipe and stock ports was marginally better than good porting and an OK pipe. Of course a great pipe and port combo was significantly better than either. On the Phat Trakka, I have gone from really mild porting to close to TR porting and on the same street pipes, it's stuck at the same revs and not a lot more power. Pipes are critical.

Is your new pipe being designed by someone who knows what they are doing or are they replicating an existing pipe dimensions?

ET and MPH: Our stock RZ350 which makes about 56 rwhp manages 1/8 times in the 8s and MPH in the low 80s. Your Taco is slightly larger capacity and with some work should be achieving something close to those numbers with a light rider. A stock heavy GT550 with 60 pound heavier rider and stock 32-35 rwhp managed low 70s at low nines.

Time to get smoking. And that reminds me, if you need 2 stroke oil, go and see the good people at Moto Liberty at 635 and 35. They used to sponsor our RS250 Cup bikes.
 

Texasstar

Can't is a four letter dirty word
Zeke reacted on the third yellow light. I waited for green. I won’t make that mistake again LOL. I am going on a Keto diet today to see if I can drop 10 in a month. I am down to 207 down 10 already from last year. Cheap weight reduction. Zeke is up 15 lbs from last year. Buying extra large pizzas at Walmart for him. The plot thickens.

I love old cycle world articles. Using a cooler plug on the front cylinder is crucial.
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teazer

Over 10,000 Posts
DTT BOTM WINNER
Nice bracket.

Why is the front plug colder? That would be because it's closer to the exhaust and the rear one is bathed in cool transfer (scavenge) gas. Junk that head a go billet with concentric squish and central plug.
 

teazer

Over 10,000 Posts
DTT BOTM WINNER
Texasstar said:
Zeke reacted on the third yellow light....

In which case he's a little slow. They say that minimal time to see the light and react is 0.5 seconds, so if you react just as the last orange starts to light up, in theory you get a 0.0 RT. I hear racers talk about when they start to move with comments about as the light just starts to light up or later. I can't see things that fast, let alone react, so I try to leave as soon as I see the last orange illuminate. Just don't stage too deeply if the plan is to go on 3 or you will redlight and hand him the win.
 

Texasstar

Can't is a four letter dirty word
We are going to be revvin’ like a banshee... CRF 50 Chinese magneto.
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Brodie

Gold Coast, Queensland
DTT SUPPORTER
Those are quite light. Check the magnets though. I have had one come loose before.
 

Texasstar

Can't is a four letter dirty word
Brodie said:
Those are quite light. Check the magnets though. I have had one come loose before.
Thanks man! Will do.


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Texasstar

Can't is a four letter dirty word
Zeke got us jigged up for the new swing arm the last two nights and bent the Chromoly
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I made the bushings
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zeke started coping
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Texasstar

Can't is a four letter dirty word
teazer said:
Nice bracket.

Why is the front plug colder? That would be because it's closer to the exhaust and the rear one is bathed in cool transfer (scavenge) gas. Junk that head a go billet with concentric squish and central plug.
Yes we are going to build our own...


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