Texas Two Step Taco

Help out an old guy with no electronics background …...…...………….. Why would you want spark at TDC?

We are using a second fuel map as launch control. Retarding the timing to Tdc limited our revs to 6k in the video. Essentially making a two step but by using the fuel instead of limiting spark. It will limit the revs on the line to 6000 rpm and when you let go of the clutch it will switch maps giving the full revs. If we don’t foul a plug. At least that is the theory. Hold my beer watch this. I have an idea we will be buying another ignition because a two step makes a huge difference in your 60’ times. We are tinkering.


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+1. it's too hard to launch hard in a sprint or drag race by holding the throttle or blipping it, so what drag racers do is to add a "two step". WTF is a two step you ask. It's not some sort of old fashioned dance.

Basically, you want to leave the line with a pre-determined revs. Let's say 6,000 so how do you hold it at 6,000 until it's time to go and then wind open the throttle? A 2 step holds the engine at whatever revs you want, and then allows the motor to step up to full revs when the clutch is out. A 2 step is an electronic rev limiter that holds revs at say 6,000 while the throttle is wide open.

As the clutch is released, revs would start to drop as it engages, so the throttle is wide open and as the clutch lever is far enough out, it switches that launch rev limit off and the motor can now rev flat out until it hits the real rev limiter.

Shifting is done wide open throttle on a shift button, so you stage and then you open the throttle wide open and at the appropriate time release the clutch without changing throttle position at all until the bike passes the finish line at the 1/8 mile or quarter mile mark - depending on the strip.

It's about consistency as much as it's about time (ET).
 
Speaking of consistency... the Bultaco Bandido and Montadero have a major problem with shifting. False neutrals etc. Fortunately after complaining about it on social media I was sent this!!!!
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Here is what the incorrect position with the trigger jammed for the pawls on selector looks like if you are in neutral. What did the racers have to do? You needed to tap shifter down to up shift.
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Here is what the pawls should look like with the update
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You have to modify the cover by removing 1mm from left side. Chucked it up in a rotary table on the mill.
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Thank you Gentlemen for the explanation. Does the shift button momentarily kill the ignition to take the load off the gear dogs?
 
I never owned a Bultaco but raced a Bandido owned by a shop in our area. Shifting was a fishing expedition so I'm guessing the shop bike had never had the "fix".
 
I never owned a Bultaco but raced a Bandido owned by a shop in our area. Shifting was a fishing expedition so I'm guessing the shop bike had never had the "fix".

That is the best explanation I have heard for shifting the Bandido Montadero


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I keep hearing that 14:1 is too much compression for our drag bike. If that is the case why did the TSS have 13.5:1?
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We fried the last set of composite plates on the dyno because they were dry and not in oil. Any advantage of going with the original metal clutch plates? I have two NOS sets of metal plates and one set of composite. Should you soak the composite in oil first?


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The 125 and 250 engines may have had a high CR but the TSS350 CR was actually very low. The reason for this was that it simply wasn't possible to bump start the engines with a higher compression, the rear wheel would just skid. I found the same problem with the Metralla - even in a high gear the 370 would just drag the tire. But even disregarding this problem it'd make sense to use a moderate figure - the heat and detonation tendencies would be a couple of reasons.

I think I've mentioned this before, but CRs with two-strokes are a game of diminishing returns. Every time you try to get an increase in torque by raising compression you lose some of it due to the decrease in EGT and pipe effectiveness. Not only that, but with a big oversquare engine like the 350 Buls there are greater heat losses with the big chamber and piston. As it turns out there isn't a hell of a lot of difference power-wise between say 9.5 or 10:1 and say 12:1. For a 350 Bul (especially on gas, and especially if you want to raise the rpm band) then a conservative figure will give good results.

As for clutches, the stock steel plates can take a fair bit of abuse. The type of oil you use has an effect on their torque capacity too. Depending on the material used composition plates may or may not survive running dry. I have no experience with the Bandido clutch but they look very similar to the Pursang style, only a bit bigger. Whatever plates you use you really need to consider them as a consumable item - even with the two step I imagine you'll be doing some practice starts to get your off-the-line technique sorted, and the launches themselves will be pretty hard on the clutch. I did some testing of different plates and oils some time ago; I'll post my notes if I can find them.
 
The 125 and 250 engines may have had a high CR but the TSS350 CR was actually very low. The reason for this was that it simply wasn't possible to bump start the engines with a higher compression, the rear wheel would just skid. I found the same problem with the Metralla - even in a high gear the 370 would just drag the tire. But even disregarding this problem it'd make sense to use a moderate figure - the heat and detonation tendencies would be a couple of reasons.

I think I've mentioned this before, but CRs with two-strokes are a game of diminishing returns. Every time you try to get an increase in torque by raising compression you lose some of it due to the decrease in EGT and pipe effectiveness. Not only that, but with a big oversquare engine like the 350 Buls there are greater heat losses with the big chamber and piston. As it turns out there isn't a hell of a lot of difference power-wise between say 9.5 or 10:1 and say 12:1. For a 350 Bul (especially on gas, and especially if you want to raise the rpm band) then a conservative figure will give good results.

As for clutches, the stock steel plates can take a fair bit of abuse. The type of oil you use has an effect on their torque capacity too. Depending on the material used composition plates may or may not survive running dry. I have no experience with the Bandido clutch but they look very similar to the Pursang style, only a bit bigger. Whatever plates you use you really need to consider them as a consumable item - even with the two step I imagine you'll be doing some practice starts to get your off-the-line technique sorted, and the launches themselves will be pretty hard on the clutch. I did some testing of different plates and oils some time ago; I'll post my notes if I can find them.

Well I am grateful I listened to your advice and switched heads. Pretty sure I would have melted another piston while dialing in the Zeeltronic if we used the 14:1 head. If I had to do it over again I would spin the engine over without the plug to set the static timing and not follow the Zeeltronic instructions.


We are making progress. We should be ready for the dyno this weekend. Have a few things to button up for putting the engines under a load and finishing the break in procedure.


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Thank you Gentlemen for the explanation. Does the shift button momentarily kill the ignition to take the load off the gear dogs?

Made a little video showing the components of the pingel airshifter




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So do you have a small 12v battery to power the solenoid?

On mine I use a small (4 ounce) CO2 bottle and regulator instead of an air tank. CO2 is around 3000psi and regulator drops that to 120-140 (adjustable). If you use a regular lead acid battery, take a look at a 4 cell LiFePo RC battery. They weigh next to nothing and are around 14v. You could probably get away with a 3 cell at 11v if it just drives the solenoid.
 
So do you have a small 12v battery to power the solenoid?

On mine I use a small (4 ounce) CO2 bottle and regulator instead of an air tank. CO2 is around 3000psi and regulator drops that to 120-140 (adjustable). If you use a regular lead acid battery, take a look at a 4 cell LiFePo RC battery. They weigh next to nothing and are around 14v. You could probably get away with a 3 cell at 11v if it just drives the solenoid.

I am using https://shopspeedcell.com/collections/batteries have several around the shop. Since we are total loss it is also powering the Zeeltronic. What is nice is that I can move it from bike to bike with the quick connectors.


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Have a few things to button up for putting the engines under a load and finishing the break in procedure.


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I don't know where the whole "heat cycle" thing started but it's all over the internet, and as you pointed out even LA Sleeve list it. The thing is though it doesn't do a thing - you can heat cycle it all you like but it has no effect on the piston at all, structurally or dimensionally. The only way I know of to make a forged piston conform (and get the initial shrinkage over with) is with high load and rpms in very short bursts at first, getting progressively longer.

In an attempt to shorten the break-in time of the forged Wossners I tried baking them in a snug fitting heavy steel muff at about 220C for an hour or so. It works - they shrink about .0025" so I only need a fairly short break-in on the dyno before they can take WOT continuously. The Wossners are very light and thin though - for a thick heavy piston like yours I suspect you may need a fairly long time to knock them into shape.
 
Not having this is probably one of the hundred reasons I stuck the other piston. Testing the Zeeltronic Rev Limiter at 6k.


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