misterww225

Neg. Vito's super stock pistons are cut straight across to simply advance the exhaust timing. There is extra "meat" in the piston land on these. The concept discussed here is an old method to effectively make the exhaust port top flat for a wide portion of that exhaust port. "More area plus a stronger pulse from the port "popping" open." -SlowMoe

Hmmmmm... http://bansheehq.com/forums/index.php?showtopic=114131

The CDI is charged by the stator. More specifically, a capacitor within the CDI is charged. When this capacitor is discharged into the coil the energy within the capacitor transfers to the coil, creating a spark. The energy within a capacitor is E=1/2 CV^2. Simply stated, the energy in a capacitor is only a linear function of the capacitor value, however, the energy in a capacitor is the SQUARE of the voltage. This means even a small increase in the stator voltage will dramatically increase the energy discharged into the coil and transferred to the spark plug. Therefore, just a few more turns on the stator will dramatically increase the spark energy. On the other hand, the capacitor has a voltage limitation when it begins to break down and dissipate energy in the form of heat and gradually degrade, eventually failing. A modest increase in the stator windings, I.E. voltage, can retain a reliable CDI system while increasing spark performance.

If anything, I would support putting on two(2) stock carbs per cylinder, as opposed to going to one large carb. The rationale is smaller carbs atomize fuel better and have better throttle response. Two(2) 26mm carbs are roughly equal to the same area as a single 37mm carb., and I would suspect would provide more top-end HP as well as acceptable throttle response. Why don't one of you guys with a lot of time and energy see if that works for ya? Tuning 4 carbs would keep your hands busy.

A lot of times the flywheel key shears because of severe detonation. You might want to make sure your racing fuel is a good batch.

When starting from a dead stop, larger flywheels are used to store kinetic energy to supplement the engine's torque. When you dump the clutch, the energy stored in the flywheel will tend to keep the engine RPM constant, therefore giving a harder launch. When shifting from gear-to-gear, the RPM will, again, tend to stay constant, which gives you a "jump" when shifting. The down side of a heavier flywheel is that while in a gear the engine will rev more slowly, as it is storing energy into the flywheel. Since, as mentioned earlier, drag racing is all about the launch, a heavier flywheel, not a PVL or shaved flywheel, will benefit you.

I would stagger the transfers I.E. Mains open, 0.5mm later Aux open, 0.5mm later boost ports open to produce more mid-range.

I disagree with the ascertion 1 degree = 0.021" for that would imply 360 degrees would be a 7.56" circumference. Divide that by Pi to get the diameter of the hole pattern = 2.406" diameter. I haven't measured it but that seems a bit too small. Others say that 1 degree is close to 1mm (0.03937"). That would be .03937*360/Pi = diameter of hole pattern = 4.511". That seems a LOT closer.

To measure the cc volume, lightly grease the cylinder to effectively "seal" it, then rotate and lock the the crank at TDC. Wipe the excessive grease off. Install the head/dome and fill the dome to the bottom of the plug threads using the syringe with oil to measure the head volume. Be sure to remove the head and clean the grease off afterwards.

Holes appear to be 0.4375" dia. and the pressed in brass 0.439" dia. Appears to be stainless ball valve. You can modify a single feed to be a dual feed by removing the plug and adding another 90* nipple as the ball valve has been drilled through. Pingle warns against twisting the fittings (possibly because it will twist the o-ring and cause it to leak).

At greater than 3/4 throttle you are using the main jets. With a bigger engine, it will suck harder on that single carb and make it run rich (it will missfire and "burble"). At full power when an engine is under-carbureted it will tend to run rich, whereas an over-carbureted engine will tend to run lean. I would put on the 34's and "dial it in". Sure it's twice the work, but with the top-end power gain you will see it will be worth it.

Many ways to "skin a cat", however, forget using a distance measurement to get degrees. As you have just discovered, several other dimensions will alter the port height. Instead, find a degree wheel and attach it to your crankshaft and use a dial indicator to find TDC. With chinese tools everywhere, this should not a problem. If you can't find a degree wheel, print one out and glue it to some posterboard. Calculate the degrees for the desired timing and after bluing the cylinder, move the crank to this position. Mark along the top edge of the piston with a 90 degree dental tool. This is a reference line. Always double/triple check the degree positions and dial indicator references before cutting. Use the same brand of base gasket for marking and assembly. Final markup can be made using arbituary symetric guidelines and/or a shape developed using 2-stroke software and/or graphics software and printing/cutting with a razor. This pattern for the port(s) can then be transfered to the blued cylinder.

To determine the change in degrees for a rotational move, do the following. Determine the diameter of the bolt holes and multiply this by Pi(3.142). This will give you the circumference of this circle. Now divide that value by 360 to get the movement for one(1)degree. Now multiply that value by the number of degrees desired. As an example, if the diameter were 5.1" and you wanted to advance the timing 4 degrees: 5.1 * 3.142 / 360 * 4 = 0.178"

Port shape- absolutely. Your description of the results of a flat roof are right, however, as we all know a flat roof will hang a ring. I keep the roof radius to 5" and, of course, bevel the edges. When beveling the edges, remember the ring sticks out the most in the center of the port, so depending on the width of the exhaust port beyond 75%, you will need more bevel in the center to, literally, press the ring back into the piston. The angle of this bevel is fairly shallow but rounds and then blends to the port passage. Back to you question though- yes, a "flatter" roof will peak the power because the sonic wave is more defined and higher in amplitude. That it is less dispersed over time means the pulse will be at a more specific RPM range. This will turn a trail pipe into a dune pipe. The idea behind the intake shape is to improve flow. You can increase flow by decreasing the effects of eddy currents and straightening the path. Eddy currents are caused by sharp changes in the flow path. Having a smooth flow path will decrease the resistance of the flow and dramatically increase the flow rate.

I would get the CPI pipes (you will eventually get there anyway and the resale value is great). You will still have a wide power curve, but who know, you might like having a lot of "grunt" as opposed to having a machine that likes to either wheelie or looking for a gear that gets you back into the power band as will changing the timing will produce. Leaving the timing will also make it a lot easier to drive on a trail. You can always make the mods later- it really wouldn't be all that much more work for a winter project. BTW, on YOUR engine, from 190 degrees to 196 degrees means raising the exhaust 0.061". An easy way to change (if you know the timing for sure) is to remove the cylinders, ink blue above the exhaust, and with small calipers set at the 0.061", scribe a line parallel along the exhaust upper edge- then you can grind to the line and re-polish the port and bevel the sharp edges. Another method (which I prefer) is to use a timing wheel. With the engine cylinders still bolted on, place each cylinder at half way down and blue the top edge of the exhaust port. Move and lock the timing wheel to 82 degrees ATDC (to get 196 degrees) and using a small 90 dental tool, scribe a line along the piston top above the exhaust port. Do the same on the other cylinder (being careful not to rotate the wrong way and remove the bluing in the cylinder you just did). Then remove both cylinders and do the grinding/polishing. Be sure to maintain the exhaust port upper edge radius and bevel the sharp edges.