The Flow Show -Testing Resting?

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Testing Resting?

The Question - I was just gazing around your web page and noticed your 270cc jug article. Did you ever dyno the motor before the two auxiliaries directly into the secondaries were drilled? Did you notice that there was an improvement/loss over any specific ranges? It's kinda difficult to figure because while you are adding more flow (So top would benefit) and cooling, there is more of a tendency for the mixture to perform more like the booster port by forcing the intake more upwards than horizontal (more of a mid benefit). Also, the turbulence would be up (good), but right at the window (bad-hampering flow), so does this gain out weigh the loss? It surely has me wondering, so if you have any numbers or info, please let me know, if not much of a prob... Thank You!

Trax310

The Response - I agree with your description of what the affects would/could/should have been - I wish I could answer this with complete certainty. I can't.

I performed that modification at the same time as the epoxy modifications so I have no specific information about that modification

alone. Up until then the barrel was bored to the 69 mm size and ported to the specs indicated but I changed another thing at that time - the vertical angle of the main transfer port walls (in other words - everything). All the modifications performed at that time were

designed to increase the power well before the power peak.

The epoxy made the tunnels longer/more round so the mixture could enter the cylinder at a flatter level - less obstruction from

changing direction and more time/area due to the better entry angle. The holes were drilled to add boost area, provide better aim and

(perhaps) aid in cooling. The main transfer port walls were aimed way back toward the rear of the cylinder (exactly at the center of the newly drilled hole) instead of across the piston.

Peak HP was up by about 1/2 HP, but power before the peak started several hundred RPM's sooner and was a few HP fatter until

just before the power peak. There was no dip or negative affect to these modifications as far as I could tell - the power was never

lower than it was before the modification at any RPM.

It may be interesting to note that the piston crown burn pattern still shows a full width flow pattern across the rear port area of the

piston, though the direction it releases its mixture has changed somewhat in the area of the ports rear wall. It shows it's directed more toward its mirror port - the other 5th (rear) port - whereas before it showed its targeted toward the outer edge of the exhaust port on the other side of the cylinder. This leads me to believe that the bulk flow from the rear port almost completely overpowers the flow from the small boost hole at the time the port is opened - making only a small impression upon its targeted path. Since both ports release their charge through the same port hole, the higher velocity upward stream from the small hole may let the port act like it has a steeper roof angle than it does.

I have wondered if these small holes produce an asymmetric change in the flow pattern of the rear ports based upon the RPM of the

engine - perhaps being enhanced by the pipes suction phase and the position of the reeds during that phase. That is to say when the

power is coming on the pipe - when the signal is very strong from the pipe to the crankcase these ports may matter and produce a

desirable condition. Below that range I think they are useless.

Driving the quad proved this set of modifications to be a power range "fattening" thing almost completely. The midrange hit was

much harder though - so much harder that I developed a riding style to accommodate it. I started chugging the dune faces in 4th, 5th

and 6th at 3500 to 5500 RPM in an effort to keep the motor from coming on the pipe. It became a game to see how low I could let the revs go before twisting the throttle open to explode out of the underrev situation.

My thinking that I would be able to move the (heavy) quad better with additional midrange RPM power than through increased

revs/upper RPM power seemed to be valid. I would learn that a hard hitting powerband with as broad a width as possible was much

more important in the dunes than high RPM peak output. I would also learn that the TRX barrel could be made to perform very well

when cut to a number of different parameters and that when cut this way it produced a dune chugger AND a very decent high output

screamer.

Rick

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Testing Resting?
The Question - I was just gazing around your web page and noticed your 270cc jug article. Did you ever dyno the motor before the two auxiliaries directly into the secondaries were drilled? Did you notice that there was an improvement/loss over any specific ranges? It's kinda difficult to figure because while you are adding more flow (So top would benefit) and cooling, there is more of a tendency for the mixture to perform more like the booster port by forcing the intake more upwards than horizontal (more of a mid benefit). Also, the turbulence would be up (good), but right at the window (bad-hampering flow), so does this gain out weigh the loss? It surely has me wondering, so if you have any numbers or info, please let me know, if not much of a prob... Thank You! Trax310
The Response - I agree with your description of what the affects would/could/should have been - I wish I could answer this with complete certainty. I can't. I performed that modification at the same time as the epoxy modifications so I have no specific information about that modification alone. Up until then the barrel was bored to the 69 mm size and ported to the specs indicated but I changed another thing at that time - the vertical angle of the main transfer port walls (in other words - everything). All the modifications performed at that time were designed to increase the power well before the power peak. The epoxy made the tunnels longer/more round so the mixture could enter the cylinder at a flatter level - less obstruction from changing direction and more time/area due to the better entry angle. The holes were drilled to add boost area, provide better aim and (perhaps) aid in cooling. The main transfer port walls were aimed way back toward the rear of the cylinder (exactly at the center of the newly drilled hole) instead of across the piston. Peak HP was up by about 1/2 HP, but power before the peak started several hundred RPM's sooner and was a few HP fatter until just before the power peak. There was no dip or negative affect to these modifications as far as I could tell - the power was never lower than it was before the modification at any RPM. It may be interesting to note that the piston crown burn pattern still shows a full width flow pattern across the rear port area of the piston, though the direction it releases its mixture has changed somewhat in the area of the ports rear wall. It shows it's directed more toward its mirror port - the other 5th (rear) port - whereas before it showed its targeted toward the outer edge of the exhaust port on the other side of the cylinder. This leads me to believe that the bulk flow from the rear port almost completely overpowers the flow from the small boost hole at the time the port is opened - making only a small impression upon its targeted path. Since both ports release their charge through the same port hole, the higher velocity upward stream from the small hole may let the port act like it has a steeper roof angle than it does. I have wondered if these small holes produce an asymmetric change in the flow pattern of the rear ports based upon the RPM of the engine - perhaps being enhanced by the pipes suction phase and the position of the reeds during that phase. That is to say when the power is coming on the pipe - when the signal is very strong from the pipe to the crankcase these ports may matter and produce a desirable condition. Below that range I think they are useless. Driving the quad proved this set of modifications to be a power range "fattening" thing almost completely. The midrange hit was much harder though - so much harder that I developed a riding style to accommodate it. I started chugging the dune faces in 4th, 5th and 6th at 3500 to 5500 RPM in an effort to keep the motor from coming on the pipe. It became a game to see how low I could let the revs go before twisting the throttle open to explode out of the underrev situation. My thinking that I would be able to move the (heavy) quad better with additional midrange RPM power than through increased revs/upper RPM power seemed to be valid. I would learn that a hard hitting powerband with as broad a width as possible was much more important in the dunes than high RPM peak output. I would also learn that the TRX barrel could be made to perform very well when cut to a number of different parameters and that when cut this way it produced a dune chugger AND a very decent high output screamer. Rick