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Author Topic: Team Go Dog, Go! Modified Partial Streamliners  (Read 521035 times)
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wobblywalrus
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« Reply #2595 on: October 23, 2016, 02:54:05 PM »

An 11 inch collector length is entered.  The diameters are optimized.  A small diameter collector is recommended.  It is only 3.125 inches diameter.

 


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wobblywalrus
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« Reply #2596 on: October 23, 2016, 02:57:48 PM »

A megga is needed to put the exhaust system outlet back behind where my foot will be.  The collector diameter is its starting diameter and a 5-inch outlet is selected for length calculation purposes.  A 21-inch long megga works great.


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wobblywalrus
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« Reply #2597 on: October 23, 2016, 03:03:05 PM »

The 21 inch length is entered.  Various end diameters are looked at.  A 6.50 inch one gives primo power.  This concludes the virtual build around the Comp Cam 9042 lobes.  These are milder than the original equipment Triumph 790cc cams.  Those Triumph cams with adjustable timing gears should work just great for all but the most radical race builds. 


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Koncretekid
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« Reply #2598 on: October 23, 2016, 06:15:25 PM »

An end diameter of 6-1/2"?  Sounds huge to me.  It might affect your aerodynamics!

You certainly end up with a wide horsepower curve.  You might consider taking it to the drags for testing.  After you're wound out in 1st and 2nd gear, it looks like you will never drop below 78 hp shifting at say 8500 rpm.

Tom
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wobblywalrus
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« Reply #2599 on: October 23, 2016, 10:18:38 PM »

This cam is one that I have a profile for.  It came on a CD that accompanied the program.  It is a good profile to use to show how I am using the program to design the engine.  Cams with more lift and duration will be used for the build and power will probably be peakier.  Power at Bonneville is 86 percent of what it is in the valley here.  Those cams give 86 / .86 = 100 flywheel HP here near Salem.  Assuming a 10 percent power loss going to the back wheel. 100 x .90 = 90 HP.  That is good for one of these engines with mild cams.  Hopefully rear wheel HP will be over 100 on the dyno in Beaverton with a hotter cam combo.
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wobblywalrus
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« Reply #2600 on: October 27, 2016, 08:16:04 PM »

Now it is time to make sense of the graphs and other input data.  This first printout is the best intake length within the range of adjustment.  It is 10.2 inches.  Note the peak in the power curve.  See the green curve in the second graph.  This is inlet port pressure and vacuum during crank rotation at 8,000 rpm.  The port pressure drops during the overlap phase.  The area under the 1.0 line and above the green line is greatest with this length.  Also, the vacuum pulse is timed to occur when the intake valve is open.  The red line is cylinder pressure vs crank rotation.  The area under the 1.0 line and the red curve is maximized with this intake length.  This shows there is the most vacuum in the cylinder with this length.  This will suck in more mixture. 


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wobblywalrus
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« Reply #2601 on: October 27, 2016, 08:25:21 PM »

This is the worst intake length within the adjustment range.  It is only an inch different at 9.2 inches.  Note that all of the good things mentioned in the previous post are not as good with this length.  Static pressure at near ambient occurs at the beginning of overlap.  This can contribute to reversion.

The users manual says to measure the intake tract lengths from the valve seat to the point of contraction where air enters the air horn (velocity stack).  This makes sense.  The waves originate at this location when the valves open and close.


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Koncretekid
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« Reply #2602 on: October 27, 2016, 09:00:34 PM »

I've always wondered about the length which is supposed to include the air horn (velocity stack).  Some modern carbs have an enlarged bell mouth which in my opinion would result in a reflection of the wave at that point which would negate the effect of a velocity stack after this point.  Any mention of that in your program?
Tom
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« Reply #2603 on: October 28, 2016, 09:30:01 AM »

My stack experience is purely anecdotal: At Bonneville I pulled off the large fram filter and pulled the stainless steel liner out of a tall traveling drink cup. I cut off the bottom where the diameter matched the carb intake diameter and attached it with a hose clamp. It's about 7" long. The following run was 4 mph faster, from 100 to 104. (I had tried to calculate the proper intake length once and it seemed ridiculously long... so I went with dumb luck.)

It might not be best, but it was better.
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wobblywalrus
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« Reply #2604 on: October 28, 2016, 09:22:25 PM »

Tom and Brian, several bell mouths are shown on the attached.  The elliptical profile reflects a soft wave and it is best if wave dynamics cannot be calculated or utilized, or if a wide power band with no humps and dips in the torque curve is the the goal.  The simple radius reflects a sharper wave and it is best if wave tuning can be done and be taken advantage of.  It will result in spikes and dips in the torque curve.  This can be a big asset if the spikes can be utilized.

The simple radius bell will be used on this build with 1/4 inch radius.  The tuned length will be based on the fully contracted cross-section 1/4 inch inside the bell mouth.  The average distance between this section and the valve seat will be the tuned length.  This is the average of the distances along the bottom of the port, the distances along each side, and the distance along the top.  This is what the users manual recommends as best as I can interpret.


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wobblywalrus
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« Reply #2605 on: October 28, 2016, 09:57:16 PM »

That image was carpy.  Here is a better one.


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« Reply #2606 on: October 29, 2016, 11:37:05 AM »

The step headers and collector arrived.  They are stainless steel. This was recommended to avoid corrosion perforation.  The headers and collector are held together by springs that attach to tabs on the pipes.  The tabs have holes in them for the hooked spring ends.  They are not welded on.  The header primary length needs to be determined first.  It can be varied six inches by cutting the lower straight part of the headers.  The next posts show how I will figure this out for the Comp Cam grind.  These pipes are made for me to the factory team mile bike race specs by Bonneville Performance in Florida.  The mile bike has a broad and flat power band with lots of HP throughout.  This engine will be tuned for a less wide power band with enhanced power in the upper mid range and top end.   


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« Reply #2607 on: October 29, 2016, 12:02:18 PM »

Bo, they look really good.

Do you think you might be building one the strongest Triumph motors around?.
I know you have a limited budget but the amount of R&D you put in is unbelievable.
Awesome man, you are one guy that keeps me going. cheers cheers cheers
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« Reply #2608 on: October 29, 2016, 12:16:49 PM »

WW;

Back in my days at NRAO we used feed horns that looked similar. These were flared ends of waveguide (a hollow tube that microwave energy travelled through) and it was important to know where the effective length of the horn was located. That point was the "phase center" of the horn.

It may be that an air horn effective length can be thought of as a similar problem-- if it could be determined just where the acoustic phase center is located in the mouth of the air horn. I haven't the slightest idea of how to calculate this- someone like Mayf may be able to determine it.

Regards, Neil  Tucson, AZ
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Regards, Neil  Tucson, AZ
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« Reply #2609 on: October 29, 2016, 01:20:21 PM »

That's a REAL NICE pipe.............I would not cut anything until your on the dyno...............and then make a long section cut so you can add incremental length...........if the pipes are about 29-inches to the Y........you may just have to remove the up-swept tail and add a short reverse mega.
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2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
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2016 AMA Record - 750cc M-CG HONDA CB750 sohc - 130.7 mph
2016 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 137.7 mph
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