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Author Topic: Team Go Dog, Go! Modified Partial Streamliners  (Read 728152 times)
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wobblywalrus
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« Reply #3255 on: January 03, 2019, 01:13:32 AM »

Experience tell me to rubber mount the carbs.  The front ends of the carbs are in rubber manifolds.  The carbs are supported by a rubber mounted stay.  Nice big fat juicy o-rings are installed in the bell mouth ends to isolate the carbs from them and the plenum chambers.

This is a bell mouth in place on the carb end.


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wobblywalrus
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« Reply #3256 on: January 03, 2019, 11:30:11 AM »

This is the bell mouth in the plenum.  The flow into the bell is less influenced by the nearby plenum wall if it projects.  There is 1/4 inch clearance between the outer edge of the bell and the wall.  This is the minimum I wanted and it dictated the bell size and shape.  The bell would be about a 1/4 inch taller and wider if it was not constrained by the wall.

This engine is not sensitive to runner lengths in relation to power output.  It is very particular about the shape of the inlet ends.  Most of the computer modeling programs and book equations address length much more than they analyze shape.  Dyno testing will be done with both the old and new intake systems.  This trial and error method is the only way I can do it.  The new system will help, hurt, or not change the power curve is my best prediction at this time   


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wobblywalrus
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« Reply #3257 on: January 07, 2019, 12:04:49 PM »

The engine design relies on four things and none are used exclusivly.  They are track experience, dyno work, equations and guidance from folks and references, and computer analysis.  All four say the intake tuned length is OK or close to it.  This is where I am very lucky.  The length cannot be increased and have at least 1/4 inch between the bell ends and nearby plenum walls.  The length cannot be shortened and have the big carbs fit behind the engine mount stays.  The intake length is dictated by geometry and it would be a big problem if it was too long or short.     


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wobblywalrus
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« Reply #3258 on: January 12, 2019, 10:10:53 AM »

The plenum volume calculations require some precise measurements of port dimensions that cannot be done with the cylinder head on the bike.  The head must be off to make those.  The head needs to be in place for the intake design and construction.  The plan is to design and build the entire intake system with the head on the bike with one exception.  The plenum volume.  That can be increased or decreased after it is calculated. The head does not need to be on the engine to do this.

The air filter flange is shown on the plenum back.  Will the plenum volume also include air filter volume if a big single hole is cut in the back side of the plenum to match the flange?  The inside face of the flange is slightly elliptical with a 2.75 inch minor diameter.  The hole would match that. 


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Old Scrambler
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« Reply #3259 on: January 13, 2019, 12:20:39 AM »

Assuming sufficient intake-air is available at maximum rpms..............you could effectively double the available plenum-air volume for each intake stroke by cross-connecting the air-chambers wink
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2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre
wobblywalrus
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« Reply #3260 on: January 13, 2019, 10:38:06 AM »

The air filters arrive on Tuesday.  They will be attached to their flanges.  The filters and flanges will be held on the backs of the plenums.  Ellipses will be scribed on the back of the plenums to show where the intake holes will go.  The holes will not be cut.

The head will be taken off and the intake port volumes, lengths, minimum diameters, and other measurements will be made.  The plenum volumes will be calculated by different methods to determine the optimum size.  This is based on Helmholz resonance principles.

The plenum volume calculation on Page 111 in "Engine Airflow" is rearranged to give plenum volume.  It is VP = Z / [(1 + j) x F] where VP is plenum volume, Z = impedance, j = the square root of -1, and F = frequency

The square root of -1 is an imaginary number.  It was sometime in college in the early eighties when I did some sort of figuring with an imaginary number.  I cannot remember how to do it.  Also, I have no idea of the desired impedance.  Can anyone help me figure this out?     
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Harold Bettes
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« Reply #3261 on: January 14, 2019, 11:47:06 PM »

Mr. WW and those that like to follow this kind of stuff,  grin

In the formula you listed that is used in my book, Engine Airflow, there is indeed a wispy old imaginary number which is the sq rt of -1. Z denotes the impedance.
Probably not a "do it this way" application that fits all.

What Engleman was trying to produce there is an acknowledgement of the oscillation of a wave that simulates an Alternating Current wave of electricity. The impedance of a circuit is simply its ratio of resistance to the capacitance oscillation. He had likened the intake system to that of a resistor and a capacitor where a circuit will oscillate as in DC circuits.

One can also look at the intake manifold (including any plenum) as a Helmholtz resonator and the ratio of the inflow resistance to the outflow that can be damped by using a plenum volume (perhaps variable) giving a boost in intake supercharging across a wider range of rpm than the normal approach of a fixed length inlet path. rolleyes

Remember that intake oscillations are more pronounced with fewer cylinders than greater. That is another way of stating the pulsations on the intake of a single cylinder are greater than the pulses on a group of cylinders joined by a plenum. Plenum volume typically damps those pulses. shocked

You two stroke guys probably remember the "boost bottle" approaches from years ago. The same kind of application can be done for a 4 stroke. cheesy

Bo, I will send you a PM to perhaps sort out the process which I hope will be of some benefit.

Regards to All,
HB2 smiley
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wobblywalrus
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« Reply #3262 on: January 15, 2019, 10:45:07 AM »

Thanks, Harold.  Any advice is appreciated.  This Helmholz tuning pretty mental for the ol' walrus.  The traditional british parallel twin has pistons that move up and down their bores at the same time and the firing occurs at opposite cycles.  The wave action and pressure and vacuum in a cylinder can be used to enhance the intake performance of its mate.  This engine has a staggered firing order caused by the rod journals being 90 degrees offset.  The wave actions in the intake are nor synchronous and this is why the plenums are being kept separate and it will be tuned like two 500 cc singles.  This was something explained to me years ago by a Harley tuner when I asked him why he always used two Mikuni carbs on separate manifolds for his race motors.  He said "with a staggered firing order one cylinder is at the last tit on the hog" or something like that.

 
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wobblywalrus
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« Reply #3263 on: January 15, 2019, 11:03:43 AM »

https://www.bbc.com/news/av/uk-england-devon-46824931/saunton-sands-hosts-giant-hercules-transport-plane-landing


This shows how the beaches in the UK are wide and fat and can be raced upon.
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Lemming Motors
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« Reply #3264 on: January 15, 2019, 12:18:26 PM »

Pendine Sands (historic LSR venue) is still used by some groups for speed runs; notably The Straightliners who are primarily motorcyclists but they are very tolerant of other wheeled craft at their events, maybe not Hercules though. shocked
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wobblywalrus
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« Reply #3265 on: January 16, 2019, 12:14:17 AM »

Pages 136 - 138 of this build diary are about Pendine.

Some expert advice in a PM, a phone call a few weeks ago, plus some references suggest the starting point for plenum sizing is 1 to 1.5 times the cylinder displacement at half stroke + port volume + external plenum volume, or the cylinder displacement, or 1.2 times the cylinder displacement.  The plenum volume must exclude the air filter volume if any of these criteria will be met.

There is a filter and a resonance chamber in the air box that Triumph made for this bike.  They are separated by a plate having a round edged slot in it.  This concept will be used on these plenums to isolate the filter.  Does anyone have flow data for different sizes of these orifi in cfm at at 28 inches of water?  The plan is to use the smallest one that will provide decent air flow.


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wobblywalrus
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« Reply #3266 on: January 16, 2019, 11:38:01 AM »

This calculation is for a round edged circular orifice.  The current filter opening is 2.825 inches in diameter with a 6.27 square inch area.  The restrictor orifice will have a 1.437 inch diameter with a 1.621 square inch area.  This is a big decrease and it should help to reduce the intake plenum volume to the needed size.


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Old Scrambler
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« Reply #3267 on: January 17, 2019, 10:53:29 PM »

Why build anything smaller than the maximum airbox for high-altitude speed at maximum rpm? Most of the 'books' were written for sea-level air.
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2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre
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