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Author Topic: Team Go Dog, Go! Modified Partial Streamliners  (Read 685244 times)
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wobblywalrus
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« Reply #645 on: January 10, 2012, 01:44:05 AM »

Thanks Mike.  I will try it tomorrow.

The only way to figure out the best spark advance curve for a bike engine is experience and lots of trial and error on a dyno.  I have neither.  Triumph Performance has developed an advance curve for 865 cc engines with the #813 cams like I have.  It is the Stage III curve.  The igniter box on these bikes controls the spark advance.  I boxed one of mine up and sent it to TP for reprogramming.  This should give me a horsepower or two.


* Box in Box.JPG (190.29 KB, 800x533 - viewed 118 times.)
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wobblywalrus
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« Reply #646 on: January 10, 2012, 11:07:12 PM »

The intake valve opens on the Triumph.  This creates a low pressure area at the intake valve and it sends a vacuum wave out toward the inlet end of the intake tract.  The wave goes through the carb venturi and it reaches the end of the velocity stack.  The stack opens into an empty area and the wave is reflected back to the valve as a pressure wave.  An open pipe end reverses the wave direction and polarity.  The pressure wave arrives just before the valve closes and it pushes additional fresh fuel air mixture into the combustion chamber before the intake valve slams shut.

This simplistic explanation describes a phenomenon that would happen if I had a very long intake tract.  In reality, I do not.  I have a short tract and the wave must bounce back and forth several times before it hits the intake valve at the right moment.  The pressure wave hits the closed intake valve a few times.  This is a closed pipe end and it reverses the wave direction but not its polarity.  A pressure wave is reflected as a pressure wave.

The waves travel at the speed of sound and the engine rpm varies.  This means that these waves will help me in a narrow rpm range.  I need to tune the inlet tract so everything is in harmony at the desired rpm range.  I do this by adjusting the inlet tract length.  This controls the length of the bounce and the instant it hits the intake valve.  A short tract causes more frequent bounces and a long tract makes fewer.

There are some good theoretical equations for determining the length.  I need to know the speed of sound in the inlet tract, the inlet tract length, the desired rpm, the intake cam timing, and the inlet tract diameter.  This input data is problematic.  It is hard to determine the reflective length of a curved inlet tract with complex shape around multiple inlet valves.  Any errors of estimate are compounded because the waves go back and forth several times.  The speed of sound is dependent on gas temperature and this is hard to estimate.

No equations, no matter how good, can give accurate predictions if the input is garbage.  I have never got the equations to work well.  My inlet tract tuning method is trial and error on a dyno.  The next few posts will explain how I do it. 
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wobblywalrus
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« Reply #647 on: January 11, 2012, 11:52:57 PM »

The inlet calculations I did in 2010 are redone so they are legible.  Tuning for the third bounce can be done within the space constraints of the Triumph.  The first try uses 1100 feet per second for the speed of sound.  Many reputable tuners use this value.  It is the speed of sound in 45 degree air.  Some tuner use 1300 feet per second.  This is the speed of sound in 245 degree air.  Note how the sound speed makes a big difference on the inlet tuned length calculations.

Both pages will be posted separately so they will be large enough to read.   


* Bounce Calcs 1.jpg (264.5 KB, 768x1004 - viewed 135 times.)
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wobblywalrus
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« Reply #648 on: January 11, 2012, 11:54:06 PM »

This is the second page.


* Bounce Calcs 2.jpg (272.47 KB, 768x1002 - viewed 128 times.)
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Koncretekid
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« Reply #649 on: January 12, 2012, 09:25:21 AM »

Bo,
I note that you are using 7000 rpm in your calculations. If your maximum horsepower is indicated at 8000 rpm, and you are gearing for this, then I think you should use 8000 instead of 7000.  You have a couple of miles or more to get up to speed and you need that last little bit of HP to get maximum speed.  Otherwise, as you pass the 7000 rpm figure, the wave will become less effective.  I applied the same logic to the length of the primary exhaust pipe.
For your intake, you can vary the length in the intake manifold, or by changing the length of the air horn on the carburetor - - it theoretically does the same thing, only sometimes more easily.  As for using the 3rd harmonic, it is sometimes still too long to be practical.  I think I calculated mine using the 5th harmonic, and came out with something like 8 inches, depending on whose online intake length calculator I used.
Tom
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Koncretekid
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« Reply #650 on: January 12, 2012, 02:47:29 PM »

For some reason I am not given the option of correcting my last post.  I have read back over your diary and now realize the big Triumph twin with your cam seems to actually develop maximum HP at less than 7000 rpm.  Therefore, your calcs are close.  My point was to try to tune everything for the rpm at which your motor makes maximum horsepower, and then gear to be at full speed at this RPM.  There is no point in overrevving past your maximum hp-rpm number unless you happen to get a nice tail wind and then you take advantage of it.  If your motor is making 90 hp at 6800 rpm, but only 88 hp at 7000, try dropping a tooth at the rear and run again.  My 2c worth.
Tom
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« Reply #651 on: January 12, 2012, 02:55:14 PM »

Tom - the reason you can't edit a post is because there's a setting in the software that limits the time during which you can make changes - to 4 hours after the post is first made.  That's there, I believe, to prevent people from making comments that might be made in the heat of an argument or inflammatory - - and then removed a day or two later when they decide that they've spread enough ill will.  while the time is variable -- I haven't felt a swell of need to change it nor to delete it.  I have occasionally been asked to make an edit or even to delete a post -- which help I've always given.

There - that's the story.  If you've got further to discuss - either start a topic on the website general suggestions topic - or get back to me off this thread.  Use email or PM, please.  Regards from Skandia, Michigan, where we're in the middle of a two-day "winter storm warning" with up to a foot of snow forecast. grin
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Jon E. Wennerberg
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Koncretekid
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« Reply #652 on: January 13, 2012, 09:07:29 AM »

Jon,
Not a big deal.  I try not to put my foot in my mouth too often, but sometimes I start typing before I put my brain in gear!

Sorry to hear about your storm warnings there in Michigan. I'm sitting on my sun porch here in Deerfield, Nova Scotia (near Yarmouth), looking out across a 90% ice free lake, with only a smattering of wet snow on the ground. I haven't had the snow blade out yet this winter, and the average temperature in December was 31* F.  Unusual winter, for sure.  Some of us actually look forward to this global warming.

Tom
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We get too soon oldt, and too late schmart!
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wobblywalrus
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« Reply #653 on: January 13, 2012, 11:43:20 PM »

Tom, I am doing exactly what you say.  I gear to run 7,500 rpm through the mile and I am trying to move the peak horsepower up to that rpm.  It is a 500 rpm shift and I can do it with intake and exhaust tuning and a different spark advance curve.  I hope.

All of this intake theory study is paying off.  I am hesitant to rely on calculations alone to tell me the correct runner length.  This is what the theory and math are telling me.

1)  Tuned length is not significantly affected by cylinder size.  I do not need to change the runner length when I go from 865 cc to 996 cc.  This is a good thing.

2)  Cam timing does change runner length.  I will need to adjust the length when I go from the 813 cam to the more radical one.  The length change is expected to be reliably calculated by the equations.  No need for an additional session of tuned length dyno testing when I fit the bumpier cam.

3)  Intake air temp significantly changes the optimal tuned length.  I need to get my cold air intakes done before the dyno work.  Also, I need to develop some length correction factors for running on exceptionally hot and cold days.  Also, I need to figure a way to adjust easily adjust the runner length on the salt.

I thought the bike would be as fast as it would go and built in five years.  It is seven years and I am just getting started on figuring out a bonehead simple NA motor.  A crazy hobby.

 
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Koncretekid
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« Reply #654 on: January 14, 2012, 09:18:18 AM »

Bo,
You and I are on the same wavelength.  I agree with your procedure, except for the part about not requiring new Dyno testing.  The great white dyno in Utah will give the best results, but it's expensive for the few runs you'll get, and it maybe difficult to assess small changes.  The real dynomometer may seem expensive, but if you have easy access to one, you should probably book some time to arrive at a starting point for jetting, timing, and to assess the new intake length with the new cam.  I hope to be able to do so but the nearest one here in NS is at least 200 miles from me.  I hope to do my final dyno work at Dan Dunn's shop in Longmont, Colorado.
Tom
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« Reply #655 on: January 14, 2012, 04:46:48 PM »

Tom - Dan runs our bikes through the dyno before Bonneville.  Since he is Longmont Co. it is 5000' which works really well for Bonneville and he knows how to tune. 
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wobblywalrus
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« Reply #656 on: January 15, 2012, 01:23:39 AM »

Yesterday was Friday the 13th.  It was 10 minutes until I was going to turn the lights out and go to bed.  The lousy minutes.  I decided to take a picture of something I am machining.  I picked up the camera off of the work bench and heard something hit the floor.  It landed with a dull thwack.  My dial caliper.  There are some nights a fellow is better off if he goes to bed early.  On Friday the 13th maybe I should stay in bed.

The intake length formulae give me all sorts of intake lengths.  They are consistent with each other on one thing.  I need to shorten the inlet tract to move the torque peak higher.  Also, an inch shorter is the usual answer.  It is time for some ABBA dyno testing.  This is when setup A is tested first with one pull, setup B is tested with two pulls, and setup A is tested one more time.

Setup A is what I am running now.  The air cleaners fit under the side covers and the tuned length matches the cam.  It produces good power for street use.  The air cleaner and velocity stack are shown.  The stack is 40 mm long.  The tuned length is measured from the valve seat to the where there is a significant change in cross-section at the upstream end of the tract.  In this case it is where the foam begins in the air cleaner.  The tuned length of the stack with the filter is 56 mm.


* Intake Mods 1.JPG (209.6 KB, 800x533 - viewed 121 times.)

* Intake Mods 2.JPG (187.29 KB, 800x533 - viewed 123 times.)
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wobblywalrus
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« Reply #657 on: January 15, 2012, 12:07:48 PM »

The B setup is the orange plastic stack.  It is 35 mm long and the tuned length is about an inch shorter than the A setup.  Everything for A are B are in the carb kit from Triumph Performance.  The ABBA dyno curves are shown.  These are averages of two pulls each so they are drawn by hand.

Years ago I asked Matt Capri about intakes for my bike.  He said the shorter the better and shape is important.  Matt's NA bike had odd looking stacks shaped like little trumpet bells.  The stacks I was using then were short enough.  They are sharp edged, unlike Matt's.  They are shown in the photo and they were hammered out of copper water pipe.

The sharp edge hurts performance.  There can be a ring of turbulent are inside the stack at the inlet edge during high air flow.  This ring of swirling air blocks flow into the stack at the edge and the flow is concentrated in the center.  This prevents proper fuel atomization with the very short stacks I use.  The proper intake edge shape is the rounded one on the orange stack.  The orange stack gives me what I want.  It is more torque at high rpm.   


* Intake Mods 3.JPG (223.02 KB, 800x461 - viewed 121 times.)

* Intake Mods 4.jpg (214.6 KB, 785x600 - viewed 119 times.)
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wobblywalrus
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« Reply #658 on: January 16, 2012, 11:45:47 AM »

The B setup gives me a little bit more torque at higher rpm and a few horsepower. The inlet changes I will do give a small advantage for this mildly tuned 865cc motor.  The big 996 motor will use the same carbs and filters.  These small changes are expected to be more of a benefit for the big bore engine.

The 39 mm FCR flatslides have the same 36mm choke diameter as the standard CVK carbs.  They are not any larger.  They do not have the restrictive throttle plates in the bores, there are all sorts of jets and other parts available, and there are special parts for alcohol fuel.  These are the 39mm flatslide advantages.  The first photo is from a page on the SUDCO on-line catalog.  It shows bellmouths for the FCR.  Shorter bellmouths with good flow characteristics are what I want.  I order the ones shown.

It would be easy to order bigger foam filters and simply clamp them onto the bells.  One big goal is to have the waves in the inlet tracts inverted and reflected by the bell openings and not by the foam-rubber interfaces in the filters.  A large and abrupt expansion in cross-sectional areas at the bellmouths will assure this happens.  Annular rings are made and attached to the bells with JB Weld.  The ring and bell separately and together are shown in the second photo.   



* Intake Mods 5.jpg (202.03 KB, 1024x684 - viewed 130 times.)

* Intake Mods 6.JPG (222.37 KB, 800x533 - viewed 123 times.)
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« Reply #659 on: January 17, 2012, 01:22:19 PM »

Wobbly, some things to think about if you havenít already--

Using your 6ms inlet flow duration and about 500ccís per cylinder, the average flow rate (assuming 100% volumetric efficiency) during induction would be about 83 liters/second, 3 cu. ft/s, or about 180 cfm.  What is the pressure drop across the the air filter at those or, more likely, higher flow rates?  Might want to consider a plenum of some sort, the bigger the better, and then the filter(s), the bigger the better.

Inlet tract wave interactions (reflections and transmissions) will occur to some degree at any change of area, including tapers.  What are the diameters of the port, runner, venturi, inlet bell?  Are they consistent or all different?  Energy is lost at each interaction as well as along the way.  Different areas everywhere will likely just make hash out of the effort to tune the inlet.  Also, the primary reflection is the strongest with each successive round trip less effective.  Can you stretch it out to use the second?  Straight is nice, but not necessarily required.

If you are not already aware of Gordon Blairís book, Design and Simulation of Four-Stroke Engines, ISBN 0-7680-0440-3, you would probably find a lot to muse over about engines, particularly the gas dynamics of inlet and exhaust systems.  While much of the underpinings of the book utilize somewhat advanced mathematics, there are also considerable qualitative descriptions and examples, and a section on using simplified empirical methods, such as what you have alluded to using so far.  And Blair seems to have had a particular affinity for British twins.   It may also provide points to be aware of when considering peculiar or unexpected dyno results.
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