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Tuned intake and exhaust track? (Read 435 times)
ebonysresearch
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Tuned intake and exhaust track?
09/26/10 at 10:47:12
 
Anyone done the tuned intake and tuned exhaust track length math?  My book with my formulas is at work...so I was just wondering if anyone has already done this.  Or what is the mathmatical redline on the suzuki 650?
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Re: Tuned intake and exhaust track?
Reply #1 - 09/26/10 at 11:14:30
 
The given redline is 6500

Only one has done any 'math' regarding the intake/exhaust that I recall, 1 to 2 years ago, don't recall who.

Diamond Jim did some great stuff on intake and exhaust tuning.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1233415444
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Charon
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Re: Tuned intake and exhaust track?
Reply #2 - 09/26/10 at 21:15:57
 
Ain't theory wunnerful? If you are going to try to run a straight pipe, you are going have lots of fun. When the exhaust valve opens, a pressure pulse travels out the pipe at the local speed of sound, which varies with gas temperature. This pulse moves faster than the gas itself. When it reaches the end of the pipe (a discontinuity) it reflects back up the pipe as a negative pressure pulse. If all goes as planned, this negative pulse arrives during the valve overlap, just before the exhaust valve closes, and as the intake valve opens. The negative pulse thus helps to start the intake flow.

Because the exhaust gas isn't "air" and because its temperature varies along the length of the pipe, you have to make an estimate of the speed of sound. Estimates range from about 1400 to about 1600 feet per second. I'll use 1400. Let's also assume you want the engine to be "on the pipe" at 5000 rpm. 5000 rpm is 83.3 rev/sec. One revolution thus takes 12 milliseconds (1000/83.3). The time from exhaust valve opening until intake opening is about half a rev, 6 milliseconds. You will have to look up cam timings to get a better number. If sound travels at 1400 fps, in 6 milliseconds it travels 8.4 feet, 100.8 inches. This is the out-and-back time, so the pipe needs to be half this, 50.4 inches. Part of the distance is in the head in the exhaust port, so the pipe needs to be about 48 inches.

Now, the complications. If the engine is turning much slower, the pulse will return before the intake opens, and will be ineffective in starting the intake flow. If the engine is turning much faster, the pulse will arrive after the exhaust closes, and will be ineffective. So the straight pipe only works over a narrow range of speeds, though sometimes it will "sort of" work at half the design speed. When "on the pipe" the negative pulse actually travels up the intake manifold into the carburetor, and can affect mixture. This is why jetting can be tricky with open exhausts. A pipe with a discontinuity in the middle (such as a Jardine which opens from pipe diameter to a larger diameter, then dumps into the atmosphere) will cause a reflection first from the change in diameter, then from the end, so you'll have two or more reflected pulses to complicate the issue.

Intake tracts are usually shorter, because of the available space. The speed of sound in the intake is about 1100 fps, which would actually need a longer intake than the exhaust. But the intake also has an air filter, which will dampen pulses. The air box serves as a reservoir, and allows the engine to take a "gulp" of air from its volume. The air box has time to refill during the three non-intake parts of the engine cycle. Factories often arrange the intake side so as not to be resonant at the same speed as the exhaust, in an effort to smooth the torque curve and make the motorcycle more user-friendly.

Hope you enjoyed that.
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Re: Tuned intake and exhaust track?
Reply #3 - 09/26/10 at 23:20:14
 
Charon,... you definitely live in the wrong Harvard...

I'm gonna' have to read that a couple more times,... but you know the why's and how's of my what's.....
Do you teach for a living?....
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justin_o_guy2
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Re: Tuned intake and exhaust track?
Reply #4 - 09/27/10 at 03:47:13
 
Good post Charon
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Re: Tuned intake and exhaust track?
Reply #5 - 09/27/10 at 04:40:37
 
Charon that was awesome. But now it makes me feel like my whole setup is wrong! Grin
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Re: Tuned intake and exhaust track?
Reply #6 - 09/27/10 at 06:33:04
 
No, I don't teach. But I do drive a school bus part-time.

Most of that is adapted from stuff I have read over the years about tuning two-stroke engines. There are reasons for the weird shapes of two-stroke exhaust expansion chambers.

By the way, I forgot to mention that there is a reason for the slash cut on the end of the pipe. A square cut makes a very sharp discontinuity and a very sharp reflected pulse. The slash makes a more gradual discontinuity and both widens and lowers the reflected pulse, which in turn slightly widens and lowers the power curve. Bet you thought it was just for looks.
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LANCER
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Re: Tuned intake and exhaust track?
Reply #7 - 09/27/10 at 07:56:29
 
Charon wrote on 09/27/10 at 06:33:04:
No, I don't teach. But I do drive a school bus part-time.

Most of that is adapted from stuff I have read over the years about tuning two-stroke engines. There are reasons for the weird shapes of two-stroke exhaust expansion chambers.

By the way, I forgot to mention that there is a reason for the slash cut on the end of the pipe. A square cut makes a very sharp discontinuity and a very sharp reflected pulse. The slash makes a more gradual discontinuity and both widens and lowers the reflected pulse, which in turn slightly widens and lowers the power curve. Bet you thought it was just for looks.


do you live at the Holiday Inn Express ? ?

just having fun ... we appreciate you espertise
Grin   Grin
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Re: Tuned intake and exhaust track?
Reply #8 - 09/27/10 at 10:28:34
 
I found some of my old engine building formulas.   I was taught the same concept but different.  we go over this at work with customers wanting shorty drag pipes...they dont realize that it pushes their power band over their red line and they will never see the power.   Even on the dyno with the EGA readings it is such a pain to get it right but with open pipes there is always a dead spot in the lower RPMS

Exhaust Header Length  *L = Pipe Length
Thermal 1st wave: L=(1380 x (180 Degrees + Exhaust Valve Opening)) / RPM Desired.

Sonic 2nd wave:L=950 x (180 degrees + Exhaust Valve Opening)) / RPM Desired

Intake Track tuning with known pipe length:
2nd pulseSad1100x 1/2 Intake cam duration x .96) /RPM =Length

3rd pulseSad1100 x 1/2 Intake cam duration x .705) / RPM = Length

4th pulseSad1100 x 1/2 Intake cam duration x .538) / RPM = Length

So now I am looking up the cam specs and will get back.  Of course I am lazy and a dumb ol Harley technician and would love for someone to check my math.  I am thinking about cherry bombing my exhaust which will pass inspection in WV as an open baffle(must have baffles to pass in WV)  but I am thinking about making a custom intake.  In school the dyno teacher turns off the lights and we started a carberated  bike and shined a flashlight a few inches out of the carb to watch the air fuel mixture...reversion is what it is called.  then we changed all sorts of exhaust and intakes to watch the changes.  Dynos dont lie...people do.

Change in post:
A:  where did the smiley faces come from in the formula?
B: Anyone have the stock cam specs?
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Re: Tuned intake and exhaust track?
Reply #9 - 09/27/10 at 10:52:03
 
I'm great at math and formulas, but know nothing about any of this stuff.

I can tell you that the sad face came from putting an opening parenthesis right after a colon.  Add a space between the colon and the parenthesis, and the face will go away....  Smiley  

Oh, whereabouts in WV are you?  I'm in St. Albans.
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Re: Tuned intake and exhaust track?
Reply #10 - 09/27/10 at 11:31:44
 
From lancer's ebay page...

Stock Cam Lift:  0.254" In / 0.244" Ex

Stock Cam Duration:  224 deg @ 0.050" lift

So now that we have all these interesting numbers... what do we do with them?
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Re: Tuned intake and exhaust track?
Reply #11 - 09/27/10 at 13:06:45
 
Carb reversion adds a whole new set of problems. I have seen carb reversion mostly on piston-port controlled two-strokes. The air enters the carb and picks up fuel. It is then blown back out, and on the way out it picks up more fuel. It is then sucked back in and picks up more fuel yet. This makes the mixture horribly rich. If the carb is jetted for this condition, it will be horribly lean elsewhere in the rpm range. It is one of the reasons two-strokers use reed valves.

If there are any folks on here who have dealt with radio transmission lines, much of the math and many of the concepts are the same (allowing for different constants).
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Re: Tuned intake and exhaust track?
Reply #12 - 09/27/10 at 13:39:01
 

Ski Doo and a lot of small 2 strokes use rotary valve to get more low end torque with out losing their high end power.Its a little more modern than reed valves.
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Re: Tuned intake and exhaust track?
Reply #13 - 09/27/10 at 14:00:24
 
These are the numbers that I get...

Exhaust:
93=(1380x(180+224))/5995

93=(950x(180+224))/4127

Intake:
29=(1100x0.5x224x0.96) /4078

29=(1100x0.5x224x0.705) /2995

29=(1100x0.5x224x0.538) /2286
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Re: Tuned intake and exhaust track?
Reply #14 - 09/27/10 at 15:31:04
 
I live in Parkersburg.  Shop is S and P Harley Davidson

I came up with similar numbers.  
EX: 92.92 @ 6000 RPM
EX: 185.84 @ 3000 RPM

IN: 21.38 @ 6000RPM
IN: 42.77 @ 3000 RPM  

Wow a 42 inch intake would be a spear sticking out.  So Does anyone have a stock cam dyno run?   in school the RPM came from the middle of the Power Band. This should be all based off the back off the ex or intake valve.  But we could get closer with a dyno run.  I am going to dyno my bike at work when its done.  but the suzuki shop has nothing in stock so I am waiting on some parts and taking my time.
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