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Message started by ebonysresearch on 09/26/10 at 10:47:12

Title: Tuned intake and exhaust track?
Post by ebonysresearch on 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?

Title: Re: Tuned intake and exhaust track?
Post by verslagen1 on 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

Title: Re: Tuned intake and exhaust track?
Post by Charon on 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.

Title: Re: Tuned intake and exhaust track?
Post by Serowbot on 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?....

Title: Re: Tuned intake and exhaust track?
Post by justin_o_guy2 on 09/27/10 at 03:47:13

Good post Charon

Title: Re: Tuned intake and exhaust track?
Post by ralfyguy on 09/27/10 at 04:40:37

Charon that was awesome. But now it makes me feel like my whole setup is wrong! ;D

Title: Re: Tuned intake and exhaust track?
Post by Charon 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.

Title: Re: Tuned intake and exhaust track?
Post by LANCER on 09/27/10 at 07:56:29

4D666F7C61600E0 wrote:

do you live at the Holiday Inn Express ? ?

just having fun ... we appreciate you espertise ;D ;D

Title: Re: Tuned intake and exhaust track?
Post by ebonysresearch on 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 pulse:(1100x 1/2 Intake cam duration x .96) /RPM =Length

3rd pulse:(1100 x 1/2 Intake cam duration x .705) / RPM = Length

4th pulse:(1100 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?

Title: Re: Tuned intake and exhaust track?
Post by babyhog on 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.... :)

Oh, whereabouts in WV are you? I'm in St. Albans.

Title: Re: Tuned intake and exhaust track?
Post by verslagen1 on 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?

Title: Re: Tuned intake and exhaust track?
Post by Charon on 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).

Title: Re: Tuned intake and exhaust track?
Post by bill67 on 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.

Title: Re: Tuned intake and exhaust track?
Post by verslagen1 on 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

Title: Re: Tuned intake and exhaust track?
Post by ebonysresearch on 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.

Title: Re: Tuned intake and exhaust track?
Post by verslagen1 on 09/27/10 at 15:50:22

Is there calculations for the optimum diameters as well?

Title: Re: Tuned intake and exhaust track?
Post by Charon on 09/27/10 at 20:52:13

Rotary valves for two-strokers are nothing new. My 1966 Bridgestone 175 had them, and they were not really new even then. Their virtue is allowing asymmetrical intake timing(not possible with piston-controlled ports), and allowing the intake to open with less flow restriction than reed valves. Their drawback is that they require the carburetor to be on the end of the engine, which works fine for one or two cylinders but has serious problems with three. They also require some fairly close tolerances to avoid leakage. This is, of course, off-topic for the Savage.

The airbox in a sense substitutes for some of the length of the intake tract. Its volume is also resonant at some engine speed. The engine sucks in a gulp of air from the airbox, and the airbox sucks in air from outside. The outside air acquires momentum as it moves in to fill the airbox. When the air stops, its momentum is converted to pressure, so the pressure in the airbox can rise above atmospheric. At some engine speed, the intake valve will open just as the pressure in the airbox is at maximum, so flow will start more quickly. If this coincides with the pulses in the exhaust tract the engine can develop a lot of "free" power. But it will be very peaky. Manufacturers may try to put the intake resonance at a point where the exhaust is "flat" in an effort to smooth the torque curve.

Title: Re: Tuned intake and exhaust track?
Post by ebonysresearch on 09/28/10 at 06:09:08

I have some carb diameter formulas and some stepped exhaust formulas. The carb diameter formula is usually done when they design the engine though...and a stepped exhaust is some serious fabrication. I'll post them after work.

Title: Re: Tuned intake and exhaust track?
Post by klx650sm2002 on 09/28/10 at 09:10:48

This is what happens at the end of a pipe.
http://i119.photobucket.com/albums/o147/klx650sm2002/Wavereflection.jpg
And this at a transition (diameter change)
http://i119.photobucket.com/albums/o147/klx650sm2002/Transition.jpg
Clive W :)

Title: Re: Tuned intake and exhaust track?
Post by ebonysresearch on 09/28/10 at 15:54:22

Carb size :
( RPM x bore squared x stroke ) / ( 108000 = square root x 24.5 ) = Carb size in mm

Carb size by intake valve diameter

( Intake valve diameter x .85 x 25.4 ) = carb size in mm

Step exhaust :
Step 1 25% of total exhaust length
Step 2 32%
Step 3 43%

Title: Re: Tuned intake and exhaust track?
Post by Trippah on 09/28/10 at 16:21:00

the aside - Charon, do you do a route? I drive a ' big yellow bus' mostly to sporting events, occassionally as a sub, also vans when everyone hides. 40 something chatty little people can sure be noisy. ;D

Title: Re: Tuned intake and exhaust track?
Post by Charon on 09/28/10 at 19:40:16

Trippah, I usually do field trips and sporting events. I sometimes run routes if one of the other drivers is unable for some reason.

We are a small K-12 school, so I get a little of everything. Perhaps the noisiest is a first or second grade field trip. The teacher will usually bring along a boombox and some children's CD. Then the kids sing along to the music. I have seriously considered earplugs.

Title: Re: Tuned intake and exhaust track?
Post by BurnPgh on 09/28/10 at 20:56:12

a boombox? My teachers always just told us to sit down and be quiet. Had one field trip where the rest of the class wouldnt do so. Teacher had the driver turn around and go back to the school. We copied a section of the dictionary for the duration of the planned field trip.

Title: Re: Tuned intake and exhaust track?
Post by verslagen1 on 09/28/10 at 21:41:50

424548495E54404B465454270 wrote:

square root of what?
and what about that equal sign, don't look like it's in the right place.

Title: Re: Tuned intake and exhaust track?
Post by Lupo on 09/28/10 at 21:52:30

Whoa...this is the third night in a row that this has made me very sleepy...............

Title: Re: Tuned intake and exhaust track?
Post by ebonysresearch on 09/29/10 at 06:22:58

I'm having some trouble with that one too. Guess I should have taken better notes. it looks like a check mark in my notes...? freakin dumb harley technicians...

I just had my heads apart too when i re did it at work so I could have measured the intake valves. I'll look through my black book at work today and see if I have that equation available with better writing.

Title: Re: Tuned intake and exhaust track?
Post by ebonysresearch on 09/30/10 at 16:46:35

All right. I found it.

Carb size:

Square root of ( RPM x Bore X Bore x Stroke / 108000 ) = Carb size in inches.

I am not finding the symbol for the Square root on my keyboard...?

Title: Re: Tuned intake and exhaust track?
Post by verslagen1 on 09/30/10 at 17:31:35

(yada yada yada)^.5

Title: Re: Tuned intake and exhaust track?
Post by LANCER on 10/01/10 at 04:13:41

OK SO WHAT ARE THE REAL NUMBERS ?