the exhaust pipe formula! - MVAgusta.net
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post #1 of 23 (permalink) Old 12-27-2011, 10:16 PM Thread Starter
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Thumbs up the exhaust pipe formula!

the exhaust pipe formula:
here it is, been around for a long time
the formula;
Length= 850 x Exhaust opening [degrees BBDC+180]/rpm[power peak]
the Exhaust opening is effective opening ie; 0.040-0.050"
Diameter, the pipe must hold, from the valve to the end of the head pipe twice the cylinder volume.
D = 2x the square root of swept cylinder volume[in cc]/8.2/L/Pi

here it is for a HP 42s calculator
01 LBL pipes
02 input "size cc" [of engine]
03 input "cyl" [# of cylinders]
04 input "rpm"
05 input "Exhaust opening" BBDC
06 180
07 +
08 850
09 X
10 recall "rpm"
11 divide
12 store "primary length"
13 recall "size cc"
14 recall "cyl"
15 divide
16 recall "primary length"
17 divide
18 8.2
19 divide
20 Pi
21 divide
22 square root
23 2
24 X
25 view "primary length"
26 end
this is for a HP calculator. it uses "RPN" reverse Polish notation!!!
the usual warnings; tight bends screw things up a bit
and it uses an average for the density of the gas in the pipe. primary length is from the valve to the end of the head pipe. collectors same length,or a multiple of it. diameter; because of the asymmetrical firing order 60 degree twin [this gets weird] you have to play with it.
ideally the pipe should taper because of frictional losses, [Mr. Bernoulli's equation]. tapering the pipe will effect the density of the gas in the pipe which will change the speed of the shockwave, ergo the length/diameter of the pipe. it is acoustics no more no less.
measure a Ducati's pipes, you'll die laughing 6 inches different, then look a the torque chart the cylinders are trying to make power at 2 different rpms causes a harmonic vibration in the crank...makes the alternator nut unscrew!!!
that's why they write different injection maps for identical pistons, cams and heads, different pipes!!!
before someone says anything; fueling for air cooled motor cylinders CAN be different.
have fun!

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post #2 of 23 (permalink) Old 12-27-2011, 10:28 PM
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Wink +10 Noel

And now I'm even more confused.
Since your on the roll today, where is that part you did on the SPR gearbox ratios - please

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post #3 of 23 (permalink) Old 12-27-2011, 10:32 PM
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The 2-Stroke Tuners Handbook......Gordon Jennings masterpiece.....where is my copy?????

I used to be fast....now I just dream about it.
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post #4 of 23 (permalink) Old 12-28-2011, 12:37 AM Thread Starter
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Wtf?

Quote:
Originally Posted by esq'z me View Post
The 2-Stroke Tuners Handbook......Gordon Jennings masturbation piece.....where is my copy?????
what a crock of shit......i've known that closet Saab freak since the '70s when he was driving around in a trashed TR-3

go look up his article on bolt stress..........

"with a round file, file a 0.1 diameter of the bolt, deep groove all the way around the bolt......"

brilliant you just reduced the tensile strength of the bolt by 36%.........and added stress risers

guess who listened to that fucking MORON??????

HONDA JAPAN!!!!!!! they grooved ALL the head bolts on the cars and had to RECALL all of them!!!!!!! because they DIDN'T LOOK AT THE NUMBERS and listened to a moron with a bully pulpit

before ONE of you opens your MOUTH.....
I worked in the Engineering Dept at HiShear Corp an aerospace fastener company, so i know about bolts

Louie Ecker the chief metallurgist at NAA and then HiShear was one of my mentors

let me think, who knows more about 2 strokes?
Siegfried Rauch
Jeorg Mueller
Don Emler
Stuart Toomey
E.C. Birt
Irv Kanemoto
and the Engineers at.....
Beta
Bultaco
Derbi
DKW
Husquvarna
Kreidler
Mordibelli
MZ
OSSA
Zundapp

if i missed anybody i'm sorry

fuck me, they are all LIGHT YEARS ahead of Gordon Jennings......

i know Siegfried from Das Motorrad
worked with Don and Stuart for ~30 years

and where is your book again?

forget it

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post #5 of 23 (permalink) Old 12-28-2011, 12:59 AM
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Smile Oi

That wasn't it

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post #6 of 23 (permalink) Old 12-28-2011, 09:11 AM
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Quote:
Originally Posted by theknurl View Post
and where is your book again?
I don't know....I lost it somewhere around 1978.

I used to be fast....now I just dream about it.
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post #7 of 23 (permalink) Old 12-28-2011, 01:37 PM Thread Starter
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Thumbs up gear ratios?

Donsy;
here you go;
http://www.mvagusta.net/forum/showth...ht=gear+ratios

Noel-theknurl

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post #8 of 23 (permalink) Old 12-28-2011, 02:50 PM
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is this the formula for a two stroke muffler?
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post #9 of 23 (permalink) Old 12-28-2011, 08:36 PM
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Thumbs up +1000:1

Quote:
Originally Posted by theknurl View Post
Thanks Noel, your a legand mate.

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post #10 of 23 (permalink) Old 12-29-2011, 03:44 AM
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i'm assuming the results are in inches?

so the exhaust opening is degrees before tdc?

wouldn't different length headers serve much the same purpose as different length inlet trumpets such as many 4 cylinder bikes have, ie., spreading the torque curve at a slight cost to the outright peak?

Last edited by brad black; 12-29-2011 at 03:50 AM.
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