intake tract volume

[scooterwerx]

anyone have info regarding intake tract volume? i am building a manifold since im sick of nb50 manifold pointing the carb straight at the shock. i know there is a tuned length for it, but how does one calculate this? i guess i could find an se50 manifold, but id rather build an optimized one...thanks

[Kenny_McCormic]

SE50 wont fit(different bolt patern), the SB50 mani is the bet for the spree style motor you have.

[noiseguy]

Ahh, I'm going to skip past asking why you need to know that.

You can calculate the volume of things like that by sealing an end and filling them with oil. Use a graduated cylinder (like from lab class) to measure the volume of oil in cc's (or whatever.)

[Bear45-70]

anyone have info regarding intake tract volume? i am building a manifold since im sick of nb50 manifold pointing the carb straight at the shock. i know there is a tuned length for it, but how does one calculate this? i guess i could find an se50 manifold, but id rather build an optimized one...thanks

Length depends on diameter, cylinder volume and rpm you are tuning to. The variables are a lot and interacting. To small and not enough air, to big and not enough air velocity, both bad.

[scooterwerx]

thanks, but i dont have a spree motor. nb50 is aero motor, the se50 manifold has the same bolt pattern, its longer and points the carb away from the rear shock. i want to know how to calculate what an optimal volume and length would be for my motor setup. i just want to know if the se50 manifold is good, or if i should build an optimized one and also not not have to have the nb50 manifold pointing the carb at the shock...
bear, is there any sort of calculation for these things your talking about? thats exactly what i need...its a 21mm carb, 69cc cylinder volume(if the stroke is 39mm, stock nb50 crank? i remember hearing it was 39mm) max power is fairly low in the rpm range, im working on a tach, so until then, id guess 7 to 8k rpm...thanks

[Bear45-70]

thanks, but i dont have a spree motor. nb50 is aero motor, the se50 manifold has the same bolt pattern, its longer and points the carb away from the rear shock. i want to know how to calculate what an optimal volume and length would be for my motor setup. i just want to know if the se50 manifold is good, or if i should build an optimized one and also not not have to have the nb50 manifold pointing the carb at the shock...
bear, is there any sort of calculation for these things your talking about? thats exactly what i need...its a 21mm carb, 69cc cylinder volume(if the stroke is 39mm, stock nb50 crank? i remember hearing it was 39mm) max power is fairly low in the rpm range, im working on a tach, so until then, id guess 7 to 8k rpm...thanks

This is the best article I know of.

http://www.team-integra.net/sections/ar ... icleID=466

Just Google "Intake manifold volume"

[scooterwerx]

yes! thats exactly what i was looking for. all of that theory they discuss is for four strokes, it all applys to the two stroke as well?

[Clivester]

anyone have info regarding intake tract volume? i am building a manifold since im sick of nb50 manifold pointing the carb straight at the shock. i know there is a tuned length for it, but how does one calculate this? i guess i could find an se50 manifold, but id rather build an optimized one...thanks

To quote from http://en.wikipedia.org/wiki/Cylinder_head_porting:

"The internal aerodynamics involved in porting is counterintuitive and complex and absolutely requires an air flow bench, a thorough knowledge of the principles involved and use of engine simulation software in order to determine what needs to be done to optimize a port."

Why don't you just take noiseguy's advice - test the internal volume of just the 2 manifolds by liquid measure. Then estimate the diameter and length. If they are close then switch. You can't account for reverse pressure wave dynamics with simple equations.

Clive.

[Bear45-70]

yes! thats exactly what i was looking for. all of that theory they discuss is for four strokes, it all applys to the two stroke as well?

Yes.

[Bear45-70]

anyone have info regarding intake tract volume? i am building a manifold since im sick of nb50 manifold pointing the carb straight at the shock. i know there is a tuned length for it, but how does one calculate this? i guess i could find an se50 manifold, but id rather build an optimized one...thanks

To quote from http://en.wikipedia.org/wiki/Cylinder_head_porting:

"The internal aerodynamics involved in porting is counterintuitive and complex and absolutely requires an air flow bench, a thorough knowledge of the principles involved and use of engine simulation software in order to determine what needs to be done to optimize a port."

Why don't you just take noiseguy's advice - test the internal volume of just the 2 manifolds by liquid measure. Then estimate the diameter and length. If they are close then switch. You can't account for reverse pressure wave dynamics with simple equations.

Clive.

You are so right. It's not like figuring out the cc of your cylinder. It's complicated even if you have all the computer programs and a flow bench.

[burnt_toast]

This may help, two-stroke tuner's handbook by gordon jennings:

http://www.scootertime.net/viewtopic.php?f=20&t=2052

[scooterwerx]

alright. i know it is difficult. i know it is complicated. will this prevent me from trying it? nope. i enjoy challenges. it it doesnt work right, i will throw it in the scrap bin and build a different one. its only metal. all i am asking for is if anyone had info regarding this subject. why? because i did not have anything but my own experience, and because i know that it is a complicated subject. so thanks for the info, those who provided. im only trying to experiment a little here....nothing wrong with that eh?

btw, the se50 manifold has much more internal volume than the nb50 one, its at least twice as long...

[scooterwerx]

In all probability, those who will read this book will have neither a computer nor the spare hours for a theoretical determination of intake tract length. Thus, it becomes necessary to arrive at this length experimentally, which fortunately is a much shorter (and more accurate) means of accomplishing the same thing.

direct quote from jennings...

[burnt_toast]

In all probability, those who will read this book will have neither a computer nor the spare hours for a theoretical determination of intake tract length. Thus, it becomes necessary to arrive at this length experimentally, which fortunately is a much shorter (and more accurate) means of accomplishing the same thing.

direct quote from jennings...

hah nice, well just gives you reassurance to experiment away

[scooterwerx]

thanks for the link, i read half of it last night! im gonna go blind now