CB desert sled - Page 19

Mr. Fisherman · 01-22-2013, 11:25 PM

Quote:

Originally Posted by Luke

Rick did some brazing this evening. You know it's serious work when we're drinking beer again.

The airbox is more of a manifold. There is one inlet that an air filter will be clamped to and 4 outlets that go to the individual carbs. Here's the progress so far:

The inlet still needs to be brazed in and then the two parts brazed together. And yes, those tabs on the side will either be folded up or cut off.

No pictures, but the little bender did a lot better on 22ga than 16ga.

Unfortunately it's still a bit wonky from yesterday's abuse.

Uhm, shouldn't the goesinta be equal or greater than the goesoutta? Cough Cough...

Luke · 01-23-2013, 12:02 AM

Quote:

Originally Posted by Mr. Fisherman

Uhm, shouldn't the goesinta be equal or greater than the goesoutta? Cough Cough...

On the factory bikes I've seen some are, some aren't.

Why?

Mr. Fisherman · 01-23-2013, 12:10 AM

Quote:

Originally Posted by Luke

On the factory bikes I've seen some are, some aren't.

Why?

Thinking I have seen lots of folks open up an air box and the exhaust to get better flow... If the filtered inlet is too small couldn't it choke those 4 carbs when you are stroking across the playa at WOT? Or maybe you could just use smaller diameter exhaust pipes

It just looked like those 4 carbs might want to suck more air than can pass through that single smallish inlet at WOT. That said I am not an engineer nor do I play one on tv

MortimerSickle · 01-23-2013, 10:12 AM

On the other hand, only one carb is drawing air at any given time, no?

Luke · 01-23-2013, 10:47 AM

Quote:

Originally Posted by Mr. Fisherman

Thinking I have seen lots of folks open up an air box and the exhaust to get better flow... If the filtered inlet is too small couldn't it choke those 4 carbs when you are stroking across the playa at WOT? Or maybe you could just use smaller diameter exhaust pipes

It just looked like those 4 carbs might want to suck more air than can pass through that single smallish inlet at WOT. That said I am not an engineer nor do I play one on tv

They're about 1" carbs, and the inlet is 2" pipe so the area is about the same.

According to a couple of online things, the inlet should flow enough air for a bit under 240hp.

Quote:

Originally Posted by MortimerSickle

On the other hand, only one carb is drawing air at any given time, no?

Yup. 4 cylinters, 4 stroke. Unless I put in a really goofy camshaft.

MortimerSickle · 01-23-2013, 11:04 AM

Quote:

Originally Posted by Luke

... a bit under 240hp.
...

Cool, you are going to need a lot of tires.

Luke · 01-23-2013, 11:08 AM

Quote:

Originally Posted by MortimerSickle

Cool, you are going to need a lot of tires.

And three or four more motors.

Low594 · 01-23-2013, 11:50 AM

Quote:

Originally Posted by Luke

And three or four more motors.

Or that BIG turbo!

MortimerSickle · 01-23-2013, 12:25 PM

Quote:

Originally Posted by Low594

Or that BIG turbo!

But then, once you get more air going in....

kellymac530 · 01-23-2013, 03:57 PM

2 things to think about on the inlet/outlet size is that a carburetor works off of flow of air...which is created by the vacum of the cylinder on INTAKE stroke. I believe that motor fires in 4 fires, not 2, so only one induction at a time. The inlet being 2" and each carb outlet being 1" means it never needs more than 1" of air at a time.

The second thing, which kind of offsets that, is that you DO want a larger and unrestricted flow before the carb...think of a velocity stack. That is import at WOT where a smooth, high flow is key.

So a balance of the 2 is important and that is calcuable.

People need to remember that in cylindrycal shapes doubling the diameter is not just twice as much....Pi x r2

I do not know the formula for his optimal inlet size, but he WELL MAY be just fine.

kellymac530 · 01-23-2013, 04:02 PM

TOO much air is just as bad. Try running a bike without an air cleaner, they blubber and bog just run like crap.
Usually even running those stupid little UNI filter socks makes them run terrible and requires re-jetting that often is never right.

kellymac530 · 01-23-2013, 04:11 PM

If the outlets are 1" and the inlet is 2" as he stated, then the area of the openings are exactly the same...

1" outlet = 0.5" radius, squared= 0.25 x 3.1415 {Pi rounded off} = 0.785375
2" inlet = 1" radius, squared= 1 x 3.1415 = 0.785375......

He might well be just fine....there is however the length of the tubing on the in and out lets...that could disturb air flow some...play with it.

Low594 · 01-23-2013, 04:32 PM

Quote:

Originally Posted by kellymac530

If the outlets are 1" and the inlet is 2" as he stated, then the area of the openings are exactly the same...

1" outlet = 0.5" radius, squared= 0.25 x 3.1415 {Pi rounded off} = 0.785375
2" inlet = 1" radius, squared= 1 x 3.1415 = 0.785375......

He might well be just fine....there is however the length of the tubing on the in and out lets...that could disturb air flow some...play with it.

I think your calculator is broken... 1 x 3.1415 = 3.1415!

RedRaptor22 · 01-23-2013, 07:57 PM

Volume, shape and baffling has a lot to do with airbox efficiency too, nowadays most bikes have airboxes tuned so that between after one intake pulse the air is still moving into the airbox at faster than normal speed so that it crams into the next intake port to fire vs just getting sucked in by vacuum alone....but that would involve lots of computer simulation and dyno time to achieve.

I think whats going on here is going to work fine, like others said, you don't want too big of an opening or you will lose serious amounts of mostly bottom and mid range power that tuning will not fix.

DRjoe · 01-23-2013, 08:23 PM

Quote:

Originally Posted by kellymac530

If the outlets are 1" and the inlet is 2" as he stated, then the area of the openings are exactly the same...

1" outlet = 0.5" radius, squared= 0.25 x 3.1415 {Pi rounded off} = 0.785375
2" inlet = 1" radius, squared= 1 x 3.1415 = 0.785375......

He might well be just fine....there is however the length of the tubing on the in and out lets...that could disturb air flow some...play with it.

Yep a 1" hole has the same area as 2" hole

I think the pain killers are getting to you.

01-23-2013, 10:12 AM	#274
MortimerSickle Semi-Adventurer Joined: Dec 2005 Location: Rainville, Orygun, where moss is a road hazard. Oddometer: 9,942	On the other hand, only one carb is drawing air at any given time, no? __________________ I miss round headlights. "When I was a young man, I liked to race my horse...." - G.H.W.S. 1878-1962

01-23-2013, 03:57 PM	#280
kellymac530 motorcycle addict Joined: Feb 2010 Location: so. cal. Oddometer: 927	2 things to think about on the inlet/outlet size is that a carburetor works off of flow of air...which is created by the vacum of the cylinder on INTAKE stroke. I believe that motor fires in 4 fires, not 2, so only one induction at a time. The inlet being 2" and each carb outlet being 1" means it never needs more than 1" of air at a time. The second thing, which kind of offsets that, is that you DO want a larger and unrestricted flow before the carb...think of a velocity stack. That is import at WOT where a smooth, high flow is key. So a balance of the 2 is important and that is calcuable. People need to remember that in cylindrycal shapes doubling the diameter is not just twice as much....Pi x r2 I do not know the formula for his optimal inlet size, but he WELL MAY be just fine. __________________ it is easier to ask for forgiveness than permission

01-23-2013, 04:02 PM	#281
kellymac530 motorcycle addict Joined: Feb 2010 Location: so. cal. Oddometer: 927	TOO much air is just as bad. Try running a bike without an air cleaner, they blubber and bog just run like crap. Usually even running those stupid little UNI filter socks makes them run terrible and requires re-jetting that often is never right. __________________ it is easier to ask for forgiveness than permission

01-23-2013, 04:11 PM	#282
kellymac530 motorcycle addict Joined: Feb 2010 Location: so. cal. Oddometer: 927	If the outlets are 1" and the inlet is 2" as he stated, then the area of the openings are exactly the same... 1" outlet = 0.5" radius, squared= 0.25 x 3.1415 {Pi rounded off} = 0.785375 2" inlet = 1" radius, squared= 1 x 3.1415 = 0.785375...... He might well be just fine....there is however the length of the tubing on the in and out lets...that could disturb air flow some...play with it. __________________ it is easier to ask for forgiveness than permission

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01-23-2013, 07:57 PM	#284
RedRaptor22 Gnarly Adventurer Joined: Jan 2012 Location: Louisiana Oddometer: 136	Volume, shape and baffling has a lot to do with airbox efficiency too, nowadays most bikes have airboxes tuned so that between after one intake pulse the air is still moving into the airbox at faster than normal speed so that it crams into the next intake port to fire vs just getting sucked in by vacuum alone....but that would involve lots of computer simulation and dyno time to achieve. I think whats going on here is going to work fine, like others said, you don't want too big of an opening or you will lose serious amounts of mostly bottom and mid range power that tuning will not fix.