velocity stacks

[Derret]

Aluminium will stay put if you use an interference fit & use green loctite on 'em. The only way it will come off is if you heat it.

That was not the problem The carb ears snappped off, bolts came loose.

 

[Derret]

Aluminium will stay put if you use an interference fit & use green loctite on 'em. The only way it will come off is if you heat it.

That was not the problem The carb ears snappped off, bolts came loose.

Or- probably the other way round- loosened bolts & vibration = failed carb ears.

 

[dr gary turner]

i beleive your talking about the 20j... jerry and i have spoken about that several times... i can see how machining the mouth and i.d of the stack will make for a almost seamless transition... the only issue with that will be i dont have a ton of carbs so testing lengths and shapes of stacks would require a ton of carbs... i would like to leave the mouths alone till i can find a length i know would work...

dr.turner,,, thank you for your insight and direction as to length...could you please elaborate more on the o-ring placement and fit to the lip of the mouth???

The O rings are NOT on the lip of the stack. They go around the stack at the base where it fits into the body of the carb. SOOOOOO the stack actually "FLOATS" and can really resonate. Gary

alden

 

[carlo cardinale]

The shape and angle of the bell mouth opening are important also. See attached, not the best quality picture but you'll get the idea:

View attachment 14955

...good info,

can you post the links???

 

[Charles Perdue]

I have been watching this thread as it progressed.

There is a lot of information floating around on this subject, some of it is good , some of it is not good and some of it is pure bull.

There is much that has to be taken into consideration when designing a carb, a bell mouth, a spray bar, ect.

One of the most common mistakes made is the assumption that the air entering the bell and thus the carb is in a contunious flow. This is very far from being accurate. When the engine is running. going from idling to the beginning of the mid range, the air and the fuel that has been drawn, is actually reversing flow on each intake pulse. Even after the engine is above this into the upper mid range and into full RPM's the air flow is pulsing each time that the intake opens and closes. If this is not take into full consideration, the theories, formulas, charts and graphs are not any help.

Just my 3 cents worth (inflation).

Charles

 

[tnrcboatracer]

I have been watching this thread as it progressed.

There is a lot of information floating around on this subject, some of it is good , some of it is not good and some of it is pure bull.

There is much that has to be taken into consideration when designing a carb, a bell mouth, a spray bar, ect.

One of the most common mistakes made is the assumption that the air entering the bell and thus the carb is in a contunious flow. This is very far from being accurate. When the engine is running. going from idling to the beginning of the mid range, the air and the fuel that has been drawn, is actually reversing flow on each intake pulse. Even after the engine is above this into the upper mid range and into full RPM's the air flow is pulsing each time that the intake opens and closes. If this is not take into full consideration, the theories, formulas, charts and graphs are not any help.

Just my 3 cents worth (inflation).

Charles

Yes, the standoff fog aboue the individual stacks on a V8 Alky motor on a dyno are something to see. A little vapor cloud forms over each venturi. Much trhe same as our boat motors.

 

[dwilfong]

I have been watching this thread as it progressed.

There is a lot of information floating around on this subject, some of it is good , some of it is not good and some of it is pure bull.

There is much that has to be taken into consideration when designing a carb, a bell mouth, a spray bar, ect.

One of the most common mistakes made is the assumption that the air entering the bell and thus the carb is in a contunious flow. This is very far from being accurate. When the engine is running. going from idling to the beginning of the mid range, the air and the fuel that has been drawn, is actually reversing flow on each intake pulse. Even after the engine is above this into the upper mid range and into full RPM's the air flow is pulsing each time that the intake opens and closes. If this is not take into full consideration, the theories, formulas, charts and graphs are not any help.

Just my 3 cents worth (inflation).

Charles

Charles

You bring up a very good point.

In your experience would making the distance from the intake valve and the spray bar lessen the intake pulse at the spray bar or would this give the fuel more of a chance to separate from the air.

There is a lot of info on 2 stroke eng with reed valves but a rotor valve eng is a different eng. The reeds limit the back pulse of the case in to the intake manifold.

When I ran my Cagiva 125 I used 2 stage reeds one laid on top of the other. This helped with the low end power.

I dont think a reed would move fast enough to keep up with the RPM's of these small eng.

David

 

[Charles Perdue]

Hello David, with the induction systems and the tuned exhaust systems that we use today it has changed the way that we approach the intake tuning.

In the earlier years when we were using stub pipes (headers only for you younguns) and megaphone exhaust, we used the different shaped and length velocity stacks to attempt to tune the intake tract, engine RPM and exhaust together for an increase in performance.

Today with the use of tuned pipes, this has really complicated using the reasonance and harmonics of the intake tract. Now we attempt to do no harm by eliminating as much of the harmonics as we can by going to the shortest intake track as possible to put the harmonics above the range of the engine RPM's. An added benefit of doing this is that with a properly tuned pipe and matching engine timing, the tuned pipe will actually draw through the carb itself for better performance.

Today, the better carbs design and shape is to try to reduce the effects of the reversion and pulsing. At best, it is still a compromise.

Charles

 

[Chris Wood]

charles,

with your work on carb as of late.. would you say the dia and shape of the bell mouth is more important over spraybar styles and dimentions or is it all play together.

p.s.. it was good to talk with you at hobart

chris

 

[Charles Perdue]

Hello Chris, it was good to meet you at Hobart, I really enjoyed myself. It was just over too quick.

On the carbs, they are just part of the total engine, pipe, fuel, plug, engine load, ect. package. As I change one part, shape or dimension on the carbs, it has an effect on the other parts. I try to strike a balance as to the engine size and on applications as I learn more. They are a work in progress.

Charles

 

[Charles Perdue]

Back to what was being discussed earlier on this thread.

The first prototype Zoom carbs used a delrin bell. Rough machine the bell to approximate dimensions with about .004 press where attached and use CA. Finish machining the parts when they are together. They will stay in place.

Another trick that I used was modeling clay to to change the shape of the bell to do a quick test on the flow bench for different shapes and profiles.

Charles

 

[dwilfong]

Charles

So if I under stand the shorter the intake track the easier it is for the pipe to draw threw the carb. this will put more in the pipe to shove back in to the cylinder.

Thanks for the insight.

David

 

[camaroboy383]

charles,, thank you very much for chiming in on this topic,, i was waitin for a reply from you as you have the experience building carbs and such...the modeling clay is a great idea for testing, as far as shape goes..

this turned out to be a great topic!!! thank you all

alden

 

[carlo cardinale]

Back to what was being discussed earlier on this thread.

The first prototype Zoom carbs used a delrin bell. Rough machine the bell to approximate dimensions with about .004 press where attached and use CA. Finish machining the parts when they are together. They will stay in place.

Another trick that I used was modeling clay to to change the shape of the bell to do a quick test on the flow bench for different shapes and profiles.

Charles

Baeutiful...

have you a flow bench???

Is homemade????

Can you post some photo of your flow bench??

I'm very interested to buy or build one.

have also dyno???

i have build one for our .12 & .21 engines

TKS

carlo cardinale

 

[Charles Perdue]

Back to what was being discussed earlier on this thread.

The first prototype Zoom carbs used a delrin bell. Rough machine the bell to approximate dimensions with about .004 press where attached and use CA. Finish machining the parts when they are together. They will stay in place.

Another trick that I used was modeling clay to to change the shape of the bell to do a quick test on the flow bench for different shapes and profiles.

Charles

Baeutiful...

have you a flow bench???

Is homemade????

Can you post some photo of your flow bench??

I'm very interested to buy or build one.

have also dyno???

i have build one for our .12 & .21 engines

TKS

carlo cardinale

Hello Carlo, you have a PM.

Thanks, Charles

 

[camaroboy383]

carlo,,, id be interested to see this dyno,, can u post a pic??? the problem ive seen with these home made dyno's is every one seems to be different and the actual numbers change constantly from one to the other... to me the only thing they are good for is measuring a difference when the engine is messed with...

some insight please..

alden

 

[carlo cardinale]

carlo,,, id be interested to see this dyno,, can u post a pic??? the problem ive seen with these home made dyno's is every one seems to be different and the actual numbers change constantly from one to the other... to me the only thing they are good for is measuring a difference when the engine is messed with...

some insight please..

alden

my homemade dyno...

 

[carlo cardinale]

my dyno at work...

http://www.wpengines.com/index.php?option=com_content&view=article&id=38&Itemid=44

 

[jetpack]

 

[Charles Perdue]

my dyno at work...

http://www.wpengines...id=38&Itemid=44

Hello Carlo, I like your dyno. I do not have a dyno at the present to test the model engines. When we raced the go karts I hade both types of dynos, a brake type and and inertia type. I like the inertia type better as you were able to view the RPM, torque and HP curves under acceleration rather than a steady speed. For us the inertia dyno helped us to work on the acceleration out of the corners. We won a lot of races by being to pull the other karts out of the corners and pass before the end of the straight-a-way.

What software and data logging package are you using. I used a package by Performance Trends.

Attached is a picture of my flow bench that I use to test the RC engine carbs.

Charles