Spray bar design and size

[dwilfong]

I have bin doing some testing on my make shift flow bench and running on the water in the last few months.

I thought I would share some of the finding I have noticed.

The newest test is with a MAC .550 carb on my EVO .77 eng.

This is a disk eng with a 67 crank and a 80 P/L in it.

I had problems with it taking the plug as it would hit the pipe and rev over.

So I have fitted the carb with a 5/32 OD brass tubing for the spray bar.

This makes a .125 ID spray bar.

I have also started using X-Large fuel line 5/32 thew the whole system and 5/32 tubing in the tanks.

Checking it for mist pattern on my flow box found the sweet spot with it sticking in about 1/4 percent of the boar.

Now this seamed like large size for this size eng but it worked very well.

Can idle and run at very low speed and will pop right off.

The throttle response is very nice and the needle is easy to set with 60% nitro.

No more lean over when it hits the pipe and Rev's.

This is leading me to believe that with high nitro a large spray bar is the best bet.

I can not say that this is the answer to all carbs or nitro % but with a large carb running high nitro it has worked very well for me.

Just some insight on what I have seen.

 

[stan simpson iv]

Did the spray bar have an angle,hole's,a slit,or just a straight pc.

 

[dwilfong]

Just strait cut off with the inside cleaned with a countersink tool and a little run of emery around the out side.

The round boar carbs did not like the slots in the back side or a hole in the front.

There is a dead spot right behind the bar that can not be filled with mist.

That is why the sweet spot is close to the edge.

Now on oval boar say a .550 with a .130 flat in the center the dead spot is not there. So the bar needs to be put further in the boar.

the mist pattern is much better with the oval boar carb.

There is some thing with the elongated boar that removes the dead spot behind the bar.

 

[Rick Pirrone]

hi David

i had a mate from our club do the same with my vac 45 spray bar and straight away i was able to pull some props that i couldn't pull before and got the pipe length down to 9.25 from 10.0.

made a huge difference to the tuning side of things

cheers rick

 

[Rick Pirrone]

hi David

i had a mate from our club do the same with my vac 45 spray bar and straight away i was able to pull some props that i couldn't pull before and got the pipe length down to 9.25 from 10.0.

made a huge difference to the tuning side of things

cheers rick

Who me LOL

of course my trusty engineer lol

 

[dwilfong]

So how big have you gone with the spray bar on the 45?

I have a .125 ID in my 1.01 and I am thinking now to go the next step larger.

 

[Rick Pirrone]

So how big have you gone with the spray bar on the 45?

I have a .125 ID in my 1.01 and I am thinking now to go the next step larger.

hi david

not sure what standard is but im at .096 id 2.5 mm

cheers rick

 

[dwilfong]

thanks Rick for the info.

That is larger than a stock 1.01 spray bar.

Kinda makes you think.

How big is to big?

 

[Jack ODonnell]

I have bin doing some testing on my make shift flow bench and running on the water in the last few months.

I thought I would share some of the finding I have noticed.

The newest test is with a MAC .550 carb on my EVO .77 eng.

This is a disk eng with a 67 crank and a 80 P/L in it.

I had problems with it taking the plug as it would hit the pipe and rev over.

So I have fitted the carb with a 5/32 OD brass tubing for the spray bar.

This makes a .125 ID spray bar.

I have also started using X-Large fuel line 5/32 thew the whole system and 5/32 tubing in the tanks.

Checking it for mist pattern on my flow box found the sweet spot with it sticking in about 1/4 percent of the boar.

Now this seamed like large size for this size eng but it worked very well.

Can idle and run at very low speed and will pop right off.

The throttle response is very nice and the needle is easy to set with 60% nitro.

No more lean over when it hits the pipe and Rev's.

This is leading me to believe that with high nitro a large spray bar is the best bet.

I can not say that this is the answer to all carbs or nitro % but with a large carb running high nitro it has worked very well for me.

Just some insight on what I have seen.

What is doing by increasing the ID of the spray bar. J

 

[dwilfong]

My thinking is it gives more of a vacuum signal to the needle by the increased are of the hole in the spray bar.

I will do some testing and hook up a vacuum gage to the spray bar and see what is what when I get time.

Also I think the hole flow across a needle in a system with larger tubing is different.

There is probably some formula to calculate it all but I am not interested in the theory per say as much as the end results.

I hate math!!!!!!!!!!!!!!!!!!!!!!

 

[anthony_marquart]

Thgis interests me also. I bet most spray bar ID's are set or tuned for car type performance. Where we don't need as much of control thru the mid range,.. I read something from Marty Davis years ago about atomization of fuel and carbs... seems like I remember he found some gains. Man,.. the older I get the more I realize I know so little!!!!!

 

[dwilfong]

Wow that is a good increase in vacuum signal to the needle.

It also goes back to you cant put 10gal of S#!T in a 5gal hat thing.

High nitro = large fuel volume.

 

[Tom Foley]

Was it the stock VAC 45 carb ?

 

[Stefan Larsson]

Hi

Race in Fsr-v i have a geared 15cc cmb 91 rs evo, What do you think of my spraybar can i also use o bigger hole?

 

[dwilfong]

Hi

Race in Fsr-v i have a geared 15cc cmb 91 rs evo, What do you think of my spraybar can i also use o bigger hole?

Open to 2.5mm if using 30% nitro.

 

[Jeff Lutz]

I have bin doing some testing on my make shift flow bench and running on the water in the last few months.

I thought I would share some of the finding I have noticed.

The newest test is with a MAC .550 carb on my EVO .77 eng.

This is a disk eng with a 67 crank and a 80 P/L in it.

I had problems with it taking the plug as it would hit the pipe and rev over.

So I have fitted the carb with a 5/32 OD brass tubing for the spray bar.

This makes a .125 ID spray bar.

I have also started using X-Large fuel line 5/32 thew the whole system and 5/32 tubing in the tanks.

Checking it for mist pattern on my flow box found the sweet spot with it sticking in about 1/4 percent of the boar.

Now this seamed like large size for this size eng but it worked very well.

Can idle and run at very low speed and will pop right off.

The throttle response is very nice and the needle is easy to set with 60% nitro.

No more lean over when it hits the pipe and Rev's.

This is leading me to believe that with high nitro a large spray bar is the best bet.

I can not say that this is the answer to all carbs or nitro % but with a large carb running high nitro it has worked very well for me.

Just some insight on what I have seen.

Many people have been running them that big for a long time. Andy Brown, and Dick Jones have even made comments about this and no one listened. I machine my spray bars with .125" i.d. Just so you know, I found no advantage to going bigger than your fuel line I.D. I tried .140" and went back to .125"

 

[dwilfong]

I have bin doing some testing on my make shift flow bench and running on the water in the last few months.

I thought I would share some of the finding I have noticed.

The newest test is with a MAC .550 carb on my EVO .77 eng.

This is a disk eng with a 67 crank and a 80 P/L in it.

I had problems with it taking the plug as it would hit the pipe and rev over.

So I have fitted the carb with a 5/32 OD brass tubing for the spray bar.

This makes a .125 ID spray bar.

I have also started using X-Large fuel line 5/32 thew the whole system and 5/32 tubing in the tanks.

Checking it for mist pattern on my flow box found the sweet spot with it sticking in about 1/4 percent of the boar.

Now this seamed like large size for this size eng but it worked very well.

Can idle and run at very low speed and will pop right off.

The throttle response is very nice and the needle is easy to set with 60% nitro.

No more lean over when it hits the pipe and Rev's.

This is leading me to believe that with high nitro a large spray bar is the best bet.

I can not say that this is the answer to all carbs or nitro % but with a large carb running high nitro it has worked very well for me.

Just some insight on what I have seen.

Many people have been running them that big for a long time. Andy Brown, and Dick Jones have even made comments about this and no one listened. I machine my spray bars with .125" i.d. Just so you know, I found no advantage to going bigger than your fuel line I.D. I tried .140" and went back to .125"

I run 5/32 ID fuel line now but the tank is only 1/8 ID tube.

Walt is building a new tank with the larger tubing and I am building a new needle on the carb.

The new system will be 5/32 ID all the way from the tank to the carb including the spray bar.

 

[Jeff Lutz]

I have bin doing some testing on my make shift flow bench and running on the water in the last few months.

I thought I would share some of the finding I have noticed.

The newest test is with a MAC .550 carb on my EVO .77 eng.

This is a disk eng with a 67 crank and a 80 P/L in it.

I had problems with it taking the plug as it would hit the pipe and rev over.

So I have fitted the carb with a 5/32 OD brass tubing for the spray bar.

This makes a .125 ID spray bar.

I have also started using X-Large fuel line 5/32 thew the whole system and 5/32 tubing in the tanks.

Checking it for mist pattern on my flow box found the sweet spot with it sticking in about 1/4 percent of the boar.

Now this seamed like large size for this size eng but it worked very well.

Can idle and run at very low speed and will pop right off.

The throttle response is very nice and the needle is easy to set with 60% nitro.

No more lean over when it hits the pipe and Rev's.

This is leading me to believe that with high nitro a large spray bar is the best bet.

I can not say that this is the answer to all carbs or nitro % but with a large carb running high nitro it has worked very well for me.

Just some insight on what I have seen.

Many people have been running them that big for a long time. Andy Brown, and Dick Jones have even made comments about this and no one listened. I machine my spray bars with .125" i.d. Just so you know, I found no advantage to going bigger than your fuel line I.D. I tried .140" and went back to .125"

I run 5/32 ID fuel line now but the tank is only 1/8 ID tube.

Walt is building a new tank with the larger tubing and I am building a new needle on the carb.

The new system will be 5/32 ID all the way from the tank to the carb including the spray bar.

That is what I have now. I build my tanks, I have .125" all the way.

 

[dwilfong]

I have bin doing some testing on my make shift flow bench and running on the water in the last few months.

I thought I would share some of the finding I have noticed.

The newest test is with a MAC .550 carb on my EVO .77 eng.

This is a disk eng with a 67 crank and a 80 P/L in it.

I had problems with it taking the plug as it would hit the pipe and rev over.

So I have fitted the carb with a 5/32 OD brass tubing for the spray bar.

This makes a .125 ID spray bar.

I have also started using X-Large fuel line 5/32 thew the whole system and 5/32 tubing in the tanks.

Checking it for mist pattern on my flow box found the sweet spot with it sticking in about 1/4 percent of the boar.

Now this seamed like large size for this size eng but it worked very well.

Can idle and run at very low speed and will pop right off.

The throttle response is very nice and the needle is easy to set with 60% nitro.

No more lean over when it hits the pipe and Rev's.

This is leading me to believe that with high nitro a large spray bar is the best bet.

I can not say that this is the answer to all carbs or nitro % but with a large carb running high nitro it has worked very well for me.

Just some insight on what I have seen.

Many people have been running them that big for a long time. Andy Brown, and Dick Jones have even made comments about this and no one listened. I machine my spray bars with .125" i.d. Just so you know, I found no advantage to going bigger than your fuel line I.D. I tried .140" and went back to .125"

I run 5/32 ID fuel line now but the tank is only 1/8 ID tube.

Walt is building a new tank with the larger tubing and I am building a new needle on the carb.

The new system will be 5/32 ID all the way from the tank to the carb including the spray bar.

That is what I have now. I build my tanks, I have .125" all the way.

When you tried the .140 was that with 1/8 line and tank tubing?

 

[Jeff Lutz]

I have bin doing some testing on my make shift flow bench and running on the water in the last few months.

I thought I would share some of the finding I have noticed.

The newest test is with a MAC .550 carb on my EVO .77 eng.

This is a disk eng with a 67 crank and a 80 P/L in it.

I had problems with it taking the plug as it would hit the pipe and rev over.

So I have fitted the carb with a 5/32 OD brass tubing for the spray bar.

This makes a .125 ID spray bar.

I have also started using X-Large fuel line 5/32 thew the whole system and 5/32 tubing in the tanks.

Checking it for mist pattern on my flow box found the sweet spot with it sticking in about 1/4 percent of the boar.

Now this seamed like large size for this size eng but it worked very well.

Can idle and run at very low speed and will pop right off.

The throttle response is very nice and the needle is easy to set with 60% nitro.

No more lean over when it hits the pipe and Rev's.

This is leading me to believe that with high nitro a large spray bar is the best bet.

I can not say that this is the answer to all carbs or nitro % but with a large carb running high nitro it has worked very well for me.

Just some insight on what I have seen.

Many people have been running them that big for a long time. Andy Brown, and Dick Jones have even made comments about this and no one listened. I machine my spray bars with .125" i.d. Just so you know, I found no advantage to going bigger than your fuel line I.D. I tried .140" and went back to .125"

I run 5/32 ID fuel line now but the tank is only 1/8 ID tube.

Walt is building a new tank with the larger tubing and I am building a new needle on the carb.

The new system will be 5/32 ID all the way from the tank to the carb including the spray bar.

That is what I have now. I build my tanks, I have .125" all the way.

When you tried the .140 was that with 1/8 line and tank tubing?

Yes, then I went back to .125 to match the lines and tank tubing.