Carb & intake path ways.

[JPriami]

Does it do much good to polish intake paths & carbs? Since I have everything taken apart I thought hey I’ll try polishing that. It’s a mirror all the way through now. I am going to try a couple of other areas next. Oh and is there a larger bore carb that boast performance on a OPS .67?

 

[Ray Sametz]

Aeromarine makes a .470 after market carb. http://www.aeromarinerc.com Polishing does'nt hurt, but that spraybar does'nt help. :unsure: :unsure:

 

[JPriami]

really?

 

[El Zorro]

really?

Cut the 45 degree angle off of the end of the spray bar and square it off ( make it 90 degrees ). It will work more efficient also if it only protrudes one third of the way into the inside diameter of the carb. Has something to do with adomizing the fuel and air mixture better before it actually gets into the engine. The controline speed guys were doing this more than 30 years ago................

Dick Tyndall

 

[JPriami]

really?

Cut the 45 degree angle off of the end of the spray bar and square it off ( make it 90 degrees ). It will work more efficient also if it only protrudes one third of the way into the inside diameter of the carb. Has something to do with adomizing the fuel and air mixture better before it actually gets into the engine. The controline speed guys were doing this more than 30 years ago................

Dick Tyndall

Dick,

Thanks for that tip. I didnt know that.

 

[barry]

To Quote Dick "adomizing the fuel and air mixture better before it actually gets into the engine" I am a automotive engineer and have built a few drag car motors in my time. Years ago we tried the polish theory on a 454 big block polishing heads, carb and intake manifold to the same finish you have done and found it didn't work. The fuel was not being agaitated eoungh to create the required air fuel mixture. From this we found a ruffer surface basicly acts like a beater where as the polished surface once the fuel entrered it was beading. The polished surface the motor produced 920 hp and ran ruff. After scouring the surface back up we got to 1150hp and ran like a top .Please keep in mind this is on a alcohol fead drag car not a nitro motor. I will be interested to here how it goes keep us posted.

Barry

 

[rmprecision]

To Quote Dick "adomizing the fuel and air mixture better before it actually gets into the engine" I am a automotive engineer and have built a few drag car motors in my time. Years ago we tried the polish theory on a 454 big block polishing heads, carb and intake manifold to the same finish you have done and found it didn't work. The fuel was not being agaitated eoungh to create the required air fuel mixture. From this we found a ruffer surface basicly acts like a beater where as the polished surface once the fuel entrered it was beading. The polished surface the motor produced 920 hp and ran ruff. After scouring the surface back up we got to 1150hp and ran like a top .Please keep in mind this is on a alcohol fead drag car not a nitro motor. I will be interested to here how it goes keep us posted.
Barry

I'm with Barry on this one.

I run ski race boats and have played around with 6ltr chevs for a while.

Currently run a 355 chev with standard dart iron heads no porting with a solid cam and a 650cfm holley.

This motor on a dyno made a gen 506hp on pump fuel(98ron)

My engine man(who works with supercars) belives you need to atomize the fuel on the intake.

This means in a rough way that a coarse inlet tract the better it will work.

This seems to work on a V8 dont know if the same theory works on model nitro motors.

There are some guys on this forum who know a hell of a lot more on this than i do.

 

[Jerry Wyss]

Careful what you polish,

Fuel and oil tend to cling to a smooth (polished) surface, removing some of it from the air/fuel charge on its

way to be ignited. A minutely rougher surface doesn't allow the fluids to cling as much and keeps more of it

in suspension with the air. The rough cast case ports accomplish this task pretty well and I have seen some

2 stroke dirt bike case ports and carb manifolds that were cast much like a miniture "Badlands" mountain

range to keep the fuel mixed with the air. Pretty extreme but you could tell that engineers had the problem

on their mind.

JW

 

[Ray Sametz]

Comparying apples an oranges. Polishing 2 stroke 60 engine carb against 454 big block. Better to have barrel rotate freely, then glass bead an jam up. MHO. Theres a theory name for air passing over square cut spray bar. Anybody know it. h34r: h34r:

 

[El Zorro]

Hi Ray! In my 40 plus years of playing with model engines I always heard that engines that ran on alcohol ( METHANOL ) would benifit most from smooth intake ports ( smooth, NOT highly polished ) and engines that ran on gas did better when the fuel/air mixture was running through casted parts ( i.e. not so smooth ). The more you break up the fuel/air mixture, the better the combustion, etc. The venturis I made for model engines were "polished" with fine Scotch- Brite pad material...........the same material that I use to buff out all of my turn fins for the boats today. I have seen model engines running on a test stand ( with an airplane propeller ) that had a highly polished venturi and at times you could actually see the fuel bead up on the inside of the venturi. I always used Scotch-Brite on my hardware, I always sanded the bottoms of my monos with 220 grit sand paper, and I never polished any props, either. I'm sure other people have other ways that they do these things, but this is what worked for me. I am not an engineer. I tried to learn from others who were sucessful in doing the things I wanted to do. I would think Jim Allen would have quite a bit of knowledge in this area..............Jim?

Don't know about the square spray bar thing..............don't believe I've ever seen one. Don't keep us in suspense any longer!

Dick Tyndall

 

[aaron alberico]

dont polish any area in the intake area's

only after it leave's the engine

regards Aaron

 

[Tim_Duggan]

dont polish any area in the intake area'sonly after it leave's the engine

regards Aaron

Well actually you can polish in front of the spraybar as the fuel is not atomised at that point, but after the spraybar is a different story. As has already been mentioned the fuel is more likely to pool back up on a smooth surface than a rougher surface. I've seen this first hand.

 

[Jim Allen]

Hi Ray! In my 40 plus years of playing with model engines I always heard that engines that ran on alcohol ( METHANOL ) would benifit most from smooth intake ports ( smooth, NOT highly polished ) and engines that ran on gas did better when the fuel/air mixture was running through casted parts ( i.e. not so smooth ). The more you break up the fuel/air mixture, the better the combustion, etc. The venturis I made for model engines were "polished" with fine Scotch- Brite pad material...........the same material that I use to buff out all of my turn fins for the boats today. I have seen model engines running on a test stand ( with an airplane propeller ) that had a highly polished venturi and at times you could actually see the fuel bead up on the inside of the venturi. I always used Scotch-Brite on my hardware, I always sanded the bottoms of my monos with 220 grit sand paper, and I never polished any props, either. I'm sure other people have other ways that they do these things, but this is what worked for me. I am not an engineer. I tried to learn from others who were sucessful in doing the things I wanted to do. I would think Jim Allen would have quite a bit of knowledge in this area..............Jim?Don't know about the square spray bar thing..............don't believe I've ever seen one. Don't keep us in suspense any longer!

Dick Tyndall

Dick,

The curvature of the intake stack can provide a substantial increase in the laminar flow of the input air & therefore an increase in the maxium quanity & velocity of air delivered. This happens when the turbulence is eliminated in the intake stack. A change in curvature of 90 degress is essential for proper performance. As an example, the .625 ID bore carburetor on my .90 engine has a 1.382 OD at the begining of the velocity stack. Velocity stacks which are polished appear to do little at idle & low RPM as well as wide open throttle RPM. A machined finish apears to be adequate.

Jim Allen

 

[El Zorro]

Hi Jim,

I totally agree with your last post. Most of my engine knowledge came from a few of the better known controline speed fliers from North Carolina many moons ago. A venturi ( or carb I. D. ) is more efficient when it is tapered on both ends............inlet and outlet, and the smallest diameter is at the spray bar or "spike" as some people call it. I always called this the "squeezing the water hose" effect. I remember one of these NC speed guys I was doing some work for told me long ago to look at the engine intakes on the jet engines on the large passenger jets. They are rather blunt and rounded and not sharp like most venturis on our model engines. It helps on the little engines, too................

Always appreciate you sharing your knowledge with us............thanks.

Dick Tyndall