Flow bench techniques Question.

[amichie]

I have seen videos and photos online of people using dyes and smoke to show where the air is flowing inside the port when on the flow bench.

Easiest thing to do is feed a cotton thread in the port when its running. Question is does this show anything useful. In mine it is only happy when its hugging the port floor and short side turn. If the thread is lifted up to the port roof it just goes nuts with what I presume is turbulence.

I was expecting the air to flow across the back of the valve and into the chamber on the centre side of the chamber since this would be the most direct route (straightest-no bends) but there is no way you can get the thread to come off the short side turn no matter how you try and feed the thread in.

Any one got any useful flow bench experience/techniques they want to share?

[V-Na]

A cotton thread won't show a streamline since it's tethered and inextensible. You need to use a gas like kerosene smoke.

[jeffro ra28]

Why cant you use perspex for your theoretical cylinder?

That way you can see what the dye is doing when used in a "wet flow" setup.

The other way to determine where the air speed is or is flowing is to use a manometer and plot it around the areas in the port to see which area gives the highest suction on the manometer. Generally the areas which suck the hardest are the area's with the most air speed.
You can also use ball bearings attached to welding rods and place them around the port to see what affects they have on the flow bench manometer aswell. They act as a restriction, so when its placed in a critical part of the port the flow on the flow bench manometer will decline, meaning that the area you placed the ball bearing is a high speed, high flow area of the port. The area's that acheiv the greater decline in flow when the "restriction" is placed there are generally the "fastest" parts of the port.

Take this information how you like. This sort of stuff can mean alot of different things to different people. But that is how i was taught and how i understand it to work. Obviously there are some inconsistencies and alot of "theory" behind it.

[amichie]

Why cant you use perspex for your theoretical cylinder?

That way you can see what the dye is doing when used in a "wet flow" setup.

The other way to determine where the air speed is or is flowing is to use a manometer and plot it around the areas in the port to see which area gives the highest suction on the manometer. Generally the areas which suck the hardest are the area's with the most air speed.
You can also use ball bearings attached to welding rods and place them around the port to see what affects they have on the flow bench manometer aswell. They act as a restriction, so when its placed in a critical part of the port the flow on the flow bench manometer will decline, meaning that the area you placed the ball bearing is a high speed, high flow area of the port. The area's that acheiv the greater decline in flow when the "restriction" is placed there are generally the "fastest" parts of the port.

Take this information how you like. This sort of stuff can mean alot of different things to different people. But that is how i was taught and how i understand it to work. Obviously there are some inconsistencies and alot of "theory" behind it.

Thanks. I found some similar info on a website today.

I think I will try the ball on a stick idea next.

Can someone give this fellow some rep. I got a message saying I need to spread mine around

[jeffro ra28]

Also, what you choose to do with the port once you have the information these techniques provide you with will either make or break the design and effectiveness the port has.

There are conflicting arguments that say once you have found the high speed area's of the port and if they are directly ontop of the port walls then this area should be tickled with the grinder. Alot of things need to be considered in this respect before taking any metal from this "high speed area". A sound understanding of how each area of the port works will help make these choices.

I can only advice in this area in some instances as most of my flow bench > dyno experience was mostly alcohol fueled V8's in sprint cars, boats and some speedway. Some of this information crosses over to multivalve engines but i am still experimenting alot with them.