Fabricating velocity probes

[86rocco]

I use a dremal with a cutting disc, that does a pretty good job of it then I use one of my small drill bit to de-burr the hole by hand.

[Nick]

I found a 1/8 tube bender at the hobby store today. It makes a nice bend. Now I have to figure out how to drill those little tiny holes. The bender was 11 bucks. My camera sucks, but here's a pic.

[86rocco]

Nice bender! As for the holes, check that same hobby shop, I'll bet they has small drill bits too. I used a #64 drill bit in my dremel, if you don't have a dremel, a pin vise or small hand drill will work fine too.

[Mousehouse1]

Most hobby stores have the drill bits. Like rocco said they are a #64 or 1/32". Buy several. I use my drill press and haven't broken on yet. Knock on wood. But they are very small and could break very easily.

Nick did you have to heat the brass tubing any to bend it? I need to see if a local hobby shop has a bender like that. I was just heating the end of the brass tube up enough to bend it. The smallest I was able to get one was around .540.

I haven't tried mine out yet but the hardest part I found was soldering the front of the brass tube and not getting any solder in the small holes. The last one I made I moved the holes back a little farther and that solved the problem.

[Nick]

No heat is needed with this thing. It's a lot like a bender you would use for roll cages.

How many holes are there supposed to be in the end? I put 2, one on each side. .040" I drilled them by hand with my fingers, It was to small to get in the drill press.

Is there any way to calibrate this deal? Or at least to see if it is in the ball park.

I finished it today and took it for a spin. I'm not to sure about it just yet. One thing for sure is you can see where the air is the fastest. At one part, just before the short turn on the right side, It will go to 33" when testing at 28". If I try hard to hold it about 1/8 off the floor right there it will go to 36". I guess this tells me that the port is choked there ??? I just don't know if it is accurate to say how fast the air speed is for sure. I really don't know how to use it. It does not seam to like being held on its side above the valve. I suppose the air is rushing in the small holes in the end.

Anyone have experience using these? Tips on how to use?

Pic below shows how I did it. I wanted brass inside and out but they were out of 1/8. I wanted it now so I just used aluminum tube for the out side, and formed it around the smaller tube on the ends, and sealed it with super glue. The black part is a 3/16 T fitting, it fits nice and snug over 1/8 tube. There is a hole in the out side tube that lines up with the T.
I'm going to make another when the store gets some brass.

Anyone have comments?


Nick

[Rick360]

Nick,
The pitot probe looks good. Nice job.

I have a Perf Trends pitot. It has 8 very little holes evenly spaced around the tube about .375" from the tip. The holes look smaller than 1/32". I don't have anything to measure it with but I'd guess .015-.020" ? ? ?, but that is just a guess.

Your d.p. readings sound about right for most heads I've probed. I have yet to see one below 28" when testing at 28". The floor at the short turn is definitely the fastest place, usually in the center.

I usually take readings in a 3x3 grid at the short turn and at the pushrod pinch for 9 velocities at each place. You will find that any place the air is turning, the air will rush to the short path and be fastest there. Pushrod side walls and short turns in most heads are where the air is fastest.

I bought mine a year ago and what an eye opener. Happy probing! :p

Rick

[Nick]

Rick
I used the formula you posted, and came up with 268fpm at the push rod point. It was stable there. My readings were in the 18" range. (1.7 CSA) Larry M posted on speed talk that:


300 FPS = 20.5" Pilot pressure when Flow testing at 28"

240 FPS = 13.14" Pilot Press when Flow testing at 28"



So I Know I'm in the ball park.

What I don't get is, what the A symbol stands for in his math.


FPS = ( Pilot_Press ^ .5 ) * 66.2
350.3 FPS = ( 28 ^ .5 ) * 66.2


Perhaps I'm retarded. Anyone know what that stands for. I would like to know how close I am to 268fpm.

Also my holes are about .5 from the end, maybe I should try making them closer to the end.

As a side note the more I mess with this 289 head the more of a pos It becomes. I did not understand what was meant by ski jump floor until I cut one in half. That was an eye opener!
Well it's fun to learn.

I also find it interesting that the area that will produce the most flow, and is causing the most turbulence, is also the hardest to get to. :angry: Also, good job Ford for putting that water jacket under the ski jump!!!!

Nick

[Rick360]

If the symbol you are talking about is ' ^ ', that is the symbol for "to the power of" in Excel. When a 2 is after it, it is the same as "squared", when there is a .5 after it, like this ' ^.5 ', it is the power of 1/2 or same thing as square root.

Rick

[86rocco]

[Mousehouse1]

I was listening to one of the speed talk cd's I bought and Joe Mondello says he uses a piece of welding rod with a small piece of string (3/4-1" long) attached to the end to check a port for dead spots.

Thought it would be an easy alternative for those that don't want to build pitot tubes. I might try it to see how it works.

[PFM]

OK,

Thanks all for the great pictures, I managed to build a nice probe over the weekend. Now I would like to calibrate it, the formula posted was for 28" I am sure there is a formula that includes test pressure and the impact velocity. Mouse?

Next with my FP1 I would love to slide the probe say 6" into the flow element and compare it's FPS reading with that of the home made velocity probe. Any input on this idea? Anyone?

Thanks in advance,

PFM

[SuperRunner]

Where do you guys get your small tubing?

[86rocco]

[86rocco]

[SuperRunner]