Tumble Meter

[jsa]

I'm wondering where to locate a tumble meter, which I imagine to be like a paddle wheel parrallel to the cylinder head ?

[Tony]

I doubt if you can buy such a thing. The problem is that there is no standard official unit of tumble to measure. So it is not really possible to build a measurement instrument with any meaningful readout.

Sure you can build a paddle wheel, and say it spins at 438 Rpm, what does that tell you exactly ?

[jsa]

Tony,

I planned on making something. Either a round magnet and a nearby coil to read frequency, or a little dc motor to generate a volt output. Driven by a paddle wheel or some other means.

I think frequency will be more stable long term as armature and brush wear would decay a voltage output over time.

In isolation the number is useless, however as a head is developed, tracking the measurement may reveal steps in the right or wrong direction. I would think if flow increased by 50% and tumble fell by 50% then that would be bad. Charting rpm per cfm might be educational

Just need to work out some way of fitting it to get a repeating measurement ?

[Tony]

It is a really tough problem. Trying to define swirling and tumbling uneven airflows into some sort of repeatable numbers. I really don't know what the solution to the problem is.

[DaveMcLain]

You might want to talk to Kevin at Perf Trends because they do offer a fixture to measure tumble using their swirl meter. I don't think that there is any real standard for swirl or tumble measurments but I would say that as long as you have a quantity you'll be able to tell if you're gaining or losing swirl or tumble with your porting.

[jsa]

Dave,

I've seen a picture of the performance trends fixture. They appear to take flow from the side of the bore fixture and then down into the bench ? I wonder if that would induce tumble all by itself.

[DaveMcLain]

That's tough to say, I have not seen that fixture in action. I guess the thing to do would be to try an experiment on your own bench using a clear cylinder. I think I would experiment with a small hole drilled through the side of the cylinder with piece of string inserted through the whole to show what the air is doing in there, might tell you something.