Desk Top Dyno
John, since a flow bench is just really for air flow improvement or correction and basic " tell what a head has for cfm", what kinda flow numbers do you think a bench would show if the camshaft lobe was involved, opening on its particular ramp, and at speed ?
Because I see guys on there flow bench running a particular lift for 10 seconds or longer, a valve isn't open at that particular lift for longer than, id guess way less than a second. I imagine the entire lobe -valve lift is done before .050 of a second ( wild *** guess)
Probably need some high speed cameras and other cool stuff to test like that. It seems that would be a more real world test.
Do you know or heard of anyone trying to test like this ?
The answer is a flow bench can never duplicate what happens in a running engine. No matter what you do it just can’t. That’s a limit of the tool.
That doesn’t mean you can’t use one and learn and make more power. As I have repeated probably a thousand times, not every number coming off the flow bench is the truth. Just like a dyno. You know what it’s like looking at all the data.
As for the question of low lift flow and guys wetting theirselves over “low lift” flow, all you need is a degree wheel and some time.
Plot out the curve, AT THE VALVE because that’s really what the engine really sees. Then let’s say you have a .600 lift cam. Look at the TIME the valve is open from .400 lift on the opening side to .400 lift on the closing side.
That’s where most of the cylinder filling occurs. The valve is moving so fast from cracking off the seat until about .400 lift that the valve moves through those low lifts so fast that the valve is really still in the way. It’s always in the way, it’s just worse at low lifts.
And, the piston is in the way at those lifts too.
And again, the pressure drop the port sees is far greater at lower lifts so flowing a port at a simple pressure drop can make the numbers look bad when they aren’t bad.
You need to bring home that flow bench, get it set up and start using it. You’ll learn so much so fast your head will spin. And you’ll most likely learn that most of what you read about flow testing is pure bullshit.
One of the best investments I made was my flow bench. It proved out who was telling the truth and who was lying.