PRP Velocity Lessons
See post 5 above. Which of Step 1 or Step 2 are you claiming is incorrect? If Step 1, please tell me which of the flow bench outputs that I should not believe (you get to choose from cfm, pressure or velocity cause that's all there is). If Step 2, then we are in agreement and we are saying the same thing in different ways.
I’ll say this, then I’m done.
The general thinking is more flow, more power. I’m saying that’s not true. Because shape (and the velocity gradients that change with shape) is what matters. A certain shape may look great on the flow bench but be a power loser. And the corollary is true. You can get less flow on the flow bench and make more power.
I thought I explained that testing at one pressure is a bad policy. That’s why so many people just write off steeper than 45 degree seats. Bad testing makes the 50 look bad, but it makes more power. Every time I’ve ever done it. And in some cases I used a 55 degree seat.
Reverse flow testing is really important.
Sound is just about as critical as anything else. A dirty, noisy port can flow more than a quiet port but if you didn’t ever look at a flow number and went in and fixed the noise it would make more power. Every time.
Would it gain or lose on a flow bench? It’s hard to say. That’s why I use the 50 degree seat as an example.
BTW, I see guys on line trying to do 50 degree seats with a stone. I won’t say it’s impossible, but it’s close to it.
And one last thing. The top cut is crucial to a good port. The angle and how it blends into the chamber makes a big difference. You’ve heard the old wives tale not to sink the valve? Like many other things, it got convoluted by the masses. I can’t tell you how many times I’ve seen heads from porters who should know better that didn’t have any top cut.
I’m not suggesting to sink a valve. I’m saying you need to get the most top cut you can. Of course, if you are fighting a reversion issue you may want to sink a valve to clean that up, but it’s a band aide at best.
