randy331 wrote: ↑
Sat Mar 10, 2018 9:29 pm
GARY C wrote: ↑
Sat Mar 10, 2018 4:23 pm
randy331 wrote: ↑
Sat Mar 10, 2018 2:41 pm
I was talkin to one of the guys from Bullet Cams about emc cams. He said of the teams he was involved with, that actually tested some cams, they all ended up very similar to what we had.
Think about all the different platforms and flowz of the various engines, yet you end up at the same location on cams.
This wouldn't include the ones that picked one cam and went with it.
That begs the question, if the flowz guy and the non flowz guy arrive at the same cam then who's right and who's wrong?
The main reason they'd end up with similar cams is, the most important paramiters for picking a cam are dictated by rules at the EMC.
The number 1 thing is rpm. The emc sets that.
Compression is one. that's set by the emc.
In a round about way valve acceleration is set by the rules, and some years/classes lift is. Those 2 things impact valve events.
Any flowz difference within the confines of the proper csa for the cubes entered would have no affect on valve events.
That's what I'm trying to say. Thinking cause you gained a few cfm you need a different cam, or if your ex flowz a few more cfm now you need less ex duration.
But isn't it interesting how easy it is to revive a thread with a low lift flow comment, or flowz speced cam comment ??? LOL
The assumption to is that the .050" numbers and lift numbers published tell the entire story.
It's the shape of the flow curve that matters
and is what the cam grinders are looking for. Again, it's a metric. If I developed the port via CFD, I'd be likely looking at mass flow, not volumetric flow. Mass flow tells you more anyway, and Mike has revealed this is actually what he's calculating (with some assumptions). Harold and Harvey, were the first ones to understand (that I could find, and going back to the early '70s) that mass flow into and out of the cylinder doesn't necessarily follow what the flowbench shows. Harold stopped designing any symmetrical lobes by the mid 1970s. Harvey used different ramp styles. Mike has true assymetrical profiles. Comp has many lobes with positive or negative offset at max lift.
That said, I'm not going to cam a hemi, where I/E ratios may be way tighter (so higher exhaust flow compared to intake) at low lifts than I would a wedge head. A 4 valve head may even have a negative I/E ratio (exhaust flows more than the intake). It's totally applicable to a point.
I think so many work on one kind of combination (SBC, BBC, or whatever) and a certain style of engine at that (10:1 street engines or the like) that they get trapped into this thinking.
I was going to post a bunch of quotes, but it's better if people just read these threads in their entirey. Lots of fantastic posts by guys like Darin Morgan, Harold Brookshire, Larry Meaux, Mike Jones, and many others.
Cam Profile In Relation to Airflow Curve, Harold?
Area Under the Curve
Head Flow vs Cam Choice
Longer Exhaust Duration... Why and When??
http://www.speedtalk.com/forum/viewtopi ... =1&t=29382
I think flow at TDC would be far more constructive