Stan Weiss wrote:If we look at the geometry of the rotating assemble we see that the rod and crank arm are at 90 degrees to each other between 70-75 degrees crank rotation ATDC and by 90 degrees crank rotation we are not gaining very much extra power per degree we keep the exhaust valve closed.
Let me ask you this. Why do I care about peak exhaust flow when the piston is well on the way up at that point. Why are we not looking at low lift flow where most of the heavy work is done?
turdwilly wrote:If exhaust port flow is completely irrelevant, why in the hell the Ford pro stock guys spend so much time/money doing this in the 1970s? Just didn't know any better back then?
CGT wrote:Warp Speed wrote:WTF is "Flowz"?!?
I think it may be Latin or an Olde English spelling of FLOW.
groberts101 wrote:4vpc wrote:groberts101 wrote:
Thank you. Goes right back to the "no need to try and get out what couldn't get in".
What if someone designed some clever gadget that forced more air in, what would that do to the in/ex valve ratios?
Easy one. It would be akin to making the old OEM Cleveland 4v intake port smaller via stuffed floors or port plates. Run that with a factory exhaust port and even the old cast manifolds and what happens to the power curve?
Would you actually think.. "exhaust port don't need any improvements in "flowz"" to help maximize the now larger amount of mass that gets squeezed in"? Or just rob peter to pay paul back some added duration and/or lift over on the exhaust lobe and call it the same end result anyways?
An engine is just a huge series of compromises to get towards the end result. All I'm getting at with all this is that if you trivialize or underestimate one piece of the puzzles worth or ability to affect some other piece?.. then you're downplaying the physics involved with the whole deal. I come here for the first hand experiences and physics breakdown of it all.. not diluted comments like.. "doesn't matter.. you won't be able to measure it or feel 5 horsepower on the street anyways". I can get that crap on some other sites.
From the standpoint of properly timing and sizing the flow window.. which is what all this needs to be dwindled down to anyways.. there are various ways to go about moving the same mass. You can vent larger amounts of mass out the cylinder throughout the low/mid range and limit lift and slow the valve down all the way to max lift. Or you can lower the low lift flow capability of same port(smaller valve size with 55° seats?) and increase the valve open speeds(rocker ratio/roller lobe?). Purely rhetorical but which combo is best? Best for what?.. valvetrain life.. higher rpm? Do both combo's make same power under 6k? Optimized cam requirements wouldn't change either?
groberts101 wrote:Upsize the exhaust valve and run more rocker ratio and you will see the results in the first half of the throttle pedal travel.
novadude wrote:groberts101 wrote:Upsize the exhaust valve and run more rocker ratio and you will see the results in the first half of the throttle pedal travel.
I'd admit that I'm just a dumba**, but I need someone to explain this one to me.
In the first half of the throttle travel (throttled intake), you are filling the cylinder less. Why would you need more flowz to evacuate it? I realize that intake pressure will be lower during overlap, but I would think that there would be no ill effects from a restrictive exhaust port. A very late EVO might even be beneficial at low throttle openings to get the most work possible out of the expanding gasses. Why open it early and worry about good low lift / mid-lift exhaust flowz if there is less "stuff" to evacuate?
Am I thinking about this wrong? Can someone explain the science?
groberts101 wrote:Lots of assumptions being made that you can actually gather any useful data "flowing" an exhaust port.....
Stan Weiss wrote:turdwilly wrote:If exhaust port flow is completely irrelevant, why in the hell the Ford pro stock guys spend so much time/money doing this in the 1970s? Just didn't know any better back then?
Because the original shape was just ugly. It had a very small radius turn in the port.