David Vizard - Which to prioritize - PORT FLOW or PORT VELOCITY?
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I give what is it ?
According to the chart it starts around 210-215 fps and lower which are generally fair size ports you'd have to go way out of your way to install. 215 fps would be 2.39" ave csa, that's bigger than a 190 trick flow, on a 5500 rpm 318.
No, So ? Point ?
I never made the case for importance of flow bench velocities, (That's DV and Chris) actually my point in this thread is somewhat contrary to DV and others.
I do tell me more about how I think or know lol
These aren't my formula's I ain't making the case that there 100% correct but they are used by some people in the industry one way or another.
A lot of times I get called out for just parroting what I've read and watched, when really most of my arguments are questioning the what I've read and watch generally the norm.
Here's a thought. After you work out what the ideal port velocity is then you can work out what the perfect fuel droplet size is to go with it.
Then after that you can tell me how you plan to control the size of that droplet?
Then after that you can tell me how you plan to control the size of that droplet?
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So here is my take on the Boss Cleveland head port. Have the factory make them the size of the grand canyon, then let the racers epoxy to optimize port size. If it is a huge factory port, it's legal, yes? Most racers need to go bigger. Maybe Ford teams went smaller? I have seen many pics of heads all epoxied up raising the floor of the port.
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I agree a lot of race teams did that but your average builder didn’t and the stock engine definitely didn’t and they dyno higher than any of the other muscle car small blocks with a relatively small cam.
Found this on Cleveland Heads:
Even though a Cleveland head had great flowing attributes, they still received serious modifications. That’s why they were so dominant back then.
First, the exhaust side had 1.400˝ milled off. An aluminum plate that thickness 2 5/8˝ high was bolted in place relocating the exhaust ports higher. This was known as high porting. The original iron part of head port was welded or brazed and recontoured to match the plate port, making the exit as smooth and straight as possible. The longer you could keep the primary header tube straight off the port, the better the flow. A 19˝ long 1˝ wide X .250˝ thick steel girdle was used on top the aluminum plate. Torque sequence and poundage was also altered.
The intake port also had radical modifications. It was ported to the max flow and the pushrod boss cut through. Then braze or epoxy sealed that area. The intake rocker studs were moved over .250˝ to the right along with the push rod slot. The guides were plates cut, rebridged and welded.
Then blades were carefully installed in the port entrance to calm the turbulence. That blade installation had to be done on a flow bench. If placement was not perfect, it could ruin the efficiency.
Then we had offset dowels to index the head. We reinforced the headdeck by posting. Posting was drilling, tapping and installing 1/2˝ studs into the larger open areas in the head’s deck against the roof. Then mill the deck smooth.
Another must were the 3/8˝ load bolts from the outside ends of the heads through tapped holes nestling against the thin intake seats on #1 and #8 to keep them round. The work done in the combustion chambers was an art form. All was handwork. No CNC.
There are also things called: Roush type 351C-4V port stuffers. Essentially giving you raised port heads in factory style castings.
Even though a Cleveland head had great flowing attributes, they still received serious modifications. That’s why they were so dominant back then.
First, the exhaust side had 1.400˝ milled off. An aluminum plate that thickness 2 5/8˝ high was bolted in place relocating the exhaust ports higher. This was known as high porting. The original iron part of head port was welded or brazed and recontoured to match the plate port, making the exit as smooth and straight as possible. The longer you could keep the primary header tube straight off the port, the better the flow. A 19˝ long 1˝ wide X .250˝ thick steel girdle was used on top the aluminum plate. Torque sequence and poundage was also altered.
The intake port also had radical modifications. It was ported to the max flow and the pushrod boss cut through. Then braze or epoxy sealed that area. The intake rocker studs were moved over .250˝ to the right along with the push rod slot. The guides were plates cut, rebridged and welded.
Then blades were carefully installed in the port entrance to calm the turbulence. That blade installation had to be done on a flow bench. If placement was not perfect, it could ruin the efficiency.
Then we had offset dowels to index the head. We reinforced the headdeck by posting. Posting was drilling, tapping and installing 1/2˝ studs into the larger open areas in the head’s deck against the roof. Then mill the deck smooth.
Another must were the 3/8˝ load bolts from the outside ends of the heads through tapped holes nestling against the thin intake seats on #1 and #8 to keep them round. The work done in the combustion chambers was an art form. All was handwork. No CNC.
There are also things called: Roush type 351C-4V port stuffers. Essentially giving you raised port heads in factory style castings.
Why you straw manning me.
Both these are way low on my priorities.
If you make decent choices these are relatively taken care of.
Pretty awesome what some teams did with them.
Seen AMC welded like 3 heads together to make their Pro stock heads.
That's what she said.
If you have reversion then you have the wrong camshaft.
I can hope he is meaning the sound/flow wave naturally created when the valve closes and the intake charge reverses??? Time that reversion with the next intake and you can overfill the cylinder. So choosing intake runner length, port velocity/size and cam shaft profile.
How about you tell us how port velocity changes during piston travel vs valve opening? Surely you have a formula for that too.....
I'm sure both are very low on the "average" engine builders priority list too.....
Anytime you have both valves open after combustion has taken place means you'll have reversion. How much you have and how you mitigate it are a different discussion altogether. If the cylinder isn't filling it isn't making power.
The intake valve should be opening towards the end of the exhaust stroke. Then the remaining exhaust push will help create a vacuum to start the intake charge early and fill faster. Is this what you mean?
What's the pressure in the chamber when the intake valve opens? Theoreticals are not realities.
Anytime you create conditions that invite reversion like bigger valves, bigger runners, bigger intake bigger carb and longer duration camshafts then you are not filling the cylinder no matter what theoretical air flow or velocity you measure on a steady airflow bench. Exhaust gases usually are innate but if you're making lots of CO during the burn that's a burnable gas that requires energy to burn again and that's diluting the next intake charge when it heads back towards the intake valve
Do you hold yourself to these top 1% of builder (pro stock nascar f1) level of standards for your builds ?
It's how you look down at anything people are doing compared to these world class builders but don't seem to hold yourself to the same level.
And ?
He generally doesn't make points or answer questions directly, he answer with question like he's a Professor or something trying to lead you to his point if he has one.
That's nice little summary, but so what, excess reversion is only a problem if you got an excess, and the power lost would have to be high enough compared to any gains from the mods, there's compromises to be made everywhere.
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