David Vizard - Which to prioritize - PORT FLOW or PORT VELOCITY?

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Hysteric said:
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?
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How far off is the average guy with a decently built and well tuned engine from being an ideal atomization, vaporization etc.. Machine ? And how much HP could one expect to gain refining their combination and how much time money and energy would it require to do so ?
 
273 said:
But I think for most of us, that aren't bound by strict rules and highly competitive racing, the average performance guy. To build an engine with Slightly less inefficient HP is generally gonna be easier and less expensive to build.

A highly efficient 1.35-1.65 lbs-ft per cid is generally gonna be out of the range for most of us.

If you want 500-550 hp and torque with peak hp around 6000 rpms most don't think to build a highly efficient 360 to do it with only 220-240 cfms but a less efficient 408 with 275-300 cfms.

Even most mild engines would require less port volume than a 273/318 head has with more cfm then it generally does.

At Peak hp @ 5000 rpms these engine would need these port volumes and cfm to have optimal velocity, 273 = 99cc/167cfms, 318 = 115cc/195cfms, 360 = 130cc/220cfm, 408 = 147cc/250cfms so generally we would need to shrink the port while gaining cfm beyond most capabilities to have ideal velocities with a mild street engine.
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In 2011 for EMC I built a 371 (.060" 360) that made 513 ft/lbs 1.38 tq/ci 532hp on pump gas with teeny tiny EQ iron Magnums that at the time only flowed 267-272 cfm . IMO I made them a bit too big in the bowls. Weiand X-celerator manifold/750 XP. That engine was surprising for what it was. When I was done with that engine I made the heads bigger for 292-300cfm and used them on a 416--made 564 ft/lbs 1.355 tq/ci----Port speed was always just way too fast but I only needed 6500 rpm. Those heads just work. J.Rob

p.s. Every EQ headed build I've done , I've been told the engine is pure majic.
 
RAMM said:
In 2011 for EMC I built a 371 (.060" 360) that made 513 ft/lbs 1.38 tq/ci 532hp on pump gas with teeny tiny EQ iron Magnums that at the time only flowed 267-272 cfm . IMO I made them a bit too big in the bowls. Weiand X-celerator manifold/750 XP. That engine was surprising for what it was. When I was done with that engine I made the heads bigger for 292-300cfm and used them on a 416--made 564 ft/lbs 1.355 tq/ci----Port speed was always just way too fast but I only needed 6500 rpm. Those heads just work. J.Rob

p.s. Every EQ headed build I've done , I've been told the engine is pure majic.
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I remember that one, was a nice build.
 
RAMM said:
If you have reversion you have overlap. If you don't have overlap you dont make much power. Overlap equals RPM. IE. You always have reversion. J.Rob
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Yeah but you don't want too much is what I was gettin at.
 
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perfacar said:
I attended a seminar put on by superflow,in 1999, harold betts was the speaker. bottom line he stated was, port shape and port velocity is everything, don't get hung up on flow numbers. port velocity fills cylinders' fast and creates more cylinder pressure, which makes more torque , also power , just food for thought.
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RAMM said:
If you have reversion you have overlap. If you don't have overlap you dont make much power. Overlap equals RPM. IE. You always have reversion. J.Rob
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So true. You have to learn to live with overlap. Otherwise power levels will drop.
 
my head porter (he is well known on this site) told me don't worry bout the big CFM #'s as long as the port has velocity. i wanted to see a certain flow #. i was a bit disappointed that the flow #'s didn't hit the magical # until i got the timeslips. i guess i didn't need the big advertised flow #.
 
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9secRR said:
my head porter (he is well known on this site) told me don't worry bout the big CFM #'s as long as the port has velocity. i wanted to see a certain flow #. i was a bit disappointed that the flow #'s didn't hit the magical # until i got the timeslips. i guess i didn't need the big advertised flow #.
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Are those your 355 W2 ? From you signature, sounds like a pretty sweet setup, like you didn't go 4".


Velocity, cfm, port volume are all interrelated if you know any two you can basically calculate the third like everything it's about balance.
 
273 said:
Are those your 355 W2 ? From you signature, sounds like a pretty sweet setup, like you didn't go 4".


Velocity, cfm, port volume are all interrelated if you know any two you can basically calculate the third like everything it's about balance.
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3.46” stroke. It has surpassed my goals so I’m very pleased with the outcome.
 
RustyRatRod said:
If you have reversion then you have the wrong camshaft.
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71GSSDemon said:
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.
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Yes. And Calvin Elston points out his (frustration) that the exhaust ports are often ignored, but the same could and should be done there. While he can't control that, he chooses the exhaust tubing diameters and lengths to keep the flow moving away from the port even as the ex. valve is shutting. Larry Meaux's Pipemax gets us pretty close especially with 4 into 1 headers.
 
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