ideal air entry

[efi-diy]

Any one play with velocity stacks or ideal air entries ?

My understanding is the lip radius and the OD of the lip are critical and are related to the runner diameter. Can anyone add the relationship details?

Say for a 2 1/8 pipe..?

[Matt Cramer]

Re: ideal air entry

(Picks up a fluid dynamics textbook as it's been a while since I studied this)

In stead flow applications, a "reentrant" pipe (basically a velocity stack with no radius) has about the worst flow rate imaginable, and the best is a pipe with a lip radius to pipe diameter ratio of 0.15 or greater curling to a flat plate with an infinite lip OD. The reason for the infinite lip OD is that the air coming in from behind the mouth of the stack separates from the edge, creating a turbulent region that constricts the flow.

In an engine as opposed to a drainage pipe, you'd have standing waves that might make this a little different. But the size of the lip radius needed to minimize restrictions isn't exactly huge in comparison to the pipe length, around 5/16" for your pipes. While pretty noticable, it's not big in comparison to the length of the pipe and I doubt it would affect the frequency of the pipe. If you're using straight stacks, I'd probably try for a 5/16" or larger lip radius and as much lip OD as you can get on there. If looks aren't an issue, you might even make an air cleaner with a flat floor, with all the pipe mouths flush with the floor.

Something like a trumpet mouth instead of the small radiused entry might produce some interesting results, but I'm not sure anyone has ever tested this on a dyno. Maybe if I ever built a motor with ITBs...

[efi-diy]

Re: ideal air entry

Matt,

Care to comment on this: http://img406.imageshack.us/my.php?i...assem1dak2.jpg

thanks

[Matt Cramer]

Re: ideal air entry

It looks a lot like a typical modern EFI manifold, except you don't want the air horns protruding into the plenum. Make their mouths flush with the plenum wall and it will flow a bit better.

[JeffMcKC]

Re: ideal air entry

new prostock engines have a donut around the runner entry, it looks like a bent tube going around the outside of the entry , just like a 1/2 inch donut

[Dynoroom]

Re: ideal air entry

It looks a lot like a typical modern EFI manifold, except you don't want the air horns protruding into the plenum. Make their mouths flush with the plenum wall and it will flow a bit better.

These inlet bells wrap all the way under themselfs if you look close.



This is another way to go.



Keep in mind that in "theory" you want 2 1/2 diameters in every direction around a inlet bell. That might be hard to accomplish in pratice......

[efi-diy]

Re: ideal air entry


Thanks guys

[VWMMP]

Re: ideal air entry

Some stuff I bookmarked. Pictures below - If you want the whole discussion. http://speedtalk.com/forum/viewtopic...t=radius+entry

[joebogey]

Re: ideal air entry

I do remember reading somewhere that some engines benefited from different lengths stacks on different cylinders. IIRC it was a small block Chevy with alternating long/short stacks did better than all long or all short.

[JeffMcKC]

Re: ideal air entry

They used to do big blocks on SCCA cars that way to alter the wide range of rpm they worked in