Tuned length for Predator & 7500 target?

noseoil

noseoil

Active Member
#1
#1
I know it has to do with rpm, cam duration, lift, timing & a bunch of other numbers I don't really understand too well. If I'm building for a 7,500 max rpm target with a hemi-predator, does anyone know what length I need for a pipe which will provide some scavenging? Thinking it would be made with some tubing & a bend or two.

There are a lot of variables involved with this question, but I'm thinking about a bike with mostly top end, so I would be willing to sacrifice some bottom end to gain at the top. Wondering if anyone knows about the length I would need. I've calculated it at 25.03" with about 1" OD material, but that seems very long to me.

Anyone know of some charts or research that's available online, or some posted dyno runs like this? Thanks, tim
 
H

Havasu Dave

Moderator
#2
#2
There is a lot of snake oil on the benefits of scavenging single cylinder, four cycle engines. No one likes to be told they have an ugly baby, so I'll not comment on small engine dynos, salesman of aftermarket fads, or internet misdirection. :laugh:

(Hint: Make yourself a megaphone with as few bends as possible, and no anti-reversion cone or silencer)

The British have been racing single cylinder, four cycle engines for a long time. You might find this article to be of interest:

Megaphone Design Comments
 
noseoil

noseoil

Active Member
#3
#3
Dave, thanks for the link, it's pretty good. There's a lot to think about here, so I'll keep looking & pondering. Anyone else have any links that would be helpful?
 
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Havasu Dave

Moderator
#5
#5
[MENTION=3072]ole4[/MENTION] I saw your pipe max chart before. Isn't that a software package for header construction, and aren't there parameters within the software to allow for collectors? Would a bugle design to achieve length, impede or change the parameters because of the bend?

I know you play a lot with flow on the intake side, and are extremely knowledgeable, but it would be good to know the rationale or the inputted parameters used to arrive at those lengths.
 
ole4

ole4

#6
#6
That is a stand alone chart from graham bell. I also use pipemax as it gives diameter. But requires complete engine specs. The two methods seem to come up with similar 3rd order lengths. Pipemax also gives length for other harmonics.
 
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