Header math

[Guest Will]

I read a couple of formulas somewhere a while back, but I don't remember them

 

How do I figure length and diameter of primaries from exhaust valve duration and desired RPM for max scavenging?

 

I have two projects:

1) equal length long tube 180 degree headers for my Northstar Fiero. This engine produces peak torque at 4400 RPM. Would building headers tuned to this RPM sacrifice much low RPM torque? The engine produces 300 HP stock, and I'm shooting for over 350 with headers and intake manifold mods.

 

2) Headers for Cadillac 4.9 in '73 Triumph Stag. This engine only produces about 200 HP, but makes 275 ftlbs from 1000 to about 3500-4000 RPM. What would be the best tuning RPM for these headers? I'd like to bolster its torque, of course, but I don't want to make the top end any weaker relative to the low end.

[pparaska]

Check this out:

http://www.headerdesign.com/

[grumpyvette]

here this may help

http://victorylibrary.com/mopar/header-tech-c.htm

 

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

 

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

[Kevin Shasteen]

Is this what you were looking for?

 

Diameter = ((SQRT(Displacement x 1900)/Primary Tube Length X Max.Rpm's

 

or

 

Primary Length = ((Displacement x 1900/(Diam^2 x RPM))

 

Kevin,

(Yea,Still an Inliner)

[Guest Will]

Originally posted by pparaska:

Check this out:

http://www.headerdesign.com/

Thanks, but...

 

I read a good bit of info on this site. A lot of what he says seems to make sense, but a lot of what he says also ranges from the non-sequitur to the ridiculous. Don't they teach computer programmers to think logically?

 

I'd like to know how he can even pretend to calculate primary tube length to the 10th of an inch without knowing what my exhaust valve duration is.

[Guest Will]

Originally posted by grumpyvette:

here this may help

http://victorylibrary.com/mopar/header-tech-c.htm

 

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

 

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

I haven't read it all yet, but that third link looks promising.

 

Thanks

[Guest Will]

Originally posted by Kevin Shasteen:

Is this what you were looking for?

 

Diameter = ((SQRT(Displacement x 1900)/Primary Tube Length X Max.Rpm's

 

or

 

Primary Length = ((Displacement x 1900/(Diam^2 x RPM))

 

Kevin,

(Yea,Still an Inliner)

Thanks. Where did you get these?

They still don't consider exhaust valve duration, though.

 

How do you solve for length when you need to know diameter, but also need to know length to solve for diameter?

[ZROSSA]

Will have a go at this

 

Primary pipe length(p)

p=(850xED/rpm)-3

Ed = 180 degrees plus the number of degrees the exhuast valve opens before BDC

RPM = engine speed being tuned to

 

Inside Diameter (ID)

ID={square root of[cc/(p+3)x25]}x 2.1

cc = cylinder volume in cc

p = primary length in inches

 

Hope that might be usefull. It looks a bloody mess on the screen.

 

Douglas