header calculation

[Peter]

Hello Guys,
After reading the small powerhouses topic I was interested in finding the optimal header for my engine.
What I calculated was the following:



Stroke: (Inches)   
3.2
Bore: (Inches)   
3.7
Number of Cylinders:   
4
Exhaust Valve Diameter: (Inches)   
1.49
Exhaust Valve Opening Point: (Degrees )   
70
Exhaust Valve Duration: (Advertised)   
282
Exhaust Valve Centerline: (Degrees)   
109
Peak Power RPM:   
8000
Volumetric Efficiency:   
12.5
 Calculate
Calculated information appears below
Input All Values please
Your Primary Tube Length is 27.33
Your Primary Tube Diameter is 1.25 inches
Your Collector Diameter is 2.16 inches   One Collector


What is interesting for me is the small tube diameter! A chart I found says youi need 1 3/4 in primaries to rev up to 7500..
Am I missing something here? one is perhaps inside dia and the other outside?

some stuff to think about

[JeeWee]

which calculator did you use?

[Erlend / bug66]

Sure you punched the right numbers?

1,25" headers does not exist..

You wont be able any way to run 27" primaries, to a collector.

[richie]

Peter


All USA built systems are quoted in OD size [as are most others now] which always seemed weird to me as I have seen different wall thickness tubing used over the years

cheers Richie 

[Zach Gomulka]

I'm curious to know how you arrived at 12.5 for volumetric efficiency.
282° exhaust valve duration, is that total? @ .050"? @.020"?
Your engine makes peak power at 8,000? Or is that max rpm?

I think the numbers are entered wrong somewhere.

[Peter]

thanks for your replies..
got the calculator from here:

http://www.wallaceracing.com/header_length.php

I found the volumetric efficiency on the small powerhouses topic... I could be wrong
282 degrees at 0.050

my heads seem to peak around 8500 on my motor (only calculated intake though) (2276 cc 48 mm valve)

[Erlend / bug66]

Shouldn't VE be alot closer to 100?

[Zach Gomulka]

Shouldn't VE be alot closer to 100?

That's what I thought, it was a percentage. If your engine is only 12.5% efficient then 1.25" headers would make sense.

Changing only the VE to 85 gives you 1.61" (roughly 1 5/8") primaries and a 2.8" collector. That sounds more on the right track.

[Erlend / bug66]

I think I used 88% on my last NA engine. Ended up with a Berg 1 3/4 big flange header.

[Erlend / bug66]

Also. Use PipeMax.

If I recall correctly, you can set the lenght of primaries to a set point (normal VW headers are 900-950mm-ish)

And that would correct the diameter needed.

[Peter]

Cool! thanks a lot!!!