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Title: header calculation Post by: Peter on September 20, 2016, 21:04:04 pm 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 :) Title: Re: header calculation Post by: JeeWee on September 21, 2016, 15:05:56 pm which calculator did you use?
Title: Re: header calculation Post by: Erlend / bug66 on September 21, 2016, 15:11:07 pm 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. :) Title: Re: header calculation Post by: richie on September 21, 2016, 15:19:32 pm 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 Title: Re: header calculation Post by: Zach Gomulka on September 21, 2016, 16:27:17 pm 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. Title: Re: header calculation Post by: Peter on September 21, 2016, 19:08:58 pm 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) Title: Re: header calculation Post by: Erlend / bug66 on September 21, 2016, 20:53:23 pm Shouldn't VE be alot closer to 100?
Title: Re: header calculation Post by: Zach Gomulka on September 22, 2016, 00:10:43 am 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. Title: Re: header calculation Post by: Erlend / bug66 on September 22, 2016, 07:20:46 am I think I used 88% on my last NA engine. Ended up with a Berg 1 3/4 big flange header.
Title: Re: header calculation Post by: Erlend / bug66 on September 22, 2016, 07:23:34 am 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. Title: Re: header calculation Post by: Peter on September 22, 2016, 10:53:47 am Cool! thanks a lot!!! :)
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