Ironhead Shovster build take2

[mrmom9r]

Originally Posted by ryder rick

Nice Pipe!

If you make it again or another make the primaries longer I think you will like that better.
Shortening the muffler section and necking down the collector to form a venturi will also help that design.

How long should the primaries be on an engine that size ,Rick?

[billeuze]

Mine are 32” rear, 33” front. Measured from exhaust port in head to the point in the collector where the 2 pipes become one.

There is a formula somewhere that calculates ideal length based on certain engine specifications including target rpm. The only part I remember of the tip of my head is that longer pipes are better for lower rpm’s. And the ideal length based on primary pressure wave is prohibitively long so the secondary pressure wave is used. Secondary wave is something like a harmonic resonance in guitar strings is the best I could understand it. My engine is 84” with 4-1/2”stroke of someone else finds the formula before I get to my computer

[billeuze]

The collector adds 5” front and 6” rear to primary length. At least thats how I interpret it



Original collector came with the muffler and pipes which was a suppertrap complete system to fit a big twin evo. Some pieces of those pipes went into what I put together to make it fit this bike.

[ryder rick]

A very nice Mashup. Way better than most systems.

Primary length varies with each combination.

I don't think a Harley chassis allows enough room, without coloring outside the lines. It has to look good and not be in the way as well as perform. Everything is a compromise.

My best pipe has primaries that end (near) past the trans. And a venturi merge.

[billeuze]

We’ll, I had to Google “Venturi merge”. Yeh, sure, next time…

Now I’m looking for a place to install an oxygen sensor bung. As far as I’m concerned it’s required for carb tuning.

[billeuze]

Originally Posted by billeuze

Mine are 32” rear, 33” front. Measured from exhaust port in head to the point in the collector where the 2 pipes become one.

There is a formula somewhere that calculates ideal length based on certain engine specifications including target rpm. The only part I remember of the tip of my head is that longer pipes are better for lower rpm’s. And the ideal length based on primary pressure wave is prohibitively long so the secondary pressure wave is used. Secondary wave is something like a harmonic resonance in guitar strings is the best I could understand it. My engine is 84” with 4-1/2”stroke of someone else finds the formula before I get to my computer

I misremembered that. It is the intake tract length that you time to the 2nd or 3rd pressure wave. As for exhaust header length, the variables are engine displacement, exhaust cam timing and header pipe diameter and gas speed which varies by exhaust gas temp so have to guess at an average number. If I plug in my values at http://www.mezporting.com/exhaust_length.html I get 42" at 4000 rpm and 39" at 4500 rpm. So yes my primaries are shorter than optimal. Just about the right length though for 5,500 rpm though which is about as high as I would want to run it.

[billeuze]

I found a nice out of the way mostly hidden place to put my oxygen sensor bung:

[billeuze]

And I discovered an advantage of moving the oil cooler assembly up is that I can now remove my front exhaust header without first removing the oil cooler

[paulc]

Originally Posted by billeuze

And I discovered an advantage of moving the oil cooler assembly up is that I can now remove my front exhaust header without first removing the oil cooler

That's good, a useful bonus
Paul

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