Exhaust diameter suggestions???

Wow! That motor looks beautiful Neevo, what material are those headers made of?

Motor was vapour blasted. Headers are PVC plumbing pipe, getting them ceramic coated as I've heard it will add a tonne of horsepower

They are just a template for the bender to make them out of stainless.

Wow nice, lookin good.

Are you going to have the same

Definitely softer larger radiuses on the bends. Bought 90 degree elbows with the pipe to make the bends easier to make.

Eg:

At what lengths from the head will you be welding in the first two mergers? Then how much further for the second merger on your 4-2-1?

Also, how did you come up with these measurements?

The ideal header length from my spreadsheet lists the ideal header length at 21" (from memory), however this would have the merges on the front of the motor. So instead I am copying the original collector location I had on the headers I got with the bike which is closer to 24-25". This will put the merges under the oil pan and is what all other headers seem to do. First set of merges will be welded around 24", then a short run to the second merge (1-2").

I've heard building exhausts is all about compromise and this header length is probably the biggest compromise overall. The header diameter should be spot on, total system length is great too. Compromises are header length and twin exhaust setup out back - for aesthetics.

These choices could reduce power a bit, but the 4-2-1 is supposed to offer a wider spread of power vs 4-1 and I'm running a 466 kit in the bike which should get back a bit of that lost power too.

Nice, looking forward to photos when you get it all sewn up tight.

Just a thought... Do you wonder what makes your spreadsheet's ideal merger length more ideal than the factory design (that had a high paid team of highly trained Honda exhaust engineers designing it?). Not to knock your spreadsheet/design in any way, but just wondering if maybe there is even a more ideal length that we are all missing?

Sounds like your spreadsheet suggests something like this.. Also making sure cylinder #1 merges with #4 and #2 with #3 due to the 180 degree crank

Jammer to answer your first post I would say my spreadsheet number points to 2 different scenarios:

1. It's wrong and my excel skills need sharpening
2. Even Honda technicians made compromises with the original header. Maybe for aesthetics or maybe because the net result wasn't that far off a header with the merges on the front

That second header looks very similar to what the spreadsheet it recommending, what's it off?

There's useful info on merge collectors here http://www.spdexhaust.com/pdfs/SPD_2013_catalog.pdf

and data on pipes at Cone Engineering http://www.coneeng.com/tech_assist.html

that last one looks like it is from a car....same concept I would guess.. both are inline 4 cylinder engines...