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What Diameter For Engine Pipes

Old 01-03-2014, 06:38 PM
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What Diameter For Engine Pipes

I want a big bore system for the bike.

What is the biggest diameter I can go for the engine pipes where they meet the exhaust ports?


My local exhaust shop is interested in having a go for me.


Also, is it necessary to have a collector as such or could I just run two single pipes with a balancer tube joining them together.


Any thoughts?


I saw a bike at a track day recently and the guy had done a similar thing with his vtr, but there was no collector or balance pipe and he seemed to be going fairly well against more modern machinery in the medium fast group.


His bike sounded mean with a pair of knocked about Micron cans on it.


While I was at the shop the guy bent a piece of 52mm I.D stainless pipe to show me the angles he could get.
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Old 01-04-2014, 05:45 AM
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I think you can go up to 5 cm or 2 inches if I recall correctly, there are aftermarket headers this size.
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Old 01-04-2014, 01:44 PM
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It will probably go like stink at full noise but it will most likely be a pig on the street.

Forced induction would fix that
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Old 01-19-2014, 04:11 PM
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2 inches rings a bell with me.

Bare in mind that larger diameter pipe does not necessarily mean better performance. It's pretty deep stuff exhaust theory/flow dynamics.

Here's some links/interesting reading though some of it is a little heavy that may help if thinking of making a custom exhaust.
Exhaust System Theory 101

http://www.epi-eng.com/piston_engine...technology.htm

exhaust port size? • Speed Talk

And a couple of pipe sizing calculators.
How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos

Pipe Sizing Calculator

(:-})
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Old 01-22-2014, 09:46 AM
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Originally Posted by cybercarl View Post
It's pretty deep stuff exhaust theory/flow dynamics.
Agreed!

That said, bigger does not mean worse either - you can still tune it to work just fine for low-mid even with 70mm or more primary side. Certainly there would be some dyno tuning involved with anything much over 50mm primary size.
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Old 01-22-2014, 10:52 AM
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Jury is still out on this one however I now have drawings for a complete Leo Vince busy stem that fits an SP1 kindly supplied by a guy in Spain.

Been riding so much that I need new tyres so $$$ will go to that at this stage.


I realy like the look of the Moriwaki headers though, shame they are so rare.
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Old 01-22-2014, 10:53 AM
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Should read system, bloody spell check.
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Old 01-22-2014, 11:42 AM
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Certainly there would be some dyno tuning involved with anything much over 50mm primary size.
And more I would have thought if doing as a performance mod. Fair enough one may be doing it from an aesthetics point of view and could get things running how they like it. It may not be perfect but acceptable.

The exhaust as you know is a tuned length (timed maybe a better description) and any changes to this affect the pulses, when and where they change from either positive to negative. If one was after a max performance mod then I would have thought it would also require altering the timing and/or porting to suit. Some engine work, as well as carb work! The first thing one needs to ask themselves is where about within the rev range they want the performance.

Everything is a comprimise and has either a positive or negative effect on another component further up or down the line which may need changing/altering to compensate for the changes. I'm waffling now so I shall shut up. LOL

I don't claim to understand it all totally, far from it actually when it comes to exhaust theory. But I do find it very interesting how the power can be shifted around the rev range. For example, Longer end can for more bottom/mid end or shorter for mid/top end etc.

(:-})
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Old 01-22-2014, 11:45 AM
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Originally Posted by kenmoore View Post
Should read system, bloody spell check.
What should "tyres" have read before it got spell checked?
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Old 01-23-2014, 01:02 AM
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Here in Oz we spell those black rubber things that go on wheels Tyres, unlike some other places in the world that spell it Tires.

Here in Oz that means its running out of steam and it tires, E.G a person tires after running a long way!


The English language is a funny thing!
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Old 01-24-2014, 09:33 PM
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kenmoore you may want to ask fellow members here who have aftermarket headers to measure the length of both head pipes before the collector or before the slip on.


This way you can get add up all of the lengths and divide by the number of submissions and this will give you an average length of all of the aftermarket head pipe headers lengths.


You need a minimum length of head pipe to allow for sufficient back pressure otherwise a too short head pipe will not work, off hand I do not have that minimum number, that is why I suggested you ask members here for a measurement.


Head pipes that are too long also take away performance.


A suggestion would be to have your shop bend a several complete circles out of the exhaust tubing that you will be using to build your exhaust from.


This way if you need a certain compound bend you can simply cut the lengths out of the pre-bent tubing circles and you wont have to stop the build for every little bend you need,


Single bends are a bitch to produce even with a high dollar pipe benders and most of the time short single bends waste material because the bender needs a certain about of piping to make one bend wasting a couple of feet of tubing on each bend, plus there is a very good chance the pipe will kink on short tubing bends as well...


From experience working with Master Honda Mechanics helping to build dirt trackers, Supermotards, and Supercross machines several head pipes would be produced for each bike and they would always bend several circles of tubing before getting started on the pipe build.


Also there are a few ways to cut the bends off of the tubing circles like using a hacksaw or a die grinder, we found out using a 4 inch common plumbing tubing cutter works the best, the cutter even produces a bevel on each cut giving a better welding surface to join the pipes together with!


Thought this may help you a little and save some cash on material.


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Old 01-25-2014, 01:01 AM
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Mate, any tips are much appreciated at this stage.

I really want a custom bigger bore system and will take your advice on board.


Cost will be a factor and any savings will be a big help.


I reckon if I give up the Jack for 2 months I'll be there.


Ah the sacrifices we make for our bikes.
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