What constitutes a good exhaust system?

Mananon · Post by **Mananon** » Sat Dec 12, 2009 8:39 am

No-one within New Zealand makes and aftermarket exhaust for an NC30. There are pleny available from overseas but what with exchange rates and postage costs they are out of my budget at the moment.
However, I run a fabrication and machining workshop where we do a great deal of stainless steel pipework.
Measuring, bending, welding etc are not problems.
What I'm wondering is just what to make's a good system good?
As we all know there are a lot of aftermarket exhausts out there.
Some are basic replacements, some cosmetic enhancements, some for outright performance.
I'm looking to enhance performance a little and put a good looking carbon end can on which I can pick up from a breakers.
Does anyone have any thoughts on what's best? 2 into 1? 4 into 1? What tube diameter? What wall thicknes? I'm guessing that all pipes should be as near to equal length as possible, that welds and bends should be kept to a minimum but I don't have a clue about the really technical side of things.
Anyone got an opinion they care to share?

fastdruid · Post by **fastdruid** » Sat Dec 12, 2009 11:55 am

Well, conventional wisdom is that 4-1 is best for outright power, 4-2 is best for midrange, 4-1-2 is best for silencing with power.

My book of 4-stroke tuning says that header length should be a multiple of secondary length but I can't remember anymore and it's packed away for moving atm.

Druid

Post by **Spike16** » Sat Dec 12, 2009 12:12 pm

Well all Iv learnt thats relevant so far on my engineering degree (first term over) about fluid dynamics is that bends are bad (create big head losses create turbulant flows) so you want to route the exhaust so that their are minimal bends, theirs no point getting the length right if their is majour losses in the system, its a compromise between the two

fastdruid · Post by **fastdruid** » Sat Dec 12, 2009 1:32 pm

Bit of an issue on the little V4's!

I loved the micron surpentine systems, pity AIUI the expense of them was one of the things that finished them. :-/

Druid

Mananon · Post by **Mananon** » Sat Dec 12, 2009 10:33 pm

That's an interesting note about multiples Fastdruid. I might have to look that up.
Reducing the number of welds, and the weld reinforcment inside the pipe, I can do. Reducing the number of bends will be harder. I'm sure Honda went to quite a bit of trouble to get the optimum route, or close to it. I don't expect to be able to improve on that too much though I might be able to keep the bend radius a little more open here and there by using different tools for each bend. I might save a few Pa that way. It's almost 20 years since I did fluid flow dynamics Spike. I've got the software at work to run it but it would be a lot of after hours work.
Any other thoughts folks?

Post by **Neosophist** » Sun Dec 13, 2009 1:31 am

Mananon wrote: Any other thoughts folks?

If you have access to a fab shop, rather than starting from scratch why don't you create a replica of an existing after-market system. If you look in the 'exhaust thread'

http://www.400greybike.info/newforum/vi ... =23&t=6071" onclick="window.open(this.href);return false;

You'll see hundreds of pics of various systems with comments / reviews from users. If you ask one of the owners of a system your fond of, i'm sure they'd be happy to measure things up so you can create a replica.

Least then you know what to expect in terms of noise / performance etc...

Mananon · Post by **Mananon** » Sun Dec 13, 2009 4:51 am

Yeah, I've looked through and seen some lovely looking exhausts, I was more after the technical aspects of tube lenth and ratios. I think I'm going to go for 4 into 2 into 1. I've found a second hand carbon can so will go from the outlets back to the can. I'll keep notes on what I come up with and post them in case anyone is interested. Cheers,

fastdruid · Post by **fastdruid** » Sun Dec 13, 2009 4:46 pm

I'm not sure if things have changed since with the advent of more processing power but IIRC according to the late John Robinson in "Motorcycle tuning - 4 stroke"[1] exhaust lengths are a bit of a black art *but* there are calculations to get a starting point, they rely mostly on EGT though which needs to be either measured or guessed.

If I hadn't packed everything away I'd find the calculations for you.

Druid

[1]
http://www.amazon.co.uk/Motorcycle-Tuni ... 0750618051" onclick="window.open(this.href);return false;
Typically the exhaust section isn't available in the preview http://books.google.co.uk/books?id=LFwW ... q=&f=false" onclick="window.open(this.href);return false;

Mananon · Post by **Mananon** » Mon Dec 14, 2009 3:48 am

Bugger. Still, I'm pretty limited on just what I can do due to space available.
I think going for matched pipe lengths must make sense though, or as near as possible.
A smaller radiator fan would allow the fron pies to run straighter but God knows where I'll find one. Hmmm.

Post by **rcv4** » Mon Dec 14, 2009 11:11 am

you will not gain anything by reducing the amount of bends,i used to make a lot of race systems,2 and 4 stroke we would make the development system stright to get the lengths sorted then make them fit the bike,all done on a dyno,90% of the time you can improve performance by using the oe lengths and making the collectors and all the joints,are lined up correctly,no potruding welds etc.....how many gp or performance bikes have stright pipes,how long did the reverse cylinder TZ's last?....can spend weeks on the dyno to end up very close to the std lengths and dia.

What constitutes a good exhaust system?

What constitutes a good exhaust system?

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Re: What constitutes a good exhaust system?

Re: What constitutes a good exhaust system?

Re: What constitutes a good exhaust system?

Re: What constitutes a good exhaust system?

Re: What constitutes a good exhaust system?

Re: What constitutes a good exhaust system?

Re: What constitutes a good exhaust system?

Re: What constitutes a good exhaust system?