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Discussion Starter #1
Bored, nothing to do? Feel like answering a bunch of moronic questions about exhaust systems???

1)Do aftermarket headers have bigger diameter tubes or are they the same diameter as stock? If so, how much bigger?

2)What other model years of exhausts will fit an '89 750?

3) On a 4-2-1, do cyls 1 and 4 join into 1 and cyls 2 and 3 join into 1?

4) About how long of a chamber is the "2" part of a 4-2-1?

To anybody crazy enough to answer any or all of these, thanks.

saved

[ 10-21-2002, 09:28 PM: Message edited by: Simon Orttan ]
 

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ok here goes. On my 86 the hindle that I replaced it with the primary tubes where larger in dia. than stock memory says about 1/8 to 1/4 inch. Dont know the diff in years. As to the joining diff manufactures have diff ideas on which cyl to pair does make a diff on where the power band goes but don't know what effects what. Lenght of the 2 part also effects power band placement now we are getting into exotic exhaust design beyound most average people. Few other misc items as I build my own end cans the lenght of the can effects the lowest freq. that the can will work down to based on quarter wave length. As for volume if the can is about 8 times 1 cyl volume the engine basicly doesn't know that there is a muffler there ie straight thru design with no baffles versus an open pipe. thises why twins need two mufflers versus fours work with a single can.The stiffness of the muffler wall material effects the tone ie soft flexible wall lower tone less bark stiffer wall more bite less low freq sound as the predominent tone and lowder overall.

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86 totally non stock
 

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the difference in headpipe diameters between stock and aftermarket would probably depend on the vintage of the motor in addition to other factors as well - in the old days, exhaust (and intake) engineering wasn't nearly quite as developed as it is now, so back then stock exhausts and intakes had noise reduction as a priority, at the expense of power. that's why on those older motors aftermarket pipes and filters would really wake them up, more than they do these days.
as with intakes, can't go too high up in headpipe diameter without losing power somewhere - larger diameters mean less velocity.

the stock 4-2-1 pipe on my bike are cylinders 1 and 2 into one, and cyls 3 and 4 into the other. i believe this is how it's done on other 4-2-1 pipes as well. and pipes with crossover tubes (like the yosh duplex) have the tubes connecting 1-2, and 3-4, similarly. the length of the '2' in the 4-2-1 on my bike is about 4-5 inches or so.

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cyl pairing is defenitely based on the firing order as not all four cyl motors have the same firing order also some four cyl engines have been designed to fire as a big twin. Just as some v8s have been configured to fire like a 4cyl.

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86 totally non stock
 

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most production engines that is true the exotic and weird is normally reserved for race engines as one normally requires the resources of a manufacturer to play with different single plane or multiple plane cranks which is what one does to change firing orders along with grinding different camshafts.

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86 totally non stock
 

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Oh no!...I'm getting that feeling that Umf (fueled on by his fork brace success) is now considering making his own exhaust system!...is this true?

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Discussion Starter #9
Hmmm, the thought has crossed my mind.

If I didn't work for a company that bends pipe and didn't have a retired pipefitter father with a full shop in his backyard, I wouldn't even think about it. If I didn't have a stock 4-2 where almost any 4-1 design would probably give me a performance gain and some serious reduction in weight the thought of fabbing a header wouldn't have even cropped up.


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'89 750---Factory ignition advancer and shift kit, Barnett Kevlar Clutch and springs, Goodridge SS brake lines.
 
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