'79 KX250A5 with '79 KDX400 engine fitted ... KX400A5

[Ted]

Hi John. I know you said it is only a club level bike but it can still be protested. The steward will just refer to the MoMS for clarification. The top triple clamp could also be protested with its vertical risers.Different meet. Different steward. Shit happens.
I don't give a toss. The bike looks great.

[John Orchard]

Ahhh Ted, in NSW you can get fined if you don't hold your mouth right when you fart!  Down here in friendly Vic we just want like-minded friends at the events.

When I was roadracing I always hated going to NSW; officials with bad attitudes & bedside manners.  Everytime race friends came down to Vic to race, they'd say " wow everything is so easy & laid-back down here".

VICTORIA, RACING A STATE OF ECSTASY  ;-)

[John Orchard]

Really loving the bike right now, with the header pipe lengthened 45mm from the stock KDX400 pipe and the larger diameter muffler core, the bike has such a wide spread of power now, love it.

The muffler core (straight through perforated core) is now 34mm ID, not any louder than the small core that was on it (a 250 muffler with 25mm core).

There is a set length that a 2-stroke stinger should be, if you continue with a muffler core of the same diameter, you effectively are lengthening the stinger; moving power up the rev range AND causing higher combustion temperatures.  Either making the muffler core markedly larger or running a mechanical-baffle with large chambers would negate this effects.

Well I did it to the KDX and I am satisfied with what I have done.

[Lozza]

There is a set length that a 2-stroke stinger should be, if you continue with a muffler core of the same diameter, you effectively are lengthening the stinger; moving power up the rev range AND causing higher combustion temperatures.  Either making the muffler core markedly larger or running a mechanical-baffle with large chambers would negate this effects.

No set lengths for stinger length, diameter is the one that holds sway. Seen and used every length from 80mm to nearly 600mm on a NSR250. Though there is a limit to how long you can go.

The KDX pipe is good idea.

[John Orchard]

There seems to be so much information around saying that a stinger that's too long/small can move power up the rev-range and produce more engine heat though, yeh?

The few things I have read, talks about a 400/500cc off-road bike (non roadrace) having a stinger approximately 400mm / 29mm ID, those dimensions seem to have worked for me.

[Lozza]

Diameter over rules everything, the stinger being 40 or 400mm will make no difference so long as the ID stayed at 29mm. Stinger ID's falls into very defined ranges, always with a lower limit. upper limit can vary 1-2mm

[John Orchard]

Well why don't they make them all 40mm long?  Would save weight & room.

[Lozza]

Packaging, wouldn't allow 40mm stinger on an up pipe

[John Orchard]

Why didn't Roger DeCoster have 40mm stinger on his RN74 downpipe?

[shelpi]

have been following and enjoying the evalution of a great build, well done

[FourstrokeForever]

A 2st pipe can be tuned at the stinger as well as any other section of the pipe.

[motomaniac]

Diameter over rules everything, the stinger being 40 or 400mm will make no difference so long as the ID stayed at 29mm. Stinger ID's falls into very defined ranges, always with a lower limit. upper limit can vary 1-2mm

That's why 500's and most enduro's  have very long mufflers, 125 short and why Eric Gorr and a host of other engine tuners other engine tuners recommended cutting mufflers on certain bikes , 93 RM 250 for eg, to get them to rev on a bit more. On and on and on....

[evo550]

Diameter over rules everything, the stinger being 40 or 400mm will make no difference so long as the ID stayed at 29mm. Stinger ID's falls into very defined ranges, always with a lower limit. upper limit can vary 1-2mm

That's why 500's and most enduro's  have very long mufflers, 125 short and why Eric Gorr and a host of other engine tuners other engine tuners recommended cutting mufflers on certain bikes , 93 RM 250 for eg, to get them to rev on a bit more. On and on and on....

I thought it was for noise....
Look at a standard mid 90's CR500 muffler and a pro circuit version, about 400mm shorter, makes more noise and not much else.

[Speed]

John, what is the actual diameter size of the out let at the end of the reflector? 
about 32mm should be close to being on the money..

[John Orchard]

Stinger 29mm ID and 420mm long, muffler on the end is 34mm ID and 300mm long .... lovin it  ;-)