expansion chamber mods

[ae86guy]

in fitting the expanshion chamber ive lost all torqe down low ive cut and welded it a few times shortening the length of the pipe hasnt made much of a difference my power band kicks in at about 28 mph need it around 10 to 15 mph do i just keep shortning the pipe .the diameter of the centre of the chamber is about 100mm should it be smaller

[Wheelman-111]

Greetings:

I dunno, dude. Seems like 38 with stock gears is a pretty strong Spree showing. Remember whatever you do to increase the midrange will come off the top end, in theory.

[mousewheels]

in fitting the expansion chamber ive lost all torque down low ive cut and welded it a few times shortening the length of the pipe hasn't made much of a difference my power band kicks in at about 28 mph need it around 10 to 15 mph do i just keep shortening the pipe

shortening is tuning for a higher rpm.

[Wheelman-111]

Greetings:

Shoot, Mouse! I was gonna say that but didn't think it through.

He's right of course. If the combustion cycles are happening quicker, you need the pressure wave to return sooner. There's a nice animation of this here. Scroll down to the animated box near the end. The exhaust pressure wave shoves the fresh mixture attempting to escape back into the CC just before the exhaust port closes. It's all about timing the echoes.

[elitedio]

Keith W has a very extensive report on how he made his spree pipe. Your other post talked about having to Flintstone the bike from a stop, surprised that you shortened the pipe further.

A 100 mm diameter is pretty big for a spree motor with near stock porting. My 86cc motor has about a 88 mm fat part of the pipe. My pipe is fatter that what most programs and simulations give but I am pleaseed with it. Like you I just cut up another pipe.

[ae86guy]

ive modified the exhaust once again now the wide part is about 63.5mm 2.5inches and alot longer than befor powerband is at about 22mph now and im toping out at about 37

[ae86guy]

this was the first attempt at the exhaust looks better than what it is now but doesnt work as good will get a pic up shortly of the exhaust it has now

[odinxxix]

that doesnt look half bad! if you have stock gears and getting 37/38 mph wonder whats going to happens when you get the taz gears. 45mph? by the way seen you pic where did you get the chrome belt cover? and do they have ones with a kicker.

[elitedio]

You can make it look perfect. When you get it how you want it I would say get your flap brush running on your hand grinder and polish down those welds.

It looks like you might be using to low of current and or to much wire feed.

[noiseguy]

The expansion chamber you're using, and it's relation to the downpipe, is very similar to what I used to build. The 180 deg turn around for the stinger is different, though. Those pipes didn't come on until about 15 MPH.

I always had problems with penetration on those welds; the 4 settings on my Lincoln; either a bit too hot or a bit too cold. I went cold and ground them out.

Make sure to add a tab support from the pipe to the engine at the fan mounting point, where the old exhaust bolted up. You will break off the exhaust at the jug otherwise.

[madskater1987]

hey ae86guy what kind of clutch springs are you using?

I'm running pretty much the same setup on my spree but with a pully mod and wider belt. It hits 44mph but bottom end sucks. I need new clutch springs.

[ae86guy]

the cover is the factory alloy one my mate works at a metal polishers he polished it up for me and i just painted in the honda red in nz we didnt get the kick start they are all electric a bit sucky if it craps out the exhaust has a mount point were the old exhaust bolts up by the cover you now this exhaust worked but not that great will get another pic up soon of the one im working on now not sure what the springs im using are supposed to be for i bought them from a shop www.scootling.co.nz they where about a 1.5mm longer than the factory springs but with a little heat and a mod to the springs got them to fit and it raised the engagement point up about 1500rpm helped a bit with take off but not as much as i was hoping

[ae86guy]

heres a closer look at my side cover i also got to it with a drill gun and to different drill bits http://images.trademe.co.nz/photoserver ... 0_full.jpg

[ae86guy]

my header pipe starts getting wider at the top of the side cover about 3 inches from the flange i read about needing a 9 inch header pipe so if i make a new header pipe should i stay the same size pipe from the flange down and make that peice 9 inches long befor i start wideing up for the cone type bit