Expansion Chambers

Discussion in 'Motorized Bicycle General Discussion' started by Cafe Racer, Jul 23, 2010.

  1. Cafe Racer

    Cafe Racer New Member

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    Whats you thought on this subject. I see a few of you guys with custom bike running a chamber. Definitely the way to go with the 2-Smokers.

    Miguel
     
  2. BarelyAWake

    BarelyAWake New Member

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    Defo a critical component only left out of the kits as a cost saving measure, by far the best bang fer the buck yer gonna get w/any of the performance mods...

    ...blarg - bad play on words there, sorry 'bout that :p
     
  3. Patr1ck

    Patr1ck New Member

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    Do the ones available (Spooky and SBP) not only effect the power but the mileage too? I bought the one from spooky tooth and was wondering where I will notice the benefit. Is it through out the whole rpm range or will it be in the 22-23mph sweet spot area. I try to keep it in that area when riding as it seems to run the best there. I havent installed the one from Spooky yet, but need some info first. Do they cause the carb to spit alot? What will extending its outlet out to the rear of the bike and then welding the stock muffler on there do?

    Thanks,
    Pat
     
  4. BarelyAWake

    BarelyAWake New Member

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    Anything that effects performance effects fuel mileage - but you may not notice that benefit as ya will prolly get on it more due to the power increase lol The Spooky one hasn't got any length of headpipe at all & the optimum headpipe length for an expansion chamber & powerband is about 12 inches (altering headpipe length allows some ability to "tune") - as you're considering extending it to a full length system, ya may wish to weld it to the stock headpipe for maximum gain as I've done w/the SBP system;

    [​IMG]

    I didn't notice any increase in spit-back, that's an interesting question! I suppose it's conceivable given the effect of an expansion chamber... but even if there was it was so marginal I didn't notice & it'd be worth it anyway I figure. As for welding the stock muffler on the end... well... I suppose it'd depend on which muffler you've got. The catalytic mufflers belong in the trash can, they just load up with unspent oil & carbon and will defeat the purpose - but the just baffled ones should be aright *shrug* I't defo quiet it down a bunch (^) I run an extended glasspack for maximum flow, but some have added utility engine/lawnmower mufflers to help with the noise...
     
    #4 BarelyAWake, Jul 24, 2010
    Last edited: Jul 24, 2010
  5. Patr1ck

    Patr1ck New Member

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    What about welding a long outlet pipe to the end of the Spooky expansion chamber that is bolted to the jug? Would I still have a performance increase? Im mainly looking for better mileage as I use this one for a commuter.

    Thanks,
    Pat
     
  6. BarelyAWake

    BarelyAWake New Member

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    I'm not sure what you're asking?

    If ya mean adding a pipe from the exhaust port on the cylinder to the Spooky expansion chamber (making yer own headpipe) you'll get better performance than no headpipe at all (so long as it's about 12") & you can even use the kit headpipe, flange n'all if ya just cut off the muffler and weld the expansion in it's place...

    As for better mileage, just about all performance modifications increase efficiency which means you can get better mileage - the trick of it is to try not to hold it at WOT alla time... which I must admit I just can't resist :p

    TBH, tho these lil 2 smokers do get good mileage - that's not their strongest attribute (which would be power to weight BTW), if ya want the best fuel efficiency - that's the 4 stroker's game. ;)
     
  7. Patr1ck

    Patr1ck New Member

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    What I mean is, in addition to welding a head pipe to it, welding a tailpipe also to take the length out to the middle of the rear tire area? What will adding this tail pipe do?

    Thanks,
    Pat
     
  8. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    If you're going to add a stinger to the end of the spooky pipe, I'd cut off the little angled nub flush with that flat back cap and grind it out large enough to fit a piece of tubing just under 1/2" in diameter. Cut the piece of tubing about 6" long and slide it into the ground out hole about 1/2", set the angle you want and then weld it. You can cut it down any length from there and even add a silencer to that if desired.
     
  9. taddthewadd

    taddthewadd New Member

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    Patr1ck, I love your setup. Your head pipe seems to be shorter than the original SBP setup. I know you say to try to make it 12" but I was just wondering how it works for you being shorter then the stock head pipe (copper pieces plus the j pipe) that came with the SBP kit.
     
  10. Cafe Racer

    Cafe Racer New Member

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    Most of the power gains would be derived from tuning the expansion chamber to the headpipe. Expansion chambers are designed to have a "certain" amount of restriction so that all of the expelled fumes do not escape. What happens is inside the chamber the exhaust wave will "bounce" back up the headpipe and back into the cylinder thus creating a more dense and powerful combustion.

    You may not know it but in the exhaust there is alot of unspent fuel. If your exhaust system is tuned properly this extra fuel will actually backfill the cylinder. If you are not properly tuned your backfilled fuel may actually enter the cylinder too soon which could possibly lean out the motor. Or it could backfill too late and inhibit proper exhaust flow.

    The design and use of an exhaust chamber it quite and art and science. When you get it right you will notice the difference.

    As for adding a long section of tailpipe after the expansion chamber. I am not sure if you will experience much in gain. Afterall the motors are pretty small. Most gains are developed with a proper expansion chamber setup.

    Miguel
     
  11. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    Spooky Tooth pipe (Grubee) on my beach cruiser...
     

    Attached Files:

  12. Tacomancini

    Tacomancini Member

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    Couple a questions on the spooky grubee pipe. Does it make the engine much louder? Does the power from the expansion help on the low end torque?
     
  13. BarelyAWake

    BarelyAWake New Member

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    Cafe Racer & Scotto are on the money, but I'd not increase the ID of the tailpipe/stinger any. While lengthening it will increase backpressure - it'll only be very slightly & the benefit will be reduced noise. With that in mind, you may wish to simply use hi-temp automotive heater hose slipped over the lil tailpipe it's got to extend it, easy & cheap and quiet too. The reason I'd not increase the ID is being a tuned pipe that ID is part of it's design (or should be if it's a good one) - increasing the inner diameter of the tailpipe may reduce the effectiveness of the chamber.


    taddthewadd - if yer talkin' about the setup in the above pic... that'd be my lil concoction :D TBH, I did that mostly for aesthetics and not so much for performance (tho it doesn't hurt anything) as it's an ol' vintage bike & I was tryin' to "blend" stuff in. The headpipe (which is cut frm a stock kit muffler BTW) is about 10" instead of the optimum 12" and that too was for looks, to place the belly of the chamber under the pedal crank and to get the angle of the glasspack to match the chainstay's.

    As for length & performance I'm afraid I didn't do a "before & after" on that bike, yet Pablo & Ghost0 have said that a mere 2" off that setup is well within optimum & I think Junster had a pretty good explanation fer peeps lookin' to get the most outa their pipe;

    So... having a 10" headpipe gives a far broader band than the Spooky pipe w/no headpipe at all, but is a touch "peaky" compared to the full 12" - it'd "get on the pipe" a lil earlier with 10" over 12" which is good fer me 'cause my ride weighs about a zillion pounds & I need the acceleration lol but if yer after max top speed then ya prolly wanna be closer to 12" - but remember, these are marginal changes, something you'd prolly not notice w/o a dyno.


    Tacomancini - I've a buddy w/the spooky pipe and while it does help performance, it's freakin' LOUD lol, but hey - some dig that sorta thing ;)
     
    #13 BarelyAWake, Jul 25, 2010
    Last edited: Jul 25, 2010
  14. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    To answer Tacomancini...yes and yes.

    Yeah that pipe has a real crackly pitch while idling and is fairly loud overall. If it was mid-bleed it'd be much quieter fo sho. It does improve performance however...fer sure. I do love expansion chambers and experimenting with them. Formulas for them are key...it's all about port timing.

    Enter induction reeds...to the formula!
     
    #14 scotto-, Jul 25, 2010
    Last edited: Jul 25, 2010
  15. Patr1ck

    Patr1ck New Member

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    Well ok, sounds like modidying the spooky pipe wont do me any good. The priority here for me is to get the exhaust out to the back of the bike, so Im gonna just lengthen the stock pipe to accomplish that. So...Does anyone want a brand new Spooky Tooth (Grubee) expansion chamber? Ill sell it for $40 plus shipping:D

    Pat
     
  16. BarelyAWake

    BarelyAWake New Member

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    o_O

    If you've access to welding equipment, using the kit headpipe welded/fitted to the chamber to lengthen it (as I did w/the SBP one above) & adding a bit of tailpipe would be fine... unless you don't wanna bother w/it - but I think the performance increase over the stock muffler (partic lengthened) would be all kindsa worth it - it's yer call tho ;)

    Here's a pic of the heater hose extension mod if yer curious;
    [​IMG]
     
  17. taddthewadd

    taddthewadd New Member

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    Barely, I was in a hurry that time and didn't realize your pic was a quote in someone else's post. Thank you for the explanation. I too, want to do what you did for aesthetics. I at the same time didn't want to do it if it dramatically decreased power. It sounds to me like it doesn't and I would rather have a broader power band anyways and I am not too worried about top speed since I am running a 56T sprocket and mostly ride off-road.
     
  18. Cafe Racer

    Cafe Racer New Member

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    Well, since I feel somewhat responsible for talking you out of doing the install I should buy it from you.

    And to think that I havent even taken my kit out of the carton yet. Still havnt put one of these motorized bikey things together. But when I do I plan on it being be real special!

    Miguel
     
  19. Patr1ck

    Patr1ck New Member

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    Thank you buddy, but it has been sold already.

    Pat
     

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