Mod question?

Discussion in 'Performance Mods' started by geebt48cc, Apr 9, 2012.

  1. geebt48cc

    geebt48cc Member

    Well, I know that it's not possible to guessl a HP setting of a modified 66cc, but very curious? Skyhawk slant 2010 GT5 66cc is said to be 2.75hp. Ok, after milled head flat (w/o head gasket),ported exhaust/intake , everything, 8mm thick copper plug wire,NGK B6, with 7" intake, speed carb,SBP air filter/expansion chamber, 25:1 synthetic/castor, so wonder what HP would now could be? Curious again....................:thinking::thinking:

    Thanks all.................

    Last edited: Apr 10, 2012

  2. motorpsycho

    motorpsycho Active Member

    2.80 h.p.???
  3. geebt48cc

    geebt48cc Member

    Thanks for ideas Moto, but one would think with that with 132 pounds of compression now, that it would be at least over 3hp?................I know that the only way you can really tell is put it on a dyno?????????????????? Wonder just how high you can get one of these little engines up to in hp, to where they still have alittle life left in them? There's a racing expansion chamber that JNmotors has now that says by bolting on stock motor will add 3hp?
  4. max350

    max350 Member

    Not a chance --- 3hp just put on an expansion chamber
  5. HeadSmess

    HeadSmess Well-Known Member

    possible with the proper design, on a decent engine...

    a ht is not a decent i start swearing in spanish again? you cannot polish :poop:. you can deodorize it slightly and make it slightly less offensive, but its still :poop:

    a stock standard HT is simply not ported to be able to gain 3hp extra. no pipe in the world will get more air through the intake as it comes, stock.

    on a kx50, id believe it. 3hp is easy. on a not without using the dremel first.

    at which point the piece of :poop: can go like its hit the fan!:whistling:
  6. geebt48cc

    geebt48cc Member

    I get your point HS,

    Ok, let me ask this???????? What are they doing internally to get these HT's to grab right at 9+ hp? Sure, high compression,expansion,reed,port work.................but 9+ hp Come on now?
  7. jaguar

    jaguar Well-Known Member

    9 hp
    stuff crank
    enlarge inner diameter of intake track and install large carburetor
    make boost port(s)
    balance engine (since vibration robs power)
    port engine
    increase compression
    install motorcycle piston
    expansion chamber
    good CDI with Honda racing coil

    unfortunately the porting and pipe have to be designed to shift all the power to top rpm so that it runs like a dog till it comes "on the pipe". that kind of powerband is not effective unless the engine has a close ratio gearbox.
  8. geebt48cc

    geebt48cc Member

    Yeah, I see........ Naaa, Jag, you know as well as anyone, that what I would be after is the torque. I could see that most everything you listed would be fantastic if I was away from all of these hills. Other than 3 intake for reed, boost ports????
  9. jaguar

    jaguar Well-Known Member

    even if not porting for high rpm power, boost ports can add power as long as they are done right. Too big and you lose power.
  10. geebt48cc

    geebt48cc Member

    So, where do I look on your listings of performance mods? Once again, I would really like lows to mids...............
  11. HeadSmess

    HeadSmess Well-Known Member

    raising compression can only do so much for a two banger. you start getting more "pumping" losses than useful power. im not saying not to shave the head, but theres only so far you can go on a 2stroke before it becomes detrimental. now, the "squish band", thats slightly more important than sheer "high compression".

    the aim is to get fuel/air mix into the cylinder, and exhaust out, with the minimum of turbulence and intermixing, with the maximum volumetric efficiency. polished/rounded corners and edges, removal of casting flash, matching ports, etc, all these little things add up to make the airflow through the engine smooth. smooth flow makes for more power with less losses.

    volumetric efficiency is a hard subject for some to comprehend.

    say you have a cylinder of 1 litre capacity. open to the atmosphere, that will be one litre of air. quite simple. thats the rated volume.

    now pump the cylinder at a certain rate. if the top was missing, it would fill to its rated capacity, and expel the same amount, 1 litre. minus the small amount of air thats compressed/rarefied on each stroke due to the momentum of the air.

    start closing the top off, like a valve or port would. as the piston descends, at first theres a lower pressure in the cylinder. the air has to "think a bit" before it starts flowing. as the chamber fills, more and more air rushes in through the (restrictive) port. it doesnt just "magically and instantaneously" fill up with air! the air speeds up, it gains momentum. inertia. it wants to keep flowing into the cylinder, even once the piston has started coming back up! etc etc.
    as the gas is expelled, once again, momentum and inertia come into play. as the piston starts descending, the air/gas still wants to keep flowing OUT of the cylinder! with well designed headers, intakes and valve times, you can get more air into a cylinder than it would otherwise hold! though volumetric efficiency usually sits around 85 to 90%.(ie, a 1 litre cylinder can only be filled up with 850 to 900 cc of air/fuel) its also RPM dependant. one setup might be useless at 3000rpm but boy, does it work well at 5500!

    superchargers raise VE by stuffing more air into a cylinder than would normally be possible.

    hence the valve overlaps and (to someone that doesnt eat breathe and :poop: engines) general valve timings always seem a little bit "illogical" a standard 4stroke will open the inlet 10-15 degrees BEFORE TDC. the exhausts still open! the exhaust closes 10-15 after TDC. then inlet closes at say, 190-200 after BDC. compress, boom, and what? the exhaust opens at roughly 90-110 after TDC! so the valves open before the piston even gets to the bottom of the stroke! etc etc. its that momentum the air gains that makes it work!

    less overlap, and open closing times closer to the TDC and BDC marks makes for slow revs, torque, no hi speeds. large overlaps and highly advanced and retarded valve times make for bad idles, with heaps of power up top.

    so, how does this apply to a twostroke? much the same way. inertia is important. but so are "pressure waves". i swear i read somewhere that (ported or valved) motors have a limiting speed of approx 30krpm. at this point, despite the ports being wide open, the air simply can get moving in time to enter it before its closed!

    its a lot like "you cant get a projectile to launch faster than the SPEED OF SOUND IN THE PROPELLANT" when dealing with pneumatic rifles. the gas CANNOT expand faster than the speed of sound within itself! (compressed air has a higher mach speed than plain air, so yes, a projectile can be launched faster than the speed of sound in a standard atmosphere)

    the pressure waves can only propogate through the gas at a certain speed, can only push on the projectile and rear of barrel at a certain rate, etc.

    back to the question.

    low/mid speed torque.... fairly large ports, stocks are way too small. a really long intake manifold, the bigger carb wont do much as the air flows through its venturi slower than it would on a stock carb, making tuning erratic, and tending to bog on WOT at low speeds. and of course, one of my weasely pipes! (which in my experience override any other mods)

    iunno. motor tuning seems like a black art at first, but it isnt. you just need to be willing to spread your knowledge around. its like playing a musical instrument. it can sound like :poop:, or can sound amazing. all about harmonising :) some physics, some metallurgy, some experience pushing a broom even, or watching smoke in the draught from under the window... then applying everything you see, smell and touch!
  12. geebt48cc

    geebt48cc Member

    Good stuff Head. No, I've done just about everything as far as mods on this 820 mile 66cc. Puch head, turned SBP expansion into torque pipe,Jag cdi,3rd intake,arrow reed,etc ........... Wonder just if anything can be done to help even more with lows & mids. Happy now considering my size.............but uno we always want more of a good thing. I've cleaned all ports, but could I even get more torque from boost ports?............What, possiably lower? Also, wondering if it would help to make the main intake port on jug 1 or 2 mm's wider only on inside of cylinder jug?
  13. jaguar

    jaguar Well-Known Member

    I think the boost ports only help at mid-top rpm.
    Directing the transfer flow more rearward may be the last missing step for your ride. That boosts low rpm power.
  14. geebt48cc

    geebt48cc Member

    Jag, do you have a picture of redirected boost ports, to help low rpm to highs?
  15. jaguar

    jaguar Well-Known Member

    >Jag, do you have a picture of redirected boost ports, to help low rpm to highs?

    I don't own a camera. When I get back to the States I will buy one. They are double cost here.
    Are the instructions on my site not clear? I don't know how better to describe the process.
    The flow can be tested by taking the cylinder off, putting your fingers into the cylinder with fingertips facing towards the transfer port you want to test, then blowing air into the bottom of the port. You will see that with the standard setup too much of the air will be forward of the center point. ALL of it needs to be from center point to rear wall of cylinder.
  16. geebt48cc

    geebt48cc Member

    Not a big deal.................I just thought that maybe you might have some older pictures, considering all that you do. Yes, I'll look even more in your instructions. Hey, hang in there big guy........................
  17. geebt48cc

    geebt48cc Member

    Correction................Now, I cleaned the boost ports up, and just really thinned them down when I was doing some other work.. I didn't reshape them, but just really rounded to edges, to allow better flow. Should I concentrate on redirecting the boost ports? Uno, there's not much to work with there?
  18. HeadSmess

    HeadSmess Well-Known Member

    is there much you can do to redirect a boost port? they usually run fairly steep, keeping the charge near the rear cylinder wall. they squirt up into the top of the cylinder, hopefully getting rid of that last bit of exhaust gas... in a non turbulent manner.

    i always wanted to get a clear perspex "head", a fog machine and a really high speed camera... like 500FPS.(only 5 frames per rev at 6grand!) then do a real time flow analysis as i spin the engine...

    being a smoker helps "see" the airflow :p.

    crankcase, with hose attached and other holes plugged up. piston in cylinder at desired height. blow smoke down hose. fun. but doesnt give a true picture of whats happening when the engines actually running :( you cant emulate the pulses on the exhaust, the opening and closing ports with constantly changing areas and shapes, or the blowdown pressure.

    gives a pretty good approximate though. the perspex head would still be handy to see what happens in a closed cylinder ;)

    in my mind, for the low speed side of things, you would really want a narrow intake port, to increase air velocity through the carb, keeping the carb small. total airflow is not an issue at low speeds!

    dont use much, if any, crankcase stuffing, to keep charge speed from the transfers low. also use slightly less "blowdown" for the same reason. reeds dont help in this regard without raising the transfers :( you dont want a big squirt, more a gentle puff to fill the case smoothly.

    fairly steep tops on the transfer, to direct the charge up into the head area as much as possible, whilst keeping to cylinder walls. keep the exhaust in the centre and towards the export, reducing intermingling.
    keep transfers fairly low, whilst widening them to increase total area, also reducing charge speed. slight shaping to direct charge away from exhaust port, towards the rear and top of cylinder.

    have the boost, if used at all, opening very late, so its only gently pushing charge towards the head, not inducing a vortex that would tend to draw exhaust gasses AWAY from the ex port and increase intermingling of exhaust and charge. then again, its really the pipes job to make boost ports even work in conjunction with the reeds.

    im inclined to agree that boost ports only assist in the high rpm range, the rest of the time, when not on the band, there simply isnt enough crankcase pressure or negative exhaust pressure to make them do anything. i wouldnt bother with them if i was making a lugger.

    raise/widen exhaust to assist in lowering cylinder pressure before transfers open. larger port lowers velocity which reduces tendency for pipe to suck out fresh charge. also allows maximum "stuffing" time on the reversion wave, after transfers have closed :)
  19. geebt48cc

    geebt48cc Member

    So, HS you would raise/widen exhaust port inside jug? See, I just don't want to kill my lows and mids? Wonder how much I need to remove from exhaust port?
  20. Fabian

    Fabian Well-Known Member

    and to think that all of this work is already done in a Morini engine, and if you are using a single speed drive method, it's just a simple case of bolting in a Morini, with all of the reliability of a Morini engine.

    Don't get me wrong, i think the work and development going into Chinese engines is great but the lowest spec Morini gives you power and reliability for a respectable price.
    If SickBikeParts made a shift kit for the Morini engine, the combination would be on my bike tomorrow.