ram air filter housing to boost mid- & hi-range power?

Discussion in 'Performance Mods' started by Nate888, Oct 7, 2016.

  1. Nate888

    Nate888 Member

    my motor's a skyhawk 2 stroke, the gt style that comes w/ reed valve (though I haven't taken in the piston skirt yet, so I dunno if the reed does me any good). I'm thinking to use a plastic cup from gas station or the plastic shade off an old florescent light to make a ram air scoop & filter. its shape will scoop air as I move forward & push it in thru the filter & into the carb thru thick rubber hose. hopefully it'll give me a little boost at speeds 20-40mph. For the actual filtering, I'm probably going to use nylons from Target wrapped around w/e object, since I need to replace the air filter I lost

    anybody tried anything like this before?

    I'm thinking I should make sure not to run lean/run it flat out WOT for too long & overheat the internals. also, it should increase compression a little, right? at speeds up to 40mph, do I need to worry about boosting compression too much or will it probably be within the safe-enough mod zone?

  2. butre

    butre Well-Known Member

    ram air doesn't do any good until you're moving about 60 mph. a cold air intake will do you much more good.

    having the carb behind the hot engine means hot air and hot fuel are going into the engine, having it in front means cold fuel and cold air. as you know, cold air and cold fuel are more dense, which leads to better power
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  3. Steve Best

    Steve Best Active Member

    Ram air doesn't work so well but resonant shapes do.
    I have an old post where I experimented with different soda bottle shapes.
    Long trumpet shape (Perrier) gave tractor like torque but killed top speed.
    Short and stubby water bottle gave best top speed.
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  4. jaguar

    jaguar Well-Known Member

    ram air would be for really high reving engines, not these engines.
    Steve, is that the one that worked best? how long is it and what's its diameter?
  5. butre

    butre Well-Known Member

    I've found this to be an ideal setup for a daily driver. long-ish intake, large but not unreasonable carb, good filter, reed valve, and have the carb set out a bit so the heat of the engine isn't heating the carb bowl and not significantly heating the air coming in.

    note that being situated on the gulf of mexico I've somehow managed to make both aluminum and stainless steel rust. it's also a good picture because it showcases every single spot where I've ruined my nice paint job by clamping junk to the frame

    Attached Files:

  6. Steve Best

    Steve Best Active Member

    This bottle worked best for 6000-10,000 power:
    The copper cap is blocking off the boost bottle port from that experiment.
    The bottle is 3/4" copper water tubing fitted to a soda bottle with a foam filter inside the bottle.

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  7. Nate888

    Nate888 Member

    whoa awesome! thank you, I would not have thought of that. what a cool idea - im gonna look up that post of yours now

    what kind of an expansion chamber do you use on there w/ it? is there any interaction between the 2 w.r.t. performance?
  8. Neptunati

    Neptunati New Member

    Ram air wouldn't work with reeds right? Because it only gulps so much air before the reeds shut right? Ram air was on hemi piston port 4 stroke. The crank is what I believe atomizes the fuel in a two stroke right? Or am I blowing smoke ou of me bum? Just like boost doesn't work on a 2 stroke with out some power valves. Ram air especially won't work with a backwards intake. Can these resonant waves work with reeds?
  9. Neptunati

    Neptunati New Member

    You gotta do this to the intake side of the piston.

    Attached Files:

  10. Steve Best

    Steve Best Active Member

    Most of the Ram Air systems used in cars and motorbikes the past 50 years have been marketing hype. You can work the numbers to find a slight gain in intake pressure as speeds go up (past 30-40mph) but with most carbs this simply messes up the air/fuel ratio. Drag racers exceeding 100mph can figure this into their jetting or box the carb, but it really isn't practical on our bikes or on a daily driven car. Ram air or freer flowing air filter or supercharging all will work with reeds because it is still a pressure differential vs restriction = flow equation. You might have to find a way to hold the charge in the cylinder (eg: more restrictive pipe) but the reeds will flow more with a larger pressure differential across them.

    Resonant wave definitely work with reeds. Experiment with it yourself by changing the shape and length of your intake tract and filter housing.

    The venturi and needle jet do the most work toward atomizing the fuel, past there it tends to be coalescing and evaporation. The crankcase does not tend to mix and chop the fuel like you'd think, but is a huge coalescing risk with the fuel dropping out of suspension. Pull a cylinder off immediately after a hard run and you will be amazed at how much wet fuel and oil is in there. The secret to keeping fuel atomized after the carb is to keep the velocity up by keeping the intake tract no larger than it has to be and allowing nowhere to get a larger cross section, such as the reed box. Here are picts of the efforts gone to to keep the reed box cross sectional area constant to keep the fuel in suspension:

    More power can often be made by filling in than porting out. This epoxy fill was a huge success.

    As far as atomization goes, there is no perfect size of fuel droplet. Max power looks for large droplets that can slow down the burn and supply cooling from their latent heat of evaporation, max fuel mileage would like to see perfectly evaporated and warmed up fuel and air to increase burn efficiency. I did work on improving fuel efficiency (of a 4 stroke) by putting a fine screen across the intake (after the carb) to further atomize the fuel by disturbance. It worked to a small degree. Might be something to try on the 2 stroke. I tried heating it electrically too also but could not see a gain.

    A huge advantage to consistent atomization in a 2 stroke is simplified jetting and broadening of powerband. Well worth achieving.