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Info Little bit about airboxes and filters.

Discussion in 'Tech Tips' started by Murdo, Feb 5, 2018.

  1. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Water injection was used at least before the first world war. My uncle rebuilt a 1912 International 3.5hp stationary engine that used water injection (I remember this as I made some bits for the carb that had rusted away).
    Most aircraft use water/methanol (55/45%) mixture (one of my jobs as first year apprentice was to check the specific gravity of the water/meth tank every day) which gives better cooling and less likely to freeze at altitude.
    The ducting to the front of the bike for cold air will probably give better hp than sucking hot air from behind the rad/cylinder head, but the rise in pressure will be negligible.
     
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  2. ShaneP

    ShaneP Well-Known Member Premium Member Contributing Member

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    Seems those early motors using water or water/methanol are using it for engine cooling rather than cooling a forced induction. Unless these aircraft were forced-induction; I couldn't imaging a 3.5ho stationary engine being boosted.
     
  3. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    The RR Merlin (for example) used a two stage centrifugal supercharger and used the water to cool the intake mixture (there were many variations of this idea) and engines like the Pratt and Whitney R4360 28 cylinder radial used a turbo to feed the supercharger and needed the water/meth as there was no room for intercoolers (although they would have worked well at the high altitudes the B29 flew at).
    The 3.5hp international used the water to stop the cylinder 'knocking' (pre ignition) when using the low grade fuels of the time (remember that tetraethyl lead was not added to petrol until the mid 1920's) under heavy load.
     
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  4. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    That seems to be the takeaway for me from this discussion. For a CV carburetor, keep the fuel hot and the air cold...best chance for thorough burning of the charge. A CV carb with a pressurised airbox was something I wanted to do, but a few too many folks said "don't". The ZXR airbox is fed cool/cold air from the LHS fairing (as Linkin mentioned). I have put a fan in front of the bike and run it flat out to see how much air was getting into the airbox. The filter and cylindrical shape of the standard ZXR airbox air inlet significantly reduced the airflow. Taking the filter out certainly increased the cold air entering the airbox. I might try this combo one day at the strip to see how much difference it makes to the bike's performance. I have run a standard/airbox and I have run no airbox at all on the bike and it made basically zero difference to my times. I run blueprinted inlet trumpets on the carbs and they work just fine.
     
  5. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Make an envelope around your airbox and fill it with dry ice or better still make a custom icebox. Why do you want the fuel to be hot?
     
  6. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    Not necessarily hot, but not cold. I'm reading about atomisation and vapouring. I believe some CV carbs have plumbing running the engines hot water through their bowls. I know you know more than most about these things, so I'm keen to hear your opinion/experience with warming fuel. I am building a plate/deflector to go around the carbs so hot air from the engine can't get near the inlets, but can be directed to the carb bodies/bowls. All this might do zip, but it's a learning experience for me.
    Airbox template.jpg
    Obviously, I'm not making it out of cardboard.
     
  7. Andych

    Andych Well-Known Member Premium Member Contributing Member

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    Its a fine line to run with any heating of fuel... too much and you risk vapour lock. Most fuel heating is done with Diesel engines to ensure the viscosity is sufficient to allow correct atomisation at the injectors or in the swirl chamber on some engines.
    I think if you are able to ensure a good supply of outside air that hasnt been heated up going past the engine then you will ultimately benefit over a system that draws intake air from around the motor.. the problem with all of these different options is the ONLY way to maximise them is to tune the bike specifically to the modification on the Dyno.
    I dont believe you will achieve much (if any) change leaving the tune as standard ... especially if you are only talking about for the Drag Strip or speed trials.. they are very specific applications and as such need very specific tunes.
    As is found on all new cars these days as well as most racing applications... they will have a "cold air box" as heat is a killer for performance applications. Most new cars wont call it a cold air box but they pretty much all take the air intake from the grill area or from under a front guard.
     
  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The heating lines for carbs I thought were for the polar bear countries. Can't see any point to doing all that extra work for any other reason. I am not saying that the fuel will freeze but all the rubber parts can become very brittle, break, leak etc. Not good when the bike catches fire.
     
  9. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    This discussion thread is getting more & more interesting, OK I'll accept I have't had that much to do with performance engines using CV carbs, all I'll say is the lest resistance to the airflow the better.
    Now changing the subject a little, you'll all remember the old theories that on a performance engine whether 4 or 2 stroke you
    MUST polish the intake ports right, well I discovered quite a few years ago for this to be rubbish.
    The cross sectional area is all that matters, In actual fact deliberately creating a rough finish or even adding multiple raised pimples, for the sake of a better word, will very much help in atomizing of the incoming fuel charge, hence higher power output & better fuel economy.
    Stihl Chainsaws introduced this feature to their high revving two stroke engines quite a few years ago.
    Next time you have a modern chainsaw apart that uses a Rubber intake manifold, take a lookat the inside & see what I'm talking about.
    Cheers.
     
  10. Andych

    Andych Well-Known Member Premium Member Contributing Member

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    Hi Mike
    It has been well known in the performance scene (motorbikes and cars) for a long time that when using carburettors or the more simple form of port fuel injection that highly polished inlet tracts are much less effective than ones which are smoothed but still a "rough" finish. The rough finish promotes swirl and helps to keep the atomised fuel in suspension.
    I was instructed on this nearly 40 years ago when doing a port and polish on a 1600cc Escort Cross Flow head.
    On direct injection engines the inlet tract can be and is often polished to a very fine surface finish specification so as to keep airspeed up (Velocity) to aid in cylinder filling. The injectors fire directly into the cylinder so the atomisation etc is only down to the injector profile and fuel pressure.
    Combustion chamber design is also critical on high performance engines as is exhaust porting (always highly polished) and camshaft design and exhaust design to encourage sufficient scavenging of the exhaust and hence affecting cylinder filling during cam overlap...
    Modern Fuel Injection and electronic ignition has made it much easier on the engine builder to produce a lot of power (some more than others)... the trick now is to make that power usable and that comes down to the mapping.
     
  11. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    Very interesting, Iv'e never had anything to do with modern direct injection Gas engines only on some of the earlier Diesel Truck engines, Iv'e had even less to do with mapped electronic Ignition systems, only solid state auto advance CDI's etc.
    Arethese two features you are referring to, that is not restricted in the use of, with the GP250 class racing?
    The Authorizing body of this class seem to have restricted the mechanical features of the engine internals quite heavily,
    is this a good idea from your point of view? or is mainly to stem the horrendous cost involved?
     
  12. Andych

    Andych Well-Known Member Premium Member Contributing Member

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    To be honest I havent looked into the rules and regs of GP250 class... I do know that MotoGP is now a class that is ruled basically by electronics and aerodynamics more than having the best engine and chassis... that is why Casey Stoner wont ride in the Championship... he wants it to be more about the rider.
    These days a rider like Marquez can throw the bike down the inside under full braking knowing that it wont lock up due to the advanced ABS and then he has traction control and wheelie control when powering out of the corner...
    I am not sure on which series you are talking about that is heavily controlled mechanically... I am guessing V8 Supercars is the one you mean... Yes, I agree with the way they are going... it is highly controlled.. to limit the spending. Imagine the spend from the likes of DJR Team Penske and Walkinshaw Andretti Autosports if they were not limited in what they can do... I mean an engine is upwards of $250K now with a mid year service costing around $50K. Heaven knows what the Kelly's put into the Nissan motor...They actually shut down the cylinder head casting line for a full day in the USA so they could cast some special heads with different cooling jackets to allow larger ports... and then they all go and do their own ignition, advance and fuel maps... That is why it is such a big money sport these days...not like in the good old A9X Torana days :)
    MotoGP is horrendously expensive but it is still to some degree a power series... although Ducati no longer holds the most power... that would currently be Honda... but for how long... Man are we off topic or what...
    Hmmm Airboxes and Filters... Filters are really important :)
     

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