Blake's Megasquirt thread..

[Blake]

Hey Extent..


tell me more about this tuned airbox?



As for the 13"..  with the airbox removed, and going straight from the intake port flange, there is quite a lot of space under the gas tank.  On my bike now i have a set of k&n pod filters that are 6" or 6.5" tall (forget which, and there still is some extra space up there.  Without having my bike here (or a garage to tinker with it at school) i havent specifically been able figure out the routing, but it should  fit.   But also, one thing i was thinking, as I started drag racing the bike at the local 1/8th mile track by me, and plus i havent really ever taken it out in the rain, i was toying with the possibility of having the last portion of the intake/throttle bodies on the outside with one on each side/facing forward (probbaly wont happen because they'd have to be WAY forward without making lots of bends).     

But about the airbox.  I know that you can actually hurt some engine's performance by opening up the airbox intakes too much (again, was on cars), but how does the tuning work?  I would imagine that it would act similar to a plenum on a situation like ours (where we dont actually have a plenum before the throttle bodies).    perhaps some sort or plenum/throttle body system?


Blake

[Extent]

Dosen't the runner length have to be measured from the throttle plate back?  so that turns into 13" + your airhorn + the airfilter?

I don't know where a good place to put your intake would be, I have a feeling that just hanging the intake out the side would put it in some pretty turbulent air, especially since the bike is mostly naked.  The best places for intakes (ram air intakes at least) are supposed to be stuck way out front of the bike (like the snorkels that Kawis use) in the undisturbed air infront of the fairing, or along the side of the fairing by making a cutaway to bring air that's flowing along the body of the bike inboard and into your induction system.

Race teams started using tuned airboxes in the early '80s I think it was.  Basically you stick a simple helmholz resonator over your air horns.  The basic formula was something like:

Resonator frequencey = 5,300 X square root of ((total area of intake pipes)/(box volume X Length of intake pipe))

You can tune the airbox to provide a boost at any rpm, so it'd to be good for smoothing out small dips in the powerband, not necisarily to run out and tune it to match peak HP.

In order for it to work the entire airbox and intake pipes must be completely sealed, if the system leaks anywhere along the line it dosen't work.

[Dynomite]

Well I've done a bit of picking around trying to find out more about injector placement, and info is pretty slim, but I pulled a couple of nuggets.  Injecting before the TB isn't a problem (as I had originally thought) as long as the intake tracts are relatively straight.  This works great at high RPMs because it gives the fuel more time to evaporate fully, but it dosen't make for smooth low RPM performance.  Apparently several Superbike engines use two sets of injectors, one close and one far, that they switch between based on RPM (and Ferrari used sliding injectors in one of their F1 engines)

Extent- yes, this is what we have found on the dyno. The exact placement of the injector below the throttle valve seems irrelevant, we have had them spraying at the runner walls, top, bottom, batch fire, sequential, and it doesn't make any noticeable difference. Injecting a long way from the valve apparently makes the engine more difficult to handle at low throttle openings as (presumably) there is more mixture separation going on. I guess it would be no different to the early TBI (single injector) cars that suffered acceleration flat spots.

The Honda CBR600 uses eight injectors, an extra set in the air box lid that come on for high speed operation. Charge cooling = significantly more power must justify the extra expense (also requires a 32 bit ECU to run them!), as an OEM wouldn't spend that much if it wasn't worth it.

Cheers,
Dyno

[Blake]

Extent,


runner legnth is from valve face to..for lack of a better word... where the intake pulse has something to bounce off of (where it opens up significantly (like a plenum on a car intake).  They use this same idea when creating open exhausts with no mufflers for drag racing (tuning the legnth after the collector to modify length).   so the actual length of the intake would be 13 minus the intake port length(around 2" i'd say?) minus thickness of flange (3/8" i was thinking)  minus some of the legnth of the throttle body itself (placed at end of runner).  i would say you would measure up to the throttle plate, as it provides a very nice place for the sonic wave to bounce back at all but WOT (would have to find a compromise on length (1-2") to find a nice mid point for all but WOT, and the extra inch  or two added to the throttle body bell for WOT).  so the real legnth of the runner itself would be somewhere near..say 8-10"? plus the distance of the throttle body (3 or so inches).


oh..but how you mentioned the air intake on the new sportbikes..  i was wondering if i could make something in that way...to get air from infront of the bike, instead of making a mistake and accidently placing the intake on the side of the bike in a low pressure zone that wouldnt help me at all.  but that's going to require some definate modifications.  if anything, I'll probabaly just have the airfilters be as forward as possible under the gastank (while looking for some source for cold air to enter)

.

Blake