thepest
|
| posted on 15/2/10 at 11:32 AM |
|
|
Airbox design, construction, efficiency
How worthwhile is such a thing? I'm done mapping my xflow with Honda CBR TB's however between runs I can see that MAT fluctuates around 12
deg.
Is having an airbox worthwhile? I bet that the intake temps would be a little more stable, but other than that are there any power gains?
If so is there a guideline to follow when making airboxes such as size and where the air inlet should be?
|
|
|
|
|
MK9R
|
| posted on 15/2/10 at 11:36 AM |
|
|
it makes a huge difference on the BECS
Cheers Austen
RGB car number 9
www.austengreenway.co.uk
www.automatedtechnologygroup.co.uk
www.trackace.co.uk
|
|
|
sucksqueezebangblow
|
| posted on 15/2/10 at 12:05 PM |
|
|
If you do fit an airbox connect it to a cold air feed pipe from a scoop or the front grille. That way you'll get a nice cold, dense air charge
giving more power than hot (thinner) air.
Better to Burnout than to Fade Away JET METAL ~ AndySparrow © 
|
|
|
v8kid
|
| posted on 15/2/10 at 12:08 PM |
|
|
I think the idea originally was to create a still area of air to draw from and varied between 3 and 10 times the engine capacity. The positionong of
the side walls and top is critical for reflected pulses. It later developed into a helmholtz resonator creating positive pressure at a particular
rpm.
Downside is a negative pressure at other speeds. Similar to exhaust tuning but different physics.
I think the pro's vary the volume on the engine dyno to get the porer curve that suits their needs.
Expensive to get right. Unfortunately bikes have a different power curve requirement from cars but your chance of betterind standard are slim unless
you spend time and money.
I guess a big box is better than nothing as it removes one variation. Loads of info available if you google it.
|
|
|
matt_gsxr
|
| posted on 15/2/10 at 02:55 PM |
|
|
The Andy Bates design is very popular in RGB with fairly well confirmed power improvements.
I am not sure whether the improvement is due to the cold and smooth airflow, or whether there is additional magic in the airbox. I don't think
that it emplys helmholtz resonance, but it may do something about clever reflection (as the lid is quite close to the openings).
Here is a photo.
They are rather expensive (from a locost perspective).
Matt
|
|
|
hobbsy
|
| posted on 15/2/10 at 03:48 PM |
|
|
Has he made them for 2003 5PW R1s yet or still only the blade engines?
Any idea on cost?
|
|
|
brianthemagical
|
| posted on 15/2/10 at 03:51 PM |
|
|
For cold air purposes they will work, as big as possible with a nice cold air feed.
If you want to gain a bit of power from it then it'll need a bit more thought.
First think to do is the length of your intake runners.
Then build a box around them. You don't want it too small as it'll start reducing the pressure as your engine loads.
Pulses can deflect off the face opposite the intake, replicating a longer runner, which is nice.
Any air box will employ Helmholtz, it's a physical certainty, to what degree is another matter. it may sap power but you'll gain power
elsewhere, it's just a case of looking at the power curve and seeing if it's where you can cope with a loss.
[Edited on 15/2/10 by brianthemagical]
|
|
|
matt_gsxr
|
| posted on 15/2/10 at 04:11 PM |
|
|
Brian,
I have read your previous posts on these matters, and you seem to know some stuff.
w.r.t. the AB box, the intake tube is around 1meter long, and 3inch diameter. The helmholtz frequency is therefore VERY low, so I don't think
this plays are real role (which is what I meant by "doesn't employ"
You say that the box shouldn't be too small. Could you quantify that perhaps as a fraction of the engine capacity.
What is a good distance for the pulses to reflect off?
I don't have complex CFD/CAD so I only really have one guess at this, so your experience here would be appreciated.
Thanks,
Matt
p.s. Hobbsy, ask him.
|
|
|
brianthemagical
|
| posted on 15/2/10 at 05:04 PM |
|
|
By any air box will employ Helmholtz i kind of meant it's there, and i do agree with your point that not only may it not have been a
consideration in the design of an air box, but the air box may also be totally unsuitable. It's just at a certain rpm, there will be some
effect, even if it's outside the operating range of the engine. The harmonics also have an effect, so just because the primary frequency is
wrong, doesn’t mean it can’t sap power.
As for what factors affect it, everything form the intake vale has an effect. The resonating volume is the total intake volume, so it can include any
cylinders with open valves, but that's a bit pointless.
The tuning method of most Helmholtz systems is the intake tube as you mentioned as it's the easiest to alter.
As for specifics, it's a bit of hard one to call. A 2 litre air box on a BEC with most of runner length in the trumpets isn't the same as
a 1 litre box on a CEC with v. short trumpets.
It's more of a case of having enough space around the bell mouths to not provide a restriction. It's usually a case of what fits on the
car. Unfortunately off the top of my head i can't really recommend volumes, but something like the engine volume is always a good bet and if you
get high rpm power dropping then increase it a bit.
For a reflection distance try something like 50-100mm ish, but it depends on where your runner length is and where you want your second boost.
I do have access to pretty powerful CFD, which does help a lot in visualisation and understanding designs. I also spent last year studying intake
design and have a CFD and CAD developed system on my car, although I’m too lazy to build an air box.
Hope that helps a bit, I’ll try and answer any more questions if i can, but I’m kind of snowed under with project work at the mo so can't really
give too much depth but when i get some time I’ll see what i can do.
[Edited on 15/2/10 by brianthemagical]
|
|
|
matt_gsxr
|
| posted on 15/2/10 at 06:15 PM |
|
|
Thanks for those pointers.
Matt
|
|
|
thepest
|
| posted on 15/2/10 at 06:16 PM |
|
|
Thanks guys, I am rather limited in size with regard to the airbox due to the bonnet. To put things simpler is it better to have one then or not?
|
|
|
brianthemagical
|
| posted on 15/2/10 at 06:18 PM |
|
|
If it's not going to provide a restriction by being too small then yes, have one but it's not going to be anything major, only a few bhp
here and there. It can also dampen the noise, but i kinda like the sound of ITBs
[Edited on 15/2/10 by brianthemagical]
|
|
|
MikeRJ
|
| posted on 15/2/10 at 06:25 PM |
|
|
quote:
Originally posted by brianthemagical
Pules can deflect off the face opposite the intake, replicating a longr runner, which is nice.
Pulse reflected from the end of an open tube are inverted though (i.e. a high pressure pulse will cause a low pressure relfection). Reflected from a
flat plate there is no inversion so it's not totally equivalent.
|
|
|
brianthemagical
|
| posted on 15/2/10 at 06:35 PM |
|
|
My spelling is appalling.
Agreed that a rarefaction causes a change in polarity, and a reflection doesn’t, which is why a runner length can't be used to specify a walls
offset with the bell mouth. They are still only half a phase out.
|
|
|
thepest
|
| posted on 15/2/10 at 07:33 PM |
|
|
wow, didnt think that there was so much detail on this topic. I got some homework to do then...
|
|
|
brianthemagical
|
| posted on 15/2/10 at 07:40 PM |
|
|
TBH, there's a hell of a lot more in it than most people first think. It's all based on various fluid dynamic and acoustic wave theories,
which are rather complex. Thankfully lots of peeps have already done the hard work and fairly simple calcs and info can be found on the net.
|
|
|
thepest
|
| posted on 15/2/10 at 07:48 PM |
|
|
could you post me some links please?
|
|
|
brianthemagical
|
| posted on 16/2/10 at 04:01 PM |
|
|
Length calculator
Bit of Integra
theory
Another length calculator form the makers of MS
Nice real world example
For any more specific or fundamental reading it's usually down to books.
Hope they're of some help.
[Edited on 16/2/10 by brianthemagical]
[Edited on 16/2/10 by brianthemagical]
|
|
|
thepest
|
| posted on 16/2/10 at 08:49 PM |
|
|
Thanks a lot!
|
|
|
