HughesR1
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| posted on 1/2/11 at 04:53 PM |
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Airbox design, Helmholtz resonator & Volume
Hi, haven't used Locost builders since completing the Striker R1 build & have lost my account details & my old email address has long
gone so just made a new account.
Anyway, as part of my project at uni I'm creating an Airbox for the striker, with the objective of reducing noise levels and increasing power.
Its currently running a pipercross open filter, which extrudes through the bonnet, therefore im limited on how large the airbox can be.
Current set-up (Yamaha R1 5VY)
We have done research on the Helmholtz resonator & airflow etc, but are still pondering with the simple question of air box volume. 
I see many people on here go with the simple rule that the larger volume the better, but I see a lot of airbox's seem to vary quite a lot in
size ?
Would it be best to stick with an airbox volume of around 8-10 litres and then calculate inlet diameter and length to suit that size ?
Cheers, Alex.
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SPYDER
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| posted on 1/2/11 at 05:01 PM |
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Haven't Yamaha already done the calculations for you?
At the risk of stating the obvious I would say mimic the standard box as a start point.
Geoff.
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BobM
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| posted on 1/2/11 at 05:21 PM |
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quote:
Originally posted by SPYDER
Haven't Yamaha already done the calculations for you?
At the risk of stating the obvious I would say mimic the standard box as a start point.
Geoff.
While I totally accept the point about Yamaha's R&D don't forget that the airbox size on a bike is even more
compromised than in our cars in that it has to fit under the fuel tank. My understanding is that the key requirements are a supply of fresh cool air,
a positive pressure (ram air) is a plus, but you then need a big volume to smooth the air flow out prior to the engine sucking it in.
Not very Locost but very BEC 
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HughesR1
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| posted on 1/2/11 at 05:50 PM |
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That was my first idea, however my lecturer hinted that they are usually restricted to there position on the bike, even Kawasaki made a hash on one of
there's in recent years.
As I'm restricted on size I think I will be best making it as large as I can as, because I don't have enough space to make it too big, but
I still would like to understand what optimum/maximum volume is :/
Does anyone have any other helpful tips/resources on Airbox design ?
I made a quick mock-up of a shape which I thought would be best for sharing air between the cylinders, instead of favouring one end of the throttle
bodies.
Side inlet Airbox design: 1
Alex.
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AdrianH
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| posted on 1/2/11 at 06:00 PM |
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I am only a guy who reads books and one in particular by Graham Bell. He seems to suggest 0.8 times the engine volume if you want a quick response to
throttle. The book suggests to me that the larger the air reservoir the the longer it takes the engine ECU to respond to change in pressure through
MAF/MAP etc.
Am I correct in thinking air box is same as Plenum?
Adrian
Why do I have to make the tools to finish the job? More time then money.
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HughesR1
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| posted on 1/2/11 at 06:24 PM |
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Yes I did read the Graham Bell book too. And yes the plenum is usually the "free" airspace for the throttle bodies to take air from. I
found that this should be clear of the filter for best performance, having the filter further up stream in the duct.
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hicost blade
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| posted on 1/2/11 at 06:39 PM |
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Not that it helps but what sort of intake are you using? a properly designed NACA duct (which you have loosely drawn) by nature, will not pressurise
the air box at all and most bike engines rely on a ram air intake system, a proper scoop would do a much better job
http://www.demon-tweeks.co.uk/Motorsport/Air_Filters_&_Accessories/Ducts_&_Ducting_Hose/1687
A few calculations on air consumption of your engine will help with your airbox design, have a look at the Race and Rally Car Source Book for some
useful information on the subject
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HughesR1
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| posted on 1/2/11 at 06:45 PM |
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Thanks for that. I wonder if I could use ram air coming off the aluminium side panel ? should do the same job. Is your Airbox a generic bike engine
one ?
Alex.
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hicost blade
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| posted on 1/2/11 at 06:50 PM |
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That is not mine , but it is a Piper X generic one and has no baffle
I did have an AB performance fireblade one on my Westie, but it's now sold
I am going over to the guys house soon so I can take some pictures and measurement’s if you like, won't be for a week or two though
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hicost blade
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| posted on 1/2/11 at 06:55 PM |
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Although a NACA duct is perfect for feeding carbs, but it has to be a proper NACA duct/submerged duct.....
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SPYDER
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| posted on 2/2/11 at 12:01 AM |
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quote:
Originally posted by AdrianH
........ Graham Bell. ....... 0.8 times the engine volume if you want a quick response to throttle.
This doesn't sound right at all. 800cc airbox on an R1 engine?
I doubt if you could make one that small.
We are running the standard airbox on our 929 blade engined Phoenix. It must be at least 4 or 5 litres.
Maybe more.
Your CAD design looks OK to my eye at least FWIW, not too dissimilar to Andy B's arrangement. Are you able to calculate the amount of noise it
might generate?
Where you site the inlet duct can be just as important as it's shape. It is difficult to achieve much Ram-Air effect at the best of times.
I dare say it is possible to design a box for optimum power that might improve on standard.
Same thing goes for noise. You might well come up with a quieter one.
You are aiming for both more power and quieter.
I still maintain that Mr. Yamaha will be difficult to beat given these two almost diametrically opposed targets.
I suspect that the absolute, no-compromise, no constraint solution will be larger than standard rather than smaller.
Only my humble opinions. I'm usually wrong though. According to my wife!
Geoff
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indykid
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| posted on 2/2/11 at 12:20 AM |
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quote:
Originally posted by HughesR1
Yes I did read the Graham Bell book too. And yes the plenum is usually the "free" airspace for the throttle bodies to take air from. I
found that this should be clear of the filter for best performance, having the filter further up stream in the duct.
the plenum is after the throttle, as on a 4 cylinder engine with single butterfly
before the throttle, it's just an airbox
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Hellfire
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| posted on 2/2/11 at 12:37 PM |
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Forget about ram air, you just couldn't reach the speeds necessary in a seven in order to achieve the benefits. I'd also take the comments
regarding which type of duct you use with a pinch of salt too, because unless you have access to a wind tunnel and understand how aerodynamics affect
your car, it's pure guesswork IMO.
Phil
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matt_gsxr
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| posted on 2/2/11 at 01:24 PM |
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Alex,
Your airbox looks good to me, where is the air filter.
I don't think you can get Helmholtz working using such a long intake as you have. The mass of air in the tube will be so large that the
resonant frequency will be too low to be useful. If you lower the mass sufficiently then the air feed will be restrictive.
If you do want Helmholtz and a cool air feed (and cool air feed is a very good plan), then you would need to have a system such as
cool air feed -> airbox1 -> Helmholtz tube -> airbox2 -> engine
I think this is shown in a Walkinshaw engine in the Bell book that has been mentioned in this thread.
I think it should be possible to test Helmholtz using a speaker and microphone and seeing at what frequency things resonate. It would make a lovely
university project as you could build some simple mock-ups to optimise the design and then build a final engineered version for your car.
Regarding Ram-air. The physics means that it is a small effect at road going speeds. I have a 3 inch front facing inlet and do see elevated pressure
in my airbox at 10krpm in the higher gears compared to the lower ones, but it is a 1% effect. So, not worth the bother.
Matt
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HughesR1
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| posted on 2/2/11 at 02:56 PM |
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Thanks for all the great replies.
The more important factor we are bothered about is the noise level, with added power being a nice bonus of adding an air box.
Considering the striker tops out around 125mph, I'm not that worried about ram air, although would be nice bonus.
The CAD model was just a quick mock-up to show where the Airbox would be suited, the filter would be placed further forward in the ducting from what
i've read to give free air in the Airbox ready for the throttle bodies to take in.
Before moving on I just want to find the optimum volume, but by the looks of previous designs, around 5-10+ litres seems to be the most favourable
size. ( I'm limited on space to around 10 litre anyway)
Cheers everyone.
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matt_gsxr
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| posted on 2/2/11 at 11:01 PM |
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The noise from the inlet will be insignificant compared to that from the exhaust once you have an airbox.
I don't know figures, but think how loud your engine is if you take the exhaust manifold off, or if you ran 10inch stub exhausts. This is what
your inlet has when you are running without an airbox.
A bigish airbox and intake hose is just like an exhaust and silencer box for your inlet.
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