Nice one Ian.

I get it...but...unless the motor is limited by airbox volume I cannot see the specifc benefit.

What about my bike - no airbox lid and using the tank as the top of the airbox..?

Surely the low pressure is a function of the engine intake consumption rather than the volume of air availble for it to suck on?

My brains not yet at 100% this morning but I hope you get me?

cheers
MARK

A bigger airbox will be an advantage. But it will offer many other benefits besides outright horsepower (if adding any at all).

FWIW I reckon Honda have squeezed the biggest standard airbox volume into the available space (without getting too close to the tank etc). So there probably will be benefits fitting a bigger one.

To quote John Robinson from the book 'Motorcycle Tuning 4-Stroke':

[The airbox] acts as a surge tank which can damp out unwanted pulsations or, it seems, can strengthen beneficial pulsations. Often the air flow and power are increased by the presence of the air box, particularly in the midrange, and sometimes at peak power. To achieve this, the airbox needs a very large volume; say 7 litres minimum for an engine giving 100hp.The zxr750 has a 12-litre airbox on an engine making 103hp, although the race tuned version is capable of about 140hp.

Note the air intake on the front of the fairing does not need to be huge (the engine uses one carburettor at a time [nc30/35's use 2 at a time!]). On a machine capable of 175mph a forward facing intake will pressurise the airbox if it is bigger than 14.8 cm squared [e.g. 7x2cm's]. The air pressure, even at this speed, is not enough to make big differences to horsepower; the maximum avaialable is about 0.6psi, it is worth something like 3% more horsepower. While 0.6psi won't do much in the way of supercharging, it can do a lot to upset carburetion. To compensate for these changes, the float bowls should be vented into the airbox.

The positioning of the airbox and the length of the carb intakes extending into it are critical and must be found by experiment.

Great read this book, especially the chapter on carburetion. No - I'm not going to type it out!

I want a big carbon airbox for my roadbike!

I like threads like this one..

Much better than the fitting of a pointy tail or carbon efect brake levers...

More info please Cammo...I reckon you must have finished work now so can kick back with a VB and sort me something to read as I start my day of drudgery.

CMSMJ1 wrote:I like threads like this one..

Much better than the fitting of a pointy tail or carbon efect brake levers...

More info please Cammo...I reckon you must have finished work now so can kick back with a VB and sort me something to read as I start my day of drudgery.

Fully agree about the tech nature of this thread!! Gotta love it.

Mark, this book (even though it was first written maybe decades ago by JR of PB magazine tech fame) is the bible for moto tuning. Everything explained clearly in understandable terms. Fark, I've read (memorised?) it so many times that I'd happily send it to you for the price of postage (5 quid?) if you can return it one day. That is if you can't find your own, tends to sell for a bit used if it comes up at all.

I'll try and get some carburetion info from this book in a thread (errr, ahem links only mods! Back off!) maybe later in the week.


Yes, das bier ist gut.

Yeah techy threads are ace, i just wish i had the money to go out and make and test stuff like this.
Your right Mark on the engine sucking causing a pressure drop which is ultimatley why air goes into the airbox but if the next cylinder sucks ( engines dont seem to really suck in air more dissapear a chunk of it) this air as its rushing to fill this space it'll be at a lower pressure because of it speed, so more volume means theres more air available to fill this space and let the other cylinders breathe the still air, theres so much going on in there it takes some getting your head round.

I've too got John Robinsons books, there great reading, i read most of the engine tech books at college as well when i was supposed to be doing me electronics (and is surprising how much thinking has changed recentley), but engines are always more interesting than maths....
I like the idea of running the bottom of the tank as an airbox lid mark, ace stuff, and yes i really dont think an 8% increase in volume would make much difference on a standard engine, but as tescos say every little helps.
Alot of the current thinking seems to come from F1 cars were exhaust tuning valves(exup's) have been band for ages so they've been working on the intake side of things and trying to use intake pulses/resonance etc to assist in engine breathing.
Cheers
Ian

so could cutting the dividers out of the standard airbox snorkel improve things as it might help more air rush in when the throttle is blipped.ok it might be a small improvement but every little helps ?

like this cheers for the pictures 400Rider

What you might see wiht that is more turbulent air in the airbox. The strakes would help the flow IMO...

You may also see the snorkel collapse if the suck is strong enough* reducing the amount of air being taken into the airbox or it could increase the velocity of the air being taken in.








*desperately trying to resist a Carry On style comment here!

I run the air-box without the snorkel at all and it doesn't seem to make any difference at all. I do have the HRC replica tray to help flow the air into the right direction, so maybe that has replaced the job of the snorkel.

What I'd really like is this. The extra plumbing looks just like the mods I had to do to run the ram-air on the track-bike,

Just get yourself a set of HRC carbs and run without a filter or airbox then you don't have to worry about it