Retrofit airbox for Kawasaki GPZ500s

[A.FreeMan]

Hi everyone! So I'm a student with a little project going on. I'm aiming to slightly increase fuel economy/ power output of a Kawasaki GPZ500s, by only changing the airbox.

I have been told that despite what the internet says, the GPZ is primarily a 'commuter' bike, so with this in mind I was thinking of aiming to improve economy/ power output for a speed in the range of ~60mph. (Let me know if this thinking is stupid)

My knowledge of Motorbikes is nearly as bad as my ability to drive one. (Never tried it!). I've been debating whether to use a cold or warm air intake. I know cold air is used to get denser oxygen to the engine and therefore is used for performance enhancing. However I have heard rumours that warm air could actually improve efficiency. The reasoning behind this is that by using warmer air, you can have the throttle open further and therefore reduce losses in the system. This will presumably only be true for a certain speed/ rpm?

My project is still fairly flexible but having been stalling for a few weeks I really need to get on a start doing things, so I guess what I'm looking for are any tips or ideas anyone has regarding this?

As I said, I am only interested in modifying the air intake, but any information would be greatly appreciated! I have been finding it difficult to find information about Bikes and improving their efficiency, all I seem to stumble upon are Forums - so I thought I'd give it a try!

thanks for any helpful suggestions!
Alfie

[whitedevil]

Check ex-500.com, iirc the best mod to the airbox was to just drill a 1 inch hole in it.
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GPZ500 sold ~ CBR600FS-2 sold ~ ZX6R sold ~ Street Triple R

[Vincent 2]

Hi , I can`t see a way of improving economy thro the Airbox , except by getting a better filter (K&N) , the engine and air intake has been design to transfer the air and make best use of the carbs at the design stage , other things you can do , are basic maintenance , tyre pressure, oil , driving style , any other tweaking would lose performance/economy

[A.FreeMan]

Ahh this is all the bad news I kinda expected to happen. Not really sure what to do about it. Thanks for the replies though guys you've helped me out here! No one got any ideas on whether warm air could potentially lead to more efficiency?

[MarJay]

This is a terrible project to choose. Motorcycle airboxes are usually very well designed by very intelligent Engineers who really know their stuff. Often the airbox design is so critical, that if it is removed from the bike, the engine can never be made to run properly.

There are so many other aspects of engine design that you could choose, it seems crazy to focus on the one thing that motorcycle factories really seem to get right. Any improvements that can be made would normally result in the airbox not fitting on the bike any more, with the space available being the limiting factor. That said, factories do tend to make good use of the available space.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Rogerborg]

I've had two bikes with the airbox removed because racebike. Putting the box back on improved them.

Fuel = energy = power. If you can find a way to improve power output while using less fuel then Volkswagon will have a job for you in the Emissionenscammenchipwaffe.

Unless you have (at least) a dynamometer, an exhaust gas analyser and some way of measuring the combustion chamber (and piston) temperature in real time then you're as likely to make the bike worse rather than better.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[A.FreeMan]

Thanks for all the replies guys.

I am aware that this probably isn't the most useful project, however it was set by my supervisor simply as a feasibility study. If it doesn't work then I can simply conclude that and give reasons for the failure!

Reading around it doesn't look as though efficiency has really been in the minds of motorcycle engineers as there isn't much demand for it? Unlike car manufacture that has a million new regulations every day, forcing them to tweek and tweek and tweek with MPG in mind!

I have access to a dynamometer in a mechanics garage.

Having just had a look at the bike, it is clear the airbox has been squeezed into the design (fairly ingeniously I must say) but the intake is under the seat (presumably fairly common). I was going to test the effect (if any) of re routing the air intake to the front of the bike, aiming to increase the pressure at the intake and reduce the temperature of the air.

To test this I was planning on doing some dyno tests and potentially a 40 odd mile trip down the motorway at as constant a speed as possible with the original airbox and the new airbox to compare the fuel economy. Thoughts?

[Vincent 2]

Have a look at bikes with ram air , a lot of bikes have this , it`s air intakes at the front of the bike (mainly on the fairing) to force air in at speed

[Rogerborg]

Ah, OK, I didn't realise you had access to moon-technology.

Then sure, ram air, but that's to get more air through which lets you get more fuel through.

For fuel efficiency you have to run lean, which means running hot. You'd be looking at fiddling with the jets and needles and seeing how high you can get the air/fuel ratio before you burn though a piston.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[iooi]

[spottedtango]

This is quite a difficult concept. Not impossible but probably very time consuming.

On top of the considerations you've mentioned.

You would also need to change the length of the snorkel that connects from the air-box to the carb/throttle body. In order to allow the engine to scavenge fuel better at low rpms (lower rpms = generally less fuel) during the valve over lap and create a "turbo charging" effect in the intake.

This generally is not a good idea as quite a few motorcycles have a slight dip in the midrange thats usually improved by tuning the air-box to these rpms and by doing this would only make it more pronounced.

But in your case it might give you small gains in the fuel consumption side provided you short shift in the lower half of the rpm scale where you've attempted to tune the engine for better efficiency.

It used to be a good idea to drill holes in air boxes but the diameter of a lot of modern air intake snorkels are more than enough for the size of the throttle body and including losses due to friction of the air filter ect.

[Wonko The Sane]

[RhynoCZ]

[Vincent 2]

If you read the whole thread you will see the understanding of this member, I was trying to explain that the only way to achieve the economy he was looking for was to do the basic things right that was maintenance and part of that maintenance was servicing, tyres , oil, driving style and including a clean filter maybe you have got a downer on K&N but it`s easier to clean that than buy a new one each time, hence the economy factor , as regards the ram air if you look at what he said he was thinking of making a pathway with air from the front straight to the airbox , I was pointing out that this was already being done with ram air bikes, unlike you he didn't profess to know everything

[RhynoCZ]

I did read it, I'm gonna post my thoughts right after I ask you once again. Do you really think that about K&N filters or are you a retailer of their products? For my particular motorcycle a K&N filter costs about 5x more than the OEM one and both are made of foam. The filter gets filthy pretty soon with the ram air intake and all the water getting there when riding in wet conditions.

Here are my thoughts:
OP, talking about efficiency is not just about fiddling with the fuel and air. It's also about reducing all the resistance in the engine itself and things that have a negative influence on the engine's power output.

You might know, that when the vast majority of manufacturers talk about kW and Nm, they always tell you the netto value. Meaing the engine is tested on a dynamometer, with external fuel pump, external coolant pump, external charging of the battery and even external oil pump and other things directly or even indirectly powered by the engine.

So, to make an engine more efficient, you have got to make all the parts lighter and achieve less rolling resistance of all the moving engine and gearbox components. Then you're gonna talk about wheels, tyre pressures and brakes drag. Worn bearings in the wheels, low tyre pressures, dragging brakes cause some of the energy produced by the engine is being wasted. The last bit you should worry about is the aerodynamics, because I can't see a reason for having a perfectly aerodynamic body shell, with all the components above having a negative influence on the efficiency of the vehicle.

I've also had a chance to see all this in practice, even changing the wheel bearings on your motorcycle makes significant difference. Now imagine you rebuild the engine, put a less restrictive oil filter there, get rid of the charging system, etc.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Snod Blatter]

Carburettors have airways to use the "ram air" pressure to pressurise the float bowl, to help sort the fuelling out in the turbulence.

Anyway! I'm with spottedtango, try lengthening the tubes from the carbs into the airbox and after that I'd perhaps try "filling" the airbox with something to reduce its capacity, to see if changing the speed at which the pressure waves reflect back inside the airbox can help. To deal with a 180 degree firing order you may have to increase the size of the airbox for that to work, though, so that the waves take longer to reflect due to the lower revs you want to use.

Vaguely interesting? Definitely testable though. You could also check out the ER-5 and KLE500, same engine but less top end horses - could give you an idea of where to go with it.
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[weasley]

Volume and shape can make a difference, as suggested above. A long, thin intake pipe can build an inertial supercharging effect, where the long column of air rushing towards the engine gathers momentum and forces itself into the engine even when the piston has stopped drawing. The downside of this is that the same inertia that helps with supercharging, also introduces some lag as you have to wait for the column of air to get going when sucked.

There is also the frequency tuning of the airbox, to match with valve opening instances. This can be used to fine tune air entry or air retention in the cylinders at specific engine speeds, usually to provide a specific result at a specific speed. Resonator chambers are often used to modulate and amplify these frequencies.

Mirroring RBorg's experience, I once modified the airbox on my Honda CRX VTEC because braaaaAAAAP! It sounded so much faster. However the best performance modification I ever did to that car was put the stock airbox back in it.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[A.FreeMan]

Thanks for all the help y'all, I didn't expect this much response!

I think I am going to see what installing a RAM air will do for me.

[Rogerborg]

By the way, good on you for having a go. Everyone's a critic, but all progress comes from determined individuals ignoring the nay-sayers who claim it can't be done.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[stinkwheel]

You couldn't possibly have picked a worse bike to try to do this with.

The airbox on a GPZ500 is very intelligantly designed. Kawasaki employed accoustic engineers to design the airboxes of their bikes in the late 80's/early 90's. That's how they managed to produce so many class-leading motorcycles and hung onto the "fastest production road bike" crown for so may years (GPZ900R then ZZR1100).

This generation of airboxes utilise pressure waves to force air into the engine. Their better efforts are reputed to be able to flow 10% more air than the capacity of the engine. The GPZ500 is largely based on the tech used in the 900R and that was the first production motorcycle todo 150mph out of the box.

As you have noticed, they built the GPZ500 round the airbox, rather than fitting an airbox into the bike.

I really can't see this being improved on. I can see attempting to convert a pressure-wave airbox to ram air resulting in a bike that wont run at all well. From my previous experience of messing about with various incarnations and combinations of the kawasaki 500 twin, I predict it almost certainly wont rev over 7,000 rpm at all. The lack of midrange pressure you cause by destroying the pressure wave will prevent the throttle valve from lifting. If it does manage to bog, cough and stutter past this point and you hit 9,000rpm, it'll set off like the hounds of hell are on it's tail. Now you need to decide if your abilities and licence can afford for you to keep it there.

That said, they are tuned for peak power. If you want to tune it for fuel efficiency, fit an ER5 airbox, main jets and throttle needles. You'll experience a roughly 10% drop in horsepower and a saving in fuel.

All the above notwithstanding, if you ride a GPZ500 at or around the speed limit and don't wring its neck, it'll return 60mpg. It's twisting your right hand that makes it inefficient.

I'm not saying don't try, I am saying you're messing with something that is already extremely well designed. My advice is don't do anything that cannot be easily reversed.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.