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Discussion Starter #1
So I was having a conversation with the general manager at Dynoman Performance and the topic of running an airbox with smoothbore carbs on my Z1 came up. Here is his response:

" The advantage to installing*performance carbs is that they flow much better than the stock carbs, however installing a stock air box will*kill any power gain that the carbs*would have given you. When we first opened our*performance shop in 1971 we modified the stock air boxes every way possible and they still did not work properly, as the turbulence*of running a stock air box is a horsepower killer. We would highly recommend that you run individual (K&N) style filters (on the Z1)"

I found that information really interesting because of the way an airbox functions; creating a stable atmosphere through which all carbs pull equal air via a velocity stack-like manifold.

I've been running the UNI on my Z and have no complaints. I will however test the above statement myself on the dyno this spring
 

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Discussion Starter #2
Here's some follow up feedback from SUDCO:

"We have not tried running the air box on the Z1 with the CR Specials so
can't say for sure on that application.
On the bikes we have run with the air box and the CR's we had to really
open them up by drilling extra holes in the air box to get more air to
those carburetors."
 

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Discussion Starter #3
I'm curious just how much additional air 29mm carbs intake VS the stock 28mm carbs
 

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Discussion Starter #4
29mm carbs should provide about a little over 9% greater area for air to flow through.

I don't know where to go from there
 

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Discussion Starter #5
I bet if I ran the airbox with no air filter I'd get plenty of airflow.

Once again, the only way to really test this is on the dyno.

My goal isn't so much top end power, but maximizing performance across the rev range.
 

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Im looking at a modern inline 4 airbox for a 750 supersport and the box under the seat of my kz1000.

It is pretty obvious to me the airbox lacks in overall volume but also intake area.

But I guess it was the best compromise at the time. More holes on the top of the airbox lid or an open lid is all I can think of.
 

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let's not forget that:

1) every bike is different

2) airboxes are engineered to the specs of the engine they are attached do in stock configuration AND to meet a specific performance metric. This isn't always maximum hp, sometimes it's drive-ability and fuel economy.


On something like a honda SOHC 750, the airbox is important because it is sized for the requirements of the entire run of the intake tract. the valves in most cb750s are small compared to the size of the cylinder so any "increase" in airflow volume and velocity is wasted because it is going to hit that small valve and neck down. The 750 is an undersquare engine at 61mm x 63mm so long duration cams and flow where more volume can be pulled through the valve opening (like bigger valves) really help the engine - but once you make those mods the airbox is no longer adequate to support the needs and it becomes the choke point.

on a bike like the z1 where the engine is perfectly square (66mm x 66mm) and the factory didn't resort to tricks like smaller valves to get fuel economy, torque, and drive-ability out of it - the carbs are the choke point. Going to any carb that can move more air volume faster than the stock setup is going to make the airbox the choke point pretty quick. In a lot of ways the Z1, and it's sister engine the GS 8v, are just better designed than the original SOHC 750, which is why when you are ready to mod it - it responds easier to bolt on stuff that increases volume and velocity much better.
 

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THE all rubber z1 airbox is acompletely shit design with zero tune involved with its design
it doesnt have trumpets or velocity stacks to get a sonic wave effect its just a shitty funky lashup
starting with the kz' 900 the airboxwas a part made with some thought as it has individual eqhal length truphets on each bellend and the each protrude into the box equally
without the trumphets extending the intake port length you loose the ability to have the target rpm at a spot somewhere just below safe mechanical redline
so those guysare ignorant that is all
all of the racing supers had trumpets,2-4 " long
having 4 kn's moves target rpm way high
but stillproly better than the z1airbox which was 3 years only
 

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eh....I wouldn't say zero tune - but a lot less focus on performance went into it. It's primary function was to hold a single square filter, but if it killed performance significantly kawasaki wouldn't have used it. Part of that I have to imagine was that kawasaki was using the VM series mukuni on pretty much all their bikes and it's a much better designed carb that could compensate for short cuts taken elsewhere. Was it optimal? probably not, but then again, what do I know, I had a kz900 and not an early z1.

I think the point we always try to make with new people when this conversation comes up is that you shouldn't assume anything. Take a measured approach and make changes and see how they make a difference. Don't assume what works for cars, or other bikes works for every bike, because it doesn't. And don't assume that just because you saw it on the internet it's correct or possible.

Either way I think we are all coming to the same conclusion that the z1 airbox is not a performance piece like on other bikes.
 

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Discussion Starter #10
I guess the next question is, how to use the CRs velocity stacks while ensuring adequate filtration but allows enough air flow
 

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it has got nothing to do with borexstroke
the optimum sonic wave tuning is highly dictated by the intake duration
an airbox should for the most part be looked at as not a flow improver but simply a clean place for the velocity stack ends ie the end on the intake port length to be exposed to atmospheric pressure
this pressurei.hat the waves ,which are firsted generated from the kinectic energy of the intake charge slamm into a closed valve
the distane to atmospheric pressue,where the wave hits and is reflecto back down the port towards valve is the endresult of the math calculations
a bonus in my opinion is less intake roar Velocity Stacks, Motorcycle Velocity Stacks, Ram Tubes, Bellmouths hand-crafted by Velocity-of-Sound.com
 

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the optimum sonic wave tuning is highly dictated by the intake duration
Agreed, which is determined in part by cam duration. I mean look at the engine big picture: Stroker engines (undersquare) like a lot of cam duration because the piston has a long distance to travel and the extra volume is in height, vs a big bore engine (oversquare) which doesn't need a lot of duration but prefers larger valves and higher lift cam so as to get the most amount of air volume into the chamber because the increase in volume is in width.

kawasaki in the 1970's had this nasty habit of making bikes whose optimal power exceeded mechanical redline, and then choked them down to bring the power back in range (you mentioned that earlier). The z1 had something like max hp at 8500rpm stock and a 9000 redline, from my experience with old H1's, they made max torque at 7000 and max power at 7500 stock and had an 8k redline, if you took the airbox off and put foam filters on it the bike would pull hard till it exploded, if you put chambers on it, depending whose design either you pushed all the power further up the range (unbaffled wirges) or you moved it back to a normal powerband range (dencos, 3-1s, etc...)
 

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Discussion Starter #15
And there's the rub... 99% of the time 99% of riders are at 1/4 To 3/4 throttle.
 

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resonance tuning of intake lengths is next level stuff. And frankly, limited to a narrow rpm band anyway.
I think what we are talking about is more just about adequate airbox volume and adequate intake area to sufficiently not choke the engine at higher rpms. Not hard to grasp.

I remember even on my 2006 bmw k1200r I had issues. It was designed with a single air trumpet and single filter intake from the front of the bike that narrowed to only about 3 inches in diameter. After opening the airbox with another large opening and filter and removing the restriction in the trumpet, I gained noticeable power from 6000rpms on.

All engines are different, but they all are basically the same, too. Air in, combustion, air out.


I wonder what the drag race Kawasaki’s use for an airbox? On a fully faired bike I think I recall reading there is an area of low pressure created behind the engine. But on a naked bike, it might not be so much an issue.
 

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I wonder what the drag race Kawasaki’s use for an airbox? On a fully faired bike I think I recall reading there is an area of low pressure created behind the engine. But on a naked bike, it might not be so much an issue.
enclosed bodywork with ram air inlets at the leading edges of the fairings. They also use short stack trumpets because they pretty much operate in a very narrow rpm range at the top of the tach. Also, Pro stock is mostly suzuki and harley now with kawasaki ducking out a long time ago and the muzzy zx-14 never really getting anywhere.
 

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enclosed bodywork with ram air inlets at the leading edges of the fairings. They also use short stack trumpets because they pretty much operate in a very narrow rpm range at the top of the tach. Also, Pro stock is mostly suzuki and harley now with kawasaki ducking out a long time ago and the muzzy zx-14 never really getting anywhere.
What about the drag bikes of the 80’s? KZ/GPZ, GS. Looks like air tech streamlining refers to a giant airbox as part of the bodywork here.

DRAG BIKE DRAGBIKE FAIRING AIRBOX AIR BOX BODY ICS FENDER WHEEL TUB BELLY PAN HEADLIGHT UNIVERSAL


The Honda CR166 crew would bring along a box full of different length manifolds etc, to use depending on the track.
Yes, but I would imagine they would have had the airbox worked out already. Did they even use one?
 
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