Interesting information regarding airboxes and high flow carbs
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Interesting information regarding airboxes and high flow carbs

This is a discussion on Interesting information regarding airboxes and high flow carbs within the Technical forums, part of the Caferacer.net Forums category; 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 ...

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  1. #1
    Senior Member CaTacL1sm's Avatar
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    Interesting information regarding airboxes and high flow carbs

    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
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

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    Senior Member CaTacL1sm's Avatar
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    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."
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

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    Senior Member CaTacL1sm's Avatar
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    I'm curious just how much additional air 29mm carbs intake VS the stock 28mm carbs
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

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    Senior Member CaTacL1sm's Avatar
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    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
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

  6. #5
    Senior Member CaTacL1sm's Avatar
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    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.
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

  7. #6
    jcw
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    Senior Member jcw's Avatar
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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.
    Last edited by jcw; 01-02-2019 at 10:50 PM.

  8. #7
    Senior Member Geeto67's Avatar
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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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    Senior Member XB33BSA's Avatar
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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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    Senior Member Geeto67's Avatar
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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.
    Last edited by Geeto67; 01-03-2019 at 09:33 AM.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

  11. #10
    Senior Member CaTacL1sm's Avatar
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    I guess the next question is, how to use the CRs velocity stacks while ensuring adequate filtration but allows enough air flow
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

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