I've seen some people that say you will have issues tuning part throttle running or something like that if you put the larger 12 throttle body on the 9. Can someone explain why this is? I'm thinking about doing this, and plan to start getting in to tuning but right now just know the basics. I'm just curious why this would be a problem. A larger TB is often a common mod on most bikes/vehicles and never a problem.
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12 TB on a 9, what's the problem?
- Thread starter snrusnak
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konarider94
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if there is no choked flow in the 9 throttle body then going bigger is no help. You want to run the smallest opening that provides enough flow so you can actually use the throttle from closed to 100%
Lets say you go larger and peak airflow of the engine can be supported at 80% throttle so there is no flow difference between 80 and 100. Now all you have done is decrease the resolution of your throttle control. All the throttling would be between 0-80 instead of 0-100. This also throws off the fuel & timing maps which are based on throttle position. This also means the same change in throttle angle would cause a larger change in airflow which could make part throttle tuning and driving less smooth.
Im not sure on the difference between the two. If its a small change and your bike can actually use the airflow than sure it would help. Basically you want full throttle to be as close to atmospheric pressure as possible. If there is still a pressure drop across the throttle at 100% open the flow is being choked. Anything you can do to increase volumetric efficiency will help. When i described bigger I was just throwing out what ifs for one that would be too large. I think you would have to do some testing to determine if the 12 was too large or not. Im assuming buell did this and the 9 TB is pretty well optimized but maybe there is room for more with supporting mods for more airflow. There are so many instruments used when doing engine testing to properly test this.
Sure you could swap it, do some tuning, and see if you get a good change on the dyno. Im not convinced one way or the other on this. I wish I still had access to gt power. I could make a computer model of the engine and change things like that. Its a pretty awesome program.
Lets say you go larger and peak airflow of the engine can be supported at 80% throttle so there is no flow difference between 80 and 100. Now all you have done is decrease the resolution of your throttle control. All the throttling would be between 0-80 instead of 0-100. This also throws off the fuel & timing maps which are based on throttle position. This also means the same change in throttle angle would cause a larger change in airflow which could make part throttle tuning and driving less smooth.
Im not sure on the difference between the two. If its a small change and your bike can actually use the airflow than sure it would help. Basically you want full throttle to be as close to atmospheric pressure as possible. If there is still a pressure drop across the throttle at 100% open the flow is being choked. Anything you can do to increase volumetric efficiency will help. When i described bigger I was just throwing out what ifs for one that would be too large. I think you would have to do some testing to determine if the 12 was too large or not. Im assuming buell did this and the 9 TB is pretty well optimized but maybe there is room for more with supporting mods for more airflow. There are so many instruments used when doing engine testing to properly test this.
Sure you could swap it, do some tuning, and see if you get a good change on the dyno. Im not convinced one way or the other on this. I wish I still had access to gt power. I could make a computer model of the engine and change things like that. Its a pretty awesome program.
konarider94
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- Sep 12, 2009
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Not everything needs to be scientifically proven to a margin of error less than 1%. If its something you want to tinker with throw it on, but Id keep the same injectors from the 9 if they are different and tune with ecmspy from there. If it feels good on the butt dyno and works the way you want that's all you really need. A dyno run or two wouldn't hurt either.
greasyxb9s
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- Oct 22, 2012
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I can see velocity dropping quite a bit..... maybe on a 1050 big bore kit with head work and cams..... or a stock motor with significant head work and cams.
