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Airbox versus Pods
I guess this subject rates up there alongside religion, politics and OILS.
I have dabbled in experiments on race and rally engines in the past, by running airboxes, with and without ram tubes(velocity stacks) and also using pod filters. On all these occasions, the racing airflow was doninantly travelling at right angles to the carb inlets. Air eddies and disturbed areas were not so evident as can be the case with a motorcycle carb setup, where the natural airflow is travelling in the opposite direction to the carb inlets. I achieved the best results when the tuned length allowed for a velocity stack to be attached to the carb's inlet surrounded by a generously sized airbox. The inlet to the airbox was paper or foam filtered and ducted cold air from the front or the car.
I have read many members opinions on the merits of both airbox and pod systems. The argument for pods goes, they should be used when running a big bore kit and after changing the exhaust to a 4-1 system. Of course, they are proven to flow more air than an airbox!!
Proponents of retaining the airbox including myself, will tell you that our bikes maintain a relatively smooth power curve when the manufacturer's tuning parameters aren't tampered with too severely.
I haven't experimented with pods on my 850, but I have read the various past threads on this forum depicting the many jetting woes that members have experienced. The current thinking is don't experiment, use a tried and proven carb kit that matches the changes you have done to your motor. That makes sense. From what I have read here and experienced myself on auto engines, the pods have performance limitations at the lower to midrange of the rpm range. There is usually a flat spot which is fixed by richening up on jets. This problem is probably not so pronounced on a CV carb setup which I gather most of our bikes use anyway.
I have gleaned some feedback on this issue from other forums of various motorcycle owners who run either carb or EFI induction systems.
There is no conclusive evidence that Pods improve an engines output anywhere in the power curve except in some cases, the very top end. Quite often, they actually reduced performance.
They are drawing in warm/hot air and worse still, in many cases, the airflow around #2&3 carbs becomes very turbulant as the road speed increases, causing a slowing of the intake velocity on the middle cylinders. You can patch this up by jetting but you are still missing out on performance, not to mention the power imbalance occuring internally.
I could find no occassions where owners had dyno tuned both airbox and pods on their motor and then did some timed runs on twisty hilly roads to compare the driveability/tractabilty characteristics of each setup.
Sure there were many dyno tests done, but that doesn't replicate the road conditions. Also, it is easy to misrepresent dyno results to the novice.
The interesting thing about the mix of pods and modern EFI systems was that the mapping sustems automatically adjusted to compensate for disturbed airflow and actually reduced the motors output accordingly in that part of the power curve.
Besides the turbulance issue with pods, I believe that there is a great benifit to retaining the rubber velocity stacks on the inlet to each carb.
I haven't dissected any motorcycle pods, but their profile doesn't seem to allow room for a bell shaped stack inside the filter. In fact many are short and tappered in the opposite direction.
I plan to experiment with increasing the airbox size and/or controlling the rate and velocity of the incoming air. Also, the shape and length of the velocity stackes. I believe that I can further increase the torque in the lower to mid power range by lengthening the stacks without loosing out in the top end.
It was surprising to read how many owners thought that pods looked better and were easier to clean, so be it, at the expence of performance.
Finally, VM26SS carbs were fitted to the 750,850 and 1000 motors in various states of tune. This demonstrates to me just how good the airflow characteristics of these carbs really is, and was a deciding factor in my decision to increase my motor's capacity to 900cc, while retaining the original induction setup.
The ultimate would appear to be EFI with a well designed and inducted cold airbox.
I would like to here from any members who have results from any controlled tests on airbox vs Pods against a given engine tuning specification.
Cheers
Ian
I have dabbled in experiments on race and rally engines in the past, by running airboxes, with and without ram tubes(velocity stacks) and also using pod filters. On all these occasions, the racing airflow was doninantly travelling at right angles to the carb inlets. Air eddies and disturbed areas were not so evident as can be the case with a motorcycle carb setup, where the natural airflow is travelling in the opposite direction to the carb inlets. I achieved the best results when the tuned length allowed for a velocity stack to be attached to the carb's inlet surrounded by a generously sized airbox. The inlet to the airbox was paper or foam filtered and ducted cold air from the front or the car.
I have read many members opinions on the merits of both airbox and pod systems. The argument for pods goes, they should be used when running a big bore kit and after changing the exhaust to a 4-1 system. Of course, they are proven to flow more air than an airbox!!
Proponents of retaining the airbox including myself, will tell you that our bikes maintain a relatively smooth power curve when the manufacturer's tuning parameters aren't tampered with too severely.
I haven't experimented with pods on my 850, but I have read the various past threads on this forum depicting the many jetting woes that members have experienced. The current thinking is don't experiment, use a tried and proven carb kit that matches the changes you have done to your motor. That makes sense. From what I have read here and experienced myself on auto engines, the pods have performance limitations at the lower to midrange of the rpm range. There is usually a flat spot which is fixed by richening up on jets. This problem is probably not so pronounced on a CV carb setup which I gather most of our bikes use anyway.
I have gleaned some feedback on this issue from other forums of various motorcycle owners who run either carb or EFI induction systems.
There is no conclusive evidence that Pods improve an engines output anywhere in the power curve except in some cases, the very top end. Quite often, they actually reduced performance.
They are drawing in warm/hot air and worse still, in many cases, the airflow around #2&3 carbs becomes very turbulant as the road speed increases, causing a slowing of the intake velocity on the middle cylinders. You can patch this up by jetting but you are still missing out on performance, not to mention the power imbalance occuring internally.
I could find no occassions where owners had dyno tuned both airbox and pods on their motor and then did some timed runs on twisty hilly roads to compare the driveability/tractabilty characteristics of each setup.
Sure there were many dyno tests done, but that doesn't replicate the road conditions. Also, it is easy to misrepresent dyno results to the novice.
The interesting thing about the mix of pods and modern EFI systems was that the mapping sustems automatically adjusted to compensate for disturbed airflow and actually reduced the motors output accordingly in that part of the power curve.
Besides the turbulance issue with pods, I believe that there is a great benifit to retaining the rubber velocity stacks on the inlet to each carb.
I haven't dissected any motorcycle pods, but their profile doesn't seem to allow room for a bell shaped stack inside the filter. In fact many are short and tappered in the opposite direction.
I plan to experiment with increasing the airbox size and/or controlling the rate and velocity of the incoming air. Also, the shape and length of the velocity stackes. I believe that I can further increase the torque in the lower to mid power range by lengthening the stacks without loosing out in the top end.
It was surprising to read how many owners thought that pods looked better and were easier to clean, so be it, at the expence of performance.
Finally, VM26SS carbs were fitted to the 750,850 and 1000 motors in various states of tune. This demonstrates to me just how good the airflow characteristics of these carbs really is, and was a deciding factor in my decision to increase my motor's capacity to 900cc, while retaining the original induction setup.
The ultimate would appear to be EFI with a well designed and inducted cold airbox.
I would like to here from any members who have results from any controlled tests on airbox vs Pods against a given engine tuning specification.
Cheers
Ian
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