Aussie_T100
Banned
I posted this on another bike forum several months ago and received much positive and some negative responses to it however I feel that the information is still relevant so at the risk of once again exposing myself to the naysayers I've decided to post it here.
Last year I spent much time reading various Triumph forums researching performance modifications for my 2008 carbed Bonneville and analyzing the results of modifications that
others had made to their Bonnies. One of the most common modifications is to remove the airbox and fit pod filters and this is usually done using one of several commercially
available airbox removal kits. The price of these kits seemed a little high to me considering that they are principally comprised of a piece of basic metal fabrication to
replace the airbox, a pair of pod filters and a couple of other bits and bobs. The cost of importing one of these kits from the US is not inconsiderable so I was reluctant to
go down that road. Several Bonnie owners had experimented with various modifications to the original airbox to improve airflow and had achieved positive results however there
was much debate over how effective these modifications were in comparison to just ditching the airbox altogether. Nobody had ever done a side by side comparison, either by
using a dyno or a flowbench, that demonstrated just how effective the various airbox mods were in comparison to pod filters.
Thinking about this conundrum I devised a testing method that may go some way at least toward settling this debate. Obviously modifying the airbox, tuning the bike and doing a
dyno run then fitting an airbox removal kit, re-tuning the bike and doing another dyno run is both time consuming and expensive so what was needed was some way of flow testing
both a modified airbox and a set of pods to compare their flow rates. Not having access to a flowbench I set about building a homemade device that would perform this task.
This is the first part of the device, it is basically a plenum chamber made from PVC pipe and fittings that is designed to fit up to an airbox in the following manner.
Attached to this plenum by an 8mm clear plastic hose is a homemade manometer.
The purpose of this manometer is to measure pressure drop over the various filters or devices being tested, that is, it compares the pressure inside the plenum chamber to
atmospheric pressure and registers the difference. The greater the difference in pressures the more restrictive the device being tested is. This restriction to airflow is
measured in millimeters of water lift, the higher the lift the greater the restriction.
Now all we are missing is a good source of vacume or airflow and for that job I chose two of these.
This vacuum is rated at 65 litres per second by the manufacturer and the device can be fitted with two of them so we have a potential flow rate of 130 litres per second. For
comparison a 900cc 4 stroke engine spinning at 9000rpm requires 67.5 litres per second of air at 100% volumetric efficiency so the two vacs provide more than enough airflow for
the purpose of this test.
To maximise flow the filters were removed from the vacuums.
All of this connected together for testing looks like this.
With one vacuum connected and the other vac inlet plugged or like this with both vacs connected.
Before detailing the tests I suppose I should describe the various airbox modifications that have been found by others to increase airflow:-
1. Snorkle removal.
2. Enlargement of the inlet hole, left by removing the snorkle, to the same size or larger than the filter inlet.
3. Removal of the internal baffle from within the airbox.
4. Making a second entry to the airbox on the right side and opening up the corresponding side of the filter element to match. Usually a foam Unifilter is used because it is
easier to get a seal against the newly opened end of the airbox with this type of filter.
5. The fitting of venturi or ram tubes to the carb inlets to replace the original rubber connecting hoses that connect the carbs to the airbox.
These mods apply to Bonneville, T100, Thruxton & Scrambler models as their airboxes are all identical.
The most commonly used pod filters on bikes with the airbox removed are oval K&N's (RC-2890 & RC-2900) and it is against these filters that the airbox mods will be compared.
I then procured the necessary components for testing.
My first test was to get a reading from the bare plenum by itself with no filters or airbox connected, with one vacuum connected the manometer read 6mm of water lift and with
two vacs connected the reading was 34mm of water lift.
Next I fitted the ram tubes to the plenum and recorded 6mm of water lift with one vac and 24mm with two vacs connected so at the higher flow rate the ram tubes had dropped
water lift by 10mm but at the lower flow rate they had no measurable effect.
Next I fitted the K&N pods which had been freshly cleaned and lightly oiled with K&N filter oil. The readings were 16mm with one vac and 56mm with two vacs so obviously the
pods don't restrict flow much at all.
Next I fitted the standard airbox complete with a new Triumph paper filter and the snorkle. The readings were 114mm with one vac and 360mm with two vacs. That's pretty damn
restrictive you have to admit.
Next I removed the snorkle - 46mm with one vac and 164mm with two vacs. That's a major difference just from removing the snorkle.
Then I opened up the primary intake hole in the filter cover like this.
Readings then dropped to 34mm with one vac and 130mm with two vacs.
I then removed the internal baffle from the airbox so now we have both the snorkle and baffle removed.
Readings were 16mm with one vac and 70mm with two vacs.
Last year I spent much time reading various Triumph forums researching performance modifications for my 2008 carbed Bonneville and analyzing the results of modifications that
others had made to their Bonnies. One of the most common modifications is to remove the airbox and fit pod filters and this is usually done using one of several commercially
available airbox removal kits. The price of these kits seemed a little high to me considering that they are principally comprised of a piece of basic metal fabrication to
replace the airbox, a pair of pod filters and a couple of other bits and bobs. The cost of importing one of these kits from the US is not inconsiderable so I was reluctant to
go down that road. Several Bonnie owners had experimented with various modifications to the original airbox to improve airflow and had achieved positive results however there
was much debate over how effective these modifications were in comparison to just ditching the airbox altogether. Nobody had ever done a side by side comparison, either by
using a dyno or a flowbench, that demonstrated just how effective the various airbox mods were in comparison to pod filters.
Thinking about this conundrum I devised a testing method that may go some way at least toward settling this debate. Obviously modifying the airbox, tuning the bike and doing a
dyno run then fitting an airbox removal kit, re-tuning the bike and doing another dyno run is both time consuming and expensive so what was needed was some way of flow testing
both a modified airbox and a set of pods to compare their flow rates. Not having access to a flowbench I set about building a homemade device that would perform this task.
This is the first part of the device, it is basically a plenum chamber made from PVC pipe and fittings that is designed to fit up to an airbox in the following manner.
Attached to this plenum by an 8mm clear plastic hose is a homemade manometer.
The purpose of this manometer is to measure pressure drop over the various filters or devices being tested, that is, it compares the pressure inside the plenum chamber to
atmospheric pressure and registers the difference. The greater the difference in pressures the more restrictive the device being tested is. This restriction to airflow is
measured in millimeters of water lift, the higher the lift the greater the restriction.
Now all we are missing is a good source of vacume or airflow and for that job I chose two of these.
This vacuum is rated at 65 litres per second by the manufacturer and the device can be fitted with two of them so we have a potential flow rate of 130 litres per second. For
comparison a 900cc 4 stroke engine spinning at 9000rpm requires 67.5 litres per second of air at 100% volumetric efficiency so the two vacs provide more than enough airflow for
the purpose of this test.
To maximise flow the filters were removed from the vacuums.
All of this connected together for testing looks like this.
With one vacuum connected and the other vac inlet plugged or like this with both vacs connected.
Before detailing the tests I suppose I should describe the various airbox modifications that have been found by others to increase airflow:-
1. Snorkle removal.
2. Enlargement of the inlet hole, left by removing the snorkle, to the same size or larger than the filter inlet.
3. Removal of the internal baffle from within the airbox.
4. Making a second entry to the airbox on the right side and opening up the corresponding side of the filter element to match. Usually a foam Unifilter is used because it is
easier to get a seal against the newly opened end of the airbox with this type of filter.
5. The fitting of venturi or ram tubes to the carb inlets to replace the original rubber connecting hoses that connect the carbs to the airbox.
These mods apply to Bonneville, T100, Thruxton & Scrambler models as their airboxes are all identical.
The most commonly used pod filters on bikes with the airbox removed are oval K&N's (RC-2890 & RC-2900) and it is against these filters that the airbox mods will be compared.
I then procured the necessary components for testing.
My first test was to get a reading from the bare plenum by itself with no filters or airbox connected, with one vacuum connected the manometer read 6mm of water lift and with
two vacs connected the reading was 34mm of water lift.
Next I fitted the ram tubes to the plenum and recorded 6mm of water lift with one vac and 24mm with two vacs connected so at the higher flow rate the ram tubes had dropped
water lift by 10mm but at the lower flow rate they had no measurable effect.
Next I fitted the K&N pods which had been freshly cleaned and lightly oiled with K&N filter oil. The readings were 16mm with one vac and 56mm with two vacs so obviously the
pods don't restrict flow much at all.
Next I fitted the standard airbox complete with a new Triumph paper filter and the snorkle. The readings were 114mm with one vac and 360mm with two vacs. That's pretty damn
restrictive you have to admit.
Next I removed the snorkle - 46mm with one vac and 164mm with two vacs. That's a major difference just from removing the snorkle.
Then I opened up the primary intake hole in the filter cover like this.
Readings then dropped to 34mm with one vac and 130mm with two vacs.
I then removed the internal baffle from the airbox so now we have both the snorkle and baffle removed.
Readings were 16mm with one vac and 70mm with two vacs.