21-06-13, 11:43 AM
The info below was lifted from the very good Suzuki Burgman 650 Race Tech Installation link mentioned in my original post above:
"Step 5 Drilling The Holes Out In The Damping Rods A bit of mixed information on this in the posts. Here's what I found.
Damping Rod ID 0.732" (18.6mm)
Damping Rod Opening Area 0.421" (10.69mm)
Existing Hole(s) 0.236" (6mm)
Existing Hole(s) Opening Area 0.044" (1.12mm)
By my calculations:
The inner diameter of the tube is 0.732" (18.59mm) which has a flow area of 0.421" (10.69mm) 100%
A 0.236" (6mm) hole has a flow area of 0.044" (1.12mm) Multiplied by 4 holes is 0.176" (4.47mm) 41%
Known Choices: A 0.313" (7.95mm) 5/16th hole has a flow area of 0.077" (1.96mm). Multiplied by 6 holes is 0.462" (11.74mm) 109% Exceeding the flow area of the rod.
A 0.354" (9mm ) hole has a flow area of ~0.098" (2.9mm) Multiplied by 4 holes is 0.392" (9.96mm) 93% Slightly restricting the flow through the rod.
A 0.375" (~ 9.5mm) 3/8th hole has a flow area of 0.110" (2.79mm). Multiplied by 4 holes is 0.440" (11.18mm) 105% Exceeding the flow area of the rod.
I used a 0.375" (~ 9.5mm) 3/8th drill and enlarged the 4 existing holes. You'll need to choose what your comfortable with and works best for you.
After talking with Kiwi Dave about the ever so slight restriction using 9mm holes, he received this response from Crown Kiwi Technical Ltd, the ones who recommended the 9mm holes:
"We had never worked out the flow area as such but irrespective the increase in hole size somewhat desrestricts the maximum allowable flow before it will "choke off" when riding over the most abrupt bumps. If the hole size can be increased further without weakening the integrity of the damper rod in that area then go for it. Adding further holes further and further up the damper rod is BAD as it takes away more and more travel where there will be little or no rebound damping."
Now I'm certainly not a fluid dynamics specialist, so to be fair, it's possible that the maximum flow through the emulator body is less than the Damping Rod to begin with and the slight restriction of the 9mm holes is irrelevant. Heck, we might even be able to go smaller. The integrity of the Damping Rod with the larger holes does not seem to be an issue reported by anyone. Luckily for me as mentioned at the start, I'm just compiling and presenting this information, you get to decide what you do yourself."
From that, the answer is not definitive, but IMO does suggest larger holes as low as possible, but without affecting the structural integrity of the damper rods. If you're prepared to take the forks apart a few times, try enlarging the two existing holes to either 8.5mm or 9mm. If this doesn't prove to be enough, drill a further two holes higher up the rod either 7.5mm or 8mm in diameter.
I went with TRX850 fork instructions, which are in a pesky .MHT file & am not sure how to upload it to photobucket or similar for everyone to peruse. Those forks are quite similar to the Fazer's forks bar their length. Nonetheless, it recommends drilling a total a six 8mm holes for TRX damper rods, which I copied in my original Gold Valve mod but reduced their size for my Debrix mod. The two uppermost holes on mine don't *seem* to have affected my damping for the worse.
"Step 5 Drilling The Holes Out In The Damping Rods A bit of mixed information on this in the posts. Here's what I found.
Damping Rod ID 0.732" (18.6mm)
Damping Rod Opening Area 0.421" (10.69mm)
Existing Hole(s) 0.236" (6mm)
Existing Hole(s) Opening Area 0.044" (1.12mm)
By my calculations:
The inner diameter of the tube is 0.732" (18.59mm) which has a flow area of 0.421" (10.69mm) 100%
A 0.236" (6mm) hole has a flow area of 0.044" (1.12mm) Multiplied by 4 holes is 0.176" (4.47mm) 41%
Known Choices: A 0.313" (7.95mm) 5/16th hole has a flow area of 0.077" (1.96mm). Multiplied by 6 holes is 0.462" (11.74mm) 109% Exceeding the flow area of the rod.
A 0.354" (9mm ) hole has a flow area of ~0.098" (2.9mm) Multiplied by 4 holes is 0.392" (9.96mm) 93% Slightly restricting the flow through the rod.
A 0.375" (~ 9.5mm) 3/8th hole has a flow area of 0.110" (2.79mm). Multiplied by 4 holes is 0.440" (11.18mm) 105% Exceeding the flow area of the rod.
I used a 0.375" (~ 9.5mm) 3/8th drill and enlarged the 4 existing holes. You'll need to choose what your comfortable with and works best for you.
After talking with Kiwi Dave about the ever so slight restriction using 9mm holes, he received this response from Crown Kiwi Technical Ltd, the ones who recommended the 9mm holes:
"We had never worked out the flow area as such but irrespective the increase in hole size somewhat desrestricts the maximum allowable flow before it will "choke off" when riding over the most abrupt bumps. If the hole size can be increased further without weakening the integrity of the damper rod in that area then go for it. Adding further holes further and further up the damper rod is BAD as it takes away more and more travel where there will be little or no rebound damping."
Now I'm certainly not a fluid dynamics specialist, so to be fair, it's possible that the maximum flow through the emulator body is less than the Damping Rod to begin with and the slight restriction of the 9mm holes is irrelevant. Heck, we might even be able to go smaller. The integrity of the Damping Rod with the larger holes does not seem to be an issue reported by anyone. Luckily for me as mentioned at the start, I'm just compiling and presenting this information, you get to decide what you do yourself."
From that, the answer is not definitive, but IMO does suggest larger holes as low as possible, but without affecting the structural integrity of the damper rods. If you're prepared to take the forks apart a few times, try enlarging the two existing holes to either 8.5mm or 9mm. If this doesn't prove to be enough, drill a further two holes higher up the rod either 7.5mm or 8mm in diameter.
I went with TRX850 fork instructions, which are in a pesky .MHT file & am not sure how to upload it to photobucket or similar for everyone to peruse. Those forks are quite similar to the Fazer's forks bar their length. Nonetheless, it recommends drilling a total a six 8mm holes for TRX damper rods, which I copied in my original Gold Valve mod but reduced their size for my Debrix mod. The two uppermost holes on mine don't *seem* to have affected my damping for the worse.