Because the heater expands when installed in manifolds with bends, you will need to calculate the correct straight length. Proper length depends on how many bends in the heated path your manifold has and the radius of each bend. Accounting for heater expansion will prevent heated sections from sticking out past the manifold and shortening the heater’s life.
Below, in figure 1, is an example of a manifold with the straight lengths marked in red. The bend groups are marked in green, blue, and orange.
Step 1. Identify and measure the straight lengths.
Using the Figure 1, you will see that there are seven straight lengths. since these do not expand, your equation should look like this:
(60mm x 4) + (25mm x 2) + 20mm = 310mm–the Total Straight Length
Step 2. Identify the bends and measure each radius.
Group length of the bends with the same radius and add them together. For example in Figure 1, you have 10 radii. Two of these are R10. Using the following formula, Length=2 x π x R x C/360, (where R=bend radius, and C=bend degrees), your equation will look like this:
2 x 3.14 x 10mm (R10 bend radius) x (180/360) = 31.4mm (length of one bend)
31.4mm + 31.4mm = 62.8mm (total length of both R10 bends)
Step 3. Adjust bend section measurements for anticipated heater expansion.
To adjust for expansion, you will need to identify the diameter of your manifold groove, (See Figure 2).
Find the column for the radius length you measured in Step 2, and then multiply by the corresponding decimal. If we continue with the example from Step 2 using the two R10 bends and assume your groove diameter is 8mm, the Expansion chart shows your expansion factor multiplier is 0.92. Given this information, this is what your equation will look like:
62.8mm (total length of R10 radii) x 0.92 = 57.78mm (adjusted total length of the R10 group of radii)
Repeat this process for each bend group identified in your manifold.
Step 4. Add straight lengths (from Step 1) with all adjusted bend lengths (from Step 3).
Once you have the adjusted lengths for all the bends, simply add them together. Using the identified bends in figure 1 as an example, your equation will look like this:
310mm (total straight lengths) + 57.776mm (R10) + 97.39mm (R12.5) + 118.1mm (R15) = 583.266 (adjusted heater length)
Step 5. Identify the correct stock part number.
In the example above, the total heater length is 583.266mm. Rounding up the the next size, the correct length is a 600mm heater or part number 80R-0600. Following these instructions, you can be assured you will not have heated sections sticking our of your manifold.
NOTE: IF your total adjusted heater length is less than 10mm from the next size up heater part number, you will need to move up two sizes in length from your calculated value. For example: your adjusted calculated heater length is 648mm, then you should select the 675mm heater instead of the 650mm one.
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