Table 2-2. Fire tube dimensions

Inside diameter (inches) Minimum length (inches) Engine power (hp) Typical engine displacement (cubic inches)
2- 16 5 10
4- 16 15 30
6 16 30 60
7 18 40 80
8 20 50 100
9 22 65 130
10 24 80 160
11 26 100 200
12 28 120 240
13 30 140 280
14 32 160 320
*A fire tube with an inside diameter of less than. 6 in. would create bridging problems with wood chips and blocks. If the engine is rated at or below 15 borsepower, use a 6-in. minimum fire tube diameter and create a throat restriktion in the bottom of the tube corresponding to the diameter entered in the above table.

NOTES: For engines with displacement rated in liters, the conversion factor is 1 liter = 61.02 cubic inches.

The horsepower listed above is the SAE net brake horsepower as measured at the rear of the transmission with standard accessories operating. Since the figures vary when a given engine is installed and used for different purposes, such figures are representative rather than exact. The above horsepower ratings are given at the engine's highest operating speed.