The poor man’s guide to custom tractor exhausts.
Posted July 17, 2011 - 05:33 PM
By Bill The Tractor Man
This here is my over view of how to do any sort of non-OEM or non-stock exhaust. There are things that need to be considered like exhaust velocity/back pressure, weight of exhaust, routing, materials to be used, and how much material you will need. All of these will either make your exhaust epic, or make give you troubles down the road.
Exhaust velocity/back pressure is important. It affects the flow of gasses in and out of the combustion chamber. 2-stroke engines use back pressure to regulate how much gas/air mixture is brought into the combustion chamber and 4-stroke engines use a similar principle but its called exhaust velocity. For example, my 1970 Sears SS12 has an HH120 Tecumseh engine in it. I have a 1-inch diameter pipe coming out of the engine, to a 90-degree fitting which does add some back pressure and slows the exhaust velocity due to cooling. Then to another fitting turning the flow 90degrees; then brought the pipe diameter down to ¾-inch. Any bend or change in size of the pipe/muffler will change the direction of the pressure waves, these pressure waves will cause back pressure. This restricts flow causing the inflow of gas/air mixture to be lessened. The high back pressure and low exhaust velocity caused the engine to die under load. To keep your systems in touch with the proper back pressure and proper exhaust velocity, minimize the length and number of bends, keeping the pipe the same size as the exhaust port on the engine. I try to keep the number of bends down to 2, and total length of pipe down to 12 inches not including the muffler. The muffler inlet should be the same size, or just a little bigger than the exhaust port diameter. Any smaller and you will most likely end up with back pressure issues. Too much back pressure will limit power and can cause damage to valves and valve seats, too little can cause the same effects as too much. Get it just right and you will have a great exhaust system.
The weight of the exhaust system is important. Too heavy and you will crack the exhaust port on your engine or strip out the threads in the exhaust port. You also should consider with any exhaust system to add a brace. The brace should connect to the exhaust and a mid-height location and come down to a point behind the exhaust port, not connecting to the exhaust port on the engine. If you connect the brace to a place on the frame the movement of the engine over time will cause the exhaust port to crack or be damaged beyond repair. The weight of a good exhaust system should not reach more than a pound or two on a single cylinder engine. A cast iron engine can handle more weight than an aluminum engine, but it should still be braced and weigh as little as possible. Aluminum engines need special care when doing a custom exhaust and I suggest using an OEM or stock exhaust instead of custom. Aluminum engines are easily damaged by any force applied to them, and weight on the exhaust port can cause damage. My opinion is that aluminum engines should not use any sort of custom exhaust. Back to cast iron engines, when bracing the exhaust system always have a slight upward pressure to compensate for the weight of it. Always tighten it down and make sure there is absolutely no sway in any direction as it will cause damage. Remember, keep it as light weight as possible and always use a brace and you will have a system that will not damage your engine and will last.
Exhaust routing is also important as these parts get very hot. For best results keep them away from anything that can melt, especially plastic. Over time things that heat and cool will rust, paint will be damaged fairly quickly by this. Another consideration is keeping it as short as possible, with limited turns for the sake of back pressure and exhaust velocity. A simple “L” shaped exhaust system will work in most cases when adding a “stack” which consists of running a pipe out past the hood of the tractor, then up with a 90degree fitting. The muffler gets attached to the fitting or to a small 1” or 2” piece of pipe coming up from the 90degree fitting. The brace should attach to where the muffler attaches to the fitting or somewhere above that point. This simple design keeps the weight down, makes for easy removal if necessary and is most likely to be the cheapest design. Now another way of doing it is to run a pipe out from the engine and down under the frame in a twisted “C” shape. This design is used for routing the exhaust down under the tractor and out the back when clearance issues are presented. I suggest if this is going to be more than 2 feet in length that you bump the pipe size up to be a quarter or a half inch in diameter larger once you’re out from the engine and past your first bend. Once you’re down below the frame it is up to you where to mount the muffler and how you route it but you should have bumped the pipe size up by now. Remember to keep any pipes away from anything that can melt or that you want to look good in the future.
Materials to be used, very simple compared to the other things that need to be included in the overall design. I highly suggest you use black pipe instead of galvanized pipe. Galvanized pipe has a zinc coating that will burn off and when inhaled can be bad for your lungs and also it smells bad until it is burned off. Black pipe is the same thing, just does not have the anti-corrosion coating to protect it from water or corrosive elements. I also believe in my experience that black pipe will last longer than galvanized. This pipe can be picked up at any hardware store, farm supply store, or any store that sells home renovation supplies. I prefer local hardware stores as you can have the pipe cut to the exact length you need and I have found it to be cheaper as well. I highly suggest using pipe lock nuts to stop any pieces of pipe from coming loose. For the muffler I suggest OEM/stock mufflers, or if you want the big tractor/”stack” look to use Stanley or OEM tractor mufflers. I myself use Stanley mufflers due to them being cheaper than contacting IH or John Deere and paying expensive dealer prices. My preferred mufflers from Stanley are the IH-1, AC-1, AC-2, FO-4, but others can be used, depending on your situation. The standard muffler clamp will work fine as long as it fits the muffler and can close the inlet of the muffler down on the fitting or pipe the muffler is to be connected to. Welding can also be done but it is a permanent attachment to the fitting or pipe and often will make removing any part of the exhaust system difficult. For the brace I suggest anything from pipe hanging strap or flat steel bent with holes drilled in it. Remember that every part used in you exhaust system MUST be capable of handling high heat or it will fail!
How much of the materials that are needed are completely dependent upon your design. My simple “L” shape design that I used to put the stack on my 1970 SS12 used one 7-inch long piece of 1-inch diameter pipe, one 90degree fitting (1-inch diameter), one two inch long piece of 1-inch diameter pipe and one Stanley IH-1 muffler. The total set up was under $50 and sounds awesome, along with it comes the cool factor. You can also add a rain cap for a bigger cool factor and to keep unwanted things out of your exhaust system too. Those are typically between $2 and $15 depending on size and where you get it, if I remember correctly mine was $3. The total price is based on your design and how much materials you will need, my most expensive system was only $75 and that was due to needing 5-feet of pipe, 6 fittings, pipe hanging strap, and the muffler with a rain cap. If I remember right $10 of that was getting pieces of pipe cut.
In conclusion everything mentioned is important to make a good looking, nice sounding exhaust system while keeping your engine running right. Every bend adjusts the sound and look if your tractor, with my explanations you can make a great exhaust system on a budget. Thanks for reading!
Example of and "L" shaped exhaust system.
- Bolens 1000, mjodrey, chopperfreak2k1 and 11 others have said thanks
Posted July 17, 2011 - 05:37 PM
Hope this is helpful to any one interested.
- ducky, MH81, tinner and 1 other said thanks
Posted July 17, 2011 - 11:12 PM
Thanks for the information.
Posted July 18, 2011 - 05:42 AM
Posted July 18, 2011 - 06:45 AM
Posted July 18, 2011 - 08:07 AM
- DanO said thank you
Posted July 18, 2011 - 08:11 AM
Posted July 18, 2011 - 09:47 AM
Posted July 18, 2011 - 10:06 AM
Posted July 18, 2011 - 06:12 PM
Hope this is helpful to any one interested.
It was interesting to me Bill. I am setting up a system on my Gardenall JB using stainless
tubing I got from my uncle. He used to work in a fertilizer plant. It will be almost identical to stock. The pipe should polish up like chrome. Too bad I can't find a stainless muffler that size.
Posted December 12, 2012 - 03:14 PM
What do you thinh?
Posted December 28, 2012 - 11:23 AM
BillTheTractorMan, I really enjoyed your article and would like to add some things I've learned while building my garden tractors for pulling.
You are absolutely right about keeping the number of bends to a minimum. When bends are needed, keeping the bend radius larger will help reduce back pressure.
Proper support bracketry is a definite must. Due to the fact that metal expands and shrinks when heated and cooled, brackets need to have enough length and be made of material that will allow them some flexibility, preventing cracks and breakage. 1/8" x 1" flat strap works very well. To give the bracket enough length you may need to move the mounting location lower on the engine block.
Lastly, the exhaust pipe can actually be tuned for greater performance. The length and diameter are very important for maximum scavaging effect. On my 18 horse V-twin Kohler I'm using 1 1/4" 16 gage tubing. The length was determined by making the tube long (start with about 36"), apply a bright colored spray paint (red, orange), start and run the engine at high idle just long enough to find the hot spot (paint darkens or burns) on the tube. Cut the tube at the hot spot for maximum cylinder scavaging. When the pipes are installed the air/fuel mixture will need to be adjusted. Although this was a trial and error process, it was alot fun and the "seat-of-the-pants" difference on the track was very noticeable. By the way my engine is completely stock outside of the exhaust system!
- MH81, Alc, Texas Deere and Horse and 3 others have said thanks
Posted January 03, 2014 - 11:34 PM
Good info & I might add a few things I've discovered in replacing stock exhausts, done mostly because of high OEM cost.
If using threaded fittings & schedule 40 pipe, I drill & tap the fittings for set screws to tighten against the thread to hold it in a desired position.
I've found that the "cool" looking vertical stacks tend to put exhaust gases in your face. Quite anoying on a long mow.
To the guy building a stainless system, motorcycle mufflers. Nice & shiney.