exhaust question

[W/H JUNKY 43]

Does it hurt the motor any if I just run a short piece of pipe or should it have the muffler for back pressure. I run all Kohler motors as of now.

[Jparkes43 329]

Does it hurt the motor any if I just run a short piece of pipe or should it have the muffler for back pressure. I run all Kohler motors as of now.

Aim to have at least some pipe coming out of the engine, straight piping is ok I want to do it but we have neighbours so we can't

James

[groundhog47 347]

I ran a B&S like that for years, a 90 turned down to deck, ran my tests on K-241 with straight and 45. Tickled me sumpin fierce, but neighbor hood prob didn't think to highly. I still smile and giggle thinkin about that sound, almost made me deaf playin with it. Remember caution of sparks flying when you back off throttle, gasoline don't sympathize with it, poof. Uh hu it happened  ... and the rest I'll leave untold except that it still runs (B&S)

[pacer 3,159]

When I was a kid - we're talking a looong time ago - I didnt know what a pipe was for my Cushman motor scooters, the louder the better! Strangly, I dont think that way anymore, I like QUIET! Where are Nelson mufflers when you need em?

[jrc0528 20]

From what I've gathered from many-a-thread debating this topic is this..

 

You need something to prevent cool air from entering the head and cooling the valves/head unevenly when you shut it off.  Can be a muffler of just a pipe with a bend or two in it.  A downward pipe is best since heat rises, the hot exhaust will try to rise back to the valve and keeps the cool air out.

[Kelly 1,028]

You may need to retune the carb if not running a muffler. 

[Jparkes43 329]

You may need to retune the carb if not running a muffler.

Yer that's true to make up for the free gases

[VinsRJ 721]

I have found on some engines you can't get enough tune out of the carb without a muffler...

[Jparkes43 329]

I have found on some engines you can't get enough tune out of the carb without a muffler...

What do you mean?

James

[Fordiesel69 205]

You should have a bend or a 45 at least to be safe.  I mowed the yard when I was 15 with a long pipe nipple threaded into a K181.  Cops came.  The best part was overchoking it, you could get the pipe to blow smoke rings.  Run times indeed.

[Jparkes43 329]

You should have a bend or a 45 at least to be safe. I mowed the yard when I was 15 with a long pipe nipple threaded into a K181. Cops came. The best part was overchoking it, you could get the pipe to blow smoke rings. Run times indeed.

How do you overchok the engine and what do you mean run times, did it blow smoke rings because it was bad for the engine? Did the cops come because it is illegal

James

Edited May 22, 2014 by Jparkes43

[shorts 182]

The basic design of these flathead engines that make torque at a relatively low speed depend on a specific amount of backpressure in the exhaust system. Don't ask how much it's not usually a published number but I'll guarantee you that when these engines are being developed and run on a dyno for tuning and durability testing their is a specific amount of backpressure required so that they are testing apples to apples and not apples and bananas.

The restriction of the exhaust also helps to control engine temperatures by helping to balance the amount of air fuel mix entering the engine

Edited May 23, 2014 by shorts

[Jparkes43 329]

The basic design of these flathead engines that make torque at a relatively low speed depend on a specific amount of backpressure in the exhaust system. Don't ask how much it's not usually a published number but I'll guarantee you that when these engines are being developed and run on a dyno for tuning and durability testing their is a specific amount of backpressure required so that they are testing apples to apples and not apples and bananas.

The restriction of the exhaust also helps to control engine temperatures by helping to balance the amount of air fuel mix entering the engine

that why you have to tune the carb, but essentially your saying its a bad idea because you loose torque, but surely the added HP will make up for the lost torque because I'm sure torque isn't that important, is it?

 

james 

[KATO 115]

Torque is the amount of work it will do....Horsepower is the speed at which it will do the work

you cant have one without the other. They will differ in rpm range from engine to engine depending on

displacement and or design. some will argue that Torque is more important (im one of them).

whatever your preference ,any increase in HP or decrease in Torque on an engine this small you

WONT notice. If there is any measurable increase in HP its likely at a higher RPM than a stock engine

should be run at. I would keep the muffler

[Jparkes43 329]

Torque is the amount of work it will do....Horsepower is the speed at which it will do the work

you cant have one without the other. They will differ in rpm range from engine to engine depending on

displacement and or design. some will argue that Torque is more important (im one of them).

whatever your preference ,any increase in HP or decrease in Torque on an engine this small you

WONT notice. If there is any measurable increase in HP its likely at a higher RPM than a stock engine

should be run at. I would keep the muffler

Hm, so many different points of views. I run a little higher than they should anyway but if I loose torque I will loose pulling power but HP will make it faster right.

James

[Jparkes43 329]

And also if it's a bad thing why do racing mowers racing tractors and racing cars run straight pipes

James

Torque is the amount of work it will do....Horsepower is the speed at which it will do the work

you cant have one without the other. They will differ in rpm range from engine to engine depending on

displacement and or design. some will argue that Torque is more important (im one of them).

whatever your preference ,any increase in HP or decrease in Torque on an engine this small you

WONT notice. If there is any measurable increase in HP its likely at a higher RPM than a stock engine

should be run at. I would keep the muffler

Would my 535cc single cylinder be suitable for any noticeable difference?

James

[KATO 115]

If your goin racing then that's a whole different can of worms....for a stock everyday use type tractor

stay with the muffler you will have a lot less trouble . Yes a bigger motor will make a difference

if in fact the 535 (what ever it is) is bigger than your Kohler. Assuming it will even fit of course.

[km3h 543]

Sounds like you want to squeeze more power out of that engine. Believe me you will never notice the difference except it will probably be louder and annoy the neighbors. Running them at more than 3600 RPM is a disaster waiting to happen. The manufacturer did their best to design a long lasting efficient engine. As I remember from my motorcycle days, removing the baffles from the muffler caused the chrome pipes to turn blue from overheating and to prevent this you would sometimes need to change the main jet. All you really get out of this is a lot of noise and in your elder years a need for expensive hearing aids. Huh, what did you say?

[Jparkes43 329]

Hmm ok maybe I won't do it. Think you for your time

James

If your goin racing then that's a whole different can of worms....for a stock everyday use type tractor

stay with the muffler you will have a lot less trouble . Yes a bigger motor will make a difference

if in fact the 535 (what ever it is) is bigger than your Kohler. Assuming it will even fit of course.

Sorry for you to be misunderstood but that is the engine that came in from stock a kawasaki fc540v 535cc single cylinder 17hp

James

Edited May 24, 2014 by Jparkes43

[Rick_in_CT 156]

James,

 

I can see you are following this post with great interest.  As I have been following your tractor customization on the Euro forum, I know that as a young man you are interested in how you can get the most power, and possibly noise out of your motor.  This thread has provided some good insight into the engineering of the flow of gasses through the engine, and how the original design considered the back pressure of the exhaust and its effect on fuel mixture and temperature.  What was expressed earlier is that the stock muffler was designed in along with a maximum RPM to provide a long lasting engine.  The designer may forsake achieving the maximum potential output in torque or HP to achieve reliability and to meet noise level regulations and health and safety requirements.

 

Now that being said, if the owners intention is to race or pull, then modifications such as straight pipes, carb. re-tuning, over revving are all going to be needed to win.  Making these modifications and taking the engine away from stock will be done at the risk of early engine failure.  Minor changes can often be done without causing any significant damage.  Here in the states, there are catalogs full of engine and exhaust system parts for automobiles that are engineered to gain horsepower, many of which are accomplished by using parts that are more expensive to produce by the manufacturer than the original automobile company could afford to use and still produce a car at a reasonable cost.  Letting the engine breath a little easier with a more efficient intake manifold or exhaust more freely with some nicely designed headers can provide some small gains that can have little long term impact.

 

Tweaking a tractor engine is a good place to start to learn how all of this mix of air and fuel and friction come together.  As long as you go into it with the understanding that going beyond what the factory had in mind leaves you open to future repairs or damage, no harm done.  People who race or pull live with this every time they take their machines out.  Its called living on the edge.  You can do little things to get little gain, or you can try big things and roll the dice.  It comes down to what you want and how much money and time you have to spend on it.  You are off to a good start by asking questions of the resources available here.  The more information you have, the more efficiently you will spend your money and hopefully have greater rewards for your work.  When you try something new and you do it with your eyes wide open and you know that there might be an associated risk, you will have a better understanding of how to analyze a failure when it occurs.  Being able to analyze the failure becomes part of the game, and you have to figure out how you can try again but do it a little differently to overcome the last problem encountered.

 

There is a lot of fun to be had with modification and experimentation to these tractors, just do it in a safe manner, and try not to bother the neighbors too much!!!

Keep asking questions, it keeps everyone thinking here.

 

Rick   

[Jparkes43 329]

Ok thanks for the reply. I'm meaning more towards not making one so far but maybe in the future when i can upgrade the engine internals.

Thanks you all for the help

James

[shorts 182]

Ok, I looked at your profile and see that you are a young man trying to learn about engines so lets start with some basics and then you can do some more research and then come back and ask more questions and we will try to help you understand what is going on.

 

Fact;  engine horsepower can not be measured, it is a mathematical computation, HP= torque x RPM divided by 5252.      these numbers are then corrected to a temperature, humidity and altitude standard so that all engines are supposedly rated on an apples to apples scale.

 

Fact;  An engine is a pump that moves air, the amount of air is controlled by the displacement of the cylinder and affected by the size and design of the valves and related duct work or manifolds or pipes.  volume of air pumped will be less than 100 percent until you get into sophisticated high rpm high performance engines or pressurized intake systems .

 

Fact;  all o the materials used in an engine have definite thermal properties at which point they become plastic and then liquid, if you exceed these thermal limits parts will fail in  spectacular ways.

 

Now back to the original question about the exhaust pipes, some of the basics are based on  mathematics and pretty finite but when you start pushing the original design limits you cross over into a grey area and their is a point where it starts to look like magic. 

You need some backpressure to keep the exhaust gasses and temps on the valve to prevent air from entering the mix and helping to continue the combustion process and super heating the valve seat and stem resulting the aforementioned thermal display.  Rule of thumb for any exhaust system is to maintain the factory designed port diameter for a sufficient length to make up the volume of the cylinder displacement.  A restricted bend like a pipe elbow will add resistance but a unrestricted mandrel bent will have minimal or no affect on back pressure.

 

I hope this gives you something to think about and someplace to start doing some research on your own.

[Tankman 3,515]

Been followin' this post, I'm exhausted! 

[Mr. 856 170]

LOL

[Callen 64]

A 14 inch pipe straight would work. Heat from the pipe itself will warm the air that comes back into the pipe. Any shorter and you should plug the end to keep heat in it till it cools.