exhaust

[Tony]

hi I need to know some opinions on what kind of exhaust is best to use on a 2 cycle engine. I dont want to make a tuned pipe. (to much math) And i would prefer something simple. The engine Is a 4hp Tecumseh.

 

[r_chez_08]

ideas

here near the bottom, and the next 2/3 pages

 

[Kaptain Krunch]

R chez, with a two stroke backpressure is very important. A two stroke without the proper backpressure will never run right, those exhaust are great for 4 strokes but with a 2 stroke will be nothing but problems.

Tony, i understand you dont want to make a tuned pipe, but trust me it will be very worth it. you could just buy a used one, probably something from an 60-85cc dirtbike would be good, maybe a 125 tops. I've seen calculators for making tuned pipes that make it very easy, but cant recall where.

 

[Tony]

I think i probably will make a tuned pipe. I heard every tuned pipe will be different so a 100cc honda will not work on a 100cc yahmaha because of timing, exhaust temp, ect. I have the website for the calculator but it just seems very hard to calculate the math involved.

 

[Kaptain Krunch]

It is true that every pipe will be different, but a pipe from a 85cc 2 stroke on your tec. will be much better than a straight pipe. If you need help come back here, im no math wiz but i may be able to help, and im sure others will help too. Also if you could post the link that would be great.

 

[Tony]

The math is fairly easy with the calculator. The problem is measuring exhaust and transfer port angles and the exhaust gas temp. The link to the site is http://www.mh-aerotools.de/airfoils/javapipe_en.htm

 

[Kaptain Krunch]

that does seem complicated but they explain it fairly well, i understand the exhaust port and transfer port angles. And for the exhaust temp just get a decent digital thermometer and hold it in from of the muffler for a few minutes and that should give you a reading that is a little lower that the actual temp (it may cool a few thousands of a degree while in the muffler).

 

[Tony]

i remember seeing a chart somewhere of the exhaust and transfer angles but i cant remember... it might have been on that site or another rc boat website...

 

[Affair_driven]

Simplest and least expensive method is a straight pipe or no pipe at all.
2 stroke utility engines engines are not dependent on back pressure.
If you don't want to go the expense of a expansion chamber, a megaphone is next best thing. It'll be noisy but worth it. Won't hurt anything.
An improperly tuned pipe can work against you.

 

[Kaptain Krunch]

Simplest and least expensive method is a straight pipe or no pipe at all.
2 stroke utility engines engines are not dependent on back pressure.
If you don't want to go the expense of a expansion chamber, a megaphone is next best thing. It'll be noisy but worth it. Won't hurt anything.
An improperly tuned pipe can work against you.

Do you consider weed wackers and chainsaws utility engines? if so they do depend on backpressure.

 

[Tony]

how long should a megaphone be for a 85cc? I just want something to improve preformance well i figure out dimensions on an expansion chamber. Also this is from a snowblower. And i dont want a straigt pipe because the powerband is very small.

 

[Affair_driven]

Trial and error is best bet for a straight pipe. Anything other than stock muffler will be a big improvement.
Read chapter 4:Two-Stroke Performance Tuning.
I have the hard cover book and consider it my Bible.

 

[Tony]

i think trial and error would be pretty hard with a megaphone...and tuned pipe

 

[Tony]

Do you consider weed wackers and chainsaws utility engines? if so they do depend on backpressure.

i think he means multipurpose engines.

 

[Affair_driven]

Tecumseh engines are low performance no matter how you slice them. In my opinion, the math involved to get what you want will give you little bang for the buck.
Is this a reed valve engine or piston ported?

 

[Affair_driven]

Do you consider weed wackers and chainsaws utility engines? if so they do depend on backpressure.

Weedies are junk at best. Professional saws use flame arresters and not mufflers. Home saws use mufflers for obvious reasons.
Take the muffler off any weedie or home saw and see/feel the difference in power.
The same cannot be said for 4 strokes.

 

[Kaptain Krunch]

Well i had a **** weed eater and took the muffler off, never ran right after that, although when it did run right it had good power (clean the carb atleast 3 times and rebuilt it once). I have a Mcculloch 10-10 pro saw (when Mcculloch wasnt crap) from the mid 70's on a MTN bike and your right, it has no exhaust just a very small chamber with a grate over it, and man that things a beast.

 

[Affair_driven]

Removing muffler will cause engine to use more fuel.
It's a good idea to use a carb that is not emissions compliant. Using original emissions carb may be reason why yours are not running right.

 

[Tony]

Well i had a **** weed eater and took the muffler off, never ran right after that, although when it did run right it had good power (clean the carb atleast 3 times and rebuilt it once). I have a Mcculloch 10-10 pro saw (when Mcculloch wasnt crap) from the mid 70's on a MTN bike and your right, it has no exhaust just a very small chamber with a grate over it, and man that things a beast.

I have a Mcculloch 250. The muffler on that thing is a joke. About a 2in. triangle thing with big holes on the end. I used to have a mcculloch 1-43. I took that thing apart and I'm making it into a kart engine. 80cc, I'm deffinitly putting a tuned pipe on that and probly put it on my mini bike or on another one i make.

 

[Kaptain Krunch]

Removing muffler will cause engine to use more fuel.
It's a good idea to use a carb that is not emissions compliant. Using original emissions carb may be reason why yours are not running right.

I'm sure thats it, but the only other carbs i have are 42mm mikunis (got 3 but i think those are a little bit too big ).