exhaust back pressure

M

motorized kodiak

New Member
Hey everyone, is back pressure important for my engine,? is it bad if i take off the baffle off my exhuast? or can i drill holes in my baffle cap? thanks
 
Back pressure is not needed.
Loud exhaust attracts the wrong kind of attention though.
Many Aussies that have been on this site try their best to stay "under the radar" with their bikes because they are not exactly legal where they live.
 
logic states back pressure on a 2 stroke is a good thing.

but...

i built a megaphone pipe for a race bike that was deafening, annoying, and worked great. :)

wouldn't ride it on the street, though. way too loud and my neighbors, dogs, old people and cops would be after me in packs.
 
my one is a 2 stroke thanks, and it isnt exactly legal where i ride but no one cares hahah, and is it bad, does it weaken the engine over time?
thanks for the replys
 
As long as you have some restriction and don't run it with NO pipe, it won't kill your engine, just your ears.
 
motorized kodiak said:
do you think it will damage it if i take off the baffle only?
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no, not unless it causes a lean run condition, otherwise it wont hurt a thing but maybe your ears, the straight through exhaust run great on my engines when I've done them, back pressure has always been a performance robber on my engines.

Map
 
On the newer engines with the cat muffler, taking the cap off can actually help performance if the engine is already running a tad fat.
 
i took off the baffle and ran it, soooooo much more power though it sounds like a chopper, so i still wanted to have some power, i drilled 2 small holes in the cap and put it back on :), good power and sounds nice now!
 
motorized kodiak said:
i took off the baffle and ran it, soooooo much more power though it sounds like a chopper, so i still wanted to have some power, i drilled 2 small holes in the cap and put it back on :), good power and sounds nice now!
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Good to hear you have it running better and still keeping the sound manageable.

I always figured an engines needs to be able to push the air out just as easily as it can take it in for the power to flow, a small amount of back pressure and I mean really small will help increase bottom end torque many times but just a tad to much and the bottom end, mid range and top end will die off and you will loose all the way around, I have tested several shade tree assembled exhaust on my bike, with baffle, without baffle, long pipe, short pipe, small outlet, large outlet..... and without exception either a expansion exhaust that isnt choked down by a very small outlet or a free flowing straight through exhaust has perfromed best on all my engines.

Map
.wee.
 
What I did with mine was bore out the stock outlet as much as I could, then took a carbide grinder and ground out the flat part of the tip on the inside. I basically made it as flush as I could with the cap.
Helped performance and made it louder.


Got a picture somewhere if you want one.
 
dodge dude94 said:
What I did with mine was bore out the stock outlet as much as I could, then took a carbide grinder and ground out the flat part of the tip on the inside. I basically made it as flush as I could with the cap.
Helped performance and made it louder.


Got a picture somewhere if you want one.
Click to expand...

Sounds good dd94, post that pic up in here if you want and that will possibly help someone else that may be looking to improve their stock exhaust.

Peace, map
reddd
 
When I had the stock muffler set-up on my bike, it would start with about a half revolution of the pedals. Now with the lower restriction exhaust, it may take it 2 to 3 full pedal revolutions before it starts.

With that being said, it certainly runs better now!
 
dodge dude94 said:
I think it could be better, but it works. lol
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If it does what you want and need it to do thats all that matters, several "fancy" exhaust out there that you could have spent good money on that wouldn't work a bit better, as it has been said (Quote)" it's your bike, build it the way you want it ".

I do what I do because thats just how I choose to do it, never been good at being a follower on things, doesn't mean I wont pick up anothers great idea and use it, but, I always just make the best of what I have and if and when I can upgrade something I will but I don't try to keep up with the Joneses for the sake of keeping up or being seen, no shame in a job well done and it sounds to me like thats what you did with your exhaust mod, just ride the snot out of it now and enjoy the added performance.

Map
reddd
 
Back pressure does rob some horsepower, but is there fore a reason.
Yes, eliminating it will give you a speed boost, and create more noise, but will also dramatically decrease the lifespan of your engine.

There are plenty of other ways of keeping proper back pressure while increasing HP, and changing the sound other than cutting up a good working muffler.

If it's a speed and performance increase you're looking for, try a speed carb first for $30.00, change out the CDI wire to a 7mm automotive HP wire, and change the plug accordingly. Then move down to a 38-T, or a 36-T rear sprocket.

I'm on a 36-T with the CDI wire change, and speed carb with a stck muffler unmodified. Right now I am topping out at 43mph.

You can do some safe mods to the baffled muffler such as adding a few holes to the baffle, but drilling out the cap, gutting it, etc. are bad ideas.
 
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Ratt_Bones said:
Back pressure does rob some horsepower, but is there fore a reason.
Yes, eliminating it will give you a speed boost, and create more noise, but will also dramatically decrease the lifespan of your engine.

There are plenty of other ways of keeping proper back pressure while increasing HP, and changing the sound other than cutting up a good working muffler.

If it's a speed and performance increase you're looking for, try a speed carb first for $30.00, change out the CDI wire to a 7mm automotive HP wire, and change the plug accordingly. Then move down to a 38-T, or a 36-T rear sprocket.

I'm on a 36-T with the CDI wire change, and speed carb with a stck muffler unmodified. Right now I am topping out at 43mph.

You can do some safe mods to the baffled muffler such as adding a few holes to the baffle, but drilling out the cap, gutting it, etc. are bad ideas.
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RBones

Explain how opening the muffler up so the engine can breathe betrer is a bad idea?

some of us here have several years experience not only with these engines but many others, and ill tell you one thing you left out or just dont know.

Carb tuning.......

If the carb is rejetted for the extra air flow through the engine a wide open exhaust wont hurt it in any way, as with any engine, extra air flow requires the fuel flow to be increase at the same time so that you dont have a lean run condition which causes the engine to run much higher temps which could potentially fry the engine, but if the engine gets a fuel flow increase that coincides with the added air flow what you get is a better running engine and more power.

The only life shortening effect that will be realized by doing this is that the rpm capability of the engone will increase and that and only that will have potential to shorten its life because now you can run it a little harder.

Not intending to be abrasive with this reply to what you said in your post but a good way to get some abrasive comment pointed your way on here is to speak as though one is an authority on something when the experienced know what you said is not the fact of the matter.

Ever been involve in Drag racing? They run open headers..... and the air/fuel mix is adjusted accordingly. ... I personally dont know of any engine that works any different.

Peace, map
.wee.
 
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