3 inches is too big for that motor unless you are running a single exhaust.
You want to keep the exhaust gas velocity high.
Folks who say 'no such thing as backpressure' are off base IMHO. Why not just run without exhaust manifolds or headers at all? Now that would be zero back pressure for sure. Try running a motor like that and see how well it runs.
Big pipes are of the 'more is better' train of thought.
In my bike shop guys would come in all day, wanting fatter and shorter pipes. And then wonder why their bike lost all their punch.
Rant off, sorry 'bout that, but my vote is for a pair of smaller diameter units.
Exactly. You cant run open pipes for one reason, noise.
Throw in emissions, then you require a certain length of pipe. Obviously, if you must run a length of pipe, you would want the size to compliment the engine output by running optimal size for optimal exhaust velocity.
The reason the gusy bike runs like chit is because the carb was tuned for certain engine characteristics which in stock form, goes all the way to the end of the tail pipe. Open up the pipe diameter, youve changed how the engine performs. You couls stop here and make the assumption the engine performs poorly due to the pipe diameter or you could tune the carb and reap the benefits. But as im gonna suggest in my next response, the pipe diameter for a certain length outside the cylinder head, I believe to play a more dramatic roll. I think folks understood this more so years ago on the ATV, as an exhaust upgrade was followed with a recommendation in increased jet size.
Next you will be saying you can run 2" primary tubes on your headers on a 250 C.I. engine, it equals less back
pressure ,right?
MDHD
No. I believe the primary tubes/length on the header or diameter of the exhaust manifold play more of a role as to how the power is made than anything else, I believe this is the critical part. There is a reason why headers length and diameter vary and companies put alot of R&D into such. Exhaust pipe diameter and length is something else all together. Now the exhaust pipe on the other hand, only reason Id imagine size would matter is as stated above, your trying to make emissions, sound components mesh with engine output and all the while compliment the engines performance....which means, maintain exhaust velocity over a given length of pipe/restrictions. Obviously too small would be a restriction, thats just good old common sense.
Just because it's Mainstream doesn't mean it's right!
Doesnt mean its wrong either.
