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Bob KellyIII · February 4th, 2022, 01:33 AM

Danno: I'd like to comment on your question of the exhaust flange matter...
in my experience on bikes in general when making an exhaust change I simply think FLOW... if you can reduce any restriction anywhere along that flow you will definitely see an improvement. this holds true for 2 strokes as well as 4 strokes... so when the stock exhaust pipe has a flange that goes into the head and then gets bigger just after it , you definitely have a restriction point !
as you suggested.... but that is a hard area to improve upon your restricted by
several things the exhaust port itself and the pipe diameter and the way the pipe is attached. which is very important !....
In my 2 stroke porting years I found almost every 2 stroke made had a restriction at the exhaust port going into a larger exhaust pipe so grinding away the metal in the port was a no brainer that one modification alone always made a huge difference in the way the bike ran ! if you can some how open up the exhaust port to receive the larger tube I am sure you would see a big improvement ! ....obviously but doing that and having no leaks is not always easy !
....
on a few of the 4 strokers that I ported and polished I even went so far as to taper the tube that went into the head so the flow was easier to pass through
without changing the internal diameter of the exhaust port....even that small of an improvement on the exhaust pipe itself helped alot !
if the exhaust pipe you are using has 30 or so square edge pipes welded into it..... it's junk because you can never improve the flow in that !
i see that mistake being made in hundreds of designs of exhaust pipes being offered for sale on the market today tubes slid inside tubes is fine if they do it the right way but usually they do not ! smaller tube into a bigger tube is fine when the exhaust is going out it.... turn the thing around and it becomes a restriction to the flow. exhaust pipes should only get bigger as they leave the head if they do not they are worse than junk they are a hinderance !
.... I have seen from the 1970's on a campane of screwed up exhaust pipes on Honda motorcycles that is enough to make me scream you take a 175cc engine and it's 1.25" exhaust header pipe and restrict it down to a 5/8" exhaust outlet and brag about how quiet it is ..... but they don't want to talk about how poorly the motor preforms with the new exhaust system on it
.... for some Unknown reason the false idea of back pressure has taken hold on the manufacturers and they are running with it !
I've had it explained to me by salesmen how you have to have back pressure
for the bike to even run ! as other stories just as silly !
....
Bob.....

February 4th, 2022, 01:33 AM	#17
Bob KellyIII Retired motorcycle Mc. Name: Robert Location: Weed, California. Join Date: Jul 2021 Motorcycle(s): 2012 Kawasaki Ninja 250R, 2021 CSC TT250, 1977 Triumph Bonneville 750cc,2001 Honda XR650L. Posts: A lot.	Danno: I'd like to comment on your question of the exhaust flange matter... in my experience on bikes in general when making an exhaust change I simply think FLOW... if you can reduce any restriction anywhere along that flow you will definitely see an improvement. this holds true for 2 strokes as well as 4 strokes... so when the stock exhaust pipe has a flange that goes into the head and then gets bigger just after it , you definitely have a restriction point ! as you suggested.... but that is a hard area to improve upon your restricted by several things the exhaust port itself and the pipe diameter and the way the pipe is attached. which is very important !.... In my 2 stroke porting years I found almost every 2 stroke made had a restriction at the exhaust port going into a larger exhaust pipe so grinding away the metal in the port was a no brainer that one modification alone always made a huge difference in the way the bike ran ! if you can some how open up the exhaust port to receive the larger tube I am sure you would see a big improvement ! ....obviously but doing that and having no leaks is not always easy ! .... on a few of the 4 strokers that I ported and polished I even went so far as to taper the tube that went into the head so the flow was easier to pass through without changing the internal diameter of the exhaust port....even that small of an improvement on the exhaust pipe itself helped alot ! if the exhaust pipe you are using has 30 or so square edge pipes welded into it..... it's junk because you can never improve the flow in that ! i see that mistake being made in hundreds of designs of exhaust pipes being offered for sale on the market today tubes slid inside tubes is fine if they do it the right way but usually they do not ! smaller tube into a bigger tube is fine when the exhaust is going out it.... turn the thing around and it becomes a restriction to the flow. exhaust pipes should only get bigger as they leave the head if they do not they are worse than junk they are a hinderance ! .... I have seen from the 1970's on a campane of screwed up exhaust pipes on Honda motorcycles that is enough to make me scream you take a 175cc engine and it's 1.25" exhaust header pipe and restrict it down to a 5/8" exhaust outlet and brag about how quiet it is ..... but they don't want to talk about how poorly the motor preforms with the new exhaust system on it .... for some Unknown reason the false idea of back pressure has taken hold on the manufacturers and they are running with it ! I've had it explained to me by salesmen how you have to have back pressure for the bike to even run ! as other stories just as silly ! .... Bob..... __________________________________________________ Its too late when you've gone too far !