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Discussion Starter · #1 ·
If this had been asked before I apologize (I did a quick search)....

It appears to me that the Converter on the CBR 300 (R or F) is located in the exhaust canister or muffler as some call it. So if that is the case...why purchase a full exhaust system for the CBR 300 as some people do...when you can just purchase a "slip-on " canister? Is the primary pipe very narrow which inhibits exhaust flow thus limits H.P.? If the converter was as with some bikes in the primary ( header) pipe I could see changing out the whole system or at least the header pipe... Thanks Laurie
 

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Aftermarket 'full' exhaust systems have a head pipe that is a larger inside diameter than that of the stock head pipe. So a full system, along with a fuel controller that has the right fuel map and is properly tuned on a dynamometer will net a few more peak ponies, maybe 2 to 3 HP at the rear wheel.

Whereas an aftermarket slip-on exhaust generally won't do much in the way of increasing HP... maybe half a HP from a well designed unit if you're lucky. Most who change out the stock muffler for an aftermarket slip-on, do so to shed some weight (depending on the slip-on, up to 15 lbs. lighter than the stock unit), improve sound, or in the case of the CBR250R, improve the overall appearance of the bike.
 

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Discussion Starter · #3 ·
So I guess that the stock converter must be pretty efficient resulting in only about a 1/2 HP increase when going to a slip on muffler. Not like the "old"days when converters would strangle an engine. BTW Thanks for the reply.
 

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Some of the slip ons will produce up to 1.5HP gain (Ive seen dyno reports). Its the wild 3-4 Hp horsepower gain claims that are unbelievable without adding a fuel controller.

I had the same dilemma trying to decide whether to go full system or just slip on and (without disputing anything Mike has said) I just couldn't see how the header pipe could make that much difference for the extra coin it was gonna cost.

One thing I do know about pipe diameters from experience is that with a smaller diameter pipe you get a higher velocity than with a larger diameter pipe. So while it may not be able to shift the same volumetric capacity as a larger pipe, it will shift it quicker. I'm no guru on this but I'm guessing this is because of the increased frictional surface area of a larger diameter pipe slowing down the movement of gases.
I'm happy to be corrected tho. :D
 

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Discussion Starter · #5 · (Edited)
Yeah.. I think that there is fact in what you are saying. I have in the past looked into dual exhaust for a 60's Muscle car and the exhaust has to be just the correct size and length...so what you are saying comes into play. The pipe has to be a length and width to 'tune' properly.



""I had the same dilemma trying to decide whether to go full system or just slip on and (without disputing anything Mike has said) I just couldn't see how the header pipe could make that much difference for the extra coin it was gonna cost.""

I couldn't agree more..
 

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A larger diameter pipe has LESS frictional surface area than a smaller pipe for the same volume of air flow. The velocity would be reduced purely because the pipes could transit the same volume of air per second with the air travelling at a slower speed. This also has the effect of reducing the pressure at the head of the pipe because it does not need to force the gasses up to the higher velocity.
 

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Check the butt dyno for a good answer... :laugh:
 
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Pah. This stuff is eeeeeasy. Come back to me when you've mastered the art of exhaust tuning on an old-school racing 2-stroke :D
 

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Wouldn't a smaller pipe at the start slowly getting bigger be more effective. the expanding gasses would be accelerated by the slowly increasing pipe size causing a scavenging effect? or would there be a decrease in power due to the lack of back preassure? I have a chance to build my own exhaust and am interested in peoples opinions.
 

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I'm not too good on the science behind stuff as I flunked it at school, so can only speak from practical experiences I've had.
One thing I have found to be true with the CBR's is that you need a certain amount of back pressure to get good low RPM torque and the stock exhaust is best at providing this.
This was brought home to me when I removed the slip on from my 250R and refitted the stock can so I could sell it. First ride I was like wow that's a noticeable improvement in bottom end power, but then the midrange and top end sucked in comparison. It seems you need to have a free flowing system to get rid of all those gasses at high RPM to make good top end power.
 

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Pah. This stuff is eeeeeasy. Come back to me when you've mastered the art of exhaust tuning on an old-school racing 2-stroke :D
If I never see an NSR RC-valve ever again it will be too soon. The margin of error was about 0.2 mm when tuning them.

Edit: Aaaaaaahhh!
 

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Wouldn't a smaller pipe at the start slowly getting bigger be more effective. the expanding gasses would be accelerated by the slowly increasing pipe size causing a scavenging effect? or would there be a decrease in power due to the lack of back preassure? I have a chance to build my own exhaust and am interested in peoples opinions.
What you've described is similar to the configuration of a two stroke expansion chamber. Four stroke exhaust systems use a head pipe that is of a consistent, uniform diameter from one end to the other. And while the I.D. of a four stroke head pipe has an effect on the power curve of the engine, it's not as critical of a tuning factor as what the design of a two stroke expansion chamber is to those engines. In other words, a two stroke motor is far more sensitive to changes to the expansion chamber, even small changes to one cone section can have a big effect on the power characteristics of a given engine.
 
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everything to do with fuel/air flow is a compromise..
it all goes in like a complicated recipe, with the result
being a certain performance potential within gears
and other dynamics such as weight etc..

changing the recipe a little doesnt ruin the cake,
but when you remove ingredients something must be
added to compensate, to keep the end result a cake
- or for us a functional road motorcycle -

honda has designed intake/exhaust flows etc,
which also influence combustion chamber
dynamics and flows, which then effect how
petrol/air mix burns and at what rate and
shape etc, which go to created performance..

so if you remove the entire exhaust system
[incl oxygen sensor] changes at the outflow end
will effect potential values at input, ie, fuel/air..
thus as members not, the need for additional
fuel/air mapping such as a fuel controller..

unless your going for maximum power ie, hp,
not necessarily torque, or real or pulling power,
best to retain the well designed honda system
while replacing the muffler only, which results in
similar performance profiles for a well designed
slip-on, with savings in weight - considerable for
carbon compared to the stock muffler -

for real road performance it boils down to power to weight
ratio.. the less weight to be moved by existing power
the easier thus faster it can be moved..
its only a small difference, 10lb or so, but it can be
noticeable.. changing out the heavy stock on my
cbr250r [mainly for an integrated well designed
muffler to suit the otherwise lovely honda lines]
for a carbon leo vince evoII slip on did the trick
in looking the way it should or would if designers
were not compelled to make the heavy stock
with cat [check out european honda race mufflers,
or moto3 honda mufflers etc for comparison]..

but she also felt, lighter, and in testing seemed
just as vertically stable if not more balanced
than with the heavy stock lump on one side..

so for outright hp full system with controller and dyno etc,
or for [cheaper] cosmetic appearance of your motorcycle
together with some weight loss, a good slip on..

[retaining the stock for possible future resale]
 

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That's a good point about the header pipe on the 300 having the O2 sensor fitted to it . A good reason not to go with a full system unless it has facility for the sensor to be fitted.

On the 250R the sensor was inside the exhaust port, just before exiting into the header pipe.
 

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I'm not too good on the science behind stuff as I flunked it at school, so can only speak from practical experiences I've had.
One thing I have found to be true with the CBR's is that you need a certain amount of back pressure to get good low RPM torque and the stock exhaust is best at providing this.
This was brought home to me when I removed the slip on from my 250R and refitted the stock can so I could sell it. First ride I was like wow that's a noticeable improvement in bottom end power, but then the midrange and top end sucked in comparison. It seems you need to have a free flowing system to get rid of all those gasses at high RPM to make good top end power.
Like my learned friend says, don't arse about with the exhaust just to make it louder as you need to spend on other areas as well to reap the benefit of greater output.
"Complicated stuff this four stroking!" and as for Two stroking best leave that till your on your own.:D;);)
 

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basically, a 4 stroke has 4 strokes to draw in, compress, burn, pushout
petrol/air mix from its combustion chanber, relying on valves,,
moved by camshaft to open and close the valves..

altho there can be scavenging on outflow of burned gasses,
from exhaust flows along the pipe, its not critical due to valves..

2 strokes have only two strokes as they dont have typical valves
or any valves, to close off combustion chamber or open to vent
burned gasses.. instead relying on cetain shumting of backpressure
in exhaust/expansion chamber, to help suck out gasses, the reason for
expanding diameter and shape of 2 stroke exhausts, together with
then reducing diameter, ending in a narrow tail pipe..

so for 4 strokes it comes down to valves thus cam triming
for maximum combustion chamber burn efficiency..

this can be designed variously, including for minimum loss of
unburned petrol/air into the atmosphere, thus pollution which
today has significant effects on an increasing scale..

2 strokes must vent some unburned or partially burned gasses
to atmosphere, typically emitting a blue smoke as normal,
which is why manufacturers have ceased making 2 strokes
for road use, due to difficulties in meeting emissions
restrictions which will continue to increase..

so 2 stroke engine esp exhaust development in racing
has become a science and art itself, and as usual
there is more to it than the basics can cover..

interestingly early engine designers incl racers
were aware of the effects of progressively
widening exhaust diameter towards the end,
resulting in a megaphone shape..

remember my cb450 honda [which flew]
had dunstall megaphone afternmarket exhausts..
 
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