Exhaust: Backpressure and all that.

[LAW]

I understand that backpressure stops blow-by with overlapping cam profiles but what's the advantage of a straight through pipe as opposed to just removing the end can?

I notice a huge difference between the street and race cans for the Hyosung. the street can makes the engine soooo much smoother revving and less snatchy on the throttle but I can feel it getting asthmatic higher in the rev range, where the race can makes it much more urgent and free revving up top. I was expecting these cans to be vey different because the guts of them are very different but what's the difference between a straight through can and an open pipe?

[*Oggy*]

Simple. by removing the end can you have in effect "Less Hyosung"... there for much much quicker...

:lmao::lmao::lmao::lmao::lmao:

[wade193]

Simple. by removing the end can you have in effect "Less Hyosung"... there for much much quicker...

:lmao::lmao::lmao::lmao::lmao:

:lmao:

[steveqwerty]

:lmao:
HAHAHA :lmao:

[LAW]

:lmao: that's not bad Oggy.

but I'm thinking of giving the tracky a "bellypan" exhaust and I want to know if it's going to blow up if I disconnect the endcan and sidepipe?

[Cedric]

Simple. by removing the end can you have in effect "Less Hyosung"... there for much much quicker...

:lmao::lmao::lmao::lmao::lmao:

Hahahaha Nice one Oggy, best thing I've read all day :lmao:

[Cedric]

:lmao: that's not bad Oggy.

but I'm thinking of giving the tracky a "bellypan" exhaust and I want to know if it's going to blow up if I disconnect the endcan and sidepipe?

Why would you want to do that anyway? Looks? Without backpressure the engine just goes *bleh* (yes that's the technical term):confused:

[r6destroyer]

when i pulled my straight thru pipe off my zx6 it was real hard to start and would not idle smoothly. Its a mystery to me how a straight thru pipe is different to a cut off pipe.

[*Oggy*]

Exhausts are a bit of a science and the lower the HP of the engine, then I guess the better exhaust pipe is needed. Its like saying why is an Arata better than a Yoshi, then they both have 4 down pipes, a connecting pipe and an end can... Its all down to the pressure waves bouncing back and how they harmonise with the exhaust valves timing...

I believe basically a 4-1 is for top end power and a 4-2-1 is for mid range power (in basic terms)...

short or straight through give no back pressure... fine if its a drag engine where your at max revs all the time with monster HP...but for the track you want back pressure without restricting the flow too much.

[LAW]

Exhausts are a bit of a science and the lower the HP of the engine, then I guess the better exhaust pipe is needed. Its like saying why is an Arata better than a Yoshi, then they both have 4 down pipes, a connecting pipe and an end can... Its all down to the pressure waves bouncing back and how they harmonise with the exhaust valves timing...

I believe basically a 4-1 is for top end power and a 4-2-1 is for mid range power (in basic terms)...

short or straight through give no back pressure... fine if its a drag engine where your at max revs all the time with monster HP...but for the track you want back pressure without restricting the flow too much.

mine's 4-1 stock, I want to take that 1 and instead of going up beside where the pillion would be just cut it off at the fairings.

[*Oggy*]

But you will need to put some sort of end can on it IMHO or you will loose much of your power....

[LAW]

But you will need to put some sort of end can on it IMHO or you will loose much of your power....

what if I just restrict the opening a bit?

[twowheeldan]

what if I just restrict the opening a bit?
farkin dodgy. you WANT to blow it up??

what scientific principal will you be using to determine the amount of restriction??

[Cedric]

Yeah that'll work, definitely :ayyy:

[*Oggy*]

Short answer..... No

Longer answer see link

http://www.cobbtuning.com/info/?ID=3222

[*Oggy*]

Primary Pipe Length -This has a huge effect on the powerband. Generally longer primaries make better low end while shorter lengths move the powerband up in the RPM range. The length affects the powerband by timing when pressure waves reach the cylinder. To put it as simply as possible, the pressure wave comes out of the cylinder and travels down the primary pipe until it hits the collector. There it gets reflected back down the primary pipe as a negative wave. When it hits the cylinder it helps pull more exhaust gasses out of the cylinder and pull more air in to the cylinder. Since power is made by mixing air and fuel and then exploding it, more air and fuel make more power. This effect is known as scavenging and is one of the main goals of a well designed header. Equal length primaries help each exhaust pulse pull the one behind it. This helps create a suction in a sense. Instead of just relying on the pressure of the exhaust stroke of the motor to get the spent gasses out, the suction of the pulse in front of it helps pull it out. One factor some header designers forget when trying to design an equal length header for the Subaru is that the length of the exhaust port is effectively part of the header and needs to be accounted for. Complicating this is the fact that the exhaust ports on the Subaru are not the same lengths. Not accounting for this effects power production.
Collector Type -The collector merges all of the primary pipes together. There are designs ranging from cheap and simple to incredibly complex and costly. If you just joined the pipes in the simplest possible way you would have something that resembled the picture on the right.
The dead space in the middle of all of the pipes would cause a lot of turbulence and hinder flow. Eliminating the dead space is the main advantage of the merge collector. This is a more cost effective way to make the pipes join smoothly. Not quite as elegant as the merge collector, but still very good.
The bad daddy of all collectors is the merge collector. It is from Burns Stainless and is one of the finest collectors you can buy.
Collector Length -The length of the collector also plays a role in determining the powerband of the motor. Generally the longer the collector the more the powerband is shifted up. You also want enough length in the collector to smoothly join the gasses coming from the primary pipes. If the junction is too abrupt they do not interact very well causing turbulence, and again hindering flow. This is also another area of a lot of testing. The volume of the collector has a fairly big effect on the powerband of the motor.
Collector Width -The width of the collector helps control how well the exhaust pulses interact with each other. Make it too big and one pulse cannot help pull the next very well and the gasses can stagnate hurting flow. Make it too small and you hinder flow by causing too much backpressure. Yet another area to test.

[LAW]

ok, so I've been doing a fair bit of research on this and it seems that as long as the pipes aren't too wide (reducing flow velocity) then the lower the backpressure the better. as long as the engine is then tuned to run properly with the new system. which is what I thought.

the engine will indeed burn lean and fry exhaust valves if the carbs aren't fiddled with to fix this.

I'm not going to change the diameter of the stock piping so the overall effect should remain the same but I'll do some experimenting anyway.

this tracky is going to be shit-hot :D

[*Oggy*]

ok, so I've been doing a fair bit of research on this and it seems that as long as the pipes aren't too wide (reducing flow velocity) then the lower the backpressure the better. as long as the engine is then tuned to run properly with the new system. which is what I thought.

the engine will indeed burn lean and fry exhaust valves if the carbs aren't fiddled with to fix this.

I'm not going to change the diameter of the stock piping so the overall effect should remain the same but I'll do some experimenting anyway.

this tracky is going to be shit-hot :D

Always good to experiment with different forms of design..... many don't work, but sometimes you can fall onto a good one.... sometimes the Vanilla world can be very bland .....