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Discussion Starter · #1 ·
Couldn't find any other very informative post, so just going to ask 2 quick questions:

what size piping for new muffler for a 2007 accent gs,

if i bought my exhaust now, can I still add-on parts for full catback in a few months, or does it all have to bought the same brand and all?
 

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interesting question and has different answers depending on how you want to go about it.

for starters, the trick with doing a performance exhaust is reducing backpressure as much as possible without sacrificing exhaust gas velocity.

keep in mind here that the old idea of 'you need backpressure to maintain torque' is a complete lie

a little background: we're speaking of exhaust valve scavenging here. what happens is during the engine cycle (suck, squeeze, bang, blow) there is a short time in a NA engine (tubro is a different story) after combustion where both the intake and exhaust valves are open. this is called valve overlap. the idea is that as exhaust gasses rush out at high speed a suction is created on the intake valve to help 'charge' the cylinder with fresh air. this is where the misconception of backpressure helping takes place.

for this to happen, the velocity of the exhaust gasses must be kept high. according to physics, if you go from a small pipe to a large pipe with much greater volume, the velcoity of the medium (exhuast gasses) will slow down. this would reduce suction on the intake and therefore reduce your power output.

all that being said, its a fine balance. for engines of this size the consensus seems to be a maximum of 2.25" piping on the exhaust. the muffler may be a little bigger to accommodate the sound deadening material or baffles. again, you don't want to go too big like the honda kids with their rice rockets.

the biggest benefit is getting piping that is mandrel bent. exhaust piping from factory is crush bent and that reduces the internal diameter at the bends. that creates a restriction and ups your backpressure. mandrel bent means there is a tool inserted into the pipe while its bent to prevent crushing on the pipe. it also creates a smooth bend.

now the second part...can you add on parts later? yes and no. depends on how much work you want to do. the new muffler could be welded on. that weld would need to be broken and re-welded later. could cut the pipe further up and weld there if its the same size as the new exhaust piping...

muffler clamps if you want to go a little ghetto. the pipe could be reformed back into shape using a pipe expander tool later. might make welding later easier.

there is no reason to have the same brand exhaust parts. its a pipe. if it works as you want, who cares?

i would recommend doing this all at once if you know that is what you want down the road. easier to do the job once. also corrosion can be an issue with welding later...can't weld rust too well.
 

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interesting question and has different answers depending on how you want to go about it.

for starters, the trick with doing a performance exhaust is reducing backpressure as much as possible without sacrificing exhaust gas velocity.

keep in mind here that the old idea of 'you need backpressure to maintain torque' is a complete lie

a little background: we're speaking of exhaust valve scavenging here. what happens is during the engine cycle (suck, squeeze, bang, blow) there is a short time in a NA engine (tubro is a different story) after combustion where both the intake and exhaust valves are open. this is called valve overlap. the idea is that as exhaust gasses rush out at high speed a suction is created on the intake valve to help 'charge' the cylinder with fresh air. this is where the misconception of backpressure helping takes place.

for this to happen, the velocity of the exhaust gasses must be kept high. according to physics, if you go from a small pipe to a large pipe with much greater volume, the velcoity of the medium (exhuast gasses) will slow down. this would reduce suction on the intake and therefore reduce your power output.

all that being said, its a fine balance. for engines of this size the consensus seems to be a maximum of 2.25" piping on the exhaust. the muffler may be a little bigger to accommodate the sound deadening material or baffles. again, you don't want to go too big like the honda kids with their rice rockets.

the biggest benefit is getting piping that is mandrel bent. exhaust piping from factory is crush bent and that reduces the internal diameter at the bends. that creates a restriction and ups your backpressure. mandrel bent means there is a tool inserted into the pipe while its bent to prevent crushing on the pipe. it also creates a smooth bend.

now the second part...can you add on parts later? yes and no. depends on how much work you want to do. the new muffler could be welded on. that weld would need to be broken and re-welded later. could cut the pipe further up and weld there if its the same size as the new exhaust piping...

muffler clamps if you want to go a little ghetto. the pipe could be reformed back into shape using a pipe expander tool later. might make welding later easier.

there is no reason to have the same brand exhaust parts. its a pipe. if it works as you want, who cares?

i would recommend doing this all at once if you know that is what you want down the road. easier to do the job once. also corrosion can be an issue with welding later...can't weld rust too well.

great info!! theres a catback exhaust system on kfx but how do i know if its mendrel bent or crushed????
also, i like the look of twin exhaust, do you think that could hurt performance???
 

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Discussion Starter · #4 ·
My friend and I didn't have what we needed to put the muffler I bought on, so for now she's straight piped LOL. blatblatblat
 

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great info!! theres a catback exhaust system on kfx but how do i know if its mendrel bent or crushed????
also, i like the look of twin exhaust, do you think that could hurt performance???
if their web site was working right now, i'd love to give you an opinion on that particular catback exhaust...but it isn't :(

sounds more like you just are unsure on what a mandrel bend looks like compared to a crush bend:



here's an example of a mandrel bend. note how the diameter of the pipe is relatively unchanged at the bend:



and now the dirty old typical crush bend:



you may not see the 'ribs' created by the crush bend on all pipes, but it is common. you will, however, see the reduced diameter. here's another example:



mandrel bottom, crush top.

if the bends are not obvious in the pics, you'd have to ask KFX how its been manufactured.

as for the twin exhaust, it could in theory hurt performance. more so at the lower end of the RPM range where gas flow is reduced. at the point where you're transitioning to a dual exhaust you're effectively doubling the cross sectional area available for gas flow which may be too much. there would likely also be an unnecessary restriction at that point where it splits. the split may create turbulence, aka backpressure. the problem is without some more in depth fluid mechanics analysis its difficult to say....and i'm lazy. my old fluid mecahnics text is about 8 ft. away on the bookshelf....lazy.
 
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