Exhaust...2.25 or 2.5in and over or under axle??? Options

[Davesceli]

Which is better for a stock 5sfe, 2.25 or 2.5in pipe? I've searched around and its a pretty even split on opinions between them. I've decided on the HKS Carbon TI muffler with the 60mm (just over 2.25 in) inlet, i know its expensive for a stock motor but it looks damn good and sounds sweet, my mind is made up. Carbon fiber is just so sweet!!!!

Now i just gotta decide what size piping, its gonna be catback, and whether or not to go under axle or over. What are the pros and cons of each??? If i go "under axle" will there be any clearance issues since my car is lowered???

i know this question comes up a few times, but im looking for a definative answer...i've searched alot and i still can't come up with a good answer.

[Punisher]

Which is better for a stock 5sfe, 2.25 or 2.5in pipe? I've searched around and its a pretty even split on opinions between them. I've decided on the HKS Carbon TI muffler with the 60mm (just over 2.25 in) inlet, i know its expensive for a stock motor but it looks damn good and sounds sweet, my mind is made up. Carbon fiber is just so sweet!!!!

Now i just gotta decide what size piping, its gonna be catback, and whether or not to go under axle or over. What are the pros and cons of each??? If i go "under axle" will there be any clearance issues since my car is lowered???

i know this question comes up a few times, but im looking for a definative answer...i've searched alot and i still can't come up with a good answer.

I would go 2 1/4"... honestly cat-back doesn't do very much to begin with.. and either under or over axle.. I doubt you will see (much of) a difference.

You should not have any clearance issues with under axle.

Some people here are running 3" under axle.. I don't know what their suspension mods are though.

Personally I'm running 3" turbo-back over axle.. even 3" is too large for probably 75% of 3sgte's. Since you are running a stock motor I would go with probably 2 1/4".. Just because any bends a muffler shop does will end up crushing the pipe down a bit..

This post has been edited by Punisher: Jan 9, 2007 - 10:35 PM

[95CelicaST]

Personally I would run under-axle just because it will eliminate the 180 degree bend over the rear axle. under-axle will flow better. You won't really notice a difference, but still.

[playr158]

under axel = shorter, smoother and thus resulting in....better flow

[Davesceli]

There shouldn't be too much performance loss tho with the over axle right, it is a stock 5s...shouldn't be much gain either.

So the general consenous, of the three of you is 2.25 is the ideal size for my engine???

[Punisher]

ideal would probably be 2" to be honest.. and go over or under the axle you won't notice a difference..

Although.. Our resident Engineer Dan seems to think differently

[hashmaster52]

doesnt over the axle creat some kind of back pressure which is good? thats wut i heard

[playr158]

ideal would probably be 2" to be honest.. and go over or under the axle you won't notice a difference..

Although.. Our resident Engineer Dan seems to think differently

you won't notice it on an ass dyno no. but there is an actual difference...length wise its shorter, and flow its smoother, why? because less bends = faster and less restricted flow...

[Punisher]

ideal would probably be 2" to be honest.. and go over or under the axle you won't notice a difference..

Although.. Our resident Engineer Dan seems to think differently

you won't notice it on an ass dyno no. but there is an actual difference...length wise its shorter, and flow its smoother, why? because less bends = faster and less restricted flow...

Yea.. that 1hp gain on a 5sfe will be really worth the hassle finding a shop to do under-axle exhaust and do it right.

[playr158]

i mean we could always let him to take your advice....
but maybe he'd end up with a backwards wastegate, screwed up ebay turbo and a tranny thats about as successful as george bush......

[Davesceli]

I think im settled on 2.25 and over the axle, IMO it looks cleaner. Plus the way cali roads i don't want to risk goin under axle with all the pot holes on our streets and freeways.

BTW: What is the size of the stock piping for a 5SFE gt???

This post has been edited by Davesceli: Jan 12, 2007 - 7:50 PM

[Punisher]

i mean we could always let him to take your advice....
but maybe he'd end up with a backwards wastegate, screwed up ebay turbo and a tranny thats about as successful as george bush......

First off Aamco screwed up my transmission.. I just today bought another e153 and did the LSD swap myself and reinstalled the trans... how many transmissions have you opened and successfully worked on?

Second.. That whole wastegate setup was done in a lot of haste.. Maybe if we were all super knowledgeable professionals like yourself we wouldn't make silly mistakes..

And I tried the "ebay turbo" for a reason.. To see if it's **** or not.. some people have had more success with it. But now I'm running a gt2871R.. anymore smack talk from mr. I'm going to import a lot of body parts from japan because i'll be really cool then and it's a big secret cuz i'm abercrombie cool?

How is that 1.8T of yours chugging along? I heard it got beat by a 5sfe and you blamed it all on "traction control".

Dave, I think the stock size is 1.75".. 2.25 over axle is a good choice and you won't regret it.

This post has been edited by Punisher: Jan 13, 2007 - 5:19 AM

[Galcobar]

Backpressure is bad. No ifs, ands or buts, or conditional possibilities. Exhaust gas being pushed back into the combustion chamber is not good for combustion, and therefore not good for power production.

The myth of backpressure being good for some engines (naturally aspirated in particular) stems from big pipes being bad for NA engines. By this logic, overeating is bad, therefore starving is good.

The point of an exhaust system is to get the exhaust gas out of the combustion chamber, since burned fuel impedes the burning of a new batch of fuel and air, just as covering ash does not help a fire burn.

A good exhaust system gets the gas out quickly. The most obvious way to increase the ability of an exhaust system to remove gas is to increase its size -- bigger pipes can move more gas, while smaller pipes get filled up and create....backpressure. Unfortunately, this doesn't hold true once you take into account what happens when you give hot gases room to expand.

In expanding, they cool down, and slow down. Now you've got cold, slow-moving gas sitting in the way of the hot gas you're trying to remove from the engine. You lose power from the engine expending energy on pushing the cold gas, which doesn't flow as quickly, and from the now-fouled air-fuel mixture.

Or put it another way. Small pipes create backpressure by lack of capacity. Big pipes create backpressure by slowing down the exhaust flow. Neither way is good.

The trouble is, the volume of gas produced varies depending on how hard an engine is working. At low revs, low volume, at high revs, high volume. Since we don't have expandable exhaust piping yet, we chose a compromise size. With luck and good design, the size is chosen to match the volume/RPM at which the best performance is desired.

Stock designs emphasize and drivability -- basically, how fast the car takes off from a stop. That means they are chosen to be most efficient at a low RPM -- and be as quiet as possible. Enthusiasts emphasize overall speed, and typically want to match their peak power with their most efficient exhaust sizing, so they go larger to accommodate the higher RPM point.

This is why people report "losing" power at the bottom end when going to larger pipes -- the engine is less efficient at lower RPMs because it can't get the exhaust out fast enough, but more efficient at higher RPMs.

And just as bigger displacement means more exhaust volume at any RPM, and therefore bigger pipes, forced induction and N2O produce more exhaust and therefore more volume.

A bend in the piping is never a good thing. It reduces the ability of exhaust to exit your system quickly, and therefore reduces the efficiency of the engine overall. It's equivalent to increasing the length of your exhaust system, about eight feet for a 90-degree bend is the rule of thumb tossed around.

So how large your piping should be is an issue of where you want your engine to be most efficient -- low RPMs, match the stock size. Higher RPMs, go up as far as 2.25" (5SFE really doesn't produce enough gas to warrant 2.5" unless you spend all day at peak). And if you don't have to worry about rough roads ripping parts of your undercarriage off, go under-axle for the smoother flow.

[Punisher]

Backpressure is bad. No ifs, ands or buts, or conditional possibilities. Exhaust gas being pushed back into the combustion chamber is not good for combustion, and therefore not good for power production.

The myth of backpressure being good for some engines (naturally aspirated in particular) stems from big pipes being bad for NA engines. By this logic, overeating is bad, therefore starving is good.

The point of an exhaust system is to get the exhaust gas out of the combustion chamber, since burned fuel impedes the burning of a new batch of fuel and air, just as covering ash does not help a fire burn.

A good exhaust system gets the gas out quickly. The most obvious way to increase the ability of an exhaust system to remove gas is to increase its size -- bigger pipes can move more gas, while smaller pipes get filled up and create....backpressure. Unfortunately, this doesn't hold true once you take into account what happens when you give hot gases room to expand.

In expanding, they cool down, and slow down. Now you've got cold, slow-moving gas sitting in the way of the hot gas you're trying to remove from the engine. You lose power from the engine expending energy on pushing the cold gas, which doesn't flow as quickly, and from the now-fouled air-fuel mixture.

Or put it another way. Small pipes create backpressure by lack of capacity. Big pipes create backpressure by slowing down the exhaust flow. Neither way is good.

The trouble is, the volume of gas produced varies depending on how hard an engine is working. At low revs, low volume, at high revs, high volume. Since we don't have expandable exhaust piping yet, we chose a compromise size. With luck and good design, the size is chosen to match the volume/RPM at which the best performance is desired.

Stock designs emphasize and drivability -- basically, how fast the car takes off from a stop. That means they are chosen to be most efficient at a low RPM -- and be as quiet as possible. Enthusiasts emphasize overall speed, and typically want to match their peak power with their most efficient exhaust sizing, so they go larger to accommodate the higher RPM point.

This is why people report "losing" power at the bottom end when going to larger pipes -- the engine is less efficient at lower RPMs because it can't get the exhaust out fast enough, but more efficient at higher RPMs.

And just as bigger displacement means more exhaust volume at any RPM, and therefore bigger pipes, forced induction and N2O produce more exhaust and therefore more volume.

A bend in the piping is never a good thing. It reduces the ability of exhaust to exit your system quickly, and therefore reduces the efficiency of the engine overall. It's equivalent to increasing the length of your exhaust system, about eight feet for a 90-degree bend is the rule of thumb tossed around.

So how large your piping should be is an issue of where you want your engine to be most efficient -- low RPMs, match the stock size. Higher RPMs, go up as far as 2.25" (5SFE really doesn't produce enough gas to warrant 2.5" unless you spend all day at peak). And if you don't have to worry about rough roads ripping parts of your undercarriage off, go under-axle for the smoother flow.

Nice write up..

You won't notice the difference on a 5sfe with over or under axle.. and under-axle can be more of a PITA. If we were talking about high horsepower... forced induction or something of that nature than I would agree with under axle.

Besides the bends on the 6gc are fairly mild.

[95CelicaRacer]

If you plan on keeping the 5sfe stock, I would not even have a bigger pipe size. Any size that you go up will cause you to lose torque, and if you have those crush bends in the pipe, you will build up turbulence in your exhaust flow. You can eliminate the secondary converter if you want to. That alone will give you a better tune coming out becuase of the less restricting air flow, and you may gain 2-4 Hp.

[95CelicaST]

you may gain 2-4 Hp.

Yeah.. on hopes and dreams he would get 2hp

[Bigmeanbulldog55]

I'll just talk from my experience. I got 2.25 over the axle on my 5sfe, and I'm glad I went with that. You might not notice a big gain unless you get everything else running smoothly. Once I did, the 2.25 was great, I wouldn't have went with any other size. As far as the axle over or under, it all depends on the welder. I've got a guy that does great work, so I had him go over it and it's still really strait and free flowing. Have fun in your 5sfe, it's better than 90% of the ignorant people on this site think they are.

[Negative]

Have fun in your 5sfe, it's better than 90% of the ignorant people on this site think they are.

Amen.
Actually I agree with your entire post but this needed to be said by someone other than me. The 5S is a great motor - and I'll stand by it. If it can move a heavy-a$$ Camry then it can move ours well.
I have had several exhaust setups on my 2 6th Gens and I have to say I like the 2.5" Catback best but I do tend to stay in 3500+ range at the track so you can see the benifit. 2.25" works for your driving habits.

This post has been edited by Negative: Jan 23, 2007 - 11:49 AM