N/A Gen 3 catback discussion

[SSIKness666]

I have used the advanced search and used these key words: +ej25 +na +n/a +exhaust +MY02 +catback +cat-back
I didn't get any good search results.

Firstly I would like to state that by my possible intention for a catback exhaust, I am not being naive, expecting big power gains out of a N/A engine. I also am quite familiar of the frequent indecision of getting an exhaust on a non-turbo car, be it a Liberty or something else. I want a CBE for 3 reasons:

1. functional daily driving (throttle response)
2. performance increase (even if it's negligible at best)
3. exhaust note
4. fuel economy? Not sure with this one.

I recently got a quote for a 2.25" catback setup and other exhaust options for my MY02 RX from Exhaust Technology (SA). The quote information is as follows:

$520 = 2.25" mild steel catback setup with small resonator, MS muffler and stainless tip, perhaps a Y pipe.
$550 = Unequal length headers
$300 = high flow cat

A fellow member who I have been discussing this topic with has owned a N/A Gen 3 with 2.5" catback and has driven a N/A Gen 3 with 2.25" CBE, with the former option being his choice though both are nigh on the same playing field.
I have been doing extensive research into this including multiple cost quotes and browsing various car forums via Google search.

When I told Mark (owner) about a member on this forum having experience both 2.25" and 2.5" systems, he still recommended 2.25" for controlling the noise. I am aware of a certain 'rule of thumb' that there are RECOMMENDED pipe diameters based on the engine size and whether the car has forced induction.

4 cyl = 2.25"
6 cyl = 2.5"
turbo = 3"

If I am off on the above information, please say so. I know it also comes down to the amount of HP your car is producing.

I am aware that one needs to be concerned with backpressure and that too large an exhaust can result in a loss of power rather than a gain.

I was told that by getting the CBE I would get some more torque in the low RPM ranges, however the other day I read on the web that you might lose power in the high RPM ranges. Can anybody verify this?

How can an extra .25" in pipe diameter from stock, provide the increase that motivates so many N/A drivers to getting a CBE in the first place?

I had a very similar topic to this posted up on OZ Liberty forums when they were still up and got almost a unanimous decision that it's a big waste of money to do these exhaust changes to a N/A car, and that if you want a better exhaust note, just to buy a muffler.

I would rather make a well informed decision NOT to go ahead with these plans, than to make an ill-informed decision to go ahead with these plans.

My apologies if this topic has been covered numerous times over (assuming it has) but I did make the effort to use the advanced search.

Thank you for your time reading this and I look forward to reading all of the replies you fellow members have to share.

[Manaz]

I have used the advanced search and used these key words: +ej25 +na +n/a +exhaust +MY02 +catback +cat-back
I didn't get any good search results.

Firstly I would like to state that by my possible intention for a catback exhaust, I am not being naive, expecting big power gains out of a N/A engine. I also am quite familiar of the frequent indecision of getting an exhaust on a non-turbo car, be it a Liberty or something else. I want a CBE for 3 reasons:

1. functional daily driving (throttle response)
2. performance increase (even if it's negligible at best)
3. exhaust note
4. fuel economy? Not sure with this one.

I recently got a quote for a 2.25" catback setup and other exhaust options for my MY02 RX from Exhaust Technology (SA). The quote information is as follows:

$520 = 2.25" mild steel catback setup with small resonator, MS muffler and stainless tip, perhaps a Y pipe.
$550 = Unequal length headers
$300 = high flow cat

That pricing doesn't seem unreasonable. Do you really need a high-flow cat for an NA engine?

A fellow member who I have been discussing this topic with has owned a N/A Gen 3 with 2.5" catback and has driven a N/A Gen 3 with 2.25" CBE, with the former option being his choice though both are nigh on the same playing field.
I have been doing extensive research into this including multiple cost quotes and browsing various car forums via Google search.

When I told Mark (owner) about a member on this forum having experience both 2.25" and 2.5" systems, he still recommended 2.25" for controlling the noise. I am aware of a certain 'rule of thumb' that there are RECOMMENDED pipe diameters based on the engine size and whether the car has forced induction.

4 cyl = 2.25"
6 cyl = 2.5"
turbo = 3"

If I am off on the above information, please say so. I know it also comes down to the amount of HP your car is producing.

Displacement and power are much more relevant than the number of cylinders. Turbo changes things, but not necessarily the way you might expect (are we talking large turbo, small turbo, low pressure turbo, etc).

I am aware that one needs to be concerned with backpressure and that too large an exhaust can result in a loss of power rather than a gain.

At low RPM on an NA engine, yes. Back pressure isn't so much the issue as gas velocity - a given volume of gas will travel quicker down a smaller pipe, and it's the velocity that is helpful in scavenging.

I was told that by getting the CBE I would get some more torque in the low RPM ranges, however the other day I read on the web that you might lose power in the high RPM ranges. Can anybody verify this?

Depends entirely on how it's built. You could have one or the other depending on how the system is put together. Generally a CBE on an NA car won't add much unless the original system was excessively restrictive anyway.

How can an extra .25" in pipe diameter from stock, provide the increase that motivates so many N/A drivers to getting a CBE in the first place?

Remember that the area through which the gas can flow is pi times the radius squared - so relatively small increases in diameter can add up to decent improvements in overall flow capacity.

I had a very similar topic to this posted up on OZ Liberty forums when they were still up and got almost a unanimous decision that it's a big waste of money to do these exhaust changes to a N/A car, and that if you want a better exhaust note, just to buy a muffler.

This is largley true. See my previous point. An exhaust largely helps power production only when it helps the engine breathe better - changing the exhaust when you're limited by the amount of air the engine can breathe in won't do a lot for performance. A rear muffler (or maybe centre resonator and muffler) to suit your requirements will almost certainly change the exhaust note without too much expense.

I would rather make a well informed decision NOT to go ahead with these plans, than to make an ill-informed decision to go ahead with these plans.

My apologies if this topic has been covered numerous times over (assuming it has) but I did make the effort to use the advanced search.

Thank you for your time reading this and I look forward to reading all of the replies you fellow members have to share.

In the end, the first thing you have to decide is "what is my goal for the car?" Let's say you want a 10% boost in power at the wheels. Then you look at where the restrictions are in you getting to this goal, and then weigh up the cost/benefit of each way to deal with the restriction. For ~$400, you can have a tune that will probably get you the gain you want (and better drivability and economy with it) without having to make any physical modifications - the physical mods may help (or give you a higher ceiling, or better drivability). Or maybe you can get there with intake and exhaust mods alone (assuming the engine and ECU can make good use of better breathing capability - though in general, the gains in efficiency with a tune come from running at more efficient AFRs, and your stock ECU won't improve these when you let the engine breathe better - it'll just inject more fuel to meet the AFR it's programmed to deliver).

[Robbks]

-set of 2nd hand WRX headers
-modify up-pipe flange to point backwards instead of upwards
-2" system, mild steel, Redback Cat ($200), Redback hotdog ($80), redback MS Oval Muffler ($200) tips of your choice ($50)

sounds like WRX, breathes fine and not too loud

there may be som fitment issues around the thermostat housing area on earlier models