Is the stock cat back and intake ok for a stage 3 level performance?

[Ceecab705]

Just like the title says, will I be OK leaving the stock cat back and intake while getting stage 3 level performance? I've got the catless downpipe already installed and the intercooler on the way. I really don't want an annoying exhaust system because I feel like that's something I've outgrown. As far as the intake, everything I've read says that the stock system is sufficient.
Thanks in advance for the help, you guys rock!

Edit: my downpipe is catted deporacing

 

[bigmanlittlecar]

Mine was considered a stage 2+ with stock exhaust. 212/306 on dyno. See my sig. And that was with a k&n drop in.

 

[Tuba_jake]

Deadhook has done turbo upgrades and gotten plenty of horsepower out of a stock cat back and a panel filter. I'm sure it well be fine for you. While they may be some gains to be had with upgrading them they are pretty minimal.

Sent from my SAMSUNG-SGH-I747 using Tapatalk

 

[Exitus04]

Just like the title says, will I be OK leaving the stock cat back and intake while getting stage 3 level performance? I've got the catless downpipe already installed and the intercooler on the way. I really don't want an annoying exhaust system because I feel like that's something I've outgrown. As far as the intake, everything I've read says that the stock system is sufficient.
Thanks in advance for the help, you guys rock!

This seems very contradictory... you installed a catless downpipe (which is illegal in IL) for better exhaust flow but you are keeping the stock exhaust? An exhaust system is only as good as its smallest point... So opening up the downpipe just to close it back off again with a smaller diameter cat-back system will gain you nothing... Also, they key to gains power in a turbo car is airflow... you need to let the engine breathe freely and exhaust freely... So, i would say NO... a stage 3 (i would assume the cobb) is not a good idea with just a down pipe and intercooler... Plus you an intercooler upgrade (which includes the piping) you are going to hurt your low end... You are making the volume of the pressure system larger without making the way to fill it larger if that makes sense... Think of it this way, you got a large beachball and you want to fill it with pressure... itll go fast enough with the normal fill hole... but then say you have a LARGER beachball and have the same size fill hole. Whats going to happen? Its going to take longer for the ball to get filled completely with pressure... Now swap the beachball with your turbo, intercooler and piping and the fill hole with your intake.

 

[Ceecab705]

Sorry, it is the catted downpipe. Also, I replaced it because I thought I damaged the OEM with the stratified tune.

 

[Exitus04]

Sorry, it is the catted downpipe.

Thats fine, but just ponder what I said... An upgraded intercooler will only help in gains above 50 mph... so youre gaining high end power at the loss of all your low end... So if you were dragging... you would get off the line very slowly but hope to catch up later down the line.

 

[Goingnowherefast]

This seems very contradictory... you installed a catless downpipe (which is illegal in IL) for better exhaust flow but you are keeping the stock exhaust? An exhaust system is only as good as its smallest point... So opening up the downpipe just to close it back off again with a smaller diameter cat-back system will gain you nothing...

That's not exactly how thermodynamics and fluid dynamics work. There are big gains to be had in removing the stock restrictive cat (in the DP obviously) with a aftermarket catted or Catless DP. In addition, going from a larger diameter to a smaller diameter, increases the velocity of the exiting gases. This is turn changes the pressure differntials throughout the whole system, and long story short leads to gains because of the lower backpressure. Take that with a grain of salt as I did lackluster in thermodynamics, and I've only been a powetrain engineer for about a year.

There are gains to be had. Just for example google the gains that a MK7 GTI gets from upgrading the stock 2.5 inch DP to a 3 inch DP, while keeping the stock 2.5 inch cat-back. Those cars gain about 20 whp just from a downpipe change, nothing else. It's all about pressure differentials.

 

[Exitus04]

That's not exactly how thermodynamics and fluid dynamics work. There are big gains to be had in removing the stock restrictive cat (in the DP obviously) with a aftermarket catted or Catless DP. In addition, going from a larger diameter to a smaller diameter, increases the velocity of the exiting gases. This is turn changes the pressure differntials throughout the whole system, and long story short leads to gains because of the lower backpressure. Take that with a grain of salt as I did lackluster in thermodynamics, and I've only been a powetrain engineer for about a year.

There are gains to be had. Just for example google the gains that a MK7 GTI gets from upgrading the stock 2.5 inch DP to a 3 inch DP, while keeping the stock 2.5 inch cat-back. Those cars gain about 20 whp just from a downpipe change, nothing else. It's all about pressure differentials.

Im not just talking about gains, im also talking about shortening the turbo lag time. But as the OP stated, it is not a catless downpipe. And you also have to remember that not all cars are running a stock 2.5" exhaust so that maybe one of the largest gains youll ever seen in a car from just a downpipe swap. Also, I think you may be backwards on the back pressure statement... When you go from a larger diameter to a smaller one you increase the exhaust pressure which in turn increases backpressure... You want a VERY small amount of back pressure in a turbo engine as it will help turbo lag become less and will not put resistance on the turbine when letting off the gas.

 

[Ceecab705]

I do feel that the turbo spools up faster and the power hits harder even with the stock cat back. My intentions with this car were to go as far as the intercooler, which is considered stage 2. When I thought I killed my OEM cat and replaced it with the deporacing catted DP, I figured I'm pretty close to stage 3 minus the cat back. My biggest issue going to a cat back is the noise.

 

[Exitus04]

Sorry, it is the catted downpipe. Also, I replaced it because I thought I damaged the OEM with the stratified tune.

I hate to say it but if its that god awful Pops and crackles tune my buddy runs on his focus st, it would not surprise me... the only thing that tune does is dump more fuel past the cylinders causing it to detonate when it hits the cat giving you the pops and crackles.

I do feel that the turbo spools up faster and the power hits harder even with the . My intentions with this car were to go as far as the intercooler, which is considered stage 2. When I thought I killed my OEM cat and replaced it with the deporacing catted DP, I figured I'm pretty close to stage 3 minus the cat back. My biggest issue going to a cat back is the noise.

Yeah that is probably true, but if you are just stopping at the intercooler then yeah... im mean youre not going to get the max amount of power out of the parts you have with the cobb stage 3 OTB tune... I would still recommend an intake to free up any restriction on the intake... and you could just have the muffler removed and keep your resonator, that might help with keeping it a little quieter... I have a race dump on my dart and that is literally a 1' section of 3" pipe after the midpipe... and my car is not that loud. When I want it to be quiet you just drive carefully! No need to BWWWAAAAP around constantly!

 

[OffTheWall503]

I was surprised by that for how short of a time he ran it (300ish miles?).

I ran it for a few miles to test it during my work commute and I grew tired of it real quick. With how intense the pops were, I was also afraid of what it may do to my stock exhaust/downpipe and oxygen sensors.

 

[Hijinx]

A cat-back and intake do not provide an appreciable increase in airflow through the engine that can be taken advantage of. Well, unless you ask MAP or Adam... In those cases a cat-back will get you 20whp.


Some Guy On The Internet

 

[Exitus04]

I do feel that the turbo spools up faster and the power hits harder even with the . My intentions with this car were to go as far as the intercooler, which is considered stage 2. When I thought I killed my OEM cat and replaced it with the deporacing catted DP, I figured I'm pretty close to stage 3 minus the cat back. My biggest issue going to a cat back is the noise.

I was surprised by that for how short of a time he ran it (300ish miles?).

I ran it for a few miles to test it during my work commute and I grew tired of it real quick. With how intense the pops were, I was also afraid of what it may do to my stock exhaust/downpipe and oxygen sensors.

Yeah, that tune is really messed up! My buddy CONSTANTLY runs it on his focus... it drives me nuts... cause hes one of those know-nothings that thinks it sounds "So nasty!" I told him... get a high HP tune and it will naturally do that without screwing anything up!

 

[Goingnowherefast]

Im not just talking about gains, im also talking about shortening the turbo lag time. But as the OP stated, it is not a catless downpipe. And you also have to remember that not all cars are running a stock 2.5" exhaust so that maybe one of the largest gains youll ever seen in a car from just a downpipe swap. Also, I think you may be backwards on the back pressure statement... When you go from a larger diameter to a smaller one you increase the exhaust pressure which in turn increases backpressure... You want a VERY small amount of back pressure in a turbo engine as it will help turbo lag become less and will not put resistance on the turbine when letting off the gas.

Firstly, my statement about backpressure was due to the fact that you are removing and/or installing a much less restrictive cat. Also the turbo provides more than enough backpressure for the system to be happy. Do you have a source that states you want a small amount of backpressure in a turbo engine? A small amount of backpressure is beneficial for spool time only, but harmful for power and efficiency. Considering we don't have turbo spool issues on the stock turbo, I'd say that's a trade anyone would take.

 

[Exitus04]

Firstly, my statement about backpressure was due to the fact that you are removing and/or installing a much less restrictive cat. Also the turbo provides more than enough backpressure for the system to be happy. Do you have a source that states you want a small amount of backpressure in a turbo engine?

Hold on one second... the turbo is run BY the exhaust and actually doesnt effect the Back pressure... the turbo is the part that is effected by the back pressure... And the only reason I dont have a source for that claim is due to the fact that it is physically impossible to have an absolute 0 in the back pressure category. Thats why I said, the best is to have a VERY small amount of back pressure but you need to have it in the exhaust manifold not in the exhaust tubing after the turbo turbine. Here is a quote from turbo company on a BMW forum...

"Pressure differential across the turbine is a very good thing to get it moving. This means that post turbine you want very little backpressure, and pre turbine the more backpressure the better for transient turbo rotor performance. But too much pressure preturbine is bad, especially at higher RPMs and power levels as it leads to reversion and incomplete cylinder exhaust gas evacuation which then leads to knock/detonation."

That comment shows that contrary to a N/A vehicle the turbo engines are split into 2 parts, pre-turbine and post-turbine. Pre-turbine meaning the intake and exhaust manifold and Post-turbine meaning from the wastegate back (downpipe, mid-pipe, exhaust piping)

 

[Goingnowherefast]

Hold on one second... the turbo is run BY the exhaust and actually doesnt effect the Back pressure... the turbo is the part that is effected by the back pressure... And the only reason I dont have a source for that claim is due to the fact that it is physically impossible to have an absolute 0 in the back pressure category. Thats why I said, the best is to have a VERY small amount of back pressure but you need to have it in the exhaust manifold not in the exhaust tubing after the turbo turbine. Here is a quote from turbo company on a BMW forum...

"Pressure differential across the turbine is a very good thing to get it moving. This means that post turbine you want very little backpressure, and pre turbine the more backpressure the better for transient turbo rotor performance. But too much pressure preturbine is bad, especially at higher RPMs and power levels as it leads to reversion and incomplete cylinder exhaust gas evacuation which then leads to knock/detonation."

That comment shows that contrary to a N/A vehicle the turbo engines are split into 2 parts, pre-turbine and post-turbine. Pre-turbine meaning the intake and exhaust manifold and Post-turbine meaning from the wastegate back (downpipe, mid-pipe, exhaust piping)

Why are you splitting it into two categories? We are in a thread talking about downpipes and cat-backs now. Nothing we are talking about has to do with pre-turbine since we are making zero changes to the exhaust manifold assuming all else stays the same. The only two things that we are talking about changing (Cat-backs and DP's right now) are both post-turbine so let's stick to that. After the turbo you want as little restriction as possible up to absolute zero (which is an unreachable number in practice).

Your original comment states "exhaust system is only as good as its smallest point... So opening up the downpipe just to close it back off again with a smaller diameter cat-back system will gain you nothing" which is incorrect when moving to a less restrictive downpipe with less cells in the hi-flow catalytic converter because it leads to a decrease in post-turbine back pressure. Which is supported by the quote: "This means that post turbine you want very little backpressure, and pre turbine the more backpressure the better for transient turbo rotor performance." That is the quote you just posted, which is goes directly against your original point.

 

[Exitus04]

Why are you splitting it into two categories? We are in a thread talking about downpipes and cat-backs. Nothing we are talking about has to do with pre-turbine since we are making zero changes to the exhaust manifold. The only two things that we are talking about changing (Cat-backs and DP's right now) are both post-turbine so let's stick to that. After the turbo you want as little restriction as possible up to absolute zero (which is an unreachable number in practice).

Your original comment states "exhaust system is only as good as its smallest point... So opening up the downpipe just to close it back off again with a smaller diameter cat-back system will gain you nothing" which is incorrect when moving to a less restrictive downpipe with less cells in the hi-flow catalytic converter because it leads to a decrease in post-turbine back pressure. Which is supported by the quote: "This means that post turbine you want very little backpressure, and pre turbine the more backpressure the better for transient turbo rotor performance." That is the quote you just posted, which is goes directly against your original point.

I was just showing a comment that I read that helps the community understand what we are talking about.... And if you really want to split hairs, the thread title is " Is the stock cat back and intake ok for a stage 3 level performance?" That being said, pre-turbine is definitely part of this conversation. The fact of the matter is this... YES a hi-flow catted or catless downpipe will HELP to reduce the restriction... but as I said which still stands true the exhaust (from the Turbine back) is only as good as its smallest point... What would be happening is, you would allow the gases to speed up a little bit right out of the turbine and through the down pipe then immediately slow them back down due to the restriction from (for example) the 3" downpipe to the 2.125" cat-back system... PLUS, if you are running a restrictive STOCK intake with an aftermarket hi-flow or catless downpipe you will be effectively choking your system. The car would be getting rid of more exhaust gasses than cold air that its able to take in... Definitely NOT optimal for performance.

 

[Hijinx]

I was just showing a comment that I read that helps the community understand what we are talking about.... And if you really want to split hairs, the thread title is " Is the stock cat back and intake ok for a stage 3 level performance?" That being said, pre-turbine is definitely part of this conversation. The fact of the matter is this... YES a hi-flow catted or catless downpipe will HELP to reduce the restriction... but as I said which still stands true the exhaust (from the Turbine back) is only as good as its smallest point... What would be happening is, you would allow the gases to speed up a little bit right out of the turbine and through the down pipe then immediately slow them back down due to the restriction from (for example) the 3" downpipe to the 2.125" cat-back system... PLUS, if you are running a restrictive STOCK intake with an aftermarket hi-flow or catless downpipe you will be effectively choking your system. The car would be getting rid of more exhaust gasses than cold air that its able to take in... Definitely NOT optimal for performance.

The Fiesta is capable of putting down at least 350whp on the stock intake and cat-back. They're not a huge restriction for us.


Some Guy On The Internet

 

[Goingnowherefast]

I was just showing a comment that I read that helps the community understand what we are talking about.... And if you really want to split hairs, the thread title is " Is the stock cat back and intake ok for a stage 3 level performance?" That being said, pre-turbine is definitely part of this conversation. The fact of the matter is this... YES a hi-flow catted or catless downpipe will HELP to reduce the restriction... but as I said which still stands true the exhaust (from the Turbine back) is only as good as its smallest point... What would be happening is, you would allow the gases to speed up a little bit right out of the turbine and through the down pipe then immediately slow them back down due to the restriction from (for example) the 3" downpipe to the 2.125" cat-back system... PLUS, if you are running a restrictive STOCK intake with an aftermarket hi-flow or catless downpipe you will be effectively choking your system. The car would be getting rid of more exhaust gasses than cold air that its able to take in... Definitely NOT optimal for performance.

Okay let's unpack this:

Assumption 1: "PLUS, if you are running a restrictive STOCK intake with an aftermarket hi-flow or catless downpipe you will be effectively choking your system."

Reality: You are assuming the intake has a 1/1 relationship with how they are designed in what they can flow but the reality is this: There's multiple cars as stated above in Hinjx comment that are running 300+ HP levels with the stock intake box. The intake box flows considerably more than people think and the results show. That is why we see 350+ HP number with stock Intake + Catback setups but we do NOT see those numbers with the stock DP.

Assumption 2: "the exhaust (from the Turbine back) is only as good as its smallest point..."

Reality: This is completely neglecting the reality that is when you move to a Catless or Hi-flow cat setup, you will see a net decrease in backpressure. Not to be confused with saying that the stock cat-back is not the bigger restriction, but the net backpressure will decrease from a Hi-flow cat/catless setup with all else being equal. This is not including the laminar flow gained from most of the aftermarket DP's with smoother surfaces and less hard-turns.

Assumption 3: "The car would be getting rid of more exhaust gasses than cold air that its able to take in... Definitely NOT optimal for performance. "

Answer: Again the reality is while it's not 100% optimal it still provides real world gains. The total intake/exhaust system does not have to be 100% balanced to be working better than factory with regards to flow numbers.

 

[Exitus04]

The Fiesta is capable of putting down at least 350whp on the stock intake and cat-back. They're not a huge restriction for us.


Some Guy On The Internet

That seems strange... when my buddy took out his stock intake and i was looking it over, it definitely looked very restrictive... But maybe thats just me after being used to short-ram intakes on everything that ive worked on LOL. As for the exhaust, that really doesnt surprise me as the FiST is a "sport" model!

Okay let's unpack this:

Assumption 1: "PLUS, if you are running a restrictive STOCK intake with an aftermarket hi-flow or catless downpipe you will be effectively choking your system."

Reality: You are assuming the intake has a 1/1 relationship with how they are designed in what they can flow but the reality is this: There's multiple cars as stated above in Hinjx comment that are running 300+ HP levels with the stock intake box. The intake box flows considerably more than people think and the results show. That is why we see 350+ HP number with stock Intake + Catback setups but we do NOT see those numbers with the stock DP.

Assumption 2: "the exhaust (from the Turbine back) is only as good as its smallest point..."

Reality: This is completely neglecting the reality that is when you move to a Catless or Hi-flow cat setup, you will see a net decrease in backpressure. Not to be confused with saying that the stock cat-back is not the bigger restriction, but the net backpressure will decrease from a Hi-flow cat/catless setup with all else being equal. This is not including the laminar flow gained from most of the aftermarket DP's with smoother surfaces and less hard-turns.

Assumption 3: "The car would be getting rid of more exhaust gasses than cold air that its able to take in... Definitely NOT optimal for performance. "

Answer: Again the reality is while it's not 100% optimal it still provides real world gains. The total intake/exhaust system does not have to be 100% balanced to be working better than factory with regards to flow numbers.

#1, Stock intakes normally are restrictive, that is not saying that the FiST does NOT have a well flowing stock intake....

#2, Yes, you are going to gain a better net flow but why not do everything together then? By a full turbo back system and gain the most instead of buying just a hi-flow cat or catless downpipe and gaining some?

#3 Yes, It provides some gains... but again when you are building to get the most performance for the mods and money you pay why would you NOT want as close to 100% optimal performance?

I live by a few mottos when it come to cars and building them... I think if you know this then youll understand my mentality better...

1. You build for the future... Set a goal (HP/TQ #) and build your car to exceed that point, more times than not people get to their goal and still want more if possible! That means making sure that dumb things like a stock intake or exhaust will not be your limiting factors when building your car up!

2. You get what you pay for... Building cars is an expensive hobby and everyone who does it knows that. If youre not willing to spend the money youre not going to have a good time. Also, that goes 2 ways cause if you buy cheap parts they are more often than not going to break down easier and sooner than quality parts!

3. Built, not Bought... I have zero respect for people that know absolutely nothing about how their car works or that do no work on it themselves but want to talk a big game. Anyone can drop $50k and buy a fast car, but it takes knowledge, patience, and skill to build a car to be fast. Also, that is NOT a poke at anyone here! I do not personally know any of you so I dont know if you turn wrenches yourself or not.