does removing the catalytic converter add HP? Options

[nate95]

Hey i was just wondering if i were to remove the catalytic converter if it would add any horse power? or what about getting a "Y" pipe before the cat. so i can still have the cat. but have it go straight out when i want to race?

[hitcachi]

No it doesn't. Sorry. You can argue better flow all you want, but......no it doesn't.

[malpaso]

Sorry for question from someone with low english... Is "catalytic converter" same as "calorifier" (direct translation of "katalizator")

[BLADDER_MASTER]

No it doesn't. Sorry. You can argue better flow all you want, but......no it doesn't.

So turbo cars don't gain HP when they removed their cats?

[94wrc]

Wrong,

Or certainly wrong on JDM cars, when you remove the cat you should see around a 3-5 BHP increase due to the exhaust gases exiting the system quicker, this has been proven on rolling roads. I removed mine on my GT-4 and there is a huge difference, the turbo spools up a lot quicker and it now spits flames out of the exhaust

Nathan

[alexjb]

Wrong,

Or certainly wrong on JDM cars, when you remove the cat you should see around a 3-5 BHP increase due to the exhaust gases exiting the system quicker, this has been proven on rolling roads. I removed mine on my GT-4 and there is a huge difference, the turbo spools up a lot quicker and it now spits flames out of the exhaust

Nathan

True, get rid of the gas quicker works for cars that are highly tuned and especialy blown.

however it sounds like the 5Sengine in the base model over there is neither, so may not make any difference to that motor.

[94wrc]

Good point, it may not help the N/A engines as they do need back pressure however turbo cars would run best with no exhaust or a tiny one as they need to get rid of gasses as quick as possible.

I stand corrected (maybe)

Nathan

[alexjb]

Good point, it may not help the N/A engines as they do need back pressure however turbo cars would run best with no exhaust or a tiny one as they need to get rid of gasses as quick as possible.

I stand corrected (maybe)

Nathan

Zactly,
we were both right

[malpaso]

Fine fellas, I'll try again...

my exhaust has four parts:



first... right names for right parts

Is in english right:

1 - horns
2 - calorifier
3 - silencer
4 - muffler



and second... if I remove part number 2, I will NOT have any HP addition really?

[bindertch]

Fine fellas, I'll try again...

my exhaust has four parts:



first... right names for right parts

Is in english right:

1 - horns
2 - calorifier
3 - silencer
4 - muffler



and second... if I remove part number 2, I will NOT have any HP addition really?

1 - horns - or flex pipe
2 - calorifier - actualy this is the catalitic converter.
3 - silencer
4 - muffler

Actually there is two cats' on the american 7AFE. The first is mounter off of the manifold right below it and the second as malpaos's picture shows is after the flex pipe. I have noticed significant gains from removing both but replacing the second with a hi-flow one and addind a hi-flow muffler, header and CAI.

[Insanity-74]

Come on guys...get yer brains into gear ...of course removing the cat will gain you BHP...be it in an N/A car or a turbo.....whats the first law of modding????? better breathing for the car, be it inlet or exhaust...the CAT restricts the exhaust gas escaping from the engine, remove ANY restriction to flow and the car is going to breath easyer.....and get more BHP (to get more air in, you have to get the spent air out etc)...in stock form there will be only a slight difference on a N/A car....turbos get much bigger benifits. Can be around 15-20BHP released from getting rid of the CAT (I got 16BHP increase from removing the CAT from the Faff...but I have seen the same type of car gain 30BHP) ...as soon as the mods start to appear, then the benifits of removing the CAT will increase Exponentially.
Also as CATs get old they start to block up with crap etc....do yourself a favour get rid of the CAT...but beware at MOT time.(Brits only)

This post has been edited by Insanity-74: Mar 28, 2006 - 6:46 AM

[94wrc]

Ahh you frequent over here too Nial, I did think that getting rid of the cat would give increases but didn't want to start an arguement

Nathan

[Bitter]

Actually there is two cats' on the american 7AFE. The first is mounter off of the manifold right below it and the second as malpaos's picture shows is after the flex pipe. I have noticed significant gains from removing both but replacing the second with a hi-flow one and addind a hi-flow muffler, header and CAI.

that depends on the emissions spec, fed spec has one and no egr i think, after 95/96 the cali spec would definatly have 2. my fed spec has ONE cat, no EGR, and NO post Cat O2 sensor.

[crismillencolin]

Got a de-cat pipe put on last thurs and i can safely say seems to make no difference at all - sounds good but thas it . (disapointed)

[94wrc]

You are the only person I know who has said it makes no difference, mind you I only know people with turbo's that have changed them and on turbo's it makes a huuuuuuuge difference. It should increase your top end though.

Nathan

[crismillencolin]

You are the only person I know who has said it makes no difference, mind you I only know people with turbo's that have changed them and on turbo's it makes a huuuuuuuge difference. It should increase your top end though.

Nathan

really . damnit , maybe its just me.....the rest of the exhaust is becoming SS on friday - maybe then it'll be a bit better . My top end is 112 anyway need that restrictor off asap

[Insanity-74]

Another good thing I tried for the first time at the weekend (slight topic change here) Toyota`s own brand injector cleaner. (as recommended and supplied by Ian Smith - anyone who knows him ... Ian is the GT-four Guru) Well it worked wonders...try some of that if performance is ****e, but it must be Toyotas own brand, I have tried others with nowhere near as good results as this stuff.

Also, try cleaning the filters, plugs dizzy cap etc

Ahh you frequent over here too Nial, I did think that getting rid of the cat would give increases but didn't want to start an arguement

Nathan

You know me mate.....always one to wade in....dont mind an argument and I think I should know enough by now to back up what I`m saying

[Vacchus]

This was the first thing that i did to my car, and i can tell you for sure that it is the easyest way to get +5 to 10 hp without any money.. You will only need to make a tube to replace it or you can make a fake catalytic converter for the case that the police look under your car. That worked for me!!
The only problem is with the inspection of gas, but you can always put the cat back in order to pass the test, and remove it again. If you are unlucky enough and when they stop you, the have a portable gas meter, then you have a big problem... So the best you can do is make a fake converter and claim that it propably dont work.. Maybe you will leave without a penalty!!

[94wrc]

Ahh the pesky restrictor, get rid, I did and I have seen 150 in mine with about 1000 revs to go on a private airfield of course you should be able to see the high side of 130 the worst thing on the stock system is the flexi, it is so restrictive, once you get a full system on there you will see a difference.

Vacchus: luckily in the UK we dont normally get the police looking under the car for the cat (they don't like getting their hands dirty ) although they sometimes do roadside emissions tests which is when you can get in trouble

Nathan

[nate95]

how hard is it to remove?what do i have to do to take it off? im not worried about getting pulled over for it, is it worth doing?

[Yellow94GT]

how hard is it to remove?what do i have to do to take it off? im not worried about getting pulled over for it, is it worth doing?

I was wondering about naturally aspirated engines and removing the catalytic converter.

I thought that naturally aspirated engines with catalytic converters were typically enginered with cams that promote delayed exhaust valve timing. Since the converter is restrictive the exhaust valves remain longer and allow spent exhaust gases to pass through the catalytic converter before closing.

Without other modifications removing converters on a naturally aspirated engines would offer little or no benefit or unless other modifications were made. Adjustable timing gears that would allow the valves to close sooner and keep the exhaust gasses in the cylinder longer on the exhaust cycle and promote better power.

I thought that in some cases with some engines when the converters were removed on non turbo engines there was a loss of power at low rpm. Since the factory cam timing was designed to flow through the converter the intake valve may be opening before the exhaust is completely closed. This is not a problem with the factory cams and catalytic converter since the gasses haven't passed entirely though the converter. With converter removed the exhaust gasses may leave a vacume and intake cycle pressure may be flowing out the exhaust before the factory cam timing cycle is complete.

I thought this was why adjustable cam gears were used to account for the change in low rpm cycle pressure losses when using pipes without the "restrictive catalytic converter".

I found when I removed my catalytic converter on my former car (Not my Celica) the power was down through most of the lower rpm.

Just my experience and my opinion,
Yellow94GT

Just what






To take advantage of
By removing the converter with the factory cam timing some engine may actually have the intake and exhaust valves would be open

[hitcachi]

No it doesn't. Sorry. You can argue better flow all you want, but......no it doesn't.

So turbo cars don't gain HP when they removed their cats?

Wrong,

Or certainly wrong on JDM cars, when you remove the cat you should see around a 3-5 BHP increase due to the exhaust gases exiting the system quicker, this has been proven on rolling roads. I removed mine on my GT-4 and there is a huge difference, the turbo spools up a lot quicker and it now spits flames out of the exhaust

Nathan

Come on guys...get yer brains into gear ...of course removing the cat will gain you BHP...be it in an N/A car or a turbo.....whats the first law of modding????? better breathing for the car, be it inlet or exhaust...the CAT restricts the exhaust gas escaping from the engine, remove ANY restriction to flow and the car is going to breath easyer.....and get more BHP (to get more air in, you have to get the spent air out etc)...in stock form there will be only a slight difference on a N/A car....turbos get much bigger benifits. Can be around 15-20BHP released from getting rid of the CAT (I got 16BHP increase from removing the CAT from the Faff...but I have seen the same type of car gain 30BHP) ...as soon as the mods start to appear, then the benifits of removing the CAT will increase Exponentially.
Also as CATs get old they start to block up with crap etc....do yourself a favour get rid of the CAT...but beware at MOT time.(Brits only)

Haha, you guys crack me up. Yes having no cat will increase hp ON A TURBO CHARGED CAR AND/OR HIGHER HP GT-FOUR. This man happens to have a Toyota Celica ST, making a whooping little over 100 hp. Hmmmmm, whats going to happen when that cat is removed. The environment is going to get more polluted and his car might get a little louder, but it wont get faster. It will just become illegal and unable to pass emissions. If you were a turbo charged car or a car that was putting out a considerable amount of HP then, YES it would help. Did you know "GASP" that they also make performance cat's that allow for excelent flow while still allowing the legality of your automobile?

[malpaso]

And what about oxygen sensors (lambda probes). I think that exhaust valve timing is modified by lambdas...

[Bitter]

And what about oxygen sensors (lambda probes). I think that exhaust valve timing is modified by lambdas...

theres no valve timing going on with your motor. (assuming its the stock 7afe)

valve timing is controlled by rpm, oil pressure, and on some engines the ecu is what opens or closes the solenoids that that move the oil which moves the cam(s).

as for what critera move the cams when its an ecu descision its probably RPM and Throttle position, i doubt that oxygen sensors have any input in that.

This post has been edited by Bitter: Mar 30, 2006 - 1:46 AM

[malpaso]

And what about oxygen sensors (lambda probes). I think that exhaust valve timing is modified by lambdas...

theres no valve timing going on with your motor. (assuming its the stock 7afe)

valve timing is controlled by rpm, oil pressure, and on some engines the ecu is what opens or closes the solenoids that that move the oil which moves the cam(s).

as for what critera move the cams when its an ecu descision its probably RPM and Throttle position, i doubt that oxygen sensors have any input in that.

I thought that oxygen sensors controls overrich mixture so combustion process also and finaly (somehow ) timing...

thanks for explanation

This post has been edited by malpaso: Mar 30, 2006 - 2:25 AM

[Bitter]

ignition timing is different than valve timing.

[malpaso]

ignition timing is different than valve timing.

My world is bigger now... again Thank you!

This post has been edited by malpaso: Mar 30, 2006 - 2:26 AM

[Bitter]

ignition timing is different than valve timing.

My world is bigger now... again Thank you!

http://www.germanmotorcars.com/Detonation.htm

http://www.centuryperformance.com/timing.asp

http://www.compcams.com/Technical/TimingTutorial/ (i normally dislike seller information articles but this one seems OK)


now read and learn and be better for it

[Niskyspy]

For about 6 years I though that removing the converter will give a gain in HP. But about a month ago I had a talk with a muffler shop mechanic who was doing exhausts for 30 years. He told me that removing the cat wont give any gain in HP because they are all designed for up to 500HP. When I asked him why do companys make high-flow cats he told me its just a $$$ thing (cuz people think that it will give them more HP). Since my Toyota has 2 cat's and one of them was leaking the muffler shop removed one of my cats and guess what I didn't feel any difference in my car well exept that the exhaust leak sound went away

[kenjamatic]

i don't know if removing your cat or putting on hi flo cat will gain hp(in an n/a motor) but i definitely feel a difference in power(in my 5sfe) in the mid-range rpms after my hi flo cat was installed with 2.25" exhaust piping...i just got my headers in a couple days ago and am going to install it later on today(if not then sometime this week)

[Batman722]

ok
first...

most US Celicas have 2 cats (primary and secondary)- 94-95 STs have 2, 96-97 STs have one - the secondary, 94-99 GTs (94-95 cali) have 2, the 94-95 fed (non-cali) have just one, the primary.

removing one or both of your cats will not "add" hp but will "free up" hp from your engine. Removing the secondary cat won't do much but removing the primary cat will give your engine a better (less restrive) air flow - removing both will be less restrictive obviously. How much you ask ? a free flowing exhaust will free up about 5-8 at maximum. That doesn't seem like much but these are economy engines, not performance engines, we are talking about here...

removing these will increse and decrease a few things

increase
flow freeing up some hp with better responce throughout the RPM band
the amount of harmful emissions emitted

decrease
gas mileage

the

[TheStreetzKing]

i punched out my cat when i did my exhaust.. made no difference at all

[j0e_p3t]

ok
first...

most US Celicas have 2 cats (primary and secondary)- 94-95 STs have 2, 96-97 STs have one - the secondary, 94-99 GTs (94-95 cali) have 2, the 94-95 fed (non-cali) have just one, the primary.

removing one or both of your cats will not "add" hp but will "free up" hp from your engine. Removing the secondary cat won't do much but removing the primary cat will give your engine a better (less restrive) air flow - removing both will be less restrictive obviously. How much you ask ? a free flowing exhaust will free up about 5-8 at maximum. That doesn't seem like much but these are economy engines, not performance engines, we are talking about here...

removing these will increse and decrease a few things

increase
flow freeing up some hp with better responce throughout the RPM band
the amount of harmful emissions emitted

decrease
gas mileage

the

so if i do my exhaust... i should remove my primary and keep my secondary? would my car still be legal if i keep at least one of my cats on there?

This post has been edited by j0e_p3t: Apr 9, 2006 - 3:39 PM

[TheStreetzKing]

all i did was punch out my secondary, i mean obviously its more air flow but u wont feel a difference

[Batman722]

so if i do my exhaust... i should remove my primary and keep my secondary? would my car still be legal if i keep at least one of my cats on there?

since you live in Cali the emission tests are pretty tough out there so removing your primary would probably make you fail. You might pass if you remove your secondary cat, but I don't know.

IMO If you get an exhaust done, get your car inspected right before, so your sticker would be good for a year and when it is ready to get inspected again, put your old system back on. Then just swap again after.

[j0e_p3t]

so if i do my exhaust... i should remove my primary and keep my secondary? would my car still be legal if i keep at least one of my cats on there?

since you live in Cali the emission tests are pretty tough out there so removing your primary would probably make you fail. You might pass if you remove your secondary cat, but I don't know.

IMO If you get an exhaust done, get your car inspected right before, so your sticker would be good for a year and when it is ready to get inspected again, put your old system back on. Then just swap again after.

tell me about it... my car would have so much more potential if cali laws weren't so anal. plus it requires a lot of money. but other than that, the gains of an exhaust aren't worth the hassle and what-not. the only real reason i want a new exhaust is for the sound. but then again, that might be a lil ricey on my slow car.

[Batman722]

I have a 95 ST just like you, I have a header (corolla one) and my sticker is up at the end of the month. I have my stock manifold and b pipe that I am going to put back on for my inspection, then after it passes, swap the header back on. It really isn't hard to do and the header will make your ST more fun to drive.

[Bitter]

how much of a difference did the header make in terms of performance? do you have a stock exhaust?

[FAQdaWorld]

On a NA 7afe, removing the cat will result in a couple (not 5- 10, more like 2 - 3 ) of gained hp, but will also likely result in a slight loss of torque. Naturally aspirated engines are designed to run with backpressure so removing that backpressure really doesnt help you all that much.

[kenjamatic]

little off topic...i just got my headers on last night ...i don't really feel any difference(except the ricey buzz) at regular(low rpm) driving but when i floor it to mid rpm it seems to not have much torque but there is a pull...then again i won't really know if there's hp's added unless i go the dyno...

[Negative]

On a NA 7afe, removing the cat will result in a couple (not 5- 10, more like 2 - 3 ) of gained hp, but will also likely result in a slight loss of torque. Naturally aspirated engines are designed to run with backpressure so removing that backpressure really doesnt help you all that much.

I agree from my experience with actually doing this. No Dyno numbers though.

little off topic...i just got my headers on last night ...i don't really feel any difference(except the ricey buzz) at regular(low rpm) driving but when i floor it to mid rpm it seems to not have much torque but there is a pull...then again i won't really know if there's hp's added unless i go the dyno...

Wait till you feel the difference at high RPM - the car now will pull through about 6500RPM. I did notice a decrease in low end torque but I was just spinning wheels at WOT anyway so a little low end loss in favor of top end gains was worth it. Lord knows the stock 5s could use some top end LOL.

Man - I can remember when I was the only person I knew with a header on a 5S Celica. Now it seems like everyone has one and my formerly beautiful SS Headers are now a very ugly collection of golds, purples and blues with a little ashy look thrown in for more bad looks. Oh well it's all about to be a moot point when the Turbo goes on this summer anyway.

[spke719]

just take it all off.....i took off all of that stuff, cat, resignator. and it still passes emmisions.

[hitcachi]

ummmmmm, 8 months later, ok....

[spke719]

ummmmmm, 8 months later, ok....

lol my bad i just read it yesterday. just thought i would put in my input.

[n1ckz0r]

Fine fellas, I'll try again...

my exhaust has four parts:



first... right names for right parts

Is in english right:

1 - horns
2 - calorifier
3 - silencer
4 - muffler



and second... if I remove part number 2, I will NOT have any HP addition really?

1 - horns - or flex pipe
2 - calorifier - actualy this is the catalitic converter.
3 - silencer
4 - muffler

Actually there is two cats' on the american 7AFE. The first is mounter off of the manifold right below it and the second as malpaos's picture shows is after the flex pipe. I have noticed significant gains from removing both but replacing the second with a hi-flow one and addind a hi-flow muffler, header and CAI.

I did the same thing... I noticed a very nice increase

[BonzaiCelica]

I've read a straight pipe in place of converter only adds 1whp. But how much louder sites it make it in decibels? Wasn't answered by Google search

[Box]

Holy thread revival Batman!

How much louder depends on a lot of variables, but the smell of raw exhaust is enough for me to leave them in place. Back in the day when they were crudely implemented and they clogged if you looked at them funny yes there were gains to be had, but ever since the late 80's/early 90's or so they really haven't imposed much restriction. Nowadays on a 400+ hp car they might result in a 1 hp loss if that, so why is it people still remove them on a new car is beyond me.

[BonzaiCelica]

Google didn't pull up any other threads. I swear. I don't mind paying 75 extra dollars for one, but the fact that they only last 2-3 years is where I'm like eek. Will have to pay for installation again. But the car is a money pit.

[Jmk91]

Yes it makes your car louder, but not that much louder. Way I look at it... Cats only last 20-50k miles for most of them... If you don't need to pass emissions than bypass it. We bypass almost all of ours whenever they fail in my area. Now some sound raspy without a cat some don't it just depends on current exhaust set up. On most of my cars it was prob as loud as going from a factory manifold to a header in terms of how much louder it was. my mr2 I had no cats with stock piping with eBay header. It sounded kinda mean at 4K Rpms. I liked it.

This post has been edited by Jmk91: Feb 15, 2016 - 1:29 AM

[BonzaiCelica]

A stainless header added to a beams motor adds 5 decibels. So i assume it'd be same for straight pipe

[Box]

If sound level is the main concern you can put in a straight through muffler in lieu of the cat to tone it down.

[igpx12]

What I'd recommend is mocking up a flanged pipe that will take the place of the cat just in case you maybe want to put a cat back on, then there's no welding involved later on.

[njccmd2002]

Removable test pipe

[BonzaiCelica]

But what frustrates me is the fact that all these converters no matter the length or diameter are slip fitment. Which means extra piping (more money) because the converters measure 2.5" inner diameter while all 16 gauge piping is 2.5" outer diameter.

Ahh. Are all catalytic converters like this?

[Box]

The direct fit ones are identical to the original in sizing and flanges etc... but you pay for it too. I know MagnaFlow offers some, then I want to say Bosal and Walker might as well.

This post has been edited by Box: Feb 19, 2016 - 2:03 PM

[BonzaiCelica]

What I recently bought. But my question is what type of gaskets do I use? The O type or copper gaskets? The other side test pipe looks the same...

This is what the Y pipe looks liken as you can see the pipe goes past the flange n there is a O type gasket like the ones found at the beginning of the two - one transition section.



This post has been edited by BonzaiCelica: Mar 13, 2016 - 9:21 PM