does removing the catalytic converter add HP? Options

[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...