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?

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

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

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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

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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.

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

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Zactly,
we were both right

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?

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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.

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

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

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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.

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)

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

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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

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

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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

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!!

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

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?

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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

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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?

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

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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

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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

ignition timing is different than valve timing.

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

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

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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

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

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)