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Lsn2this
Dodge Dakota
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9/09/2006
17:50:06
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 Subject: cat removal =HP?
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Before anyone says it, i know it is illegal. But i am wondering if removing my catalitic (spelled wrong) converter and replacing with straight pipe will gain me any Hp? i know the exhaust note will sound much more throathy, just wondering powerwise.
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screwuphead
Dodge Dakota
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9/09/2006
18:24:28
|  RE: cat removal =HP?
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power wise your not gonna gain anything too extreme your better off but adding a highflow catalytic converter and staying emissions friendly and have the same amount of power. Our truck require a certin amount of volcity to get the exhuast out to get a better burn in the comustion chamber. By removing the cat you can hurt that blance and lose some of your low end which alot of people blam on back pressure. Unless you have a race car you shouldnt be worried about removing the cat
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xmr2
Dodge Dakota
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9/09/2006
18:26:02
| RE: cat removal =HP?
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actually you will lose enough bottom end power you would regret it.
The 3.9 need the back pressure from the cat to produce torque.
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N56629
Dodge Dakota
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9/09/2006
22:15:38
| RE: cat removal =HP?
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Backpressure is grossly over-rated. You won't gain anything because your y-pipe is probably more restrictive than the cat.
Why do people assume that cats are restrictive? To be restrictive a cat or muffler would have to have flow less than either the inlet or outlet. I wonder if anyone has actually flow tested a cat.
This need to remove the cat reminds of people that feel the need to install an air filter that is capable of flowing 2000 cfm on an engine that needs less than 750 cfm even on a good day.
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Kenkura
Dodge Dakota
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9/10/2006
11:10:35
| RE: cat removal =HP?
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I'm gonna have to say you guys are wrong... My cat was clogged so my dad and I cut it off and put a straight pipe on (Emissions Exempt area) I have all my low-end and then some, Also gave me quite a bit more power. Not to mention it sounds bad ass, and its a stock Muffler I am going to have a flowmaster put on in a week or so. And if you have ever seen what is in a cat it is EXTREMELY restrictive, imagine a grid of 1-2mm diameter honey-comb, hundreds of them that run for 1-1 1/2 ft its very restrictive...
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screwuphead
Dodge Dakota
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9/10/2006
12:33:28
| RE: cat removal =HP?
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If your cat was clogged and you removed it of course its going to feel like theres more power cause you undid the clog, doesnt mean that if you would of replaced it you would of felt more power too but i bet if you test it you would feel more with the cat on.
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Lsn2this
Dodge Dakota
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9/10/2006
12:57:30
| RE: cat removal =HP?
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hmmm i have seen the inside of a cat before thats why i was wondering. the honeycomb does seen very restrictive. As far as back pressure and a propper burn in the chamber. thats all B.S. you dont need back any kind of back pressure at all ZERO! and burn in the combustion chamber happens when the valves are closed and has nothing to do at all with you exhaust at all.
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Kenkura
Dodge Dakota
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9/10/2006
13:19:19
| RE: cat removal =HP?
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screwuphead, It was not always like that the cat was clogged for maybe a a week tops and I think after a year or so driving my truck with the cat perfectly fine and now without one I'd notice a difference if I lost my low end I can idle up my driveway and its pretty steep, before the cat cloged I'd have to give it atleast some gas a very minimal amount but some yes. all of my friends that have riden with me before and riden with me after we straight piped it, said that it really opened it up and gave me more power than i had before easily, my friends acctually getting a little nervous that if I keep doing stuff like that which costs almost nothing I'll catch up to his mustangs power easily. and I'd say a good test of torqe would be a nice burnout I ususaly rev to 3000 then dump the clutch I have yet to do it yet but I'll notice it for sure then if I lost any. but it gets up and goes from Idle to Redline much better than it did before my cat was cloged. I'll have to borrow my friends G-Tech to really test it out and get some numbers thou. Besides the Y-Pipe and Muffler should provide a minimal amount of backpreasure, enough to keep my torqe, now I think if I went to true-duals with no cats and flowmasters that'd probably kill my torqe. besides non of the old muscle cars had cats are you gonna try to say they had no torqe?
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2000dak
Dodge Dakota
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9/10/2006
13:36:40
| RE: cat removal =HP?
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I would believe that you would get some kind of increase in power if you removed the cat, it only makes sense, less restriction, more power under full acceleration. Don't forget about exhaust scavenging and how headers work to increase performance. Some are getting on this forum and know nothing, ask a bunch of questions at the start, now they think they can give advice. Get real!
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toolfan
GenIII
9/10/2006
16:09:46
|  RE: cat removal =HP?
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dont take it off leave it on. replace the Y-pipe if you want performance. your gas mileage will go down and the power you gain isn't worth the time you take to take it off.
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GB2000
GenIII
9/10/2006
17:15:55
| RE: cat removal =HP?
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hmmm i have seen the inside of a cat before thats why i was wondering. the honeycomb does seen very restrictive. As far as back pressure and a propper burn in the chamber. thats all B.S. you dont need back any kind of back pressure at all ZERO! and burn in the combustion chamber happens when the valves are closed and has nothing to do at all with you exhaust at all.
Okay...you know what...put on a set of headers and run 3" true duals with no cats or mufflers. Then I want you to come back here and honestly tell us that your V6 doesn't take 2 1/2 minutes to hit 60mph. Backpressure IS necessary if you want low-end...don't believe me? Try it.
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screwuphead
Dodge Dakota
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9/10/2006
21:01:47
| RE: cat removal =HP?
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its not back pressure its volocity in the exhuast pipe. It is blamed on back pressure. Its pysics. COME ON NOW! if the exhuast has no high pressure to low pressure to go to then the exhuast will stay within the combustion chamber. THEREFORE MAKING THE NON-PROPER BURN i was talking about. And your telling me that there must be zero back pressure! I spit at you! the top race cars in world have atleast 1-3 psi of back pressure.
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N56629
Dodge Dakota
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9/10/2006
22:25:16
| RE: cat removal =HP?
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"It was not always like that the cat was clogged for maybe a a week tops"
Sorry, but it can years to plug up a cat, not days or even a week. Besides, what would you plug it up with? Running leaded gas? Do you have an extremly crappy running engine? I've had cars and trucks run hundreds of thousand of miles without any need to replace that cat.
I'm not suggesting that a high-pro engine won't benefit from replacing it or eliminating it but a mostly stock engine will not see any difference.
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Kenkura
Dodge Dakota
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9/11/2006
00:01:54
| RE: cat removal =HP?
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No engine runs great nice and strong it probably cloged cause i removed my stupid air pump and it was no longer getting the air it needed to burn the un used fuel or i guess its possible that the MSD is making my exhaust hotter and burned it up either way from my own personal experiences i got a nice exhaust tone and a good deal more power so take it or leave it. i still have plenty of low end grunt to go around i can get up to speed for the freeway much much faster now than i could before, again its not like i'm running no cats true duals that'd probably kill all back pressure i do want atleast some as the engine does need it but i dont need as much as i had.. and from everyone i knew that had cat problems in the past with other cars it slowly came on over a period of about 1 month then they lost all power completely, thou my friends Thunderbird SC when its cat cloged it shot its guts out the muffler...
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N56629
Dodge Dakota
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9/11/2006
06:40:11
| RE: cat removal =HP?
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Obviously if you have cat problems you replace it, but claiming improved performance is nothing short of a guess unless you make comparisons to a new cat. Now all you have to do is deal with trouble codes and a computer that is mis-reading the air-fuel mixture.
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Bob Lincoln
Dodge Dakota
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9/11/2006
08:36:27
| RE: cat removal =HP?
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I love how people can judge how much power they gained without any dynamometer testing (especially right after fixing a defective vehicle), and how they can just look at something and decide what its performance is like.
*Measure* the power to back up your claims. Experts have measured cars on dynos, and removing the cat gains only about 1-2 hp, which you will NEVER feel.
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N56629
Dodge Dakota
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9/11/2006
10:45:38
| RE: cat removal =HP?
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Newer cats are also more efficient than the older ones but old tales of improving performance by removing the cats haven't changed. Most likely the same people that remove their cats also think that throttle body spacers improve performance.
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BP guy
Dodge Dakota
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9/11/2006
16:13:36
| RE: cat removal =HP?
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If this "back pressure" were useless,why does every engine manufacturer waste time and money on designing an exhaust system.heck why aren't all exhausts the same then?
Anyone who thinks "back pressure" doesn't do anything probably never rode a 2-stroke dirt bike.Ever notice how an aftermarket pipe makes the powerband come on at different RPMs?That's because the reversing pressure waves in the exhaust reach the combustion chamber at different times when compared at the same RPM.Four strokes are almost the same.My 91 Mazda b2200 amazingly got 8 more MPG after I replaced the muffler that rusted out...Why???
all engines have a point in their power producing stages where the intake and exhaust are both open at the same time.This is most important in understanding "back pressure" as everyone calls it....
The pressure waves serve 2 purposes while both exhaust and intake valves(or ports in the case of 2-strokes)are open.The resultant exhaust pulses create a "pull" or scavenging effect on the combustion chamber by their net velocity(which is basically dictated by the size shape and characteristics of the exhaust system).This helps to pull exhaust out of the combustion chamber while at that same time "pulling" in fresh intake charges.This is almost(but not quite)similar to an engine with a few PSI of boost at that particular engine speed.So then if you know the speed of induction and exhaust pulses,the length of intake runners and exhaust headers,etc. and the amount of CFMs which are flowing through the engine,you can mathematically come up with a "sweet spot" where the engine is at it's highest volumetric efficiency,using the net pressure from induction and exhaust pulses(or back pressure).So you see, back pressure is EXTREMELY important when it comes to producing any kind of usable,predictable power.A good way to demonstrates this would be to just take off your headers.If you can get the engine to even idle,I will be surprised.Tell me now why "back pressure" doesn't mean squat?
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N56629
Dodge Dakota
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9/11/2006
19:30:56
| RE: cat removal =HP?
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Pressure waves and backpressure are not the same thing. Backpressure is an unavoidable byproduct of velocity. In headers different size tubes are used to tune the power range. They are not picked because they produce a certain amount of backpressure.
If you think backpressure is the primary ingredient try installing some Supertrap mufflers and experiment with them. I can guarantee you that you will be wasting a lot of money.
"The resultant exhaust pulses create a "pull" or scavenging effect on the combustion chamber by their net velocity(which is basically dictated by the size shape and characteristics of the exhaust system).This helps to pull exhaust out of the combustion chamber while at that same time "pulling" in fresh intake charges."
You are right but at what point in the exhaust system does this occur? In headers it occurs in the collector. Do you have to maintain this magical backpressure all the way back to the end of the tail pipe?
As far as your question about why they spend so much money on designing exhaust systems, they don't really spend all that much money on it. I would bet that performance comes after emissions, noise and cost. That's very likely the correct order too.
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J and J Auto
GenII
9/11/2006
21:30:25
| RE: cat removal =HP?
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LOL
take the manifolds off start your motor and try
and rev it
with 0 back pressure it will break up and sputer
and not rev over 2000rpm
There is more to an exhaust system than just flow
it must pulse right to get the max hp this you
can hear
a hum bad flow
a nice rap its pulsing corectly
If you take a look at a cat you will see its also
a chamber were exhaust can expand
we are running the hemi's with cats and blowers
10 pounds of boost 7000rpm now tell me the cat
is restricting the system when they are pulling
500 plus rear wheel hp
A good high flow has very little to do with the
system back pressure pipe size and muff is most
of the back pressure
Larry
J&J Auto
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Obio3
Dodge Dakota
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9/11/2006
21:38:03
| RE: cat removal =HP?
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BP.With all due respect,you best do some reading on engine design. There is absolutly no way you can compare a 2 stroke to a 4 stroke. Totally differant approach to how and why they run. 2 strokes have to have back pressure to keep from dumping the next charge right into the exhaust. 4 strokes have intake and evhaust valves to handle this. The reed is the only help a 2 stroke gets and I'm not so sure they all have a reed. In days past none had one. Yes.... 4 strokes are designed to match the engine but there designed to just do as needed so the engine can run FREELY and keep expence down. Drill a hole in the exhaust pipe directly in front of the cat to hook a pressure guage to. Guess what. Most pressure you will have at any given time is 1 &1/2 lbs of pressure. Almost none at all. SO MUCH FOR BACK PRESSURE. Now... If you do have more you have a serious problem you best fix prior to burning valves. Do some reading at the library and learn what's real. then bring it here to share.
So many problems .... So little time
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