Restricted Exhaust

[jheiv]

Long story short-- blew a Pushrod and FPR. Now I fixed both of them but after I warm up my engine my engine LACKS POWER! Like you have no idea... I have a 3.1 Turbocharged V-6... it used to take off at traffic lights-- now I'm STRUGGLING to KEEP UP WITH a 4 cylinder Toyota. Something is wrong... I'm pretty sure it's my cat too. The problem is, I don't really feel like getting OEM... I'm actually seriously considering replacing with straight pipe. (I dont know if this matters but I go from turbo to exhaust pipe to cat to y pipe to mufflers (stock dual exhaust)).

 

Here are my problems,

1) I'm not positive if it is indeed my cat... any ideas, what do you think?

2) I'm not a welder... I'd really prefer to avoid having to weld a new cat or straight pipe in, can I do something about this

3) If I do go straight pipe, just to replace the cat, what size should I go? Would that just fit in?

4) And how would I connect this?

 

ANY suggestions or comments would be GREATLY appreciated. Thanks

[DaveFromColorado]

pull the cat, and go straightpipe you'll be much happier in the longrun.

 

--Dave.

[93CutlassSupreme]

i always thought that you could get some clamps and clamp the pipe tight instead of welding it, at least that's what my gm service manual suggests to do when replacing a muffler

[93GTP]

I recommend buying a highflow carsound cat off ebay. They're only around 40 dollars and they perform awesome, and are awesome quality.

 

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=2462953016&category=33629&sspagename=WDVW

 

Well whatever you do don't forget you'll need to a reducer to go from the 2.5" downpipe to the 2.25" midpipe.

[DaveFromColorado]

on the flowbench, we found nearly no difference between the high-flo cat's and regular ones.

[93GTP]

Was it a carsound cat? If not the test doesn't really mean a whole lot.

 

People shouldn't be so careless when it comes to replacing cats with straight pipe these days. Cat's really do help the environment by converting monoxides to dioxides.

 

Besides 60*V6's sound better with a cat.

[DaveFromColorado]

A three-way catalytic converter: Note the two separate catalysts.

 

The Reduction Catalyst

The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:

 

 

2NO => N2 + O2 or 2NO2 => N2 + 2O2

 

The Oxidization Catalyst

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:

 

 

2CO + O2 => 2CO2

 

now, if you put a modern car well maintained and tuned up on a 5 gas analyzer you will see that most often a Catalytic Converter is not needed, in fact it hinders the performance as it will not allow all the exhaust gasses out of the cylinder, causing extremely high cylinder tempatures and a loss of performance as this will start to burn into the rings and cause oil to be mixed into the combustion chamber.

 

it's a lose - lose situation.

 

I still say, from a performance aspect, removing the cat is going to be a good performance upgrade, as you need to open the exuaust, especially on a turbocharged car. But that's just me.

 

--Dave.

[93CutlassSupreme]

without a cat, you'd need more emissions controls on the engine to make it meet emissions, look under a car from the mid or late70's before cats, and then after cats came out, cats took a lot of strain off the engine in meeting emission laws

[93GTP]

now, if you put a modern car well maintained and tuned up on a 5 gas analyzer you will see that most often a Catalytic Converter is not needed, in fact it hinders the performance as it will not allow all the exhaust gasses out of the cylinder, causing extremely high cylinder tempatures and a loss of performance as this will start to burn into the rings and cause oil to be mixed into the combustion chamber.

 

it's a lose - lose situation.

 

I still say, from a performance aspect, removing the cat is going to be a good performance upgrade, as you need to open the exuaust, especially on a turbocharged car. But that's just me.

 

--Dave.

 

Well, this is the reason the EGR was developed. A working EGR greatly reduces combustion chamber temperatures.

 

And just because a car does the pass the emission requirements without a cat, doesnt mean a cat shouldn't be installed. The cleaner the exhaust emissions the better.

 

The rings of an engine will never wear out because of the installation of a functioning cat into the exhaust system. How many 60*V6's even have ring problems? It takes a LOT of miles to wear out the rings of a 60.

[jheiv]

Here are my problems,

1) I'm not positive if it is indeed my cat... any ideas, what do you think?

2) I'm not a welder... I'd really prefer to avoid having to weld a new cat or straight pipe in, can I do something about this

3) If I do go straight pipe, just to replace the cat, what size should I go? Would that just fit in?

4) And how would I connect this?

 

ANY suggestions or comments would be GREATLY appreciated. Thanks

[93CutlassSupreme]

i always thought that you could get some clamps and clamp the pipe tight instead of welding it, at least that's what my gm service manual suggests to do when replacing a muffler

 

#2

[DaveFromColorado]

let's think about this the exhaust gas re-circulation system takes the hottest exhaust gasses and forces them back into the intake heating up the intake charge taking the place of cleaner air.

 

so we have 1) hot gasses placed in the engine

and we have 2) exhaust gasses displacing clean cool air

 

now how does this reduce chamber temperatures, you ask, well it reduces them essentially by taking up space and not allowing a good a/f mixture to even enter the chamber.

 

Oh, wait that doesn't make sense that's because I neglected to mention - emissions control systems such as air pumps (designed to add oxygen to the exhaust to help the catalytic converter "heat up") are used to increase chamber temperatures, not reduce them as this will help burn fuel much more cleanly - more heat = more stuff will burn, this is also why detonation is such a problem on modern cars, higher chamber temperatures mean less power and a higher likelihood to create an environment to knock (fuel burning before it's supposed to, too quickly, or uncontrolled) there's anti-knock detergents used is most gasoline but those still don't make up for longer hydrocarbon chains (higher octane), along with a solution of alcohol to help "clean" the emissions by adding an oxidizer (also higher octane) thus making a catalytic converter nearly worthless.

 

I'm happy you feel that you need a catalytic converter on an automobile to help clean emissions, you're doing your job, I still won't run one as it hinders performance, and it's truly not needed.

 

--Dave

[93CutlassSupreme]

how about corvettes and vipers and shit that make 400 and 500 horsepower? they run cats

[DaveFromColorado]

here's a perfect example for you.

 

we had a car pulling 476 to the rear wheels on the dyno, we pulled the cat's off (headers only) and got 509 to the rear wheels, the car went way lean and we could have tuned it for much more power, but it was too loud that way.

 

my Uncle has an 87 Corvette, pulle the cat's off, and is getting more power, I don't have the numbers right now, so I can't quote them, but I remember it was a significent difference.

 

I haven't expiremented with any Vipers.

 

--Dave.

[93CutlassSupreme]

to be honest, i agree with you, you do make more power without a cat, but it isn't worth it to me, espeically when emissions testing might be coming back where i live

[DaveFromColorado]

do what I did, make a straight pipe, same size as the cat, put flanges on both sides of the cat and the pipe, so it's as simple as changing a few bolts.

 

--Dave.

[Hippie]

without a cat, you'd need more emissions controls on the engine to make it meet emissions, look under a car from the mid or late70's before cats, and then after cats came out, cats took a lot of strain off the engine in meeting emission laws

 

Nation wide emissions really hit in '73 with EGR and AIR pumps and catalytic converters became std. equipment in 1974............ 1972 was the last "good" year and they were seriously detuned from what they had been just 2 short years before in 1970............

 

The catalytic converters used today are light years ahead of what we had to deal with back in the day. Those things stunk..................... literally !

[93CutlassSupreme]

i'm glad i don't have an air pump, that's all i need one more thing dragging on the engine

[THe_DeTAiL3R]

With our engines that are n/a (pushrod anyways) I've read that taking the cat off is bad, cause there isn't enough backpressure and the ECM/PCM can't compensate for the difference to make an improvement.

 

But this is a TURBOcharged engine, so less back pressure the better :!:

 

i always thought that you could get some clamps and clamp the pipe tight instead of welding it, at least that's what my gm service manual suggests to do when replacing a muffler

 

When the main pipe disconnected from my muffler the muff shops said that a weld wouldn't hold very long, due to the age (rust) of the muffler/pipe. Since my car is dual exhaust with the muffler that has a pipe that goes in and one that goes out (to the other muffler) it was damn expensive even for cheap ones. SO I got some aluminum tape, muffler cement, sheet metal, and a big clamp and sandwitched it all together. Been a year now and its still holding fine.

[93CutlassSupreme]

yup, i see a lot of mufflers that are just clamped on