Question about the cats


Robert_1967

Robert_1967

15+ Year Member

V8 Engine Swap
Joined
Nov 7, 2009
Messages
1,802
Points
3,101
City
White Pine, TN
Vehicle Year
1988/1989
Transmission
Automatic
I put a new T-sat in my truck a few weeks ago, found out the hard way that I didn't have one, now the truck runs at the proper temp, but I notice now when I let of the gas and down shift, after a few seconds, I get the sick sounding rumble of a glasspack on a 2.3 and then a few little pops of backfire, I notice yesterday that there where a few peices of honeycomb laying on the ground where the tail pipe ends, after taking the the pipes loose, I could see that my cat is empty, nothing in it, almost like a strait pipe.

would this cause me to lose power and fuel milage ??
I heard once on the "powerblocks" "Horsepower" that there needed to be some restriction in the system to help with milage and power on 4 cylinders, something about "back pressure".

thank you
Robert
 
Your cat gutted itself....... probably a previous owner did it, really. No it won't cause you to lose power or fuel mileage..... probably gain actually (I did when my cat fell off..... I posted a thread about that)
but its required by law to have one, so you can either pretend like you have a cat (which is still illegel) or replace it

In no way do I condone running a vehicle on the street without a cat "this is my disclaimer"

Frank
 
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Thanks Frank, I live in Tennessee, we dont have inspection stickers or smog control, so no one but me will know, and you ...... and all of TRS. :)
 
If it were my truck, I'd get a new cat.
 
TRS does not allow discussion of removing legally required emissions equipment.
 
fastpakr said:
TRS does not allow discussion of removing legally required emissions equipment.
Click to expand...

we know, we arent condoing it. he asked why he found pieces of honey combs by his tailpipe. and found out his cat is gutted.

then he asked if he would lose hp and gas mileage by having it that way.

we never said to remove it.\

i say put a new one on. but thats just me.

you think im gonna run cats on my truck, no lol, my truck is 25 years old and in new york, after 25 years, you can do what you want.

yes i understand that i SHOULD have cats on it, but ill deal with it if someone wants to bust nads

I ALSO IN NO WAY CONDONE THE REMOVE OF EMISSIONS EQUIPMENT. WHAT I SAY IS MY PERSONAL STATEMENTS AND MEAN NOTHING TO ANYBODY.
 
Trs doesn't allow it? WOW.....Anyways, I had a 99 ranger and I removed the cats.....Check engine light followed and the truck ran and sounded like crap. Bought new cats from Magnaflow got some of the low end torque back but I did notice that my truck didn't pick up rpm as quick as it did without the cats. As far as gas mileage I think the computer over compensate and either runs rich or lean without cats.....So I say go get you a free flowing cat....However let it be known its FACT that if you have a tuner with the rear 02 sensor turned off, you can benifit from no cats on the big end....Like stated before its against the law so to each his own.....
 
We can forget about the silly term 'backpressure'...

It all comes down to a loss of exhaust gas velocity...do some reading and it'll all make sense

Replace the cat, or take other means to get some of your velocity back :icon_thumby:
 
BlackBII said:
We can forget about the silly term 'backpressure'...

It all comes down to a loss of exhaust gas velocity...do some reading and it'll all make sense

Replace the cat, or take other means to get some of your velocity back :icon_thumby:
Click to expand...

:agree: Everytime I see someone say "backpressure" I have to prevent myself from typing a page long explanation .
 
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Yellowsplash said:
:agree: Everytime I see someone say "backpressure" I have to prevent myself from typing a page long explaination.
Click to expand...

I could use the explanation. And I am serious. Not being a smart ass. Help me to overcome my lack of knowledge and having to ask dumb questions. Especially since I am trying to figure out whats up with my engine/exhaust relationship.
 
Maybe if everyone understands it they will stop yanking the cats and the moderators won't have to get all bunched up over it.
 
The moderators get "bunched up" over it because by federal law you cannot promote removing an emissions component from a street driven vehicle. This is federal law regardless of what Joe Schmoe said...

The shortest explanation possible....

Exhaust velocity is the only important factor here, but thats where the confusion starts. Backpressure is bad on every engine. The issue is that in order for a stock engine to maintain the correct exhaust velocity it will incur some sort of backpressure.

A properly tuned exhaust system will create vacuum in the exhaust known as scavenging. As a pulse of gas leaves the cylinder it will create the vacuum as it flows through the exhaust and will help "pull" the gas from the next cylinder out of the combustion chamber. If the system is not sized correctly the piston has to push the gas out of the cylinder creating more parasitic loss on the engine.
By "gutting" a cat you essentially add a huge chamber of room for the gas to expand in. As it flows through it must taper back down to flow back into the pipe. You can clearly see the issue here.
Lastly, removing a cat on an electronically controlled vehicle without tuning will cause more problems than help.
 
Well aware of why they get bunched up over it. I was just saying to enlighten the guys who want to remove them so the moderators don't have to get bunched up over the issue. Or maybe they like to. Gives them something to look forward to. I don't know.

Sounds like whether you use the term back pressure or exhaust velocity, it's essentially the same thing. They are intertwined. high velocity, lower pressure, lower velocity (plugs) higher pressure. Which is why guys can check for plugged exhaust using their vacuum gauges, right? So all little Johnny-Yank-His-Cats has to know is he's risking a $25,000 fine so he can screw up his truck and my lungs, right?
 
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