High flow cat

Project1500

Well-Known Member
If I put a high flow cat on my 1998 5.7L chevy will I throw a engine code? There are 02 sensors after my headers and one after my last cat (I have 2). Or will hallowing out my stock cats throw a code?

What can't kill you will only make you stronger
 

cleartoy

Well-Known Member
If you live in CA, its illegal to put a cat on that is not factory new or rebuilt factory. This applies to all 96 and newer OBD2 vehicles. I dont think it will trigger a code, just not pass visiual inspection.

A hollow or poorly functioning cat will trigger a code stating cat below efficiency threshold.

94 Toyota stdcab 2x4
99 Yamaha YZ250

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kjmiller1

Well-Known Member
mccleod mufflers in placentia recomended I get one on my old truck that had about 250K miles on it, but when I asked him about getting one for my current truck with about 130K miles he said stick to the original honeycomb. I think it just means that you can reduce the amount of back pressure as much as you would want with just a muffler

93 f150
 

Project1500

Well-Known Member
Miller what is your current truck?

Cleartoy I thought any vehicles newer than 5 years you cant mess with the cat?

What can't kill you will only make you stronger
 

cleartoy

Well-Known Member
96 is 7 years right now. You can open the cat up to accept larger piping, but not replace it with a universal cat on OBD 2. Pain in the ass and expensive.



94 Toyota stdcab 2x4
99 Yamaha YZ250

Got Sand??
 

dezerts10

BANG!! BANG!!
to get rid of the cat on your new truck you need to get an O2 sensor simulator. i bought one for my truck it was like 45 bucks i think for 2 its like 90. it just basiclly plugs into your sesor and loops back to the sensor telling your computer everything is ok. look in the summit online catalog for o2 sensor simulators and there should be a company called casper electronics where you can buy the simulator.
 

kjmiller1

Well-Known Member
its a 93 f150, got a flowmaster with 3" pipe from the cat to it and no pipe from it. I definitely noticed a loss of low end torque, but stock that is where all of my power was and now it seems to be smoothed out more throughout all rpms. But thats my almost stock ford 5.8L, my 82 c10 350 with 250K miles really came alive with the high flow cat and muffler.

93 f150
 

WeldnFab

Well-Known Member
To quickly answer your engine code question, it won't through a code if you put a HIgh flow Cat. I work for MagnaFlow / Carsound. And my company produces high flow cat.s in house. You will only notice increase in fuel economy and not much in power increase. And you won't lose torque and power either.
 

Project1500

Well-Known Member
What a salesman..j/k How much louder would my exhaust be If I put on a high flow cat? it allready exits under the passenger seat and isnt too loud surprisingly.

I dont know why you would loose torque because look at the amount of bends on a 5.7L 96-98 and its exhaust is pretty restrictive no mandrel bends.

On a 99+ with the 5.3 the exhaust is run really well and it has just as much torque as my truck. I know thats not just because of the exhaust tubing.
 

kjmiller1

Well-Known Member
maybe I don't know how to tell what loss of torque feals like, but my truck kicks down a gear on hills I drive everyday that before my new exhaust it would not
 

Project1500

Well-Known Member
I know what a loss of torque would feel like. I just don't get how people say you loose torque when shortning exhaust? I just want to know the theory behind it. NTSQD maybe you could explain or someone else?
 

kjmiller1

Well-Known Member
I don't claim this as fact, just something to think about:
most people would agree when getting exhaust out, faster is better. But it is important to get it out smoothly. Imagine the explosion happening in a cylinder and the exhuast valve opening. No backpressure would let the exhaust leave nice and quick, but right after a vacuum would form. This vacuum might kind of suck some of your exhuast you just let out back in, or at least disrupt the flow leaving the exhuast, and cause turbulence inside the cylinder disrupting your air/fuel mixture coming in. And at lower rpms, I could imagine this is where the problem is more likely to occur because it has more time to build a fat vacuum condition. A little backpressure prevents exhuaust from leaving too quickly so a vacuum doesn't form, at least not much different than what chevy expected so the flow is nice and smooth. I'm sure you would be happy with a high flow cat, how much of a difference they make is another story, but they are a lot cheaper than the ones you would buy from chevy.
 

Kritter

Krittro Campbell
Thats what could happen when you run open headers that are too short or open exhaust manifolds...commmonly referred to as "sucking up a valve"
 

Project1500

Well-Known Member
Makes sense. Seems like a 5 foot piece of muffler tubing with a few bends in it would eliminate the back pressure problem. It also depends on tubing size etc I would think. My tubing is 2" from each header then goes to a single 3". My exhaust comes out under the passenger seat. It would be interesting to see if anyone else has another theory.

Kritter your refering to bending a valve because of the cold air being sucked back up correct?
 
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