ForceFed said:
ok i know i'm gonna get flamed on this one from someone but here it goes!
High-flow(supossed)cats are a joke!All cats must meet the the same EPA requirements regardless of whether they are high flow or stock.(period!)The only thing that makes a high flow(once again supossed)cat any different than a stock one is the size of the inlet and outlet.(2 inch vs. 3 inch for example)The inners of all cats look the same and have the same restrictive type honeycomb material that makes them function.Yes you may put a bigger high flow(supossed)cat on your ride but will it really flow any better?It probably will but not enough to justify the cost of them for performance reasons.The internals of the cat are what makes them restrictive.
Have you guys preaching about high flow cats ever wondered why the companies that produce these don't put up flow comparison charts?Well I know why!Because they don't produce enough of a difference to justify them.If you are going for performance(especially on a turbo car)you need a higher flowing exhaust .You may gain a small amount of overall exhaust flow by putting in a single high flow cat,but it will be gained primarily by eliminating one of the cats.I.E. less restriction.You may even gain a little more from upping the exhaust piping size and putting on a high flow but you will still be restricted by the cat,period.If you want the least amount of restriction then the absolute best way to go is no cats at all!Yes I understand the environmental issues you are referring to and yes a cat would solve the CEL issue but most of the guys on these boards with MSP's are looking for the best bang for the buck when it comes to making the MSP fly!The only drawback that these types of guys are going to run into is staring at the dreaded CEL light till we get the permanant fix together to trick the ECU.
This is not a rant and this is by no means directed at any one person,This is just the way I see things!
This is my .02 cents,feel free to chip in yours!
Matt
couple things i want to clear up here on your post.
high flow cats and OE cats do have basically the same internal catalyst components. i dont know if you have read any of my proir posts either in this thread ot others so i will clarify and restate.(BTW i know you said it wasnt directed to any one individual
)
high flow cats as per the name is a little ignorant. the reason they are effective are two fold. because they are able to "clean up" the emmisions from your engine and they have a higher "FLOW CAPACITY" then your stock converter.
there is a difference when you say restriction, backpressure or flow capacity.
for example when you turbo charge your vehicle and are flowing a larger volume of air at the given rpm your exhaust has to have the same ability to capasitate the flow of exhaust gases. thru the years and sufistication of fuel injection, ignition and A/F metering devises (O2 sensor and closed loop operation occuring sooner in most systems) the need for a very "restrictive" catalyst isnt there like there was in the early 80's when they still had feedback carbs and throttle body injection. the cats today from the OE manufacturers are really not that restrictive to the point where they create backpressure, they are restrictive in their capacity to how much they can flow.
many people think that when they increase the size of the exhaust from the cat back they are getting more power. they think there was so much "backpressure" in the system that it will stiffle flow and create less power. this is wrong. the system can only ingest and expell so much. but the engine can produce whatever it was designed to pump out.when they see a hp gain they see it in the upper rpm range when the engine is at its peak efficiency and needs the additional capacity to flow what it was allready able to produce but couldnt because the "piping " was to small in diameter. there is also a difference in keeping velocity in the system and allowing too little flow and losing some needed torque, thru scavenging and tuned exhaust gas harmonics in the lower part of the rpm band.
those exhaust pulses low in rpm is what gives you the initial power your looking for but the hp needed to sustain power levels needs to have an exhaust system that can breathe well in the upper limits also. stock cats are ok but just not enogh when your looking to increase the amount of CFM thru the engine faster than N/A operation as with forced induction.
backpressure is a myth,restriction to flow is another. its flow capacity and exhaust pipe diameter that controls that.
i preach about cats only because it will save you headaches with the smog boys and unless you have an experienced tuner that can tune your car with a piggy or standalone you will never pass emmisions.
and we all want to stay legal right??
so the larger flow capacity cat WILL help for power gains.
but if you dont care about emmisions testing and the ecu funcion than go catless.
like i said in an earlier post, we can be here all day discussing this topic but i tried to put as much info as i can in "real world" terms to get my point across.
im sure there is some stuff i skipped so i can go into detail if someone would like to ask.
