high flow cats? how loud will they be? do they do much performace wise? such as hp and torqu

 

Replace all 4 with 2 Magnaflow 94106s and youll notice a 40% sound increase. You wont notice much of anything as far as performance gains.

 

is it worth it to go that route if i have an all new exhaust to go with it

 

Here is some reference information from flow tests conducted on cat converters.
Flow tests on a flow bench at 20.4 inches of water pressure show a flow of 2.2 cfm per 1 hp is min before power begins to suffer.
Removing cats only gained about 8 hp on an actual dyno test. Not enough to hardly be felt in the driver's seat.
If you know the cat flow in CFM then you can find the HP supported without much loss by dividing the total flow by 2.2 to = the gas flow supported HP.
For example a flow of 550 cfm divided by 2.2 = 250 hp.
If you spend money on hi-flow cats be sure they truely are higher flowing and then be sure the rest of the exhaust system is not killing the increase or you end up with no chance of power improvement from the investment.
Bottom line is on a stock truck the cats are not much of a restriction for the volume of gas that flows.
To help key in on this a little closer, consider an old 302/5L Ford motor will pump about 500 cfm at 5000 rpm.
This is calculated by cylinder displacement x 8 at the desired rpm minus head flow losses and other flow restrictions between the inlet and the outlets.
So the 4.6L is smaller but heads flows a bit better so the airflow would be somewhere in line with 500 at 5000 but you don't normally run down the road at those rpms.
Bottom line is not to place to much emphisis on a high flow cat change unless the motor is highly modified to make much more hp (pass more air) at higher rpm where the extra flow makes a difference..
Thinking of any performance increase at normal driving speeds from cat replacement is just not realistic because the gas flow is well below any cat restriction point unless the cats are getting blocked for some other reason such as missfire causing temperatures to go so high the internal structure melts and forms a restriction or they break up.
The factory does not leave very much on the table for HP loss from exhaust systems on the normal truck application.
They can't afford to do so from a competitive point.

 

for exhaust volume yes.

 

 

x3. They are strictly to improve the volume, and to which I must say they do a GREAT job. I love mine.

You can have them shipped to your door for $100 and installed for roughly that same amount depending on the shop.

 

Can't you cut out the PRE-cats and just go with TWO Hi-flow Magnaflow cats??--DirtySCREW

 

Same thing. whether your replacing the rear with 2 high flows and cutting out the 2 pre cats, or replacing all 4 with 2 high flow. Its the same thing.

 

when replacing all four with just 2 you wont have any CEL's come on right?

 

There are 4 OX senors, two on each side.
The rear sensors are in the 'middle' of the stock rear cats.
You will need to place rear sensor 'bungs' at some point just back of the last cat unless the rear cats have that sensor port.
If these rear OX sensors are missing or do not work as designed you will get efficiency failure codes or if missing, two codes telling you the heater circuits are open and there is no signal from the sensors.
The computer is expecting to detect the presents of all the sensors.
Good luck.

 

Very good explanation and so true...

Great Bottom Line as well -

Yea that's good. Want you want to achieve or improve is your low end torque and @ the lowest possible rpms. That will get you up to speed under NORMAL acceleration that much quicker. - It will also make it easier on the engine when towing. They call it usable HP. The exhaust has to be right, you can improve the intake a little and efans also help a good deal down low. Do those three correctly and you'll notice a little improvement. You can even tune it in on the dino and get a little more after those three mods. That's about as far as you can go without serious engine modifications and /or get blown.

 

What I see over long term monitoring general operation is that Ford pulls back aggressive ignition timing and leaned the fuel injection. The reasons are another story why.
This loses power and low end torque.
Since we can't have any control over it without some type of adjustable tuner, we live with what we have.
Trying to improve the situation by altering the OEM design usually does not meet with results that are thought to be there because you forget you are 'fighting' the PCM program that needs to be altered to take advantage of the changes "so it's not too productive", for the total 'cost', of disappointment, at the results you get.
Said another way, the motor is being controlled by the PCM program.
Changing parts for expected gains only interfers with the program such that it takes corrective action and nullifies much of the gains you try to introduce.
This is why after market tuning (program changes) by a good shop will net worthwhile gains in the right places depending on the specific intent.
BASICLY the mfger and the Gov. don't want you making changes to anything on the truck.
Ventureing to the 'left', it's called Liberal or socialistic control.
The latest versons of PCM control are built to add an 'inquiry' transmitter and receiver on board your vehichle so it can be accessed by a gov. enity.
They could look at your PCM for codes while your driving and send you a notice to have it fixed if any are detected along with the VIN.
"On Star" is just a step below all this, now.

 

Best Highflow Cat on the market is made by Makita:

 

^^^