I have recently bought an 03' supercrew and was wondering if i could fit 3 inch pipe from the cat back

 

probably could but i wouldnt go with anything larger than your stock size pipes otherwise you will loose power!

 

I would have to disagree sd150guy. You will probably gain HP. Magnaflows catback SI/SO system is all 3" pipe and they show good HP gains. Anything larger than 3" and you will probably lose, but with 3" you should see more benefit. I am doing my SCrew with a Magnaflow 3" setup tomorrow night.

 

Part of the answer depends on what size engine ? ( I have sigs turned off )

4.2 I wouldn't, that might jack up the flow too much and reduce TQ.

4.6 Maybe would work.

5.4 Should work, dual 2.5" pipes work fine, so with a single 3" pie beign less area then dual 2.5" pipes, should not be a problem here. Also depends on the guy bending the pipe.

Can I ask another question, is this just from the factory Y pipe back, or are you looking at getting the after market Y pipe which is dual 2.5" pipes in, single 3" pipe out ?

Converting it after the factory Y pipe and before the muffler, I am unsure how much this is going to do for you. After the muffler, single 3" that is another story. Taking the flow from 2.5" to 3" mid stream might do something to the xhst gas flow, and take TQ in the crapper. Depends if you are looking at a flow tested unit, or the muffler shop type build out.

Sorry more questions then answers on this post.

 

I was wanting to do one pipe off of one side of engines cats and another off the other with no mufflers

 

If you're planning on true duals then 3" is too big. Use 2.5 or 2.25 and install some sort of x over pipe.

 

V10 man said it, don't bother with dual 3"

Do 16 ga 304 SS pipe, 2.5", and regardless of mufflers ( brand independant ) or straight pipes, put in the X pipe.

This is for the scavenger effect in the gas flow.

I did the true duals, 2.5" from each side into a X pipe and then to SI/SO mufflers, both in and out are 2.5".

Going to 16 ga 304 SS in 3" is a waste, opening up the flow too much ( maybe don't know never seen dual 3" on a 5.4L even S/C'd ) and a waste of money in the cost of the pipe.

Don't cheap it, go SS pipe at least to the output of the X pipe ( SS X pipe also ). Going aluminized will allow the xhst gas to cool too much, and cause a loss of xhst gas velocity.
Find a shop that can bend and weld SS pipe. I did the clamp thing, and then later added a weld line 180* from each other at each joint. Belt and suspenders type install, that only would need a quick zing of a angle grinder to remove.

Good luck.

Steve