I have a 5.3 in my 04 Silverado and I am looking for a little better throttle response, a wee bit more power, and Loud exhaust. This is my prerunner desert truck and DD so I need it to be California smog legal. I want feedback and lots of it please. I plan on doing some shortys or possibly Thorley (thy-310-c) I heard there carb legal. I was wondering if gutted cats will still pass the sniffer if not then ill just make them bolt in for smog and leave them out for normal day to day, then go into a X pipe and have it run back to 2 magnabullets or similar mufflers and exit out of my passenger side bedside before the tire with some nice tips. I plan on running 2.5" from the X pipes back is that a good idea? Enough for back pressure? then wrap it all up with a good ol' tune!

 

Anyone wanna help me out?

 

2.5" exhaust is perfect, 3" is to big and causes a loss in velocity speed of exhaust pulses which results in a loss of low end power.

I would go with pacesetter ceramic coated longtube headers. Usually can find them for under $400 online. I have these headers and they still look brand new after 30K. Don't waste your time or money on shorty headers they give about half the power you can get from longtubes.

The cats are what make it pass emissions, so don't gut them. I bought High flow magnaflow cats for $75 a piece and have zero emission issues in texas, so I would do some research on a proper cat that will allow you to pass emissions.

If you want it loud get cut-outs from summit $40 a piece and then if the cut-outs get on your nerves you can close them and let it run out the mufflers.

 

You do not want back pressure, it is a term commonly mistaken for low velocity of exhaust flow. But you shouldn't have any back pressure issues with 2.5" x/h pipes are a good idea since the driver side exhaust is roughly 2-3ft longer from crossing over the transmission, so the x/h pipe will help equalize the velocity and keep the ECU happy.

A CAI, LT with true dual 2.5" x pipe and a good tune, will dramatically change how your truck drives compared to stock not only with power but also increase you mpgs 2-3

 

From my understanding long tube headers are a no go in California!

 

I read most shops don't care about the visual aspect of the longtubes, but High flow cats are illegal. You could have the exhaust shop save and remount your stock converters or find a shop that just checks the smog.

With a good tuner and cats you shouldn't have any problems passing, but I understand not wanting to try and cheat by the system.

Worse case get some shorty headers they will still give you 10-15 rwhp/tq over stock but the longtubes will give 20-25

 

I don't mind spending 200 or so on some used shortys but is it worth it to get them over stock?

 

I don't know where you got your info from 69camaro but in California visual is a big MUST to pass, if the cats aren't in the stock location they will fail you. And many shops are now wary of willie nillie just passing anyone because CARB is cracking down and revoking smog tech's licenses for illegally passing people. And IMO the shorties aren't worth the price. Not sayin thorleys are the end all be all, but for me they're the best option.

 

anything you put on your truck that does not have a CARB O.E. number will fail a smog test. gutted cats will fail a smog test every time. if you make your cats bolt in they have to be the OE parts. i still think that may be questionable to pass the visual test but im not 100% on that.

had the shortys on my truck for a while. the edelbrock ones actually. i didnt feel a bit of a difference. in california they now plug into the OBD 2 port and can detect any PCM changes to your truck. i was just talking to my buddy who is a STAR certified smog tech. its very tough to mod a cali vehicle and pass smog.

 

California is ******* ridiculous...