They are in, but what a pain in the tailpipe!

The headers fit just fine. It really helps to have a lift. The drivers side went on no problems and lined up perfect with the cat. We just had to cut the cat pipe .5" or so before the cap and weld on the flange provided with the kit. Stock plug wire are perfect for these headers.

The passenger side was not as easy. The collector flange ended up about 3" (toward the driveshaft) from the cat. No way to move it over without putting the headers in a bind and hitting the tranny heatshield. So the kitties had to go. If I would have stopped and thought about it, the headers are designed for the factory Y-pipe common to the 5.3 and 4.8 engines, the VHO has the dual pipes back to the muffler. the one that didn't fit was the one to the outside. Duh!

Of course, we had to add to the fun. The front right O2 was cross-threaded from the factory. We filed the threads back to life and got it in with a little finesse and prayer.

Now for the sound. It sounds absolutely wicked at idle. The truck actually has a slight lope to it. At mid throttle it has that classic no-cat tin can sound, but the FloPro keeps the overall noise pretty low with no resonance. At WOT it sounds pretty good! Some tin can effects and alot like an F-body, which makes sense but feels odd. I can also hear alot of air moving out the tip at mid & full throttle. No whistle just a hiss. I didn't expect this, but I'll get used to it.

And finally the performance. At low throttle, I can feel no gains and maybe a small loss. At mid throttle I can feel some gain. At WOT, oh yeah, I can feel it. It may be awhile before I get to the dyno or track, so I'll try to get out with the GTech and make some runs. The tires do spin a little more on launch. It is just hard to get out in this 100 deg heat and do anything.

 

Sounds good... did you install nickel chromes or ceramic thorleys? Do the connector pipes still come in pieces?

 

These have the nickel chrome coating. The package had the complete headers with small flanges that mate up with the collector flange on the header. There was also some bolts and gaskets for this connection. I reused my manifold bolts and bought new manifold gaskets.

 

Doesn't it feel good to punch it from 80-100ish??? I highly recommend the Thorley's for the Vortecs.

 

do these headers have the air fittings? if so, how did you take care of them?
for a regular 5.3 04 1500 4wd will these headers just bolt up or is there cutting and welding to do? and where and for how much did you buy these?

thanks
jerome

 

They do have the air fittings for egr, but what I did, like most people, is cut a piece of metal to go over the hole and bolted/RTV'd the piece down. This takes care of the egr.

You'll have to cut your y-pipe in front of the cats and weld the headers back up to the exhaust.

 

I installed the Thorley headers on my K2500 LQ4 with Dual exhaust. The only problem that I had was that the angle of the passenger side collector pipe and flange was kicked-up toward the floor pan too much. The installer had to fabricate a S pipe. See the pictures on my web site.

Steve

 

Collector pipe from drivers side didn't reach all the way to the flange on pass side-had a piece welded in-line to fix it. No leaks and no loose bolts at all.