Semopar Forum

**Redtruck-VA** · 04-24-2011, 05:59 PM

Mark, it is hard to say for certain, but my guess dumping the OEM cat will make good gains for you. Do you have 2-1/2" inlet and a 3" outlet? If so, then you have several options. You could use the Magnaflow style "Y" pipe in place of the cat and install a 3" in/out single cat further down the line. Or headers and run dual cats, still using a high flowing "Y" pipe to take it back to a single pipe. Or maybe true duals if you have the room. I ran one of my chevies with only a cat and no muffler. It was piped all the way to the rear and sounded good. Just climb under the truck and start figuring what you want. More than likely your gas mileage will like whatever you do.

**txbass06** · 04-24-2011, 08:03 PM

Pretty sure it's 2 1/2" in. I know for certain it's 2 1/2" out back of the cat. I'll get under there and take a look tonight. The plan is LT's, Y-pipe into a single hi-flow cat, cutout, then probably a 3" dumped bullet

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**Redtruck-VA** · 04-24-2011, 08:14 PM

Pick your parts and go with it. With LT's you should be able to gp 3" all the way to the muffler. The 03 OEM cat flows very well and they are available used.

**Redtruck-VA** · 04-25-2011, 08:45 AM

Update,
ok I'm not happy with the size of the OEM cat (6" diameter) this is a real disappointment because I have been planning on using them for some time. But I really don't like how tight they fit. The location is good, just above the cross member, but tight. So I ordered a pair of 4" diameter cat for a #6000 vehicle. This ought to be good.

http://www.summitracing.com/parts/MPE-59959/

Did I mention I'm a real pain in the ass when it comes to fit and finished.

ORT · 04-25-2011, 10:26 AM

Hopefully that cat will perform better for you than the stocker would anyway. I tried going back to stock cats at one point after using high flows bc I had heard some talk that the stockers actually performed better. It wasn't the case at all, I lost a couple tenths in the 1/8 by going to stockers. Put high flows back on and got the couple of tenths right back.

**Redtruck-VA** · 04-25-2011, 11:02 AM

Jason,
I hope I didn't screw you up with the comments I have made about Hiflow cats. I thought I would experiement a little last year when I was installing the wideband and kill two birds with one stone and installed what I thought was a Hiflow cat and lost a couple tenths. The cat looked good as it came with two o2 bungs built in. But now I believe this cat is a standard universal and not a Hiflow. So any statement I have made about OEM cats out flowing the Hiflow was in error. When this cat (Hiflow?) was installed I lost about 2 tenths in 0-60mph runs. I am a big fan of OEM cats. But with the two new Magnaflow cats going in I'll have peace of mind as I will never have had the chance to compare them heads up with the OEM cats. But these two will surely out perform a single OEM, so all is good.

**Redtruck-VA** · 04-26-2011, 09:46 AM

Gentlemen, I got the tracking number for the new cats and they will arrive tomorrow. This is actually a day sooner than I expected. I am so ready to finish this up.

**Redtruck-VA** · 04-27-2011, 07:20 PM

Ok, it's 7pm and I just got the cats delivered, first thing in the morning I'm getting some welding done and I'll have Red back together. I'll post up some video's to share what it sounds like. These mods are fairly simple but damn it seems I have a bit of a time getting them finished. All is good.

**Silverbullet08** · 04-27-2011, 07:50 PM

sweet! im about to pull the trigger on my exhaust

ORT · 04-27-2011, 08:22 PM

Originally Posted by Redtruck-VA

Ok, it's 7pm and I just got the cats delivered, first thing in the morning I'm getting some welding done and I'll have Red back together. I'll post up some video's to share what it sounds like. These mods are fairly simple but damn it seems I have a bit of a time getting them finished. All is good.

Get those things on so we can hear that exhaust!