Measured against no cats of course... How much of a difference are we talking?

 

Less restrictive than a 3" open pipe.

Rich

 

"Less restrictive than a 3" open pipe."-rskrause

So a high flow cat is less restrictive then a straight through 3" pipe?!? How so?

 

Because its larger in diameter than a 3" open pipe.

Buddy of mine was running no cats on his 98 T/A. Denny at Mufflex talked him into trying dual 3" Carsound cats. The car ran a 1/10th faster with the cats. I run dual 3" Carsounds, and drop them out and replace them with 3" Borla XR1 shorties for the track (running heavily leaded C16 fuel) and we haven't noticed any significant differences in HP.

I think Lingenfelter claimed less than 5HP lost with factory cats on his 383 LT1's.

 

What really matters is the cross section of the catalyst. The more area
of the cross section, the more flow. You can have 2.5" and 3" inlet/outlet
cats with the same cross section. Most of the larger body cats are similar,
like Carsound, Magnaflow, etc. Avoid the mini-cats. The other advantage
of cats is they eliminate that raspy sound of the exhaust.

 

I bought a Dynomax bullet muffler to go in place of may high flow Magnaflow cat. I can switch between the cat and the bullet in less than twenty minutes cause I have a 3 bolt flange on one end and a ball flange on the other end.

The bullet muffler kills the unpleasant raspy sound that you get with a straight pipe just like the cat.

I can feel a slight SOTP improvement with the bullet muffler, however I am going to the dyno in a few weeks and I am going to run both the cat and the bullet to but the issue to bed once and for all.

 

I have almost the same set-up as wrd1972, but I have a Carsound high flow cat and also a 3 inch straight pipe that I can bolt in with the 3 bolt header flange/ball flange setup. I have to say that I prefer the sound of the straight pipe, but like the low end torque and less smell from the cat. I don't actually feel much of a difference up top with the cat.

 

Just out of curiousity, what is wrong with the mini-cats?

 

Thanks guys. I just had a Magnaflow high flow cat welded up.



Now I need to re-torque those header bolts. Am I going for a spec here, or just tighten?

 

Just tighten them, its pretty hard to get a torque wrench in there.

 

Oh... yeah, right.

 

What I do is torque one reachable bolt to spec. Then, I put a box end wrench on that bolt and "feel" how tight it is. Get the other ones close and your set.

Ryan

 

Nothing is wrong with them unless you are after the most flow you can get
through your exhaust system.

I'll give you an example. Take a mini-cat with a 3" in/out and a 5" catalyst
cross section. The area of the catalyst cross section is 19.6 square inches.
Now take a 3" in/out 4" x 7" oval carsound catalyst. The area is 24.6 square
inches. The area of the carsound is 25% greater than the mini.

Now if that mini is really more like 4" cross section then the carsound will have
95% more area.

 

Just curious, my choices were kind of limited on the drivers side due to bad clearance everywhere (torque arm, fuel lines, brake lines, floor board) and the mini-cats were my best option.

 

I took a peek inside my carsound cat. Had two bricks of catalyst at entry and exit, about 2.5 inches thick each, and looked like a window screen. Didn't look too flow friendly to me, at least not as a 3" pipe through it ???