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Hi-flo cats or No cats?

3K views 30 replies 13 participants last post by  nmaier2201 
#1 ·
I just got my exhaust finished. Its custom built 2.5" w/Hpipe and straight through hooker max flow mufflers. This set up is super quite. Its a little louder than stock outside and somehow got quieter than stock inside. All I plan on doing is: I have a shifter on order from pisunoff, K&N dropin, and will be getting a W4M tune. With the tune will I get more power with or without hi-flo cats. Also, without cats how is the interior exhaust sound levels? I live in florida and emisions is no issue.
 
#2 ·
Even though emissions are not regulated in our fair state right now, I suggest you run high flow cats. The car will retain a nice exhaust note, pollute less, the power diff is negligible, no fuel stink, and you'll be on the right side of the line when emissions standards come to Florida. With so many car enthusiasts yanking their cats, it's a matter of time before they start regulating emissions, then annual inspections, etc.
 
#3 ·
Save the smelly exhaust. Run high flow cats! They flow just as well.
 
#4 ·
I went with highflow to play it safe, But sometimes I wish I went catt-less for the extra 5-8hp.

But I was affraid of smell, most guys say it doesnt bother them. If you leave the car running in one spot for 1-2 minutes it kinda smells like ass in the car after is what I noiced on some of my buddies camaros.
 
#8 ·
Random Tech makes some high quality units at $700/pair. They are a direct bolt in replacement for the stock units.

Magnaflow makes some that are less than $100 a piece (see Autopartswarehouse for example). These have 2.5 inch inlets and outlets but would need to be welded in. Magaflow may make some bolt-ins but I did not search that far.
 
#11 ·
The Random Techs will operate with no error codes (DTCs). In that sense they are 100% street legal.

The others tend to trigger DTCs. The DTCs are of no consequence if you are going to tune out the secondary 02 sensors anyway. The others, as far as I know, effectively eliminate the no-cat smell. Finally, the others (Magnaflow for example) are what comes from the header makers (e.g. Kooks).
 
#13 ·
Thanks...I found the Random Techs online for $421...

http://www.jdmhub.com/index.php?route=product/product&product_id=237882&path=2_1114_1115_85015_85016

The site says they are for the '04-'05 CTS-V 5.7L.....will they work on an '06? Thanks for your help!
Maybe. Random Tech only lists 2 units (left & right) for 2004-2005. GMPartsDirect lists the OEM cats for the 2004-2005 and OEM cats for the 2006-2007. GMPartsDirect does not give part numbers but the prices for the 04-05 units are identical with the prices for the 06-07 units even though the right side prices differ from the left side price by a few bucks.
 
#16 ·
$900 for just the cats? For a few hundred more, you can get high flow cats and headers that bolt right up...
 
#18 ·
I am going the random tech way for ease, as for headers, been there, done that with my Z28, enjoyed it fir a while, then got tired of smelling like gas all the time. The magnaflows just sound like more fab work than there worth, adding up the price of welding, making new pipes, and finding someone to tune out the rear O2's, it could get to be expensive too
 
#20 ·
I ended up going the no-cats route. I wanted headers, but there just isn't much room in there. So I landed some custom fabbed off road pipes from Ted. They almost fit like a glove and I'm super happy with them. You can tell the engine is breathing a little better with them off. yes it throws codes and yes you need to tune out the rear O2 to make it a real viable solution.... for me anyways... maybe not your cup of tea.

The smell? yeah the smell is different from the cold startup smell. I kind of like it, reminds me of pit lane. The wife? not so much... she keeps asking why my car smells like it's burning... I just tell her to relax baby, it's supposed to be that way... then I say well I bet if I got a Ron Davis radiator or a better Tstat or such it might help :) .....always gotta lay that path down for the eventual upgrade... it's called "managing expectations"

Oh yeah... NUKE THE WHALES..... j/k but running w/o cats could be argued that it pollutes a little more than needed.... but it's all in the pursuit of speed baby!
 
#21 ·
I ended up going the no-cats route. I wanted headers, but there just isn't much room in there. So I landed some custom fabbed off road pipes from Ted. They almost fit like a glove and I'm super happy with them. You can tell the engine is breathing a little better with them off. yes it throws codes and yes you need to tune out the rear O2 to make it a real viable solution.... for me anyways... maybe not your cup of tea.

The smell? yeah the smell is different from the cold startup smell. I kind of like it, reminds me of pit lane. The wife? not so much... she keeps asking why my car smells like it's burning... I just tell her to relax baby, it's supposed to be that way... then I say well I bet if I got a Ron Davis radiator or a better Tstat or such it might help :) .....always gotta lay that path down for the eventual upgrade... it's called "managing expectations"

Oh yeah... NUKE THE WHALES..... j/k but running w/o cats could be argued that it pollutes a little more than needed.... but it's all in the pursuit of speed baby!
I am trying understand how this strategy works. You get a Ron Davis radiator :thumbsup:, but the catless smell remains. So then, what's your next move ace?
 
#22 ·
more upgrades! :) If it smells hot then a radiator or tstat maybe will help! :) If not then you think of what your next mod will be... MAYBE those mods will help! some mufflers :) or a X-pipe! The sky is the limit. :) Then maybe a pair of better breathing heads and a cam! as long as you set the expection! Then when your mod list is empty you can just shake your head and say.... "well all these mods do have me getting 8mpg maybe I can't solve it after all. Maybe it's just the way the LS series motor runs"

:)
 
#23 ·
more upgrades! :) If it smells hot then a radiator or tstat maybe will help! :) If not then you think of what your next mod will be... MAYBE those mods will help! some mufflers :) or a X-pipe! The sky is the limit. :) Then maybe a pair of better breathing heads and a cam! as long as you set the expection! Then when your mod list is empty you can just shake your head and say.... "well all these mods do have me getting 8mpg maybe I can't solve it after all. Maybe it's just the way the LS series motor runs"

:)
Got it. So, how do we explain the RPM Stage V?
 
#24 ·
I need one as well... My thoughts are as follows. Tell her RPM takes your old trans in and sends you a rebuilt one... but if you wait until your trans fails... and it's ruined RPM doesn't want it. Therefore! the best thing to do is to get the RPM before yours fails and send yours in as a core charge. Then instead of being way behind on repair bills... you will have minimized the cost AND tell your lady this solution will not leave her (or you) stranded anywhere....You know you could go into detail on how rare the T56 M12 is and how much they cost from the stealership...getting a RPM Stave V is really the most economical thing to do!
 
#26 ·
A Maggie will push the smell out the exhaust before you can smell it :D
 
#28 ·
You cat queens crack me up...I had 4 built Cobra's all catless. The V is no different. I love the distinct sound of the off-road pipes and wouldn't have it any other way.
 
#29 ·
+1 to that.... I have gutted stock cans though... so it's not loud at all.



(when I say Gutted I just peeled em open and removed the fiberglass packing... they are not totally gutted.)
 
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