Catalytic Converter Option For Forced Induction Rigs

[turbocruiser]

Fine folks, thought that I would share another morsel I recently researched and went with in the hope it helps others. I recently started throwing some codes for catalytic converter inefficiency. I cleared the code once writing it off to wet gas or whatever but when the code returned after another couple hundred miles I thought that it was time to replace the cat.

Informationally: I originally had a Magnaflow 3" Hi-Flow catalytic converter mounted in front of the Man-A-Fre 3" ceramic coated exhaust I got several years ago which actually came with a Magnaflow 3" Hi-Flow muffler (at least at that time). In front of the cat was simply 3" ceramic coated pipe (to match the exhaust's coating) up to the turbo's down tube. I basically just copied Man-A-Fre's system which was "cat-back" and made it into a complete system with matching components from Magnaflow on both ends and the same type of tube and the same type of coating. It works wonderfully well for FI exhaust needs.

Anyways, when this cat threw those two codes after about five year's usage (50K miles) I was going to go ahead and replace it with the same thing from Magnaflow but a minor modification to that particular part number (an "air-tube") caused me to call the tech line at Magnaflow and ask if that particular part number was still the spec for my rig.

Turns out that although the air-tube made no matter (because they basically just cap it off) there is now a much more appropriate option for our rigs for Forced Induction in general and for Turboed Forced Induction in specific. Magnaflow is now making a "HM" line of cats that claim to have much higher levels of the Heavy Metals that cats use so that they last longer and so that they are able to withstand higher heat from exhaust and also able to withstand much higher and much faster fluctuations of exhaust temperatures. They also apparently flow much freer than the equivalent non "HM" versions! Although many of these features would help with supercharged rigs, they really help with turbocharged rigs according to the tech at Magnaflow.

I went with a 99009-HM cat which is their 3" Hi-Flow, Heavy-Metal version but they make this same cat starting with the 9900 number and different endings that designate 2.5", 2.0" etc. Surprisingly the HM version of the same cat was only $30 more than the regular version and according to all the advertising will last twice as long! All together including the installation I paid $193. Anyway, just in the hope it helps others who have to replace their cat.

Product Search Results - MagnaFlow Catalytic Converters by Car Sound

 

[Miescha]

So I have a couple of ignorant questions if you have the patience for ignorant types. I've searched around a fair amount and see lots of threads and stuff in the FAQ about exhaust and cats and mufflers, but nothing that answers my general questions.

My '96 exhaust seems just fine - no codes, no smell, no noise, no rust = no problems.

However, I banged the forward facing portion of the y-pipe (just before the bend back toward the cats) recently and in the process broke the bracket at the rear of the cats. Apparently, I also loosened one or both connections at the top of the Y-pipe as I now have a minor exhaust leak that results in me hearing a 'gurling' type sound under load (tough to hear, but its there). I've also noticed a minor loss of low-end power, but that could just be age (me or the cruiser, or both). Recent major tune-up made no power differences, and I'm now thinking it is maybe the exhaust leak.

So, I've got the flange/seal/gasket for the y-pipes and I just need to drop them now and I can fix the bracket while I'm at it.

But here is the question, is there any benefit to going with larger exhaust - say 3" instead of the 2.5" stock stuff? Likewise, is there any benefit in going with the MAF headers? A new straight cat? a different muffler?

My truck has no SC and probably never will (I'm the idiot who sold mine without ever taking it out of the box several years after I purchased it new from my dealer).

I'm not looking to throw money at a non-problem, I'm really just wondering (if I'm going to spend the time to drop the y-pipe and fix the rear cat bracket, maybe I should just put new stuff back - especially if it is better anyway). So really, the time is the most expensive part for me (if I could find a reliable shop, I'd just take it to them).

On the cost issue, how the heck did you get that done for so little? I asked several local shops to just drop the y-pipe and replace the gasket/seals/flange things and then do a quick fix on the broken bracket and they all wanted $100 or more.

 

[turbocruiser]

I don't think that the larger pipe will make much difference without Forced Induction. I do think that a single straight high-flow/high-performance cat will help with performance vs. two busted up broken up original cats and I always think that a freer flowing muffler helps. I think the reason the cost was so low was that they simply cut the old cat out and welded the new cat in; there was no pipe work or bracing or brackets that needed work it was just in and out. HTH.

 

[fzjconvert]

Thanks for the info TC I will add this to my list of parts for my future turbo build.

I have a question though.. Have you ever noticed a lack of back pressure for engine braking using just one cat?

Dave

 

[turbocruiser]

Thanks for the info TC I will add this to my list of parts for my future turbo build.

I have a question though.. Have you ever noticed a lack of back pressure for engine braking using just one cat?

Dave

No, I never noticed any. HTH.

 

[fzjconvert]

Very cool thanks!

 

[turbocruiser]

Very cool thanks!

You bet, I should clarify though that the cat shouldn't really be producing back pressure as such - that should be a function of rings and valves more than something specific in the exhaust that causes that. HTH.

 

[fzjconvert]

Hmmm? I always thought that exhaust has a role in this. And that is why some do not recommend having too much of a free flowing exhaust. I do realize that rings and valves have a major role in back pressure but I alway thought exhaust did too. You know I have never asked anyone. Who says you can't teach an old dog. I'm feeling like this right now Guess I am going to go sit in the garage and ponder this with my friend

dave

 

[turbocruiser]

Hmmm? I always thought that exhaust has a role in this. And that is why some do not recommend having too much of a free flowing exhaust. I do realize that rings and valves have a major role in back pressure but I alway thought exhaust did too. You know I have never asked anyone. Who says you can't teach an old dog. I'm feeling like this right now Guess I am going to go sit in the garage and ponder this with my friend

dave

No I'm not saying that the exhaust system doesn't develop any backpressure - the mere fact that yer forcing fumes from the front of the rig to the back of the rig and through a tube causes that to an extent - I'm just saying that cats are not designed to develop "extra" back pressure and that there isn't one thing within the exhaust system that is "supposed" to develop "extra" backpressure but in reality the sum of the parts does that (the length of tubing, the diameter of tubing, the cat, the muffler, the resonator etc.). I'm sorry if what I wrote was confusing, I'm just saying you don't need to worry about reducing backpressure to a harmful extent by placing a high flow/high performance cat on. In my case all the backpressure I need for proper valve operation and engine operation comes from the turbo and in your case all the backpressure you'll need will come from staying w/ stock diameter tubing, running a cat, running a muffler, etc. HTH.