catylitic converter flow

[IndianaVX]

sigh......just a queston, if anyone knows, but is there a certian amount of flow that needs to be taken into concideration when replacing the cats??
i will be more specific.....is there a specific amout (cubic feet per minute, for example) of exhaust that needs to be concidered when replacing the cats???
the dealer is saying he doesnt want to put a cat on there that may do damage because its too constrictive, or wont handle the exhaust flow. he is telling me that if the wrong cat is put on, i could bend valves, and tear up the engine.
so what im looking for, since i cant get it from him, are some numbers to ask some of these supplieers what the specs are on the cats they are selling. (does that make sense??)
its getting rediculas, really, it is....

thanks for the help, as always...........

[tom4bren]

I'm no expert but my humble opinion is that the less restriction on an exhaust, the better (that's why headers improve performance). I'd look for the highest flow cats that will fit in the space available.

Since I'm no expert I thank my lucky stars that there is a guy in my town that I trust. I'd never take any of my cars to a dealer for exhaust work (unless under warantee). This guy is a great welder and does nothing but exhaust even though he works at a tire shop. I'm only saying this to suggest that you get a second opinion from someone who knows what they are doing. Your mechanic seems focused on what can't be done rather than what should be done.

[IndianaVX]

Gulp....my mechanic IS the dealer, the cats are under warranty. and i think that warranty may be the problem, instead of the solution.

Ahhh, i remember the days i too had a mechanic that i trusted, that is till he started all this mess with my truck before the dealer got it....

thanks tom, i appreciate the reply..

[etlsport]

there IS point where too much flow will start to result in a loss of torque... i would try to PM Morgan-Tec about this, he knows the 3.5L very well and also knows his exhaust.. from my experience hes been very helpful about answering questions

[tom4bren]

ETL, I stand humbly corrected.

[VCrossfan]

If you PM Moran-Tec ask him if These's would work...

[Kenny]

I would tell your "mechanic" to take a few lessons from pros and not be scared to ask other exhaust specialists the stuff they really don't know anything about. I mean, I hope they aren't installing the cats if this is the ignorance they are proclaiming to you - I'm picturing them installing the cats with a propane torch and pipe solder wondering why the pipe isn't getting hot enough...

Basically, get an "SUV" or "Truck" universal cat (or the Isuzu ones listed above by VCrrossfan) and you're fine, it'll be sized robust and larger pipe ends.

If you try and stick on a "car" universal cat with a 1.5" or smaller pipe end, then I'd be concerned...

Good luck man, and keep up the patience.

NOTE: high flow cats will increase exhaust volume, but probably not all that much with that monster stock Isuzu muffler...

[IndianaVX]

Thanks kenny,
well, i finally got some numbers, but i dont know what it means, and i may not matter anyway. the service manager said 3.5" pre converter, 1 pound exhaust back pressure on low side.........whatever.
so anyway, i asked today, what i need to look for, and the guy said they have decided to use the magnaflow cats that i had brought to their attention, and you, kenny, brought to my attention. but they couldnt find any anywhere. i called him back in under 10 minutes with a phone number, and a order number from a company, (i posted in the other cat thread) and made sure they were in stock, and they were. magnaflow 50000 series, same as yours kenny, but not all bling bling stainless.....lol....just black lookin.
so things may be looking up, i didnt get a call back, and was working too late toight to call him tonight.
Vehicrossfan, i havent called, but i saw ALOT of ads similar to that, and when caled, was told they dont have a listing.
im no gear head, but i had atleast heard of magnaflow before all this, so that means something.....lol
im not sure what brand that was you posted, but i would suppose they would work also.

thanks guys

[MrCrowley]

I hate to jump in late, but I would be afraid of ANYONE who thinks a restrictive exhaust would actually bend valves, etc. Last time I checked, air was compressible. Even a restrictive exhaust cannot generate extreme pressure enough to deform metal. Even completely blocked, the engine would not perform any revolutions once the exhaust pipe is pressurized. An exhaust seal would blow before pressurization great enough to bend valves occurred. What is a "jake brake" someone might ask. This device actually restricts exhaust flow which provides this same backpressure we are discussing, which then retards the revolution of the engine, to decelerate a vehicle. This is the stuttering Da Da Da Da Da Da noise you hear when a dump truck, tractor trailer, etc is slowing down. A restictive exhaust will do nothing more than "bog" your engine, and retard its revolutions. Several GM( ) cars have a problem with crap blocking the ceramic honeycomb in the cat. They merely run like they have a clogged fuel filter. I misdiagnosed one for that reason as the symptoms are identical, plus this particular car had 90,000 miles with never a filter change- go figure. Idles great, bogs down when the accelerator is pushed more than 1/2 throttle, or when the rpms are up. No known bent valves have occured to my or sevral knowledgeable friends.

None of this is a direct relationship to your issue, but when dealing with people with a lack of knowledge in physics- especially your mechanic, "Be afraid, be very afraid" lol. I would probably go somewhere else and deal with someone who seems to know more about these systems. Of course gasses need to flow out of the darn thing, and unless you actually choose to install something MORE restrictive, which is never the case. Why would anyone talk about less restrictive cats to a customer? Are there secret societies driving around with tiny riding lawnmower sized cats meeting in the woods at night? We are always looking for less restrictive cats. Why the heck would anyone go out of their way to put on something MORE restrictive? Hell, even if you did, no mechanical devices in your engine would be damaged at all. You would just lose power, and engine efficiency.

This person should be telling you that of all the options he has produced, if any, how the flow should be the same as stock or greater. The only real hair splitting you should be dealing with is how much catalyzing and earth friendliness your new higher flow converter, giving you more power, still gives the gas escaping your tailpipe. How about just buying a high performance cat, and just having that installed?

When I have to deal with mechanics, I always remember what a buddy of mine told me once. To claim superiority during a certain situation, he stated, "I was a mechanic for eleven years". My reply was, " and I was smart enough to NOT be a mechanic for eleven years". Good luck with whatever happens.