Correct exhaust size?
 

I'm looking for the stock exhaust size for my 87 r10 5.7L. Its getting pretty bad, so I'm going to replace it. I'm going to use this high flow cat (is it actually a high flow??) off of amazon. But for some reason, I was thinking the stock exhaust was 3" and not 2.5". Since its a single exhaust. Anyone see any reason I shouldn't buy this?

Amazon.com: Magnaflow 94006 Universal Catalytic...

Re: Correct exhaust size?
 

bump

Re: Correct exhaust size?
 

A good muffler shop wil have adapters to weld in no problem ;)

Re: Correct exhaust size?
 

2.5" pipe will flow 550 cfm. A 350 at 5000 rpm can flow maximum of 500 cfm at a volumetric efficiency of 1.0, which is an unattainable ideal.

2.5" is plenty.

Re: Correct exhaust size?
 

Rich,

How do you know this stuff? Hahaha good to know though. I have 2.5 x pipe.

Re: Correct exhaust size?
 

Rich, do you think a mild cammed 454 with headers can be hurt if 3" exhaust is installed??

Re: Correct exhaust size?
 

I don't really know, but I don't think so. A 3" exhaust will flow almost 800 cfm, and a 454 at 5000 rpm only flows 650 cfm, assuming an ideal volumetric efficiency of 1.

Then again, 2.5 pipe is not enough, and I think 3 is the next size up. I would use 3" on a single exhaust for a 454.

Re: Correct exhaust size?
 

Thank you sir. Now you speaka my langua.

Can anyone tell if that is what is known as a "high flow" cat? It would seem to be higher flow than stock, but I was just curious if it fits the "high flow" idea. Doesn't really matter, its going to be a lot higher flow than my half clogged giant old dinosaur from 1987.

Re: Correct exhaust size?
 

I'm also curious to this. I don't need them but wouldn't mind throwing them on to help with pollution and that horrible carburetor gasoline smell. But do they or don't they kill some of your performance??

Re: Correct exhaust size?
 

If you have foul smelling exhaust, you'll overwork the cat and it'll melt down into a solid lump and plug up in one trip. A properly tuned well running engine is required if you need/want to use a cat. A modern converter has virtually no impact on performance, provided it has not been abused.

High Flow refers to the design of the catalyst. Modern converters are a honeycomb design often called "high flow". A large brick of very fine honeycomb like ceramic is impregnated with metals and minerals that act as a catalyst to speed the breakdown of gasses in the exhaust. Air flows through the honeycomb passages virtually unrestricted. Earlier designs were a large chamber full of ceramic beads impregnated with those elements and were quite restrictive. These are the wide flat converters with a plug in them where the beads were added. Often called "pancake" style.

Re: Correct exhaust size?
 

The exhaust isn't what I would call foul smelling but just that usual gasoline smell you get with carbureted cars. I always thought it had that smell because there aren't any cats installed...

Re: Correct exhaust size?
 

In 1968, the feds mandated AIR pumps, and timing was delayed so the mixture was still burning on its way into the exhaust manifold. Together with the air that was being pumped in, that burned up the extra whatevers and cleaned up the exhaust. Also helped the cats along. Unless you are going back to an AIR pump and 4* BTDC timing and ported vacuum, the cats won't clean that smell up.

Re: Correct exhaust size?
 

They'll definitely improve performance, over stock cats. "High flow" ones, that is. I don't think this is what's called a "mini cat". Or a "high flow" cat. But like he said, its a lot higher flow than the old junkers like the one I have on.

Anything that's not a straight pipe should be some hindrance to flow. I've seen the inside of the new ones and they're not a straight through flow design. Granted I don't know if its enough of a restriction to slow down the flowing gas. But it sure looks like it should.

Mine's not foul smelling either, just the exhaust fumes are quite noticeable. They just smell like normal fumes. But when you stand in the right spot, they seem a little... much. I ordered it and I'll report back if the cat helps this, I'm making a guess that it will help some. But I'm replacing it because the truck is displaying typical symptoms of an impedance in the exhaust.