3" exhaust after cat?

[Ryan S.]

Was talking to an old truck driver guy today about diesels, pulling, etc. Ended up talking a little about cruisers too. He said to add a 3" pipe after the cat to gain some power. Claims this doesn't change backpressure and helped on his 95 Ford. Any thoughts on that?

BTW, he said he has seen Perkins and John Deere diesels in cruisers. Never heard of a Perkins before, but this guy has been into diesels for 50+ years.

 

[NocalFJ60]

I don't think it would be worth doing. You could actually lose power making it alittle bigger in diameter. But I think the power gain/lossed here is very small and probably not noticable.

John Deere cruiser...cool

 

[Corbet]

I would just make sure that what ever is behind the cat is the same size as in front. No bigger no smaller.

 

[FL cruiser]

You can use a smaller pipe after the cat than before it without any decrease in performance. The exhaust temp cools in the cat and muffler, decreasing the volume of the exh gas, therefore reducing the need of a large pipe.
Here's an article on it:

http://www.boyleworks.com/ta400/psp/exhaust.html

 

[Mike S]

When talking F engines, power gain is a relative thing. Even a 5% increase (not likely with what you are suggesting) would not really be noticeable.

Beyond a good tune, the best that can be done for a 'stock 2F' is the have Jim C rebuild the head with better valving and rebuild your carb. About $700.

M

 

[Tinker]

FL -
What do you think happens in the cat to cool off the exhaust? The FSM test for cat performance states the output temp of a working cat is significantly higher than the input.

The stock 2F is asphyxiated & constipated by design. I don't think you'd burn a valve if you cut the pipe off after the cat - it's the bottleneck. But I also don't think you'd gain a lot of power.

On the other hand, a good, equal-length header is generally considered to improve performance.

 

[FL cruiser]

I was thinking about the heat disipation through the metal casing just like a muffler.
But I wasn't thinking about the conversion done in the converter and hotter steam vapor exiting.
I'm probably wrong. What I get for assuming.