Nice article imperial

 

Yes it is a good article. But it implied that a ceramic core cat is just as good as a metallic core for an NA car. This would be an incorrect generalization. The best indicator of whether a cat (or any exhaust component for that matter) will help or hurt HP is how well it flows. This is why aftermarket headers and straight-thru mufflers increase HP output on our car, because they flow so much better (i.e. are less restrictive) than the stock components they replace.

The most important info in the article is the flow bench data on the second to the last page. You can see by the graphs that the ceramic core cat flows only about 2/3 as well as the metallic core. Using David Vizard's calculations to convert flow into loss-free HP, the Magnaflow ceramic core cat is loss-free up to 138BHP while the metallic core is good up to 224BHP.

If that same ceramic cat were to be installed into an otherwise stock 160BHP tC's exhaust, back-to-back dynos would show a small loss of WHP, because the cat would now be the most restrictive part of the exhaust system.

A dyno with the metallic core cat would show the same WHP numbers as stock because the metallic core is not restricting exhaust flow (as the stock manifold & muffler are.) In fact this cat could be installed on any NA or S/C tC putting out up to 224 HP at the flywheel and not restrict exhaust flow enough to reduce power.

Not that you can't use a ceramic cat if NA, you just need to buy one with higher flow. This may mean buying one with larger inlet/outlet - for example 3" ceramic cat - and using bell adapters to fit it to your 2-1/2" exhaust pipe. The larger ceramic will probably still be cheaper than the smaller metallic, and work just as well.

I haven't shopped for aftermarket cats but I would recommend not buying one unless you have the flow bench numbers on it and can be sure it won't restrict your exhaust setup.

 

You can feel free to correct me if I'm wrong, but I'm pretty sure the article didn't imply anything. They mentioned that the ceramic core is ALMOST as good as the metallic core, IF you're not building the engine.. i.e. only upgrading exhaust.

You shouldn't have a cat on a built* NA Motor.

 

For a track car, no you can just put on a test pipe. For a street car - built motor or not - there's no reason not to put on a cat with suitable flow.

Cats help to muffle exhaust noise, help maintain low-end torque, and as mentioned earlier keep your car from becoming a rolling stinkbomb.

 

Yes, but if you're going to BUILD an NA motor.. you're going to want every last horsepower out of it. You're going to sacrifice a convenience for power.. and as I said, yes, for a street car, cat's are good. But the point of the article was saying there isn't much of a difference power wise.. on an everyday car with maybe some bolt ons.

 

I'm not understanding your point. You won't lose any HP on any setup with a cat - even on a track car - as long as the cat can flow equal to or greater than the maximum exhaust flow at the rated maximum power of the engine. Within limits of course - I'm assuming we're not talking about a Bugatti Veyron.

For an NA tC the racer may choose to bolt-on a test pipe, usually because the pipe is cheaper than a hi-flow cat. But there will be no sacrifice of HP if a cat with the correct flow is used.

 

forget it.