Hi-Flow Cats
 

I have a 93 Rx-7 with 44k miles on it. Parts include HKS downpipe, Greddy EVO Exhaust, Apexi Fuel managment, Greddy SM intercooler, K&N airbox, Greddy hard elbow peices, and I have a HKS BOV coming. What should I do next for more power? I have the stock cats in my car, and I want more tone to my greddy exhaust. Will Bonez cats give me a lot of power? will they brighten my exhaust? Are they raspy at all? Help me guys...thanks

Also what about underdrive pulleys? are they good or bad?

engine pic
 

just a picture

The hi flow cat will help, have you changed your fuel pump..and you can get a boost controller too...underdrive pulleys will help too...

the stock cat is a "factory" high flow. you won't feel a noticable power gain...you might see a slight one on a dyno.

Oh, and make sure to also change your radiator for a reliability mod, I did not see that on your list...

ok so the hi-flows dont give you any more power? do they make the exhaust note sweeter? should I just get the Apexi commander for my boost? I did not to a radiator, and I have a new fuel pump but have not installed it.. will the fuel pump make any difference?

does the new radiator make a BIG difference?

for reliability yes, lol

the radiator if for reliability just so you dont ruin your engine when your stock one cracks, it also keeps your water temps lower, the fuel pump helps you when you try to boost at a higher than stock boost level and the high flow cat will help it is better thatn the stock cat.

1) high flows will give you some power and they certainly make the exhaust note sound much better.

2) A radiator is a good reliability mod. If yours looks like the plastic is going to crack any day, then get a koyo or fluidyne.

You should see a big gain in a high flow cat, If you go 3" all the way. You have a downpipe so its an excellent add on. For one its about a 1/2 in diameter bigger than stock and will allow you to add more boost, mind you have the proper fuel mixture for it. And it will have a deeper tone to the exhaust. Since you have an apexi, I would just tune it for a midpipe.

I just put in a Hiflow Bonez yesterday. I had a stock cat punched out, so basically a 2.5 inch midpipe. I got sick of the smell, so I got the Bonez Hi flow Cat. Let me tell you this, I still boost 12 psi with the same settings I had before, and I feel NO noticable difference. So I would say from my experience, the Hiflow cat flows almost as good as a 2.5 in midpipe, without the NASTY smell.

An efini y-pipe would be a nice addition for you.

Going from a stock non-modified cat to a hi-flow like the Bonez should yield a noticeable increase in power, especially in the midrange. The fuel pump will make no difference unless you go to larger injectors.

go single, then you have an excuse for a midpipe..... :)

sorry, i just had to say that!

There is some misinformation in this thread. Check my site for before/after dynos with a highflow cat. It gets you about 10 hp from about 5500 rpm.

which is not a lot, who is to say a new STOCK cat wouldn't yield the same results?

I'm with 93BlackFD on the notion that "hi-flow" cats are much over rated.

I have seen a few "aftermarket" cats just simply melt.

Also, most of these supposed HF cats are ones that u can get from a muffler shop for $150 installed granted that u provide a MP.

Sure the stock main cat has a longer cat material, but doesn't the greater width allow for a larger surface area which in turn allows for a better flow design than the "hi-flow" cats?

hmmm the plot thickens.So then the high flows are really a bunch of bullshit.
glad I didnt pick one up then.

How can you say 10hp is not a lot? What's next, are you going to tell me an intake only gives you 5 hp, a catback only gives you 15 and a intercooler only gives you 15? It all adds up. Somebody here mentioned the efini y-pipe. Now if you want to talk about "not a lot" that is where it is at. $225 for about 2-3 hp makes a HF cat look real nice. IMHO a HF cat is a great alternative to a mid-pipe, which is loud, stinky, won't pass emissions, creates boost problems and decreases low end torque. I think for around $200-$300 10hp is great compared to the thousands we spend on other things that don't do squat. That’s more hp per $ than most mods.

With that mentality I'd say stay stock or go all out with a 3 rotor and 2 T78s. Leave the exhaust stock though and don't upgrade the intercooler;)

As for compared to the stock unit it has 2.5" piping. The cat itself might be great but I have seen no data to back that up. Perhaps replacing just the pipes might be great but my site offers graphs that show for a fact that a HF cat adds power.

As for HF cats melting, this is true. They are often of lower quality and when the air pump is removed or doesn't function normally (like when a PFC is added) the cat's life is shortened.
dis1

I don't think anyone has CFM numbers.

I think that if anyone feels that it "works" it's probably has to do with just replacing an old clogged up original cat.

Not to mention the weight savings... so you get a deeper exhaust tone, 10 or 15 more rwhp depending on your mods, and save about 20lbs in weight. sounds like a good deal to me ;). Plus you replace a 10 year old beat up cat that it probably not flowing very well to begin with.

It's laughable to see hi-flow cats turn into LO-FLOW cats after a few boosted runs and/or running a rich mixture.

Factory main cats can take more beating than that.

My stock ones still passed smog when it had 210k miles.

It flowed good enough to so that I saw boost spikes at 16psi.

There are many solutions that can tune and tone down the decibels and frequencies much better than implementing a "hi-flo" cat.