mhk

Like the question states: Would high-flow cats make any difference over the stock cats? If so, what brand would be best for a GT? Magnaflow, bassani?

Thanks

LEO_06GT

I don't think so. I say it's all or nothing. If you want to go catless do it but don't halfa$$ IMO.

DarkFireGT

Everyone says no, but if they'd don't flow any better than stock, then how come they're louder than stock?

mhk

I'm worried that if I go catless it will be too loud.

LEO_06GT

If your concered with it being to loud then I'd suggest just leaving it as is and changing out the axle backs if you haven't already done so.

mhk

Yes, I already have magnaflows. Just want to get some more flow going instead of the stock cats.

Thanks

281GT

High flow cats do flow better than the stock cats. The difference isn't extremly significant but there is an improvement.
I have long tube headers with an x-pipe and high flow cats along with the stock mufflers. At idle and light throttle it sounds almost the same as stock but when I "get on it" the sound is different than stock and is significantly louder. Some of this is due to the long tube headers but I'd bet most of the sound increase is due to the high flow cats.
I'd also like to point out that the stock mufflers flow as well as most aftermarket mufflers, therefore the only reason to swap the muffers would be to change the sound.
As always sound is purely subjective but I love the way my car sounds and I have none of the drone that many with aftermarket mufflers have experienced.

mustangbrad01

Don't waste your money on that junk. Either keep it factory or switch to o/r. Depending on your states emission laws, or if you wanna change back when it's time, get the o/r setup. I can feel less torque down low on the o/r pipes though.

m05fastbackGT

No offense, but I believe that long tube headers, would provide more of a significant difference over aftermarket high-flow cats..

As a matter of fact..Anderson Ford Motorsport, did an 05 exhaust shootout back in October 2005. Which consisted of the stock exhaust, followed by the MAC high-flow catted Prochamber, BASSANI X-pipe w/high-flow cats, and finally the MAGNAFLOW X-pipe w/high-flow cats..And the results were

Mac high-flow catted prochamber - 295.2 Max HP 318.2 Max ft lbs Torque
Bassani X-pipe w/high-flow cats - 294.6 Max HP 320.2 Max ft lbs Torque Magnaflow X-pipe w/high-flow cats-293.9 Max HP 318.8 Max ft lbs Torque
Stock H-pipe w/factory cats - 292.8 Max HP 316.9 Max ft lbs Torque

According to Anderson's shootout results ! there was no significant difference in flow, between any of the high-flow catted pipes, over the factory catted H-pipe..Unless you consider a 2.4 HP difference, as significant lol.

Therefore, as far as I'm concerned. Unless your just going for sound !
high-flow cats, really don't offer much benefit over the factory cats..

Glenn

how much are the high flow cats selling for?

281GT

No offense taken. Thanks for posting actual numbers. It certainly clarifies the issue. While high flow cats do appear to flow slightly better than stock cats I would say that if one were to change only the cats the performance per dollar value just isn't there and not worth doing.
In my case I had no choice as it's basically impossible to use the stock cats with long tube headers. I agree that in my case practically all of my gains came from the long tube headers.
In regards to the original poster's question, I would agree that replacing the cats alone isn't worth the money.
It's been said before but I'll reitterate that on the S197 GT cars the only significant gains in the exhaust will come from long tube headers.

mhk

Ok guys, thanks. I guess the stock cats are pretty high-flow already. Might go with an o/r pipe after all. I don't have any drone now, is there a chance that i'll get a drone if I go o/r with my existing magnaflow axlebacks?

89Trooper

There's a chance it'll sound like crap.

I have Flowmasters with the stock H-Pipe and love the sound. I put on an O/R H-pipe and couldn't get the stock one back on fast enough.

DarkFireGT

What are you going for? Sound or performance? It appears the gains with high-flow cats are 2-4HP (if we can trust those numbers) and 7-10HP with off-road pipe. If you're mostly going for sound and have emissions testing, then I would go with the high-flow cats. If you don't have emissions testing, you might as well go with the off-road pipe. But either high-flow or off-road, you'll definitely get a louder set-up.

As far as drone and such, you have to match the off-road pipe to the mufflers. I have an off-road x and magnaflow straight throughs and the drone and trumpets are very noticible. On my other car I have off road h and Violators and I have no drone or trumpets, and the off-road pipe actually got rid of the bit of drone I had with the stock mid-pipe.

m05fastbackGT

Perhaps It's due, that their smaller in size than stock. Or it could also be due, to being located further downstream the pipe area as well

bob

Does anybody have the flow #'s for the stock cats? If they flow more than enough for the simple upgrades people generally do, then aftermarket cats really wont shine, you need to stress the system to get an idea on what they offer. The number most often used is about a 20-30% increase in flow, big deal if your bolt on GT produces 300 cfm of exhuat flow (just a number, not actual), and the stock system can handle 350 cfm of flow, a 30% increase would make that 455 cfm (again just a number illustration), now do the full boogey on the engine and all of a sudden your GT is pumping 380 cfm into the exhaust, that 30% increase means something.

bob

From what I understand, the hi-flow cats allow the catalyst to expand significantly when they get hit with the increased volume of hotter gas.

When I was putting my SLP X-pipe and resonators on my 02 I took a gander into the cat and pointed it into the light and you could actually see through the thing (not well but you could make out whatever you were looking at through the cat). So the idea that the catalyst expands seems plausible.

m05fastbackGT

As for trusting those numbers ! Well who really knows for certain, if the 7-10HP gains with off-road pipes, can really be trusted..


However, I suppose that if Brenspeed did the exhaust shootout, instead of Anderson Ford Motorsport ! would you have posted that very same question chances are, probably not lol..

Although I haven't dealt with Anderson Ford Motorsport personally ! I do know that he's very well known in the performance industry, and has been for many years.

Therefore I have every reason to trust his independent test results.. much in the same way, as I trust Brenspeed's..

m05fastbackGT

If the high-flow cat design, is the same for the 05 and up.. this would also seem to make a lot of sense as well, Bob

DarkFireGT

I was assuming Anderson's numbers were done for a magazine, from the way that you stated it. That's why I said "If those numbers can be trusted". But I won't start with my distrust of dynos.