Magnaflow Hi-flow cats on 1997 K1500

[MountainDew]

I've got a 1997 K1500 with the 5.7L Vortec in it. My current exhaust setup is stock cats to true duals with Flowmaster Super 40s with 3" (maybe 3.5"?) tips straight out the back. I was wondering what kind of performance gains (if any) and sound changes would occur if I replaced both of the stock cats with two Magnaflow hi-flow cats. I've heard that I won't get any noticeable performance gains but that I'll get a deeper sound and a louder sound under acceleration. These are the cats that I was thinking about getting.

http://www.amazon.com/Magnaflow-9410...pr_product_top

[1988 GMC 355]

if yours are original then yes high flow cats will help, not sound wise though.

[MountainDew]

if yours are original then yes high flow cats will help, not sound wise though.

So I will see some performance gains but the sound won't change? What kind of performance gains could I expect to see? (and yes, I do have the OE cats on there. Replaced two of the O2 sensors a few months ago.) Also, why wouldn't I get any change in the sound?

[1988 GMC 355]

So I will see some performance gains but the sound won't change? What kind of performance gains could I expect to see? (and yes, I do have the OE cats on there. Replaced two of the O2 sensors a few months ago.) Also, why wouldn't I get any change in the sound?

Well the stockers have how many miles on them? so yes new high flows will net better flow and better performance. Maybe a little louder but it won't be noticable. taking the cats out would make it louder and more raspy and hollow, but having any type of cat is going to tone the exhaust down.

[MountainDew]

Well the stockers have how many miles on them? so yes new high flows will net better flow and better performance. Maybe a little louder but it won't be noticable. taking the cats out would make it louder and more raspy and hollow, but having any type of cat is going to tone the exhaust down.

The stock cats have almost 190k on them. Never been touched to my knowledge. My parents just moved to North Carolina where there's annual emissions testing so taking off the cats isn't an option anymore. Never been a fan of the no cats sound though. So if high flow cats won't make a noticeable change in sound, is there anything I can do (save gutting or deleting the cats) that will give me a deeper tone or more volume? I was reading through this thread http://www.f150online.com/forums/exh...tock-cats.html and it seemed like replacing the stock cats with the high flows gave a very noticeable volume increase.

Also, for those who care, this is what the truck sounds like now.

[1988 GMC 355]

Well that is a ford forum you have a Chevy. You will notice a difference but it isn't going to make a gigantic difference.

On a side note there is hundreds of threads on here about the question you asked, but you spent time searching on a Ford forum?

[MountainDew]

Well that is a ford forum you have a Chevy. You will notice a difference but it isn't going to make a gigantic difference.

On a side note there is hundreds of threads on here about the question you asked, but you spent time searching on a Ford forum?

Haha, yeah that was one of the top google results I got so I read through it. All of the threads on here that I read about making the exhaust louder suggested deleting the cats or getting different mufflers. Like I said before, deleting or gutting the cats isn't an option and I would rather not replace my Flowmasters since I really like the tone they have. I simply want to gain a little bit of performance and maybe get a volume increase.

[1988 GMC 355]

Well high flow cats will give you that IMO.

[MountainDew]

Well high flow cats will give you that IMO.

Awesome. I was talking to a buddy of mine this morning and he said that the Chevy cats are already high flow. He has a NBS Chevy though, so I'm kind of doubtful that my '97 has stock high flows. Anybody with a '97 or OBS truck care to set the record straight? Does the 1997 K1500 have stock high flow cats?

[1988 GMC 355]

No they do not.

[MountainDew]

No they do not.

You are the man. Thanks a ton for the info. I called the muffler shop today and they said they would install the new cats for $90. I'll be selling my cats to a friend for $60 piece I think. Can't wait to get them installed!

[1988 GMC 355]

Awesome! that is a good price.

[Badass69]

Upping the size of your front headpipes will do a lot more. Even without headers the 1 7/8" head pipes on the half ton Vortec 350 trucks is garbage. Magnaflow for one anyways makes a complete 2.5" bolt in system that replaces the piping from the manifolds to where the stock muffler was.

[MountainDew]

All right, I've been doing some research here and have another question. Magnaflow seems to be the most popular high-flow cat, but I keep hearing about Thunderbolt cats that seem to be less restrictive and a bit cheaper than Magnaflow cats. Anybody here use them? What's the difference between them and Magnaflows aside from simply being smaller?

[1988 GMC 355]

They are probably of less quality and may not last as long. I run one on my setup and have had 0 issues for over two years and 20K+ miles.

[MountainDew]

They are probably of less quality and may not last as long. I run one on my setup and have had 0 issues for over two years and 20K+ miles.

From what I've heard I will have no problems passing emissions with the Magnaflow cats. How about the Thunderbolt ones? Also, would there be a sound or power gain difference between the Thunderbolt and Magnaflow cats? Sorry for all the questions, I really know nothing about this kind of stuff.

[outsider27]

Put the Magnaflow cats on my 1999 Suburban back in October. There was a slight increase in power, but the stockers were shot. I bought the kit, which gives the pipes from the manifolds through the cats. Pretty good set up. Planning on doing a Magnaflow single in/dual out muffler soon.

[1988 GMC 355]

You won't see a difference in sound or issues passing emissions with either cat.

[8716valver]

Where do I find one of these Magnaflow Kits that replaces the downpipes and cats only?

[1988 GMC 355]

CHeck on their site.