96 5.7 exhaust question/help

[Brian G]

Ok, so I'm finally going to bite the bullet and get a hi flo exhaust, so I'm hoping someone can give me a knowledgable response on my suggested setup.
I'm going with the Doug Thorley Tri-Y Cali legal headers, stock cats, and after the cats either a 3 or 3.5" pipe and magnaflow muffler, I'm looking at the 14" by 9" muffler at this time and the pipe will be routed approximitly the same as the stock setup.
This is a daily driver with only occasional tow duties of about 3500 aerodynamics lbs.
I'm looking for power and efficiency not noise.


The question is-should I use a 3.5" pipe/muff after the cats? Will this help or hinder the mostly stock engine in a RCSB. Also, is the 14x9" magnaflow hi flow muff fully piped going to be really loud, or just a bit more at idle and cruising speeds?
Current mods/setup as follows:

mpfi upgrade
Tuned per mail order
5 spd

In the future I'm either going refreshed stock engine with lt4 cam or maybe a 6.0 or 6.2 engine.

Thanks in advance.

[Mrgoodwrench3]

I think a 3" pipe is plenty for your motor.

[96gmctruck]

if you are going to be using it for towing i would go with a 3inch inlet muffler with a 2 1/2 inch outlet. if you want to keep low end torque you will need backpressure. i wouldn't go bigger than 3inch on a nearly stock motor.

[96gmctruck]

also i dont know how you feel about flowmasters but if you want to take a look at those, the 70 series and 50 series are pretty good sound wise. nice tone and fairly quiet.
http://www.flowmastermufflers.com/index.php?cat=1

[proskreet]

will sound and run alot better if you go ahead and yank those cats off.

[sandman101]

i thought the cats on his truck helped balance the backpressure because thats why they are offset from one another?

[Brian G]

Keeping the cats-need cafe legal vehicle, and I've heard these vortec engines run poorly w/o them!
Well, I think I might stick w the duel 2.5 in a nd single 3" out, that is if I can find one-all the muffs I've seen thus far are single in duel out...If I can't find a d in s out that a duel 2.5 in/out will suffice. I've heard the magnaflows are the best hi flow mufflers out there, I want hi flow but a quite as possible-any suggestions?
I'll do a search on the flowmaster 50/70 series.

[Pauly]

Originally Posted by sandman101

i thought the cats on his truck helped balance the backpressure because thats why they are offset from one another?

They are offset to keep the pipes between the manifold and the cats as close to the same length on both banks. If the cats were side by side, the drivers side tube would be longer. This would cause the engines 2 banks to make different power levels at different rpms from one another.

Its not so much about backpressure as it is about exhaust pulse tuning.



The cats arent as much of a restriction as the dual 1 7/8" headpipes that crimp down way smaller at the bends.

He is installing Thorley tri Y headers, he wont be experiencing any sort of low rpm torque loss.
I went from a stock exhaust, to a set of lontube Hookers into dual 2 1/2" headpipes into dual 2 1/2" cats that dumped directly into turndowns. I noticed nothing but torque GAINS.

The stock cats are pretty good, I know of guys that have cut off the inlet/outlets and welded up larger pipes.

A single 3" exhaust is more than enough for this engine.

peace
PAuly

[Brian G]

Thanks Pauly, your always such a wealth of information!!
Pauly, how small are the stock cat inlet outlet pipes? Should I consider cutting the stock pipes out and welding in 2.5 pipe?
Thanks man.

[91z71355]

i just got a flowmaster 50 series 2.5dual input 3 output from summit racing

[Ross.Wiwcharuk]

Originally Posted by Brian G

Ok, so I'm finally going to bite the bullet and get a hi flo exhaust, so I'm hoping someone can give me a knowledgable response on my suggested setup.
I'm going with the Doug Thorley Tri-Y Cali legal headers, stock cats, and after the cats either a 3 or 3.5" pipe and magnaflow muffler, I'm looking at the 14" by 9" muffler at this time and the pipe will be routed approximitly the same as the stock setup.
This is a daily driver with only occasional tow duties of about 3500 aerodynamics lbs.
I'm looking for power and efficiency not noise.


The question is-should I use a 3.5" pipe/muff after the cats? Will this help or hinder the mostly stock engine in a RCSB. Also, is the 14x9" magnaflow hi flow muff fully piped going to be really loud, or just a bit more at idle and cruising speeds?
Current mods/setup as follows:

mpfi upgrade
Tuned per mail order
5 spd

In the future I'm either going refreshed stock engine with lt4 cam or maybe a 6.0 or 6.2 engine.

Thanks in advance.

I have a 1998 silverado with no cats, lol canada.... no laws in saskatchewan for that although to much pressure pops like a cow! i have 2.25 pipe mainly 2.5 is the biggest you should go on dual exaust i would dual it if ur really planning a new exaust, and i have flowmaster 40 series on my truck.. its nice rumble with cats not to loud at all, but once cats are gone.. holy sh!t!!!

[jbt56]

Since I work for The Exhaust Technology Company, I'm somewhat biased, of course, but here's my $.02:
1) Don't listen to folks telling you to remove your cats;
2) If you want to stay with a single tailpipe, use a 70 Series muffler. That'll be just a bit more sound than stock, with a *much* better tone, and all the performance we're famous for. If you want the dual look, check out our bolt-on systems- they're good for a 5% gain in HP/torque from idle to redline- not just peak HP.
Glasspacks may look good on flow benches, but really, you're talking about 75-year-old 'technology'. Many are very well built these days (Magnaflow comes to mind), but look beyond the marketing. After all, when was the last time you saw a flow bench under someone's hood?

[the moose]

Tri Ys and a 70 series owuld be great on your truck. i loved my flowmaster mufflers on the GTO.

id also go with a 3 inch pipe not 3.5