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5" exhaust pro/con

5K views 18 replies 8 participants last post by  Airstreamer67 
#1 ·
My 97 has the 6637 mod with a K&N air box as well as a 3" down pipe. Exhaust is stock from there back. How much performance will a 5" straight pipe give me? I like loud ,but not obnoxious ,will this be a good move or not?
 
#6 ·
Not much performance difference between 4" and 5". You will notice a difference once you remove the stock piping.

I did 3" DP and 5" exhaust but once I threw a filter on there then it really woke it up.

It's all about the combination but as far as benefits i'd weigh exhaust and gauges about the same, both are needed.
 
#7 · (Edited)
When you say stock exhaust after the 3-inch down pipe I assume you mean factory 3.5-inch pipe with a cat and muffler. The cat and muffler are restrictions in the flow of the exhaust gases but depending may be required (emissions testing, local laws, etc.).

If you remove the cat and/or muffler, flow will be improved therefore improving performance to some degree. As long as the exhaust pipe after the down pipe is at least 3-inch diameter performance won't change. Think of the exhaust system like a chain; the chain is only as strong as the weakest link. Exhaust systems only flow as good as the most restrictive component allows.

I have a 3-inch down pipe and 4-inch straight pipe to the exit behind the rear tire. There is nothing else in the system that is more restrictive than the 3-inch down pipe so it will flow as freely as that DP will allow. I could put 12-inch straight pipe after the DP and it would still flow just like it does now. The sound would most likely change but that's about it.

My truck isn't terribly loud with the current set up. The previous suggestions are good ones. A good intake and gauges are a must. You're more than half way there with the intake and 3-inch DP so getting rid of the stock exhaust (local laws permitting of course) and putting on a 4- or 5-inch kit would be worth the time and $$.

My truck was pretty stock with 199k miles when I bought it. The previous owner installed the straight pipe exhaust. I did the intake kit, 3-inch DP, and a TS-6 fairly soon after I purchased the truck and I've never regretted spending the money.
 
#8 ·
Thanks for the input,as it sits now I'm looking at a Edge Evolution CTS2 and deleting the cat and muffler. Will the step up to 4" vs just deleting and running the stock pipe be measurable? I haven't inquired at any muffler shops as them deleting the cat , I don't know the legal end,just know it's exempt of smog checks. The shop prices may be as much as me installing a new larger pipe.
 
#9 ·
I believe the stock pipe is 3.5-inch diameter. Cutting out the muffler and cat and putting in straight 3.5-inch pipe in their place would be an improvement. Might be more economical as well.
 
#10 ·
Well a visit to the muffler shop and minus 1 muffler, they wouldn't remove the cat, kinda figured that. I can't hear any difference,but i'm not outside to hear it under load. So I have a 6637 cold air,down pipe ,muffler delete and a CTS2 , so I think i'm done for a while.
 
#11 ·
It isn't a cat, it's a screened resonator at most.

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#13 ·
Honestly they'll call it that but I've cut it open and all it is pretty much is screen door mesh in parallel.

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#14 ·
It's a "cat" to some states. Provides no purpose. Requires what we have today as a regen to burn it all off.

Some states and counties require factory emissions crap. Depends on local laws and some shops won't remove emissions equipment even if not required by local testing. Just a liability they avoid.
 
#16 ·
OK that clears that up. Is there much restriction or should I just leave it alone. I'm not building a hot rod ,just want get it to flow.
 
#19 ·
I took off the fake cat and left the muffler. I didn't want any drone on the highway, where mine lives towing a trailer.

I don't think the factory muffler presents much back-pressure anyway since it's a straight-through design, about as free-flowing as a glasspac. I've got all the power I need, and my fuel mileage is good: 14 mpg towing a travel trailer at 60 mph, and 21 mpg when unladen on the highway at 70 mph.

I do have a Tymar big-filter intake and a 3-inch-round down-pipe.
 
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