2" exhaust too restrictive?
2" exhaust too restrictive? This is on a stock 5.3 going into my beater '71 C10. It came with dual exhaust that is in good shape and seemed to work well on the original 350, but was just curious as to what others thought.
Joined: Jul 2007
Posts: 1,502
Likes: 177
From: ELSA, South TEXAS (956) 802-7700
i would think too restrictive on old 350 to begin with and even more on 5.3. these newer motors like to breathe more as evidenced by the oem head flow compared to the older sbc's and their power potential. its always cheaper to go with what you got but in this case yeah it is too restrictive imho.
If your not building it for speed i think it will be fine. Will you gain power going to 2.5"...yes, but I wouldnt spend the money for a bone stock 5.3 in a truck.
If you think about it how big is the single exhaust on a truck?
2"x2= 4" of exhaust.
If you think about it how big is the single exhaust on a truck?
2"x2= 4" of exhaust.
This was kind of my thinking too, although I think two pipes that are 2" is probably less than 4" in volume, maybe closer to around 3". I'm sure I would pick up some power with a bigger exhaust, but I wasn't sure if it would make my fuel mileage go way down also? The bone stock truck got 12 mpg no matter how easy I drove it. It had a rebuilt carb and was tuned up and ran great, just was super thirsty! I'll probably run the 2" for now and later on replace it with 2 1/2".
TECH Fanatic
Joined: May 2010
Posts: 1,081
Likes: 8
From: Atlanta, Ga
The 2" should be fine for most normal driving conditions. I would be more concerned about the muffler restriction than simply pipe size. Another consideration is how the pipes were bent, mandrel or pinch bender. This is a greater impact than simply size. As for volume, you are closer at the 3", more like 2.5", which is just less than the 2.75" stock tail pipe size on these trucks.
here's a rough estimate for horsepower supported based on exhaust size. for what it's worth, my 05 Yukon 5.3 was 3" single after the cats/y-pipe (I've since put a cat-back on it). The exhaust system is fully mandrel bent from the factory, too. That shows to be better-flowing than dual 2" pipes.
Your dual 2" exhaust is similar in area to the single 2.75" exhaust typically used by GM behind the 5.3's. My opinion is that its too restrictive IF it was crush or pinch bent at the local muffler shop.
Have you thought about picking up a stock exhaust from a newer truck (y pipe & all) and making it fit your '71? Most of them were stainless and can be bought for next to nothing. Stop in your local muffler shop & see if they've got any take-offs, you may be surprised at how cheap you can pick up a nice, system.
Have you thought about picking up a stock exhaust from a newer truck (y pipe & all) and making it fit your '71? Most of them were stainless and can be bought for next to nothing. Stop in your local muffler shop & see if they've got any take-offs, you may be surprised at how cheap you can pick up a nice, system.
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TECH Fanatic
Joined: Jul 2005
Posts: 1,685
Likes: 7
From: Beebe, Arkansas
Just run it! Then later when you have the cash up grade. Then compare the 2'' system to some thing large MPG wise. Be interesting to see the difference.
TECH Resident
Joined: Mar 2012
Posts: 821
Likes: 4
From: Elkridge MD
Eric, my Thunderbird was 2.25" single with an exhaust shop "merge" (see my topic last page) from 2009 until about two months ago when I changed it to 2.5" duals. The car ran fine and never feel sluggish under normal driving. I have to admit I have noticed a small difference at WOT, but you don't drive like I do so you'll be fine.
We're just poking a little fun, nothing malicious. 2" pipe usually gives that raspy, blat-blat sound.(..and that is a scientific description). Especially with a long tail pipe. Cut it off at the muffler for a deeper tone. Like most people, I've got to spend money where it's needed first too. It's already there, run it.
I had the exhaust on 4.8 in my s10 shoehorned into the sto 4cyl muffler and tailpipe (single 2-1/4") for a while. Went to 3" with mangaflow and really didn't notice any difference driving other than the noise, might have gained about 1/2 mpg.
