Exhaust Pipe Diameter

[teamssc]

I'm replacing the dual exhaust on my 78 K10. I'm using the K20/350ci diagram on the Walker site. I'm suprised that the Walker site has 2.5" on the drivers side and 2.25" on the passenger side, back to the muffler that is. I bought all the pipe based on their diagram and it just didn't click there was a difference. I'm also not crazy that the exhaust pipe are 2" but I wanted pre-formed as this is my first exhaust and I don't have many tools.

So the question, does it matter that they are different. I would guess not considering that is a stock configuration but it still sucks they aren't the same.

 

[Jims86]

The 2" tail pipes are just fine, don let a bunch of idiots tell you otherwise. Smaller pipe is better for torque, which is what you want. Use straight through mufflers, and its even better. Speaking from experience, Walker is good Quality stuff, and fit and finish are #1.

 

[teamssc]

Thanks for the positive vote on the Walker pipes.

I talked with a guy at work who builds muscle cars and he said I'm fine also. He said the 2 pipes are different diameter coming off the manifolds because of the bends in them; thus it's by design to get the back pressure balanced just as you said.

I picked up a pipe sizing tool at Harbor Freight on the way home because I am going to be adding and H crossover pipe and I'd like for the pipes to match up vs using a bunch of adapters. So bumping the 2.25" pipe to 2.5" shouldn't be harmful and easy.

As far as the 2" pipes off the back of the 2.5" mufflers I'll use adapters cause I doubt you can resize a 2" pipe to 2.5".

Re: the mufflers. I bought Dynomax Super Turbo, 20".

Feel free to jump in if anyone thinks I'm going down the wrong path.

Thanks for the help!

 

[Jims86]

Super turbos are fine, they have the flow deflectors inside, and no internal resonators to slow them down. One thing, any back pressure is bad, the key is flow velocity...which smaller pipes are good for. As far as sizing, well thats more of a fitment issue than anything. You could equal out the pipe sizes, but i garentee you will not notice a difference.

 

[austinado16]

I've long heard that back pressure is good. It creates excellent scavenging from the cylinders to make sure there is no exhaust left behind to pollute the fresh charge of air and fuel. My understanding is that is why large diameter pipe doesn't make the kind of torque (power) down low that correctly sized smaller diameter pipe does. As you say Jim, velocity, but also the returning pressure wave from the back pressure that creates the scavenging.

 

[Jims86]

I've long heard that back pressure is good. It creates excellent scavenging from the cylinders to make sure there is no exhaust left behind to pollute the fresh charge of air and fuel. My understanding is that is why large diameter pipe doesn't make the kind of torque (power) down low that correctly sized smaller diameter pipe does. As you say Jim, velocity, but also the returning pressure wave from the back pressure that creates the scavenging.

Nope, no engine NEEDS back pressure, it is just a by product of the need to evacuate spent gasses to the rear of the vehicle, I.e; adding pipes with bends, and exaserbating it with mufflers.
Smaller pipe promotes flow velocity.....ummmm, like a pulse jet engine. Large at the combustion chamber, but has a taper to a much smaller outlet. the combustion pulse, increases in speed as it exits, assisting inthe air intake for the next cycle.
If you get pipe thats too big, flow velocity slows, sometimes to the point where exhaust gasses start to tumble, and slow, reducing/ eliminating the scavenging effect completely.

 

[MrMarty51]

I have the stock y pipe on Mine 93 GMC 1500, 350 V8, it comes out at three inch, goes into the C-convertor, comes out at three inch and I replaced the stock muffler with a 3 inch in-out straight through glass pack and three inch all the way out the back, exiting behind the left rear wheel, single exhaust.
Do You think that this configuration is harming the flow or would make no difference by going to a smaller pipe out of the muffler.
I`m a thinking with the cat in the way that the three inch would be about as good as it could get, just a guess though.

 

[austinado16]

Thanks for clarifying. Now, where can I find good quality headers that won't require any mods for installation?