Looking for advice on exhaust pipe size

[Peters02]

The goal with my 72 is to keep it more stock than not.  My concessions to this are a subtly more aggressive cam and, if possible, nicer wheels and a dual exhaust (originally it had a single exhaust).  Well I am at the exhaust part and looking at various systems to come off the original 318 manifolds.  For the record this will be running a 2bbl - again stock.
My question is will 2.5" pipes coming from and manifolds be too draining of power at the low end?  Should I be looking for a smaller pipe or will it not really matter?
(Comparing TTI with Accurate Exhaust and besides crying over the price, I am scratching my head on this one as I am not an expert on exhaust system dynamics - scavenging effect, etc.)

If anyone has experience here or advice, I'd really appreciate it.

Thank you.
Peter

[firefighter3931]

Peter, with a mild smallblock you don't need more than 2.25in exhaust. Use a good quality straight thru design muffler like a Dynomax Ultraflow or a Magnaflow...either are excellent choices and won't create any backpressure. 



Ron

[06Daytona]

I'm going the same route with my 72. 318 2bbl with a mild cam and was told by a performance exhaust shop that I didn't need to go bigger than 2 1/2 with a good set of mufflers.

[darrenb811]

2.5" pipes won't 'drain' any power, you will just have to adjust your tune up (slightly)
Your system pipe dia. will likely have minimal effect on performance if your not changing to headers.

[Peters02]

Thanks, guys.  This is helpful.  I understand 2.25 is about all I need, but if I were to go to 2.5 I am taking away from these posts that there will not likely be any issues.
So with the comment on tuning...I've not even 'thought' about tuning the thing.  What is the likely affect - changing the timing or dealing with the carb?

Thanks

[darrenb811]

you probably won't have to change the tune at all., with headers, maybe you could lean it a little, maybe +2 degrees initial timing with no other changes. just my view.

[firefighter3931]

If the pipe is too big scavenging will be reduced and intake dilution will result. If you're making less than 400hp a 2.25 in tube if the "correct" size. 


Ron

[doctor4766]

Actually I've been told to change the tail pipe sizes to 2 1/4 in order to reduce the irritating drone that the 2 1/2" system is creating inside the cabin.
Opinions on that?

[64dartgt]

I have a similar set up.  Pypes has a good price, but most sets are for cars with headers.  A muffler shop could make up the difference though.

http://www.summitracing.com/parts/PYE-SMB10/

[firefighter3931]

Actually I've been told to change the tail pipe sizes to 2 1/4 in order to reduce the irritating drone that the 2 1/2" system is creating inside the cabin.
Opinions on that?

A smaller tailpipe will reduce noise and won't hurt performance. Exhaust gases cool as they exit the motor so they do not require the same size pipe to maintain velocity. 

A 2.5 extension to 2.25 tail pipe is acceptable 


Ron

[doctor4766]

Actually I've been told to change the tail pipe sizes to 2 1/4 in order to reduce the irritating drone that the 2 1/2" system is creating inside the cabin.
Opinions on that?

A smaller tailpipe will reduce noise and won't hurt performance. Exhaust gases cool as they exit the motor so they do not require the same size pipe to maintain velocity. 
A 2.5 extension to 2.25 tail pipe is acceptable 
Ron

Cheers and thanks for clarifying that Ron