Will smaller tailpipes restrict any flow in a cat-back system?
 

Kinda of a silly question, I know...But here's the deal:

Right now I currently have a 3" Flowmaster AT cat-back (80 series) on my '95 Z28 that came off of an LS1 T/A. I also have a 3" Flowtech cutout with the DMH E-plate on the I-pipe right before the axle.

Anyway, this Flowmaster muffler HAS to go. Something is obviously wrong with it because it is honestly quieter than a stock OEM muffler (I'm not kidding!). So, rather than replace it with a whole new Hooker cat-back system (what I want), I just want to cut off the existing muffler and weld in a new Hooker Aerochamber replacement. However, I'm only planning on using some stock OEM tailpipes & Z28 tips since that is what will fit this Hooker replacement-style muffler.

My question is, since the stock tailpipes are only 2.25", will that restrict any noticeable flow as compared to the 2.5" tailpipes that come with the complete Hooker cat-back system? I doubt only a 1/4 of an inch would make any difference (especially since these are just tailpipes and come after the muffler). But just buying only the muffler would save me a ton of money over going with the full cat-back (plus I don't lose my E-cutout that is already welded into the existing I-pipe).

Thanks,

Mike

Re: Will smaller tailpipes restrict any flow in a cat-back system?
 

TTT

Re: Will smaller tailpipes restrict any flow in a cat-back system?
 

It is a good question. You are likely to get some specualtion. Let me help as best I can :). Not very many people have hard, dyno'd info comparison info of before and after info of strictly tailpipe changes. That being said...who knows. I'm sure a fluid dynamics engineer could tell you the flow differential between ehaust before/after the fuller and which pipe would have the best effect on horsepower. A smaller pipe might help velocity. A larger pipe might help flow more volume. After the muffler,. the exhaust tempature decrease. How much? I don't know, never measured.

After all of that...I just want to let you know that could be a very technical question, but at the same time, it comes down to real world numbers.

Good luck in your search. I have also wondered, but suscribed to the idea of having a larger pipe. For example, I have 4" exhaust, and I also have a 4" exhaust tail pipe.

Ryan

Re: Will smaller tailpipes restrict any flow in a cat-back system?
 

Ezhaust cools signifigantly as it travels down the system and in doing so contracts and has less volume(not the sound kind), what would worry me would be more the quality of bends in stock replacement type parts a 2.25" crush bent pipe will flow a signifigant amount less than a 2.5" mandrel. Small diameter changes actually do make for much larger than expected flow differences. Think about it this way envision a bunch of 1" tubed inside a 3" tube, ignoring tube thickness I can easily picture 5 tubes fitting inside with irregular shaped space leftover so the 3" would probably flow 6 times as much as the 1" not just 3 times as much.

Re: Will smaller tailpipes restrict any flow in a cat-back system?
 

Hmmm...Thanks for the info guys...

I mean, people replace their stock OEM mufflers with aftermarket ones using the same inlets/outlets as stock all the time...However, I already have a 3" Flowmaster cat-back that also uses 3" tailpipes on the car (so going with a muffler that uses a 2.75" inlet and dual 2.25" outlets would reduce everything at the point of the muffler to the tips...

It doesn't sound like that is the best idea then if I'm looking to keep my flow as fluid as possible...

Edit: I just noticed on Thunderracing.com's site that they also sell a direct replacement Hooker Aerochamber muffler with a 3" inlet and dual 2.5" outlets....So I know for a fact that would work perfectly with what I have and not cost me any flow (afterall, those are the same dimensions Hooker uses with their full 3" cat-back system). ;)

Re: Will smaller tailpipes restrict any flow in a cat-back system?
 

As far as flow area, assuming about .060 in. thick wall on the EOM tailpipes, two pipes 2.25 outside diameter have about the same inside area as one pipe 3-1/8 inches outside diameter.

Of course the 2 smaller pipes have more surface area to cause friction and some flow restriction, so if your headpipe is 3 inches, it pretty much evens out. All of this assumes the flow (in cfm for example) out of the muffler is the same as the flow into the muffler. Not so, however...

There are fewer cfm coming out of the mufler than going in. In fact there are a lot fewer cfm coming out of the tailpipes than coming out of the engine. Hot gasses expand, so as they cool they contract. 1200 degree header inlet gasses (at max power) are only a few hundred degrees coming out of the tailpipes. You may lose 300-400 degrees (at max power) across the muffler. The farther aft of the engine you go, the cooler the gasses and the lower the cfm. Mass flow doesn't change, of course, just volume.

So, unless your single headpipe is larger than 3-1/2 inches, two 2-1/4 tailpipes shouldn't cost you power. You can lose power through the muffler due to restriction. The series and brand you are removing is not very high on flow numbers. I would look at something like a 3 inch in/out Magnaflow or Dynomax Ultraflow welded with published flow numbers above 800 cfm (@ 28 in. H2O), then split into the 2 tailpipes after the muffler. If you keep putting restrictive mufflers on, the size of the tailpipes doesn't matter, because the muffler is the choke point.

My $.02