Anybody know the size of the stock intermediate pipe for the 91 3.1 RS? I was thinking it was 2 1/4". If so would going to 2 1/2" help that much power and sound wise?
Thanks


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'91 RS Flowmaster, K&N, modified air box

#3

 

umm i actually think it might be 2"...i think it was 2" off my 89..then went to 3"...made a nice difference in sound and upper rpm power

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" I'd rather run last in a full out race, than to NOT run at all ".

 

Definately don't quote me on this ... I think the intermediate is 2 1/2" and the tail pipes are 2 1/4".

If I were you I'd go out to your car and measure yours.

 

yea measure yours...mine was 2" (just checked)

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" I'd rather run last in a full out race, than to NOT run at all ".

 

I haven't measured yet, but if it is 2 1/2" then would going to 3" make a ***** sound or make it deeper? Way back when I ordered my Flomaster muffler from Summit, they told me to keep all the pipes the stock size or I would get a ***** sound. The guy that put it on for me said not to worry about it and he went w/ bigger tail pipes.

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'91 RS Flowmaster, K&N, modified air box

#3

 

Okay, I measured and the intermediate pipe is 2". Should I go all the way to a 3" or just 2 1/2"?

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'91 RS Flowmaster, K&N, modified air box

#3

 

3" is what the V-8's run. That said 2-1/2" is about right. If you go too big the flow slows and the hp increase isn't as much. There is a balance that needs to be maintained, you need a pipe large enough to flow freely but no so large that the the gasses slow in the pipe so as to cause back preassure(sp?). Now, you have a 3.1. I have a 8.2 and a 6.6. With yours being half of mine I'd reccomend a single 2-1/2" pipe. (I run dual 3" and have 10:1 CR with better flowing heads.) The real problem is you will still only flow as much as the most restrictive part of the system. Mixing and matching pipe for sound is not a good idea. You should save you $ and invest in a full system.

 

I've heard people saying 3" is just fine.
I got so slammed on the other board, when I made the exact same comment about the 60* engine pipes.
I guess that the 3.8's make more power & can use a 3" size pipe to engine advantage.
Me?
I'd ask the guy the cost difference between the two.
BUT definetly make it a uniform set up, not mix & match.
On my S-10 Blazer, I have 2 1/2" from engine to 2 1/2" in & out of CC and 2 1/2" into a Flowmaster w/2, 2" exhausts outta that muffler. My system workes so well, really helped the higher RPM breathing & NO LOSS of lower RPM torque (ask the cop with the radar gun that tagged me. He was stunned. Still got the ticket, drat, nice cop, tho. He had the same type Blazer & wanted to know how I made mine go so Zoomy!)

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Chat Soon,
KED85
Karl
1985 Firebird 2.8 to 3.4 swap project for Smog Happy LA, CA

 

As back-up for the 2.5 vs 3.0 inch I-pipe debate:

The Dynomax cat-back system (#17493) I use has all 2.5 inch piping. This same #17493 system is used for Firebird/Camaro 305 v8's! If 2.5 inches is enough for a v8...


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Looks like I'm gonna be going w/ the 2.5". but first must get other things fixed. (see burnt wire post)

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'91 RS Flowmaster, K&N, modified air box

#3