[ITSBACK]

428 unported 72cc Edelbrock heads,Old Faithful SD Performance cam. I already have the 2-1/2" pypes exhaust and spoke with pypes this morning about swapping and paying the difference. They told me to stick with the 2-1/2 as I would not really see the difference in a mainly street car and 500hp was on the edge for the change. They also said it would be extremely load at 3". Anyone have any input on this?
Thanks,
Bill

[Qball]

Sounds like Pypes is looking out for you. I'd stick with the 2-1/2, myself.

[Nicks67GTO]

Depends on what you call loud. It also depends on what you have for a muffler. My Nova had a +/- 500hp sbc. 1-7/8" primary headers, 3" pipes into a flowtech x and out a pair of ultraflos that ended before the rear axle. It sounded great at idle and moderate at cruising speed. In fact there were spots in the rpm range I could barely hear it inside the car on the interstate. Now open her up to WOT and she sang. It was quieter than the dronemasters and no crossover I had before and didn't resonate real bad inside the car. I went with the same setup for my GTO but I added 2.5" tailpipes after the 3" mufflers.

I think its your call.

[ta man]

You could do what I did just do the 3 inch at the front ,set of cone reducers into your mufflers.

[rad400]

I would say do 3" to 2 1/2 out the back.

[Cliff R]

+1

3" head pipes into the mufflers, 2.5 is OK out the back. Pontiac engines like the larger head pipes. It made a noticable improvment on my car years ago when I went from 2.5 to 3" head pipes into the mufflers. The larger pipes give you some room to grow as well, I'd make the swap.....Cliff

[PONTIAC DUDE]

Here ya go.


http://www.angelfire.com/fl4/pontiac...xh.sizing.html

[GT182]

I've got a Walker dual 2-1/2" exhaust system with H-pipe, and their "Cherry Bombs" on my 400. Loud, yes but fun.

A friend back in 68 at college, had a '66 428 4speed 2+2 Catalina that he put 3" exhaust on. Not sure what the mufflers were but it sounded nice. A nice mellow tone that was a little louder than stock and didn't drive you nuts.

[amcmike]

I think it depends on whether you're running an X-pipe or not. If it has an X-pipe you can get away with the 2.5", but without out it, the 2.5" would be choking it. The X-pipe also tends to make it more quiet.

[Old Goat Racer]

Assuming you have 3.5" collectors I think you would want 3" pipes from those

[Superchief455]

Originally Posted by ITSBACK

428 unported 72cc Edelbrock heads,Old Faithful SD Performance cam. I already have the 2-1/2" pypes exhaust and spoke with pypes this morning about swapping and paying the difference. They told me to stick with the 2-1/2 as I would not really see the difference in a mainly street car and 500hp was on the edge for the change. They also said it would be extremely load at 3". Anyone have any input on this?
Thanks,
Bill

Your exhaust much like your engine is a "package deal" and should be treated as such if your looking to get max performance. There are plenty of things to take into "consideration" as far as the exhaust is concerned and LOUD is what i would call a relative term. What is loud and unreasonable to some is tolerable to others, but if the exhaust is "well thought out as a package" you can have all the horsepower you want and at reasonable sound levels.

Bruce Wilkie has posted this link as well as myself before in the exhaust section and it's definitely worth the read. Jim Hand has some good reading on exhaust system testing as well as mufflers he's tested as well. I personally would take some time and "do some homework" on this deal as to "what YOUR looking for and what makes YOU happy". I personally like "custom" exhaust systems done by a competent shop/installer as the only "issues" are making the complete exhaust from the start not modifying what was already made/suppose to fit. FWIW

--------------------------------------------------------------------------------

http://www.superchevy.com/technical/...exh/index.html

[i82much]

I did the 3" to X pipe to 3" muffler inlet to 2.5 outlet thing, Race Pros. From the reading I did it was supposed to be pretty quiet. As it turned out ... uh, no. Still pretty loud even w/2.5 tailpipes. But it does sound and run awfully good, so no complaints.

[ITSBACK]

Thanks for the input guys, I will call SD tomorrow as well as PY and see about that 3" front and 2.5 rear deal. I was reading earler in the Jim Hand book where they tried that and it ran with very minor change as far as performance.

[ITSBACK]

Well I took all your information and spoke with Dave at SD and went with his full call and called pypes today and went 3" all the way. Maybe I dont need it all right now but 500-550hp might not be enough so I will prepare for it now.
Thanks again guys,
Bill

[TIN TIGR]

i think p-dudes sizes are a little small..

fun story..just built a nice 350 sbc..106 ls cammy..good stuff, with 1 7/8 to a 3 1/2 collector..told customer to but 3.5 inches on it..the "muffler/exhaust experts" built him a non mandrel 2 1/2 system..now on these motors i hone the exhausts guide a little because i have seen them stick out of the box.."inexpensive" aluminum heads...the seals keep oil from entering the exhaust, but not exhaust pressure from squeaking by into engine..never any problems..

the bottom line, it blew the intake seals right out..it feels like an air hose is going off back of the engine..customer brought car back, yelling at me..i found the issue and let him feel it..changed breathers around and killed oil leak..he is now going to exhaust shop, and having them change exhaust on their dollar..cant eat thanksgiving dinner, and put a cork up your butt when ya wanna poo..

so , in closing, put big pipes on anything you can..it does not hurt performance..you dont need backpressure to make low end torque..lmao..who ever started that lie?

when in doubt, go big...never a mistake..

[ITSBACK]

I hear that, bigger is better and leaves the future open.

[67cruiser]

i TOOK MY turbo,s down to local muffler store and had em opened to accomidate my 3 inch going in, probably wrong thing to do. started out at 2.5 and opened em up for my 3 inch, alot of stretching!!

[ITSBACK]

I just went to the Enlishtown swap meet Saturday and swapped my Pypes 2.5 stainless for 3" stainless front to back. Oh my God those things look like diesel pipes. I cant wait to hear them.

[GTO TOM]

I have a 66 GTO with a stroked 400 to 461, Kaufmann heads, tri-power and Hooker headers. The chassis dyno says 450 at the rear wheels so I went with a Pypes 3 inch with x-pipe and cut outs to the mufflers then 2 1/2 on out. Although I have not gone back to the dyno yet, I think the HP with the cut outs closed is much greater than before. Before was 2 1/2 with cut outs to mufflers and 2 1/4 on out. I would loose 40 hp when I closed the cut outs. Now it feels about the same, open cut outs or closed.

I used the Street Pro mufflers and the sound is great. Actually a little quieter inside the car from the old Flowmaster 40s but louder out back. Really sounds great. The installation was easy. Everything fit just like it should.

[TIN TIGR]

if exhaust noise bothers you, dont dsrive a pontiac, ands especially not a gto..they were meant to be IN YOUR FACE!!!..SCREW YOU MUSTANG OR DODGE SUPERBEE, KNEEL TO THE STREET KING..LOL..

SO MANY STORIES ABOUND OF GUYS WITH STOCK PONTIACS ROASTING CARS AROUND TOWN..EVEN WHEN THE OTHER GUY TURNED FASTER STRIP TIMES..

embrace the noise, revel in it..feel the freedom..

screw noise laws anyway..i need more medication..