2.5" vs 3" Exhaust and Muffler Options

[badd68]

3" Magnaflow stainless mandrel bent system with X pipe here, I really like it. Fit is good, sound is great.

[fryedaddy]

on my 428 i have 3 inch with x pipe and 3 inch mufflers and 3 inch pipe all the way to the back.i makes the 428 sound like a much bigger engine,big throaty sound,i love it.

[bluef100fe]

I have 3” X-pipe with cut outs for when I wanna race, hooker max flow’s probably 8-10 years  old by now and probably need replacing… 3” mandrel bends over the axle a set of Dyno max race bullets after the axle and then a short section of straight pipe out the rear of my truck. Really like the sound the x-pipe gives it… was almost unbearable loud  in the cab until I added the x pipe. Still has some but bite to it when standing on the loud pedal but cruising at 3000 rpm you can still hear the radio, it is turned up pretty high but you get the idea. I’m looking at going to a 3.5” x-pipe and cutouts, and leaving the 3” tail pipes and mufflers when I have it apart next time for new headers.. 800hp N/A build

[WerbyFord]

https://www.youtube.com/watch?v=_PVXvHkr-Vs

2.5" is down 20hp/20ftlb along the curve compared to 3.0" on a 600hp combo, would think a 700hp setup would be hurting it more. 

Maybe just me, but to reach 700hp would seem to mean optimizing heads (ported vs cast), compression, cam duration/lift...right to a high level.  Then seems odd to go back and de-optimize the motor with small exhaust when there absolutely is an alternative with minimal drawback beyond being tougher to fit (but possible). 

Now, if this was a street/strip combo where the exhaust is getting dropped at the track, that's a different scenario but I read this as street only.

Great video, especially the sarcasm about the old "an engine needs backpressure" urban legend.

Incredible though, to me, that all that 2.5" pipe ONLY killed off 21hp out of 622hp (if it was jetted rich enough with open headers to begin with).
That's only a 3.4% power loss.
So only a tenth or so ET and maybe 1.5mph assuming that Rat was in a Camaro/Nova.

Seems that good old Glass Packs  / Cherry Bombs from the 1960s-70s are still very hard to beat, if they're done right:
* Same pipe diameter as the exhaust pipe - no narrowing down
* Perforated, not louvered. Louvers are for fastback rear windows.
* Big case with lots of glass to cancel noise & waves.

[CV355]

Turns out I have to go with a 2.5" dual side exhaust.  Short of giving the exhaust fabricator a new reason to drink, there is no simple way to get the exhaust up and over the M9 and out the back.  It strikes everywhere.  I'm not about to pay someone $3000 for 6' of wedge slice tig artwork, though I'm sure it would look amazing.

Now the challenge becomes putting the side exhaust on and clearing the full length subframes.  There are fiberglass skirts for making a side exhaust look "correct" but the subframes don't end soon enough to clear them.  I might have to design and fabricate some sort of oval adapter with a recession to clear it.

...and here I thought the exhaust would be the easy part 

[My427stang]

What is different on your car? The only place I have seen them hit is along the gas tank on one side.  Maybe he is trying to crush bend and can't make a tight radius, that'd do it.  However you could buy some J-bends and have him weld the shape he needs

If forced into 2.5, you could even do stock exit Flowmaster 2.5 tail pipes, they fit easy.

[CV355]

I have -10an fuel lines coming from a rear-sump tank and wrapping around on the passenger side.  I kept them as close to the tank as possible to allow for the pipes.  The problem is that the M9 back brace requires us rolling the over-axle pipe outward, and at that point it either strikes the fuel lines or points the exhaust against the tank.  Could it be made to work with some custom bends and a full day or two at an exhaust fabricator?  Absolutely, but it would be a small fortune.  These pipes were from the Magnaflow 2.5 stainless exhaust for a '69 Mustang, so I really thought they would fit with adequate clearance..  We all agreed that side exit would be far less expensive and make for easier access around the fuel pump and such. 

[My427stang]

That makes perfect sense, and nothing wrong with the Trans-am era side exit look either.

[CV355]

Here's what I'm looking at:
https://fiberglassspecialtiesnv.com/1969-1970-mustang-ground-effects-side-skirts-for-side-exit-exhaust/

I think it's subtle enough that it won't "ruin" the car.  I was trying to keep the exterior of the car as close to original as possible, but the subframes are already visible in that area, so this would actually clean it up if I can figure out a way to have the exhaust exit through the skirts.

[Gaugster]

Have you considered using a total of four exhaust tail pipes? Like 3" to each straight through muffler, to a short "Y" and then dual 2" or 2.5" out the back. Alternately a chambered muffler with one input and two outputs. Side pipes look to be more simple and less weight too.

[CV355]

Have you considered using a total of four exhaust tail pipes? Like 3" to each straight through muffler, to a short "Y" and then dual 2" or 2.5" out the back. Alternately a chambered muffler with one input and two outputs. Side pipes look to be more simple and less weight too.

Originally I was planning on two out the back and two out the side (from elec cutouts).  I suppose I could go oval from the muffler back, but that gets really expensive really quick.

The more I think about the side exhaust, the more I'm liking it.