new 392 but old exhaust

rebel65 said:

hey all.


so i know this must have been answered but i tried searching for it and i just ended up with a bunch of searches that had nothing to do with what i searched for.

anywhoo. got a new 351w stroked to 392 with the prettiest things possible that no one will ever see ( hopefully ) lots of cam, AFR 185 heads with the big valves. and some killer headers.

what i want to know is is there a reason to go 3". because i'm not revving over 6500 on the engine and i can't find 3" mandrel bent tail pipes lol.

is 2.5 for a 500 hp engine that doesn't rev too high good? or is 3" actually going to help performance wise?

thanks and sorry if it's been answered to death take care.

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Magnaflow has a complete 3" "Header Back" mandrel bent kit with an "X" pipe that includes 3" mandrel bent tailpipes . . . you might want to check them out . . .

rebel65 said:

yea, and it's also absurdly expensive. $655 + shipping is way more than i want to spend on a kit. although it is stainless which is nice.
the summit universal kit is 90 bucks.

i can get the summit 3"universal kit,summit cutouts with summit electric cutouts, flowmaster mufflers, some glass pack resonators, and still have money to get it welded before i even get to $600.

but what i am mainly asking is if 3" pipe the whole way is too big. + i don't like the magnaflow mufflers as much as flows..

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I think you can get the 3" Magnaflow kit from Performancepeddler.com for something like $498 shipped . . .

Also, it's my understanding that the Magnaflow mufflers are quieter than the Flowmasters

I'm using the 2-1/2" Magnaflow kit, but I'm replacing the "X-pipe" with a dual inlet/dual outlet Magnaflow "X-Flow" muffler, and am using a set of 20" body, 2-1/2" offset inlet--2-1/2" center outlet DynoMax Super Turbo mufflers, and am adding a pair of DynoMax 12" X 2-1/2" Race Bullets to the upper portion of the tailpipe as resonators, and a set of resonated 2-1/2" oval tips (I have a '70 Mustang, and they used oval tips that year).

I am using a set of Patriot Ceramic Coated shorty "Clippster" headers that have the collectors located at about the same place as the original exhaust system.

I've got a pair of 90-degree pipes welded on each side of the inlets of the Magnaflow muffler in an "S" shape toward the front of the car.

I've finished welding up the pipe from the header to the Magnaflow muffler on the right side, and have to finish the left side now.

Once I get the left side done, then I'll mount the muffler, tack the pipes to the "S" curve pipes I've welded onto the muffler, and then place hangers at the rear of it to support it, pull it off the car and weld it all up.

The connection between the Magnaflow dual inlet/dual outlet and the pipes to the SuperTurbo mufflers are Flowmaster ball joint connectors, for ease of pulling the exhaust to remove the trans if needed. I've already welded one portion of these connectors to the outlet side of the Magnaflow muffler, and will weld the other side to the pipe that will go to the SuperTurbos.

I will be cutting the original muffler hanger mounts from the reproduction mufflers, and welding them onto the back of the SuperTurbo mufflers, and since the difference between them and the original mufflers was only 1", they should fit right up with no problems.

I'll probably just clamp the tailpipes to the SuperTurbos, but I'll weld in the Race Bullets in the location where the original resonators on these cars went, and then probably clamp on the tips at the rear.

By the time I get done, it should be relatively quiet, but still have great flow and a good tone to it.

You might be able to do the same thing with the 3" Magnaflow kit, get a 14" long dual inlet/dual outlet "X-Flow" with 3" Inlets and Outlets, and use a set of DynoMax 3" inlet/outlet SuperTurbo mufflers like I am to quiet it down.

At least it would flow really well, and it would be as quiet as you could possibly get it with 3" pipe, especially if you put a set of 3" DynoMax Race Bullets in the tailpipes and get a set of resonated tips like I am . . .

However--it ain't cheap! I will have something like around $830 including a set of new collector adapters after selling off the two Magnaflow mufflers that came with the kit.

I already had the dual inlet/dual outlet Magnaflow, but I bought it several years ago and just had it laying around, but I think I paid something like $85 for it, and it's included in the price I listed above.

If you want it quiet, you're probably going to have to do it similarly to what I have done, but if you like a little louder, then you can eliminate some of the steps I have taken . . . maybe just add the SuperTurbo mufflers--it might be quiet enough for your taste with those on there, and you could get it done for around $500 after selling off the mufflers that come with the kit like I did, and whatever it will cost to get it welded up.

you arent going to see a huge difference in a good high flow 2.5 system and a 3" system except a huge difference in noise. You may see 10hp at extreme top end. I have a 408 and I am going to use FRPP dual mode muffs, I have borlas now, I may add some electric cutouts for when I wanna really draw attention.