Exhaust size question

[mikester]

Went to a well known exhaust shop yesterday. I wanted to get prices on the wagon and for the coupe when its finished.
All along I had the idea of a 2 1/2" for the wagon. The owner of the shop said I should go with 2 1/4" instead due to running a 350/330. . When I told him I also didnt want the wagon to be a loud car he suggested a Dynomax 18" muffler. Wasnt specific on the model just the size. Opinions ?
I also asked about SS or aluminized steel. SS was 200-300 more. This is all mandrill bent. $900 complete without an X or H pipe. That was my choice.

The coupe in SS with 3" pipe, Flowmaster Super 40s, X pipe (which I might delete) came to $1500. Since I have other expenses coming up I might go with aluminized for that one too. I really wanted 2 1/2" tailpipes but it seems like once the shops set up to do 3" thats what everything is until they have to change the dies.

 

[565bbchevy]

Why don't you piece together a kit and install it yourself in the size you want?

 

[ck80]

Question... isn't factory recommendation on the 350/330 engine to use a 2.5"pipe? Or am I just making things up in my head?

I'm wondering if, without seeing things, he's recommending the 2.25" to make it a little easier to bend/fit where it's all supposed to go?

I don't think it was noise related, 2.5/2.25 aren't a huge difference in my mind other than one being slightly deeper in tone. Muffler would have more to do with that.

It's always easiest to spend someone else's money, but, if you do the math you're running about 20% more to go SS. At that price I'd rather pay and be done with it once, never worry about winter condensation making seams and spots rust out and need replacement.

 

[mikester]

Question... isn't factory recommendation on the 350/330 engine to use a 2.5"pipe? Or am I just making things up in my head?

I'm wondering if, without seeing things, he's recommending the 2.25" to make it a little easier to bend/fit where it's all supposed to go?

I don't think it was noise related, 2.5/2.25 aren't a huge difference in my mind other than one being slightly deeper in tone. Muffler would have more to do with that.

It's always easiest to spend someone else's money, but, if you do the math you're running about 20% more to go SS. At that price I'd rather pay and be done with it once, never worry about winter condensation making seams and spots rust out and need replacement.

Nope, the pipe size wasnt noise related at all. His feeling is the motor would be a dog low end with the larger size. I'll look into the requirements in the specs for the motor. Oddly enough I think they recommend 1 3/4" headers.
I thought about the condensation rusting out the welds but the cars in a garage that doesnt go under 45-50 all winter. I was surprised the owner didnt have the series of the muffler, just the length.

 

[mikester]

Why don't you piece together a kit and install it yourself in the size you want?

Most have the X pipe which I dont want. Plus Im running shorty headers. I dont weld.

 

[ck80]

Nope, the pipe size wasnt noise related at all. His feeling is the motor would be a dog low end with the larger size. I'll look into the requirements in the specs for the motor. Oddly enough I think they recommend 1 3/4" headers.
I thought about the condensation rusting out the welds but the cars in a garage that doesnt go under 45-50 all winter. I was surprised the owner didnt have the series of the muffler, just the length.

I got bored and here is a page from an old spec sheet from 2014. I doubt the updated it since, but, it's what they used to recommend.

 

[melloelky]

congrats on finding a place that mandrel bends,that's not easy to find.first/foremost figure out what you can afford to run,go from there.money'$ usually the great equalizer in these decisions..
what grade of stainless do they offer? the 300 series or 400?the latter seems to be the standard stainless grade these days.seeing you're going mandrel i can't imagine there's gonna be a large overall difference with your set up/intended usage,it's such a minute difference with those two sizes.if you were going back and fourth from 3" to 2-1/2 I'd say the smaller of the two but that's just me.

 

[SS_Malibu]

I just did the exhaust on my malibu a couple months ago. I used 2 1/2 pipe from the long tube headers back with no "X" or "H" pipe. I Dumped them out behind the rear tires like the Grand National. They fit fine over the axle. A shop that is mandrel bending should have no problem with fitment. "X" pipes will generally give a louder sound kinda like the exotic cars but scavenge the exhaust better and equal out each side of the engine but lose some lower end torque. "H" pipes will help to add some lower end torque with minimal sound increase. Muffler choice will keep the sound to a minimum. You could add a resonator to quite the car some more. I used Patriot ceramic coated long tubes (which I wouldn't buy again) with no "X" or "H" pipe. That wasn't in the budget. I did lose some lower end torque but set the exhaust for the new motor that's not here yet. I does make that slightly worn 305 sound good.
Hope any of this helps.

 

[JD1964]

If I could design an exhaust just the way I want it would include and x pipe. I would prefer the x over the h for the purposes of installing a single wideband o2 sensor downstream of the x. I believe a single sensor downstream of the x will still get a decent mix of both engine banks, since the x will cross and mix the exhaust of both engine banks.

I use a single wideband o2 downstream of an x on my 92 Foxbody. It's a nice way to monitor the actual real time fuel conditions.

I suppose the only way to do it better is two wideband sensors, one on each pipe.

 

[pagrunt]

Most have the X pipe which I dont want. Plus Im running shorty headers. I dont weld.

Looks like the only true dual kit w/o any cross over pipe is the Jegs stainless kits but won't ship until the end of Dec.

JEGS 30525: JEGS Exhaust Kit - Header-Back Dual G Body Exhaust Kit 197801988 GM - JEGS

Note: Exhaust kit is designed for 1978-88 G-Body that was originally equipped with a SB-Chevy. Does not fit ANY Cutlass Supreme model. Designed for us

www.jegs.com

Searching & it looks like the only kits now out there for our cars would be this one, the Dynomax aluminized 2.25" kit. Then there is the Hooker "LS" kits w/ X in 2.50" & 3", the Pypes w/ X in 3" w/o cats or 2.5" w/ cats ($$$), and one from American Racing in 3" ($$$$). Looks like we're now loosing options on kits got our cars.