Dual Exhaust or Big Single

[Fresh Air Inspector]

Hello All,

I have an '88 Plymouth Caravelle (aka Gran Fury), that I eventually would like to convert to a better exhaust system. Bear in mind that mine has the vented fuel tank so moving it over to accommodate the drivers side tail pipe is not an option. So, my thoughts are as follows;

1. Run dual 2 1/4" tail pipes side by side on the passenger side.

OR

2. Run a single 3 or 3 1/2" tail pipe on the passenger side.

There are a number of muffler suppliers that offer dual inlet / dual outlet as well as dual inlet / single outlet to accommodate either of the above options.

Has anyone done either setup? If so, please share some pictures of your set up.

Looking forward to the feedback.

 

[Mikes5thAve]

Move the gas tank over and there's room for the second pipe down the drivers side. It would be a very tight fit to get two pipes down the passenger side.

 

[M_Body_Coupe]

Unless you insist on having stock appearing exhaust tips, may I suggest the behind the wheel option?

3", x-pipe here...sounds great!

 

[Oldiron440]

Stock 318? You don’t need more than a single 2 1/4” tailpipe.

 

[jasperjacko]

360 ran 2.5" y into 3" single, straight through borla with resonator in tailpipe. sounds great, flows great

 

[M_Body_Coupe]

Stock 318? You don’t need more than a single 2 1/4” tailpipe.

You know, I always wonder about just how much backpressure is in the system?

A while back as my brain was short-circuiting on this very thing I looked around for some low-psi pressure sensors that I could hook up to my Innovate data capture box...never found anything (but it was a spur-of-the-moment kinda thing), but if someone has an idea I'd love to hear about it.

In my setup I have the O2 sensor threaded into one of the X-pipes and that leaves an empty slot in the other side...easy to mount a sensor, go for a ride and capture some data!!

 

[Mikes5thAve]

My 88 with 360 has a true Canadian Y-pipe going into an R body muffler and tail pipe, which had to be cut down to fit an M body. I think it's 2 1/2 but have to double check that.
I bought the y-pipe new, my only partial regret is that we cut it at one point to add a cat to it but it was starting to rust at that point anyway since it wasn't galvanized.

 

[Duke5A]

Completely depends on the intended usage. Personally I like duals out to the bumper, but as said the tanks needs moving over a strap. This was easy on the earlier model cars, but the newer like yours is a pain in the ass. The tank has a hump in the center for the vent and that fits in a depression in the trunk floor. If you're just doing something mild 2.25" duals off of the manifolds to a single 2.5" out the back will give you room for upgrades.

 

[Sub03]

I think Aspen500 have a dual pipe setup on the passenger side. Beautiful work IMO.
There is at least one thread on this forum with pictures of it.

Edit: found it.

factory F body dual exhaust?

 

[Aspen500]

It was a ton of work doing my exhaust. Dual 2 1/2" pipes will fit going out the passenger side, JUST. There's about 1/8" tolerance or they'll hit the fuel tank, or spring shackle.

 

[Magnum Aspen]

They did a episode of the Engine Masters TV show about this question. It was episode 60.
They had a 430 hp small block and compared dual 2.5 in vs 3 inch single.
The takeaways were, at that power level, muffler design and pipe merge design on the single exhaust made a bigger difference than pipe size. On dual exhaust it was less sensitive to muffler design. Single pipe needs an efficient muffler.
The difference was not insignificant.

A lower power engine will probably be less sensitive to these changes.

My Aspen has single 3 inch.

 

[Fresh Air Inspector]

Hello All,

I'm overwhelmed by the number of responses - thank you!! A few comments.

M_Body_Coupe - VERY NICE looking exhaust system. Where did you find the pipes? Mandrel bent stainless pipe is hard to find. Lyell's exhaust in Burlington, ON sells pieces for welding up. Here in NS nobody does mandrel bent exhaust pipe. :-( Did you find the interior exhaust noise increased with the 'behind the wheel' exit?

Back pressure is a huge discussion point. There is an interesting YouTube video by David Vizard on the subject of 'zero loss exhaust' including comments on back pressure.



Like you, I plan to add a wide band O2 sensor connected to a air fuel ratio meter to see what is happening in the combustion chamber.

Sub03 - thanks for the link to Aspen500's exhaust system, quite the work of art. Hats off to you. Amazing!

Once again - many thanks to all of you for the feedback, it has given me a great deal to think about. My car is a long term project (just finished reinstalling the rear axle; 8 1/4 with 3.55 limited slip). Hope to have it on the road by the Spring of 2025. Fingers crossed.

 

[Fresh Air Inspector]

Aspen500,

Forgot to ask, what brand of muffler did you put on your car. BTW the underside of your car is pristine - well done!

 

[M_Body_Coupe]

M_Body_Coupe - VERY NICE looking exhaust system. Where did you find the pipes? Mandrel bent stainless pipe is hard to find. Lyell's exhaust in Burlington, ON sells pieces for welding up. Here in NS nobody does mandrel bent exhaust pipe. :-( Did you find the interior exhaust noise increased with the 'behind the wheel' exit?

The exhaust was entirely done by a local race shop, so custom work all around.

Having said that, some of the piping did come out of a SummitRacing H-kit I picked up, thought it would have been an 'almost fit' on my coupe, but didn't like at all how ad-hoc the piping ended up once test-fitted. So I abandonded that approach, brought the car to the shop and had them do the work. Was very happy with the results.

Noise wise, what can I tell ya? The motor was already a hotter setup (238/244 @0.050 duration on 108LSA), so with headers and straight-through Hooker MaxFlow mufflers it's hard to talk about noise increase. Sure, it's louder, but that's "music to my ears" LOL

Further on, the current combo is a 408 W2 stroker (slightly bigger cam, roller actually but on 112 LSA), with 1-7/8" primary tube header (TTI) feeding into this system, and for that I do have a short clip, take a look HERE.

 

[Aspen500]

Aspen500,

Forgot to ask, what brand of muffler did you put on your car. BTW the underside of your car is pristine - well done!

Thank you!

At first it had Super Dynomax mufflers. Sounded nice but the interior drone was unbearable. Swapped to Dynomax Ultra Flo Welded mufflers. Drone is gone, but they are louder than I'd like. Added Vibrant Performance bottle style resonators behind the flex pipes up front. They toned down the high frequency notes but it's still loud.

These are the resonators.

 

[Fresh Air Inspector]

Aspen500.

Thanks for the follow-up. I'm curious as to why you added the flex pipes? I added a flex pipe to my Volvo 940 Turbo (2.3L 4 cyl. RWD, 3" downpipe and converter then 2.5" to a SS Magnaflow muffler at rear bumper), in an attempt to reduce drone which I assumed was from vibration. Didn't seem to make any difference. Planning to change the system to remove the flex pipe / cat and replace with a 3" Vibrant resonator. Will probably switch to stainless steel pipe as this vehicle is a year around DD.

 

[80mirada]

Adding the flex pipes can help with exhaust clearance when you have a tight fit, allows the pipes to be more firmly mounted. For guys with headers, it usually help prevent cracking and collector gasket failure.

 

[Fresh Air Inspector]

Hello 80mirada,

Nice piece of insight especially the point about headers. Thanks!!

 

[AHBguru]

Best exhaust I had was dual 2.25, h-pipe, all out the rear, with factory-appearing turndowns.

Slide the tank over, finesse a spot (BFH) for the rollover valve, and hook it all back up. Of course, that's also the time to replace the tank and all the crusty old lines back there.