Duals vs. Single 3" vs. Single 2.5" on CFI

[darkwriter77]

Been trying to decide whether it's even worth the hassle/expense of converting my '84 CFI Fox to duals, so I'm considering alternatives. This is my DD, not my weekend toy, so I don't plan to do any major mods to it in the future like heads or anything else, and I plan to keep it CFI for the sake of fuel economy and general drivability. I'd just like to uncork the exhaust a bit to hopefully give the thing a little more pep (maybe even improve the fuel economy just a tad, if it allows it to run more efficiently) and to give the thing some better sound - right now, it sounds exactly like a friggin' stock late-80's Crown Vic.

1. Is there any performance difference between duals and a 3" single exhaust?

2. Aside from a couple of minor upgrades (electric fan with 3G upgrade, drop-in K&N filter, bumped timing), on an otherwise stock CFI motor, would I even NEED to go with a 3" exhaust, or would a single 2.5" exhaust be sufficient?

3. If I do go with a 3" exhaust, would I need to have an entirely new exhaust made from the header flanges back, or could I use the existing downpipes (I'm assuming they're 2.5" on both sides?) and have a muffler shop merge them into a new 3" single pipe?

4. Anyone got any pics of their single exhaust setups on Foxes?

Mucho thanks in advance.

[Hemlock]

This page should help a bit

http://www.torquetechexh.com/whichsize.htm

http://www.torquetechexh.com/Web%20P...Which%2026.gif

Robert

[Marz]

My LTD LX has a 1991 mustang roller motor, 1985 Mustang 2.5" tubular exhaust manifolds with heat risers, a 1985 Mustang 2.5" dual y pipe that has been converted from a 2.5" single to a 3" single. It then has 3" single all the way to the back with a Dynomax ultraflo 3" in and 3" out muffler with a 2.5" dual tip that looks factory. I also added a late 1985 Mustang computer.

It's louder than my 85 Mustang and it's 86+ true dual conversion with Ultraflo mufflers and 2.5" cat back system.

[darkwriter77]

This page should help a bit

http://www.torquetechexh.com/whichsize.htm

http://www.torquetechexh.com/Web%20P...Which%2026.gif

Robert

Cool. So, according to that, a 2.5" single exhaust should be about all that I really need, given my limited plans for this car.

My LTD LX has a 1991 mustang roller motor, 1985 Mustang 2.5" tubular exhaust manifolds with heat risers, a 1985 Mustang 2.5" dual y pipe that has been converted from a 2.5" single to a 3" single. It then has 3" single all the way to the back with a Dynomax ultraflo 3" in and 3" out muffler with a 2.5" dual tip that looks factory. I also added a late 1985 Mustang computer.

It's louder than my 85 Mustang and it's 86+ true dual conversion with Ultraflo mufflers and 2.5" cat back system.

Cool. With the restrictive heads and CFI intake I'll still have on mine, and from what the above chart lists, I think 3" would be overkill in my case. I'm thinking a single 2.5" Magnaflow going out to a single 2.5" LX-style tail would be okay. I'd just have to have an exhaust shop bend up a better Y-pipe, or maybe find one from an '85 model (I've got a double-hump crossmember on hand, FWIW), before I could do anything else with it.

Cool deal, then. Just outta curiosity, do you have any pics of your setup?

[TuxStang]

I'm also going the 2.5" single exhaust route ... for the Y-pipe, i'll just modify a used off-road X-pipe i have laying around but cutting and weld shut its passenger exit ... this will give a better, i think, gaz flow than the pre-85 (don't know the shape of the '85) factory Y-pipe. Off course, i change exhaust manifolds to shorties too.

[Hemlock]

The stock 84 RS 5.0 Capri with the HO motor came factory with a Y pipe to single 2.5 exhaust all the way out the back with a duel exhaust tip(at least mine did) and it would be a direct fit for your car Dark if you could find one in a junkyard somewhere.

Just a thought,
Robert

[darkwriter77]

The stock 84 RS 5.0 Capri with the HO motor came factory with a Y pipe to single 2.5 exhaust all the way out the back with a duel exhaust tip(at least mine did) and it would be a direct fit for your car Dark if you could find one in a junkyard somewhere.

Just a thought,
Robert

True. I'm just thinking that it would be a slight improvement to have a shop bend up some fresh 2.5" pipe after the downpipes because that one going across from the driver's side to the passenger's side before it Y's into the cat is WAY smooshed by design (it's almost half-flat where it passes under the tranny) ... unless the other HO Y-pipes were a bit different and less restrictive. I think, if nothing else, I could probably buy an OEM replacement Y-pipe from Dynomax that would be less crimped and smooshed and then bolt up basically one half of a standard cat-back kit on there.

I should crawl under my car and snap pictures sometime. The stock system is friggin' horrible the way it's set up. And WTF is that stupid vacuum-actuated valve doing on the driver's side exhaust manifold, anyway? I have a set of 87+ headers sitting in my closet that I'd throw on there while I'm at it, if I knew they would bolt up to a stock Y-pipe...

[mattquerio]

Is the fuel for this debate weighing originality vs performance? IMO I'd just get a double hump crossmember, and a new h pipe, and run true duals all the way out. Nothing looks better on these cars to me than a set of OE 2.25 polished stainless pipes.

[Marz]

True. I'm just thinking that it would be a slight improvement to have a shop bend up some fresh 2.5" pipe after the downpipes because that one going across from the driver's side to the passenger's side before it Y's into the cat is WAY smooshed by design (it's almost half-flat where it passes under the tranny) ... unless the other HO Y-pipes were a bit different and less restrictive. I think, if nothing else, I could probably buy an OEM replacement Y-pipe from Dynomax that would be less crimped and smooshed and then bolt up basically one half of a standard cat-back kit on there.

I should crawl under my car and snap pictures sometime. The stock system is friggin' horrible the way it's set up. And WTF is that stupid vacuum-actuated valve doing on the driver's side exhaust manifold, anyway? I have a set of 87+ headers sitting in my closet that I'd throw on there while I'm at it, if I knew they would bolt up to a stock Y-pipe...

The 85 Roller HO's and the late 85 CFI HO's had a much better exhaust. As said... The 85 tubular exhaust manifolds had a 2 1/2" collector to 2 1/2" duals to a 2.5" single, through a cat then split again to 2 1/4" duals.

Even just grabbing the 85 (4 into one) tubular exhaust manifolds and y-pipe and then have a shop finish the job with a 2 1/2" single to the rear with a nice looking dual tip would look stock.