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  1. #1
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    Default 85 Stock exhaust vs duals - gains?

    Long story short, stock 85 Mustang had a Dynomax catback on it when I got it. The sound wasn't bad, but they cheapened out and put non-polished tips on it. I recently bought a set of Flowmaster polished tips to put on it off Craigslist. Now I reconsidering if I should put a later offroad Hpipe and true duals, so it's 2 1/2" all the way. Realizing, I'll also have to get a double hump crossmember.

    Is there any performance gains on a stock motor, or is it a huge waste of money to go true duals? I've seen few threads, but they are conflicting in responses.

  2. #2

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    Uncorking exhaust = gains in performance and efficiency on anything.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
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  3. #3
    FEP Super Member escogt's Avatar
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    To me the sound alone is worth the effort.
    '85GT Bright Atlantic Blue
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  4. #4

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    I'd do it, it opens up tons of exhaust options for you as well.
    1984.5 G.T.350 had since 16y/o
    95 Cobra, Crystal White

  5. #5

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    We so need a like button^^^^^, lol!
    1984.5 G.T.350 had since 16y/o
    95 Cobra, Crystal White

  6. #6

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    My guess is 10 or so horsepower vs 85 exhaust, probably more on my even more restricted 84. Totally worth it for the sound too
    1984.5 GT 5.0 5 Speed ANALOG
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  7. #7
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    Default

    Thanks for the input, I figure there is some minimal gain, just trying to figure out if $350 = 10 hp is worth it or not. It sounds pretty good now, but the non-polished tailpipes has bugged me for some time, glad I lucked on to them.

  8. #8

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    87 xr7 was rated at 150hp with a y pipe and small tail pipe through manifolds. With a y split fake dual in 88, they rated it at 155hp with no other changes.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  9. #9
    FEP Member brianj's Avatar
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    Quote Originally Posted by escogt View Post
    To me the sound alone is worth the effort.
    This. Also, if you are concerned with gaining horsepower now, it will only get worse. It IS addictive. If you plan on any other performance mods later, an improved exhaust is mandatory. Buy an exhaust now that may be overkill, but never need to redo it.
    1983 Mustang G.T. No-option stripper- I like strippers.
    5.0, GT40P heads, Comp Cams XE270HR-12 on 1.6 rockers, TFI spring kit, Weiand 174 blower, Holley 750 mechanical secondarys, Mishimoto radiator, Edelbrock street performer mechanical pump, BBK shortys, T-5 conversion, 8.8 rear, 3.73 gears, carbon fiber clutches, SS Machine lowers, Maximum Motorsport XL subframes, "B" springs.

  10. #10
    FEP Super Member erratic50's Avatar
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    We've all spent way more than $350 based solely upon how something looks.

    there are several articles from when these cars were new that guys would go to aftermarket headers and catless H pipes the drop the cat-back and go 0.2 faster and around 5 mph faster in the 1/4 mile and that's on the "open" 86 and up cars.

    That being said free flowing exhaust is a joy to listen to while driving and it is also a critical foundation piece to making a fox rev and produce power up top. There are big gains to be had even on a stock headed car by freeing up the airflow and huge gains to be had once cams and heads and intakes, etc, enter the equation. But none of those gains are realized if the motor can't get the spent gases out the tail pipe so by all means, upgrade the exhaust to true duals!

    I believe hotrod did a fox oriented article back in the early 90's that discussed single vs true dual. If memory serves me correctly they saw over 15 HP and 750 RPM of additional usable rev range appear on a single exhaust fox just by opening it up with true duals.

    I would go to either long tube or equal shorty headers if you budget allows. At one time guys would port the head flange side of the stockers but headers are so cheap and common these days that the only reason you would ever consider that is looks under the hood on an modified original IMO. You really want 1 5/8" o 1 3/4" header tubes feeding 2.5-3" pipes in the end which the factory is far from.

    I would not say that larger pipes are always better - or we would all run 5". There are space and fit concerns. For a power plant up to 500 HP 2.5" is generally sufficient although the big power guys will start seeing gains up top with 3".

    long vs short tube is an age old debate. On the street a stock 5.0 if often guilty of too much low end torque so only go long if you've played with cam and heads, etc, and now want some low end back. Equal shorties are often a good compromise.

    X pipe vs H pipe is a matter of choice in sound preference and power delivery attributes. X pipes make 1-2 HP more and more torque up top past peak than H, but honestly having equal shorties and catted X and the same old flow masters I've had forever- I miss the sound of the H pipe. The X sounds a little too ricer for a fox in my opinion.

    you could always just go aftermarket headers and electronic dumps. That would remove the performance part of the conversation and you would have the sound you appreciate and the look that's stock when it's not uncorked. Total sleeper move IMO.

    we don't see many single exhaust foxes in large part due to the performance facts. Back in the 90's when I was looking at foxes to buy there was only 1 83 Capri for sale in my area that had single. Everything else four eyed with 5.0 and 5 speed and low enough miles had already been converted to duals or came factory with them. (Trx wheels, 4 barrel, etc - cool car BTW)

    . Opening one up and preserving the year correct configuration seems to me to be the best of both worlds.

    Enjoy your car!

  11. #11
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    Quote Originally Posted by brianj View Post
    This. Also, if you are concerned with gaining horsepower now, it will only get worse. It IS addictive. If you plan on any other performance mods later, an improved exhaust is mandatory. Buy an exhaust now that may be overkill, but never need to redo it.

    Appreciate everyone's input. I've got another car that's heavily modded, and satifies my need for speed. This car only has 63K miles on it, so I'm trying (hard) to keep it mostly stock. I did order a set of subframe connectors. I think I am going to pursue getting something going with the exhaust. I will say I do like the sound of flowmasters on someone else's car. I find them pretty annoying for anything I'm riding in, so that choice is out. I prefer the H-pipe sound, so I'll loose that extra couple there.

  12. #12
    FEP Senior Member burntorange84's Avatar
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    If you keep it mostly stock, just put the tail pipes on and enjoy it. There are other things like header ball flanges and losing the heat riser and warm up tubes on the 85 headers to consider. It can be all done, but the effort is probably not worth it for the small performance gain. Losing the cats will confound other problems if you don't use a cated H/X pipe....unless you enjoy stinky exhaust. Now, if you had the 84 or early 85 single exit system, then I think it's all worth the effort. The 85 semi duals is not terribly restrictive on a stock system.

    -j
    _________________________________________
    1984.5 Mustang GT: org. 5.0, 5spd, 3.27's;
    GT-40's w/93 exhaust; t-bird TC brakes....

  13. #13

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    Quote Originally Posted by burntorange84 View Post
    If you keep it mostly stock, just put the tail pipes on and enjoy it. There are other things like header ball flanges and losing the heat riser and warm up tubes on the 85 headers to consider. It can be all done, but the effort is probably not worth it for the small performance gain. Losing the cats will confound other problems if you don't use a cated H/X pipe....unless you enjoy stinky exhaust. Now, if you had the 84 or early 85 single exit system, then I think it's all worth the effort. The 85 semi duals is not terribly restrictive on a stock system.

    -j
    This X100. Will your car have more power? YES, no question. What everyone above said is correct. You might gain 10 HP. Lets say you do. You want to know the bad news? Every car with a carburetor on it has 10 more HP on some days and 10 less on other days. Even with no changes made. ALL of them. Do they end up being towed home? Not hardly. It's called that's how it works. There is no way you would ever notice the difference on a stock car during daily driving. Can't be done. It WILL sound better though but you aren't asking about sound.
    Liberty once lost is lost forever.

    John Adams
    July 7, 1775

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