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  1. #1

    Default Going full dual exhaust on 85

    My stock style exhaust is about to fall off my 85 and I was thinking about switching to full dual 86 style. Forgive the question, but I will need to convert to a double hump transmission crossmember, correct? I have read lots of threads, but still confused. Any advice is appreciated.

  2. #2
    FEP Member 5pointoh's Avatar
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    Yes, that is correct you will need a double hump transmission cross member. On a side if you really want the old school five oh sound I would suggest getting the Flowmaster 40 series mufflers. You have to buy them as individual mufflers. Unfortunately they do not offer the 40 series in the cat back kits.

  3. #3

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    Someone else will have to verify but also I want to mention to at least check on this. I don't recall if the '85 models still had that valve on the passenger side or not. It goes at the end of header collector and before the Y pipe. If yours does, you will have to get '86-93 headers as well because I don't think that EGR/vacuum valve (not sure what the correct name of it is) will mate to the stock H Pipe. Like I said, I could sure enough be wrong, just at least check on that. It's a fairly easy project overall.
    Last edited by homer302; 11-04-2018 at 03:59 PM.

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    FEP Member 5pointoh's Avatar
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    Not 100% sure about the EGR valve. But I went BBK equal length headers, BBK off road H pipe and welded in Flowmaster 40 series mufflers....you will be very happy. This is thee classic five oh exhaust set up going back in the day. This will all fit 86 to 93 Mustang and 85 Mustang with the cross member in place.

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    Be aware that you will have to reroute your rear brake lines if you convert from single to dual exhaust.

    Some good reading here:
    http://vb.foureyedpride.com/showthre...e+line+routing

    and here (although there is some seemingly incorrect information in here; pay attention to post #12):
    http://vb.foureyedpride.com/showthre...e+line+routing
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  6. #6

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    Quote Originally Posted by KevinVarnes View Post
    Be aware that you will have to reroute your rear brake lines if you convert from single to dual exhaust.

    Some good reading here:
    http://vb.foureyedpride.com/showthre...e+line+routing

    and here (although there is some seemingly incorrect information in here; pay attention to post #12):
    http://vb.foureyedpride.com/showthre...e+line+routing
    Actually, none of this is relevant to you. The '85 GT already had dual mufflers and tailpipes from the factory. It just had a Y pipe instead of an H pipe.

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    Hmm. My bad. From his post I was under the impression that he was converting from a single exhaust to a dual system.
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  8. #8
    FEP Super Member Bryan Knebworth's Avatar
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    Early '85s, built before 11/18/84, were equipped with single exhaust.

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    FEP Super Member bwguardian's Avatar
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    The 85 had a center support transfer for the rear brake lines. It will work with an offroad exhaust. However, if and when you change the 7.5" rear end to a 8.8" rear end, this center support is different...longer/shorter, but a unit for an 86 will work.
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    Quote Originally Posted by Bryan Knebworth View Post
    Early '85s, built before 11/18/84, were equipped with single exhaust.
    Mr. Bryan, you might want to recheck that date.

    My '85 was built in 10/84 and had dual exhaust with the center rear brake line location. It's also a 5-speed which by default makes it carbed.

    Is it possible you are confusing all production with just the CFI 5.0's?
    '85 GT

  11. #11
    FEP Super Member Bryan Knebworth's Avatar
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    Quote Originally Posted by qikgts View Post
    Mr. Bryan, you might want to recheck that date.

    My '85 was built in 10/84 and had dual exhaust with the center rear brake line location. It's also a 5-speed which by default makes it carbed.

    Is it possible you are confusing all production with just the CFI 5.0's?
    CFI models only, this is correct. Interestingly, the 7.5 rear was used at the beginning of the '85 model year as well, not sure on the changeover date on that, however...

  12. #12

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    Quote Originally Posted by Bryan Knebworth View Post
    Early '85s, built before 11/18/84, were equipped with single exhaust.
    All 1985 Mustang GTs were equipped with a single exhaust. Every single one of them. Dual mufflers are not the same thing as dual exhaust. If it passes through one pipe anywhere, it's single exhaust.

  13. #13
    FEP Super Member Bryan Knebworth's Avatar
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    Quote Originally Posted by homer302 View Post
    All 1985 Mustang GTs were equipped with a single exhaust. Every single one of them. Dual mufflers are not the same thing as dual exhaust. If it passes through one pipe anywhere, it's single exhaust.
    I can't tell if you're joking or serious lol I know for a fact that some (early) '85 GTs left the factory with the '82-'84 GT style exhaust with the single splitter pipe. As far as 'what constitutes TRUE dual exhaust', I guess that's up for debate.

  14. #14
    FEP Member 5pointoh's Avatar
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    Bryan: In almost 30 years I have never seen an 85 GT with the 82 to 84 single splitter pipe. I also owned an 85 for about 27 years too. Have you actually seen an early 85 GT in person with this set up?

    I think most would consider the Y pipe in 85 to be a pseudo dual exhaust.

  15. #15
    FEP Super Member sowaxeman's Avatar
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    Quite simple and not really worth bickering about. 1985 = single/pseudo/fake-dual exhaust....1986+ = TRUE dual exhaust. As for the early 85's with true-single exhaust, I believe I have seen it in pictures but never in person.
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    FEP Member 5pointoh's Avatar
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    Quote Originally Posted by sowaxeman View Post
    Quite simple and not really worth bickering about. 1985 = single/pseudo/fake-dual exhaust....1986+ = TRUE dual exhaust. As for the early 85's with true-single exhaust, I believe I have seen it in pictures but never in person.
    Yes, agreed

  17. #17
    FEP Super Member Ken P's Avatar
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    Did it on my 85 GT. Mac shorty headers & two cat high flow H pipe. Double crossmember. Might need the double hanger on the trans mount as well. It's been a long time but I also vaguely remember having to shift the clutch cable & speedo cable over to the side towards the transmission.
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  18. #18

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    Thanks for all the advice. I ordered a Pypes x pipe and mufflers/tailpipes. Reviews seem good and the setup fits my budget. I didn’t get the cats. Thanks again.

  19. #19
    FEP Super Member sowaxeman's Avatar
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    I've used Pypes before and was very happy with the quality, fit & finish for the $$ Just realize your exhaust is going to smell a lot stronger than you are use to without the cats.
    Jason Smith
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  20. #20

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    Quote Originally Posted by sowaxeman View Post
    I've used Pypes before and was very happy with the quality, fit & finish for the $$ Just realize your exhaust is going to smell a lot stronger than you are use to without the cats.
    Hi yes, I’m planning for that. Truth is the 85 is running like dog crap recently. I am planning to run through the entire fuel, exhaust and emissions systems this winter. Ordered every vacuum line size I could find in the car, a rebuild kit for the 4180C and converting to true dual exhaust. Plan is to get all that done and order some mini cats in the spring if the smell is bad. Gas smell is terrible now- carb running super rich. Just planning to tackle everything in stages. I’m literally on this site reading threads every night! Lol! Lots of good information! Thanks!

  21. #21
    FEP Super Member sowaxeman's Avatar
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    Get'er running by May and bring it to the Shelby Spring Fling in Brown County State Park! Its a great weekend event, you won't be disappointed
    Jason Smith
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  22. #22

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    Quote Originally Posted by sowaxeman View Post
    Get'er running by May and bring it to the Shelby Spring Fling in Brown County State Park! Its a great weekend event, you won't be disappointed
    Sounds great!

  23. #23
    FEP Member 5pointoh's Avatar
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    If it is not your daily the gas smell is worth it for the performance of not having cats. It really frees up the exhaust flow and sound!
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  24. #24
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    sorry to stir it up...but I believe the 1985 CFI GT cars came came with the 84 GT exhaust or at least the early ones did.

  25. #25

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    Got all my stuff from LMR. I’m really happy with the quality of the Pypes system. As I look at my current exhaust, I can see that I needed the dual hump cross member, but looks like the exhaust hanger bracket on the crossmember would work with duals. I’ll take some comparison pics when I get started.

    I have a question about the stock smog/air pump tube that currently feeds into the y pipe ahead of the cat. I know I don’t need this for the new setup and if I install the aftermarket mini cats, they won’t need the air injection. I plan to keep the air pump and stock belt configuration. Do I just remove the tube going to the exhaust? It no longer serves a function that way, but I eventually want to get all the emissions vacuum lines, charcoal canister, etc, back to stock. Would there be any issues with that?

    Thanks to everyone who has offered advice- much appreciated!
    Last edited by GT Town; 12-02-2018 at 07:55 AM. Reason: said thanks!

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