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6.9 Exaust


Old 03-09-2018, 11:14 AM
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6.9 Exaust

I got a 1986 f250 6.9 ext cab and I want to put a new exaust system on it. I know there isn't much out there for bigger exaust for the 6.9 but do you think it would be cheaper to go to a preformance shop and make pipes for my truck or to buy a hypermax or one of the few ones out there. Also what would you suggest for headers to buy that would be the best preformance wise. Thanks
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Old 03-09-2018, 12:10 PM
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Julian unless there's a good exhaust system I'm not aware of, I suggest you go to a local muffler shop. The owner can give you advice and exhaust shops usually carry "house brand" mufflers which will save you some money.

I know there are headers available for the 6.9l and 7.3l IDI, but I'm not sure who makes them. I've read that they have fitment issues. Hopefully someone else will chime in.
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Old 03-09-2018, 06:46 PM
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Old 03-10-2018, 10:36 AM
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Aside from replacing a plugged muffler with something better, you aren't going to get any noticeable performance gains from a 'performance' exhaust. It's just... not that much a restriction.
The limiting factor with an IDI is air in. Simple as that. Once you pass 'peak torque' at 1600RPM, the engine is drawing a vacuum and pulling less and less air per revolution, which means less and less power(per rev - less torque). This is why the torque curve peaks at 1600 and then drops above that.

If you want better performance, there's one good way of doing it: Add a turbo. Simple as that.
If you add a turbo, you just add power, period.
The limiting factor on a 6.9 with a turbo is head bolts(blowing a head gasket), so if you want to push more than, say, 6PSI of boost(effectively adding perhaps another 50HP or so), you need headstuds.

(Note that if the fuel system is worn out, has been in there for over 100K, installing a new IP and injectors will net you some gain, up to near stock performance).

Installing a turbo is one of those things that you think "Eh, really? It's expensive, a pain to work around" etc... Until the day you install one. Then, you can't live without it.
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Old 03-10-2018, 08:31 PM
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I was in a pinch for time when my exhaust was falling apart. My downpipe off the turbo was good but everything after that has rotted out and fallen off. I wanted a striaght piece of 3" pipe about 8' or however long to before the rear wheel, and a 90* bend right in front of the wheel. I stopped by a local shop and asked for that in 3", they said $700... I said that's insane for one clamp or weld at the front, a 90* bend, and possibly a second joint if too long to do in one piece, and 2-3 hangers. Ordered a length of 3' pipe, mandrel 90*, and a chrome tip off Summit along with some clamps and ahngers and did it myself for under $100.

Yes headers are available for these engines. If you are really adament about staying naturally aspirated go ahead nad get them adn do a dual 2.5" system preferably with a crossover. It will help, but nothing compared to a turbo. For what an exhaust shop would charge you for a new exhaust you can get a used "stock" turbo (i.e. one of the 3 bolt on kits). Just get a turbo and be done with it, you'll just have to rework the exhaust later when you get one, so now if the time to start looking.
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Old 03-13-2018, 11:31 PM
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As i recall a thread on OB, the headers do not really gain you anything, the results were well within the dynos margin of error. The reason is quite simple, the cam in the IDI is so tame, there isnt enough overlap, nor the rpms, to have any real effect on exhaust scavenging. Dual 2" with a free flowing muffler will be more than adequate. As others have mentioned, the best exhaust upgrade there is, is a turbo.
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Old 03-13-2018, 11:38 PM
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i always run straight pipes on my 6.9 they sound great
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