2.5" exhaust - 986 Forum - The Community for Porsche Boxster & Cayman Owners

ike84 · 02-14-2021, 05:42 PM

Hey gals and guys, here's my (almost) finished 2.5" straight pipe exhaust I rigged up. I know this sounds rather excessive, but there is a method to the madness lol.

So, without further adeu...

Gut the stock system. Yuck. Seriously, this is an awful exhaust. So.much weight, such little pipes, I get it (emissions, sound ordinances, yadda yadda) but geez come on. 1.5” pipes after the second cats? I'm amazed the poor girl can breathe at all.

After thats out, clean er up real nice nice and get ready for the goods - Chinese headers of course! Painted with high temp grill paint and then wrapped. (everything is painted, not for thermal effect, just for rust prevention).

Here's the tricky part - the collector on these is only 2". Not big enough. The 987 collectors are 2.25". Getting better but at a grand a pair that's just ridiculous. So what to do? Fab an adapter! This was the hardest part, finding a 2.5" "collector reducer" that I could then weld a 2" flange on the other side. That took 10 seconds to type out but it took me 2 weeks of endless searching to find the dang part that would work. Anyway, I digress... These were too short to wrap but did get a triple coat of paint.

After the 2 to 2.5 adapter comes the 2.5 pipes. Offset was needed here. Again this took quite a bit of searching but hedman made just the right set. Painted and wrapped just like the heads.

Last but not least the pretty part h simple 2.5" chrome turndowns. They're tucked up under the car to far to see currently, but they won't be like that for ever.

Now for the assembly. All joints get aluminum crush gaskets with a thin coat of the copper silicone gasket goop. Adapters in the headers, headers onto block. First snag encountered - O2 sensors too long to fit in first sensor bung on passenger side. Thanks china. No problem, moved down to second bung, got some slack on the harness, and used the postcat sensor (which as far as I can tell is the same sensor but with a longer harness). Problem averted. From there the offset pipes go on, sneaking past the strut tower and over the sway bars. Good clearance on driver's side, super tight on passenger side. Now the tips went on (with a generous coating of antisieze) and pointed down and out. Lastly the diagonal bars and aluminum plate went back in. The trapezoidal bar that supports the aluminum plate in the rear touches the passengers side pipe (grrrrr) but clears the driver's. Everything torqued to spec and voi la.

Now, I would like some opinions. I do not like the fact that the pipes touch rigid structures. My concern is that something will break. I think that I need put a donut with spring bolts between the 2-2.5" adapter and the offset pipes. This will suck donkey nuts because I will have to disassemble everything, unwrap the pipes, and then put everything back together. But, I sure as hell don't want to crack anything, especially at the block (go ahead, ask me how long it takes to drill one of those out and retap the hole lol). What are yalls thoughts about this?

Anyway, I hope everyone enjoys!

Best,
Ike

Oh, one other thing - the aluminum plate came off in the beginning without effort. It took a bit of oomph to get back on. I was gonna have the alignment checked before going crazy, has anyone else encountered this?

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Starter986 · 02-15-2021, 03:21 AM

Niiiiiiice.

ike84 · 02-15-2021, 04:06 AM

Quote:

Originally Posted by Starter986

Niiiiiiice.

Thanks man!

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itsnotanova · 02-15-2021, 08:42 AM

The parts rubbing will make a knocking noise but I'm not sure you'll hear it because that car will be LOUD. You're going to wake up the neighborhood with that exhaust. lol

ike84 · 02-15-2021, 09:50 AM

Quote:

Originally Posted by itsnotanova

The parts rubbing will make a knocking noise but I'm not sure you'll hear it because that car will be LOUD. You're going to wake up the neighborhood with that exhaust. lol

Our boat has a 454 bbc and it definitely rivals that! I haven't had. It back on the road yet, we'll see what is sounds like at that point. If it's so loud that I can't hear myself think then I'll probably put some single chamber mufflers on it. I figured it would rattle a bit through contact, but you don't think it will actually crack anything?

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howdy · 02-15-2021, 10:13 AM

Header wrap and water do not play well together. Even worse if you live in an area where they salt the roads.

ike84 · 02-15-2021, 12:23 PM

Quote:

Originally Posted by howdy

Header wrap and water do not play well together. Even worse if you live in an area where they salt the roads.

Is that because they trap moisture against the pipe? I anticipated this, that's why I painted everything. Or does it wear down the wrap? I don't drive much in the rain but it will definitely happen at some point. No salt though, that's what the truck is for.

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rfuerst911sc · 02-15-2021, 12:54 PM

I like what you have done except the no muffler ........ that is going to be loud . Report back after you have driven it a while .

ike84 · 02-15-2021, 02:03 PM

Quote:

Originally Posted by rfuerst911sc

I like what you have done except the no muffler ........ that is going to be loud . Report back after you have driven it a while .

Will do. Ive gotta check alignment and push 996 row tune on it before I can start running her around but I will keep the post updated.

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911monty · 02-15-2021, 02:21 PM

While you ultimately wanted to reduce back pressure by using the 2 X 2.5" adapter that actually will increase pressure. Expanding the diameter reduces velocity of the gas, reduce velocity increase pressure. Just my .02.

rfuerst911sc · 02-16-2021, 02:07 AM

In a perfect world you would have done before and after chassis dyno runs . Start with stock tune and exhaust and then start with mods . Being able to monitor any changes ( positive or negative ) is the only way to truly know the results . But very few have access and $$$ to blow on multiple dyno runs .

ike84 · 02-16-2021, 05:59 AM

Quote:

Originally Posted by rfuerst911sc

In a perfect world you would have done before and after chassis dyno runs . Start with stock tune and exhaust and then start with mods . Being able to monitor any changes ( positive or negative ) is the only way to truly know the results . But very few have access and $$$ to blow on multiple dyno runs .

There's actually a shop not to far from me that rents a dyno trailer for a day, which I'm gonna try to get my hands on once it warms up. I didn't dyno before because, well, I just didn't have the time to get down there to do so. I am gonna do a bunch of runs though to test the whole package (intake and straight exhaust with 996 row tune), and then try different tunes (row vs us) and also some minor changes (resonance flapper deleted, single chamber mufflers, etc). I will definitely post them once it happens, not sure when though.

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ike84 · 04-18-2021, 05:14 PM

Time for the update - it took a while to sort out some coolant issues but I've been running the straight pipes for about 50 miles... It's too loud... Way too loud... Like permanent hearing loss by the end of summer too loud. Not only that, but dirty too. At 100mph you don't notice any fumes, but you will reek of fumes every time you drive. This may be because the exhaust terminated under the car and not behind the car, but never the less the whole setup wasn't a good fit for a DD.

So, here's what I've done. I added high flow universal cats at the end of the 2.5" pipes. Quieted things down but my wife still refused to get in the car lol. So I stuffed some bored out internal baffles (db killers) into the pipe before the cat. And now my wife (and I) love it! It's not quiet by any means, still on the loud side (probably will get your name brought up in an HOA meeting) but it's got a phenomenal deep growl and you can have a conversation while standing behind the car.

On an interesting side note, while the car was straight piped, there was still a drone! Exactly where it ought to be - 2-2.8k rpm. Unbelievable! It's clear to me now that this a feature of the engine harmonics and not the exhaust system, and the only way Porsche was able to kill it was with a choked off set of pipes and a gas tank sized muffler. Ahhh the m96 motor, what a marvel of engineering this machine it. If anyone has ever ported their head, I would love to know what effect that had on the drone.

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ike84 · 05-12-2021, 05:11 PM

Update 2

The idea of the internal baffles bothered me, so I removed them and added shorty glass packs following the cats. Good thing I did! The damn things had dislodged and were eating through the cat matrix (I should've seen that one coming. Oh well, ya live and ya learn).

Interesting side note - the heat wrap works. I had a bit of trouble lining up the pipes perfectly when I installed the glass packs so I left it and figured I would straighten out another day. The top 1" or so of the passengers side muffler overlapped the bottom of the bumper with about an inch between the two. Well, that was close enough that it melted the bumper! The melting point of fiberglass is 2050 deg F so, like I said, the heat wrap is clearly working lol. This gives me a good excuse to now make the "aero mods" to the rear bumper I've been scheming for a while now.

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