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Old 12-11-2015, 01:09 PM   #1
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Default Naturally Aspirated Exhausts

I am currently building a DD VVT Miata. I am about to start working on the exhaust part of it. Currently it has a cheap OBX header, it came with the car and will be staying on for the time being. Long term I will be switching to a RB header to use. I found a local RB exhaust for sale for $300, it includes the test pipe, mid pipe, and axle back. I am tempted to pick it up. On the other hand I could fab up my own 2.5" exhaust for slightly less then it. Won't be stainless steel, but it will work. The RB exhaust is 2.375", will a 2.5" make a bit more power? I am tempted to just grab the RB exhaust because it is already made and would be quick and easy to swap on, but if building myself one would make a bit more power I could be tempted to go that route. What do the masses say?
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Old 12-11-2015, 01:15 PM   #2
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building a DD VVT Miata...

make a bit more power?
Probably only north of 5000 rpm. I'd assume a smaller diameter exhaust for a N/A car would actually give you more torque down low.

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I am tempted to just grab the RB exhaust because it is already made and would be quick and easy to swap
That's what I'd do. You have to consider how much your time is worth to you too.

Sort of related, cool video:
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Old 12-11-2015, 01:18 PM   #3
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Probably only north of 5000 rpm. I'd assume a smaller diameter exhaust for a N/A car would actually give you more torque down low.



That's what I'd do. You have to consider how much your time is worth to you too.

Sort of related, cool video: No More Exhaust Myths - /ENGINEERED - YouTube
Watching the video now.
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Old 12-11-2015, 01:19 PM   #4
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2.5 might make a little bit more power and can probably be made a bit lighter. I know plenty of guys who fabbed their own exhaust and didn't use stainless and its holding up fine. A 2.5 with a resonator and muffler will sound great.

For a DD I still vote easy button and go with the RB.
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Old 12-11-2015, 01:32 PM   #5
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I miss my RB muffler

It sounded so pretty.
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Old 12-11-2015, 01:38 PM   #6
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I have a RB exhaust on mine that I bought used.

Previous Owner of the exhaust had welded in a resonator on the midpipe. One word of caution, if you put a round resonator on, it becomes a low point of the exhaust. I bottomed out on a bridge over a small bayou yesterday and busted the resonator open. Had the resonator removed and a straight pipe welded in it's place (back to the original RB configuration) just this morning. It's definitely louder, but it sounds good and I haven't noticed any droning.
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Old 12-11-2015, 02:04 PM   #7
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sounds like 2.5" is good till 250hp over that you'll want 3"
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Old 12-11-2015, 02:55 PM   #8
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I am just going to build my own exhaust. Going with a Magnaflow 12577, which is the same muffler I use with my turbo setups, just 2.5" inlets and outlets. If it is not quiet enough then I will add a resonator or two.
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Old 12-11-2015, 02:59 PM   #9
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Only thing I really have to add is that the RB cat back (with resonator at least) sounds great for a street car as far as Miatas go. I also have a JR Header and Enthuza OBD-II cat, so I'm sure it'll differ from a different header and test pipe, but I've been happy with it for 3+ years now. Also, plug n' play.
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Old 12-11-2015, 03:09 PM   #10
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It comes down to the guy who has the RB exhaust won't take PP. I have the money sitting in PP to spend. So he is missing out. Muffler has been ordered, $82 shipped to my house. The rest of the piping is being ordered now.
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Old 12-11-2015, 03:10 PM   #11
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It comes down to the guy who has the RB exhaust won't take PP. .
What a dingus.
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Old 12-11-2015, 03:23 PM   #12
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What a dingus.
Yeah his loss. It will keep sitting on CL for longer and longer.

Time to build the exhaust is not a huge factor. I can reuse the jigs I have for my turbo setups. Besides the muffler the only pieces I don't have in stock at home are the flange at the header, and an expander to go from stock size to 2.5".

Long term I am hoping to do some dyno testing between the eBay header, RB header, and the new crazy CXRacing header.
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Old 12-11-2015, 03:44 PM   #13
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build own. add 2 resonators (or plan to) and the big monster muff.

the RB system is loud and obnox compared to the big muffler on a turbo car.
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Old 12-11-2015, 08:40 PM   #14
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3" straight pipe or bust.
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Old 12-11-2015, 11:02 PM   #15
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Old 12-12-2015, 12:20 AM   #16
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3" straight pipe or bust.
Thats what I run... made it out of some ally tube. 3" and N/A is very very loud though!
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