Budget Street/Autocross/Track 2.5 NC Project!

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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby MitchC635 » Sat Dec 22, 2018 4:52 pm

Is that a dual Helmholtz chamber muffler centered at 62 & 117Hz with some packing in the larger chamber? Does it sound as good as it looks?
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby Chuck H » Mon Dec 24, 2018 2:00 pm

Pretty sure it's a Roadstersport II muffler with a large Helmholtz chamber in front of it. Brian was talking about doing a really big Helmholtz chamber and mounting it transversely in front of the RS II to really fill up that empty space under the trunk almost like the factory muffler. And look how much attenuation it's getting -- that's going to sound awesome -- nice and throaty when you stick your foot in it, and no drone when you let off. :D

Not sure where the 62 Hz attenuation is coming from, but I'm pretty sure the chamber is tuned more in the 120 Hz range.

If you looked at a cutaway of that muffler setup, I'm guessing that the inlet neck for the RSII goes straight through the first muffler canister, and that there's a small side-branch in the canister to tune the resonator. Then the "second" muffler is a conventional RSII interally.
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby Brian » Tue Dec 25, 2018 6:02 am

As a keen observer of exhaust tech Chuck has it pretty well figured up as usual. Indeed that's an RSII can pushed closer to the bumper and thus shorter exit pipes to tips, which then makes room for Helmholtz chamber toward the front of the space. We indeed started with idea of having the flow pipe go right through the middle of the helmholtz chamber but soon realized that for production assembly that would make welding in the tight space between the two cans very much a challenge. Given the helmholtz can is smaller diameter we quickly realized we could offset flow pipe a little under the helmholtz can and straight into the RSII for clean straight flow and much easier assembly. Lots of testing to do still but happy so far with how it is going.
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby MitchC635 » Wed Dec 26, 2018 1:30 pm

Looks like it would be a little more expensive than the Super Q, and about the weight of the stock muffler overall but better flow and sounds. Should give the extra volume under full throttle that many want, but without drone or much extra volume while cruising. Definitely interested in this for my PRHT - any idea on likelihood of it being offered for sale and when it might be ready?
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby Brian » Wed Dec 26, 2018 7:50 pm

I certainly hope something good comes to the shelf from the efforts, we are over 2 weeks into just the new exhaust prototypes and testing. Odds are good something makes production from these efforts, but it's a team exercise and our Team will all drive the results and see if we can reach consensus. There are a few more prototypes I have not revealed yet, like this one:
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby Chuck H » Thu Dec 27, 2018 9:46 am

Another interesting variation -- Helmholtz SuperQ, I assume. :wink:

I like the RSII version a little better, just because the design is a little simpler. The center inlet on the RSII muffler body makes for less piping overall.

Keep the new ideas coming, though. It's cool to see you folks still interested in developing new stuff for the NC platform when everyone else just seems to be sitting on their existing product line and putting all their R&D into the ND.

And I know that I sound like the spoiled kid who's never happy with anything, but any spy shots of the prototype MAX midpipe? :oops:
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby LateNights » Thu Dec 27, 2018 7:24 pm

Chuck H wrote:And I know that I sound like the spoiled kid who's never happy with anything, but any spy shots of the prototype MAX midpipe? :oops:


Similar thoughts here - I read the thread on miata.net, and you (Brian), made mention of a dual HH set-up - any chance of seeing what that sounds like?
Last edited by LateNights on Thu Dec 27, 2018 8:38 pm, edited 1 time in total.
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby Brian » Thu Dec 27, 2018 8:37 pm

Midpipe with 5 inch cat.
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby BryanH915 » Sat Dec 29, 2018 12:09 pm

I think I will hold off on the purchase of a complete exhaust system until we find out where you are going to go with this Brian.
Or do you already have an idea if this will not work as well as the available midpipe/Super Q for a street/touring PRHT??
Thanks for doing all the R & D work once again!

Cheers
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Postby Brian » Sat Dec 29, 2018 2:22 pm

BryanH915 wrote:I think I will hold off on the purchase of a complete exhaust system until we find out where you are going to go with this Brian.
Or do you already have an idea if this will not work as well as the available midpipe/Super Q for a street/touring PRHT??
Thanks for doing all the R & D work once again!

Cheers


If you are within miles of stock the bigger 5 inch body converter won't really show results for you, it's really development work for the boosted and 2.5 conversion crowd, and it will cost more than current standard midpipe (best guess today is $100 over our standard midpipe). One of the interesting things about the helmholtz is that the further up the system the helmholtz can do it's job, the better job it does. So, we actually need bigger version in the muffler area to equal the current Helmholtz Midpipe that already exists which is amazingly effective, and was tuned in my wife's 2012 PRHT. So, if not adding turbo or 2.5, for a PRHT our current street header with helmholtz midpipe and SuperQ is the popular combo and I don't expect new options to be more effective or cost any less for the full combo (particularly since new options must be quoted with higher materials costs thanks to Trump's trade war which has spiked costs on all metal raw materials by big percentages). Moreover, all the tooling for existing parts was paid off years ago.

Thus, assuming you are normally aspirated 2.0 the only thing that might really be tempting here for standard 2.0 street customers is option for putting helmholtz at the rear if either the Helmholtz RSII or Helmholtz SuperQ makes it to market, that will make the install just a bit easier than the helmholtz midpipe that some less experienced customers find challenging simply because it is stuffing so much into the center tunnel. But in terms of effectiveness per dollar, I don't expect the new bits to beat current system actually developed on the PRHT in particular.

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