2GR Exhaust Design Discussion - MR2 Owners Club Message Board
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post #1 of 31 (permalink) Old May 29th, 2019, 13:44 Thread Starter
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2GR Exhaust Design Discussion

I posted a few months ago about a new center exit exhaust that I built for my car. https://wilhelmraceworks.com/blog/ce...-exhaust-build




I love the look, especially with the diffuser that I built around it, and by all accounts it sounds good and isn't too terribly loud from outside the car. But inside the car, it drones something awful in the 2k-3k range, and is loud enough at WOT to be annoying. The drone has been improved on quite a bit with the addition of a Helmholtz resonator, and rubberized undercoating on both sides of the trunk floor has helped a little as well but it's certainly not fixed completely. I had a theory that I had caused it by mounting the exhaust to the trunk floor, but I have since built a new cross bar that mounts it to the stock muffler hanger locations and that hasn't cured it either (though it may have helped a little).

So... I'm thinking about building another one, and I'm looking for muffler and other design suggestions.

One thing I have been thinking is to use a single inlet dual outlet muffler, rather than the single outlet / twin tip I have now. The theory being then you have two perforated pipes through the muffler, kinda like having two mufflers in parallel. On the other hand, you probably have more volume of pipe and less volume of muffler packing, so maybe that wouldn't be an improvement.

A larger muffler is probably the best solution, although I cannot go much larger and still have it fit. My current Borla is 9.5" wide, 4" thick, and 14" long. Put a 3" pipe through that, and there is very little packing on the top / bottom of the pipe. Maybe this Vibrant would be better: https://vibrantperformance.com/catal...a3fedcaed0b2a? It's an inch longer (negligible, but every little bit helps), and an inch thicker which puts a lot more muffler top and bottom around the pipes. Also adds the above "two small pipes vs one big one" theory, and overall the Vibrant looks like a much more square shape rather than the Borla's very flat elipse, so it should have a larger volume. But I'm not sure how much real world difference all that might add up to...

Another option that might work is to use a larger transverse mount muffler such as this one https://vibrantperformance.com/catal...0a3fedcaed0b2a Much larger (and going transverse like this is the only way I will get substantially more muffler size), but certainly lends itself more to a traditional dual exhaust, and I'm not sure if it will tuck up above my diffuser. Some measurements will be required. I think it would be reasonably easy to bring the pipes back to the center for the outlet, and while all of this will probably throw away any weight savings I have with my current design, it feels like it might be the most likely to work just because of the muffler size.

One thing I have been wondering is if part of the problem is the extremely short length of my current setup. I know it's a totally different motor, and smaller diameter piping as well, but I have the exact same Borla muffler and cat on my MKI (also with headers) and it is extremely quite with zero drone. If this is in fact the case, then the large transverse Vibrant muffler might be the ticket, as it would also require a couple feet of pipe after the muffler.

Any other thoughts?


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post #2 of 31 (permalink) Old May 29th, 2019, 14:15
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My setup is Gouky headers, DDPR y-pipe, and Berk exhaust. It had a super annoying drone at highway speed 2500-3500RPM. So I used some cheap tailpipe inserts/baffles and this eliminated the drone entirely. This seemed nearly miraculous. The inserts can be removed and replaced easily when desired. On my MK3, the performance exhaust that I purchased was sold with a similar optional silencer included and it makes a big difference for that car too. Obviously this is an exhaust restriction and it has consequences. There's always a trade-off between performance and comfort. This might be something worth looking into for situations where comfort takes priority.
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post #3 of 31 (permalink) Old May 29th, 2019, 14:26 Thread Starter
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Yeah, I suppose it might be possible to make an insert like that that slips into my current Borla. Might be a little tough with the tip on it, but maybe... Does seem worth trying before building a whole new exhaust. And for around town and cruising down the highway, a loss of power isn't of any real consequence.

Interestingly, my OG Berk from the first group buy back in 2006 or so doesn't really drone at all...


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post #4 of 31 (permalink) Old May 29th, 2019, 16:08
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a little bit of restriction goes a very long way towards quieting things down. if you wanted a very quiet car when you're not at the track i'd look at adding an electronic dump valve inline with the current exhaust and put a 3/4" hole in it. that 3/4" hole will flow enough that you'll only lose 20, maybe 30hp but it'll be super quiet until you hit the switch and you'll get your power right back but with the noise for track use. (note i'm saying in-line, not as an actual dump)
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post #5 of 31 (permalink) Old May 29th, 2019, 19:57
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I would put a vacuum actuated valve before or just after the muffler (where ever you have the space really). Something like this. You can get them to completely open before 0 vac in the intake manifold, so no real restriction whatsoever on an NA engine. You might need to trim a little of the flapper or always hold it open a tad to keep some flow area, but the engine really doesn't need much at like -15 in-Hg intake manifold MAP before the valve is going to start opening.

https://www.ebay.com/itm/76mm-3-Vacu...frcectupt=true


I assume you can tweak the actuator preload a bit to vary the opening MAP parameters, and of course, per the description it is "precise, beautiful" and has "roar sound." I don't see how you can go wrong with it.
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post #6 of 31 (permalink) Old May 29th, 2019, 20:49
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A link to said inserts, please?
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post #7 of 31 (permalink) Old May 30th, 2019, 02:40
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Originally Posted by sarnodude View Post
A link to said inserts, please?
These are the ones that I bought:
https://www.amazon.com/dp/B00CP8K43S...40_TE_3p_dp_i1

Currently out of stock but similar/same units are available from other sellers at about the same price of $15-$17 each. The size for the Berk tailpipes is 4-inch. The units are available in other sizes to fit any exhaust.

PS> I found the same as mine listed on eBay
https://www.ebay.com/itm/Black-Unive...oAAOSwvfZaJiJl

Last edited by merryfrankster; May 30th, 2019 at 03:30.
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post #8 of 31 (permalink) Old May 30th, 2019, 07:14
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I ran two of the 3" Borla XS mufflers in series, not with the turbo. A 180 degree bend going back into the other. Not and MR2 but mid engine. I don't know if there is the room on an MR2, The only thing I hear at WOT is the intake. No drone at all. It's pretty quite.
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post #9 of 31 (permalink) Old May 30th, 2019, 08:28
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The length does have a lot to do with it. For my exhaust I mimicked the stock exhaust with a straight through perf core 5" x 8" x 24" muffler. It's pretty quite (relative to berk, etc,) maybe even too quiet? Definitely big and not the lightest option. I doubt its any more restrictive than the other options since on a dynojet it returned the highest numbers I'd seen for a stock 2gr before Gouky came out with his intake. I don't know how it would fit with your diffuser though.

Maybe you could do a paperclip bend like an Evora exhaust to get the length with the center exit? I know there all kinds of engineering models and equations out there for turning exhaust length, but I don't think we have enough room to for an 'ideal' length.
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post #10 of 31 (permalink) Old May 31st, 2019, 06:48
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https://www.lotustalk.com/forums/f17...64/index2.html

Kinda shows what Lotus does to get length.
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post #11 of 31 (permalink) Old May 31st, 2019, 07:48
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I would look into the SpinTech mufflers. They are known for not having drone due to their unique design.

https://spintechmufflers.com/street-mufflers/
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post #12 of 31 (permalink) Old June 1st, 2019, 23:02 Thread Starter
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Quote:
Originally Posted by Gouky View Post
a little bit of restriction goes a very long way towards quieting things down. if you wanted a very quiet car when you're not at the track i'd look at adding an electronic dump valve inline with the current exhaust and put a 3/4" hole in it. that 3/4" hole will flow enough that you'll only lose 20, maybe 30hp but it'll be super quiet until you hit the switch and you'll get your power right back but with the noise for track use. (note i'm saying in-line, not as an actual dump)
It certainly does! To test all of these theories, I built a couple of caps for the exhaust tips out of soup cans and hose clamps. With one side of the tip plugged and the other with a 1" hole it was VERY quiet. Almost too quiet, and it gave the exhaust a weird whistling noise. I then drilled a 1" hole in the other cap as well, and it's just about perfect for street driving / highway cruising. The drone is GONE, and it's much quieter overall, but still has a nice roar at higher RPM.

So, I think the easiest solution is just to get or make a slip in silencer that restricts the tips to around 1". As long as they are easy to install / remove I'm not too opposed to it being a manual thing, although the idea of an electric or vacuum operated valve is also appealing. I like the passive aspect of the vacuum valve, except for the fact that it will still be loud at higher throttle positions, no "quiet all the time" mode like you would have with an electric valve.

Oh, as a side note, I also got a db reading on my exhaust at an autocross today. 97db. So, not quiet, but not absurd either. It's really not the overall sound level that I'm looking to change, just the in car drone.


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post #13 of 31 (permalink) Old June 3rd, 2019, 22:34
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The electric valves don't seem to last very long - motors still get exposed to quite a bit of heat and they can't handle it.

You could always put a solenoid valve on a vacuum line and run it on a slightly hidden switch. Have it be normally closed, then flip the switch when you want to get rowdy.
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post #14 of 31 (permalink) Old June 4th, 2019, 12:51
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If I remember correctly, Hytech Exhaust have used twin loop mufflers to help reduce noise. I don't know the effects it would have on droning but they have a lot of experiencing in exhaust tuning so maybe you can consult with them?

https://www.hytechexhaust.com/about_us.html
https://www.facebook.com/hytechexhaust
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post #15 of 31 (permalink) Old June 4th, 2019, 14:40
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So, I think the easiest solution is just to get or make a slip in silencer that restricts the tips to around 1".
This solution will never gain any traction because a. it's too easy b. it's too cheap and c. it's too effective. Can you please come up with something else that involves some fancy expensive gizmos? LOL.
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post #16 of 31 (permalink) Old June 4th, 2019, 17:18
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I hope I don't need them, but jic I do, thx!
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post #17 of 31 (permalink) Old June 4th, 2019, 20:20
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Originally Posted by merryfrankster View Post
This solution will never gain any traction because a. it's too easy b. it's too cheap and c. it's too effective. Can you please come up with something else that involves some fancy expensive gizmos? LOL.
The problem is that you only have the exhaust area of a roughly 1.5" diameter pipe. I can't see that not choking down a ~300 rwhp engine REALLY badly.

Sure, you can remove the silencer, but everytime it's in the engine feels like poo at WOT. I ended up never running my silencer on my old SR20DET S13 as a result, because it turned a 400 rwhp car into like a 180 rwhp car.

FWIW, I run 2 x ~1.6" diameter silencers in my MR2's Berk exhaust because it seems way louder than other Berk exhausts. It doesn't seem to really affect power that much in the low 300 rwhp range, but it can be seen on the datalogs so it is causing a power drop. This is ~2.5x the exit area Alex is talking about using, so to say it's choking things down with a tiny exit area is the BEST solution... I'd struggle with that.

Now if Alex was talking about using some 1.5-1.75" diameter silencers and had a good sound reduction using them, maybe. But in my experience, but the time you're not choking down the power much, the sound reduction from a silencer isn't great.
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post #18 of 31 (permalink) Old June 5th, 2019, 04:55
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The 1 5/8 silencers I use on my Berk exhaust are giving a massive sound reduction at cruise and if they cost me 20-30HP at WOT so be it with my cams and 8000 rpm limit I've got at least 20-30HP on the rest of youze anyway ha ha.

PS. Bad idea to put back pressure on a turbo, definitely.
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post #19 of 31 (permalink) Old June 5th, 2019, 09:02
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I'm telling you... This is the answer. A patented design based on physics:

Why not try one of these mufflers? Power without the drone.

Spin Tech... How it works:

https://spintechmufflers.com/about-spintech/
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post #20 of 31 (permalink) Old June 5th, 2019, 11:16
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Quote:
Originally Posted by Dr.Pete View Post
I'm telling you... This is the answer. A patented design based on physics:

Why not try one of these mufflers? Power without the drone.

Spin Tech... How it works:

https://spintechmufflers.com/about-spintech/
Their "physics" explanation is completely nonsensical. That's just a chambered muffler with a different chamber arrangement than the usual tube dumping into a box setup.

Chambered mufflers definitely cost power over a straight through muffler.
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