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Rotrex exhaust/muffler selection

 
Old 02-27-2018, 10:26 AM
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Default Rotrex exhaust/muffler selection

Yeah, I know, Rotrex is lame. I also know that the MT consensus for turbo cars is using the Magnaflow 12589. I am a bit skeptic as it regards using it in a Rotrex car as I will not have the muffling action of the turbo. What would be your suggestions for a low-tone, burbling but not droning system?
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Old 02-27-2018, 10:13 PM
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Probably that magnaflow and as much resonator and/or bullet muffler as you can fit in the tunnel.
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Old 02-28-2018, 06:54 AM
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Originally Posted by Leafy View Post
Probably that magnaflow and as much resonator and/or bullet muffler as you can fit in the tunnel.
I would agree.
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Old 02-28-2018, 09:48 AM
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Should be fine with the magnaflow and a resonator in the straight. IMO, shouldn't be that much different.
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Old 02-28-2018, 09:50 AM
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For another data point: I had a Flyin Miata NA exhaust on my rotrex'ed car. It was medium-loud and a little droney on the highway but definitely not the worst I've heard. My car was also mostly gutted so noisy in general.
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Old 02-28-2018, 11:08 AM
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I am going to be fabricating my own 3 inch exhaust from stainless and as many resonators as I can fit. Fortunately I have lots of scrap from working at a BMW dealership. I am looking for quiet 3 inch muffler suggestions in addition to the resonators. I'll be sure to post sound clips, hopefully within a couple weeks. 1.8 bp4w with c30-94
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Old 02-28-2018, 02:48 PM
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Keep it simple and run the full Racing Beat exhaust, it keeps things quiet and doesn't hurt you on power.
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Old 02-28-2018, 02:51 PM
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has anyone done a 2.5 vs 3 inch dyno on a rotrex setup?
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Old 02-28-2018, 03:03 PM
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Originally Posted by Twibs415 View Post
has anyone done a 2.5 vs 3 inch dyno on a rotrex setup?
I've seen some old posts about modifying the standard RB header to merge to 3" and do a full 3" exhaust but that is about it. Too expensive to dyno test that sort of thing, for 95% of builds off the shelf RB bits will get the job done. You are splitting hairs compared to a 2.5 inch set up when the RB is 2.375 diameter.
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Old 02-28-2018, 03:15 PM
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Originally Posted by Lincoln Logs View Post
I've seen some old posts about modifying the standard RB header to merge to 3" and do a full 3" exhaust but that is about it. Too expensive to dyno test that sort of thing, for 95% of builds off the shelf RB bits will get the job done. You are splitting hairs compared to a 2.5 inch set up when the RB is 2.375 diameter.
What he said... splitting hairs for your application.

You can watch this YT which does a 2.5" vs 3" on a v8 that makes more HP than a rotrex miata.


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Old 02-28-2018, 04:04 PM
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The diameter matters way more on a turbo car. On something with an SC you can run a smaller exhaust and still make good power. I'm running a raceland header, test pipe and RB catback (resonated midpipe) and it sounds great, with absolutely no drone. I'm making 234 whp at 4500ft on a 1.6 with that exhaust.
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Old 02-28-2018, 07:12 PM
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I used the RoadsterSport 3 muffler (Goodwin Racing) along with their midpipe and liked the sound a lot with my Rotrex.
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Old 02-28-2018, 07:15 PM
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Originally Posted by Mobius View Post
I used the RoadsterSport 3 muffler (Goodwin Racing) along with their midpipe and liked the sound a lot with my Rotrex.
The channel "The Driver's Perspective" on Youtube actually has a clip of a launch with the racing beat, and a launch with the roadstersport from similar distances/angles. AFAIK he started with the RB, moved to the roadstersport and then switched back. His videos are why I ended up with the RB setup.
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Old 02-28-2018, 09:25 PM
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Yeah I think itís not the same when you want to push 300hp through it.
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Old 03-01-2018, 11:18 AM
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Originally Posted by soot View Post
The channel "The Driver's Perspective" on Youtube actually has a clip of a launch with the racing beat, and a launch with the roadstersport from similar distances/angles. AFAIK he started with the RB, moved to the roadstersport and then switched back. His videos are why I ended up with the RB setup.
Lincoln Logs, who responded earlier, is the guy in those videos.
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Old 03-01-2018, 11:26 AM
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Old 03-01-2018, 12:00 PM
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Thanks for the thread Brain:

Originally Posted by hornetball View Post
Turbo cars are much more sensitive to the exhaust size because the turbine acts as a backpressure multiplier.

The considerations for a SC car are different and more like doing the exhaust for an NA car (taking into consideration some additional flow). Things like sizing the pipe diameter and length to promote scavenging become important. Bottom line, on an SC car run a good header and an exhaust system matched to the header. That will likely be smaller than a 3".
Originally Posted by EO2K View Post
^^ This. Everything I've read backs this up. The only person with an SC setup that I've seen that is running anything bigger is TrackDayHooky. At one point he was running one of the discontinued 949Racing 2.75" exhausts on a 400+HP C38 Rotrex build. No clue what that car has on it now.

Ok, back to the trubo stuff. Who has more apples to apples comparison data for exhaust upgrades?
This matches everything I have read as well. The RB exhaust still seems like the easy button for Rotrex setups until you start making really big power.
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Old 03-02-2018, 06:31 AM
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Thanks guys, much appreciated. Original question was mostly related to sound, diameter will most likely be 2.25" or 2.5". The RB exhaust is sweet, however being located in Europe, it will be a bit more difficult to get one. Most probably gonna get a large Maglaflow backbox plus a smaller one as a midpipe resonator.
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Old 03-02-2018, 02:08 PM
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I ran a 2.5" system before my RB (old muffler core broke, was cheap) and it had a nice deep tone. It did drone a bit, but the muffler was pretty minimal. I'd think that a big back box and resonator(s) should help with that.
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