SSpeed Posted April 15, 2012 Share Posted April 15, 2012 I've been struggling to find the ideal exhaust solution and have an idea, first my setup: BNR evo3 3in from turbo to Y-pipe 2.5" on each Y to the 1.5" stuck muffler inlets (think that's right) I contemplated changing out my stock mufflers for Borlas, but I like how quiet the car is at cruise and idle and Borlas would definitely change that. I would just like it louder at WOT. Soooo... I thought about using an electronic cutout, http://www.quicktimeperformance.com/QTEC/index.php, to use just one set of the mufflers under specific conditions, separating exhaust at the Y-pipe. Cruise and idle could use the stock muffler (although 1.5" inlet is way too small for one muffler and may kill the idea). WOT, or specific conditions would switch the cutout over to a 3in Borla. My roadblocks are: 1) I'd want it to happen automatically based on set ECU parameters whether that be switching to open loop or whatever. 2) Would that be a tuning nightmare for WGDC and such? 3) One 1.5" inlet stock muffler for idle and cruise is too small. Ideas? Criticisms? Suggestions? Link to comment Share on other sites More sharing options...
fahr_side Posted April 16, 2012 Share Posted April 16, 2012 I wish someone would just make a muffler with a spring-loaded flapper inside. The older Evo models had one to short-circuit the guts of the muffler when backpressure rises, we discussed it here. Elegant, effective and simple. I really like this idea because it's on the one hand so simple... no wiring, software configuration, electronics, motors to fail, air lines to split or melt. OTOH it does exactly what you want... we're concerned that an exhaust that's quiet in light load will be cause too much backpressure at high load, or that one that has low backpressure will be too loud in cruise. With a spring and flapper you basically put a cap on backpressure. When pressure rises high enough to open the flapper, pressure stays constant (until the new passageway itself is choked) as flow continues to rise. I don't think 1.5" is necessarily too small for cruise. The stock GH8 midpipe and muffler entry are a tiny 2" and yet support about 280whp at full-chat. Perhaps you could create a sort of constant-backpressure system by as you suggest using one stock muffler and one aftermarket 2.5" or 3" muffler. Perhaps leave the stock pipe in place on one side and a bigger run to a 3" muffler on the other side. Then you put in a flapper to control flow through the secondary muffler. The flapper could be anywhere between the Y-pipe splitter itself and the tailpipe of the secondary muffler. All the gas will run through the one stock muffler until pressure overcomes the spring and then also begins to flow through the second, less restrictive muffler. It's easy to tune for this sort of set-up as it's very linear. Very little difference in fact from tuning for an aftermarket performance system. If you really want to have control via air pressure or electronics you can use a butterfly type cutout valve instead of a spring-loaded valve, but from a performance perspective there's no advantage to the extra complication once you find a suitable spring to load the flapper. Then you have some tough choices which were laid out in that other thread. 1. Mechanical boost reference. Tee a line into the intake plumbing to operate a valve somewhat like a wastegate solenoid. Lines split or melt and you have a leak messing with your fueling and boost control. 2. Electronic boost reference. Requires a sensor, a controller, and an electric cut-out. Electric cut-outs are notoriously unreliable and short-lived. Simple electronics might not operate at the sort of speed you'd like and delays will make tuning a bit trickier. 3. RPM or some other reference. Same problems as above and even more complexity. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
SSpeed Posted April 16, 2012 Author Share Posted April 16, 2012 I saw the DynoMax VT with the spring loaded valve, but everyone complains of them clicking incessantly. Hmmm.... I know Porsche has a valved muffler of some sort as well... Link to comment Share on other sites More sharing options...
fahr_side Posted April 16, 2012 Share Posted April 16, 2012 I know Porsche has a valved muffler of some sort as well... More German over-engineering. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
PutnamCO Posted April 16, 2012 Share Posted April 16, 2012 After reading TRSCobra's thread on an exhaust cutout (http://legacygt.com/forums/showthread.php/electric-exhaust-cutout-installed-w-pics-best-both-worldsi-163580.html?t=163580&highlight=exhaust+cutout) I ordered the cutout and motor that he used. It should be here on Tuesday, and I'll get it installed and tuned next Monday if you want to go for a ride. I'm thinking that most of the time, I will keep the cutout partway open, to achieve something similar to what you're looking for. It may be louder than you want, but seriously let me know if you want to hear if for yourself. Link to comment Share on other sites More sharing options...
SSpeed Posted April 16, 2012 Author Share Posted April 16, 2012 Definitely, I'll check it out. PM when you have it installed. What part of Denver are you in? Thanks for all the info fahr_side, the roadblocks you put up were what I worried about as well. Link to comment Share on other sites More sharing options...
SSpeed Posted April 16, 2012 Author Share Posted April 16, 2012 2. Electronic boost reference. Requires a sensor, a controller, and an electric cut-out. Electric cut-outs are notoriously unreliable and short-lived. Simple electronics might not operate at the sort of speed you'd like and delays will make tuning a bit trickier. I watched the electronic cutout videos online, 5 seconds to full open is way longer than I would want for this. I would need something that moved as quickly as a throttle plate. In my younger, more stupid days, I might have thought about finding another dirve by wire throttle body, but put it in the exhaust line instead, running it in parallel with the original throttle body. It has the response time I'd want and would follow the curve closely of the noise ratios I'm looking for. I doubt it's rated for exhaust temps though. Link to comment Share on other sites More sharing options...
SSpeed Posted April 16, 2012 Author Share Posted April 16, 2012 You know, I wonder what size the inlet is on WRX/STI mufflers? If they were designed for a one muffler system they probably have a bigger inlet. Two of those mufflers would give me a throatier exhaust while still staying rather quiet. Link to comment Share on other sites More sharing options...
fahr_side Posted April 16, 2012 Share Posted April 16, 2012 A spring-loaded flapper really is the best way. Second best might be an EWG type of deal with the actuator referenced to exhaust pressure or boost pressure. In both cases you need to tweak spring pressure to get it right. Referencing exhaust pressure is better because the one stock muffler won't choke flow until higher revs while boost comes up long before that point. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
fahr_side Posted April 16, 2012 Share Posted April 16, 2012 You know, I wonder what size the inlet is on WRX/STI mufflers? The GH8 midpipe and muffler entry are 53mm OD and I'm pretty sure the GRB is the same. As I recall the GD models were around 60mm. Maybe the newer 4-door models have useful donor mufflers since they come with twins? Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
SSpeed Posted April 16, 2012 Author Share Posted April 16, 2012 A spring loaded flapper seems best, all the YouTube videos I saw though had annoying rattling, and some posters said they removed it because of that. EWG is good idea, dumb of me not to think of that. I checked on nabisco, stock STI muffler inlet is 2.25".. that would mate up nearly perfectly to my AVO Y... I wonder what two of those would sound like compared to the Legacy mufflers? Link to comment Share on other sites More sharing options...
fahr_side Posted April 16, 2012 Share Posted April 16, 2012 Not sure how two would be. I like the old GDB STi mufflers... nice tone to them and not too loud. I had one on my old GF. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
SSpeed Posted April 16, 2012 Author Share Posted April 16, 2012 I don't know the acronyms that well, would that be 2004+ STI? Link to comment Share on other sites More sharing options...
fahr_side Posted April 16, 2012 Share Posted April 16, 2012 I don't know the acronyms that well, would that be 2004+ STI? Yes, AKA peanut-eye and pignose STi. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
utc_pyro Posted April 16, 2012 Share Posted April 16, 2012 Two methods for actuating it: Boost pressure switch: http://www.aquastealth.com/pressureswitch.aspx Set it for ~10PSI and let it open your cutout. Vacuum/Boost actuator: Use a vacuum or boost actuator to quickly open/close your cutout/flapper. Think your wastegate actuator, or even use a wastegate actuator. A version of the overseas early 90's LGT actually had a muffler with something like this inside. It was activated by the ECU under certain conditions, but just having it trigger at a boost level should be sufficient. Link to comment Share on other sites More sharing options...
PutnamCO Posted April 17, 2012 Share Posted April 17, 2012 Definitely, I'll check it out. PM when you have it installed. What part of Denver are you in? Thanks for all the info fahr_side, the roadblocks you put up were what I worried about as well. I live just south of DU. I will definitely let you know when I get everything all set with the cutout. Link to comment Share on other sites More sharing options...
fahr_side Posted April 17, 2012 Share Posted April 17, 2012 If you open the valve at high boost / low rpm you're making noise for no gain. It's exhaust back-pressure that robs performance and it's likely that this is not an issue until the upper midrange. For this reason it makes more sense to measure or reference this parameter. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
SSpeed Posted April 17, 2012 Author Share Posted April 17, 2012 What does the stock tone of the '11 STI sound like? Looks like they use twin-tipped Legacy style mufflers as you suggested and inlet size is about equal to my AVO Y-pipe. I've been searching around on nabisco, but haven't confirmed if the WRX and STI are same inlet size. Link to comment Share on other sites More sharing options...
fahr_side Posted April 18, 2012 Share Posted April 18, 2012 What does the stock tone of the '11 STI sound like? Looks like they use twin-tipped Legacy style mufflers as you suggested and inlet size is about equal to my AVO Y-pipe. I've been searching around on nabisco, but haven't confirmed if the WRX and STI are same inlet size. I haven't seen or heard a 4D '08~ STi in person so I can't help you there. All the ones I've seen or worked on were 5D models and TBH most of those had an aftermarket system on them. I'd go look around on IWSTI.com IIWY... better class of STi owner over there. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
PutnamCO Posted April 18, 2012 Share Posted April 18, 2012 What does the stock tone of the '11 STI sound like? Looks like they use twin-tipped Legacy style mufflers as you suggested and inlet size is about equal to my AVO Y-pipe. I've been searching around on nabisco, but haven't confirmed if the WRX and STI are same inlet size. I have '11 STi cans on my car that were modified to mate up to my Perrin mid. It is quite a bit louder than stock, but much louder when on the throttle rather than cruising. I would say it's slightly louder when accelerating slowly, and at constant RPMs, but has a nice growl when I get on it. I bought the cans for $50 and paid $130 for a shop to rotate the inlets and extend the tips. If you search for the "'11 STi cans" thread, you can hear sound clips of stock vs. the STi cans. Link to comment Share on other sites More sharing options...
SSpeed Posted April 18, 2012 Author Share Posted April 18, 2012 Thanks for the tip on that, I'll have to do some research and see if '08 and on is what I'm looking for? Link to comment Share on other sites More sharing options...
PutnamCO Posted April 18, 2012 Share Posted April 18, 2012 As far as I know, 2011-12 STI cans are the only ones that work. Found mine on AWDpirates.net Here's the link to the thread I was talking about: http://legacygt.com/forums/showthread.php/2011-sti-mufflers-wagon-178311.html?highlight=sti+cans Link to comment Share on other sites More sharing options...
SSpeed Posted April 18, 2012 Author Share Posted April 18, 2012 Awesome, thanks for that info... So the inlets aren't just bolt up and go? Do you know what diameter the inlets are? In the pictures in that thread they don't look much larger than the LGT ones? Link to comment Share on other sites More sharing options...
PutnamCO Posted April 18, 2012 Share Posted April 18, 2012 No, they're not bolt-on because the inlets have to be cut and rotated, approximately 40 degrees I think. The hangers also have to be moved. The inlets looked the same size, but there are two outlets on the STI cans, that each look the same size as the one outlet on the LGT cans. Link to comment Share on other sites More sharing options...
SSpeed Posted April 18, 2012 Author Share Posted April 18, 2012 Hmm, perhaps if I'm going to be super anal about that step in my exhaust from the AVO Y-pipe (2.5" I think) to the stock mufflers (1.5ish" I think) (reel me back in fahr_side), maybe i can find a 2.5" to 1.5" header reducer and have those welded to the stock muffler so the inlet is 2.5" at the Y-pipe connection, but smoothly reduces to the muffler inlet size. I love the stock muffler quietness, that step in the pipe and turbulence/back pressure it probably causes keeps me awake at night though.. http://www.grainger.com/Grainger/PARKER-Concentric-Reducer-1WCV8 http://productimages.grainger.com/is/image/Grainger/1WCV5_AS01?$productdetail$ Link to comment Share on other sites More sharing options...
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