Jump to content
LegacyGT.com

Exhaust thread, info on the exhausts out there


Mines

Recommended Posts

  • Replies 50
  • Created
  • Last Reply
The 25hp gains that WRX's showed were not from Catbacks, they were from DP's and Uppipes. Usually a catback will give you about 5hp more, or if you do engine management and other exhuast work maybe 10hp. I consider the catback usefull only for looks and sound really. You do get a little hp, but most everyone will agree the first thing they look for is looks and sound. From the ones posted on the first page the Fujisutobo's would be the ones I would get, although I still hope prodrive comes out with an exhaust for this car, I loved my prodrive exhausts on the WRX. Could you imagine 2 oval tip wrx type mufflers on the legacy, that would be sweet :) So prodrive if your reading this. PLEASE make a exhaust sytem for this car, with two oval tips just like the ones on the WRX. And make it sound just like the oval tiped wrx muffler. I would buy one today if they had it!!
Link to comment
Share on other sites

My question is the dual exit tail pipes. Why did Subaru do this? A single exit on a single turbo is all that is necessary. Now if it was N/A and had full true duals, then OK. OR....if it has dual turbo's and full true duals, then OK even more. But to split a single exhaust stream (restriction #1) just for looks is just stupid IMO. Plus, have you seen the frame pics of the Legacy in the brochures....Looks like the pipes are only like 1-1/2" bending into the rear mufflers....Thats a bit small...no? And as for a turbocharged engine loosing power with regard to backpressure reduction.... I always thought that rule DID NOT apply to turboed engines but only to N/A ones. Maybe I'm only thinking about Turbo Diesels? Someone care to elaborate more on this? The less back pressure, the faster/quicker the turbo can spin, no?
Link to comment
Share on other sites

[quote name='TLS']My question is the dual exit tail pipes. Why did Subaru do this? A single exit on a single turbo is all that is necessary. Now if it was N/A and had full true duals, then OK. OR....if it has dual turbo's and full true duals, then OK even more. But to split a single exhaust stream (restriction #1) just for looks is just stupid IMO. Plus, have you seen the frame pics of the Legacy in the brochures....Looks like the pipes are only like 1-1/2" bending into the rear mufflers....Thats a bit small...no? And as for a turbocharged engine loosing power with regard to backpressure reduction.... I always thought that rule DID NOT apply to turboed engines but only to N/A ones. Maybe I'm only thinking about Turbo Diesels? Someone care to elaborate more on this? The less back pressure, the faster/quicker the turbo can spin, no?[/quote] Because it looks really cool? And it does indeed. Kevin
Link to comment
Share on other sites

[quote name='TLS']My question is the dual exit tail pipes. Why did Subaru do this? A single exit on a single turbo is all that is necessary. Now if it was N/A and had full true duals, then OK. OR....if it has dual turbo's and full true duals, then OK even more. But to split a single exhaust stream (restriction #1) just for looks is just stupid IMO. Plus, have you seen the frame pics of the Legacy in the brochures....Looks like the pipes are only like 1-1/2" bending into the rear mufflers....Thats a bit small...no? And as for a turbocharged engine loosing power with regard to backpressure reduction.... I always thought that rule DID NOT apply to turboed engines but only to N/A ones. Maybe I'm only thinking about Turbo Diesels? Someone care to elaborate more on this? The less back pressure, the faster/quicker the turbo can spin, no?[/quote] As far the the dual exhaust goes....I suppose it is supposed to be less restrictive using two outlets of smaller diamter rather than one outlet with a larger outlet, but I assume it's mainly for styling? In reguards to the turbo and backpressure, you are correct. Turbo cars do benefit from a decrese in backpressure as well as any motor. Backpressure is always the enemy. This article goes into detail why: [url]http://www.autospeed.com/cms/article.html?&A=0046[/url]
Link to comment
Share on other sites

But in a N/A engine, backpressure is necessary for low end torque. Remove all backpressure and it's dead until you hit the higher revs. This is what I was getting at.
Link to comment
Share on other sites

[quote name='TLS']But in a N/A engine, backpressure is necessary for low end torque. Remove all backpressure and it's dead until you hit the higher revs. This is what I was getting at.[/quote] Read the article I posted. Backpressure is never good under any cirumstance.
Link to comment
Share on other sites

[quote name='TLS']What article? But with regards to your above statement....I'm going to disagree with you. Thats from personal experience as well as documented accounts.[/quote] Here it is again: [url]http://www.autospeed.com/cms/article.html?&A=0046[/url] This a huge misconceoption that many people have. It simply isn't true.
Link to comment
Share on other sites

Well, then I'm now officially DISAGREEING with Julian Edgar. A dyno does NOT and will NEVER duplicate real world Seat Of Pants feel. I'm talking about just off idle, non WOT torque. NOT full WOT high rpm torque peaks. His dyno was measuring torque PEAK and that was at 4700 rpm. Clearly NOT what I was talking about. But as for turbos....less is better.
Link to comment
Share on other sites

That's a bummer if the piping is that small going to the rear mufflers. I like the look of the exhaust tips and I don't mind the stock sound so I was hoping to use a setup similar to the TXS 'stealthback', with a catless downpipe and one high flow cat in the mid-pipe. Chris S.
Link to comment
Share on other sites

Guest *Jedimaster*
[quote name='Drift Monkey'][quote name='SUBE555']Please stay ON-TOPIC.[/quote] *bling*[/quote] We's just having some fun. A nice diversion from all teh seriousneses. Pardon teh grammer.
Link to comment
Share on other sites

[quote name='TLS']Well, then I'm now officially DISAGREEING with Julian Edgar. A dyno does NOT and will NEVER duplicate real world Seat Of Pants feel. I'm talking about just off idle, non WOT torque. NOT full WOT high rpm torque peaks. His dyno was measuring torque PEAK and that was at 4700 rpm. Clearly NOT what I was talking about. But as for turbos....less is better.[/quote] I guess you disagree with Josh Tenny and Cobb Tuning too: [url]http://www.cobbtuning.com/tech/exhaustdesign/index.html[/url] - This aricle discusses exhaust gas theory, both turbo and NA. When looking at exhaust systems, backpressure is not the key issue, its exhaust gas velocity. When enlarging an exhaust diameter, you will slow your exhaust gas velocity from by making too large of a volume for the gas to fill. Too small and the backpressure will slow the flow. The most critical part IMO is your header, depending on primary length and diameter you can drastically change the powerband. To use an example from Subaru tunning, MRT headers give 16 hp gains past 4000 rpm, but don't do anything before that point, cobb tuning headers on the other hand give a nice 17 ft-lb gain from 2000-4500 rpm with the rest of the exhaust being identical to the mrt, while showing only about a 10 hp gain past 4500 rpm.
Link to comment
Share on other sites

[quote name='TLS']What article? But with regards to your above statement....I'm going to disagree with you. Thats from personal experience as well as documented accounts.[/quote] It's not backpressure, it's harmonic resonance. Tuning the exhaust to act like a tuning fork, resonating at low frequencies will help exhaust flow at low frequencies, and have different effects at other frequencies. This is not backpressure.
Link to comment
Share on other sites

Backpressure is the enemy, but - Your engine/turbo in stock form has been tuned for appropriate amounts of backpressure. Remove it completely, and it will run like crap. Sure, you may have 15 more hp up high, but you'll have lost 40hp where you need it the most, at low rpms. Throwing on a straight pipe system doesn't automatically equal more hp, for instance. I've experienced both types of systems, a very free-flow muffler vs. a somewhat restrictive, tuned muffler. Fujitsubo vs. HKS, on a stock twin turbo B4. The HKS free-flow made about 5-10 more hp at peak. The Fujitsubo made about 30 more hp than the HKS at 3000rpms. Whatever you argue about theory, real-world, a properly tuned exhaust will walk all over a coffee-can attached to the end of a gutter pipe. Peak hp is only useful when you are in that rev range - a system that increases power over a 5000rpm range is more useful than one that gives more power in a 1500rpm range. Admittedly, that was on a stock ECU setup. If you actually tuned for that HKS all is generally good. But then you've taken a setup that produced good power at all revs while maintaining a sane level of exhaust noise, and likely added a droning exhaust system that drives you crazy while cruising for the pleasure of a bit more hp for 5% of your driving. Or you can just go with a proper setup that reduces backpressure, keeps a lot of the checks and balances in place to keep that pleasant tone that was designed by corps of relatively clued in engineers, and reap the benefits of both worlds with both power gains and peace of cruising. Cheers, Paul Hansen [url]www.apexjapan.com[/url]
Link to comment
Share on other sites

[quote name='apexjapan']Backpressure is the enemy, but - Your engine/turbo in stock form has been tuned for appropriate amounts of backpressure. Remove it completely, and it will run like crap. Sure, you may have 15 more hp up high, but you'll have lost 40hp where you need it the most, at low rpms. Throwing on a straight pipe system doesn't automatically equal more hp, for instance. [/quote] Paul, Well, at least I'm not the only one feeling this way about backpressure. However, I always thought that a turboed engine likes 0 restriction for ANY rpm range. Anything that helps the turbo spool up quicker is best. With no backpressure slowing the exhaust post turbo, it enters and exits the turbine quicker. But like I said earlier, my turbo experience is with oil burning engines without spark plugs or throttle plates, and more than double the displacement. So those in the know please correct me on this aspect.
Link to comment
Share on other sites

While the theory is somewhat sound, it's the variables that affect that actual result. The way the turbo is designed, for one, the way exhaust flows is another, does enough air actually come in from the intake side to support the flow on the exhaust side, etc. For instance, people installing big exhaust systems on the USDM STi are experiencing problems with boost creep, since the system wasn't designed for total flow exhaust side. I'm not an engineer, and I don't even play one on tv - I tend to follow their advice, though, and there doesn't seem to be any actual benefits to just throwing on a huge back-pressure free system until the other areas, such as engine management, have been addressed first. It reminds me of a car I saw with nearly everything bolted to it but engine management - and it was making less hp than stock. Even putting a piggyback on resulted in a 60hp gain... Cheers, Paul Hansen
Link to comment
Share on other sites

  • 2 weeks later...
[quote name='powbmps']That's a bummer if the piping is that small going to the rear mufflers. I like the look of the exhaust tips and I don't mind the stock sound so I was hoping to use a setup similar to the TXS 'stealthback', with a catless downpipe and one high flow cat in the mid-pipe. Chris S.[/quote] Hey but the good news is the Legacy GT 5M runs a 14.2 with those restrictive pipes, and useless dual mufflers. Personally I can't wait to see the difference a good aftermarket system makes for this car.
Link to comment
Share on other sites

  • 7 months later...
  • 2 weeks later...

Archived

This topic is now archived and is closed to further replies.




×
×
  • Create New...

Important Information

Terms of Use