Dual exhaust benefits

Messages
660
Location
New Hampshire USA
Getting back to duals vs single, if the single system is restrictive then duals will help move exhaust out. this then means more air in which means more fuel and more power.up to the capabilities of the valve events and intake tract. This according to the contributions herin this thread.
 
Messages
6,773
Location
Fort Lauderdale, FL
Originally Posted by SubieRubyRoo
Originally Posted by DoubleWasp
Depends on the engine, mostly the Volumetric Efficiency. How much air and fuel gets into the cylinder per pump of the piston at WOT. Engines that have high VE above 5252 rpm will continue to increase torque past that limit. This is seriously uncommon in street engines, but the Honda S2000 is one exception that I believe does this. There is always torque. Think of horsepower as the effect of torque causing rpm. Torque can exist with or without rpm, but because there is nothing locking a crankshaft in place, it spins in response to the actions of explosions acting on the Pistons and rods. So why is the torque dropping after 5252 say on your typical V8? That's because of the design of the engine. The engine is designed for best cylinder filling of air and fuel (through tuning of the intake/exhaust velocity) at lower rpms, for most torque where it will be used the most. The smaller and longer tracts are great at doing at this at lower rpms. The smaller and shorter camshaft durations and lifts are also great at doing this. But there is a limit. At higher rpms, the engine starts to choke a little. Intake runners are too small to flow the air the cylinder wants, long enough that restriction is increasing, and those valves are too small and aren't open big enough or long enough to meet demand. VE at that speed begins to suffer. Torque past the limit of greatest VE begins to drop. But guess what? The engine is still increasing in rpm. It's doing a bad job of processing air and fuel efficiently, but it's still getting by. It's getting less air and fuel per pump of piston but it's doing a lot more pumping. Less force of torque, but still more actions are being performed by the torque that is being produced, and hence the horsepower number is still above the torque number. If you look at those dyno sheets, you will see that horsepower takes a dump not long after torque takes a dump as VE becomes so bad that the engine is literally hitting a wall, or the electronic or mechanical rpm limit just shuts the whole thing down before the engine flings into pieces.
It's been quite some time since I've seen anything as blatantly false as the garbage you spewed here. HP and torque crossing at 5252rpm has nothing whatsoever to do with the design of the engine, and has absolutely everything to do with the way HP is calculated. The truth about TQ and HP
It's hasn't been a long time since I have dealt with a person who chose to comment without reading. At no point in either of my two posts do I EVER address the crossing of HP and Torque at 5252rpm. Only which direction torque goes after 5252rpm and why.
 

wtd

Messages
2,440
Location
southwest Mo.
My 2014 Mustang GT has factory duel exhaust with an H crossover pipe and duel mufflers and the factory headers. I later added over the axle pipes from a 2013 GT 500 that eliminated the resonators and GT 500 single tip mufflers that are the same size as the original mufflers except for bigger diameter tips. No difference in power that I could tell but slightly louder and deeper tone of the exhaust. My 98 Chevy 1500 truck with the 5.7 had duel pipes going into one muffler and than one pipe coming out. I later added a Borla duel cat-back system that had duel pipes going into one muffler and than duel pipes coming out. This system also does not have an H or X pipe. I don't really remember much if any difference in felt power after adding the after market system but a lot better sound. My 70 Monte Carlo has duel exhaust with stock exhaust manifolds and separate pipes going into separate turbo mufflers on each side with no H or X pipe.
 
Messages
14,515
Location
Santa Barbara, CA
Originally Posted by wtd
My 2014 Mustang GT has factory duel exhaust with an H crossover pipe and duel mufflers and the factory headers. I later added over the axle pipes from a 2013 GT 500 that eliminated the resonators and GT 500 single tip mufflers that are the same size as the original mufflers except for bigger diameter tips. No difference in power that I could tell but slightly louder and deeper tone of the exhaust.
Same with my '14 GT except I did the Borla ATAK catback. Sounds a heck of a lot better than it did stock.
 
Originally Posted by DoubleWasp
It's hasn't been a long time since I have dealt with a person who chose to comment without reading. At no point in either of my two posts do I EVER address the crossing of HP and Torque at 5252rpm. Only which direction torque goes after 5252rpm and why.
My bad, I was posting at 2am and obviously wasn't thinking well. Apologies.
 
Messages
1,130
Location
California
Dual exhaust modification on modern vehicles causes abusive noise levels in residential areas that were once peaceful. Any gains in power, torque and efficiency are so small that they simply cannot be justified by the cost of the modification. Thanks to all the "enthusiasts" with noisy street exhaust that "sounds awesome" and require extra attention to be super cool feel better about themselves. Grow up.
 
Messages
14,515
Location
Santa Barbara, CA
Originally Posted by DGXR
Dual exhaust modification on modern vehicles causes abusive noise levels in residential areas that were once peaceful. Any gains in power, torque and efficiency are so small that they simply cannot be justified by the cost of the modification. Thanks to all the "enthusiasts" with noisy street exhaust that "sounds awesome" and require extra attention to be super cool feel better about themselves. Grow up.
FWIW I have not had a single complaint from a neighbor about my exhaust. Either with my current Mustang with Borla ATAKs or my 98 GT that had an offroad x-pipe and Spintechs. I also drive very responsibly, actually been yelled at for driving too slow before in the neighborhood. All the dads in the neighborhood seem jealous that I am not stuck with a minivan.
 
Messages
410
Location
West Yorkshire, UK
One thing to remember, unless you have moving pipes, you can't have an exhaust that has perfect flow at all RPMs, there has to be SOME compromise and trade off. Depending on the engine this could be a small or high compromise, often the higher the tune (power per capacity unit), the bigger the compromise is. Also, the exhaust is one part of an air pumping system and dependant on the characteristics of other parts of the engine in that system, some quite complex relationships and dynamics as you are trying to capture continuous intake supply, through cyclic events (piston combustion) and out, whilst trying to meet design aims of economy, emissions, power/torque and noise. Engines are dynamic, flow and back pressure varies relative to rpm and load. To say lower back pressure is better is fine ideologically, but to put in practise is a hard thing to do, eg optimise for peak power at high RPM and you can (and is often seen when trying to reach peak power with wild cam configurations) reduce advantages of techniques such as of scavenging at lower RPMs, leading to less lower/torque at low/mid RPM and relates to what I mention above about compromise. When optimising for maximum performance you want to look at the desired common operational RPM of the engine for your use cases and optimise for maximum area under the torque curve in that range - as that is mathematically equivalent to the average maximum torque across your desired rev range which equates to best overall acceleration.
 
Messages
6,773
Location
Fort Lauderdale, FL
Indeed. My point was that nobody who knows a lick about exhaust is considering engineering in back pressure. An exhaust, once properly engineered for it's application may have a certain amount of back pressure, but that was never ever ever the target at all. What back pressure there may be is doing absolutely nothing for the engine at all, and adding back pressure will not do anything at all. Simply the result of engineering that is actually relevant. One saying back pressure helps an exhaust is taking an inevitable result that was never a factor of design, and assigning it as the cause.
 
Messages
2,661
Location
Chicagoland
Originally Posted by DGXR
Dual exhaust modification on modern vehicles causes abusive noise levels in residential areas that were once peaceful. Any gains in power, torque and efficiency are so small that they simply cannot be justified by the cost of the modification. Thanks to all the "enthusiasts" with noisy street exhaust that "sounds awesome" and require extra attention to be super cool feel better about themselves. Grow up.
"People enjoy things that I don't, therefore they need to grow up! *angrily shakes fist from front lawn*" There's obnoxious straight pipes, then there is tasteful. I removed the resonators on my Durango, always got complemented on how it sounded by my neighbors. My brothers Daytona has active exhaust straight from the factory... start it up and the valves open for that sweet sweet v8 start up, then close back off to quiet it back down. Cruising down the road they're closed, but step on it and it gets loud again. That being said, some of these motorcycles are down right ridiculous. I've heard gun shots quieter than them.
 
Last edited:
Messages
3,122
Location
BC, Canada
Dual tail pipes from a common single exhaust pipe, is different from a dual exhaust system originating at the engine. What are we talking about here? Is the following statement true? Tuning an exhaust system ( which includes exhaust camshaft timing, valve lift, rate of lift and exhaust valve size) will add torque at a narrow rpm range, often at the expense of lower torque elsewhere in the engine's operating range. Obviously we want to increase torque in the rpm range where it will increase the performance of the vehicle. Retaining heat in the exhaust gasses might be a good place to start.
 
Messages
2,661
Location
Chicagoland
Originally Posted by userfriendly
Dual tail pipes from a common single exhaust pipe, is different from a dual exhaust system originating at the engine. What are we talking about here? Is the following statement true? Tuning an exhaust system ( which includes exhaust camshaft timing, valve lift, rate of lift and exhaust valve size) will add torque at a narrow rpm range, often at the expense of lower torque elsewhere in the engine's operating range. Obviously we want to increase torque in the rpm range where it will increase the performance of the vehicle. Retaining heat in the exhaust gasses might be a good place to start.
Well, everything works as a system. Tweak the exhaust, naturally you'll need to tweak the intake. Generally though, you'd have to pick one... you want low end grunt? That'll cost you power up top. Want maximum power? Gonna cost you some torque. But the nice thing about newer cars with things like DOHC with VVT and variable valve lift is you can get the best of both worlds. The torque down low, click everything over, and still maintain your power up high. Through all that you get engines like FCA's 305hp Pentastar V6 that makes 90+% of peak torque from a mere 1800rpm and carry it all the way to 6,350rpm while running on regular 87 octane!
 
Messages
2,661
Location
Chicagoland
Originally Posted by userfriendly
In general with fixed valve timing, do long tube headers and dual exhaust add torque at one rpm range at the expense of torque at another?
Yes. We will assume the headers are the same size in both my examples, let's say 1 7/8" primaries, and the only difference is the rest of the exhaust. Narrower exhaust, like our headers dumping into 2" exhaust pipes, will keep the exhaust gas velocity higher resulting in more torque at lower RPM. The issue though is at higher RPM the exhaust becomes a restriction. Those same headers, dumping into a 3" exhaust, will make more power on the top end, but less torque at low ROM's.
 
Messages
3,122
Location
BC, Canada
What about shorty headers? They might not add or subtract torque at different rpm like long tubes. Wrap them to retain heat and run them into a large single exhaust? You could still split the tail pipes for the dual exhaust look.
 
Messages
2,661
Location
Chicagoland
Originally Posted by userfriendly
What about shorty headers? They might not add or subtract torque at different rpm like long tubes. Wrap them to retain heat and run them into a large single exhaust? You could still split the tail pipes for the dual exhaust look.
Hot Rod already did a test and has written it far better than I can lol, granted it's a dual exhaust set up they used, they were ONLY comparing the headers in this test. The rest of the exhaust, assuming you're not trying to cram it into a tiny little pipe, will have a rather negligible affect on power and torque compared to the headers. True dual, 2 into 1, 2 into 1 into 2 (some ram trucks do this), X pipe, h pipe won't affect power like the headers will. https://www.hotrod.com/articles/headers-dyno-test/
 
Last edited:
Top