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Alright everyone, I'm starting this thread to help guys figure out whether or not they're a good candidate for true dual exhaust, or if they'd be better off with a single exhaust. This write up will touch on the subjects of backpressure, scavenging, reversion, h pipes, x pipes and anything else in between.:lol5:

I already have a great write up explaining exhaust system theory in general and it goes into great detail on the different types of mufflers and talks about scavenging, etc. Toyota Tundra performance exhaust sytems You can actually see the birth of the very first hand made BAmuffler in that thread:lol5:

This write up will focus more specifically on the above subjects and how they pertain to our beloved 5.7L Tundra exhaust systems. I'll start off by explaining 3 huge players in any exhaust system; Backpressure, scavenging, and the rare secret.......reversion. I will not use scientific terms or examples, I intend to keep it all the way that i understand it, or in other words K.I.S.S (keep it simple silly) So here goes:

Backpressure:
I'd like to start out by repeating what I used to hear as a teenager and always thought to be true, "you need some back pressure or you'll lose low end torque" This statement false, you can almost say that it is partially true. Back pressure is bad, it's your enemy, it doesn't make HP, it robs it. It is a compromise to use back pressure to make low end torque. For example, the way that I make my mufflers uses back pressure to make low end torque. At low rpm your exhaust flows as a series of high pressure pulses. As 'the first' pulse enters the mufflers it expands into the can thru the perforated center core. This happens because the muffler can is much bigger in diameter than the exhaust tubing itself, the lower pressure in the can causes the exhaust pulse to expand and slow. The pulse behind the 'first pulse' collides with the first pulse and it too slows, then the next pulse collides with the one before, etc. This back pressure makes the exhaust system 'act' like a smaller system and promotes low end torque.

The nice thing about the design of my muffler is that as the rpm's increase the exhaust becomes more of a steady high pressure flow instead of a series of high pressure pulses. This high pressure flow keeps constant pressure in the muffler can and instead of the high pressure flow expanding into the muffler and slowing, it goes straight thru having much less back pressure, keeping up velocity. And we all know that velocity creates what???

Scavenging:

This section will be much longer than the last, I tend to like to focus on what works and why, instead of on why back pressure is bad for HP. We all know that restriction is bad and can figure out why. But what is scavenging, and how does it work? Simply put, your exhaust will siphon itself out of your cylinders at peak volumetric efficiency.......if your exhaust system is properly designed. Most of already know this, but not many know why:lol5: Ever siphon out an aquarium? You know, suck on a hose to get the water flowing and it will siphon itself out? Or you can also hook up the hose to the spigot, turn on the water, hold up the end, turn off the water. Un-hook the hose off the spigot and hold up that end equal height to the other end. Then, with the hose full of water drop 1 end in the aquarium and the other on the ground, as long as the aquarium water level is higher than the end on the ground water will siphon out until the aquarium is empty. Simple, right?

As I said, your exhaust will do the same thing and it does it best right where it goes from high pressure pulses and turns into more of a high pressure flow if the tubing sizing is correct. What most people don't know is that not only will the exhaust siphon itself out, it will also draw in the intake charge during valve overlap. Valve overlap is what you hear when an old school muscle car with a big cam sits there with a huge 'lope'. That uneven lope is actually caused by reversion during idle.......LOL, I'll go into that last because this is more fun with mystery LOL. We need to completely understand valve overlap for the next sections to make sense.

Valve overlap is simply when your intake and exhaust valve are open AT THE SAME TIME for a split second. If your exhaust system is sized right and velocity is high enough to cause scavenging, then it makes sense to hold open both intake and exhaust valves at the same time (I realize each cylinder on our heads has 4valves, kept it simple there) As the high pressure pulse exits the head and into the exhaust system it is followed by a low pressure pulse. This low pressure pulse will actually pull on the intake air of that cylinder and it will pull on the exhaust pulse of the next firing cylinder. The problem is, if you have valve overlap at idle it will cause a lope, and some of the intake charge is actually pulled out into the exhaust system and hydrocarbons increase dramatically.

To make the engine take advantage of valve overlap without the poor idle quality and bad emissions of a 'big cam' Toyota uses VVTI, or variable valve timing. There is a small lobe pushing down each valve at idle and very slow cruise. So 4 cam lobes for all 4 valves., At freeway cruise and when really on the throttle, the 2 rocker arms of the intake valves connect with a 3rd rocker arm right in the middle of them. The exhaust valves do the same thing. This 3rd rocker arm rides on a cam lobe that is between the 2 smaller lobes. This 3rd lobe has much more lift and duration which makes power by itself. To make even more power, the ecu also has the ability to advance or retard the cams. In other words, the computer can decide when to hold both exhaust valves and both intake valves open at the same time.

By adding long tube headers you increase velocity at low speeds which makes for much more scavenging. But what happens if you try to size your exhaust tubing too big, what do you get??

Reversion:

Simply put, reversion is the opposite of scavenging. That is super simply put and much more complicated than that. Here's a great article going into great detail about reversion. Intake Reversion - Reversion Explained For Racing Engines - Circle Track Magazine

How does this relate to our beloved Tundra's? Well, we have all seen the 'hidden pipe' in our exhaust system, right?





When I first discovered it I posted it all over these boards and there was much discussion as why Toyota did this?? Well, I now know why:lol5: And I believe in giving credit where credit is due. As you can see in this thread, this page, post 758 http://www.tundratalk.net/forums/tundra-performance-modifications/93857-bamuffler-installed-51.html I have recently visited the exhaust masterminds at JBA. Their 'new products' engineer Don Linfors and I had an in depth chat about Tundra exhaust systems (my favorite subject), I explained to him that I installed 2.5" diameter mid pipes on my stock exhaust manifolds. I then complained that there was a major loss of low end torque. The grunt of my beloved truck was now gone. It pulled much harder at the top end (7HP and 15lbs tq harder to be exact:lol5: on the dyno)
But on the freeway and around town it sucked. It was hunting for gears, I had to step on the throttle much harder than usual to get the truck to move forward, etc. I then told him I took out the hidden pipe and showed him the above pics. He said matter of factly, that's because you slowed down your velocity and it caused reversion.

Before I 'googled' the term reversion I asked him for a laymans definition. His definition was much too detailed to say it was laymans, but simply put, once again, it's the opposite of scavenging. Without that tiny 2" hidden pipe the exhaust gases won't go fast enough at moderate engine speeds to create scavenging. The exhaust gases aren't going any specific direction. They're under pressure and that pressure just goes to the path of least resistance. Instead of siphoning out to the tailpipe, they actually back up. The high pressure pulse of the first firing cylinder actually backs up into the next cylinder in the firing order and during valve overlap instead of pulling out the exhaust gases and pulling in the intake charge, that pressure actually pushes the intake charge out of the cylinder and back into the intake manifold. This causes less a/f charge to be burnt as now there is only as much a/f entering the cylinder as the piston can pull in, no more. You see, scavenging during valve overlap will actually supercharge your engine and make in take in more than 5.7L displacement, but reversion stops this supercharging effect and performance suffers during normal driving.


So let's sum it up, Toyota hides a section of tubing in your exhaust system that is only 2" in diameter to keep up velocity, not backpressure, so that reversion is avoided and scavenging can occur. This 'supercharges' your engine making more power. Back pressure is an after effect that unfortunately can't be helped unless we make the exhaust tubing diameter variable, which ain't gonna happen:mad: So what do we do? How do we make more power and not affect driveability?? Here are some good guidelines to keep in mind.

Dual exhaust

When should you ditch the single exhaust configuration that Toyota has created for us and go true duals? My official recommendation is only when you have long tube headers. Without the velocity and scavenging caused by a good set of headers there is no benefit to true duals........unless you're supercharged that is:lol5: You see, reversion CAN'T happen when you're supercharged:lol5: The supercharger keeps pressure on the intake valves, it keeps everything flowing the right direction. The exhaust CAN'T back up into the cylinder, the cylinders are pressurized thru the intake valve more than by the exhaust. The exhaust will always follow the path of least resistance. By holding pressure in the intake tract the exhaust will naturally travel down the exhaust system on it's own.

I hear this 10 times a week, "I just love the looks of dual exhaust, I gotta have it on my truck" That's when I start to ask the customer critical questions: What do you use your truck for? Is it supercharged? Do you ever plan to add headers? Do you plan to aggressively re-gear the truck? Do you drive around with the pedal to the metal all the time? Do you drag race the truck? Most guys just use the truck as a daily driver and don't want to make a race car out of their 5500lb 4 door pick up truck:) They just want it to sound as badass as it looks, a little pick up in power is a bonus, and most importantly, they don't want the wife to complain that it's too loud.

At this point I try to explain the benefits to going with a single exhaust system that ties back into the stock tailpipe. Toyota spent millions in R&D. Our exhaust system was only a program in a thermal dynamics simulation for a long time before a single piece of exhaust tubing was cut or bent. Why on earth would we try to outsmart that? Haha, but on the other hand, I get it. We didn't buy a pinto, we bought a badass truck that fits the whole family, looks good and needs to sound good too!! Most of the time a single exhaust system is the right system.

That said, if ya gotta have true duals, at least we should do it right:lol5: Let's size the tubing appropriately, lets size the mufflers based on the customers sound level desires, lets add in a pair of helmholtz resonators 'tuned' to cancel out 150hz so we don't have to hear drone on the freeway, and most importantly.........let's add an X pipe to equalize the pressure and the flow of our odd/uneven firing V8 engine. If we do all of the above we can minimize reversion, maximize scavenging, and have a truck that sounds as good as it looks:cool: All of this should come in a nice neat package that you can bolt in using common hand tools with no cutting or welding required.

Here's some great formula's to keep in mind when trying to decide which exhaust system suits your needs best:

Stock manifolds, stock cats, stock 2" hidden pipe= single exhaust, mufflers sizing based on sound levels required, use stock taipipe, install a bolt in helmholtz resonator into stock tailpipe to kill drone. This system will gain 3hp and 3lb tq over stock. It will make the tq curve come on sooner and stronger at lower rpm and it will hold more torque throughout the entire torque curve. It will give you seat of the pants faster feel and is economical. Install takes an average of 20 mins and is very easy to do right in your driveway. Every Tundra should have this system installed. Here's a great example in SS

Untitled by bamufflers, on Flickr

Supercharged, stock manifolds, burnt out cats, stock or aftermarket cat back. You can actually justify running off road mid pipes (off road use only, not legal for sale or use on any pollution controlled vehicle) The cost of the pipes is cheaper than new cats, especially dealer cats. You will lose minimal low end torque, and you will gain a reasonable amount of HP/TQ. It's hard to justify these if you cats are good though, why not install long tube headers:lol5:


Catless 2010+ mid pipes by bamufflers, on Flickr


OBX long tubes, well, exhaust choices are unlimited now, as long as you size the tubing correctly. You can run either single exhaust, dual exhaust, cats, no cats, etc. You'll make the most power using 2.5" tubing, no cats, all mandrel bends, X pipe, etc. You can run 2 mufflers (1 in each bank) or 4 mufflers (2 in each bank). Having 2 mufflers is better for top end, 4 is better for bottom end. There is no loss of hp or tq, the curve is just slightly moved. running 2 mufflers will be really loud and you'll get a really raspy sound, but it's cheaper. My favorite example of the ultimate 5.7L exhaust system to date is on Sngo's truck:

Tundra Obx long tubes complete bolt on exhaust system. by bamufflers, on Flickr

Tundra Obx long tubes complete bolt on exhaust system. by bamufflers, on Flickr
The above system sounds like a cross between a ferrari and a zr6 corvette. It's not raspy, not too loud, not too quiet, drone is minimal, etc. If you remove the mid pipes from the system you can also realize gains on a stock manifold stock cats truck, but the gains are negligible and you get better low end torque with single exhaust.

Let's just say your truck is just a weekend toy/drag racer, as in RCSB, supercharged, Pacesetter long tubes, off road mid pipes, don't care if it's loud, just want it fast as possible and on a budget too, here's what works real well for that:lol5:

Untitled by bamufflers, on Flickr

Untitled by bamufflers, on Flickr

Untitled by bamufflers, on Flickr
The above system also works on a stock manifold truck, but gains are huge with long tube headers.

For guys who absolutely have to use dual exhaust and were considering the TRD system because it's nice an quiet, but still sounds like a v8, has a pair of nice pipes with sweet tips, why not customize the system? use whatever size mufflers you want, instead of 1 size fits all (26X6" mufflers!!!) rebuild the system the BAmufflers way using tubing that is twice as thick, an X pipe, coated in high temp black, but you can use any size muffler you want and still get to use the awesome TRD tailpipes that are coated in high temp black for free:lol5:

Untitled by bamufflers, on Flickr
Built in a 'TRD jig'

TRD system by bamufflers, on Flickr

Untitled by bamufflers, on Flickr

Untitled by bamufflers, on Flickr
using these tailpipes

TRD tailpipes by bamufflers, on Flickr

TRD tailpipes by bamufflers, on Flickr

So there you have it, scavenging, back pressure, velocity, REVERSION, true duals, X pipe, 5.7L Toyota Tundra true dual exhaust. The ultimate Toyota Tundra exhaust systems thread:lol5:
 

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Great write up Keith, can't wait to get mine on!!! (Hopefully before I leave town)
 

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You are really making me want to do this. For now I am resisting your Jedi mind tricks.
 

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Nice!! Since im in the market for an exhaust system this is right up my alley!! Of course going with the BAMUFFLER!! :)
 

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Looks like another 5 star thread!
Great write up Keith!
-
 

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Nice thread with lots of info for thought. Since you are adding OBX Long Tubes, larger mid pipes and BAMUFFLER to my TRD tail pipes do I need to send you another set of cats to make 4?
 

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One of the most interesting threads I have read on this website since the Turbo 5.7 thread came out in January. Great write up man!
 

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Ever had your exhaust dyno tested? That would be good thing to do so people could see gains or losses.
 

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Thanks for confirming my decision to get a true dual exhuast :D
 

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Discussion Starter #12
Ever had your exhaust dyno tested? That would be good thing to do so people could see gains or losses.
Yessir. My standard bolt on adds 3hp 3lb tq to an otherwise stock truck. Off road mid pipes add another 7hp and 15ft lbs tq. But like I said above, low end is so blown out there is no point going off road mid pipes unless you have a supercharger.
 

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And if a full blown dual system is not your thing here's a short before and after video that will help you decide if you want to just add the 8" Bolt On BAmuffler:


Dirty Deeds Industries 8" BAmuffler Tundra Before & After Video by RobPettis | Photobucket

Use the Youtube link to watch direct and use the photobucket link to download to your portable device.

No Power Loss, No MPG Loss (well, except for my right foot), super easy to install, reasonable price (compared to others out there, well, there is no comparison actually, so great price).

That's all I got to say about it.
Rob
 

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UM it sounds better, but how come it isn't blowing smoke in the before and is in the after??
Great question. To be honest I wondered the same thing myself when I watched it for the first time. And immediately thought I blew a ring or two....luckily I did not.

I am not an expert but I believe it can be attributed to one of two things.

One, and this is my first thought, the ECM was not allowed to adjust properly and therefore for the first 5 minutes the engine was running rich.......this is totally expected. And the ECM will adjust in like 2 to 3 tank fulls. Totally normal. Who knows, maybe I was just blowing all the carbon outta the cats. I really never had a reason to rev it up before that day :D

And when you have a man child like me behind the wheel and a passion for all things crazy, after doing the install and hearing this truck finally come to life, I was just happy I didn't blow it up. Heck the RTV on the Helmholtz was still wet and setting up! I thought I was gonna blow that out too........

Ok, or theory number two.

Even though it looks like all smoke some of it it is really steam. No, I am serious, I did this install on a day when there was about 110% humidity in the air. It was cloudy and getting ready to rain any minute. It rained the day before and I live in the country. We get fog on sunny days it's so humid all the time where I live because of the tall trees shading the sun.

Or possibly a combination of the two. I agree, the smoke is blueish/white and I see it even blowing rings and if you listen close you can hear it pop a couple times too. And like I said, my first thought when I watched the video playback was, "Great, nice going dumb ass", "You screwed up again". But there was no fuel smell lingering in the air......

Since the day I shot this video I have not had another issue with it smoking or popping. I swear. But to make sure everyone believes me I will shoot another video this weekend.

I have to say though, you are the first person to mention it. And again, Great question!

Rob
 
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