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I am writing this article today to try and help my fellow Toyota owners. In the recent past I have not only researched this subject, but I have also debated theory with a Thermal Dynamics Engineer for NASA (my neighbor), at the peak of his career he helped with design work on the Apollo program. I have tested many theories based on what I've read, what other forum members have suggested, my neighbor's sometimes crazy ideas, etc. So far the point of all of the above is not to 'brag' nor is it to 'defend' what I am about to say. The point of an opening paragraph like the above is only to give background and to relay information that I have learned through tons of trial and error and experience. As for the rest of this article, my goal is to not only pass on my knowledge of exhaust theory, and real life practice, it's to help guys get the right thing for their truck the first time.

I bought my first Toyota in 2003 brand new. The purpose of the truck was to replace my wife's Mustang, which I wrecked. I purchased the truck with the intention of someday making it into my desert toy. Well someday has come and gone and here is how the truck sits today:


Within the first week I bought a single in dual out exhaust system (to remain un named for the sake of professionalism) The first thing that I noticed was that this system didn't sound nearly as good on my Toyota as it did on my 5.0 Mustang. As a matter of fact, it sounded terrible. Lot's of deep noise with zero improvement in acceleration. Matter of fact acceleration suffered to the point that even my wife complained about how much slower the truck was. Just to maintain speed going up hill the truck would have to downshift a couple gears. Then let's talk about drone, I would but I can't hear anymore since I am now deaf. LOL.

Enough about why I am at this point 9 years later, here's what I have learned in this nearly decade long journey:

Exhaust literally flows like water. Not only that, but a very good analogy about automotive exhaust is that it flows like traffic on the freeway. For the sake of "keep it simple" I'll use the freeway analogy in this article.

Picture 3 very busy on ramps in Los Angelos, or Atlanta rush hour traffic. These 3 on ramps are only 20' apart from each other and have only a 100' runway before they force themselves through all 3 lanes of traffic and merge you right into the fast lane at a 90* angle. That is your stock exhaust manifold.

From there you travel 1/4 mile or so and you reach an area of the freeway that not only has painted lanes to separate traffic, but lining the lanes there are steel poles. Not only are there poles lining the lanes but the poles cause the lane to become so narrow that there is only a foot of clearance on either side of the vehicle. This is your first catalytic converter. Then you travel the length of a football field and come to another field of narrow lanes lined by steel poles, that's your second catalytic converter.

Now, it's smooth sailing for another quarter mile and you merge with an entirely new 3 lane freeway that just went through what you went through, all 6 lanes have to merge back into a 3 lane highway, this is the y pipe.

Continue on for another 1/4 mile and there is a huge brick wall right in the middle of the freeway!!! This brick wall blocks all 3 lanes! With no signs saying which way to go to get around it. Some traffic is going right, some left. But ether way you go the only option is get right up to the wall, stop, then go around using the left or right shoulder of the freeway. Now go around 2 more brick walls right in the way of the lanes!! This would best describe your muffler.

Continue down some sweeping long curves with very little obstruction and exit the freeway into oblivion, this would be your tailpipe.:cheers:

What does all of this tell you? What part of this freeway would you fix first? Obviously the brick walls in the middle of the freeway are causing the most back up in the entire system. For goodness sake, you have to completely stop and in no certain order go around the walls before you can continue on to the long sweeping curve that is the tailpipe.

What's next, well the 3 congested on ramps cause some traffic to completely stop before other traffic can merge right? If you were to take those 3 on ramps and extend them to 1/4 mile instead of the 100' that they are, you would give the traffic time to blend, especially if you made them face the freeway at a 45* angle, not a 90* angle. Instead of forcing each on ramp into the fast lane you allow each on ramp to take the lane of least resistance you can substantially speed up the freeway.

In the case of Long Tubes versus stock manifolds: As the exhaust exits the port in the head there is not only tremendous force, there is also a lot of expansion due to heat. In the case of stock manifolds this expansion turns into pressure. Now that the manifold is under pressure with very little velocity to release this pressure, the next cylinder expands into the pressurized manifold and meets resistance. This resistance keeps the cylinder from evacuating all of it's exhaust completely making less power. Not only that, but the exhaust, from the very beginning, has very little velocity, only pressure (back pressure). In contrast, allow that exhaust charge to expand into a long narrow tube and that pressure never builds up, it turns into velocity. This velocity quickly evacuates the cylinder and rushes into the collector, then the exhaust travels through the system at a very high speed. If you encourage that speed to continue by properly sizing the rest of the system you have created optimal conditions for scavenging to occur, but I'll discuss that later in this article.

The next thing in our freeway (exhaust) system that needs to be fixed is the catalytic converters. As you can see we're jumping around. I didn't say fix the manifolds first, even though they're the beginning of the freeway, it is obviously not the most restrictive part of the system. The huge brick wall that is our muffler is the most restrictive. With this replaced, if we still want power we move to the next most restrictive part, the manifolds (freeway on ramps) Well we now have traffic able to flow smoothly, these steel poles lining the lanes are causing cars (exhaust) to slow down so that they don't clip one, right? It's important to note, the poles lining the lanes only cause cars to slow, not stop like the short on ramps and brick walls did. So now you ask, "Keith, what's your point?" Fix what needs it first!!

Notice how there was no part of this article saying that the freeway narrowed down below 3 lanes? Also, for the sake of this whole analogy, there will never be more cars than what 3 clear lanes can handle. This means, you don't need to have bigger than stock tubing unless you add more cars. (exhaust flow) How do you add more cars? (exhaust flow) Well, the most common way in the case of the FJ Cruiser is to bolt on a TRD supercharger. You could also speed up the engine by raising the shift point to something crazy like 7500 rpm. (not really cost effective on the FJ) or you could inject nitrous.

Also, notice how I described the tailpipe as a long sweeping lane. Does that sound very restrictive? NO! In the case of exhaust, what happens if you take a perfectly sized tailpipe and make it bigger for no reason? Well the exhaust slows down. Now the engine has to pump out the exhaust instead of it scavenging on it's own. Again, I mentioned scavenging, I'll go into that later into this article.

Let's summarize: What is the best bang for the buck to un-cork the exhaust system? The muffler, period. If you don't change those stock manifolds, but are looking for a little more flow, the muffler is all you're going to need to change. After that, the only thing that 'stops traffic' is the stock manifolds. The cats 'slow traffic' but by no means do they 'stop traffic'. So why take them out? The only thing you get is noise:cheers:LOL To speed up exhaust flow you first have to remove what causes it to stop. You have to start at the most restrictive part, the muffler.

After you've replaced the muffler and the stock manifolds, you can move on to the cats, get rid of em. What do you have left? The y pipe. Well, now you have options. If you keep a long sweeping merge, the traffic can continue to flow, if designed right it only has to slow slightly to make the merge. I can tell you that the stock y pipe is very efficient. Unless you're adding more 'cars' flow, there is no need to replace this y pipe. Toyota has engineered a very efficient y pipe for the FJ.

Where does this leave people on the exhaust market with an FJ? Well there are 2 types of buyers: Guys who should replace only the muffler, and guys who could replace the entire system from header to tailpipe. You know why I say this? So that YOU DON'T WASTE MONEY!! I hear it all too often, guys will replace their muffler with the wrong muffler (I'll go into this later in the article) then thinking that they're making power they'll replace their tailpipe with a new 3" version LOL. The stock exhaust system with stock manifolds was barely able to flow enough for the stock tailpipe. Especially with the last 1/3 of the system being so cool it's velocity has slowed substantially compared to how it was when it was going through the first 1/3 of the system. Another common mistake is to build dual tailpipes after the muffler. All you're creating is 2 low pressure expansion chambers that suck up velocity, causing your engine to have to pump out the exhaust through 2 tailpipes, instead of it scavenging (yup, I said scavenging again)

With how important this is, I'll repeat it once again, If not changing out your stock manifolds for long tubes and you want a little more performance, change your muffler, that's it. Don't change anything else, the only thing more restrictive than the muffler is the stock manifolds. If you're the guy who is willing to change out the stock manifolds for Long Tubes, this next paragraph is for you:rocker:

If changing out your manifolds for Long Tube headers you have now opened up a whole new set of options. You can chose to keep the rest of the system stock, keeping stock cats, stock y pipe, stock tailpipe, and obviously the stock muffler is long gone as it is literally as restrictive as a brick wall LOL.

Seeing as it is now midnight I am going to leave it at that for now. However, I will continue to add to this article as time permits. Future subjects will describe various set-ups using Long Tube headers. I will also describe scavenging in great detail (will probably spend a full night on the subject), I intend to go into various ways to quiet down an exhaust system and the different types of mufflers that accomplish these goals, including the stock brick wall. Tubing sizes and velocity will be discussed. Oh, and I will answer any questions from other forum members as they are posted, so please feel free to post up any and all questions/feedback.:wave:
 

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Great write up so far. Looking forward to reading your future posts.
Great analogy too. The freeway example explaining continuum mechanics and fluid dynamics is one that a engineering professor of mine used often.
Great looking truck too. :bigthumb:

:cheers:
 

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I'm curious how you determined that the stock Y pipe is so efficient.

I'm far from an expert, but when I removed mine, I couldn't believe they had opted to compress the flow down that far to just over an inch in diameter at the Y. Based on your comments, would I have gained even more MPG by leaving the stock Y in place instead?
 

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^^^ yea I'm with his guy, I was wanting the re-route the exhaust to keep it away from the transfer case, after taking off the stock y-pipe and you see where they crimped both pipes into half circles then slipped a 1 3/4 pipe over both of them (the smallest diameter pipe size in the whole exhaust system). Before that, the pipe is flatten to give more ground clearance, all of which is contained in a 90 degree S-bend curve. That's the way it's build on a 2011 model anyway.
 

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Just subscribed, good stuff! :cheers:
 

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great read! i cant wait to hear more to see what i can do to get more gains. i already have a flowmaster muffler with a dual exit (which you said was bad) but i like the sound it gave and the added mpg was a plus as well
 

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Nice article. Guess thats why i just changed my stock muffler out to a 20" Magnaflow and installed a TRD (TRQ) look a like tip. I thought i was too broke to afford an entire exhaust system.Glad i just did the muffler.
 

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Are you planning on talking about exhaust temperatures, volume/density changes as it cools moving thru the exhaust system?

DEWFPO
 

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^ Yes. Always yes
 

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What's the best exhaust to pair with the TRD SC?
 

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Discussion Starter #16
I'm curious how you determined that the stock Y pipe is so efficient.

I'm far from an expert, but when I removed mine, I couldn't believe they had opted to compress the flow down that far to just over an inch in diameter at the Y. Based on your comments, would I have gained even more MPG by leaving the stock Y in place instead?
That's exactly how they designed the 1gen Tundra's Y pipe. I have tried many different configurations with Tundra Y pipe's. My conclusion: Changing the Y pipe without changing the manifolds is pointless. It is not the bottleneck. The stock manifolds cause the exhaust to build pressure, not velocity.

I will go into velocity/scavenging versus backpressure hopefully tomorrow. Here it is 11PM and I just got out of the shop for the night, been working since 9a.m. Take the work while it's there, right? I saw the email notifications throughout the day today, but was behind a chop saw, plasma cutter, and welder all day trying to get a few projects finished up this week.
 

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Discussion Starter #17
Nice article. Guess thats why i just changed my stock muffler out to a 20" Magnaflow and installed a TRD (TRQ) look a like tip. I thought i was too broke to afford an entire exhaust system.Glad i just did the muffler.
And unless you intend to go with headers, you're done:bigthumb:
 

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Discussion Starter #19
What's the best exhaust to pair with the TRD SC?
True length Long Tube headers with 2 1/2" collectors. delete cats, correctly designed X pipe (one that ALLOWS the 2 banks to merge if one bank has lower pressure than the other, not one that FORCES the 2 banks together) just after the X pipe run a pair of flow thru mufflers like Borla, Magnaflow, or BAmufflers. You can either chose to exit both sides just before the rear tires, or go up and over the rear end, but it's real tight.

Be warned, this will be extremely loud! But it is good for an honest 10-15HP over running cats and single exhaust.
 

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Discussion Starter #20
So it's been a real long day, I'm checking out for the night. I have a much easier day scheduled for tomorrow. I'll try and get on here earlier and write the next part of my article.

Keith
 
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