Re: conflicting exhaust info......

Many companies sell you on the idea that 'Bigger is Better', of course this is not always true. R+D needs to be done on a wide range of engine combinations. One size does not fit all in the case of exhaust. A totally stock engine will require less exhaust flow than an engine modified to flow better or one that has a supercharger for example. You will get many opinions here and out there, the best is to see how many are using what you are thinking of getting, what mods they have, and what they have experienced. My personal experience and suggestion would be to go no larger than 2 1/2", then install a nice 3 1/2" exhaust tip if you want the big look.

 

Re: conflicting exhaust info......

I agree. These companies live on selling things you like to hear not what works across the board.

Larry

 

Re: conflicting exhaust info......

Although you may not like this, the stock exhaust with a replacement muffler is the best all around set up.

Go bigger, and you lose your low-end torque. Go smaller...well...you choke your engine.

I used to have dual 2.5" pipes with an X-pipe and two F/M mufflers. My low end was....bad. I recently went back to a single 2.5" pipe with 1 F/M muffler. I simply reused what pipe I had, and put the stock y-pipe back in.

I have be VERY happy with this set up. Gave me my low end back.

 

Re: conflicting exhaust info......

Many V8's need backpressure, the Tundra V8 will do just fine even with a 2 inch system. I have a 455 V8 and even that one does not really need a 3 inch system, but the two 3” pipes do look nice coming out at the back

 

Re: conflicting exhaust info......

Although you may not like this, the stock exhaust with a replacement muffler is the best all around set up.

Go bigger, and you lose your low-end torque. Go smaller...well...you choke your engine.

I used to have dual 2.5" pipes with an X-pipe and two F/M mufflers. My low end was....bad. I recently went back to a single 2.5" pipe with 1 F/M muffler. I simply reused what pipe I had, and put the stock y-pipe back in.

I have be VERY happy with this set up. Gave me my low end back.

You were probably running very rich with the higher flowing exhaust. Had you used electronics such as URD or Unichip to lean out the a/f ratio, it would have returned the low end without swapping back to the smaller system.

 

Re: conflicting exhaust info......

I was planning on ordering my stuff from Magnaflow Exhaust Systems And Performance Mufflers - Justmagnaflow.com they seem to be the cheapest that I have found. I am thinking I am going to do a 3" from the resinator back. I will replace the factory resinator and from there back use 3". By the time that I buy the muffler, resinator, and do the install with 3" I will still be less than if I went with the Magnaflow bolt-on kit.......

 

Re: conflicting exhaust info......

Many companies sell you on the idea that 'Bigger is Better', of course this is not always true. R+D needs to be done on a wide range of engine combinations. One size does not fit all in the case of exhaust. A totally stock engine will require less exhaust flow than an engine modified to flow better or one that has a supercharger for example. You will get many opinions here and out there, the best is to see how many are using what you are thinking of getting, what mods they have, and what they have experienced. My personal experience and suggestion would be to go no larger than 2 1/2", then install a nice 3 1/2" exhaust tip if you want the big look.

Take this info as true and correct.

Dead on right. Could not have said it any better.

LT

 

Re: conflicting exhaust info......

then why would they post up a dyno showing the results with the 3" piping change. I personally know from experience on a 2JZ motor I-6 that the increase in piping achieved a higher TQ rating as well as HP on the dyno. I was N/A on a 3.0 liter motor....this is a 4.7...........I currently have 2.5 piping on my L24 2.4 motor......it just seems to me that 2.5 would be restrictive....

 

Re: conflicting exhaust info......

You can easily use bigger piping and it will make a difference, however too big can be defeating. I have an older Toy with a 20R bored out to 2.4L running 10:1 with a 500 CFM Holley, mid range high duration cam and long tube headers. I experimented with 2.5" and thought I had something good. Later on I re-did the system with 2.25" piping and saw a vast improvement in mid range. That 1/4" of cross-section made a big difference and gave me additional power where I wanted it.

The normal rule is that backpressure improves bottom end and open flow improves top end performance. The whole trick is to strike a balance for the best overall performance and sound quality, unless you have a specific RPM band in mind. Publishing a dyno number is meaningless if it is out of the normal RPM range you use for most of your driving. Simply having more high RPM power may not help if it takes longer for you to get there because your bottom end has suffered. I would suggest that whatever system you are considering, look at the dyno results carefully at all points and see where the curve concentrates the power increase, make your decision that way.

 

Re: conflicting exhaust info......

Smaller diameter pipes improve low end. Properly Designed back pressure tunes a Torque range to a specific RPM range.
Bigger is not always better!! Most of the time it is worse. Concentrate on your cats, resonators/mufflers or H pipes if your app. allows.

Full open pipes only benefit WOT. This is not where driveability is found.
LT

 

Re: conflicting exhaust info......

I thought that this rule held true for carborated motors and not TBI. By the way my Z is a Draw-thru carb turbo setup.....I have to keep the 2.5 to keep the turbo spooling earlier and faster ( due to the backpressure needed). People with a TBI set-up go with 3 inch and GAIN HP. Your rule is true for carborated set ups.

 

Re: conflicting exhaust info......

I thought that this rule held true for carborated motors and not TBI. By the way my Z is a Draw-thru carb turbo setup.....I have to keep the 2.5 to keep the turbo spooling earlier and faster ( due to the backpressure needed). People with a TBI set-up go with 3 inch and GAIN HP. Your rule is true for carborated set ups.

Not entirely correct due to cam overlap... loss of backpressure will steal some intake charge into the exhaust ( thus popping noise with low backpressure systems ). Although the EFI will compensate with fuel delivery, it is the partially lost air charge that you don't recover. EFI systems will not suffer as much as carbuarted systems but they will.

 

Re: conflicting exhaust info......

It is also important to qualify the exhaust components and their affect on back pressure. For example just to say a 3" exhaust system doesn't tell the whole story. A properly designed 3" exhaust may not give adequate back pressure for a particular engine, however a 3" system comprising of poorly bent piping, restrictive muffler, may work as it is really no better than properly designed 2.5" system. Pipe length is one variable that affects backpressure, since exhaust pulses from the engine, there is a pulse "wavelength" (similar to radio waves). Just like tuning an antenna's length will provide the best reception and transmission of band of frequencies of a radio. There is always an ideal frequency that peaks and the rest slope downwards on each side kind of like a bell graph. Exhaust works the same way, a proper length pipe will enhance flow while an improper length will cause the pulses to reflect back. A muffler is designed to cause some reflection of these pulse to cancel the noise, this results in backpressure even in a seemingly straight through muffler. Bends in piping can cause slowdowns just like bends in a river. A crossover pipe ( "H" or "X" ) will enhance flow by using the vacuum generated from one's bank exhaust pulses to help draw exhaust from the other bank, this also balances the back pressure of the engine. The position of the crossover will also have a bearing on it's effect. However do not take it as the crossover takes away all the backpressure, the length of pulse will only draw a certain amount of exhaust as compared to my statement about the loss of intake charge. The performance of a crossover is also affected by what is behind it, even in an open exhaust race engine, the pipe length is tuned.

There is a fairly complex set of calculations to design the ideal exhaust system, but even with those it will still be based on a particular RPM for best flow.

Am I suggesting you sit down and calculate it all out ?, no, just look at the whole picture and if reliable dyno results for a "particular" set of exhaust components is available then take the time to make sure it matches your primary driving needs. By all means consider the comments by owners that have upgraded their exhaust systems and what they have specifically used. Generalizing on size alone is not enough information to guarantee the best results.

 

Re: conflicting exhaust info......

$hit $hit $hit $hit.........lol
I guess it is back to the drawing board...it seems as though there are so many things out there for us to do to these trucks that no one else has done. I hate to just spend money and spend money and not get good results. I was going to change out the y pipe and get a replacement from TundraRacing homepage to help with flow as well. I also wanted to get a set of good long tube headers to help with flow as well. In my changeing out the piping size I was trying to get flow. I am not intending on changeing out the whole thing to have merely a 3" exhaust from front to back. I was changeing out the factory resinator and from there I was going to use 3" to a 3" in/out muffler to the rear factory location. I am intending on using the same lentgh of piping that was used from the factory but a larger diameter.......

 

Re: conflicting exhaust info......

Here are a couple of choice that will work for you to make a cat back system. You can use a "Y" pipe into a muffler and tail pipe. Another choice is to use a dual in/single out muffler that is similar internally to a "Y" pipe, Borla makes one. For pipe size I would recommend 2.5" from the cats to the muffler and 2.5" out. This size will be very forgiving for variances in mufflers.

You can go up to 3" on the tail pipe if you want but any popping noticed upon decel will tell you that more backpressure would be nice. In this case it is an easy fix, you can install a 3" in/out "race bottle" ( only 8" long ) in the tail pipe anywhere after the muffler ( same holds for 2.5" but seldom needed). This will help slightly increase backpressure and also can get rid of any annoying drone as it will change the tone of the exhaust.

I personally run JBA headers/factory cats with 2.5" pipes to a dual in/single out Ultraflow muffler, then a 2.5" tail pipe. Works well and sounds good, get lots of compliments. If I had to do it over again I would most likely use the Borla muffler as described above.

 

Re: conflicting exhaust info......

Hi all,
First post here... I'm a mechanical engineer and past master mechanic...

Does anyone have actual DATA that shows the losses from "lack of backpressure"?

Engines don't require backpressure, but they do require exhaust scavenging.

My guess is the losses are a result of inapropriate ignition timing, AFR, or a change in resonance.

I'd love to see proof of this (before and after dyno runs with a list of modifications performed). Post it up!!!

 

Re: conflicting exhaust info......

Engines ARE designed with a degree of backpressure, it helps to balance torque output.

 

Re: conflicting exhaust info......

The statement that engines do not require backpressure is somewhat correct however but not really relevant in the context of this thread. If you take away all the backpressure from an engine it will run, no arguement. However since the Tundra engine and similar gasoline light truck engines were designed to be used over a wide RPM range, have an exhaust system, and pass emission requirements, they have been designed around that fact with cam profile, fuel delivery, timing curve, air intake etc. If we wish to throw that all out the window and run no back pressure, then yes you can blame loss of power on A/F ratio and ignition timing etc. as it is no longer optimum for the application anyway. The nice fact that we have ECM's to make changes ( within limits ) to fuel delivery, ignition timing etc. allows us some latitude in exhaust modification along with other things.

As far as dyno results to prove loss of horsepower with little or no backpressure, I am sure some of the exhaust kit manufacturers that provide results have tested more than one size of exhaust. Some will market a good all around system, and some will market a larger more RPM oriented system. But none will publish their failures. As for the rest of us that bought a Tundra instead of a dyno, most of us use that famous old "Buttometer" (to steal a phrase ). We can usually tell if our trucks are running better or worse ( some high milers practically live in them). Some of us race and have a different perspective or method to test results. The main connection is that many of us like a little added grunt at the expense of quiet trucks. Many like the throaty sound as well. I can also tell you from experience that you can go to far and lose some of that elusive and precious horsepower.

If we want to talk about race engines that utilize what we would consider no backpressure, then we must also talk about the latitude in the design allowing this ( something we don't have ). It should also be mentioned that race engines are designed to operate in the higher RPM levels and are not designed for low end torque. I can add about six pages here but it wouldn't help out trucks. We can talk about diesel engines and little to no backpressure, but then again we are bringing oranges to an apple sale as the design characteristics,fuel properties, A/F ratios ( vastly different), also narrow RPM band just doesn't fit our scenario. Constant RPM engines used in marine or aircraft applications are again designed differently as their power is concentrated within a narrower range, many are designed to run at a constant RPM. Our applications ( light trucks ,also cars ) are amoung the most demanding for useable RPM range, as we want power out of the hole and right up to redline ( at least I do ).

 

Re: conflicting exhaust info......

As long as exhaust scavenging is not comprimised the less backpressure the better. The requirement for backpressure actually comes from running larger diameter primary tubes in the headers in an effort to increase overall flow. What happens when you put larger than optimum primary tubes is you get a loss in exhaust scavenging. At lower speeds there will be a loss, this loss is eventually overcome by the higher overall flow at higher speeds. This requires a higher idle speed and moves the power higher in the rev range.

The stock shorty header is a 4 into 1 design. This header does little to help torque. A 4-2-1 header would get better torque numbers. This is a moot point, however, as Toyota decided to move the cats into the headers. The proximity of the Cat to the exhaust port creates a hotter exhaust mixture entering the Cat. I'm sure the straight line flow of the Cat is similar to a straight pipe. The problem comes with the destruction of resonance that aids exhaust scavenging.

As an example, my FZ! motorcycle comes with two Cats, one in the muffler, and one in the exhaust, just after the header collector. I removed the cat in the collector and saw a huge jump in torque in the 4-9k (12k redline, so comprable to 2-4.5k on the Toyotas) range on the dyno, still running the stock restrictive exhaust.

I guess I'm trying to make the point that there is more at work here than resistance to flow...

An abrupt transfer from a 2.25 inch exhaust pipe to a 3 inch pipe can have more restriction from buffeting at the joint than the smaller exhaust, but that is of much lesser magnitude that the other factors.

 

Re: conflicting exhaust info......

I agree, the exhaust design of the Tundra is not optimal, but it most likely serves the expectations for performance they initailly laid out. I also agree a long tube header with 4-2-1 is a far superior method, I know from my 4 cylinder days, torque comparison was very noticeable between long tube and "shorty" headers.

My reason for suggesting we need backpressure was to aid in dampening the resonance to help scavanging while keeping some balance of torque taken the components we have to work with. I didn't want to get too complicated here and lose some people.

But unless we do a redesign ( unfortunately at some cost ), then relieving any unneccessary restriction from the cats back is something attainable for most here. I have heard of anything from 2.5" to running straight pipes right out of the cats (latter on another thread). The results of straight pipes didn't sound encouraging or comfortable on the ears. The right combination is what is important here, and try to dispell that bigger is always better.

(A bigger beer is always better than a smaller one, unless it is the one too many.)

 

Re: conflicting exhaust info......

You were probably running very rich with the higher flowing exhaust. Had you used electronics such as URD or Unichip to lean out the a/f ratio, it would have returned the low end without swapping back to the smaller system.

Possibly, but I did run my truck on a Dyno before any of my other mods (exhaust only) andI wasn't running rich. I was told my A/F ratio was fine. I think by that point, the computer had adjusted. I got stock 4.7 V8 Tundra hp and tq numbers.

My big, fancy, expensive exhaust did absolutely nothing in terms or increased horsepower or torque. Just changed the torque curve, and not for the better.

But you are right, a URD MAF calibrator would be nice to have, even now with my other modifications.

It's not worth it buy a big company manufactured exhaust for 500-600 bucks when you can just by their muffler for $100 and get a muffler shop to put it in for you for 50 bucks.

 

Re: conflicting exhaust info......

And that is what I am trying to do but with a twist.....use the muffler they have in their system but use my own crush bent pipe ( instead of mandrel) to help create some preassure as I go up 1/2" in diameter piping. I am only wanting to help my system breath better than it does.......I will only use the 3" piping from the muffler back........I have decided in the interest of backpressure to change the piping diameter from the muffler back and also change the factory resinator to a aftermarket unit....( usig the same piping diameter)

 

Re: conflicting exhaust info......

And that is what I am trying to do but with a twist.....use the muffler they have in their system but use my own crush bent pipe ( instead of mandrel) to help create some preassure as I go up 1/2" in diameter piping. I am only wanting to help my system breath better than it does.......I will only use the 3" piping from the muffler back........I have decided in the interest of backpressure to change the piping diameter from the muffler back and also change the factory resinator to a aftermarket unit....( usig the same piping diameter)

That doesn't sound like a bad plan. You just putting a strait pipe in where the original resonator is? As of now, I have a single 2.5" crush bent system after the stock y-pipe but with no resonator (had it put back in). And, a 3" tip :tu:

It performs well, and so far I have no regrets about getting rid of my duals, which were dual 2.5" pipe with an X-pipe. You can see pictures of my old exhaust in my photo gallery under one of the albums. It sounded amazing, but off the line it just bogged. And, it did absolutely nothing to increase power. It just moved the torque curve. Stock pipes, or 2.5", are probably the best bet, especially before the muffler which provides the most restriction in the system. What you do after that shouldn't have as much of an affect as before the muffler. It's all about scavenging and keeping the exhaust hot and flowing fast! Big pipes just mean cooling and bad scavenging.

There has been some good info in this tread, and in many treads before it. For optimum overall performance you do have to possibly sacrifice sound, and that "cool dual exhaust" In the end, functionality prevails. So, sound like you have a pretty choice of an exhaust. What muffler do you plan on using?

 

Re: conflicting exhaust info......

For me, a mandrel bent system is the only way to go . Crush bent turns may be a tuning aid technique on a sysytem that wasn't carefully planned out to begin with.

LT

 

Re: conflicting exhaust info......

For me, a mandrel bent system is the only way to go . Crush bent turns may be a tuning aid technique on a sysytem that wasn't carefully planned out to begin with.

LT

I agree mandrel bent is nice...but too nice for my truck. I'm not going to spend hundreds of dollars more for cleaner bends on something that most people will never see, and won't impact engine performance a whole lot. In the end, how much more power are you making with mandrel bends.

Plus, with pre-made systems, you're just paying for the name anyway.