Dual Exhaust=Torque Loss [Archive] - Toyota Tundra Forums : Tundra Solutions Forum

: Dual Exhaust=Torque Loss



Tundratow
12-16-2003, 10:50 AM
I read in a post that said torque goes down after installing a dual exhaust with free flowing mufflers.
Can someone explain why? Does this also hold true for a single exhaust with free-flowing muffler?
I tow and need all the torque I can get out of the 4.7.
Thanks

peid
12-16-2003, 10:53 AM
I read in a post that said torque goes down after installing a dual exhaust with free flowing mufflers.
Can someone explain why? Does this also hold true for a single exhaust with free-flowing muffler?
I tow and need all the torque I can get out of the 4.7.
Thanks

Back Pressure.

I have the dual exhaust and lost quite a bit of throttle response, like when getting on it from a stop light. A stock Tundra will blow me a way I think.

But man it sounds cool.

The sound means more to me than the 0-60 times.

I don't think you will lose as much with just a single, but the stock is about as good as it gets, except it is quieter than most cars!

mike.elmes
12-16-2003, 12:56 PM
Is the torque really lost? Perhaps it's just relocated somewhere higher in the RPM range. True for towing the torque is better to have low in the rpm but where does it re-appear? If it's just a 1000-2000 rpm higher it's still on tap but will require more foot.;)

RockyMtnRay
12-16-2003, 04:54 PM
I read in a post that said torque goes down after installing a dual exhaust with free flowing mufflers.
Can someone explain why? Does this also hold true for a single exhaust with free-flowing muffler?
I tow and need all the torque I can get out of the 4.7.
Thanks

I'm going to be towing as well...over Colorado's high passes so torque is also supremely important to me. I've done hours and hours of research on this issue to see how I can optimize the torque on my Tundra in that all-important-for-towing 2500 to 3500 RPM range.

From my research, I've concluded the key to getting maximum mid range torque is to maximize exhaust energy (heat) and velocity all the way to the end of the tailpipe...at the exhaust volumes and flow rates the engine produces in the mid range.

Furthermore, if possible, the pulses (from the exhaust valve openings) in the exhaust flow should be maintained...the low pressure on the back edge of one pulse helps pull along the high pressure on the leading edge of the next pulse. This is the principal of a scavenging exhaust.

The reason that dual exhausts...or overly large (like 2.5 inch and larger) single exhausts reduce low to mid range torque is they allow the exhaust gasses to expand (which cools them) and to lose velocity. The cooled air is denser/heavier...and the exhaust pulses more or less are merged together further losing their velocity and scavenging action. The net result is the larger exhaust pipes become essentially long tanks of semi-stagnant gas which has to be pushed out by the incoming exhaust...it's no longer self-scavenging. Or, in other words, a larger or dual exhaust has higher effective backpressure than a smaller, single exhaust at mid-range RPM . Yes, the larger/dual pipes have less wall friction on the gasses than the smaller single pipes but this effect is nullified by the loss of energy/velocity in the larger or dual pipes. It's very important to note this situation applies to the mid-RPM ranges...at very high RPM (like near redline), there's enough energy, volume, and velocity in the exhaust gasses to maintain scavenging all the way to the end of the pipes (even duals) and the lower wall friction of the larger pipes does come into play.

Bottom line: for mid RPM ranges, intuition is wrong...there's more effective back pressure (or less scavenging) in large or dual exhausts; for top end RPM, intuition is right...large/dual exhausts have lower backpressure. And at any RPM, backpressure is just plain bad for torque. There's a myth out there that engines need backpressure to make more torque. This is wrong. Backpressure is resistance and you want the least resistance. If you look at the dyno results and comments posted by V8toilet about his various systems you'll see that he got noticeably better mid range torque than stock by using a single 2.25 pipe running through a fairly low restriction Spintech muffler...and much, much better mid range torque than with either 2.5 inch single pipe or with dual exhausts.

I'm personally going to leave the truck's stock 2.25 inch pipe alone...I totally agree with V8toilet that it's really the right diameter for maximum torque from a 4.7 L engine. I am, however, going to try replacing the stock muffler with an allegedly lower restriction unit from Gibson. Interestingly, the Gibson, which is a baffled straight through design, is just slightly louder (about 3 db) than the stock muffler. IOW, louder does not equate at all to more power. I've considered using a Spintech muffler instead of Gibson but there are too many comments on this board and others that indicate the Spintech (even the quietest one) is just too loud for my tastes.

Imdone
12-16-2003, 05:54 PM
Also the tundra's stock exhaust system is not exactly set up for scanvenging.

The stock system is really pushing the exhaust out of the pipe rather than it being pulled out via scavenging vacuum. If you change the stock muffler and tailpipe to 3" without changing the rest of the system you will notice a drop in lower end torque.

If you change the rest of the system to something that promotes scavenging you will find that a larger diameter pipe will work but you can still over-size the pipes and have the same problem.

dsconstructs
12-16-2003, 07:17 PM
This seemed like a good discussion concerning the dual exhaust setup. Anyone know what kind of a difference a blower makes with this. First off, it is on a V6 and if some other header makers don't come through soon I am considering going dual catbacks or something along those lines to open the exhaust up some more. I may be misunderstanding some of the many exhaust topics I've read on, but, I am thinking I may get a happy medium (well happy enough) by going dual catback. Any thoughts?

Agent WD-40
12-16-2003, 07:21 PM
What would happen if you put a vacuum like device on the tail pipe? Would it help pull the exhaust gas out better and make more power? It of course would have to make more power than it used to run itself. But in theroy, would that work?

RockyMtnRay
12-16-2003, 07:32 PM
Also the tundra's stock exhaust system is not exactly set up for scanvenging.

The stock system is really pushing the exhaust out of the pipe rather than it being pulled out via scavenging vacuum. If you change the stock muffler and tailpipe to 3" without changing the rest of the system you will notice a drop in lower end torque.

If you change the rest of the system to something that promotes scavenging you will find that a larger diameter pipe will work but you can still over-size the pipes and have the same problem.

Definitely. Especially the exhaust manifold. That "log", as you've conclusively proven (to me anyway :)) with your tests of the long tube S&S headers, significantly kills scavenging and produces a lot of backpressure...at both mid range or top end RPM. This thread was basically about cat-back improvements but you're totally right...incorrectly mucking with tailpipe and muffler (like duals or overly large pipes) can really hurt torque but in actuality there's not a lot of torque gain available over stock (maybe 10 to 15 lbs-feet). As others have noted, the stock muffler isn't all that bad for flow. OTOH, a new properly sized torque-increasing muffler (specifically Gibson or Spintech) at around $150 in stainless is a heckuva lot more cost effective than headers that provide 3 times the torque gain at 6 times the price.

But if those of us who tow really want to boost mid range torque and are willing to pay the price, then headers tuned for low to mid range are definitely the answer...in particular S&S or JBA. With even a stock muffler/tailpipe, I'm estimating the torque gain at the rear wheels will be around 20 lbs-feet at about 3000 RPM (roughly 10% over rear wheel stock torque).

RockyMtnRay
12-16-2003, 07:43 PM
This seemed like a good discussion concerning the dual exhaust setup. Anyone know what kind of a difference a blower makes with this. First off, it is on a V6 and if some other header makers don't come through soon I am considering going dual catbacks or something along those lines to open the exhaust up some more. I may be misunderstanding some of the many exhaust topics I've read on, but, I am thinking I may get a happy medium (well happy enough) by going dual catback. Any thoughts?

If you dig deep enough on this forum with your searches, you'll find several posts that indicate the 3.4L V6 with blower is effectively a 4.7L engine from a volumetric viewpoint. IOW, you've now sorta got the V8. :)

With regard to opening up the exhaust system, the first question has to be where do you want more power? Do you want it in the mid range (as in for towing)...or do you want it more toward the top end (as in for drag racing, highway passing, etc.?). If the top end, then duals make some sense...but don't go much over 2 inches on your pipe sizes. If mid-range, then the points about tuning the V8 for mid range power apply: a proper header with smallish primaries (1.5 inches), single exhaust of no more than 2.25 inches.

Lots and lots of people on this forum think that "opening up the exhaust" is going to really boost their power. In most cases, they are thinking big pipes and/or duals when they use that phrase. The reality is that such "opening" will actually really hurt their power output at most RPMs because the "opened" exhaust is just a big, fat tube of almost stagnant gas at anything much below redline RPM.

RockyMtnRay
12-16-2003, 07:56 PM
What would happen if you put a vacuum like device on the tail pipe? Would it help pull the exhaust gas out better and make more power? It of course would have to make more power than it used to run itself. But in theroy, would that work?

Good question and from my knowledge of fluid dynamics, yes it would somewhat...but only somewhat...pull out exhaust faster to make for more power. As for providing a net power gain after subtracting the pumping losses, I'm not so sure and, to be honest, pretty doubtful.

The real point of my post on this topic is that "Theory of Exhaust 101" isn't a simple nor particularly intuitive knowlege area. There are really a lot of hard to sort out things happening inside that exhaust system...not only do you have the relatively long-wave (acoustically speaking) pulses coming from exhaust valves opening and closing but there's a lot of strong higher frequency (short wavelength) sonic pressure waves bouncing around as well. Those wave interactions can, if properly timed in suitably sized resonant chambers cancel themselves out...or...produce standing waves that really block up gas flow.

But as a general principal...and acoustics notwithstanding...the best flow is going to happen if both exhaust velocity and energy (heat) is maintained. Higher or lower pressure at the exit of the tailpipe are secondary to these in-pipe fluid dynamics concerns...mainly because the gas pressure at the beginning of the exhaust tubing (e.g. at the exhaust valve) is very, very high compared to atmospheric pressure.

KLS
12-16-2003, 09:26 PM
There are only two advantages of true dual exhaust...smaller diameter mufflers for more ground clearance and that great V8 sound.

Assuming correct sizing (probably 2" for duals on our small V8) duals with an H-pipe crossover will produce more power that individual duals. An X-pipe crossover will produce even more power, about the same as a properly sized single.
http://www.drgas.com/art-syncronicity.asp


Ken

RockyMtnRay
12-16-2003, 09:57 PM
There are only two advantages of true dual exhaust...smaller diameter mufflers for more ground clearance and that great V8 sound.

Assuming correct sizing (probably 2" for duals on our small V8) duals with an H-pipe crossover will produce more power that individual duals. An X-pipe crossover will produce even more power, about the same as a properly sized single.
http://www.drgas.com/art-syncronicity.asp


Ken

Ahh...excellent source there Ken...kinda "Exhaust Theory 102" :)

But sorta doubt the X-pipe crossover is going to ever be real popular with the sound-is-more-important-than-performance crowd given this comment in the link "The deep growl common to V-8s is replaced by a smoother, higher-pitched sound, almost like a high-RPM Japanese motorcycle engine or the shriek of an Indy car".

And then there's the issue of what works best for racing optimizations (usually high RPM operations) isn't always...or perhaps not even often...what's best for maximizing the low to mid-range RPM torque peak for towing. Towing (especially mountain towing with long (5 to 10 mile) demands) is a special case that not many worry about. I've researched the RV.NET forums (particularly the the "Tow Vehicle" forum) very carefully for any mentions of mufflers or exhausts or catback systems and the only regular positive mention/recommendation is for Gibson mufflers/single sideswept catback systems. Also found a fair number of negative mentions about Flowmasters, almost nothing about the other systems commonly mentioned here (Borla, Bassani, etc.)...and that says something to me.

v8Toilet
12-17-2003, 03:47 AM
I agree with what RockyMtnRay said. I have found though that the stock exhaust pipe diameter is actually about 2-3/8" in diameter and not 2-1/4" diameter. Just wanted to let you guys know if you are going to order a muffler to get the 2.5" inlet outlet muffler and use 2-3/8" exhaust pipe not 2-1/2" pipe. I say that because in the case with Spintech you can't get a 2-3/8" inlet outlet muffler. You have to get either 2-1/4" or 2-1/2".

RockyMtnRay
12-17-2003, 09:02 AM
I agree with what RockyMtnRay said. I have found though that the stock exhaust pipe diameter is actually about 2-3/8" in diameter and not 2-1/4" diameter. Just wanted to let you guys know if you are going to order a muffler to get the 2.5" inlet outlet muffler and use 2-3/8" exhaust pipe not 2-1/2" pipe. I say that because in the case with Spintech you can't get a 2-3/8" inlet outlet muffler. You have to get either 2-1/4" or 2-1/2".

Appreciate the agreement...especially since your numerous and solid posts on the topic were the basis for a good part of my conclusions. :)

But I am a bit confused that you're now recommending a 2.5 inch inlet/outlet muffler with the stock pipe. In many previous posts on the topic...
such as this one (http://www.tundrasolutions.com/forums/showthread.php?t=14797)...you've been pretty explicit about recommending the Spintech 3222XL muffler which is 2.25 inch inlet/outlet. You've also commented that 2.5 inch piping (as in the JBA Evol system you tried) slightly reduced torque in the lower RPM ranges. Soooo, any particular reason why you're now recommending the slightly larger muffler/pipe? :confused: It seems to me that a 2.25 inch muffler with the stock pipe would be better for towing where torque between 2500 and 3500 RPM is most important.

v8Toilet
12-17-2003, 02:46 PM
Appreciate the agreement...especially since your numerous and solid posts on the topic were the basis for a good part of my conclusions. :)

But I am a bit confused that you're now recommending a 2.5 inch inlet/outlet muffler with the stock pipe. In many previous posts on the topic...
such as this one (http://www.tundrasolutions.com/forums/showthread.php?t=14797)...you've been pretty explicit about recommending the Spintech 3222XL muffler which is 2.25 inch inlet/outlet. You've also commented that 2.5 inch piping (as in the JBA Evol system you tried) slightly reduced torque in the lower RPM ranges. Soooo, any particular reason why you're now recommending the slightly larger muffler/pipe? :confused: It seems to me that a 2.25 inch muffler with the stock pipe would be better for towing where torque between 2500 and 3500 RPM is most important.

Im only changing my recommendation on the muffler inlet outlet size not the exhaust pipe diameter for the rest of the system. The stock exhaust pipe diameter is a bit larger than 2-1/4 and its actually more like 2-3/8 in diameter. Im recommending that anyone who installs a muffler get a 2-1/2 inlet outlet muffler and reuse the stock 2-3/8 exhaust pipe. If you get the 2-1/4 muffler youll just have a short section of pipe that has a slightly smaller inside diameter than the stock pipe. Its not a big issue because were only talking about a few inches of pipe. I did my testing with a 2-1/2 inlet outlet Spintech muffler welded to the stock 2-3/8 exhaust pipe.

I still do not recommend 2-1/2 diameter exhaust pipe based on my own experiences. Sorry for the confusion! I used to think that the stock pipe was 2-1/4 because I used a tape measure to measure it but later on I used a venire caliper and got 2-3/8 OD diameter.

RockyMtnRay
12-17-2003, 09:29 PM
Im only changing my recommendation on the muffler inlet outlet size not the exhaust pipe diameter for the rest of the system. The stock exhaust pipe diameter is a bit larger than 2-1/4 and its actually more like 2-3/8 in diameter. Im recommending that anyone who installs a muffler get a 2-1/2 inlet outlet muffler and reuse the stock 2-3/8 exhaust pipe. If you get the 2-1/4 muffler youll just have a short section of pipe that has a slightly smaller inside diameter than the stock pipe. Its not a big issue because were only talking about a few inches of pipe. I did my testing with a 2-1/2 inlet outlet Spintech muffler welded to the stock 2-3/8 exhaust pipe.

I still do not recommend 2-1/2 diameter exhaust pipe based on my own experiences. Sorry for the confusion! I used to think that the stock pipe was 2-1/4 because I used a tape measure to measure it but later on I used a venire caliper and got 2-3/8 OD diameter.

Ok, that clears that up...thanks muchly for taking the time to explain the apparent contradiction. The bottom line is still the same one you and I have been preaching: for more mid range torque change to a known free flowing muffler (apparently just Spintech (for those who like more sound) or Gibson (for those who like quieter performance mufflers)) and don't even think about mucking with the rest of the exhaust tubing behind the headers/manifold.

v8Toilet
12-18-2003, 07:18 AM
Ok, that clears that up...thanks muchly for taking the time to explain the apparent contradiction. The bottom line is still the same one you and I have been preaching: for more mid range torque change to a known free flowing muffler (apparently just Spintech (for those who like more sound) or Gibson (for those who like quieter performance mufflers)) and don't even think about mucking with the rest of the exhaust tubing behind the headers/manifold.

Yes the bottom line is don't change the overall pipe diameter from stock!!! :tu:

Tundratow
12-19-2003, 07:00 AM
Thanks for the scientific replies.You guys really made sense out of a very confusing issue. I even passed this info onto freinds that tow also, and they were shocked at the real facts. Thanks as always.

treystoys
12-19-2003, 09:42 PM
Guys I wanted to add this one choice in there for those of you looking for an alternative to the mufflers above. I went with a Magnaflow...I've been using these on my trucks (2 Tacomas) and cars for a few years now, and have always been happy with the results, and their quality. I talked briefly with V8toilet about system suggestions and decided for my own reasons, and because of his suggestions just to add the muffler. It cost me a total of $105 to have the muffler installed at my local shop. The results are a nice low key growl, nothing loud, but if you stand on it, its vocal enough. I went with the 14" magnaflow, but there is an available 18" which I was told by the owner/friend of the shop that it would be no louder than stock. The Magnaflows are straight through designs, and come with a limited lifetime warenty. Makes me think the one I have is a good inbetween for the gibson and spintech, sound wise. Performance wise, I can't say I noticed much change either way, good thing, cause low end lose I'd have probably picked up on, and the typical gains you'd see from a simple mod like this you'd likely never notice unless your dynoed before and after or did a few track runs both before and after the change. All in all, I'm very pleased, and thankfull I asked a few quiestions before I dished out the money.

Just thought I'd throw that out there for another choice especially those who may not have ever heard of these mufflers, if you go looking for a shop, and they carry these, you'll have a little background on them now ;o)

later guys

Tundradad
12-20-2003, 08:59 AM
Guys I wanted to add this one choice in there for those of you looking for an alternative to the mufflers above. I went with a Magnaflow...I've been using these on my trucks (2 Tacomas) and cars for a few years now, and have always been happy with the results, and their quality. I talked briefly with V8toilet about system suggestions and decided for my own reasons, and because of his suggestions just to add the muffler. It cost me a total of $105 to have the muffler installed at my local shop. The results are a nice low key growl, nothing loud, but if you stand on it, its vocal enough. I went with the 14" magnaflow, but there is an available 18" which I was told by the owner/friend of the shop that it would be no louder than stock. The Magnaflows are straight through designs, and come with a limited lifetime warenty. Makes me think the one I have is a good inbetween for the gibson and spintech, sound wise. Performance wise, I can't say I noticed much change either way, good thing, cause low end lose I'd have probably picked up on, and the typical gains you'd see from a simple mod like this you'd likely never notice unless your dynoed before and after or did a few track runs both before and after the change. All in all, I'm very pleased, and thankfull I asked a few quiestions before I dished out the money.

Just thought I'd throw that out there for another choice especially those who may not have ever heard of these mufflers, if you go looking for a shop, and they carry these, you'll have a little background on them now ;o)

later guys


Also have Magnaflow system after doing much research, best quality , warrenty, engineering, sound, & best muffler for the $$. been on a long time & still like it's performance & sound. Sounds like a Trundra should , inmho..

davidk
12-22-2003, 08:53 AM
Isn't there an Ivan Stewart model Tundra that comes with the TRD cat back dual exhaust? If the TRD dual exhaust reduces torque specs wouldn't Toyota have to publish reduced specs for the Ivan Stewart model? Maybe the computer is programmed different?

What do you think?

so40
12-22-2003, 09:14 AM
Isn't there an Ivan Stewart model Tundra that comes with the TRD cat back dual exhaust? If the TRD dual exhaust reduces torque specs wouldn't Toyota have to publish reduced specs for the Ivan Stewart model? Maybe the computer is programmed different?

What do you think?

Possible, but I doubt it. They usually post the torque figures as the highest torque reading for that motor at whatever RPM it occurs. Most likely the high figure is the same (or very close) regardless of single or dual exhaust. They are not going to post different torque readings for different RPM ranges. I might be wrong though.

Mike

dupont24
12-22-2003, 08:16 PM
Guys come on, it doesn't reduce anything, it just changes where the tourque is made. Any gains will probably be to high in the RPM range for the average person to notice.

Verndog
12-22-2003, 11:02 PM
OK...now that this thread has taken on so much interest time for the other side. I stuck with 2 1/4 pipe, removed the factory y pipe, added H crossover into DUAL flowmster 70s, and ran out the back. I experianced no loss of torque noticeable (and I tow a boat), and I also GAINED power from 2800 RPM and up. That is usable power for towing and where I needed it. Plus I am getting about 1 MPG improved mileage with dual and TRD filter. I would not go back to single, and people know I have a V8 without having to prove it.

I love true dual, recomend it and would do it again.

True dual with H crossover (http://www.tundrasolutions.com/photopost/data/560/17849Exhaust-H.jpg)

Kevin

Monkeytown
12-23-2003, 05:20 PM
What would happen if you put a vacuum like device on the tail pipe? Would it help pull the exhaust gas out better and make more power? It of course would have to make more power than it used to run itself. But in theroy, would that work?

Actually you could think of a Turbo charger as working exactly like that.

Brian's Toy
12-26-2003, 06:21 AM
Great info. guys, it all makes very good sense. I hope I'm not deviating from the topic too much by asking this:

The conclusions for the duel exhaust / larger diam. piping with a stock exhaust manifold is a low to mid range RPM torque loss with a possibly slightly higher HP output @ high RPM's. Now if headers (TRD or other type) were added; would this conclusion still hold?

I wish TRD or some other source would test and report the outcome of headers / stock exhaust vs. headers / duel or larger diam. single exhaust, and various combinations with charts. Would'nt that make our personal preferances for an appropriate exhaust so much easier.

I personally have stock exhaust manifold and the TRD duel outlet exhaust. I love the look and sound but agree I've probably lost torque as a result. If I had the time and patience, it would be interesting if I reinstalled the original exhaust and did a seat of the pants comparison, I could be surprised!

Brian

H2O_MAN
12-26-2003, 06:54 AM
It been my real world experience that these small cube engines (3.4L and 4.7L) make the best, broad range,
useable power with a single small (stock) diameter exhaust pipe with or without headers.

v8Toilet
12-26-2003, 02:08 PM
It been my real world experience that these small cube engines (3.4L and 4.7L) make the best, broad range,
useable power with a single small (stock) diameter exhaust pipe with or without headers.

My experience too!

so40
12-26-2003, 07:21 PM
It been my real world experience that these small cube engines (3.4L and 4.7L) make the best, broad range,
useable power with a single small (stock) diameter exhaust pipe with or without headers.

Have you ever had a single in dual out on either of the two engines you listed above?

H2O_MAN
12-26-2003, 08:39 PM
Have you ever had a single in dual out on either of the two engines you listed above?
Nope. That would collectively give you a larger diameter tail pipe and reduce power to the rear wheels.

Toasted Coastie
02-26-2005, 09:23 AM
True dual with H crossover (http://www.tundrasolutions.com/photopost/data/560/17849Exhaust-H.jpg)

Kevin
Kevin, is that 2 mufflers welded together? Did you remove the cats?

Alin10123
02-27-2005, 01:59 AM
What about just putting in a freeflow muffler? For example, if i wanted the look of dual exhaust. Could i just use the factory size tubing and then move the outlet straight back instead of out the side? and then change to a magnaflow muffler, and then just have a "dummy pipe" on the left side? Would i loose hp or torque anywhere?

thanks

Salty_Dog
07-09-2007, 06:58 AM
I'm resurrecting this thread because I have a few questions on the subject. I too have noticed some loss of low-end torque ever since I installed my Borla duals.

If I understand the gist of this discussion correctly, the bottom line is that bigger pipes mean that exhaust gasses cool down faster which means the engine has to work harder to push them out.

If that is the case, then it would it make sense to decrease the diameter of the pipes just before the exhaust is vented to the atmosphere? In other words, would a "restrictor plate" in the pipes force the exhaust gas to stay hotter until just before they are vented therby bringing the torque back?

tuesdayd
07-10-2007, 10:32 AM
I'm resurrecting this thread because I have a few questions on the subject. I too have noticed some loss of low-end torque ever since I installed my Borla duals.

If I understand the gist of this discussion correctly, the bottom line is that bigger pipes mean that exhaust gasses cool down faster which means the engine has to work harder to push them out.

If that is the case, then it would it make sense to decrease the diameter of the pipes just before the exhaust is vented to the atmosphere? In other words, would a "restrictor plate" in the pipes force the exhaust gas to stay hotter until just before they are vented therby bringing the torque back?


That's pretty much it, Billy. If you go to dual exhaust you need to keep the pipe size smaller so the overall volume remains about the same.

Just to keep it simple let's say the stock exhaust pipe is 2 & 3/8 inches in diameter (I think), and five feet long (no idea, but it'll work for now) so the volume would be...

pi * radius squared * height

or

3.1415 * 1.188 squared * 60 inches = 266 cubic inches

That's how much space the exhaust gases have. In a nutshell, increase the space, and they'll flow more slowly at a given RPM. It's at the low RPM's where you want the scavanging provided by the smaller pipe, but at higher RPM's, when there are more gasses flowing, a bigger pipe might be better. It really depends on what you want out of your truck.

But even if you go down to two inch pipe you still increase the volume...

3.1415 * 1 squared * 60 = 188 cubic inches - for one half of the dual. Double it for the other side, and it's about 377 cubic inches. Even though the pipe was downsized there's still a lot more volume for the same amount of exhaust than the single stock 266.

Jump way down to 1.75 inch pipe, and you get pretty close to the same volume as the stock single exhaust - only 22 cubic inches more.

RMassaro
07-30-2007, 11:44 AM
I'm a novice...I had the dealer install the TRD dual exhaust. What, if any, improvement has happened?

Thanks

Demo8BX68
07-30-2007, 12:51 PM
I will be using a magnaflow muffler 2 in 2 out with the x center to help with scavenging, and 2.25" pipe, and comments on power loss or increase?

ericb
07-30-2007, 12:56 PM
I'm a novice...I had the dealer install the TRD dual exhaust. What, if any, improvement has happened?

Thanks
Probably nothing or a loss of low-end torque, plus a severe flattening of the wallet. If you read this thread from the beginning, the consensus is that, aside from headers and/or replacing JUST the muffler, there isn't much you can do to improve on the stock exhaust. The same is true of the stock intake. Toyota picked most of the low hanging fruit when they engineered the Tundra. An under-drive pulley is probably the most bang for buck performance improvement.

Jetes03tundra
08-02-2007, 08:17 PM
OK, i just switched out my magnaflow (too quiet), and upgraded to single in - dual out Flowmaster 40 series that exit straight back with 2.5" piping from the resonator back (resonator was removed). I love it and sounds 2x better than the magnaflow! However i will say i didn't lose any low end power and to me it seems to be alot more responsive and I always wondered about everyone saying you will lose torque and power with duals, but i dont feel it and i didnt think i would anyway! go with flowmaster!

ericb
08-03-2007, 12:04 PM
Your Flowmaster is single-in, dual-out which is essentially a single exhaust system as opposed to true dual, so it should pretty much act like a single. You also have stock pipe to the muffler which is another good thing.

Jetes03tundra
08-03-2007, 09:00 PM
Your Flowmaster is single-in, dual-out which is essentially a single exhaust system as opposed to true dual, so it should pretty much act like a single. You also have stock pipe to the muffler which is another good thing.

no mine is 2.5" from the cat to the muffler too!

pug407
08-07-2007, 02:21 PM
I have a V6 Tacoma 3.4L and just ordered gibson headers, they advertise low to mid power and torque gain. I know most (if not all) like JBA but I will give Gibson a chance, I read an article that Ford F150 got 13 rear wheel horse power and 21 lbs-ft of torque between 3,000 and 3,800 rpms with Gibson headers and exhaust. Maybe you think it's too little power, remember that many advertise gains of 20 horsepower but in the flywheel (you loose a lot with the transmission) and the power is usually high in the rpm.

If the header goes well I'll add Gibson exhaust....

05DC
08-13-2007, 02:24 PM
Well, I've just about got enought money saved for TRD cat back (dual exit). Someone please tell me that I WILL NOT notice any kind of power loss once this is installed. I've been wanting this TRD cat back for quite some time and would be very dissappointed to know that it would be a performance down grade if installed. If you have a 4.7L with TRD cat back, please reply with your opinions. The heaviest thing I tow is a small trailer with a four wheeler.

Mr. Creosote
08-13-2007, 06:54 PM
There was no change in quarter mile times going from stock to that exact system.