Backpressure IS NOT the result of a free flowing design. Free flowing is the exact opposite of backpressure. With backpressure, the engine can not get rid of the spent fuel in time for the next power cycle, and as a result it stays in the cylinder and dillutes the incoming air/fuel charge. Less power. No torque to be made here, just lost power.

A system tuned for low end will always have more restriction than a system for max power, like you say, sure. But what is the application? Race car? Tractor? The restriction happens when the engine is revved beyond what the system is designed for. Tune for all the low end you want, but dont expect ANY gains beyond the RPM band you design the exhaust system for. Tune for max power (torque) at 2000 RPM, and no more power will be made above that because the exhaust system cant flow anything more than that. ANYTHING above max velocity is restricted flow.

"The engine will NOT have much low end torque."

Hell of a thing to say. Any V8 worth its weight will have torque regardless of what the exhaust system is hooked to it. Its displacement, cam profile, induction, tuning etc. An exhaust system WILL NOT kill all torque and make an engine a gutless wonder.

"It WILL be able to make use of the open headers at WOT, for making maximum horsepower. This is not the same thing as torque."

Horsepower is a byproduct of torque. They ARE the same thing

 

bob and steve, yall are confusing backpressure and velocity....backpressure is bad...always...the motor has to work harder to push the gases out, and you dont get as good of combustion because of exhaust gases that remain in the cylinder.

a smaller pipe gives the exhaust more velocity which helps to scavenge the gases.


im not going to try and explain details, because it would take up half of a page

 

a smaller pipe gives the exhaust more velocity which helps to scavenge the gases.


im not going to try and explain details, because it would take up half of a pagePLEASE try to explain yourself. It isn't possible to. Think about it. A smaller pipe works better then a larger pipe only for low end torque. If they helped for WOT horsepower, NASCAR and Top fuel dragsters would use them, instead of the biggest pipes they can fit on the car. A SMALLER PIPE NATURALLY HAS MORE BACK PRESSURE THEN A LARGER DIAMETER, if they are the same length. Try blowing through a straw, and then through the same length of 1/2" PVC pipe. The resistance of flow you feel in the straw is called back pressure.

Sorry, but everything I've said is true. I've been building cars, trucks and engines for over 30 years. I also have a close understanding of the relationships of horsepower vs. torque, and flow, velocity, backpressure and thermal dynamics. A good exhaust system has much to do with all of those terms. It's up to y'all to try to prove me wrong. Good luck. I always have all the links ready to prove everything I say. Here's the difference between horsepower and torque. I also never said that it is the backpressure which makes the torque. I said that the exhaust system tuned to make torque has more back pressure then ...........Right?
Read this quote from the following site.....So, you want a small exhaust tube diameter to keep velocity as high as possible without it being so small that the exhaust can't get through it. Kind of a pain since the optimum size at WOT is obvioulsy not the optimum size at idle. Of course, on a street car, you compromise.


http://www.4x4extremesports.com/exhaust.php

Horsepower = torque x rpm / 5252
This is a mathmatical equation, so How can they be the same thing?

http://www.revsearch.com/dynamometer/torque_vs_horsepower.html
http://vettenet.org/torquehp.html
http://www.allpar.com/eek/hp-vs-torque.html
http://www.off-road.com/hummer/tech/power.html
http://www.nightrider.com/biketech/exhaust.htm

Just for fun, we decided to uncork the headers to see if there really is a difference in power without the restriction of an exhaust system. We gained an eye-opening 9.2 hp by simply opening the headers. But check out the torque. We lost 2.5 lb-ft of torque. Why? Because the exhaust system helps the engine make torque via backpressure, which—given the right cam profile—increases cylinder pressure. Horsepower nearly always increases when we uncap the headers. Torque almost always decreases. Derek Real of Mike Morgan Motorsports tells Mustang Monthly that torque would improve with a 2½- or 3-inch diameter exhaust system.
http://www.mustangmonthly.com/howto/26824/

 

"A smaller pipe works better then a larger pipe only for low end torque. If they helped for WOT horsepower, NASCAR and Top fuel dragsters would use them, instead of the biggest pipes they can fit on the car"

wrong....if they used the biggest pipes they could fit in nascar, the exhaust would cool too quickly(which means it slows down) while in the pipe aand they would lose the scavenging effect which would create backpressure and slow the flow down. Top fuel doesnt matter...these are supercharged running on the verge of hydrolock from fuel.

"A SMALLER PIPE NATURALLY HAS MORE BACK PRESSURE THEN A LARGER DIAMETER"

yes, this is atrue to a point if the exact came cfm is used. if too big a pipe see above...
this is why pipe sizing for scavenging at the desired rpm range is important...not creating backpressure....backpressure eats horsepower and torque from idle to redline.


"I also have a close understanding of the relationships of horsepower vs. torque, and flow, velocity, backpressure and thermal dynamics. A good exhaust system has much to do with all of those terms. I I also never said that it is the backpressure which makes the torque. I said that the exhaust system tuned to make torque has more back pressure then ...........Right?"

i agree with most of what you saying,but it seems like you have contradicted yourself...in no situation is backpressure good...0 backpressure with the optimum velocity for the desired power range is what is desired

and yes, i know about horsepower and torque etc etc

"Just for fun, we decided to uncork the headers to see if there really is a difference in power without the restriction of an exhaust system. We gained an eye-opening 9.2 hp by simply opening the headers. But check out the torque. We lost 2.5 lb-ft of torque. Why? Because the exhaust system helps the engine make torque via backpressure"
we are along the same lines, but your view on the matter is still wrong if you are saying backpressure helps produce and amount of power or torque....they lost torque because they took the ability for the exhaust to scavenge at low rpms away.


and about the commonly used straw example, exhaust gasses are completly different, because you are dealing with heated(which is gradually cooling) gas coming out in pulses..not steady flow.





i thought the general concensus in this thread was people are saying that if you dont have backpressure you will lose torque. ...this is wrong

there are many more factors which determine this "loss of torque"

btw, i cant spell

 

not to flog a dead horse , but , in stock form , there is in fact a difference , between chevys and fords ,and the amount of restriction needed for torque, you did however , clean it up nicely with this answer , my 2c's, respectfully , bob

 

i think we are all saying the same thing only in different languages, respectfuly , bob

 

Um, yeah. I heard more backpressure was a good thing so I went to my local pick-a-part and bought up all of the 4 cylinder Nissan/Mazda/Vega catalytic converters I could find. I bought seven of them and made sure that none of them had a pipe size bigger than 1.5 inches. I installed them in series on my 521 stroker using a single pipe and the factory exhaust manifolds. I think my engine still doesn't have enough torque. I'm thinking of stuffing a potato in the end of my exhaust pipe. Will this give me more torque because of more backpressure? Thanks.

/BEING FACETIOUS!!!!!!


Cody

 

LoL cody good point man.Well thanks alot for the answers guys, I really appreciate both sides to this arguement. I do kind of think that I will probably cut the cats out, or possibly get a high flow cat, and hopefully the less restriction will not only make my ol 97 sound alot meaner, but improve the performance a tad, and hopefully the gas will burn more effeciently Again guys I really do appreciate all the knowledge.

 

yes...if you weld the end of the exhaus tpipe shut, that will give you over 50 ft lbs or torque...just from that mod right there

 

stevef100s, great article specially your attachments with formulas, figures vs BS, the figures are solid proof.
.....=o&o>.....

 

internet sources mean nothing to me, anyone can spout their opinion...for instance...this guy is quite lost..
http://web.tampabay.rr.com/redroby/3liter/exhaust.html

..but if you want sources..

http://www.miata.net/garage/KnowYourCar/S4_Back.html
http://www.warnertechnology.com/Cars/backpressure.shtml
http://www.uucmotorwerks.com/html_pr...torquemyth.htm
http://sandlizrd.baja.com/exhaust.htm

this is my fav-http://www.rbracing-rsr.com/exhausttech.htm

 

im totally impressed , bob

 

Sorry, but they DO use the biggest pipes they can fit on the car. Most of them are oval, and are either equal to a 3 1/2" pipe or a 4" pipe. There are two of these. They are actual round pipe that has been ovalized, and then joined at the top and bottom with flat metal. I've built a "few" sets of these myself, and tested them on a dyno. They do this in order to fit the pipes under the car. On tracks where more low end torque is needed, they swap to a smaller ovalized pipe. Some all the way down to 2 1/2" pipe.

http://www.drgas.com/store/home.php?cat=2

If you say so. Then why do people switch to smaller exhaust to gain more low end torque? This is not an old wives tale. It actually is done every single day, by people who have spent millions of dollars in R&D. A single 3" Gibson exhaust behind a stock small block Ford, produces higher torque at lower RPM's then if the same exact truck with a dual 2 1/4", or even a dual 2 1/2 or 3" free flowing exhaust. The dyno doesn't lie. Take the single 3" exhaust and install it on a light weight, higer revving car 5.0 engine. The single 3" produces less horsepower then a dual 2 1/4 or 2 1/2" system.

This quote came from one of Kubota's links........Then, just to make things complicated, these pressure waves develop in closed-looped-exhaust systems. When one cylinder fires, it sends a pressure wave down another cylinder's pipe and this affects the exhaust of that cylinder. At high revs this creates dead spots.

So, the bigger the pipe, the less back pressure and the better top end (within reason). The less restrictive the outlet, the less back pressure and your low-end power might drop off. The wrong loop in the pipe at the wrong RPM and you suffer power loss.

It probably would've been simpler to say, "you need some back pressure, or your motor won't run, and you can vary the back pressure for different performance.

And here's another from your source......When the exhaust leaves your motor, it absolutely positively needs some pipe to run through. A slight bit of back pressure is required to make your motor run. It's mysterious but true.

If there's too much back pressure, the cylinders don't scavenge enough, so the next intake doesn't get enough fuel and your power drops.

There's a lot of people talking stuff, but I'm the only person coming up with proof. I guess you people are just too smart for me. Must be I've wasted my education. I've got nothing else to say on the matter, except that I know where I've been, and what I've done. I've spent many hours in the dyno room. I 100% know what type and size of exhaust to go to which application, and what effect it will have. Can anybody else say that?
As my young co-workers say, peace out.

 

amen, i can say that...but probably not as many hours as you

 

Nope. The pipe size and design is optimized for the RPM they will be running at, and where they want max power. Its not like Jack Roush said "Hey, I have a great idea. Lets just stick the biggest pipe we can under this car. It should make MAD power then!!" If 8" pipe made more power, you can bet they will find a way to stuff it under there.


Sure it is.

MIGHT being the key word here. A big MIGHT. Since you have spent so many hours watching dyno runs, you should know that most peaks and valleys in the dyno plot can be fixed with proper tuning. This includes low end torque, which by your way of thinking will all but be MIA if someone wants a free flowing exhaust system.

Please. You can vary the design for max velocity for different torque peaks, but it isnt backpressure thats helping. I really like the part about my engine NEEDING backpressure or "it wont run". My truck runs just fine, thank you with dual 2.5" and Magnaflows and 3" after the mufflers for a deeper sound. By your posts, my little .060 over 292 should not have enough torque to get itself moving.

You said that, not anyone else. Im sure you know your stuff about a lot of things. Too bad you are taking it personally that some people disagree with you. However, your posts nor mine are the end all to this discussion. Like KubotaOrange said, internet sources mean nothing to me. There are some really uneducated people out there spouting information like they know it all. And like so many sheep, people will take it and preach it as gospel. Look at all the people who buy the Tornado and think it gave them 245.82234 horsepower.

As have I. However, I would NEVER claim to know everything about every exhaust design for every vehicle without knowing drivers habits, state of tune, etc before I would ever make a call on what needs to be done. But you say you have nothing left to say in the matter, so I wont expect a witty answer to anyting I have said.

and to bob arrington-