az_eaglescout_pilot

iTrader: (1)

Will running for about a week with no muffler be detrimental to the engine? 2" piping to a cat and another 2 feet of pipe after the cat, I figure it still has good enough back pressure not to mess up any valves or.rings but what are your opinions? And if you must know the old one fell off today hahaha with a little help from my foot hut it was 80% if the way off...

ToyoTech559

you can run no muffler on anything. muffler is mainly to muffle the sound. back pressure is actually bad and not what you need or want.

Stevesk88

"back pressure is actually bad and not what you need or want."

OOOOOOhhhhh boy here we go again. .

It goes both ways dude. Most engines need at least a little back pressure. If i didn't know this, my honkey butt would be running around town open headers for optimum performance. . .

Stevesk88

Op....you'll be fine for awhile. Just makes more noise and you might get dirty looks. But over a short course of time you'll be just fine.

az_eaglescout_pilot

iTrader: (1)

That's what I figured. Just have to wait until I get paid. Now the tough decision of choosing which muffler I want...

ToyoTech559

you want exhaust velocity not backpressure as this really is bad.

http://en.wikipedia.org/wiki/Back_pressure

Back pressure caused by the http://en.wikipedia.org/wiki/Exhaust_system (consisting of the http://en.wikipedia.org/wiki/Exhaust_manifold, http://en.wikipedia.org/wiki/Catalytic_converter, http://en.wikipedia.org/wiki/Muffler and connecting http://en.wikipedia.org/wiki/Pipe_%28fluid_conveyance%29) of an automotive http://en.wikipedia.org/wiki/Four-stroke_engine has a negative effect on http://en.wikipedia.org/wiki/Engine_efficiency resulting in a decrease of http://en.wikipedia.org/wiki/Power_%28physics%29 output that must be compensated by increasing http://en.wikipedia.org/wiki/Fuel_economy_in_automobiles.

Because it is really resistance, the term back pressure is misleading as the pressure remains and causes flow in the same direction, but the flow is reduced due to resistance. For example, an automotive exhaust http://en.wikipedia.org/wiki/Muffler with a particularly high number of twists, bends, turns and right angles could be described as having particularly high back pressure.http://en.wikipedia.org/wiki/Back_pressure#cite_note-1

wyoming9

iTrader: (1)

No wonder those top fuel dragsters have such slow times running just tuned headers.

Better to be running a full exhaust system NOT!!

RSR

On backpressure: http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

Yotatech exhaust clips: http://www.pnw4runners.com/exhaust/exhaust.htm

Big 3 options are Flowmaster, Magnaflow, and Borla.

Flowmaster:


Magnaflow:


Borla:


The gains from flowmaster are very, very marginal (less than 1hp usually) relative to the magnaflow. Most prefer the magnaflow sound to the flowmaster on the 22re... Borla are arguably the best, but I don't know that you get much more than with the costing less than half Magnaflow.

lobukbuild

as with any exhaust system it must be tuned to your motor and purpose or visa versa motor and purpose must be tuned for the exhaust. back presssure increases low end , less back pressure helps top end. it is a complete package designed to work together. toyotas and top fuel dragsters dont have the same purpose and any comparison of two would be ridiculous. put zoomies on a stock toyota and drive down the highway at 75 allday and see how long the motor holds up. as for driving without a muffler for a few days wouldnt do any harm as long as common sense is used, but ill bet your gas mileage and power will be less.

RSR

Not exactly right. The issue at hand isn't backpressure as ToyoTech559 previously mentioned. The issue is one of exhaust gas speed and keeping that speed consistent throughout the exhaust.
The two main variables are:
1) The RPM of the engine and volume of exhaust produced at given RPMs -- higher RPMs are dumping both more exhaust volume-wise (air and fuel in cylinders increase in line with increased RPMs) and also due to the exhaust being dumped into the exhaust manifolds at a greater rate...
2) That exhaust is expanded most at the highest temps -- those being immediately upon leaving the engine at the exhaust header and again within and leaving the cat (cat's combust excess fuel causing heat, though often not as hot as at headers). Moving past these hot points, the exhaust gas cools rapidly -- metal exhaust is cooled by air (provided entire exhaust isn't ceramic coated, if so that coating slows exhaust cooling -- which is a good thing is some respects as same diameter pipe used throughout doesn't rob power). That's why most modern cars have larger diameter piping through cat and then smaller diameter piping from cat back -- hot exhaust needs more space, cooler exhaust contracts, and reducing pipe size allows that cooler exhaust to move through at the same speed as when it entered the exhaust manifold. And also why mandrel bends are important -- either you have restrictions at each bend, or you oversize your pipe and produce slow moving spots between the crush bends w/ crush bends flowing at ideal rate...

When talking about tuning, one basically needs to figure out at what engine RPMs one wants optimized performance. If lower RPMs, all things being equal, that means a smaller diameter exhaust is needed for optimal performance. If higher RPMs, that means a larger diameter exhaust is needed...

This does an excellent job on exhaust theory at a high level: http://www.gomog.com/allmorgan/exhaustbackpressure.html

This does a pretty good job of describing the math behind exhaust sizes:
http://www.exhaustvideos.com/faq/how...pipe-diameter/

This is detailed and has all the specs for diesels, but formulas and approximate temps for all: http://www.asia.donaldson.com/en/exh...ry/1053747.pdf

This calculator is great if you know your valve lift and all those type of details:
http://dairally.net/daihard/chas/Mis...s/DaiPipes.htm

lobukbuild

i agree. but thats saying pretty much what i said on a very advanced level. exhaust should be sized fitted and tuned per output of the engine its attached to as well as its intended purpose. cutting off an exhaust at the cat would not always increase performance on todays engines and could actualy have a negative effect unless said engine is modified and or tuned for it. damage isnt always going to happen but is possible in extreme cases. basically its a package and all parts must work together efficiently. i think the op of this post was just looking to find out if he would damage his motor by running w/out an exhaust until he could get it fixed. id say he is fine in doing so but i wouldnt over abuse the motor. was trying to keep it simple ,

az_eaglescout_pilot

iTrader: (1)

nice lots to read here, found a guy at work who has a flowmaster laying around he said i could have for free!! i just need to drive through one parking garage before i put it on hahahaha it is a 2.5" inlet/outlet but i was planning on going to 2.25 or 2.5 when i have the whole system redone anyways. i did make an observation after driving on the freeway this weekend, before the muffler was "un-installed" i could run at 75 mph at 2800 rpm, this time however i had to run 3200 rpm to keep 75 going down the same section of highway also by the seat of my pants i can tell there is less torque in the low end so from what i briefly read in some of the posted articles it is seeming to me that a muffler does have a positive effect on performance if it is sized correctly.

thanks for a ll the replies, hopefully some more people will find this thread useful as well.

I'm going to miss the horrible exhaust note I have come to love/hate, sure is entertaining to spook people sitting at lights!

RSR

Cutting off your cat is illegal (violation of federal EPA laws), but unless you have an 02 sensor after your cat (the California version of our trucks only do), you won't cause any harm/have any issues running w/o it.

Chip N Sawbones

Are you sure about this? The engine is always going to produce the same speed for a given RPM, unless you've driving in a lower gear or you've adjusted the tire size or gear ratios. Taking the muffler off won't affect any of that.