No muffler

[wsimpson86]

Is it bad on the motor to drive it without a muffler, i was told i could blow my motor doing it.

[vrg3]

It's fine for the motor.

[Psychoreo]

exactly, It won't do anything to the motor... it'll just be loud and annoying... hmmm maybe i should remove mine..

[wsimpson86]

It actually doesn't sound that bad, i kind of like it. Im gonna put a glasspack on it to hear what it sounds like.

[drewdogg]

On a stock engine, no muffler means practically no back pressure which in the not too distant future will be real bad for the engine.

Remember the crap ass honda's from like 4 years ago where all they did was put a HUGE muffler on the stock exhaust and an intake and they thought they were the sh** cuz it was rattly and loud as hell? Well, notice how little of them are on the road these days? All their engines are dying and they dont know why. Most people now a days with those mufflers are puttin them on their honda-replacement cars still thinkin they're the sh**.

[greg donovan]

i ran w/2 glass packs and 2.25" piping from the cat back. i loved how it sounded on my N/A legacy. i think it had a little better throttle response but not too much.

[BAC5.2]

On a stock engine, no muffler means practically no back pressure which in the not too distant future will be real bad for the engine.

Remember the crap ass honda's from like 4 years ago where all they did was put a HUGE muffler on the stock exhaust and an intake and they thought they were the sh** cuz it was rattly and loud as hell? Well, notice how little of them are on the road these days? All their engines are dying and they dont know why. Most people now a days with those mufflers are puttin them on their honda-replacement cars still thinkin they're the sh**.

I think your wrong. The headers do the scavenging work, and the pipes just move it along.

Backpressure is the enemy of an exhaust system.

I'm running a VERY free flowing exhaust, and have been for more than 15,000 miles, and I STILL make more power than most stage2 WRX's. And I still see a TON of hondas with shitty exhausts.

[drewdogg]

I'm running a VERY free flowing exhaust, and have been for more than 15,000 miles, and I STILL make more power than most stage2 WRX's. And I still see a TON of hondas with shitty exhausts.

you have a turbo? then there's all your back pressure right there, and there you'd be right, it just directs what's left to the back of the car.

[jamal]

Care to explain the mechanics behind the whole "civics with huge mufflers break down because of the huge muffler" theory?

From what I hear, backpressure is bad in any case. Velocity is good, though. Too large of an exhaust, and the gasses aren't moving quickly enough.


hey guys, I have an exhaust leak. Think I should just take it off past the cat? Maybe a side dump. Heh heh. Actually I'll probably see what the exhaust shop down the street wants for a custom exhaust and some cheap flowmaster-like muffler. I had some rattling heat shields tack welded, and noticed they had plenty of SS tubing and a mandrel bender. I bet it'd be super cheap if I paid cash (or claimed to be with the INS.)

[drewdogg]

If you have a stock engine, especially if it has alot of miles, nothing rebuild, low tolerances and all that and you have no back pressure there's nothing to keep it from reving much higher than it was built for. This will then allow for parts to wear heavily and will start to come apart and now compression is changing, seals are leaking (oil, piston rings, etc), bearings are wearing heavier. This might sound kinda dumb, but you could compare it to parachuting. Imagine a stock engine is you, a person. You're falling pretty fast, it's fun and exiting, but you still need a parachute to hit the ground farely sharply but safe. You take off the exhaust, and it's like taking away the parachute. You're falling fast still, and it's fun as hell, but you're getting faster and faster as you fall, and when you hit the ground...... i dont know, i tried to come up with something there

If you compare to racing engines, which have practically no exhaust 'system' or even barely any headers sometimes, they're build with very high tolerances in the engine components, high quality internals, forged everything. This will reduce or have very little wear which will lead to practically no changes in engine performance in the long run which leads to consistent engine performance. Yes, alot of drag racing engines are rebuild after one run, but thats because the performance needs are much higher than the ability of the materials. Some drag strip cars are pushing close to 7000hp yes on ethanol and all that but still out performs what cost and materials allow, and they are looking to reproduce that kind of power again and again.

[BAC5.2]

So are you trying to tell us that the rev limit is soley dependant on exhaust backpressure?

I think your on crack cocaine.

Backpressure is the enemy. Period. Exhaust velocity is good, and exhaust size is decided on what gives the best velocity, without increasing backpressure or decreasing velocity.

Imagine this scenario. Go get a stirring straw and a McDonalds straw (larger ID), and a Slurpee straw (largest ID). Now, while this is highly unscientific, it will prove my point.

Blow in the stirring straw. It's difficult to acheive a whole lot of volume and flow, right? You gotta turn red in the face to get a reasonable amount of air flowing at a reasonable velocity.

Now get the McDonalds straw. Blow with the same effort into the straw. Notice how easily air flows through the straw. Given the same effort, you can move MUCH more air, MUCH faster. You've increased your own efficiency.

Now take the Slurpee straw. Again, use the same effort. You'll notice that the air is coming out slower than it was with the McDonalds straw. The pipe is simply to large to help the "exhaust" gas escape quickly. Air is going from a small chamber to a far-to-large chamber and is slowing down as it's attempting to fill the volume of the straw.

This is all very similar to exhaust setups. Granted, I'm no fluids engineer, and I have very limited knowledge of fluid dynamics, but I feel like I've got a slight grasp on the general idea behind exhaust systems. To large an exhaust, and you lose exhaust velocity. To small, and you increase backpressure (your cheeks puffing up, unable to move the air out of your mouth). Just right, and you can easily move all the air you need to, at as high rate of speed as possible.

Think about this for a minute. With backpressure, you are, effectively, attempting to KEEP exhaust in the cylinder. Now, why wouldn't you want all exhaust gases to exit the cylinder? Spent air stuck in the cylinder isn't going to be very performance, or gas, friendly. But move it quickly and efficiently out of the cylinder, and you aid the intake of fresh air into the cylinder. The more air that leaves on the exhaust stroke, the better. The easier it can leave, the less "compression braking" effect the backpressure has on the piston.

Turbo's do provide backpressure, which is why, generally speaking, turbo camshafts have very little overlap. Naturally aspirated camshafts increase overlap to help with drawing out the exhaust. Headers also play a BIG role in exhaust scavenging (essentially sucking air out of the cylinder), as does port design and overall combustion chamber design. There are people on this board that know more about this stuff than I do (Matt Monson, Professor, Evoloutionmovement, and VRG3 to name just a few).

And to clear up my comment at the beginning of this post, redline is not dictated on whether or not you have a muffler. It's controlled by a few things. One, and most commonly, is the ECU. The computer stops the engine from revving to prevent damage. Two, is physically limited. There is a point where the valves will float (and on an interference engine, kiss it goodbye), and there is a point where something will simply fail. None of these is really related to backpressure, or lack thereof.

[drewdogg]

I completely agree with everything you said, but what you said also adds to what im tryin to say perfectly.

Your engine from subaru was designed with certain parameters, and with those parameters the engine can only go so fast (rpm's/power/etc) like what i said before about tolerances. So based off of those parameters the engineers decide that if a consumer would try to over achieve the engine's capabilities, that they will limit it by designing into it a cut off at a certain speed/rpm so that the engine doesn't shake itself to pieces. Everything in the engine comes that size for a reason. Why doesnt it come from the factory with a 3" instead of the 2" or whatever stock? They know that with the normal 'Joe Shmoe' driver, it will run to 300,000 miles versus i dont know 100,000 with no exhaust.

Back to the straw... you're right that the Micky D's straw will blow much easier due to the fact that it is much shorter and has a larger diameter. But now do the same test without a straw. Sooner than later (which is really all i meant by starting this), you will get very dizzy and out of breath, much easier and sooner than with a McDonalds or Slurpy straw.

[Legacy777]

Guys.....are we talking about turbo engines or n/a engines????

That will make the difference whether you're arguing about nothing or not.

For turbo engines....I agree.....little to no back pressure is best. Any exhaust pulse scavenging is completely gone after it goes through the turbine in the turbo.

For n/a engines, it's trickier, you don't really want back pressure, but in order to reduce back pressure you increase exhaust pipe diameter, and therefore reduce velocity, which reduces/inhibits the effectiveness of exhaust pulses aiding in exhaust scavenging. So for n/a engines, I would say there is a "right" size exhaust, depending on the engine, and various modifications.

[drewdogg]

For n/a engines, it's trickier, you don't really want back pressure, but in order to reduce back pressure you increase exhaust pipe diameter, and therefore reduce velocity, which reduces/inhibits the effectiveness of exhaust pulses aiding in exhaust scavenging. So for n/a engines, I would say there is a "right" size exhaust, depending on the engine, and various modifications.

yea, that's kinda what i was trying to get across.

Not to make any new sort of argument here, but just to add... Sound waves/pulses like what legacy777 said play a big role in the velocity too. this is engineered HEAVILY in 2 cycle engine performance. The sound from the engine (exhausting combustion noice on opening valve and all that) travels down the exaust and the size of it determines how the sound travels and what of it returns to the engine. With the return of the sound wave, it pulls gases out from the cylinder increasing the exhaust velocity. Yes this is about 2 cycles (or 2 stoke which ever you like) but still has some play for 4 cycle car engines.

i guess all i can really say is someone do a test and take your exhaust off (NA here), and let me know how many mile you drove without exhaust until it died, lol.

[BAC5.2]

You completely changed your story. First, you say that mufflers dictate Redline. Then you say that I'm right, but think that everything is designed perfectly for optimum output from the factory. Now your saying that I was definately right that backpressure is the enemy. And you go from saying that no muffler will kill your engine, now your saying that it will kill your engine without ANY exhaust. Make up your mind, and you'll make a more convincing argument (that's just a tip for ya). Oh, and redlines aren't in place to prevent someone from trying to grip more power out of the car. More RPM's doesn't mean more power. Look at my dyno numbers, and anyone who wants to make more power at or beyond the factory redline, knows how to remove or raise the factory set rev limiter.

Exhaust pulses would be RPM dependant, and not really dependant on the actual tone of the exhaust. Raspy hondas aren't making lots of power, and it isn't due to the raspy noise. Exhaust pulses and pulse spacing comes from cam timing (duration of exhaust valve opening). Higher RPM, the exhaust valves are open the same duration of cam rotation, but shorter time, and the frequency of pulses get closer together. It doesn't have anything to do with the noise the exhaust valves make.

And the straw example was based on the straws all being the same length. I figured that would be implied, because that was the argument at hand. Go try it for yourself, get 3 different diameter straws, cut to the same length, and do it. Backpressure is bad. Period.

Why don't cars come with 3" pipes from the factory? I'll let you read consumer reports and do the math. I'll also let you call the EPA and your local law enforcement agency and figure it out. Here's a search tip: Ask what the maximum decibel level of your exhaust can be. Another tip: don't ask in Virginia (as any modified exhaust is illegal). The federal regulation is, I believe, still 95dB. Car manufacturers sell cars because they are quiet, comfortable, and safe. Do you think Grandma would want to drive to church in a straight piped EVO? Probably not. She want's her quiet caddy. Mom and dad want a 117dB Dodge Caravan to go on road trips? Again, unlikely. I've heard a 117dB exhaust, and it's ungodly. It's the same reason lots of cars are designed with so much understeer from the factory. And the same reason every stock car out there favors saftey over performance. Catering to the least common denominator. Marketing 101. Build what more people will buy.

To provide another example, look at Lemans cars. They will be driven harder in 24 hours than you will drive your car in 300,000 miles, and they manage to do alright.

Another factor to "free-flowing kills" is the driver. When you make the decision and pull the trigger to run a free-flowing exhaust, it's implied that you'll be running the car MUCH harder than you would when the car was stock. When you look for power, it's implied you'll use it. You don't build a 300whp car, to drive it to the grocery store. And if you DID build that car, and DID drive it to the store, it would likely last just as long as it would if it was stock.

[drewdogg]

Im not going to bother typing any else to try to discuss this you're just bein a pain in the *** not wanting to understand where im coming from.

and no before you even say anything, im not sayin this because i have no response, i have plenty just not worth my time typing.

[BAC5.2]

Whatever dude. I'm not TRYING to be a dick, I was trying to inform you. If you don't agree, that's fine and it's no skin off my balls. But don't go telling non-truths, then changing your story around. I'd rather help you understand, than have you simply agree or disagree. If you don't want to listen to me, that's cool. But I still want you to understand.

I apologize for coming off harsh.

[Psychoreo]

wow drew...they don't like engineers

[simbey1982]

yeah drewdogg.....your wrong....

[Binford]

The original post of NO MUFFLER being hard on an engine is bull. There is plenty of restriction in the rest of the exhuast to not do any damage. The only damage I've ever heard of happening from NO EXHUAST is burnt valves. This is on V8's, particularly Ford 302's. There is a huge difference between NO MUFFLER and NO EXHUAST.


And Drewdogg is not coming off as an engineer to me. Pretty vague arguments if you ask me.

[IronMonkeyL255]

Most all of what BAC has been saying rings true.

Having recently taken a class that included some fluid dynamics, I noticed his arguments seem firmly based in proven fact.

I'm honestly not sure if having no muffler would kill an engine any quicker than if it had one on.

I think the reason that these honda ricers are breaking their engines is because they like the sound at high revs, and thus wind it out too far too often.

[Project_Legacy]

basically they get their motors REALLY close to redline, or sometimes bounce off the revlimiter. thats how those honda's kill their engines. basically all their power is right there near redline. thats why. i know because i know a lot of people with hondas.

and no my friend's honda is not slow that shit is pretty fast as fuck for a stock motor. (motor swap)

[BAC5.2]

The rev-limiter is there to PREVENT you from damaging the engine. Our cars can sit at 6500 RPM all day if they wanted. It's engineered into them to be capable of doing this.

It's honda kids flat-shifting, and running around at 7000 RPM in 1st gear all night long. And they do so without doing any proper maintainence whatsoever.

[Project_Legacy]

yea but the longer you sit up higher in the rev range, like 6.5k, the more wear it puts on the motor than say, only revving at 3k. correct?

the honda kids i see around here are ALWAYS up in their redline and thats why they keep messin up their motors.

[vrg3]

Hold up... I think we're focusing too much on the exact words drewdogg actually said instead of what he was trying to say.

drewdogg - When you say "revving higher" and whatnot, it sounds like you mean exceeding stock output.

So your argument is that by exceeding stock output you're also exceeding the engineering parameters of the system?

Because that's absolutely correct. Almost all motor upgrades rely on the expectation that the engine is capable of a good deal more than what it delivers from the factory.

Most of what I've seen indicates that that expectation is valid, though. Have you seen evidence to the contrary?

Another thing to keep in mind -- most Hondas are speed density these days, right? A speed density engine management system will start to run lean when exhaust backpressure is reduced. That further pushes things out of spec because the leaner mixtures increase combustion temperatures. So, even if there is evidence of good exhausts killing Hondas, I'd still be wary of extending that to engines in general. Our cars don't lean out just because of improved flow.