[AKbmw]

i just got them installed.. (quads..) and i LOVE the sound and looks...
but i dont know if its just me or is it possible that there is a decrease in power?

[AKbmw]

bump?

[D-Rock]

if there is no muffler and its a stright pipe. Then yes you will lose back presure, there for you will lose power. If not then i dont know what it could be.

hope that helps

[AKbmw]

theres a picture.. there called magnaflow RACE mufflers?

[Cadillac Johnson]

Originally Posted by D-Rock

if there is no muffler and its a stright pipe. Then yes you will lose back presure, there for you will lose power. If not then i dont know what it could be.

hope that helps

Uhh... what?

Sorry but that is absolutely incorrect.

Back pressure does absolutely nothing, except hinder power. The least amount of back pressure the better. The best exhaust is no exhaust.

[AKbmw]

Originally Posted by Cadillac Johnson

Uhh... what?

Sorry but that is absolutely incorrect.

Back pressure does absolutely nothing, except hinder power. The least amount of back pressure the better. The best exhaust is no exhaust.

so are you saying i didnt loose any power?

someone please help me!

[Cadillac Johnson]

No you didn't lose any power, by putting a straight through muffler on your car you created less restriction, which reduces back pressure, which increases power.

I posted this write up on exhaust sizing, and why some people think that back pressure is good, when in fact it is not.

VE= volumetric efficiency

A smartly designed normally aspirated exhaust has a mechanism to convert exhaust gas energy into negative pressure. This is a collector. If the collector and primary tubes are designed properly (and many are not), they will actually enable each exhaust gas pulse to gently 'suck' on the other primary tubes as it passes through the collector and on out into the exhaust pipe. The greater the 'suck' action, the greater the positive effect on VE and the reduction in pumping losses. This is known as scavenging. If the exhaust is enlarged enough to reduce exhaust gas velocity through the collector, the exhaust pulses do not have enough energy to make the collector work, and our power isn't there. This is often misinterpreted as not having enough 'backpressure', which is incorrect. Of course, if the exhaust is too small, this increases pressure in the system, which begins to cut into our power as well. Anything more than ~2 psi in a normally aspirated exhaust system is going to reduce power, so sizing normally aspirated systems is like designing/sizing a musical instrument to sound a specific musical note when we blow into it.

A turbo exhaust has no such mechanism to create something positive from exhaust energy. Once that exhaust pulse spins its way out of the turbine, it can do nothing but get in the way. If pressure is created on the backside of the turbine, it just reduces turbine efficiency and VE as well.

With a turbo car, a larger exhaust will make the most difference at peak power, where the engine is consuming the greatest rate of mass air flow. IF we find that a larger exhaust somehow reduced power, it's because it increased VE and leaned our fuel mixture enough to make a difference. If we re-tune, we will get our power back, plus some.

[AKbmw]

so basically i added power?
thanks alot for you help man.. even tough i barely understodd all that .. but when i first got the car back after not driving it for 2 days.. if felt like the push into your seat when you gun it from a roll wasnt as hard.. maybe its not broken in yet (the exhaust)..

[D-Rock]

Originally Posted by Cadillac Johnson

Uhh... what?

Sorry but that is absolutely incorrect.

Back pressure does absolutely nothing, except hinder power. The least amount of back pressure the better. The best exhaust is no exhaust.

No it is correct . In his case he should have not lot any power.

But if you have no muffler , you would lose back preasure there for or rmps for 1-3 or 4 whatever it maybe you will lose a little power.

In his case yes since he has a 335 but in a non turno car it is the other way around.

[D-Rock]

Originally Posted by AKbmw

so basically i added power?
thanks alot for you help man.. even tough i barely understodd all that .. but when i first got the car back after not driving it for 2 days.. if felt like the push into your seat when you gun it from a roll wasnt as hard.. maybe its not broken in yet (the exhaust)..

Yes you did add power. Maybe you feel it is slower just in your head or maybe cause of break in of the new pipes.

[Cadillac Johnson]

Yes you added power.

Think of it like this, exhaust pulses spin the turbine wheel, which spins the compressor wheel. The compressor wheel, compresses air and forces it into the motor. The exhaust after passing through the turbine housing is pushed through the exhaust. The less resistance (back pressure) the turbine wheel feels, the faster it is able to spin, creating more power. If there is resistance because the exhaust cannot expell the gases fast enough it builds up and pushes back on the turbine wheel. This slows the turbine wheel and therefore reduces power.

[AKbmw]

wow.. thanks alot man! maybe i should just drive it hard for a little to break it in or something and itll get better maybe by tomarow (just got it today) ill let you know if i feel anythign different!

[Cadillac Johnson]

Originally Posted by D-Rock

No it is correct . In his case he should have not lot any power.

But if you have no muffler , you would lose back preasure there for or rmps for 1-3 or 4 whatever it maybe you will lose a little power.

In his case yes since he has a 335 but in a non turno car it is the other way around.

*deleted*

the post below can explain it better than I can.

[Cadillac Johnson]

Here is a great article about back pressure on NA motors. Every forum I've ever joined there is always the "some back pressure is good" crowd. The address is below, I also pasted it as well. It is long, but it will give you a better understanding of why back pressure is not good, on any motor.

http://people.msoe.edu/~lannanm/TECH...andtorque.html

Hey yall. I've been asked this question on a number of occasions. Why does backpressure effect torque? Which is usually accompanied my the generalization that low backpressure reduces torque. Well, I figured an article was in order after the last time it was asked.

Your assumption of the effect of backpressure is the same as most peoples. That is, that having less backpressure decreases torque and increases horsepower. Likewise, having more backpressure increases torque and decreases horsepower.

I've heard this from countless people, and I always try to convince them otherwise, usually to no effect. So I'll try with you. Hopefully I can explain this well enough. The real crux of all this is at the bottom. But read the article carefully. There is a serious flaw in the logic of this assumption about torque. The rule is generalizing on a level that almost seems greedy.

As a general rule that assumption is correct for the lower revs of an engine. That is, if you took a standard engine, and had nothing more than a set of headers on it, you would find that the low-end torque is somewhat less than that of the same engine with some fairly restrictive mufflers. Likewise, the engine's torque, at bigger revs, would be higher than that of the same engine with mufflers. For conversation's sake, I'll consider low-end to be anywhere from 0-1,800rpm, mid-range to be about 1,800-3,000, and high-end to be 3,000rpm and greater.

I'm not sure where people have come up with the idea that there is a counter-productive variation in horsepower by opening up the exhaust system. I've never come across any studies that prove that horsepower is adversely effected by open exhaust. Not that that is what you claimed; but again. I've heard it from several people.

What it all comes down to is what range your looking at. If you want big horsepower and torque; it's going to have to be with an open exhaust. There is no way to really look at it other than that. The more air you can remove, the more air you can take in. More air means more power. And engine with opened exhaust will always make more peak horsepower and torque than a restricted engine. It will just be at a higher revs.

Exhaust modifications are done purely to alter the mass of air that can exit the engine (duh). Here's a story for you. A friend of mine put a new, uncorked, exhaust system on his truck. The engine is an otherwise stock, injected, small block. He put the exhaust on, and his fuel efficiency went way down, torque went down the drain, and his horsepower was basically non-existent. "But I don't get it. I was supposed to get 10hp out of that."

Why did that happen? Because the engine was outside of it's stochiometric ratio. What is that? That's the chemically "neutral" balance of air/fuel ratio. It has been shown that engines produce maximum horsepower at 14.7:1 (air/fuel) by mass. The problem is that when you alter the backpressure of the exhaust system, the ratio will also be altered. If you reduce backpressure, the engine is allowed to flow more air out. More air out means more air in. If the fuel system is not compensated for the increased air mass, the engine runs lean. If the backpressure is increased, the mass of air leaving is decreased. Less air out means less air in. Again, if the fuel system is not calibrated for the change, the engine will run rich.

As far as normal engines are concerned, alterations on the order of 1.3 parts of air to fuel would result in significant loss of performance. And yes, that's loss; no matter which way it goes. Contrary to popular beliefs, lean engines do not produce more horsepower and/or torque than neutral. So taking an engine, tuned for a specific amount of backpressure, and altering it, would result in the engine running outside of its stochiometric range. The engine would thereby run substantially lean, and be running quite poorly.

Now note that I said it was an injected small block. You might be thinking "well doesn't the ECM calibrate itself for the differing air mass?" Yes, it would. To an extent. Once you start getting somewhere in the range of about 1.5:1 outside of neutral, ECMs are typically unresponsive. As a general rule a code would be thrown and the ECM would just swing to it's maximum ability.

To most people's surprise, the "flowability" of an exhaust system is determined more by its exhaust manifold than the mufflers that are installed. Keep in mind that headers, of whatever style, are nothing more than exhaust manifolds. It is possible to have a low restriction exhaust that boosts low-end torque. That is truly what is wanted if you're looking for low-end torque. Since the backpressure isn't the "direct" cause of the situation at hand; but rather an indirect cause. Keep reading and you'll see what I mean.

A common street-stock exhaust system has about 15-20psi of parasitic pressure loss. Compare that to a typical muffled performance system of about 5psi of parasitic loss. A tube header and extension pipe with no baffling or resonators (an open header system) would have about 2psi of loss.

A street-stock system is one in which all the usual stock equipment is on the vehicle. That is a cast style exhaust manifold, reverse-flowing mufflers, and standard diameter tubing with heavy bend kinks. A performance system is one where the engine employs tubular headers, larger exhaust tubing (usually) and a perforated straight-through baffle muffler. Notice I did not say turbo muffler or sound canceling system like Flowmasters. That's all an article in itself.

Now for the REAL meat of the issue.

That's all well and good, but why does it affect torque at low revs? Because backpressure restricts velocity. It's the velocity of the air that actually dictates the performance characteristics of the system. High velocity exhaust increases the scavenging effect of the vacuum behind the air mass. The vacuum helps pull the remaining gasses from the combustion chamber.

There's a balance of velocity and flow that has to be taken into consideration. Take this in for instance. You can install a 6" exhaust system on your car. The backpressure will be extremely low. But so will the velocity. The exiting emissions will have a very large tube to travel in, which allows radial travel of the gasses further outward. Thereby reducing the linear force the gas withholds. That intern reduces velocity and the scavenging effect. But, the system has the ability to flow a greater quantity. On the same note, if you have a system with too much backpressure, like a system with a very small tube, the velocity will be very high. But the amount the system can flow will be very low.

The real performance gains happen when the balance between the flow and velocity is in unison. That is, the system with less pressure requires a higher amount of flow to achieve the same velocity as the higher restriction system. Lets take a totally uncalculated example. One engine with a 3" system and an engine with a 1" system. The "magic velocity" for our fake example will be 5m/s. For argument's sake, the 3" engine needs to run at 6,000rpm to achieve an exhaust velocity of 5m/s. Where as the 1" engine only needs to run at about 2,000rpm to achieve 5m/s of exhaust velocity. Keep in mind that this is by no means a calculated example.

The engine in this example has the greatest scavenging effect when the exaust velocity is at 5m/s. The system with the least backpressure (the 3" system) requires more revs to hit 5m/s worth of exhaust velocity. The system with the most backpressure (the 1" system) needs less revs to hit an exhaust velocity od 5m/s.

Each engine has a different "magic number". That is, the velocity of exiting emissions that produces the highest scavenging efficiency. The lower the backpressure; the higher the flow required to reach the desired velocity. The higher the flow required, the higher the rpm required. Thereby defining that a lower backpressure system makes the big torque at higher rpms. And makes less torque at lower revs. But as an overall scenario, the least backpressure makes the most horsepower in the end.

[TheLegacy]

Haha some people aren't car geeks like us.

Yes you got a LITTLE more power now. The more free flowing exhaust on a turbo car like yours, the better you are off for performance. So good move.

However with NA cars (non turbo) you have to becareful with pipe size.

same goes with Turbo though... No exhaust or to big will lose low end power, maybe gain in high ends... if you have perfect diam for piping your set. Been playing with this kind of shit on all sorts of cars

[AKbmw]

how can i know if mine is perfect size or not?

[down4it]

Originally Posted by AKbmw

how can i know if mine is perfect size or not?

What do you mean? You only got mufflers not full piping. I would say that 2.5" all the way is best but if your going to take your block apart and build your car into a 700whp monster then i would say do a full 3" exhaust...

[AKbmw]

^^ haha no i wasnt planning on doing that.. i was just afraid yesterday that i lost power.. (dono why) but like i just went out for a quick drive and it feels amazing.. agin.. maybe it was just like a break in thing wqith the exhaust.. cant really call it an exhaust since its only mufflers.. but it sounds amazing.. wanna meet up with u soon

[Chesmu]

they look great.

[nyc3r]

Originally Posted by TheLegacy

Haha some people aren't car geeks like us.

Yes you got a LITTLE more power now. The more free flowing exhaust on a turbo car like yours, the better you are off for performance. So good move.

However with NA cars (non turbo) you have to becareful with pipe size.

same goes with Turbo though... No exhaust or to big will lose low end power, maybe gain in high ends... if you have perfect diam for piping your set. Been playing with this kind of shit on all sorts of cars

Like the little civics with huge exhaust that I can put my foot in. Loud as hell but slow like sh*t.