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Muffler deletes,why they are not always the way to go.

Over the years  terms like  "res delete" , "muffler delete" or "straight pipe" have become popular. So what are these? what do they mean? and are they the right choice for you and your car.

To understand all this we first need to understand some performance exhaust fundamentals which are all too often overlooked by enthusiasts and surprisingly many exhaust shops. We'll break this down into parts which are all factors and combine to determine what is right for your car and your preferences.

Gas Flow & Velocity

An Exhaust system is made to carry gas to the exit of the vehicle, we all know this part, but what is actually happening inside that tube? Your engine is producing complex pulses and sound waves along with velocity which varies with engine RPM and in turn changes those pulses and waves.

For example, we have all used a garden hose with no spray fitting on the end, turn the hose on and water runs out on the ground in volume but with no real velocity, begin to put your finger over the end and that velocity increases and the water is no longer running on the ground but spraying much further! Your exhaust is much like this, however we are aiming for the optimum gas velocity without too much restriction, velocity assists in making power and torque. If your  pipes too big you will lose power and torque through a lack of gas velocity.

Gas pressure

If we think of our garden hose here, when we press our finger over the end of the hose too much and we now lose volume, the water has already reached a high velocity and we begin to really restrict flow, the same is true for your exhaust system. What we are looking for is the optimum volume of gas and optimum velocity to keep things moving, in the case of headers or "extractors" velocity will actually help pull burnt gas from the cylinder, thats really a whole other Blog so we'll leave that for now.

So we can understand from these points that it is important to choose the right size exhaust to maximise performance, so, what about sound? how does all this effect the sound? after all this is super important as we do want a nice sounding system also. To achieve our extra performance and great sound we have now increased the tube size, now our car is performing better and sounds great. but we want more! what can we do? remove some mufflers, resonator delete etc I hear you say. Yes this makes sense, less mufflers = More noise. Yes but no, you will have more noise but not necessarily more "sound". The sound you have and love will not always simply increase, it will change so be prepared for this.

You may also now become acquainted with our old nemesis, Drone or cabin drone.

Drone or resonance

"The reinforcement or prolongation of sound by reflection from a surface or by the synchronous vibration of a neighboring object."

So what does the Physics definition mean for our exhaust? With our larger high flowing exhaust which works great we also have sub optimal gas velocity at lower RPM, for example cruising on the freeway at 100km at 1200 Rpm. Now that gas is literally not flowing straight under velocity like it will at "performance" RPM. Now its bouncing around in the tube, or reflecting from one side of the tube to the other, AKA reverberating, causing resonance and now that droning sound in your cabin.

So, now we have removed our resonator or rear muffler, we have more noise but we have also gained something we did not want, Cabin drone, as it turns out our resonator or muffler was preventing this nasty side effect. There is a reason the resonator or muffler is there. So it is important to understand the above when considering your options for exhaust modifications or purchasing a system.

We have always successfully worked from this simple rule of thumb, for every 1 to 1.5m of tube there should be a resonator or muffler of some type to control and dampen resonance or drone, it will also help to produce a great sound rather than simply noise. But race cars don't do this! and I want my car to sound like a race car! you might say, yes this is true. But race cars also do not drive at low cruising RPM to often do they? So with a performance exhaust for the street we have other considerations, yes we want extra performance, we also want to minimise unwanted side effects like drone or resonance. We also need the system to produce the best performance across a much broader RPM range.

So bigger is not necessarily better, and less mufflers is not always the best either. Consider your goals and every day driving when choosing or modifying your exhaust. We hope this blog has been helpful for you, if you have any questions or need advice, click the contact us tab and send us an email. We are happy to help you.