Hi there
I always try to improve the sound of my motors, no matter what I own. But I read about straight through pipes and resonator delete.

It's only recently I've heard people talking of "Resonators".
Resonators (I believe) are straight through perforated and glass packed silencers. Like we use on motorbikes but call "End Cans". Is this right?

Mufflers are similar but usually have an "off set" in and out so aren't straight through?

So if someone says they have straight pipes or straight through, is this without mufflers (back box) and just resonators in line? Or nothing in line, just straight pipes no resonator/silencer/muffler?

I had a mk1 v6 Capri 3000E I cut all silencers off and just had one cherry bomb on the end of each pipe that sounder fantastic.

If I removed the silencers/resonators from say the XFR would this be raspy loud or throaty loud? When I get my XFR I will make up the rear pipes using cherry bombs instead of back boxes as these are cheap and affordable development "tools".
As much info on silencers/resonators as possible would be much appreciated. TIA.

 

Dicky, a resonator is not a muffler or a glass pack. It resonates. The idea being that it is set to resonate at a spacific frequency which is where the motor normally operates at (or something close). By having the resonator resonate, it smoothes out the exhaust pulses which are what makes the noise. If you smooth out the exhaust flow, it makes less noise while allowing the same air volume. You cna see the effect by using a balloon. If you blow up a balloon and just let it release the air, it makes a lot of noise because the air is starting and stopping because the end of the balloon is moving around. If you blow up the same balloon and hold the end of the balloon still, the same amount of air comes out, but because it is a solid stream, it makes much less noise.

 

Excellent thanks...every day's a school day! Although I thought they had fibre wadding around the perforated tube? Are they tuned to the resonant frequency of the exhaust tone or pulses? So diameter and length would be different for different engine capacity?

 

My mechanic said he held his hand over the end of my exhaust and could barely feel anything coming out....5 mufflers and two resonators will do that plus where the pipe goes over the half shaft it is crimped almost closed....that 4.02 must have been one noisy assed motor to require that many mufflers

 

Dicky, this is where installing resonators can be tricky. The tubing will do one thing at a given diameter length and the resonator can be tuned to a different frequency. The best way I can explain the exhaust pipe is to think of a xylophone. The lower notes use a bigger diameter pipe that is also longer. This would relate to a lower engine RPM. Now, toss in the complexity of only using a quarter wave (ie, 1/4th of a full sine wave) and this is where you get a performance boost as you will have one end of the pipe with a high pressure and the other end will be at a much lower pressure. Where this is beneficial is if you can place the resonator/muffler where the high pressure is just entering the muffler/resonator on a tuned pipe, this will put a low pressure at the exhaust valves which will help evacuate the cylinder faster, allowing more fresh air to enter on the next stroke, allowing for more power gain. So, interuptions in the pipe can help generate power at specific points in the RPM bands. This is why placement of an X-pipe is critical for power gains. This is where a bit of science can help you create an exhaust system specific to what you are after. This is also why one exhaust system can do wonders for a car,but another can do nothing. Yes, a freer flowing exhaust will also change stuff as you are affecting the back pressure seen by the engine. But, that is a different wrinkle in this whole argument. Another one of those "did I consider ......".

 

Thanks for the lesson Thermo, interesting stuff. I'll play around with the back boxes with straight through mufflers/resonators.

What are people doing to their exhausts and how has it effected their performance? I've seen hundreds of YouTube vids, most of them sound very similar but not many explain what they have done.

 

Quicksilver back boxes only!

 

Dicky, not sure how much you know about how mufflers are numbered. If you look, most mufflers fall into a few number categories. You have Series 70, Series 50, Series 44 and Series 40. The lower the number, the less muffling they do. Factory mufflers are actually probably around a Series 75 if not Series 80. So, they do a fair amount of muffling. So, simply pulling your factory mufflers off of the car (keeping the resonators), if you stepped up to say a Series 50 muffler setup, you can net the additional noise and free up the exhaust system to get a bit more power out of the car. How much that will net, hard to say. Just keep in mind that by opening up the exhaust, you are allowing it to flow freer which will give you top end power, but also hurt the low end grunt a little bit. So, it is a balance between how open you make things and how driveable the car is in town. I think a quality dual Series 50 muffler setup would do what you are after without a large cost outlay. I used a Flowmaster muffler on my truck. While I used a Series 70 on it, the exhaust got a bit more throaty and there was a nice performance improvement. Granted, I also stepped up from a single 2.25" pipe to a true dual 2.5" setup. So, the larger pipe had an effect too. The big benefit to my truck setup was I kept the pipes separate all the way back to the muffler. So, I have very long tubes to make the low end power be there.

If you want to get an idea of what RPM the pipes are going to be most effective, there are calculators on the internet that you can calculate the resonant frequency of pipes. From there, multiple that number by 30 and that should be your ideal RPM power gain point. The 30 comes from the fact that you have 4 cylinders firing into each exhaust header, but you are tuning it to 1/4 wave. The motor is a 4 stroke, so, it is only firing the cylinders every other stroke. You then need to multiple by 60 to go from seconds to minutes. So, 4 x 1/4 / 2 x 60 = 30. From there, you just need to measure your exhaust system diameter and the length from the head to your first point where the pipe opens up (muffler, resonator, etc). Crunch a few numbers and see where it falls into your RPM range.