bb123

I need factual info. I installed a Borla muffler but left he resonator on due to back pressure concerns and the issue with vacuum in the pipes.

Everyone keeps saying NASCARS don't have them. But to me it's simple. You have street applications and race. With racing you spend most of your time at high RPMs therefore the flow will be greater thus requiring less back pressure. Im street applications, since the RPMs will be lower most of the time, you need it so the scavenging effect takes place. Otherwise you'll have no torque on the low end and only extra horses on the top end like race cars. As a result you lose low end torque and ability to pull through the lower gears and RPMs. Let's not mention fuel economy loss.

You NEED back pressure to create the scavenging effect more so in trucks. It's a large vehicle that requires torque to get the large body moving, not horsepower. Horsepower takes effect at the upper end of the spectrum where torque isn't required as much.

Mustangs are light and have high output motors. Stop and go traffic will destroy your fuel economy BUT with a free flowing exhaust, your horses will be higher so in race applications where you're at almost redline, you'll notice the benefits. I don't know very many people that spend that much time at high RPMs while driving to work, so it's not the most economical. You choose how you want your pocket book to go. Poor fuel until you hit redline or decent fuel the way the car was designed and sacrifice the upper end. Take your pick, you can't get both.

this is my understanding and could be wrong but his is what I've gathered.

My question is, if I stay at around the stock size of 2.75" and go resonator delete, should I be fine since the pipe is small enough to create the pull of exhaust?

randyman02-13

On my 5.0 f150 I cut off the factory muffler and resonater and installed a 3 in pipe to a 14 in round magnaflow then a Y pipe and 2.5 in pipe all the way to the back. I have not noticed any drop in fuel mileage or power. If you look up Engine Masters on YouTube they have an episode about good and bad mufflers and one on 2.5in pipe and 3in pipe and they are very educational about back pressure

Hope this helps you out.

SALEEN961

iTrader: (1)

Talk to an engineer; you want no back pressure, or as little as possible in a given application. The caveat is that 10" pipes while providing no back pressure would also provide no scavenging. The ideal exhaust will provide a strong scavenging effect while also having little to no back pressure, and this is tough to achieve without serious planing.

Without good scavenging larger pipes can cause you to lose power and this is where the back pressure myth comes from.

PerryB

Wow, somebody who actually gets it! I can't tell you how many times I've gone around with somebody who insists an engine will make more power with "a little backpressure". No, not, nada. The trick (as obviously you know) is to maintain adequate velocity of the gas column which generates the scavenging effect.

Andy13186

How is scavenging achieved?

bb123

Since the truck stock is 2.75", removing the resonator will not hurt anything. Is this correct provided the same size piping is used?

My understanding is that when the piping it too large the scavenging cannot take place thus doing the opposite of what you are desiring.

If this chart is followed I'm assuming you'll achieve the fine medium of pipe size to exhaust size to horsepower ratio.

Stinger23

This guy gets it as far as non-turbo exhaust is concerned.

For a turbo engine, the best exhaust is no exhaust (meaning as large as possible) for peak power. Turbos also don't like baffled or chambered mufflers since they are designed to use exhaust pulses to help scavenging but there is no pulse post-turbo so all the baffle does is cause a restriction. So the best muffler type for a turbo application is one that maintains pipe diameter all the way through and that you can see through.

bb123

I don't have a turbo so that doesn't apply to me. I'm wondering the effect of removing the stock resonator and leavingbit at the stock 2.75" diameter.

Stinger23

You never said anything about which engine you have in your original post so I was making sure both options were covered.

Removing the resonator will not hurt power in any way. You do not "need" backpressure.

bb123

Thanks man. Yea, I'm mixing up two different threads where I stated it in another. I decided to cut the resonator off and just finished at the shop. Sounds MUCH better! I went 3" cat back with my Borla Pro XS.