Muffler delete without losing torque? (11 Viewers)

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Eicca

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With the help of YouTube, I have successfully convinced my mom that the best solution to her ghetto-sounding rattly muffler is to just straight pipe it. Just the muffler.

Now I've studied all the fun stuff about exhaust back pressure and flow velocity, and I know the muffler (and whole exhaust) is tuned to get just the right amount of restriction to facilitate gas flow, like putting your finger over the hose.

So, if we replaced the muffler with a pipe a few steps smaller than the rest of the system, would that retain the same amount of backpressure and keep the low end torque?
 
If you're going to do a muffler delete use the same size pipe as the inlet and outlet of the muffler.

Backpressure in exhaust systems (when relating to performance) is largely a myth, particularly that far back in the system.
 
If your exhaust is rattling my money is on it being loose catalytic shields, 2 minutes with a big clamp solves that issue.

To your other question, I've never really subscribed to the thought that back pressure improves engine performance in any aspect. Engines are air pumps and restrictions are just restrictions (noise and pollution are reasons for leaving exhausts intact, not performance). Any scavenging effect the exhaust might have is far outweighed by the pressure from the engine itself.

If you check out Engine Masters on youtube they have an episode where they test different mufflers for back pressure performance gains. Spoiler-- bigger exhaust/fewer restrictions make more hp/torque throughout the range.

I say if you are changing the muffler go with something like a magnaflow that is basically open, but will control the sound a little better than a straight pipe

Whichever way you go have fun wrenching! and let us know if you get any power gains sans muffler!
 
If your exhaust is rattling my money is on it being loose catalytic shields, 2 minutes with a big clamp solves that issue.

To your other question, I've never really subscribed to the thought that back pressure improves engine performance in any aspect. Engines are air pumps and restrictions are just restrictions (noise and pollution are reasons for leaving exhausts intact, not performance). Any scavenging effect the exhaust might have is far outweighed by the pressure from the engine itself.

If you check out Engine Masters on youtube they have an episode where they test different mufflers for back pressure performance gains. Spoiler-- bigger exhaust/fewer restrictions make more hp/torque throughout the range.

I say if you are changing the muffler go with something like a magnaflow that is basically open, but will control the sound a little better than a straight pipe

Whichever way you go have fun wrenching! and let us know if you get any power gains sans muffler!

Diesels will not start without back pressure.
Backpressure is a thing, to much restricts and suffocates the engine, think Jake Brake on a semi.
To little backpressure and you shorten the life of the exhaust valves because they run to hot.
As far as how far back the backpressure dissipates...if the engine is running it does not dissipate until it leave the tailpipe.
 
Diesels will not start without back pressure.
Backpressure is a thing, to much restricts and suffocates the engine, think Jake Brake on a semi.
To little backpressure and you shorten the life of the exhaust valves because they run to hot.
As far as how far back the backpressure dissipates...if the engine is running it does not dissipate until it leave the tailpipe.


I didn't mean to imply that back pressure isn't real, it surely is, but suffocating the engine is about all it is good for. We often mix up back pressure and exit velocity of the exhaust. Back pressure is simply a measure of how hard the engine has to work to push the exhaust out of the way. The harder the engine has to push the exhaust the less energy available to turn the wheels. A properly sized exhaust will maximize the speed at which the hot gas leaves the combustion chamber without inducing unnecessary drag, thus cooling valves more efficiently. (at least that's how I understand it... it's been a long time since physics class)

I'd love to learn more about diesels not starting without back pressure, I'd always believed that the valves provided all the pressure containment needed for combustion? I'd run some tests on my truck, but it's got a turbo sitting in the middle of the exhaust and more sensors than I know what to do with... Anyone have an old N/A tractor with straight pipes?
 
The only engine that needs back pressure is a 2 stroke. As far as diesels go, I've had several Cummings trucks and ran nothing but a turbo. They started all the time.
But, I guess if you wanted to argue semantics, a turbo is a muffler.
 
Exhaust velocity is what I was going for.
 
Speaking out of total ignorance, I have to suspect that back pressure is factored into the highly computerized engine. A change here more than likely will end up with a computer controlled change elsewhere in the system.

Wonder if the gain is worth the pain.....
 
The only engine that needs back pressure is a 2 stroke. As far as diesels go, I've had several Cummings trucks and ran nothing but a turbo. They started all the time.
But, I guess if you wanted to argue semantics, a turbo is a muffler.

I cannot say if a turbo changed diesel will start without a exhaust or not, I have not experienced that, yours did, so it can.
All of the ones I've dealt with/heard of were non turbo diesels.
 
I didn't mean to imply that back pressure isn't real, it surely is, but suffocating the engine is about all it is good for. We often mix up back pressure and exit velocity of the exhaust. Back pressure is simply a measure of how hard the engine has to work to push the exhaust out of the way. The harder the engine has to push the exhaust the less energy available to turn the wheels. A properly sized exhaust will maximize the speed at which the hot gas leaves the combustion chamber without inducing unnecessary drag, thus cooling valves more efficiently. (at least that's how I understand it... it's been a long time since physics class)

I'd love to learn more about diesels not starting without back pressure, I'd always believed that the valves provided all the pressure containment needed for combustion? I'd run some tests on my truck, but it's got a turbo sitting in the middle of the exhaust and more sensors than I know what to do with... Anyone have an old N/A tractor with straight pipes?

Now I understand what you were saying.

The exhaust valves closed provide compression but not back pressure, the exhaust leaving will be leaving to fast and can actually pull the intake air out of the cyclinder, there is a fraction of a minut second that both valves are open at the same time just before/right at TDC, this is all assuming no variable valve timing.
Combustion temps on a gasoline engine are 3000 degrees Fahrenheit. The exhaust gas pulls heat away from the valves and cylinder head.
It does not provide cooling unless it sits there for a second, if it leaves to fast, the valves will destroy themselves, modern hardened valves will last upto 50,000 miles of normal driving that way, racing etc and they wont last long at all.
 
...and so will your mom.
Rob's talking about your mom! I'd take offense!
Jk
I agree with your comment and with this in mind and considering I'm about to cut off the final resonator to change the location of the last bit of my exhaust what muffler does everyone recommend? If I could have it silent, I'd prefer it that way along with all the possible power. But since I know those are at odds then what is the best compromise? I see one vote for Magnaflow up there.
 
Personally speaking, deleting the main muffler would make your rig sound like crap from the outside and inside.

I recently installed a MF 12286 which is a unversal fit- 24" body 30"overall 2.5" in and out centered. It requires being welded in place. Muffler and install should be between $150-200.

It actually feels like it provides a "bit" more low end power, minimal noise increase with the rear resonator still attached. Remove the resonator and the interior noise gets a little louder in city driving, but not really noticeable at HWY speeds.

This is a good muffler thread.
Got Direct Fit Muffler Replacement Experience
 
Diesels don't need backpressure. Many many thousands of diesel trucks are running straight exhaust right out of the turbo. Two strokes don't need backpressure either. I run a 500hp two stroke turbocharged 8v92 tour bus 20,000 miles a year on a straight exhaust. Only recently did I throw on an Aero muffler because I was tired of the noise. Bus has 450,000 miles on it. Sorry for the thread drift, but the backpressure argument has been busted long ago. If you want to run straight, go for it but our 4.7's sound like oversized lawn mowers with straight exhaust....
Here's a juicy vid of my two stroke bus with an aero muffler

https://photos.app.goo.gl/vGw2YazXejn0Ha6y2
 
Your turbo is providing enough backpressure for the engine to start.
Remove turbo...no start when cold. When hot it'll start, but not when cold.
 
Your turbo is providing enough backpressure for the engine to start.
Remove turbo...no start when cold. When hot it'll start, but not when cold.

Negative, here's a video of a straight piped NA 8v71 two stroke with a straight pipe being started and running just fine. Maybe there are certain diesels that won't start without backpressure but none that I'm aware of?? I'd love to learn more about this, can you post some more info?
 
I love it!! I can watch diesels all day long on YouTube. Cold starts and hard working glowing turbos are my favs.

Our mechanic at work, the mobile mechanic and my oldest son who is a mechanic in the US Army all have said no, a N/A diesel will not start when cold with no backpressure.
Now that may be because of specific circumstances that we did not go into, but their general rule of thumb was they will not start.
 
I know the army still has a bunch of 8v92 two strokes in service...self propelled howitzers used to use them...cool stuff.
 

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