Exhauste Flapper Removal

[markt111]

3 cats and two mufflers on mine

[300 Blackout]

Lots of talk about back pressure and what it does and so on...   By the time exhaust reaches the cats and into the system, the power has already been made, exhaust is the waste exiting... Im i missing something? The more open, more free flowing your exhaust to get as much waste out the better it is, No? Holding in exhaust gasses in the exhaust pipe to make more TQ doesnt make sense to me.   Feeel free to explain otherwise, im all ears. 

Back pressure isn’t the correct terminology but is widely used to refer to a phenomenon similar to siphoning called “scavenging.”  (People may also be referring to the fact that increasing tube diameter in an exhaust may decrease exhaust velocity which would have an impact on the pressure differential in the system needed to produce the phenomenon of scavenging).   

 

As exhaust exits one cylinder’s header tube and enters into the collector (where all of the header tubes meet) it will help draw additional exhaust gasses out of the other header tubes just as their gases lose enough velocity to exit on their own. If the header is properly tuned (engineered to maximize this phenomenon) then you can cause more exhaust gas to exit the cylinder than it would in a less restricted system.  

 

Think of someone smoking in their car with all windows down on a completely wind free day. The smoke would linger in the cabin much longer if it only used the energy of someone exhaling. But if you drive the car down the freeway with all the windows down (or even half way down), the smoke gets drawn out of the cabin much faster than just exhaling. It’s not because of back pressure, it’s because of scavenging.

 

Scavenging is the result of a pressure differential caused by high velocity gasses (the cylinder actively ejecting exhaust) flowing next to low velocity gasses (the “lingering” exhaust gasses left over from the previous cylinder’s exhaust cycle). The higher pressure gasses (low velocity) will naturally flow to the area of lower pressure (high velocity). The diameter of exhaust tubing will have an impact on exhaust gas velocity and therefore an impact on the pressure differential which causes the gas to flow or “scavenge.”

 

Everything needs to be tuned (optimized) for the specific set up t is on. If you have a supercharger you will be exhausting more gases and need larger diameter tubes to get the same benefit. Too narrow and you get fast gas but restricted flow. Too wide and you get slow gas with no scavenging resulting in lingering exhaust.

[Mileguru]

3 hours ago, 300 Blackout said:

Everything needs to be tuned (optimized) for the specific set up t is on. If you have a supercharger you will be exhausting more gases and need larger diameter tubes to get the same benefit. Too narrow and you get fast gas but restricted flow. Too wide and you get slow gas with no scavenging resulting in lingering exhaust.

So perhaps the loss of power is because Magnuson's tune is based on a stock truck (stock except for the blower, of course). Magnuson says that you can do any cat-back work you want without needing a retune though, so that's a bit contradictory to what I'm seeing happen.

[300 Blackout]

So perhaps the loss of power is because Magnuson's tune is based on a stock truck (stock except for the blower, of course). Magnuson says that you can do any cat-back work you want without needing a retune though, so that's a bit contradictory to what I'm seeing happen.

Are you 100% sure, without a doubt, that the flapper is being opened and is not obstructed? I know it sounds obvious but the fact is most of us haven’t inserted a bore cam into the exhaust to confirm what is actually happening. I can see no other reason why, based on manipulation of the flapper, that your engine would be experiencing any issues unless of course you were somehow restricting the flow. Although unusual, it wouldn’t be unheard of if the part was rusted, bent or was improperly assembled or installed.

1SLOW1500 ran into big issues with his turbo related to an exhaust insert that was restricting flow.

Bore cams are $20 on amazon. Pick one up that’s long enough and see what’s going on in there. Or cut the thing off and call it good. If nothing works, remove the supercharger and put it in a postage paid box to be delivered to me and I’ll test it for the next 10 years to confirm satisfactory operation. [emoji16]

[Mileguru]

9 hours ago, 300 Blackout said:

Are you 100% sure, without a doubt, that the flapper is being opened and is not obstructed? I know it sounds obvious but the fact is most of us haven’t inserted a bore cam into the exhaust to confirm what is actually happening. I can see no other reason why, based on manipulation of the flapper, that your engine would be experiencing any issues unless of course you were somehow restricting the flow. Although unusual, it wouldn’t be unheard of if the part was rusted, bent or was improperly assembled or installed.

1SLOW1500 ran into big issues with his turbo related to an exhaust insert that was restricting flow.

Bore cams are $20 on amazon. Pick one up that’s long enough and see what’s going on in there. Or cut the thing off and call it good. If nothing works, remove the supercharger and put it in a postage paid box to be delivered to me and I’ll test it for the next 10 years to confirm satisfactory operation.

100% sure? No. I'm assuming it's shut when the truck is off and then fully opened when I turn it all the way counterclockwise.

 

You're right though, it could all be in the SC. What's your address? 

[markt111]

On 11/1/2018 at 10:21 AM, Centex14 said:

Only way that flapper would hinder performance is if it’s locked in the closed position. Otherwise it’s just a small piece of metal that’s running parallel to the air flow, just like your throttle body.


2014 z71 LTZ
Volant Intake
Borla Exhaust
Diablo
Bilstein 5100
Rough Country Level

On a 6.2 with a blower, if I was him I would want as free flowing of an exhaust as possible, look at the pic are you saying that the flapper valve dies not restrict flow?

[Centex14]

Does it restrict flow?  Sure.  Is having it wired open any more restriction than letting it move on it's own?  Absolutely not.  Which was my point.  Wired open will be no different than letting it move on it's own.

[markt111]

that makes sense, remove it totally!

[powerhaulic]

I installed a Magnaflow on my '17 6.2 max tow, with a custom tail pipe. Sounded great not to loud and no flat spots or ill behavior at all.