OE Exhaust vs aftermarket on flow efficiency alone

[Dunbar]

How efficient is the stock exhaust as far as flow? I read here somewhere that at WOT it passes exhaust via some internal cutout whereas at lower throttle demand it goes through the entire route. I haven't heard that confirmed by someone who has dissected the OE muffler. Regardless, I like the rumble note of the Dirty Deeds exhaust but like even more the stealthy quiet OE system. So I would only replace the OE system if it flowed significantly better. I have on order a Harrop supercharger and rather hope I can keep the OE exhaust without losing significant throughput I could achieve with an aftermarket exhaust. The question applies to both CAT back and heads back. So if I sourced either the long or short headers and added a aftermarket CAT back exhaust will that flow significantly better than stock?

Background:
MY FJ62 had headwork done by Jim Chenoweth, SS Chevy valves port & polish etc. It is desmogged and has an overbored throttle body and larger exhaust from the head back. Magnaflow muffler and originally a 2 into 1 CAT. The CAT eventually failed and I put in a Y-pipe. With the change to Y pipe the truck got stupid loud. With the H55F five speed the truck really performs, for a tractor. I am willing to give up some of its performance gain to quiet it down to a reasonable level. My Lexus LS460 sedan has the same engine family as the 200/570LX and is wicked fast but super quiet. The stealth counts on the LS and on a blown 200, don't want the Popo focusing on me.

 

[Dunbar]

Searching Tundra forums because @cruiseroutfit has not seen this thread or had time to reply. He has installed many superchargers and will know the answers. However, I find that Keith from DirtyDeeds replied to the following question as seen. Still not sure if it means that the OE exhaust will be just fine with a SC or if there are gains to be made by building aftermarket.

Your engine is basically an air pump. When you change something in the suck, bang, blow process, you're changing how the vehicle was designed to manage and utilize that airflow. Honestly, if you want to slap some sort of forced induction on any vehicle, you should be thinking about the entire process, including a new tune to work with it. It's not as simple as slapping a SC on it and calling it good.

EDIT: Should also mention that when you do add more power you should also look at whether your engine and driveline components can handle it, as those may need upgrading too.

When you run the Magnusson blower, the engine is no longer an air pump, the blower is. Not only is the blower and air pump, it’s a positive displacement air pump. When those rotors are turning the air is forced From one side to the other. If there is something in the way, it gets blown up.
I’ve seen guys custom tune our trucks with long tube headers and supercharger, and their times are the same as my truck. There’s very little power in the exhaust when supercharged. It’s all about the cam phasing and pulley on the charger. Exhaust is simply there to reduce the pressure from the stock muffler.

 

[Dunbar]

I called ProSpeed to check on shipping on my supercharger and it is there and ready to be picked up. I also asked about exhaust and he said that Harrop designed the unit to work with the OE exhaust. So until someone cracks the 2020-2021 ECU and stage 2 becomes available, it's a moot point. It will be interesting to see if it is still stealthy quiet like it is now.

 

[AnyMal]

Subbed and very interested. I don’t know about post 1 but if I dig in the entire exhaust profile changes on my truck. It goes from tame to deep throat level at WOT and you get all the low end notes that were previously missing. Very curious to see if that bypass is real since I eventually want to SC and probably go down the road you are thinking about.