Downpipe questions

[JAWTB]

Good afternoon, all!

I currently have a 2021 Supra with a Dual Tomei exhaust. Just shipped out my ECU today to Femto.
Looking into some downpipes. I'm a little confused... For example the East Coast Supra downpipe is 3.5" but most others I've seen are 4.5"...
Which downpipe will actually fit my car? Both claim direct fit, but somethings go to give if there are two different sizes?

When I look up the Dual Tomei measurements it says 3.51" diameter on the main pipe...

Any insight is appreciated.

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[Pizza]

So there are downpipes of many shapes and sizes for this car, but 90% of them all reduce to the OEM 3.15" diameter where the downpipe meets the exhaust. So most of the "different sized" downpipes will be 3.5" or 4.5", hell even MST's downpipe is 6" diameter in the middle section, but it basically is all just marketing snake oil because the flow of all of them is limited by the smallest diameter. Which is The stock 3.15" connection. This is mainly done so that when people get a downpipe it will fit with their exhaust (whether it's stock or aftermarket) without any custom fabrication needed. Your Tomei exhaust connection to the DP is still the OEM 3.15"

 

[i3igpete]

but it basically is all just marketing snake oil because the flow of all of them is limited by the smallest diameter. Which is The stock 3.15" connection.

What is the Catalyst area open to flow for the typical GESI cats used? that should tell you the absolute minimum cross section diameter needed in the cat section. (hint, it shouldnt be 3.15 inch)

 

[CafeRacerQueen]

the biggest thing to consider is if you're actually trying to do things the RIGHT WAY is that when you get that downpipe installed, the shop you choose can actually do exhaust fabrication and make it so your downpipe to catback connection is modified to be a 3.5" connection.

I did just that on my AA downpipe and catback and was surprised to hear a distinct tonal difference after removing that 3.18" section for a full 3.5". Deeper and fuller.

 

[Extreme Power House]

in terms of power, you can go with any downpipe 4" or larger.
the 4.5" inch is the standard that every company uses, MAD and MST offer larger downpipes
the larger the mid section is, the deeper the downpipe tone. its not about adding power, but rather changing the sound.

 

[Meraki Autoworks]

One downpipe you need. AA Catted downpipe.

-Josh

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