Downpipe Exit Size

[FahadB5]

I was wondering if downpipe exit size would make any difference for stock turbo.
most aftermarket downpipes have a 3.15” exit to fit the OEM Exhaust, and hence most after market catbacks have a 3.15” connection.
ETS makes the 4” exit downpipe which fits with their 4” Catback. However, they don’t make them catless anymore, only the catted version is pffered on their website.
I saw Apex Built with 4” Exit catless downpipes, but I think it’s an AliBaba product that I can find way cheaper.
I have a 3.5” cat back, and I’m thinking of switching to a 4” Exit to smoothen the flow.
I don’t like the fact that it goes 4.5” to 3.15” then back to 3.5”. 4.5” to 4” to 3.5” makes more sense to me with a smoother tapering.

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[Thraxbert]

Enlarging the exit and body diameter of the DP to 4" is worth 10-20WHP on the stock turbo, depending on the tune. This is with no other changes to the vehicle except the DP swap.

 

[e_iva]

Bumping this thread because I'm also curious, who still makes a catless downpipe with a 4" exit? I'm having a hell of a time finding options.

 

[FahadB5]

Bumping this thread because I'm also curious, who still makes a catless downpipe with a 4" exit? I'm having a hell of a time finding options.

Didn’t find enough answers so I decided I’ll give it a try myself. I’m trying Ali Express for the first time, asked them to make a custom DP. Will see how it ends up and will update once I install everything . My car has an RK Titanium Signature Single Exit, which is 3.5” should be smoother with the 4”.
One way to find out.

 

[bushido]

Bumping this thread because I'm also curious, who still makes a catless downpipe with a 4" exit? I'm having a hell of a time finding options.

depending on the downpipe design, you can swedge/swage the OEM section up to 3.5", or cut the OEM section and be left with a 4" section

 

[Diversion]

Also interested because the AWE exhausts offer an optional 4" exit (pretty sure anyways or maybe it was 3.5") and can't find any solid options for larger than 3.15" catless DP.

 

[Mason]

Just dump it. No downpipe needed

 

[e_iva]

Didn’t find enough answers so I decided I’ll give it a try myself. I’m trying Ali Express for the first time, asked them to make a custom DP. Will see how it ends up and will update once I install everything . My car has an RK Titanium Signature Single Exit, which is 3.5” should be smoother with the 4”.
One way to find out.

I was hoping you'd try the Apex Built option I don't really have a brand preference, because pipe is pipe as long as fitment is fine, but definitely keep us posted!

 

[FahadB5]

I was hoping you'd try the Apex Built option I don't really have a brand preference, because pipe is pipe as long as fitment is fine, but definitely keep us posted!

Hello again, just finished installing the 4” Exit DP, you can find everything in the video (which I can’t upload here, it says it’s too large, so DM me on Instagram: FahadB5). Apart from a cold start with the new DP.
Verdict: Mission Failed successfully
-Not much of a difference in sound, however, you can hear the turbo spool ever so slightly.
- Smoother Idle
- I used to have alot of metal to metal crackling inside the car at idle and low speeds. It’s completely gone now (for now at least)
Solution: Big Turbo with an external waste gate

 

[CafeRacerQueen]

Crazy, I noticed a distinct but subtle tone change when I removed the 3.15” neck down from my catted downpipe to 3.5” AA catback.

it’s more full bodied, has more bass, is smoother, slightly louder exhaust note, turbo is louder, spools faster, torque hit is harder and sounds extremely musical and less reedy.

my spouse who is a musician (trumpet player) then gave me a 30 minute TED talk on the how and why this small change made a very noticeable change in the overall tone of my Supra. All about the sound waves

 

[UYCR]

For those still looking to get a 4" DP I'd suggest contacting ETS for a catless option. I'm pretty sure they would still make one for you but they are probably avoiding all the legal implication of having it as an option in the website. I picked up the ETS 4" catted one cuz I'm not tuning yet but FWIW the cat on it is rated for 850HP. Another option is the Leviathan turboback system for maximum flow.

 

[AJRMKV]

Crazy, I noticed a distinct but subtle tone change when I removed the 3.15” neck down from my catted downpipe to 3.5” AA catback.

it’s more full bodied, has more bass, is smoother, slightly louder exhaust note, turbo is louder, spools faster, torque hit is harder and sounds extremely musical and less reedy.

my spouse who is a musician (trumpet player) then gave me a 30 minute TED talk on the how and why this small change made a very noticeable change in the overall tone of my Supra. All about the sound waves

I got the MAD 5" Catless with 4" exit and expanded my MBRP midpipe to a 4" connection so I still have the valved option.

The car has a larger turbo though, I'll take a sound clip when possible.

 

[FahadB5]

Crazy, I noticed a distinct but subtle tone change when I removed the 3.15” neck down from my catted downpipe to 3.5” AA catback.

it’s more full bodied, has more bass, is smoother, slightly louder exhaust note, turbo is louder, spools faster, torque hit is harder and sounds extremely musical and less reedy.

my spouse who is a musician (trumpet player) then gave me a 30 minute TED talk on the how and why this small change made a very noticeable change in the overall tone of my Supra. All about the sound waves

As you said the change is subtle, the sound is more refined and smooth. I still haven’t got the chance to push on the car. Literally installed few hours ago. It’s starting to get hot in Saudi, and I don’t a have a reference 60-130 on this weather. But I’ll give it a try.

 

[FahadB5]

Hello again, just finished installing the 4” Exit DP, you can find everything in the video (which I can’t upload here, it says it’s too large, so DM me on Instagram: FahadB5). Apart from a cold start with the new DP.
Verdict: Mission Failed successfully
-Not much of a difference in sound, however, you can hear the turbo spool ever so slightly.
- Smoother Idle
- I used to have alot of metal to metal crackling inside the car at idle and low speeds. It’s completely gone now (for now at least)
Solution: Big Turbo with an external waste gate

picture for reference

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