FL5 Downpipe Comparison (PRL vs RV6 vs Milltek vs Scorpion) – Dyno Data, Design Differences & Catless Setup

[MainMind]

Hi all,

I’m currently planning a Stage 2 setup on a Honda Civic Type R FL5, and I want to approach this from a data-driven / engineering perspective, not just subjective impressions.

My goal is a 100% catless setup (no catalytic converter, no GPF) combined with Hondata, while maintaining a clean and usable exhaust note.

1. Dyno data (critical question)
Has anyone tested before/after dyno results for different FL5 downpipes?
Ideally:
Same car
Same dyno
Same tune (Hondata)
Any direct comparison between:
PRL Motorsports
RV6 Performance
Milltek Sport
Scorpion Exhausts

Looking for:
WHP / WTQ gains
Spool characteristics (RPM vs boost)
Any measurable differences between brands

2. Flow / design engineering
From what I’ve seen:
Some downpipes are mandrel-bent, one-piece (Milltek style)
Others are fabricated with multiple sections and welds (PRL/RV6)

Questions:
Has anyone compared internal geometry or flow characteristics?
Does the collector / turbo outlet design differ significantly between brands?
Any CFD, flow bench, or real-world data available?

3. Catless vs high-flow (real data only)
I’m specifically interested in full decat setups, but:
Has anyone compared:
Catless vs 200 cpsi
Same setup, same tune
Looking for:
Measurable gains (not just sound)
Impact on spool and midrange torque

4. Rasp / sound behavior (with data if possible)
For those running:
Catless downpipe
OEM exhaust (possibly with one resonator removed)
Questions:
Which setups produce rasp and which don’t?
Any frequency analysis or recordings under load?
Does downpipe design influence rasp, or is it mostly the exhaust/resonators?

5. Thermal / performance logs
If anyone has logs (Hondata or similar):
Boost vs RPM
WGDC changes after downpipe
IAT / EGT behavior
Especially interested in:
Differences between brands under sustained load (track use)

6. Fitment & sensor configuration
Any differences in:
O2 sensor placement
Fitment tolerances
Need for spacers or modifications?

Goal
I’m trying to determine:
Whether different downpipe brands actually produce measurable performance differences,
or if once you go catless, they are effectively equivalent from a performance standpoint.

Any dyno graphs, logs, or objective data would be greatly appreciated.
Thanks in advance

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[axion_industries]

You should look up our Axion Industries 2n1 downpipe, only downpipe on the market that comes catted and can swap to catless in 10 min, perfect for street and track events www.axionperformanceparts.com

 

[Cueyo]

You should look up our Axion Industries 2n1 downpipe, only downpipe on the market that comes catted and can swap to catless in 10 min, perfect for street and track events www.axionperformanceparts.com

The exact one I'm eyeing as well, the ability to go catless that easy and never have a CEL during daily driving is unmatched by anyone else.

 

[axion_industries]

The exact one I'm eyeing as well, the ability to go catless that easy and never have a CEL during daily driving is unmatched by anyone else.

We were using the 200cel cats for the last 5 batches we did and work great but the demand with people wanting a 400 cel was hurting us to attract more people. Glad to see people understand our vision on these which was my idea a long time ago and we finally made it a reality

 

[MainMind]

The exact one I'm eyeing as well, the ability to go catless that easy and never have a CEL during daily driving is unmatched by anyone else.

That actually looks like a very interesting solution, especially for street/track flexibility.

However, I do have a technical concern:
Since this design introduces an additional joint (V-band / interchangeable section) very close to the turbo, how does it handle:
Thermal expansion at high EGTs
Long-term sealing reliability (leaks over time)
Repeated install/remove cycles
In a traditional one-piece downpipe, there are fewer failure points, so I’m curious if you’ve tested durability under sustained load (track use).

Also, do you have any dyno or logging data (boost, WGDC, etc.) comparing the catted vs catless configuration?

 

[axion_industries]

That actually looks like a very interesting solution, especially for street/track flexibility.

However, I do have a technical concern:
Since this design introduces an additional joint (V-band / interchangeable section) very close to the turbo, how does it handle:
Thermal expansion at high EGTs
Long-term sealing reliability (leaks over time)
Repeated install/remove cycles
In a traditional one-piece downpipe, there are fewer failure points, so I’m curious if you’ve tested durability under sustained load (track use).

Also, do you have any dyno or logging data (boost, WGDC, etc.) comparing the catted vs catless configuration?

Vband clamps are the best in the industries and will not break or leak

I have over 300 downpipes being used for 1.5t and 2.0t and no warranty claims. These are hand welded in the USA by us in house not robot welded in china like most on the market.

We are going to be offering a cerakote finish and we offer our own downpipe blanket to manage heat.

 

[axion_industries]

Cerakoted 1.5t downpipe we just did for pricing

 

[MainMind]

Thanks for the detailed reply, that makes sense regarding the V-band reliability.

From a performance standpoint, I’m trying to understand how it compares to other FL5 downpipes.

Do you have any data on:
Dyno gains (before/after)
Boost vs RPM / spool characteristics
WGDC changes
Also, have you compared the flow or performance against fixed one-piece designs (PRL, RV6, etc.)?

 

[axion_industries]

Thanks for the detailed reply, that makes sense regarding the V-band reliability.

From a performance standpoint, I’m trying to understand how it compares to other FL5 downpipes.

Do you have any data on:
Dyno gains (before/after)
Boost vs RPM / spool characteristics
WGDC changes
Also, have you compared the flow or performance against fixed one-piece designs (PRL, RV6, etc.)?

Well PRL, RV6 and many others only offer catted downpipes. PRL dont even make any downpipes and havent for 3 years now.

Catless will make 5-10whp more over catted but that also depends on the mods you have or oem to larger turbos

 

[roguestatus88]

I've been seeing the Axion option pop up more and more. I don't really have a need to ever swap out to catless, but the choice to do it is unique. How does this play as far as emissions go? Will it throw a code or is there any kind of "no code guarantee" like TSP has?

 

[axion_industries]

I've been seeing the Axion option pop up more and more. I don't really have a need to ever swap out to catless, but the choice to do it is unique. How does this play as far as emissions go? Will it throw a code or is there any kind of "no code guarantee" like TSP has?

Our next batch is using 400cel cats so no codes will be present and will pass smog in most States as some States have visual which no aftermarket cat will pass emissions

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