Down pipe vs Katmod ( aka gutted cat)

First what is Katmod?

Here in europe Katmod is guting the Precat. or hollowing the first cat next to the turbo.

Advantage:
- Cost Zero or just labor if you are bad with your hand. super easy mod.
- still pass the snif test that we need to do often to get car register as they only test car when hot and precat is for cold start.
- Look OEM for visual inspection ( police, insurance inspector in case of crash.....)

Some say that it is a bad mod but their is a famous tuner for VW/AUDI in europe that offer it a lot for the Golf GTI 6 211 hp to their customer on a budget stage 2.
So as they post on their FB page almost a dyno of each car they do with the list of the modification I went on to check inside those to get some number.
To get a better picture of it and stop listening to some internet rumor about talk about turbulence.............. and get some real hard number's

So those are sure different car ( Golf 6 GTI) on different day's but on same Dyno with same stage 2 file. all are ROW Golf 6 GTI

As it is a Budget mod most off the guy doing the KATMOD don't have an intake ( just using OEM airbox) I could only find one with Carbonio intake and Katmod.

The number are quite interesting on my point of view. specially as it is not the number of only One car.

DOWN PIPE After market ( mostly Milltek) / Carbon intake ( mostly Carbonio)


AIRBOX Gasoline Crank Hp Torque Nm

Carbon Airbox 93 312 460
Carbon Airbox 93 314 453
Carbon Airbox 93 305 428
Carbon Airbox 93 301 446
Carbon Airbox 97 aki/ 102 RON 315 463


KATMOD/ Oem intake

AIRBOX Gasoline Crank Hp Torque Nm


OEM 93 297 427
OEM 93 299 452
OEM 93 301 439
OEM 93 298 429
OEM 97 Aki/102 Ron 305 450


Kat Mod /Carbon intake

AIRBOX Gasoline Crank Hp Torque Nm

Carbon intake 93 309 450


Average of car's with Down pipe/ Carbon intake and 93 gas is 308 CrankHp and 446NM

Average of car with with KATMOD/ OEM airbox and 93 gas is 298.7 Crank Hp and 436 Nm

Only one car with KATMOD/ Carbon Intake and 93 gas at 309 Crank HP and 450 Nm.


Just one exemple of Katmod with a picture of the mod. You can search for more of them on their FB. https://www.facebook.com/JDEngineering.nl/posts/1932308990149040

Golf GTI stage 1 on their dyno with their tune does average 274hp and 410Nm

At the end the gutted precat may be work as the FMF MEGA bomb MX exhaust header!!!!
their they don't think turbulence are a problem


https://shop.1stmx.co.uk/motocross-...-megabomb-4-stroke-motocross-header-pipe.html

Just joking their

Marketing BS or true???

"By positioning this “Bomb” at a key point in the system, increased performance and flow is achieved through the expansion and contraction of exhaust sonics through the system. Result is a flow increase of nearly 10%! The outer chamber in the Powerbomb allows the air to expand, cool and ramp back up at a higher velocity. Additionally, the PowerBomb is a “pre-muffler” "

https://www.fmfracing.com/Product/ProductDetail?CategoryID=44&ParentCategoryID=32&Priority=

Very funny how on all forum you get guy's saying gutted Cat is bad because of exhaust gas expending and then compressing creating turbulence and on the other side FMF for their 4 stroke exhaust explain the same thing is great and add power!!!!