mikellucci

iTrader: (56)

Has anyone decatted or gutted the cats on the stock IS-F headers? I'm really curious as to how restrictive the cats are on the headers or if the runner design is just that bad. Something is a miss if Sikky and PPE can easily achieve a 30+ whp output.

Just wondering if anyone has looked into it further besides buying an aftermarket option?
I have both Sikky headers and a spare set of oem headers that I had jet-hoat coated in case I added a nitrous setup. Trying to decide if it makes more sense to just install the oem headers (and gut the cats) with the realization nitrous is in my future.

MisterSkiz

iTrader: (2)

I was wondering this myself as well....wonder if anyone (Sikky, PPE) has put them up to a flow bench....

mikellucci

iTrader: (56)

I was just reading up on past Nitrous threads and it got me thinking about the runners seeing that aftermarket headers pose issues on a high shot whereas the stocks seem OK. If the stock runners are decent enough to flow with NOS the cats have to be the real bottleneck perhaps?

I'm in a position right now where I can swap my stock manifolds in pretty easily or keep the Sikkys...not sure what I'm going to do.

H60Driver

Bump for curious owner wanting to know the difference between sikkys and catless stock?

rmillsISF

I can almost promise you the 30HP+ gain is 99% from removing cats. 2gr engine is the same way.

flowrider

iTrader: (9)

^^^^The attached graph says different. The JoeZ is a much improved exhaust vs. stock and does remove cats, but is worth 20 HP over stock.

Lou

occxlr8ed

^ uh where is the stock decatted headers on the graph??

MK4Sup_isF

iTrader: (10)

Joe Z is a cat back system because the exhaust pipes start behind the main cats. It removes secondary cats only, which are much less restrictive than the main cats

mikellucci

iTrader: (56)

This all started discussing Exhaust MANIFOLDS and the Main/Primary cats removal. Not sure why we are talking secondary cats as the information is clearly out there.

I'm assuming no one really knows the answer to the original question and the gains are likely greater just going with a Sikky or PPE header. However, on a high nitrous shot aftermarket headers prove deficient vs the stock manifold runner design. A decatted stock manifold could prove to be a better choice for those of us running or considering a nitrous setup.

flowrider

iTrader: (9)

Sorry, I misunderstood. You're talking about removing the primary cats. If that were to happen, the stock manifolds would require major surgery since the primaries are part of the manifold. I'm not aware of anyone doing this.

Lou

MK4Sup_isF

iTrader: (10)

Not really hard once you have the manifolds off the motor. You can just chip at the inside of the cats and clear up the inside. This has been done countless times on other cars

I8ABMR

Will the car pass a smog test with secondary cats out ?? Are these exhausts for "off road use" only . Many members have exhausts and we have cars that are now 5-6 years old. Im sure some had to go through smog

VtotheJ

iTrader: (2)

This is interesting. Many people like myself have removed secondary cats but not primary cats. Removing the primaries would definitely cause a CEL, not sure how you'd fix that...maybe the same way you do it with aftermarket?

mikellucci

iTrader: (56)

Any o2 sim should correct the CEL just as if a pair of sikky or ppe catless headers were installed.

It's pretty easy to DECat any header catalytic converter even on the vehicle. I've seen it done many years ago with a pry bar and torch.

I have a set of oem headers that have been jethot coated:

etohprn247

OMG you guys are Hardcore Ballers or your a train mechanic ....With CEL issues and having to drop half or part of engine to install/modify primary cats etc.( in our ISF specifically) and if issues arrive or reselling, yall just pay another $1k to reinstall headers back to stock? Mikelucci...did you remove catalytic converters just to jetcoat them, man that's a lot of work ;P