Gutted Header & Front Pipe - Dyno Inside

[churchx]

pros:
- probably 60-80%? gain of aftermarket catless ones
- cheapest performance oriented "upgrade" (if one leaves aside need to get some ECU upgrade to disable CELs)
- 100% stock looking, for where there are visual checks during MOT testing
cons:
- less performance gains. If NA tuning already is expected to be limited & expensive, why not try to get most what's possible for not that big of price vs some other possible mods?
- no completely stock & with functioning cat header left to bolt back, in case if it's needed to pass MOT or to be put back prior selling off car

[Irace86.2.0]

If this is collapsible then I would shove this in where the cat was like deploying a stent in an artery versus trying to weld in a pipe if I was looking to get better flow while remaining stealthy.

[bfrank1972]

On the expense side, a person would really be 'splitting hairs' vs a used aftermarket header. You can pick up a good aftermarket header used for around $400+/- some, and then you still have the OEM header intact if you want to return it to stock (or sell it for $50-$100). Paying someone to remove the cat and weld in an new pipe will be a couple hundred bucks at least. If you do the screwdriver + hammer method, that works, but flow is even less ideal and I hear it sounds pretty bad due to the resonance in the empty cat area.

[nikitopo]

Are you guys referring to the first post? Difference is 12whp and most of it is from the tune (~8whp). It is not from the gutted header and the front pipe. Aftermarket catless headers might give more, but it is because of the better header design and not the catalyst. Don't try to mix apples and oranges.

[bfrank1972]

Originally Posted by nikitopo

Are you guys referring to the first post? Difference is 12whp and most of it is from the tune (~8whp). It is not from the gutted header and the front pipe. Aftermarket catless headers might give more, but it is because of the better header design and not the catalyst. Don't try to mix apples and oranges.

Well part of it is the cat - the big thing with headers on these cars is removal of the torque dip. The first post shows that a decatted stock header can do that - a tune by itself can't do that to the torque dip. That said, for marginally more money you could have a better design, and a spare stock header.

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[ApexEight]

Originally Posted by nikitopo

Are you guys referring to the first post? Difference is 12whp and most of it is from the tune (~8whp). It is not from the gutted header and the front pipe. Aftermarket catless headers might give more, but it is because of the better header design and not the catalyst. Don't try to mix apples and oranges.

But the curve looks much better. Idk if that has to do with just the tune, but I would imagine the gutted cat helped with that. The curve is more important than peak gains.

[Irace86.2.0]

Originally Posted by bfrank1972

On the expense side, a person would really be 'splitting hairs' vs a used aftermarket header. You can pick up a good aftermarket header used for around $400+/- some, and then you still have the OEM header intact if you want to return it to stock (or sell it for $50-$100). Paying someone to remove the cat and weld in an new pipe will be a couple hundred bucks at least. If you do the screwdriver + hammer method, that works, but flow is even less ideal and I hear it sounds pretty bad due to the resonance in the empty cat area.

Cost is one factor. I’m not an advocate of removing the cats, yet regardless of my opinion, some may wish to remove the cats, but are afraid to run catless. Fines in California are really expensive. A way to reduce the risk is to gut the cat or weld in a straight pipe. Welding in a straight pipe won’t fool an officer looking for a straight pipe (maybe I’m wrong, maybe the heat shield would cover the section that was modified). A gutted cat would be about as stealthy as someone could take things.

Back to the mod, I wonder if boring the cat would be better to be able to press fit a straight pipe in the center. Basically leave the surrounding cat intact. Ideas?

[nikitopo]

Originally Posted by bfrank1972

Well part of it is the cat - the big thing with headers on these cars is removal of the torque dip. The first post shows that a decatted stock header can do that - a tune by itself can't do that to the torque dip. That said, for marginally more money you could have a better design, and a spare stock header.

Originally Posted by ApexEight

But the curve looks much better. Idk if that has to do with just the tune, but I would imagine the gutted cat helped with that. The curve is more important than peak gains.

Sure gains in the dip area are much better. Personally, I never worried about the torque dip. I guess it is the way I drive the car and my focus on a track oriented setup (peak gains at high revs).

[Harey]

Originally Posted by nikitopo

Sure gains in the dip area are much better. Personally, I never worried about the torque dip. I guess it is the way I drive the car and my focus on a track oriented setup (peak gains at high revs).

Not a single corner falls below 4750rpm? They say the fastest way around a corner is most of the time to stay in the higher gear.

[nikitopo]

Originally Posted by Harey

Not a single corner falls below 4750rpm? They say the fastest way around a corner is most of the time to stay in the higher gear.

Depends where you drive. If you want to go fast on a track or on an autobahn without speed limits, then you'll be above 5000rpm. If you want to go fast on a country b-road, I agree that many times you'll be below 4750rpm. However, you are already going fast and going faster means you don't obey any speed limits and you take too much risk to lose your car. This is not an AWD car and requires a lot of skill and risk to go really fast in anything than perfect tarmac. The only area I can think mid-torque improvement can help is on drag racing from stop.

[Harey]

Originally Posted by nikitopo

Depends where you drive. If you want to go fast on a track or on an autobahn without speed limits, then you'll be above 5000rpm. If you want to go fast on a country b-road, I agree that many times you'll be below 4750rpm. However, you are already going fast and going faster means you don't obey any speed limits and you take too much risk to lose your car. This is not an AWD car and requires a lot of skill and risk to go really fast in anything than perfect tarmac. The only area I can think mid-torque improvement can help is on drag racing from stop.

I take mine to a race track (Phillip island, Australia) and there are at least 2 corners that rpm drops into the low to mid 4krpms.

[nikitopo]

Originally Posted by Harey

I take mine to a race track (Phillip island, Australia) and there are at least 2 corners that rpm drops into the low to mid 4krpms.

If your rpm's are so low and you are in the correct gear, then you need to change your final drive ratio to a shorter one. Maybe a 4.55 will match good on such track. It always depends the track. It is not optimal to solve your issue by eliminating the torque dip. No matter how good is the curve in the mid rpm's, you won't get the maximum acceleration. You'll need to have the revs on the higher end area for the best acceleration.

[Lantanafrs2]

Sheesh I'd rather swap a header than rear end gears

[ApexEight]

What's that guy's deal lol. Better change your final drive bro, he says you need to