question about cat removal

[werewolf]

Let's say you're considering a pulley upgrade. Or the soon-to-be-released blower upgrade from Whipple. And you figure, the last thing a supercharged motor needs is a choked-up exhaust. To hell with exhaust tuning/scavaging theory ... we're blown, baby ! :biggrin

So maybe one starts to think about removing the catalytic converters ... I don't know ... to maybe install the long tube headers from FRPP/Borla. For off-road only use, of course.

Well the workshop manual shows the (now commonplace) 2 pairs of O2 sensors ... one pair before the cats, called the "upstream heated oxygen sensors (HO2S)", and another pair of downstream "catalyst monitor sensors (CMS)". The question is, will disconnect/removal of the CMS sensors cause a Check Engine Light (CEL) condition? And will the computer go into some sort of "limp home" mode because of an emissions problem?

The answer to the CEL question for Mustangs used to be yes ... you needed to connect a little trick circuit to the downstream O2 sensor plug, to trick the PCM into thinking the cat was still connected and functioning.

Any such thing required for the Ford GT?

 

[FGT4me]

You have to do the same thing with the Viper (down stream sensor) to trick the computer.

 

[Jason Watt]

Thats the route I'm going, but I wonder how loud it will be...

 

[werewolf]

Thanks guys.

Has anyone actually removed or gutted the cats on the GT yet?

 

[SLF360]

gutted cats, good cats !

Thanks guys.

Has anyone actually removed or gutted the cats on the GT yet?

yes. Baron has :biggrin

 

[PILOTJPW1]

Cats

Yes, I believe he gutted them by cutting them in half and then removal of baffle and then rewelding them. I am interested in removing them but need way to bypass sensors.

Can you give more info on parts needed to trick the O2sensors?

 

[barondw]

1. Yes the cats are restrictive and you can gut them (see second thoughts in item #6) or remove them depending on how you will get past emissions testing. Varies by individual state here and I forget how MOT works in the UK or in Europe.
2. The cats are more tricky than difficult to remove and replace, especially the right side (driver's side in UK). There is significantly less clearance. Look for a previous post by me outlining how to remove them and replace them including disconnecting the battery. The chance of shorting out the electrical system is very real and should not be ignored. The big pain is removing the belly panels and raising the car. About 2 - 3 hours to remove and replace cats, conservative estimate.
The cats appear to be titanium and are a bitch to weld together after they are gutted.
3. Leave the O2 sensors alone. Install a resistor, Viper guys and any decent speed shop know how to do it. Install on the O2 sensor after the cat on the return line and the check engine light will not come on. Obviously I cannot speak about the European version but I would think it would be the same. This gets the car past state inspection in New York.
4. The combination of gutted cats and a smaller pulley provides 25-30 RWHP +/-.
5. No I do not know the size of the pulley or belt. I have asked and am still waiting for a response which may or may not be forth coming as Stefan is aware of.
6. As to sound there is a significant difference after the cats are gutted. The car loses its quietness and becomes throatier and louder. Can be noticed inside and outside at all speeds. Due to harmonics makes using 6th on a trip a problem unless you are going more than 95 mph. The louder noise would make me think twice about doing it again and I don't think I would.

If you use the car on the track cooling is a major problem and the optional tran-axle cooler is a must. Hopefully there are still pictures posted if not let me know and I can re-post them.

However, engine temps will still get close to 240 which is a danger point this happened in June in 90 degree F weather. Later track dates in August presented less of a problem as the air temp was 70-75 degrees F. Even tried removing the rear license plate / number plate to get better air flow.

Also for track use get the front brake ducts opened, mine will be done in the spring, to allow better cooling. Brakes will last significantly less than 10,000 miles if used for track and road. Recommend having a spare set of pads and even rotors for track use. 10,000 + should be attainable for street driving only.

If go the Whipple route be sure to have the car dynoed before and after by an independent source and not the vendor.

Dave

 

[Jason Watt]

Dave,

I cannot believe that cats AND pulley is only worth 25-30HP...
Are those figures you got from dynoing yours before and after the mods, or is your car now 580HP, and perhaps could have been less than the claimed 550 as standard??

 

[barondw]

101
The car originally dynoed at 551 rwhp and 472 rw torque SAE corrected. That's it. Verified on 2 dyno's including one operated by a very prominent racing team.

Keep in mind all the numbers I post are rear wheel (rw) not crank/flywheel which is what is advertised and what you cite as the 550 number.

To put in flywheel numbers stock the car did 551 rw = 648 flywheel. Now it does 575/580 RW which is 676/682 flywheel.

John Coletti's car had the same mods and a re-flash at did 590/592 rwhp. So the numbers don't seem to be strange.

As to the pulley I believe they resized it when the changed the original advertised (flywheel) hp from 500 to 550. Thus how much more can you get? There is a point of dimishing return.

Dave

Dave,

I cannot believe that cats AND pulley is only worth 25-30HP...
Are those figures you got from dynoing yours before and after the mods, or is your car now 580HP, and perhaps could have been less than the claimed 550 as standard??

 

[werewolf]

Thanks for the great info Dave!