GTA turbo catalytic converter fitment - Much power loss?

When my 1988 GTA turbo was imported to Australia the owner was required to fit a catalytic converter.

I purchased the car after the cat was fitted.

Not having driven a non-cat GTA turbo I do wonder how much the fitment of the cat has affected performance.

Can anyone shed some light as to roughly how much the power output would have reduced.

[mettersl]

I can't comment too precisely, but on an A610 you gain about 20 BHP by removing the standard CAT and raising the boost a little- for example the ART boost controller- from 250 - 270 BHP . Beyond that greater power outputs need serious work (and are getting close to the gearbox maximum torque anyway).
On the GTA it will be hard to tell the likely loss as it depends how much work was done.
There is an EU cat version (D502, inc Le Mans, not sure if there is a power loss at all) and a Swiss version- lower power .
From memory the Swiss GTA Turbo was rated at 170-180BHP- this has a different Cat from the rest or Europe, a Lambda sensor and a Cat temperature sensor.
To guess more accurately factors such as how big is the CAT, was a Lambda sensor fitted at the same time, was the ECU changed to EU or Swiss spec?
I'm sure that Stephen will be able to tell you for sure what the D502 output (Cat GTA turbo) should be in both EU and Swiss versions.

You should be able to get most of this back by upping the boost I would expect.....

If the exhaust size is taken out to 3" with a cat to match, and straight through resonator instead of the std muffler, more likely a power gain would result, despite the cat. My guess is the addition of the cat would have made little difference.

The point of most restiction is actually the inlet to the exhaust turbine which is much smaller than a square inch.

I would suggest there is probably more power lost via the std muffler than a modern cat. If you get rid of the original muffler for a new oval single outlet resonator, you will also lose approx 10Kg from the back of the car, saving the std muffler mounts from breaking regularly.

Doesn't look as pretty as the twin pipes, but is much cheaper and works well.

What are the South Australian rules regarding mods of this kind?

[mettersl]

From the site.....D502 includes le mans and standard GTA's with a CAT.

1990 saw the launch of the special edition wide bodied GTA 'Le Mans'. Otherwise identical mechanically to the V6 Turbo, the engine was fitted with a catalytic converter and power was reduced to 185BHP.

And that isn't the Swiss one either.....

Sounds like you might want that resonator exhaust....and more boost...