Thread: Do all Pumas have a cat converter??

Not being overly mechanically savy..cat converter or no cat does it really affect the engines performance..my 89 zook has 1, so they have been around for awhile.

As I understand a cat can act as a restriction...so removing it allows the turbo to spool up faster and better economy...whether or not that is true Im not sure but did notice a better tone and a litle better performance by losing the silencer with a straight thru pipe in its place...

Originally Posted by dawsey

Not being overly mechanically savy..cat converter or no cat does it really affect the engines performance..my 89 zook has 1, so they have been around for awhile.

It's a pollution control device, reduces amount of nitrous oxides in the exhaust (NOx).
They have been fitted to most cars since 1983... so living behind the times much ;-)
Generally frowned upon to remove them, due to emissions issues.

Originally Posted by Tikka7mm08

As I understand a cat can act as a restriction...so removing it allows the turbo to spool up faster and better economy...whether or not that is true Im not sure but did notice a better tone and a litle better performance by losing the silencer with a straight thru pipe in its place...

Cats come up to temp before they are effective, so not really working in a pollution control capacity until operating temp. Some cars introduce oxygen into the cats to aid heat up time, to warm the catalyst. Yes they are a restriction, but if we want to split hairs, we'd all be running turbo dump pipes with screamer pipes so we have no restriction at all!
Generally with a turbo system (in petrol at least) you want as little backpressure in the exhaust as possible. Similarly as little intake resistance as possible.

It is pretty much the same on diesel turbo - less restriction = better response.
I would be interested if somebody, who used the bypass (kit or otherwise) and at the same time has ECU remapped, did any particular changes to programme where the fuel trim is controlled? I am assuming they replace the sensor back when bypass is created. Or, is it negligible at all? I have never considered that option before - no need really, just being curious.
Cheers.

Performance difference will not be noticeable. The factory engineers make sure the cat isn't a bottleneck.

I seem to recall that having too little restriction might also be an issue, because it might allow the turbine blades to overspeed under certain conditions. I don't know what issue that causes, but I'd imagine production model turbos are designed to specific flow rates etc...

Originally Posted by Dougal

Performance difference will not be noticeable. The factory engineers make sure the cat isn't a bottleneck.

As I have done my mods progressively I would disagree. The cat is quite a restriction and does cause heat build up in the cylinder head whilst restricting exhaust gases. A decat will allow the engine to run cooler and the turbo to spool up noticeably quicker. I found that if did a lot of short journeys the motor would become sluggish, however after a 50/100 k run performance would be restored.I attribute this to the cat becoming coked up. Factory engineers are in my opinion are more interested in obtaining type approval.

Originally Posted by BilboBoggles

I seem to recall that having too little restriction might also be an issue, because it might allow the turbine blades to overspeed under certain conditions. I don't know what issue that causes, but I'd imagine production model turbos are designed to specific flow rates etc...

Gary at Alive tuning advised me to retain the standard back box for that very reason, stating that it was a common reason for turbo failure ( over speed ) .