hey guys i have a 1992 xjs V12 if i pull off all my catalytic convertes how much horsepower would i free up? and would their be any warning lights pop up on my dash

 

US cars from what I have seen have a catalytic element in the downpipes. Lost of people remove this from all 4 pipes.

If your Cats are working properly and not blocked removing them (Not the ones in the PIPES) will have very little difference on a stock engine.

To increase the power on the 5.3L there is a couple of things you can do.

Remove the Cat elements in the downpipes.
Increase the size of the trumpets on the air filter boxes
Fit a cold air intake, this can be over the radiator like the TWR cars.
Fit K&N filter elements.

Here is a pic of what TWR did for CIA on the XJS. You can just see it in the bottom right of the pic.

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Warrjon,

I've read the published specs for the US catted 5.3 is 30hp lower than the same model in EU config ( no cats ). Was that incorrect?

 

EU model had different valve clearance and compression ratio of 12.5:1, instead of 11:1 for US model. I removed all cats on my '82 HE and gained better power, but only because my lower cats were half melted. That power increase also came at a cost of awful fuel consumption, due to lack of back pressure. Right now I plan installing generic converters in place of the empty lower units. Also I will do what Warren suggested above, for noticeable power gain.

 

Isn't it more likely that your bad fuel mileage is from poor fuel/air ratios since your lambda sensors are reading nothing?

 

SWEET so iF i pull all of my cats off, i will get 30 HP? but will i get any check engine lights on my dash

 

My cat- and lambdasond-free 89 has according to its papers 295 bhp which would result in 302 ps. Just a 'TMYK' fact...

Models with cats had around 268 hp (272 ps) here in Germany (mine is a UK import).

 

It is correct, at least for pre facelift V12s anyway. The US version has a lower compression ratio and cats, etc.


Greg

 

No, as Warrjon explained, that will not do much. You need induction changes as well as the European spec compression ratio.


Greg

 

An engine needs air to create power, fuel is then added to make correct AFR. Around 12 to 13:1 for power (max torque) in a NA car and 14.7 to 15:1 for cruising leaner if the engine is resistant to detonation.

Just removing the Cats will result in very small power gains. To take advantage of the free flowing exhaust you need to get more air (actually OXYGEN) into the engine.

EU and Aussie spec cars had higher CR due to the higher octane fuel available in those markets, this makes a HUGE difference as the additional Quench acts to cool the charge as it's Squished helping to reduce detonation.

My Australian spec 1989 with O2 sensors and Cats is listed at 213kW (284hp). TWR managed another 30hp from the 5.3L with CAI, larger intake trumpets, K&N Filter and free flowing exhaust.

As far as I can tell all Jaguar did to adjust the CR for markets was to change the head gasket thickness. The parts catalog lists a couple of different part numbers.

 

I have often wondered and asked people, but nobody seemed to know. This seems a very sensible way to do it, can anyone 100% verify? I have a friend who wants to up his CR from US spec to UK.
Greg

 

Different pistons!


Cheers
DD

 

Is that definite, Doug? excuse my asking.
Greg

 

What happened to that 5 degree advance?


https://www.jaguarforums.com/forum/x...ssible-128515/

 

Doug is right there is standard and high compression pistons listed for the HE.

 

only saw standard for my 5.3... jaguar-sport high and low...


oh any one need the standard VE numbers for the 5.3

 

No point in going above 5,500 RPM then! Where did you get these figures, Jonathan? Are they for the USA spec engine?
greg

 

This makes those big throttle bodies look WAY more attractive!

 

The stock throttle bodies flow 600fcm EACH, putting bigger ones on is a total waste of time.

My 6.7L will run stock TB's with just a profile on the inlet and velocity stack.

 

Kirby Palms book has a section talking about increasing the airflow, minor modifications to the air filter housings and milling a radius on the throttle body outer side to smooth the flow.