Chimaera Pre-cats

[chim326]

Can anyone tell me which is the easiest way too remove the pre-cats from the manifolds. Don't want to by new decatted manifolds as i've just had to lay out for new cam (Maybe later!). Also any tips on setting up Vernier timing on cam chain timing gear.
Thanks in advance. Steve.

[GreenV8S]

They might fall out, or you might need to take a chisel to them. They're tough little b*ggers!

[chim326]

Thanks Pete
Will every little speck come out with a chissel or does it leave residue and some pre-cat stuck to the outside of the manifold housing?
Thanks
Steve

[aerospoke]

Mine required atleast an hour of chiseling and drilling each!
When you got them out you can scrape the remains from the manifolds inside with a sharp screwdriver or file.
Try not to loose too much pieces of your knuckles an have fun!

Cheers Jens

[GreenV8S]

chim326 said:

Thanks Pete
Will every little speck come out with a chisel or does it leave residue and some pre-cat stuck to the outside of the manifold housing?
Thanks
Steve

If they're well attached then it's possible that parts of the cat will stay attached to the manifold. Up to you whether you chisel them off or leave them; if they're well attached then they aren't going to do any harm IMO.

[chim326]

thanks fellas took me 2 hours and no knuckles left! removed every spec even though they were in perfect condition after 60000 miles.
cheers steve.

[TVRobin]

What is the MOT implication of removing the Pre-Cats?

[pupp]

TVRobin said:

What is the MOT implication of removing the Pre-Cats?

Should still pass provided main cat functioning properly (and warm). Have heard of completely decatted cars passing... (not sure I'm entirely believing 'though)

[TVRobin]

Does it make a big difference to the power of the engine? Mine had a phyically damaged Lambda sensor that could have been damaged by the pre-cat breaking up! It might be worth removing them to save the £80 sensors!

[GreenV8S]

TVRobin said:

Does it make a big difference to the power of the engine?

No, not unless the precats are damaged and are blocking the exhaust.

[pupp]

Although I've not measured the effect, it certainly lowers temperatures in the engine bay. Which is beneficial.

[RichardD]

GreenV8S said:

TVRobin said:

Does it make a big difference to the power of the engine?

No, not unless the precats are damaged and are blocking the exhaust.

Peter, assume you mean a a small difference? I've been told about 2% ish, so about 6 bhp on a good 500 engine. Assuming this general RV8 tuning rule of £100 per bhp, then its a very good value for money mod

[GreenV8S]

You might get a couple of BHP out of it, but that isn't enough to measure reliably let alone be noticeable to the driver. If you've got the manifold in your hand and willing to spend a few hours hacking the cats out then there's no particular reason not to, just not something I'd go out of my way to do.

[V8 Kieran]

I noticed zero difference in performance (one OE had split so s/s pre-catless replaced) however the sounds improved - slightly louder in the cockpit and a nicer tone - although this might be due to s/s rather than pre-cats ...and shiny stuff in engine bay, which is nice!

(somewhat different change with the 'cherries' - mwoah-ah-ah-ah )

[chrisA]

Sound like a nice easy mod (Which is great).

How different is the sound with the standard de-pre-catted manifolds?

Is it necessary to replace the gaskets when you remove the maniflods?

[GreenV8S]

chrisA said:

How different is the sound with the standard de-pre-catted manifolds?

Negligeable difference to sound or power, unless the precats are blocked. Yes you will need new gaskets if you take the headers off.