Decat questions

[drew.h]

Half of the stuff I read says no and half says yes, so lets try again with my specific car:

If I de-cat my '93 Chimera 400, would it pass an MOT?

Also, is there an idiots guide to DIY removal, with pictures (not that I'm an idiot, or literate)?

TIA,
Drew

[MuffDaddy]

I'll give you a simple and conclusive answer as soon as my car returns. It's currently has a fuse box issue, slipping clutch and blown manifold gasket so I figured whilst the manifold was off it made sense to remove the precats. Should have it back next week. Now I'm not a fan of loud, I'd rather have a decent tone at a reasonable volume. I'll report back when I can.

[V8 Animal]

Im considering removing the precats when i remove the manifolds in a couple of weeks.
But can't make my mind up to as the exhaust noise changes apparently and i don't know weather i'll like it.
And theres no turning back once you've done it.
Benefits as i see is lower under hood temps well the cars been ok for 13 years.
So undecided.
V8 Animal

[Tvrjock]

Hi Guys
Have removed my pre-cats and also have a sleeved exhaust, i was running the car with the sleeved exhaust before i removed the pre-cats and it is not much louder but does have a deeper tone and revs much more freeley as for the temp under the bonnet it does improve this much more , the car runs at 65C and not 70, cooling time when the temp has gone up in traffic is also improved she cools a lot faster.
Graeme

[Chimjunkie]

Is the OP asking about removing main cat? or precats? I removed my precats and the exhaust did increase in volume, but not too much. Dont forget that removing the main cat will make the car smelly to follow

[slideways]

I've just decatted mine also it had an offords sleeved exhaust prior to the decat now its fkin loud basicly its a straight through system
and im concidering a stainless exhaust with the centre box as standard
Rich

[thenick]

drew.h said:

If I de-cat my '93 Chimera 400, would it pass an MOT?

I can't believe no one has yet answered the only question he asked?!

In short: No it won't... You'll need a friendly MOT tester (plenty of them around)

[drew.h]

Thanks for the replies.

So from what I can conclude from these and other posts, removing the pre-cats is OK for MOT and will reduce engine bay temperature. If I wanted no cats at all I would need a replacement to pass MOT and change the resistor accordingly

Is there a guide anywhere for removing the pre-cats? Also what value of resistor should I have now and what should it be changed to if I remove all the cats (3.7KOhm suggested in another post)?

[dhf]

My 450 passed the MOT with its pre cats removed as did my current 500.it is now in ireland where we have a stricter test which it has had no problem passing.i now have a straight through system and just replace the Y piece with cat for the NCT(MOT) and change the tune resister back to its 'cat in' setting.i do however make sure the engine is hot before it is tested.
As to diy removal which i have'nt tried,pre cats as per factory advise,remove manifolds and stick a broom handle down to dislodge them.they weren't very keen to discuss this !, main cat is a split,remove and reweld job.hope that helps.

[slideways]

the hardest part of decatting the manifolds is getting them off, plenty of info in the search menu for this,i did mine from above and underneath the car, make sure you use the correct size spanner i think its 9/16 i tried a 14mm openended and it was a tad to big and i rounded one of the heads(you really dont want to do this). one thing replace the bolts with arp bolts you will be glad you did. you will need a hammer and long screwdriver or similar, face mask and gloves and a vice then bash away again do a search loads of info,oh and take out the lambdas with a 17 mm long reach socket with a slot cut in so you can thread the wires through, made mine with an angle grinder it took a couple of minutes.
you will only have to use the green tune resistor if you take out the main cat in the Y piece and dont want to use the lambdas,
I still run on a white resistor with lambdas but full decat, the engine seams to breath a lot better than standard
Rich

[GreenV8S]

slideways said:

make sure you use the correct size spanner i think its 9/16 i tried a 14mm openended and it was a tad to big and i rounded one of the heads

The bolts are notionally 9/16" but in practice are always a bit of a sloppy fit. 14mm is a fraction smaller and usually fits nice and snug. You definitely don't want to be using open ended spanners on them, always use a ring spanner.

[Dave81]

Bought my car (Standard 400) back in Feb. Had the Pre-Cats removed in June. The difference is that it make the car slightly louder with a slightly deeper note (in a good way, still in the sense of the normal sound). The main benefits were that the car seems to be much more responsive on the throttle with the blockages (precats) removed and the temps have dropped.

In July i had Offords do there magic. The sleeved exhaust had changed the note/tone of the noise. I personally don't like it when its cold (too much like a tug boat), but when its warm/hot it sounds amazing. Its also amazing how different it sounds between being revved on the spot and being put under load on the road.

The pre cats to me are a no brainer......with all the benefits just get them removed.

The sleeved exhaust is down to personal taste. Would i have it done again........yes, its bloody addictive going through small villages with the pops and bangs....
Also when you go back to listen to a standard car it just seems to quiet.....Mine's now perfect!!!!

Never had the car tested before but at the Griff Growl my car with the above done, gave out a 112.3 db. (just incase people were wondering about track days).

Also i have heard that removing the main cat, removing the gauze and replacing can give an undesirable tinny sound to the exhaust. If you wan't to go complete decat, id invest in a proper 'designed to be' decatted y piece.

My 2p's.
Dave

[blitzracing]

drew.h said:

Thanks for the replies.

So from what I can conclude from these and other posts, removing the pre-cats is OK for MOT and will reduce engine bay temperature. If I wanted no cats at all I would need a replacement to pass MOT and change the resistor accordingly

Is there a guide anywhere for removing the pre-cats? Also what value of resistor should I have now and what should it be changed to if I remove all the cats (3.7KOhm suggested in another post)?

You dont need to change the resistor, (yours will be 3.7k at the moment) just running the catalyst fuel map, without physical cats is just fine, and best MPG as well. The only reason to switch to a non cat map is to reduce the snatching at low rpm some cars have, but it richens the mixture somewhat, so you will have now to sleep with the MOT tester!

Mark

[dhf]

visit www.v8enchancements.co.uk and talk to Clive. re decat Y piece and Tune Resister.

[Meatball]

dhf said:

visit www.v8enchancements.co.uk and talk to Clive. re decat Y piece and Tune Resister.

Anyone know what the power increase is losing the main cat?

What increase will the v8enhancements y piece have over the above?

[dhf]

Ask the man from....V8 enchancements !

[dhf]

p.s. its worth doing judging by the way my 5 litre goes and sounds....

[Chimjunkie]

Meatball said:

dhf said:

visit www.v8enchancements.co.uk and talk to Clive. re decat Y piece and Tune Resister.

Anyone know what the power increase is losing the main cat?

What increase will the v8enhancements y piece have over the above?

In a recent thread Clive recons 5 bhp without any tuning for removing the cat alone. Not sure if the decat manifold itself would have any effect. Only Clive has the answer!

[dogbucket]

GreenV8S said:

slideways said:

make sure you use the correct size spanner i think its 9/16 i tried a 14mm openended and it was a tad to big and i rounded one of the heads

The bolts are notionally 9/16" but in practice are always a bit of a sloppy fit. 14mm is a fraction smaller and usually fits nice and snug. You definitely don't want to be using open ended spanners on them, always use a ring spanner.

although on the one you cannot get a ring spanner on an open ended is the only option. A Snap-on 14mm 'Flank drive plus' wrench is worth the investment as it grips the sides rather than the corners even using its open end.

[Meatball]

Chimjunkie said:

Meatball said:

dhf said:

visit www.v8enchancements.co.uk and talk to Clive. re decat Y piece and Tune Resister.

Anyone know what the power increase is losing the main cat?

What increase will the v8enhancements y piece have over the above?

In a recent thread Clive recons 5 bhp without any tuning for removing the cat alone. Not sure if the decat manifold itself would have any effect. Only Clive has the answer!

Jon, I cant get my head around this - Do you mean taking the main cat out gives you another 5 bhp over keeping the cat in or changing to the v8d y piece will give you an extra 5 bhp?

Its been a long day.