Thinking of Decatting...

[Matzo]

Interested in hearing the pros & cons from anyone who's decatted their griff.

Does it really improve the noise, throttle response & make it more free revving ?

Also when the MOT comes around how do u get it thru ??

Can u recommend where to get it done properly ??

Wud love to hear anyones personal experiences.

[mongoose]

hi matzo,i had mine de-catted(pre cats only)a few months ago and it was well worth it.its made the bottom end smoother and easier to drive around town.the exhaust noise is slightly better without being o.t.t. and the car still passes the emmissions as the main cat is still in place.its worth mentioning though that my car is a 500hc which are less tractable at the bottom end,so i think your main improvement is in the sound dept only unless you have a hc spec 500? as for power increase,forget it,probably in the region of 1 or 2 bhp if at all-you wont notice(no loss though).all the afore mentioned were assured to me by mark addams when we discussed it some time ago,and he got it all spot on as usual!

[Matzo]

Thanks Mongoose - Is it easy to take the pre-cats out ?

[simpo two]

'Does it really improve the noise'

Yes, greatly.

'throttle response & make it more free revving ?'

Yes, greatly.

'Also when the MOT comes around how do u get it thru ??'

You can't, not properly.

'Can u recommend where to get it done properly ??'

The MOT or the operation?

[Matzo]

Both !!

[mongoose]

hi again matzo!in theory its quite simple to take the pre-cats out,but there are one or two little points worth bearing in mind.you can do it a couple of different ways,either cut them out or smash them out.i preferred the smash em out method as i didnt fancy having my manifolds re-welded.the cats are apparently harder to smash than youd think though.possible bolt shearing problems can arise when removing the manifolds as well.also,i was warned by the specialist i used about passing the emmissions etc,but m.a said it should be ok and it was,(this may be because its a hc,im not sure,and mileage and engine condition must surely play their part)hc's run slightly on the lean side compared to std 500 according to mark.unless your handy with the spanners id advise to take it to a specialist.-cheers mv

[Moto]

This is interesting as I have been looking at decatting but by taking out the main cat and leaving the pre-cats. Anyone understand what difference this would make ??

Also what's the difference between the HC and non-HC engine. How do you know what you've got - is this the 320bhp / 340bhp versions ?

[simpo two]

Moto said:

Also what's the difference between the HC and non-HC engine. How do you know what you've got - is this the 320bhp / 340bhp versions ?

High-lift cam. All 500s are HC. The drop to '320'bhp is done via the ECU.

[B19GRR]

Where do the pre cats lurk and for that matter the main cat?

For future reference you understand

Cheers,
Rob

[mongoose]

in reply to questions in order:-if you look at the plenum on top of that lovely engine is says 500 or 500hc.this isnt idiot proof however as some 500's have had a hc badge put on them.in my handbook that came with the car the spec sheet is for a 500hc car and there are no other engine options included,so presumably if yours is std 500 then itll just say 500.the best wat to tell is by drivig comarisons imho but obviously thats not allways possible.as for the cats,theres one in each manifold just after the four pipes go into one,(pre-cats)and one in the fat part of the 'y' peice(main cat).cheers-mv,

[simpo two]

B19GRR said:

Where do the pre cats lurk and for that matter the main cat?

Easy to spot - the main cat is where the pipes join - you'll see the canister about 5" across in the vertical section. The precats are in similar but smaller cylinders on each side and horizonal - you'll see what I mean.

[Ballistic Banana]

I as planning to do this to mine at some point.
But the amount of comments I have had about how nice it sounds with just the straight through pipes in the rear box conversion and decided not to bother.

Saves maybe the emmisions problem cropping up too, that would always be at the back of my mind come MOT time, of course unless you are a bit friendly with your MOT Tester

BB

[budd]

My Griff 500 is de-catted,(both pre and main) and it sounds wonderful, also made a massive difference to power output and delivery, however the O/E cat had collapsed and was restricting exhaust gas flow so don't expect big gains if replacing a good cat.
Used an ACT replacement pipe knocked out the precats (easier said than done) changed the ECU chip and tune resistor(both supplied by TVR), and I've had no problems in the 18 months since I did the work(except the extra power killing the clutch)but a new AP racing item fixed that.
The MOT is likely to be the main problem with this mod, it is possible to refit the O/E cat at MOT time then swap back when the ticket is obtained but this is a pain and would take the best part of a day to complete, a much better option is to find a friendly tester, which what I did.He had the emission test done before I arrived! great service that man.

[B19GRR]

Has anyone had Blackthorn Auto Catalysts refurb their Y section with a 200cell psi rather than the 400cpsi?

www.autocats.com/html/tvr_frame.htm

Not sure if removing the pre-cats is part of the deal though.

Cheers,
Rob

[Matzo]

Just wondered... If u take out just the pre cats... Does that put any strain on the function of the main cat or shorten its life ???

Also.. If u smash all 3 of the cats, Is the guy driveable or do u really need to reprogramme the ECU ??

[2 sheds]

Removing just the pre-cats is now common practice, we recommend fitting non reversal cone in the cavity once cat is removed, if you don't want to shell out on long primary manifolds.
the main cat will cope with emmisions, also gives the car a "crisper" note.
Tim

[alans]

2 sheds said:

Removing just the pre-cats is now common practice, we recommend fitting non reversal cone in the cavity once cat is removed, if you don't want to shell out on long primary manifolds. the main cat will cope with emmisions, also gives the car a "crisper" note. Tim

Hi Tim, thinking of doing my precats, what is a "non reversal cone"?

Alan

[2 sheds]

When we supply decatted manifolds, they are cut open cat removed and fitted in the same position as the old cat we fit a cone to 1 reduce effective bore to appropriate size and 2 the cone reduces reverse pulses, acting like a one way valve, this will help to compensate for the very short primary pipes.
Tim

[Matzo]

OK... I've decided to remove just the pre-cats.
However, after I took the manifolds off it became apparent that the pre-cats are the metal & not the ceramic variety. They dont seem 'smashable' nor particularly keen on moving anywhere !

Can anyone recommend where I could possibly get my hands on new manifolds without pre-cats or let me know a specialist who could help me...