de-cat or de-pre-cat
Discussion
o.k. here it goes (touchy subject)
:
is it possible to de-cat a Griff 500 in such a way that it is easy to put the cat's back for the MOT?
or is it wiser to only remove the pre-cat, which should be o.k. for the MOT and still gives a nice power/response gain (after re-tuning of course)
: is it possible to de-cat a Griff 500 in such a way that it is easy to put the cat's back for the MOT?
or is it wiser to only remove the pre-cat, which should be o.k. for the MOT and still gives a nice power/response gain (after re-tuning of course)
quote:
o.k. here it goes (touchy subject)
is it possible to de-cat a Griff 500 in such a way that it is easy to put the cat's back for the MOT?
or is it wiser to only remove the pre-cat, which should be o.k. for the MOT and still gives a nice power/response gain (after re-tuning of course)
Precats definitely have to go, also suggest you get Tower View to send you a pair of cone inserts to go in their place for an little extra mid-range. I believe this is completely legal and above board (as long as your insurers know). Main cat - far more contentious and I think strictly speaking it would be illegal, def need to make sure your insurers are happy in any case. If you go this route I think you can get a modified downpipe with a 'bolt-in' cat section that you can swap at MOT time, seem to remember seeing something of the sort on Zertec's web site?
quote:
hi Peter,
how difficult is it to get the pre-cats out? Will it damage the manifolds?
Mine were rattling loose and fell out on their own, I gather this is quite common. If they're still intact you need some brute force to get them out. They're basically a metal honeycomb section, and reasonably tough. But the manifold they're in is very substantial and should easily withstand you poking around inside to get the precats out.
quote:
o.k. here it goes (touchy subject)
is it possible to de-cat a Griff 500 in such a way that it is easy to put the cat's back for the MOT?
or is it wiser to only remove the pre-cat, which should be o.k. for the MOT and still gives a nice power/response gain (after re-tuning of course)
Don't expect too much (if any) power improvement if the cats are removed. It might breathe better especially if the cats are blocked.
My Griff 500 is decatted (by previous owner and its passed its MOT for the last two years and the insurers are happy with it). Made very little difference to the power until the cam was changed, big throttle body and air flow followed by a Mark Adams rechip and so on. Now this work on its own could be responsible for the power increase on its own.
Easiest thing is to remove the pre-cats and leave the big cat in place.
Steve
If the cats are removed, the ECU needs to be rechipped so that it works in open loop mode without the lamda sensors.
'My Griff 500 is decatted (by previous owner and its passed its MOT for the last two years and the insurers are happy with it).'
Steve: This flies in the face of all received wisdom and logic! Great trick, but how does it do it? A friend's Griff 500 is 'ex felis' but can't get CO and HC under the limit at the same time...
Steve: This flies in the face of all received wisdom and logic! Great trick, but how does it do it? A friend's Griff 500 is 'ex felis' but can't get CO and HC under the limit at the same time...
... I believe this is completely legal and above board (as long as your insurers know). Main cat - far more contentious and I think strictly speaking it would be illegal, def need to make sure your insurers are happy...
It's good to talk in terms of legal. The only thing you have to bear in mind is the difference in UK and Dutch MOT standards.
Insurers couldn't care less in Holland.
Cheers
Custom 218 hybrid cam... modified inlet, bigger plenum and throttle body, Jag Airflow meter and many hours of Mark Adams time on a rolling road are the mods it has had.
Some engines can get away with it... some don't apparently. I have the original manifolds which I can swap back but haven't needed to yet. It is borderline apparently and you may have to tip the car up to the right angle
As I said the car was like it when I got it. Funny thing is that everyone raves about cars sounding so much better and distinctive when decatted but I don't think anyone has come upto me and asked the question or made any comment on the way it sounds. What does that tell you?
Steve
Some engines can get away with it... some don't apparently. I have the original manifolds which I can swap back but haven't needed to yet. It is borderline apparently and you may have to tip the car up to the right angle
As I said the car was like it when I got it. Funny thing is that everyone raves about cars sounding so much better and distinctive when decatted but I don't think anyone has come upto me and asked the question or made any comment on the way it sounds. What does that tell you?
Steve
There IS a difference, trust me. If you want a decent sound you have to reduce the exhaust bore , ie if you remove the cats but leave an empty bucket it will sound like a gurgling yank tank, even the precat Griff has an oversized "Y" piece.having owned 7 wedges including 2 SEAC's i am used to a fantastic exhaust note, now owning a precat griff i really miss that crisp SEAC bellow, although the Griffith sounds OK, when i upgrade the engine will definately fit a modified exhaust.
Tim
>> Edited by 2 Sheds on Sunday 14th July 10:53
Tim
>> Edited by 2 Sheds on Sunday 14th July 10:53
o.k. the shopping list for the coming period is clear:
remove precat, modified inlet, bigger plenum,throttle body, Jag Airflow meter, Mark Adams magic.
with this extra power, do I need to upgrade the brakes? I already found them fading a bit at Zolder, which surprised me, especially since I wasn't going flat out at the time. Later when I was pushing a bit, the brakes were o.k. Strange isn't it?
I see a hugh investment coming. Definitely need to be creative about the funding.
remove precat, modified inlet, bigger plenum,throttle body, Jag Airflow meter, Mark Adams magic.
with this extra power, do I need to upgrade the brakes? I already found them fading a bit at Zolder, which surprised me, especially since I wasn't going flat out at the time. Later when I was pushing a bit, the brakes were o.k. Strange isn't it?
I see a hugh investment coming. Definitely need to be creative about the funding.
quote:
with this extra power, do I need to upgrade the brakes? I already found them fading a bit at Zolder, which surprised me, especially since I wasn't going flat out at the time. Later when I was pushing a bit, the brakes were o.k. Strange isn't it?
Had the brakes been properly bedded in before the track day? With most pads, this involves braking progressively harder and harder until they start to fade, cooling them down between runs. Until this has happened, they'll fade quite easily.
quote:
Had the brakes been properly bedded in before the track day? With most pads, this involves braking progressively harder and harder until they start to fade, cooling them down between runs. Until this has happened, they'll fade quite easily.
Had this with the Griff too. Just fitted my Wedge Wilwoods and 283mm discs and it took a lot and I mean a lot to get them bedded in. Main culprit was the disc, even though they had had been cleaned before installation.
Steve
o.k. I guess my brakes are now properly bedded in then (the were indeed new when I took delivery of the car)
but after the power hike: can they still cope or should I upgrade? if so, what do you recommend? also, do I need the adjust the front/rear bias at the same time and how?
thanks guys
but after the power hike: can they still cope or should I upgrade? if so, what do you recommend? also, do I need the adjust the front/rear bias at the same time and how?
thanks guys
You might get around 20 bhp more so I would say yes for no better reason than your insurance company may insist. Then it is a question of how much do you want to spend? It is easy to blow several thousand on brakes! Most of the intermediate upgrades like the one I have require no mods to the rear or brake balance.
The cheapest way is to reuse the existing callipers but with bigger discs. Next stage is to use four pot callipers and then we get into serious money as well as serious running costs like replacement pads and rotors.
Steve
www.tvrbooks.co.uk
>> Edited by shpub on Tuesday 16th July 07:19
The cheapest way is to reuse the existing callipers but with bigger discs. Next stage is to use four pot callipers and then we get into serious money as well as serious running costs like replacement pads and rotors.
Steve
www.tvrbooks.co.uk
>> Edited by shpub on Tuesday 16th July 07:19
As one with a fully de-catted 500 Chimaera, here's my two-pennarth.
I had all 3 cats removed, and replaced with new factory cat-free manifolds and Y piece. Different part numbers. Thats over a grands worth, but I still have all 3 catted parts to refit if necessary.
Yes, it does sound different. Noticeably. This was my motivation for getting the de-cat, and I am happy with the difference - but it does not sound like an SEAC as I had hoped. It does sound "well ard" though.
One slight downside is the cavernous empty Y piece creates a noise quite similar to a leaking manifold (metallic tick/hiss), so from the front it does sound a little ropey. You do get interesting pops and bangs on the overrun (and flames apparently, though for obvious reasons I have never seen this myself).
Tickover has been erratic since the decat; it was 'rechipped' to suit but could do with some rolling road magic to sort it completely I think. Its been like that for 3 years and hasn't bothered me enough to get it done though, so it's not that bad.
MoT has not been a problem so far. I normally take it back to the dealer who decatted it, which may help in this respect!
I may yet revert to cats. While I like the difference, my little boy is not so keen - he is frightened of "daddys noisy TVR". Petrified in fact since I started it up with the Y piece and exhaust removed completely. (I was cleaning up the chassis and was curious what it would sound like - hard to describe, but if you have ever been to Santa Pod then you will be familiar with the sound!)
I had all 3 cats removed, and replaced with new factory cat-free manifolds and Y piece. Different part numbers. Thats over a grands worth, but I still have all 3 catted parts to refit if necessary.
Yes, it does sound different. Noticeably. This was my motivation for getting the de-cat, and I am happy with the difference - but it does not sound like an SEAC as I had hoped. It does sound "well ard" though.
One slight downside is the cavernous empty Y piece creates a noise quite similar to a leaking manifold (metallic tick/hiss), so from the front it does sound a little ropey. You do get interesting pops and bangs on the overrun (and flames apparently, though for obvious reasons I have never seen this myself).
Tickover has been erratic since the decat; it was 'rechipped' to suit but could do with some rolling road magic to sort it completely I think. Its been like that for 3 years and hasn't bothered me enough to get it done though, so it's not that bad.
MoT has not been a problem so far. I normally take it back to the dealer who decatted it, which may help in this respect!
I may yet revert to cats. While I like the difference, my little boy is not so keen - he is frightened of "daddys noisy TVR". Petrified in fact since I started it up with the Y piece and exhaust removed completely. (I was cleaning up the chassis and was curious what it would sound like - hard to describe, but if you have ever been to Santa Pod then you will be familiar with the sound!)
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