Standard 500 exhaust system restrictive ?

[Chilliman]

At what point in terms of induction/gas flowing/head mods will the standard exhaust system become restrictive ? When I get the old girl back she'll have MS2, no AFM (or dizzy), which general concensus says is restrictive from about 280 ponies upwards, but what about the plumbing on the outlet side of the engine ? Will be removing the pre-cats as a matter of course, but am wondering how much of the potential power from the usual top end mods will not reach the wheels because of the standard exhaust set up. I don't need a new exhaust system and don't want to spend loadsa money on one if the standard set up is good for say up to 350 big ones...

Whaddya think chaps ?

[haircutmike]

The whole system is big bore, I should think the only restriction is the main cat.

I am going to remove mine, (cat) and heat wrap the dustbin while I decice what to do with my engine!

In your case, you will probably need a cat Y piece for your MOT.

[darkcat]

TBH i think its fine for 350 British Horse power (BHP), its a BIG pipe at the end of the day.

[Chilliman]

Hmm, also in the process of deciding what to do with mine at the mo. It may be a trifle fubarred but won't know for sure till its out and stripped (next week). Oh the joys......

[Pupp]

It's not the bore of the pipework that's the problem but the length and configuration of the primaries (headers). There's far more to exhausts than simple capacity to flow...

now, let's see who is first to mention 'back presure'

[Simon says]

Pupp said:

It's not the bore of the pipework that's the problem but the length and configuration of the primaries (headers). There's far more to exhausts than simple capacity to flow...

now, let's see who is first to mention 'back presure'

[Chilliman]

Pupp said:

It's not the bore of the pipework that's the problem but the length and configuration of the primaries (headers). There's far more to exhausts than simple capacity to flow...

now, let's see who is first to mention 'back presure'

Thats a given, but no concensus on the answer to my question yet.... Seems removing all three cats and sticking the main cat back in for the MOT is standard MO on the tuning front....

Edited by Chilliman on Monday 4th July 12:42

[Overhere]

By the way, I think Rob R would be a good guy to ask, when I asked him about my XXX exhaust manifolds he didn't recon it gave any particular performance boost over a standard exhaust system, although it looks and sounds better.

I have an issue with removing cats completly, I want to do this but my understanding is that it becomes an MOT failure, if I have an accident and the car is found to not meet MOT/emission standards then my insurance will not pay out. This is my understanding, am I wrong about this? I keep hearing about people removing cats...

[carsy]

If you are unfortunate enough to have a bump. Do you think that the police or insurance companys are going to go to the lengths of checking emmisions. I think not.

[Overhere]

Hmmm... So the ony time I have had a bump, years ago, an adjuster did come around. I think the question is of risk and probability, if it's a bump I guess probably not, if it's a bad accident and thats when big money is at stake, I guess an adjuster would come out. would they check to see if my engine wasn't as declaired? would they know? Am I willing to take the risk...

It seems people here are willing to take that risk and I'm also willing to expolre the risk, just wanted to know what others think

[v8 racing]

have you seen the size of the main cat on these engines!!, IMHO they will flow a 500 bhp with very little restriction, IF the cat is in good condition i would say leave it alone, if its blocked then thats a different story, i have seen engines running over 370 bhp on the stock exhausts that will meet emisions come mot time, take the cat out and they would fail, clive did a back to back test on a cat then a de cat and peak bhp went up by 5bhp, so yes there was a gain but on an engine making 300 bhp would you really feel an extra 5?

[Alexdaredevilz]

I'm going to have to disagree with you on that one Rob,

I cut my cat open and blew threw it, and defiantly saw a restriction

Plus
Extra heat kept under the bonnet
Weight
And dampening a beautiful exhaust note

I will post a picture later of the cat

[v8 racing]

Alexdaredevilz said:

I'm going to have to disagree with you on that one Rob,

I cut my cat open and blew threw it, and defiantly saw a restriction

Plus
Extra heat kept under the bonnet
Weight
And dampening a beautiful exhaust note

I will post a picture later of the cat

Hi Alex, if you cant blow through your main cat it must have been solid!, hence why i said if the cat is in good condition leave it alone, if its blocked then thats a different story.

[spend]

Biggest impact IMHO is where the head exhaust ports meet the manifolds & the transition of head - flange - manifold pipe (where it all bends & twists). I suspect some of the back-back tests have given false impressions because of the level of detail in that small area differing. Just think of it like porting your heads through to the point where the pipe becomes straight..

[Alexdaredevilz]

[Chris71]

Grappling with this at the moment. With the engine out currently, now would be a logical time to put a cat-equipped system back in if I was going to do so. I'm considering this for two reasons. Firstly, I might be marginally more likely to pass track day noise tests with a standard exhaust system. Secondly, it would make MOT tests a little more straightforward.

But I gather it's not too difficult to find MOT stations that ... how shall we say? Understand the specific needs of de-catted TVRs when it comes to emissions tests?

[Alexdaredevilz]

100-101 db's my system makes with out all its cats in on a 4.6

Tested stock system minutes before at 99-100 on a 4.5

The tester is calibrated

[haircutmike]

Wot, you're calibrated?

[Alexdaredevilz]

haircutmike said:

Wot, you're calibrated?

I got proof that you were trying to calibrate your thumbs

Edit, are you sure your necks not broken?

Edited by Alexdaredevilz on Saturday 9th July 21:29

[Chilliman]

Oo-er