Exhaust, port, chip combination

[e42]

Hi, I don't actually have a problem with my 1991 SE, but would appreciate advice on reaching a decision.

The car is currently at the garage having been serviced, MOT and new cambelt (the Dayco kit popular on here). The standard exhaust has seen better days, hence I plan to take the opportunity to go for some extra power. I'm in the dark regarding closed-loop, open-loop, and the jury may still be out over the effectiveness of the Piper down pipe! But could you advise if the following changes seem to be a safe combination:

Piper 2.25 inch exhaust, waste gate ported to 21mm, standard down pipe, Everest chip?

I'm not sure what a 'PCE' actually is, but would I add this to the list above?

Apologies for what might be a basic question, but the best exhaust option has me baffled (lame humour!)

Thanks all in advance,

Dom

[dapinky]

Hi Dom,

Such decisions are full of different opinions......

All I can do is state that I run pretty much that combination (except I have the PCE, and the chip is the 'switcher' type).

I have never had boost creep (but I ported the wastegate before I fitted the Piper).

I am extremely happy with the way it runs (either in Open or Closed loop system) - the only noticable difference in the Open vs Closed is that on a run I get better fuel consumption in Closed loop mode - and the emmissions are well within the MOT limits (they were always a bit marginal before I fitted the O2 sensor).

For short trips it makes no difference between Open & Closed as the ECU will always run Open Loop until it reaches operating temperature anyway.

[e42]

Hi Dave, thanks for the information. Just to clarify, can the PCE be fitted with the standard down pipe? Also, what is the benefit of a 'switchable' chip? I have no plans for track days if that makes any difference?

Thanks,

Dom

[dapinky]

Hi Dom,

Before I just say 'yes' or 'no' to your question, it is important to know that we are talking about the same bits and pieces....

The term 'downpipe' isn't used by Lotus (AFAIK), but it has achieved some commonality on LEC by people developing the entire exhaust system from the turbo backwards, and is often used to describe the pipe and/or bits of cast iron between the turbo wastegate manifold and the front of the actual exhaust pipe.

If your current system is totally standard, you should have bits that look like this:- (albeit joined together and hidden from view behind various heat shields!)

dustbin.jpg

The rather large (and therefore heavy!) cast iron lump at the bottom of the picture is the Pre-catalyst chamber, and on an SE it is empty and useless (Foreign - and later Domestic - markets demanded different emmission controls) - you will notice that it is a very cylindrical shape, so gasflow through it isn't exactly efficient either.

By replacing that part with a stainless steel 'cone' you can reduce weight and improve gasflow - hence the PCE (or to give it its full title, Pre Cat Eliminator) - you end up with it looking like this:-

PCE.jpg

Now, to go one step further (or not, depending on your point of view!) the whole assembly can be replaced with a single "Downpipe", of which there have been quite a few variations over the years - the Original was made by Stevo, and was basically a 2 1/2" stainless pipe, bent and welded to a couple of flanges (okay, it was FAR more [and better] than that, but thats the general idea) - this became known colloqially as "The Stiffy" and if one ever came up for sale there would probably be a big bidding war!

Then another variation was made by Knox over in USA using a different pipe routing from the wastegate (this is generally regarded as being the best way to do it) - but only one was ever made and it never went into production - it was a hand-made item and would be quite expensive to replicate as a one-off - that said, it is on my list of things to have a go at when i get round to it!

The only one currently availlable is the one from Piper which is an adaptation of the Stiffy design.

The one thing that all of the systems have in common is the start and end positions - thus any one of them will fit between the wastegate housing and the 'standard' exhaust pipe - and the Piper (and other aftermarket makes) of pipe all start at the same point, so it is a real 'mix and match' possibility, with options for anyone!

As I'm sure you've already seen from the Piper catalogue, there are quite a few variations - i went for a 2 1/4", single silencer system (and have compare the 'noise' with Rips car which has the 2 silencers - not much difference, and hardly noticable) and it passes the sound level requirements at evey track I have been on.

Unless you are really looking for maximum power, then a 2 1/2" isn't really necessary (if you are keeping the OE turbo, then you won't notice much/any difference between the 2 diameters) but if you are considering upping the turbo at a later date, then it may well be worthwhile.

By fitting an Everest chip, you will get better output from the 2 1/4" or 2 1/2" vs the 'standard' 2" pipe, but it is all a bit marginal to go any larger as it is the turbo flow/boost rate which is the limiting factor (along with the fueling rate).

For road use, I wouldn't think it necessary to go any further (but each to their own!).

For a totally focussed track car you may want to go for every option in the book (bigger turbo/downpipe/wide exhaust) but would also need to upgrade the fuel injectors/MAP sensor/ECU) and then consider the clutch - and don't forget the suspension, tyres and brakes - the list goes on and on.....

....and it may or may not make any difference to your times round a track (my blue one is only a few seconds a lap faster round Castle Combe than my old red one - and that had standard everything, except the wastegate was ported and it had an aftermarked exhaust which was on the car when i bought it, so don't know what make it was).

To be honest, the biggest change in lap times is down to the tyre choice, and brake pads used - I've no doubt that a really good driver might get more out of it, but it is the grip limitation more than the power which gets me. (hopefully my renewed suspension will make some difference - we'll see in May at Castle Combe!).

When it comes to the chip, I went for a switcher so i coulkd have different settings on the road and track, but in the real world, I hardly ever change the settings so wouldn't be likely to bother another time. It is nice to have the option to switch to open loop if the O2 sensor goes wrong when I'm miles from home, but it hasn't happened yet.

I am not in a position to say which each component in the exhaust sytem adds to anything, as I swapped it all at the same time that I rebuilt the turbo, so can't say that the PCE is or isn't worthwhile (but it saves a few kilos of weight and theoretically has to improve gas flow) - but the whole package transformed the car from what it was like beforehand, and gives a much nicer driving experience, and far safer real-world power (overtaking accelleration).

[e42]

Dave, thank you for taking the time out to give such a comprehensive reply. I'd heard that this was one of those particularly active forums with a wealth of knowledge, absolutely agree with that now, thanks!

I have a much clearer idea now, looking forward to seeing the difference with the new set up!

Cheers, Dom

[nicowalker1]

Don't worry Dave has all the time in the world these days
I have a pecco 2.25" and I am yet to port my wastegate, my advice would be to do the lot in one go. I only get overboost if I absolutely floor it in cold weather but it is extremely embarrassing.

[HJ2]

Whatever you do: Don't do as I did:

1. replace rusty OEM exhaustline with PECO 2.25", whilst empty the pre-cat (the one in the downpipe) at the same time
2. Admire the effect of overboost
3. Buy one of Alan's fabulous mountain chips
4. Admire the lack on effect to cure my overboost
5. Take the turbo out and port the wastgate
6. Admire the perfect system
7. Ruin your downpipe, flexible section AND exhaust manifold whilst blasting away in Ypres, Belgium
8. Swap the downpipe + empty pre-cat for a Piper downpipe & replace manifold.
9. Admire the effect of overboost once again!
10. Have a nice discussion here on LEC about fluid dynamics, be ignorant remove and change some details of the Piper downpipe and put it back
11. Once again: admire a perfect system again

If i Were you:

Do the entire exhaust line, either use a piper downpipe, empty the pre-cat housing or use a piper PCE (the latter works fine, see above) and port the waste-gate, buy one of Alan's famous mountain chips, i prefer Everest, all in one go!

[dapinky]

If i Were you:

Do the entire exhaust line, either use a piper downpipe, empty the pre-cat housing or use a piper PCE (the latter works fine, see above) and port the waste-gate, buy one of Alan's famous mountain chips, i prefer Everest, all in one go!

Not a problem on this car, Henk-Jan - the UK market didn't have anything in them!!! (well, not on a '91 SE anyway).

[HJ2]

Than that's an easy fix!