How to make an Activa CT perform....

[XantiaMan]

This is a quick guide based on my experience gained so far.

As standard, the Activa has 150 bhp and 171 lbft of torque produced at 2500rpm. Its classed as a low pressure unit and designed to produce a constant and flat torque curve instead of a traditional turbo wallop.

It has a low compression ratio of 8-1 which helps keep it smooth, but does decrease efficency at low revs and off boost, which explains the sometimes poor mpg.

Generally, the low compression would mean you could use a lower octane fuel but due to the way the engine is mapped, can cause pinking. For this reason Citroen recommended a minimum 97 octane fuel. Fuel economy is also better on the higher octane fuel, and obvious benefits with performance..

The engine runs a Bosch motronic mp3.2 ecu. It is in my opinion pretty good for a stock manangement, emissions are very well controlled aswell as coping with small modification to boost.

However because it relies on a lot of sensor to ensure strict emission control, if you start playing about it will throw a wobbly and the k-light will alert you to a stored fault code.

The maximum boost the engine is mapped for is 1 bar, beyond this the ecu will cut the spark abruptly.

The ecu controls the boost control solenoid. As standard, the boost will peak at up to 9psi at low revs, dropping a little to 7psi. It varies a lot and a boost gauge will reveal exactly what is going on.

This is all great for a smooth delivery but it is pretty unexciting. You can sometimes feel the process as if the engine is being held back.

The first step in improving the performance should be to remove the pipes leading to the boost control valve and fitting a manual boost controller in its place.
I use a ball and spring type for better boost response, some people use a bleed valve but I wouldn't as I care too much for my engine!

Leave the multiplug connection on the original controller as the ecu will see if its been unplugged and will go into limp home mode with the k light on constantly.

I have set my boost to 12.5psi peak, which drops a little to 12 and then 10 psi over 5000rpm. The drop is due to the small turbocharger not capable of maintaining boost at high revs but would be helped with a de-cat and bigger exhaust system.

Just this mod alone improves performance enough for most people, with rough estimates of 175bhp and 190lb ft. It also knocks over a second off the 0-60 time!

The power delivery is far more urgent and responsive.
Be aware that due to the fast spool up the boost can sometimes spike a little too high, the odd fault code can show up and put the ecu into default.

I have found 5 minutes with the battery disconnected clears this fault and puts the ecu back to adaptive mode which learns your driving style, it does help a lot with top end pull too so check your k-light on start up, it should go out straight away, if it stays on for a few seconds after you need to clear this fault to get full performance.

TBC...

[XantiaMan]

Continued-

The turbocharger fitted to the Activa engine is a purpose designed unit made by Garrett. It is generically called a T25 but runs a special flange to mount onto the manifold, so upgrading to a different unit is not straightforward unless you change manifolds.

It has a small turbine and compressor trim optimised for quick spool and response but because of its size, ultimate power will never be reached because the compressor cannot generate enough flow and will also heat up the inlet temperatures significantly when 12psi + is used, so its a good idea to keep it below this level as you will not gain any useable power in doing so.

The options available are as above, a different manifold such as a Turbo Technics item, there is also a bespoke tubular manifold which is a work of art, but its 600 euros... not expensive in the tuning world but a bit over kill for a road car. You can then fit a wide variaty of turbochargers with a T25 flange such as that off a Nissan 200 SX (T28) which is a good unit.

To save hassle and keep it looking standard but still get good gains, consider having a bigger compressor wheel fitted to the original unit.

Moving onto fuels. As previously mentioned a high octane unleaded is specified by Citroen, however not all high octane fuels are the same!

There is Shell V-Power (99) Total Excellium (97), Tesco Super (99) and BP Ultimate (97), aswell as other generic super unleadeds.

All will stop the pinking you sometimes get, but not all seem to give maximum power and torque.

I have used Shell, Tesco and now BP. The first 2 are higher octane (RON) rating than the others, Tesco 99 does work but, its a quick and dirty SUL with a 95 unleaded base and ethanol added to increase the octane. A true super unleaded will have a 97 octane base, and this is where the MON rating comes in.

Shell scores better in this area but is also a 95 octane based fuel, whereas BP Ultimate is made as a Super Unleaded from the start, and it shows!

I recently tried BP Ultimate and despite the lower octane rating, performance was significantly better as to be noticeable. The first time i used it was after a visit to Santa Pod and driving it flat out all day, i would notice a change, this fuel certainly does work for me and its now my first choice, followed by Shell and then Tesco.

As long as you use a super unleaded though, any difference should not be drastically noticable between brands so chose what you feel is best and locally available.

The Activa does not have a dump valve fitted. No dump valve will give you extra power but some re-circulating dump valves can reduce lag.This isnt really a problem for the Activa and re-circulating the air can increase the inlet temperatures. Apart from the noise of an atmospheric DV which i like, you can leave this area alone as the turbocharger is not running enough boost to decrease its life by compressor stall.

Exhaust systems - The Activa is not blessed with a big enough bore for performance and if you dont mind the expense, i would recommend a custom 2.5 inch system from the turbo back, with a de-cat pipe which reduces the restriction even further. With 2 boxes a well designed system will not boom excessivly and give a much nicer note and more top end power, plus even quicker turbo spooling! The better flowing exhaust will reduce backpressure and also decrease EGT (exhaust gas temperature) which will also lower the inlet temperature for any given boost, and because its lower, you'll get more power

Induction - The filter will flow enough for over 200bhp but could be improved with a relocated air feed picking up cooler air, and a k&n element. Open cone filters sound great but pick up engine heat especially in the summer and reduce your power, so forget it!

Fuelling - The ECU is capable of adapting to higher boost pressures, it uses MAP not AFM which is much more reliable, the injectors have just enough flow to cope with mild mods but beyond this i would look into upgrading the flow, however unless you have a bigger turbo and running up to 14psi you should not need to worry about it.

If you want to truely break to 200bhp barrier i would definatly recommend an aftermarket ECU, mainly to save hassle with fault codes but custom maps to suit the mods can give excellent gains, one make i would consider it Emerald, but your looking at £1200 quid plus for this.

The engine internals are plenty strong enough unless you abuse it by trying to run too much boost on a standard turbo. Detonation caused by high inlet temperaures will kill the pistons! So keep it sensible.

The cylinder head has good sized valves and i would not touch it until i had done everything else, unless the head was off, where a simple tidy up of the valve throats and 3-angle valve seats will keep you going. Its easy to remove casting marks too whilst your at it!


So basically, its fairly simple to get an extra 20-30 bhp from this engine, the magic '200bhp' figure so many people like to use requires more than a boost control valve...

[CitroJim]

Excellent pair of articles Gareth

I have to agree on fuels. I like neither Tesco SUL or their diesel and nor do my cars My 2.1TD does not like Tesco diesel at all and shows it's displeasure in a reduced MPG and very slightly ragged running.

I've only used Shell, BP and Esso SUL in My Activa and of the three, I have to agree, BP is good stuff. Esso seems OK as well. My Activa has had a couple of tanks of it recently.

One thing for sure. A good SUL does improve economy and BP, Esso and and Shell seem to give about the same improvement.

Mine has had Esso, Shell, Esso and BP in the last four fill-ups.

[XantiaMan]

A lot of it is down to personal choicen, maybe even a bit of placebo effect, but having been using these fuels for years I can usually tell the difference.

I run the TD on whatever (obviously!) and not noticed any difference in diesel fuel. I have a 5p voucher so that will fill up the TD on payday.

[Sl4yer]

Oops... Been feeding mine regular unleaded! Should have RTFM!

Interesting point about poor fuel economy when off boost. Makes sense I suppose. I've been driving mine like a diesel, trying to avoid boost when cruising. I'll try to be a bit more aggressive this week!

James

[CitroJim]

I'll try to be a bit more aggressive this week!

No need James, just drive so as to keep the revs up and the turbo spinning. Trouble is, the engine has so much low-down grunt it is easy to drive it like a diesel! Resist the temptation

[handyman]

Hi Gareth, nice write up, real chapter and verse, clear and concise.

What's the mode on the bigger compressor wheel? Is this a bit of parts swapping between turbos, like the T28? Can't imagine it involves machining existing components. What's the likely gain?

I've currently got an 8V head on my bench and can only see a small amount of work needed in the valve throat, most of it blending. I am tempted to look at slightly larger inlet valves, at 43mm, with three angle valve seats. I have been advised that this is as large as it is possible to go on a road engine, safely.

Handyman

[XantiaMan]

Hi Gareth, nice write up, real chapter and verse, clear and concise.

What's the mode on the bigger compressor wheel? Is this a bit of parts swapping between turbos, like the T28? Can't imagine it involves machining existing components. What's the likely gain?

I've currently got an 8V head on my bench and can only see a small amount of work needed in the valve throat, most of it blending. I am tempted to look at slightly larger inlet valves, at 43mm, with three angle valve seats. I have been advised that this is as large as it is possible to go on a road engine, safely.

Handyman

From what i know, the valves are already 43mm! They are definatly big enough! The head isnt a weak point for overall flow but any head can be improved.

With the turbo, a bigger compressor wheel and the housing machined to match should be enough to give an extra 15bhp on like for like boost. It won't have to work as hard so some of the gain comes from the higher volume and lower temperatures. Because the exhaust side is untouched spool up is virtually unaffected.

A t28 turbo is a hybrid of t25 turbine and t3 compressor housing mounted onto a t25 centre core.

I've not yet mentioned the camshaft. A different type of profile such as one fitted to the NASP XU10 from a Xantia 2.0i has a more aggressive profile. I need to do more reading up, but this is meant to help push the power band up further. I would be keen on keeping the cam stock though for the time being, due the valves and ports on the big side the last thing you want is too much lift. A smidge more duration should do the job. It could also be worth looking at the cam timing to make sure it is spot on, or maybe even a bit more advance. It can help increase power at the top end but you need it on a RR to see the difference it makes.

Inlet manifolds- the Activa does not have a plenum chamber which can bee seen as a downside. The inlet runners are quite short too. A 306 XSI one is meant to be better flowing. The throttle body IS too small though, not sure why it is as small as it is but it looks as though power could be restricted. Be nice to know which throttle body would bolt straight on and be a few mm bigger.

Gareth

[XantiaMan]

Having changed the original backbox from a huge heavily baffled type to a straight through box, I can recommend this option because noise does not increase hugely and seems to make the engine more willing to rev, boost also fractionally increased, a sign that backpressure has been reduced. The bore size appears to be around the 2.25 inch mark, fine for a stock system. Once the CAT is replaced even more improvements should be noticed.

[handyman]

By replacement of the cat, do you mean complete disposal?

This bit of meaningless technology, the catalytic converter, has done more to make the internal combustion engine burn more fuel, than would have been the case if manufacturers had invested in other forms of technology to improve combustion. Just a cheap quick fix.

As an aside, the idiot who developed the technology, whose name escapes me, has only recently died. He was an American.

Handyman

[XantiaMan]

Yes, get rid of the whole thing! Unfortunatly the cat is part of the downpipe and I would want to obtain a spare first and remove the cat part of the section with the correct sized pipe. I reckon a few bhp is available or more by getting shot of it, and were it not for its absence not be noticed at mot time as they run very clean.

[handyman]

I did make a recommendation on Activanet about cutting open the can, removing the innards and rewelding it. If it were done on top, chances are MOTman would not see it, if it were done neatly. It is still on one of my to do lists as I have a spare, good downpipe. If I fit it onto one of my cars and it fail the emissions test I would just refit the cat.

Will let you know how the car fairs, but it wont be until February when the MOTs due.

Handyman

[Sl4yer]

Does it matter if the MOT man sees the weld or not? Surely the pass or fail is down to the test results?

A used-up cat will be intact, but empty!

James

[CitroJim]

A used-up cat will be intact, but empty!

No, not quite James. It might be inactive but the ceramic honeycomb will be well clogged up after all those miles and thus reduce flow considerably, negating the whole point of removing the cat.

Due to the right-angled nature of the Activa cat, the old trick of ramming a bar down it to break up the honeycomb is unlikely to work effectively.

Handyman, it's going to be intersting to see how yours goes for the MOT catless. Judging by both Gareth's and my emissions results from the last MOT, it should sail it

[handyman]

I have a couple of MOT test centres near where I live and most of them are quite amenable so I may try a before and after emissions test, prior to the MOT, assuming they can do a test without being hooked up to a booked, scheduled test.

Will post up results as soon as I can.

I wonder what the legal position is with regard to driving a post 1992 vehicle, sans cat?

Handyman