Romford Astra
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Registered: 13th Aug 01
Location: Romford, Essex Drives:Honda S2000
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The induction systems on the XE engines are the main power restrictors when it comes to unleashing the true potential of these machines.
During the development of the 1.6XE Vauxhall were worried that this powerful little lump may detract from the desirability of the larger 1.8 and 2.0 litre engines (the corsa is not the only vauxhall to use this engine, it shares it with the astra, vectra and zafira models).
The easiest way for them to reduce it's power to a much more modest, but still adequate 106bhp, was to fit it with a restrictive induction system. Admitedly the lack of power is not just because Vauxhall/Opel were afraid that this engine would embarass others in their range, but has also got alot to do with the Ecotec system.
The easiest and cheapest way to reclaim some of the engines gusto is to remove the restrictor in the standard air box. Doing this allows the engine to rev stronger right up to the rev limiter, although in doing this I have noticed that the engine develops slight hints of a flat spot around 3000-4000rpm.
One thing always to bear in mind when tuning an engine is that there is no such thing as a free lunch, and more often than not a power gain in one area is at the sacrifice of power in another. This will always be the case with 'bolt on tuning' such as air filter induction kits, cams and exhausts. To get true gains from modified engine components the factory ECU needs to be replaced with a fully adjustable unit.
Getting back to the main content of this page and the induction system for the XE engines, the only true way to rid the problem is to scrap the old induction system in favour of a better one.
There are various after market induction systems available.
RAM AIR
The first is a ram air induction kit including airbox and throttle body.The manifold is acousticaly tuned to make use of standing resonant waves in the induction system, this style is good for up to a 20bhp increase in power on the i.6 ecotec engines used in the astra and vectra models.
If you were to think for a moment of a bath full of water, if i was to make a wave in the bath at one end and then watch the wave progress up the bath hit the other end then return, at the moment that it reaches my end of the bath I repeat the making of the wave, this amplifies the wave, if I was to continue to do this the waves would get stronger and stronger. Well this is exactly what happens here in the acoustically tuned system only instead of water we are dealing with air and instead of me causing the wave it is the piston drawing air in on the induction stroke, when the returning wave reaches the inlet valve at the exact moment of opening, the air rushes into the engine greatly reducing the ammount of work that the piston has to do during the induction stroke.
A good system like this is available for alittle under £600 from Peter Maiden Components This type is easy to fit and involves the least amount of modification and set up, it is quite literally a bolt on kit.
There are various kits available but the only ones that I have been able to get photos of are made by lexmaul, the same as sold by PVD.
The x1.6xel engine used in the vectra and astra models can be boosted by 20bhp using the complete Lexmaul kit shown above and the 1.4 and 1.6 16v corsa engines can be boosted by 10 and 15bhp respectively by adding the chamber that bolts directly on top of the existing manifold. The power increases can be seen on the Lexmaul test data below.
As can be seen here in the first graph, which is the one that is most relevant to this site, the benefits for the 1.6 only come into play after the 5500rpm point. At this point I would like you to think for a moment if this modification is the one for you, will you, or do you spend alot of time above the 5500rpm mark? if the answer is yes then go for it but dont forget to strengthen the big end, a set of heavy duty rod bolts from SBD ought to do the trick. The 1.4 on the other hand shows a much better value for money increase, the benefit is seen much earlier and is active over a larger range than on the 1.6.
Throughout these pages I will endeavour to discover the best way for the roadusing corsa enthusiast to improve the engine of his/her car and what I mean by best, in my opinion anyway, is the most horses for the least bucks, but at the same time the power increase needs to be useful for everyday driving (2000-6000rpm) not just at peak rpm
It might also be worth upgrading the injectors when fitting this kit, if you intend on altering the fueling to cope with greater flow, injectors from the vauxhall 2.2LN 16v engine found in the calibra and the cav, these injectors should be easy to get from your local breakers yard, but be careful to check that they are not worn out!
THROTTLE BODIES
The second is a four throttle race style system as shown on the engine in the site map. This uses either one or two injectors per cylinder. This system is really amazing because of the power it produces, it's very usable even for a road go'er. This unit has been developed by SBD who tune vauxhall engines for race use in caterham style kit cars based on the lotus 7. This kit comes from SBD and is good for an amazing 168bhp.
Cost?
Well you are talking about £1,700 , but you will have to fit the thing aswell. SBD also found that with an uprated crank, con rods, pistons and a careful bit of head work they could manage an awsome 235bhp. SBD will also supply a complete and fully tuned race engine on request.
The 168 bhp race kit is a good set up if you are intent on racing, sure it has bags of power, but it is mostly after the 6000rpm point how often do you spend driving about at that kind of rpm on the roads? Further investigation on this matter lead me to an example where A. Graham Bell (author of 'Modern Engine Tuning') used an old pair of weber DCOE 42mm sidedraught carbs to fabricate 42mm throttle bodies in a low budget excercise to achieve 150bhp from an Opel Ecotec 1.6 corsa. The following section taken from his book tells us what he has done:
"Recently some testing was carried out on the Opel Corsa with an Ecotec 1.6 4-valve engine. The owner wanted a cheap but competitive dual purpose road/clubsport car preferably with no internal engine modifications and about 150hp. This seemed a fairly tall order as the factory quoted the power output as being only 107hp at 6000rpm. First the factory fuel injection system and electronic engine management system were scrapped. A new throttle body arrangement was fabricated from an old pair of Weber 42 DCOE sidedraughts as it was felt that the commercially available 45mm bore throttle bodies as used on 220hp race engines would upset the mid-range power. The new engine management system was a laptop programmable unit"
The table below shows the excellent results and clearly shows the tuning potential of this engine.
Table taken from 'Modern Engine Tuning By A. Graham Bell' The table produced the graphs below which show clearly the effect of the modification.
These kits, however are not designed to run with a catalyst but there are race catalysts which when used with the lambda engine controlled supplied by SBD, will keep your engine running within the emission legislation.
Since the text quoted above has gone to print there are now throttle bodies available in a vast range of sizes and configurations.
It might also be worth upgrading the injectors when fitting this kit, if you intend on altering the fueling to cope with greater flow, injectors from the vauxhall 2.2LN 16v engine found in the calibra and the cav, these injectors should be easy to get from your local breakers yard, but be careful to check that they are not worn out!
The Mantzel Powerbox.
The Powerbox from Mantzel has been available for some time now on the European continent. Over the past year we have seen it become more readily available here in the UK with the arrival of Mantzel UK. The device has no moving parts and is surprisingly simple. We all know by now that the 1.4 and 1.6 XE engines are both a bit asthmatic. Well the Powerbox is a simple bolt on solution, it does away with the more restrictive parts of the induction system but manages to incorperate the existing throttle, map sensors and air flow meter allowing the original ECU to be kept, this is good news in terms of insurance.
The Powerbox is a replacement Plenm chamber, What's that? Its a resonance chamber, like an organ pipe it is tuned to a specific frequency or frequncies. The principle is much the same as for the complete ram induction systems available although I would suspect that the Powerbox would flow better simply because it cuts out the section of inductive piping that goes round the back of the engine from the throttle to the air box.
Introducing the Powerbox to the engine can see an average increase of as much as 15bhp on the 1.6 engine. Mantzel do several kits, the kit for the GSI includes a replacement lower manifold section. The kits are good for future tuning too, the rpm limit can be safly raised to ~7500rpm to extract a little bit extra or the kit could be used in conjunction with a turbo conversion. The reason it would work with a turbo is because it flows better than the standard system this reduces the pressure in the induction between the turbo and the manifold and keeps the charge cooler. What I mean by pressure is the pressure caused by restrictions in the flow not boost pressure by the way. In an engine bay this cluttered there isnt all that much space for large intercoolers etc.
Exhaust Systems
The Exhaust is as important a part of the tuning process as anything aelse mentioned in these pages, it is vital that there is good flow both into and out of the engine. As Exhausts go the one fitted to the corsa sports aren't of bad design, infact they flow quite well from the cat back., what does restrict is the manifold the air injection reactor system the down pipes and the catalyst. The myth goes that if you remove these your car will run like a clapped out doubledecker and fail every emission test out there. Not true, if the car is set up correctly and combusting fuel in the most efficent way that it can then there is no problem passing the emission tests.
Recently more of the products that have been available in contenental Europe are becoming easily available through UK importers. Four branch manifolds are now available from Mantzel Lexmaul and SBD. Installing one of these need not mean that you should go without a catalyst, High flow racing catalysts are also available from Mantzel among others.
The SBD manifold (pictured above) is designed to work with their throttle body kits.
The primary pipes on the SBD manifold are longer than those on the Lexmaul and so I would advise you to stick with SBD if you have or are intending to fit throttle bodies and likewise use the Lexmaul manifold when using one of their ram induction systems etc.. This is simply because they have been designed to harmonise with each other.
As for the rest of the system I advise anything as long as it is free flowing and between 1.5 and 2 inches in diameter.
Dispite what the adverts and manufacturers tell you changing only the back box will have little else effect other than make the car louder. The main resistance in the exhaust comes from the manifold the down pipes and the catalyst.
Cams
There are various cam upgrades available to the educated corsa sport modifier, but I think that it is worth a mention about the traidoff's involved with a set of bolt on cams.
The 1.6XE has quite a high compression ratio, meaning that the piston comes real close to the cylinder head at the top of its stroke. The valves in the cylinder head are mounted in a 'V' formation, this allows for larger diameter valves to be used. As a result of the 'V' like valve arrangement and the high compression ratio, the top of the piston has recesses called valve pockets. These pockets prevent collision between piston and valve at the top of the stroke.
The combustion chamber does not leave a great deal of room for increased valve movement, hense the traidoff. In order to allow the valves to open more and for longer the valve timing is altered away from the optimum position. This is why after fitting a set of uprated cams the engine looses some of its torque as a traidoff for more power around the higher rev ranges. This also explains why there are only slight power gains to be made by fitting the 1.6XE with uprated cams on their own.
All is not lost though. The valve timing in these engines are set up so as to give nice and low emissions at low rpm, by adjusting the cam timing using a set of vernier pulleys (now available from piper) you can set the standard cams to their optimal position without the need for serious open engine surgery. However if you want a cam with greater lift and duration and don't mind stripping the engine, Omega pistons are available with deeper valve pockets which allow the valve timing to be moved closer to the optimum. These pistons will have a slightly lower compression ratio than the standard ones and would therefore be of interest if you were considering a
Forced Induction
A forced induction system increases the power and performance of an engine by offering a much more ready supply of air. A naturally aspirated four-stroke engine needs to draw the fuel/air charge into the cylinder, by forcing the charge into the cylinder we are not draining the engines momentum.
There are two main types when it comes to forced induction systems;
A. Turbocharging
A turbocharger is a compressor driven at high rpm by expanding exhaust gases flowing through a turbine
B. Supercharging
A supercharger is a compressor driven either mechanically from the engine or electrically
Both these methods have their followers in the motorsport world. A supercharger gives a smooth power boost to the engine right across the range, this is one aspect that it has in favour over the turbo. The turbo on the other hand since it is not driven mechanically by the engine and relies on the flow of exhaust gas across the turbine, as a result suffers 'turbo lag'. Turbo lag is a low engine rpm occurance just below the turbo's productive range. As the turbo gains speed it becomes much more efficient than a supercharger. The supercharger, as mentioned, relies on either mechanical or electrical energy (both of which impose a load onto the engine). The turbo, on the other hand, is powered by energy reclaimed from otherwise waste exhaust gases.
The development of engines using suprchargers dates fight back to the early days of motorsport in the first half of the last century, amongst the pioneers were the Auto Union (no known as Audi) won the Le Mans with a huge V16 supercharged angine that ould not have looked out of place in a fighter plane of the same era. During World War2 the Spitfire was powered by a V12 Merlin which was also supercharged. For some time Superchargers remained at the top but as technology advanced turbochargers began to show real gains over superchargers. Superchargers were heavy pieces of kit sometimes adding nearly 10kg to the weight of the engine, this is where the almost tiny turbocharger came into play. Not only did the turbo not require a mechanical power take off from the engine but its space saving design meant that was lighter and could easily be designed to fit under most bonnets. Turbos soon became the choice for motorsport, so successful was their deployment on F1 engines that they were soon banned to make the cars less powerful and safer. In the seventies teams like Cosworth were extracting 1,000bhp from a 1.6l turbocharged race engine.
Rallying on the otherhand liked the turbo and let it stay and for this reason we have the fine turbocharged cars that are around today. Rallying demand so much more than top speed from an engine with it's stop, start style, this caused problems for the turbo as rallying enines suffered from lag. You would come flying into a corner, slam on the brakes, wiggle the tail out ready for the turn then back on the gas to power round the corner, only the engine wouldn't do much, then once you were out of the corner by about a cars length the turbo would kick in and the car would take off again. This caused much head scratching amongst the factory teams and cunning plans were devised to try and resolve this problem.
The Lancia team in the height of their rallying days were a serious force to be reckoned with and in part this has to do with their plan to smooth out the power of their turbocharged engine that they used in their delta. Their solution was to be found in the form of the S4 Rally Special. This car used a large turbo to produce great top end power in tandem with a supercharger to get the engine past the flat spot in the low rev range and so the modern type of rally car was born. This was a great development and combined with all wheel drive, lead to a top class competition car of the day, but the car used 2 intercoolers and had a heavy roots type supercharger bolted on to the engine.
Time passed and rallying also recognised that the cars were getting too powerful and compromises were being made towards the safety of both drivers and spectators.
The death of a spectator hit by a Ford RS200 saw the eventual ban of the factory special class.
The cars you see today are based much more on the roadcars sold by the manufacturers, engines are limited to one turbocharger with one turbine and one compressor at opposing ends of the bearing housing and 35mm restrictors are placed in the induction system between the turbo and the engine. Teams get past this by using large turbos to increase the pressure but this leads to lag problems. The way they get around the lag problem now is a smart one, when the driver takes their foot off the throttle the ECU injects fuel into the exhaust manifold, then when the driver puts the foot back on the gas the fuel in the exhaust expoldes with a loud pop causing the turbo to spool instantly to working speed. However I think that this system would not be an ideal setup for a road car, but worth a mention all the same.
Turbo Systems
The 1.6XE will take a turbo, but as I mentioned earlier there are some pretty complex electronics to get around.
You could go for the easiest and most likely least expensive option and whip all the electronic gadgetry out of the engine and start a fresh, fitting new and independant ignition and fueling control systems. This will, however, render useless all the engine diagnostics which are there for very good reasons, mainly damage limitation.
You could go for a ready developed kit. Courtenay Sport sell a good one which uses a low pressure turbine. The low pressure turbine gives better power in the more usable power range between 2,000 and 4,000 rpm where it is most needed on the roads. They use a low pressure turbo because the compression ratio in the 1.4 and 1.6XE engines is quite high (over 10:1) if a high pressure turbo was to be used on this engine without any effort to reduce the compression ratio then detonation would occur, this is when the fuel air mix ignites before we want it to and can cause the pistons and cylinder head to disintegrate. The main advantage to this system as used by Courtenay is that it uses a modified diagnostics card which will show the turbo when checked at your local vaux service garage. This kit is thoroughly thought out and fits into the car like it has been there since it was made, and so it should do retailing at a cool £3,000 Courtenay Sport do not sell this kit by mail order and insist that they must fit it at their workshop. This is unfortunate for those of us who are unable to get there, but thats because the new engine management needs to be set up correctly and they would prefer that it was done correctly.
However creating a kit to fit is no big deal. The most important thing is to ensure that the turbo is corectly matched to the engine. This sounds simple but a poorly matched turbo will ruin the performance of the car. Motor companies spend millions each year developing turbocharged cars ensuring that the turbos are correctly matched to the engines. Matching one yourself needn't cost you millions but to take the fear out of choosing a turbo from the shelf try a reconditioned turbo from an engine with a similar engine capacity and working rev range. Compression ratios should also be quite close although work can be done to reduce the compression ratio using shorter con rods thicker gaskets and shallower pistons. If you fancy buying a turbo off the shelf then something like the Garrett gt15 or gt17 would make a good quick spooling turbo for the 1.4 and 1.6 engine sizes and the gt25 would be at the top of the scale.
Do keep in mind that the bigger the turbo, the more energy and time it will take to spool up to speed. A large turbo at 30psi might be dynamite on the race track but it probably won't even kick in until say maybe 4.5 to 5 tho rpm, this would not be much fun for everyday driving. On the road it is best to go for a smaller turbo, it will come up on the engine alot quicker and you can keep it on the right side of the surge line using a wastegate control on the exhaust turbine.
If making a kit up yourself than you will need to replace the ECU with one that is capable of monitoring a turbo this will also get all that emission control equipment off the scene although I would advise that you keep a lambda sensor in the exhaust as this will help the efficient use of fuel and avoid backfires. Newer versions of the CorsaB are fitted with a piece of emissions gear called an Air Injector Reactor System or AIR for short, If you could find a way of retaining this it would work in your favor. The AIR system works by pumping air into the exhaust manifold, the air then helps burn off any unburnt reactants and so reduces exhaust hydrocarbons and carbon monoxide. The main reason why I am recomending you keep this kit is not for its eco safty but the fact that pumping air ino the exhaust manifold helps the turbo spool in less time.
You can either modify the existing manifold to accept a turbo via a mounting plate or you could aquire a turbo manifold like those used in the Courtenay Kit, Courtenay will however supply you a manifold for the 1.6 and 1.4 engines for about £259. Then either a charge cooler, intercooler or water injection should be used to increase the density of the incomming air, your choice of these will most likely be based on available space. Keep in mind the fact that an intercooler needs cold air flowing over it for it to cool the air within, so position is essential slinging one in front of an already busy radiator may not be the best place, this may block air flow to the radiator and cause the engine to run hotter in doing so you may end up heating the charge rather than cooling it. An uprated oil pump and oil cooler along with a oil swirl tank might also be worth fair consideration at this point, the turbo will cause frothing of the oil.
You may choose to keep the original induction system on the car but if you are going to the bother of fitting the above then you might as well go the full hog and up rate this as well. Any restriction in the tract from the turbo to the engine will cause the temp of the charge to rise, and this is not wanted. May I recomend using one of the free flowing induction systems mentioned in the induction systems page of this site like the Mantzel powerbox or the induction tube from Velos. There are also throttle body conversions which allow for adding a turbo such as that offered by Regal Autosport.
With your adapted turbo kit in place let the testing begin, dyno testing is a good tool in the setup of the turbo especialy if your ECU can give a readout of boost across the rev range so that this along with ignition, fueling and power output can be compared to tell if the turbo is performing correctly. If the boost is too high then go for a compressor with lower trim than the existing, and vice versa if the boost is too low get a compressor with increased trim. In alot of cases the only things that need changed here are the compressor wheel and housing to match the wheel.
Supercharging
Suprcharging is the oldest method of forced induction this is perhaps why there are so many types of supercharger in use today from turbines similar to jet engines to roots type positive displacement chargers like those favoured by the drag racers to the modern electically driven efforts like the turbopac 1500.
The supercharger gets its power direct from the engine or in the case of the electonic versions from the battery but that in turn places a load on the alternator. The mechanically driven ones will however be the first up for discussion here.
The mechanical supercharger has its pro's and con's like turbos, although you might think that being driven directly by the engine would mean that the boost was in proportion to the rpm. Well it does work that way to a point. The boost is much more linear than the turbo producing a more smooth output. But the turbo can protect itself against surge using a wastegate to divert some of the driving energy away from the exhaust turbine. Surge is when the aerodynamics of the compressor drop drasticaly in efficiency due to excessive speed, this is the case of the mechanically driven suprcharger, boost is fine but then drops off at higher speed. The mechanically driven supercharger can however be geared to suit the needs of the engine to somewhat reduce surge conditions. Dump valves can be used to have some control over the boost. The roots type is one that suffers most in this way. Lancia had the best of both worlds in their rally special the S4 which used a supercharger to assist where the turbo fell short and vice versa.
Headwork and other internals
The standard head for these engines is not of bad design in fact most head tuners are unable to achieve more than about a 10% power increase, as opposed to 15-20% on other vaux models.
Head work is expensive in comparison to the power gained by the modifications done, and therefore I would suggest that if you were planning on really going to town on the engine then do the head work last as there are cheaper and easier ways to achieve a 10% power increase, but if you have done everything else, you want more power,money is of no consequence what so ever and you would like that edge, then go for it.
The combustion chamber is of good design and flows well, the valve size is ample for roadgoing use although SBD do sell a head with altered valves as part of their 235BHP kit. This may make the engine too tempermental at lower rpm. Atmo also provide a reworked head (available via Courtenay) adding 10BHP. I know very little about what work is infact performed on these heads mentioned above but I can offer some suggestions for those who feel up to having a go at altering a head.
Leave the valve size alone as the head flows fine, squish and chamber shape are also good so there is no real need for change there either. Not altering the chamber and squish mean that you will save yourself the work on skimming and balancing the chamber volumes to ensure that every cylinder has exactly the same compression ratio, and the correct ratio at that.
Replacement valves are available with sodium cores to conduct the heat away from the valve face, these valves will also come with narrower stems to aid flow. you may need valve seats reworked.
The ports are the main area for improvement in the head, the walls of the ports will be rough from the casting process, polishing these will most certainly improve flow. Radius any irregular changes in direction within the port. Any lips or rough sections should be smoothed. Where the port splits in two the split could be made as aerodynamic as possible creating a sharp edge and polished surfaces.
The valve guide and boss should not be ground back to the port wall but instead tapered to the valve stem. Be careful not to taper the guide to a knife edge but rather radius it instead this will make its shape stronger and more stable and resist breaking up.
With the ports radiused and polished and the valve guides more streamlined that only leaves the manifolds to be matched to the ports. This is precision work here and requires care to get them good.
Like most other modifications on this site this works best alongside other modifications. The increased flow that a worked head gives, will allow the engine to rev higher. With this will come increased stresses and strains on the remaining unmodified components of the engine such as pistons, rods, pins and the crank. A good steel crank is available from SDB. If you replace the crank then it is really best to strip the rest of the engine down and strengthen other parts also. SBD supply a superior range of internal upgrades for this engine, ranging from strengthened con-rod cap bolts which they recomend that you fit in conjunction with their injection systems in order to allow the engine to cope with the increase in power and the higher rev range (the ECU rev limiter is reset with these kits).
Replacing the internals like the crank and con-rods will not have a great effect on the performance of the engine, but the use of standard parts in an engine that revs to 7700rpm may result in significant internal damage due to component failure.
Carbs
As mentioned before the main restriction on the performance of the 1.4 & 1.6XE are their induction systems.
By replacing the old induction system with a set of carbs dramatically improves the power and performance of the engine. In much the same way as fitting the fuel injection system as supplied by SBD, fitting the engine with carbs dramatically improves the air flow.
A set of well set up pair of weber 45DCOE carbs will add approx 60bhp to the out put of the 1.6XE engine, 35's or 40's would be enough for the 1.4.
Engine noise and fuel consumption will both be up, and I would advise that you fit a sturdy flame proof exhaust as this set up os likely to backfire more than a fuel injection system. Careful consideration will be needed if you intend to use carbs with a catalyst as catalysts P/1.1
Warm air is a common problem encountered by people who add a cone filter to the engine but fail to supply it with an adequate supply of cold air. The Corsa suffers from quite stuffy conditions in the engine bay especially on some of the better spec'd models where air flow is restricted (due to the presence of air-con and power steering machinery).
Submitted by AgentBlue
[Edited on 31-12-2004 by Ian]
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