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IntroductionI wrote this page in bits as I worked on the engine. Some of my thoughts from the the early days are no longer the same as my thoughts now. But I decided to leave it alone so you can go through the same stages.
There were a number of engine variants fitted to the Astra GTE. Firstly there was the 1.8i which knocked out a decent 115BHP. Then came the 2L unit, essentially a bored and stroked 1.8. This was identical to the Sri 130 engine as fitted to Cavaliers with engine codes 20SER or 20SEH. It made 130BHP and 132lb-ft of torque. It was a tuned up version of the standard 115BHP 2.0 litre 20NE engine that was fitted to mainstream Cavaliers or MK3 Astras. At the top of the tree was the 20XE 16v version which produced 155BHP in original spec. The 16v unit shares the same bottom end as the 8v but with a Cosworth developed 16v twin cam head and an improved fuelling system with a hot wire air flow sensor rather than the flap type fitted to the 8v.
The 20SEH engine is a sturdy bit of kit with few weaknesses. Its main claim to fame is that at 130BHP in a car that weighs in at just under a tonne it gives a decent BHP per tonne ratio. Torque curves.
I had long term plans for more power. In the first case however, I decided to do the obvious air filter and exhaust changes. This is a good starting point for any engine since it'll free up the engine a bit, giving better responsivness and maybe a few BHP (sometimes a decent amount) , depending on the particular engine.
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Fuelling systemSoon after I bought the car I noticed that it sometimes died on me when under hard accleration. If I backed off for a second that it would recover. After pondering this for a while I came to the conclusion that it was probably to do with the fuel system. It was like the pump wasn't getting enough fuel to the engine. Suspect parts were then replaced: fuel filter, damper and pressure regulator. This seemed to improve things a bit. The injectors themselves were next in the firing line. I tried Redex fuel system cleaner - not much happened. Then I tried some Wynes Professional stuff (£8 trade). Not much change either. After a few months during which I sorted the air filter the problem seemed to have gone, only to be replaced by a new annoying one....There was a lump point at small throttle angles. Imagine slowing down in heavy traffic. As the throttle was released the engine slowed not smoothly but in a sudden, jerky lump. With stiffened and rebuilt suspension this became even more annoying. Eventually I concluded that the throttle position potentiometer was to blame. The reasoning behind this was that if I pumped the accelerator up and down the problem would go. It cost a bank breaking £67 for the potentiometer, but it seemed to solve the problem.
I investigated performance ECU chips. For around £240 a
Superchip would offer 10% more torque and power. How this works. BBR Starchips were another big name. I decided not to use an aftermarket chip due to some negative reports and because of future plans that would require complete replacement of the fuel injection software.I also considered a FSE power boost valve. This is an adjustable fuel pressure regulator. By setting this with the car on a rolling road it is possible to tweak the air/fuel ratio across the engine operating range.
I tried a crude experiment with the standard pressure regulator. I placed it in a vice with sockets as spacers and compressed it by about 0.8mm. This should increase the force necessary to open the release valve and therefore raise the fuel pressure. It's not advisable to do this since without an exhaust gas analyser you have no idea as to whether the engine is running lean or rich. I did notice a slight change after the compression. Things felt a little bit more positive and keen. This would make sense since the FSE claim that their valve helps iron out flat spots and makes the engine more responsive.
The mid term plan is to fit an adjustable pressure regulator (such as the FSE) if a rolling road session shows the engine to be running substantially lean or rich. The long term plan is an uprated fuelling system if it ever comes to it.
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Air filter
Exhaust systemThere were two things that I wanted from the exhaust system.
- It should enhance the looks but in a subtle way. I wanted something simple like a single 3" exit or maybe twin squares which can look pretty good on the Astra.
- I wanted a gain in torque, power and driveability but not too much noise. About 4-5% gains in torque and power would be reasonable for a system (middle section and back box). The exhaust manifold and downpipe will affect the performance too. I took some advice from a number of sources concerning the manifold. I was told that the stock manifold and downpipe are pretty good. They will restrict major top end power gains, but aren't too bad for mid range and mild top end gains. Since I was aiming for an eventual 20-25% gain and was retaining the standard cams, it was concluded that the standard manifold could stay if necessary.
Magnex are considered to be the market leaders by a lot of people. They produce a fully stainless system including a 4-1 manifold. They faxed performance curves through to me that showed a 9% power gain at the flywheel and a torque gain of about 5-6% throughout the rest of the range. A systems would cost £390 (inc VAT).
Jetex sell fully stainless systems, but I was interested in their Aluminised system. These fit to the downpipe and are made from 2" tube rather than the 1.75" of the standard car. The same engine produces 130BHP in European Opels over the UK 125BHP for this very reason. At the same time I did consider a Regal manifold which would have offered 4BHP gain. The price of the Jetex system (£150) + the manifold (£190) made the Magnex system more attractive if I was going to replace the manifold.After months! of deliberation I snapped and bought the Jetex Aluminised system. This was because I didn't think a fully Stainless system necessary, I wanted to save some money, I didn't want too much noise and the performance difference between the Jetex and Magnex wasn't worth worrying about too much. Bill Blydenstein (famous Vuaxhall tuner and cylinder head modifier) recommends Jetex too. I ordered it from Online Autosport for £160 including VAT and delivery.
When the kit arrived I was pleased to find that it included a performance downpipe. The standard downpipe is a major culprit so replacing it was a smart move. The pipe diameter was obviously larger than the standard system. I measured it at 2"ish compared with 1.75" (1.5" on corners) of the old system. A Graham Bell recommends 2.5", with 2" as a minimum in his book "Modern engine tuning". The kit contained all of the necessary brackets, hangers and clamps. It fitted together really well with no trimming required. About fitting the exhaust system
After fitting the system...- I was well pleased with the look of the tail pipe. Not outrageous, just simple and effective.
- The noise levels inside were unaffected apart from a slight rise from the downpipe end at max throttle. With the window open extra noise was more noticeable. It couldn't accurately be described as loud. I almost wished that there was a bit more noise, but nothing like my previous Peco system.
- The engine definitely appreciated the lower back pressure. It felt more lively, especially in the mid to top range.
Dyno results.| Stainless system.
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Engine tuning - Phase 2The next phase was to try and add another 10-15% to the torque across the rev range. In order to make a car suitably quicker it is necessary to add torque everywhere in the used range, or to move the working rev range higher so that more power is made. Taking a redline of 6400rpm then the lowest speed after changing occurs from 1st to 2nd and comes in at around 4000rpm. However, I often drive the car at below 3000rpm so no substantial loss of torque will be acceptable at low revs. Therefore I have looked at methods of increasing torque without losses elswhere.
Many tuners told me that big power gains are difficult to make with the 8v engine. I already had 129lb-ft, 133BHP and 101.5BHP at wheels (performance figures). After doing my research I concluded that 145lb-ft & 155BHP were realistic targets. That should give max speed about 135mph (214Km/h) and a 0-60 of the mid 7s (General calculations Detailed calculations). That's pretty much like the standard 16v, which is logical, since the 16v is the 8v engine with a higher flow head by way of the increased valve flow area and improved combustion chamber geometry.
The modifications planned to achieve this were:
Modification Expected increase Actual increase Cost Irmscher large tract inlet manifold +12 lb-ft +8BHP +2 lb-ft +2 BHP £300 Blydenstein B+ pack cylinder head +12 lb-ft +12 BHP +12 lb-ft +12 BHP £450 Vernier Cam pulley Fine tune 0 +2 BHP £45 Estimated combined gains + 15 lb-ft + 20 BHP + 8 lb-ft +16 BHP £795 Giving 145 lb-ft 153 BHP 138 lb-ft 148 BHP I did also consider changing the Cam to a Schrick fast road item. The advice given was that the standard cam was pretty much the best item for the job. Since I wanted to retain the standard rev limit and keep the max power at the same rpm I decided to leave the standard cam in place. The trouble with fast road cams is that they have to be only a mild cam in order to retain low speed torque and smooth idle. Roughly speaking, the more power gain they promise, the less tractable they will be at low engine speeds. No cam can offer a gain everywhere, they mainly allow you to gain in one speed range for a loss elsewhere.
Another idea was to change the final drive ratio in the gearbox to give more torque at the wheels. That would also limit the top speed since as standard the engine revs are almost peaking out at top speed. The box from a 1.8 Sri Astra has the same gear ratios but a final drive ratio of 3.72 compared with 3.55 for the 2.0i. That would give a 3.72/3.55=1.047, ie: a 5% torque gain at the wheels. But top speed would be delimited by 5% as well since the engine would rev higher for a given road speed. After doing some maths on this it appeared to make only a 0.1s difference on the 0-60 time. Not worth it really since the standard ratios are pretty good.
Another mod under consideration is flywheel lightening. The flywheel acts to smooth out engine vibrations that result from the two ignitions per rev of the crank shaft. A large flyheel will damp more, but it will rob acceleration, since the inertia is another load that the engine torque has to overcome. Lightening the flywheel can significantly improve acceleration and make the engine respond to throttle more quickly.
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Irmscher inlet manifold
I'd heard about Irmscher (the Opel tuning people)
making a replacement inlet manifold that offered an extra 8BHP and 12Lb-ft when fitted to an otherwise
standard engine. It achieves this by having longer, straighter and larger diameter runners. Unfortunately sourcing
one of these proved difficult. CC Motorsport tried to search out similar
items from other manufacturers for me. In the end I phoned Irmscher UK
directly. At first they said that they no longer stocked these. After some more talk they said
"hang on a minute". Three or four minutes later they came back to the phone with the good news that
they did have one and that I could buy it via Online Autosport. Costing £300 I
thought about it for a week and eventually decided to go for it. If it gained 10lb-ft of torque and
8BHP then it'd be better than a fast road cam, and it'd provide extra benefit with the head. Remember I
was planning on only doing a few modifications and this one had "right move" written all over it.About fitting inlet manifold | How does this work?
On the road the engine it took me a few days to appreciate the difference. At first it felt like nothing had changed. However, after a while I noticed an improvement in performance from 3000rpm upwards. It felt like about 5-6% extra at the wheels. It seemed to smooth things out a bit round town as well.
After two weeks the conclusion was that this mod is amazing. Got to get it rolling roaded, it feels like 7-8% more torque from 3000rpm to 5000rpm with a tapering off after that. Revs happier as well and it sounds happier at 6000rpm up to the rev limit.
Dyno results. | 1/4 mile results
Well the rolling road data suggests that the manifold has done very little! There's a few things to say about that. Firstly, even if I've gained nothing so far, it will complement the future modifications, like the cylinder head. Secondly I could feel the difference and that counts for a lot. Something that I've come to appreciate is that torque curves have a meaning, but there is something else, lots of details, that make some engines feel better than others. Either that or I'm imagining it all, which could be the case!
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Blydenstein B+ cylinder headBlydenstein engineering offer the B+ pack, a modified cylinder head with larger valves. This offers a claimed 14-16% torque and power gain at the wheels after it's been in place for at least 2000 miles (performance improves after coking up). So in reality I expected 12BHP at wheels, which is about 8% at the flywheel. An 8% improvement everywhere is going to be better than a 15% gain at the top and a loss at lower speeds.
Most of the gain is made is made by careful grinding work on the inlet port and by fitting of slightly larger inlet and exhaust valves. Bill Blydenstein hand grinds the important bits and balances up the chamber volumes. More info.
I did also consider a Vauxspeed head since I've heard good things about them.
After a good deal of thought and time, I decided to go for the Blydenstein head. Everyone who I had talked to recommended Blydenstein for Vauxhall engines. And Mr Bill Blydenstein was extremely helpful when I talked to him on the phone a number of times.
After fitting the head I did a 420 mile trip. At first I was very careful, as it is recommened to drive very gently whilst the stem seals bed in. The engine felt quite normal, maybe a bit more keen. Temptation took hold a few times and I gave it some short bursts of stick. It did feel a bit faster, but I wasn't sure. When the roads cleared later at night I gave a few more bursts of proper stick and was exhilarated to find it really did pull that much harder. It pulled more smoothly, harder and keener. And I also noticed that the ECU derived jump when driving on almost no throttle had been reduced consideredably.
The next day I went down to the MIG rolling road session at Interpro near Bristol. I was very pleased, the car definitely had moved into the next performance bracket. On the way home I had a chance to compare performance with a 16v GTE owned by another MIG member. His car was estimated to produce 160BHP. On acceleration from 40 to censored we were absolutely identical. He had an advantage from the higher rev limit because I lost a few feet on each gear change. I was very pleased.
Dyno results: at 500 miles,at 5,000 miles
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Lightened flywheelThe flywheel sits on the end of the crankshaft near the clutch. It's job is to smooth out the force impulses that occur as a results of the two cylinder burns per complete rotation. It's effect is greatest at low speeds where there is a considerable time between sparks.
When the car is accelerating then the torque produced by the engine acts through the transmission system to provide a force acting on the car. A proportion of this torque is used to accelerate the flywheel in a rotation sense. Therefore reducing the inertia of the flywheel allows more of the torque to accelerate the car. It is possible to mathematically derive the equation for the acceleration of the car as a function of engine torque, gear ratio, tyre diameter, mass of car and flywheel inertia.
The standard 2L Vauxhall engine has a flywheel with a mass of around 7Kg. I found that SBD sold a 5Kg flywheel for £65. They did not quote the inertia of the unit. If it is assumed that all material is removed from the side of the flywheel then the inertia and mass are directly proportional. I did some sums on a solid disc and calculated that a Steel disc of 290mm diameter and 14.5mm thick would have a mass of 7.5KG and a moment of inertia of 0.08Kgm2. Reducing the thickness to 9.5mm would give a mass of 5Kg and a moment of inertia of 0.05Kgm2. Therefore this flywheel would offer approximately a 0.03Kgm2 inertia reduction. Plugging these numbers into my maths model predicted that I would get about a 2% acceleration improvement in 1st gear, tapering off to almost nothing in 5th gear.
The car idles fine with the lightened flywheel. On the road I thought that I could feel an acceleration difference. Nothing astounding though.
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Vernier cam pulleyA vernier cam pulley allows the angle of the camshaft to be fine tuned relative to the cam sprocket. This means that the moment when the valves open and close can be moved forwards or backwards in the combustion cycle. There's two advantages to this. Firstly production tolerances mean that the standard timing can in fact be a bit out. The second is that adjusting the cam timing allows the torque curve to be squished one way or another. Advancing the cam timing will push up power but drop low speed torque slightly, retarding will have the opposite effect.
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ThrottleAfter fitting the head and running the car for a while my attention focussed on what was holding back power delivery at the top end. Online Autosport told me that bored out 1.8GTEs made more power than 2L 8v engines with identical modifications. The reason for this was that the 1.8s had a twin throttle housing, rather than the single 55mm of the 8v GTE. Futher more in "modern engine tuning" I read that a 56mm plate was sufficient for around 140BHP, so I was already asking for too much.
As a first step I modified the existing throttle housing. The steps in the wall either side of the polished throttle section were smoothed out using a hand held grinder. The spindle was halved by hacksawing half of it off. It was calculated that this would produce a 6% increase in flow area. It was observed that the throttle was not quite opening fully due to wear in a plastic bush on the mechanism. This was rectified by filing away the end stop. The linkage plate end stop was then carefully bent so that the plate was horizontal when the end stops were touching. Finally one of the return springs was removed to give a lighter feel to the throttle.
Read my warning about cutting the throttle spindle.
On the road the lightened throttle felt a lot better. Around town it required a bit more leg muscle to hold my foot off. In fact lightening the tension is probably a bad move since it begs you to press down more often. The engine seemed to run smoother, which is odd, maybe I was imagining that. Never the less, for a few hours and virtually no cost I might have picked up a percent or two. Every little helps.
Whilst studying the throttle plates I made a series of measurements of the flow passage sizes.
Everything except the throttle plate is larger than the air flow meter. The modifications to the 2.0 plate were estimated to have increased the flow area by 7%, up from 78% of the air flow meter area to 85%. However, moving to the 3.0 unit would increase the area to 113% relative to the air flow meter. Modifying the 3.0 unit is probably not necessary, though I think I'll halve the spindle because it looks cool!Part Dimensions in mm Cross sectional area in mm2 Cross sectional area relative to air flow meter Air flow meter 50 x 50 2500 1 Inlet pipe 65 3320 1.32 std 2.0 throttle housing outlet 60 2830 1.13 standard 2.0 throttle plate 54, 6mm spindle 1966 0.78 modified 2.0 throttle plate 54, 3mm spindle 2128 0.85 3.0 throttle housing outlet 70 3850 1.54 standard 3.0 throttle plate 64 2832 1.13 modified 3.0 throttle plate 64 3024 1.21 About fitting the 3.0 throttle housing.
On the road I immediately notice an increase in engine response. The noise was different too. There was less roar and more induction boom. In some ways better, in some ways not so good. Because I'd not fitted the throttle gearing down linkage pulling away in traffic was a bit more of an art.
After I got the car back from its respray and had the injectors cleaned I found it to be unacceptably jerky round town. I managed to solve this, as explained here.
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InjectorsI had the injectors ultrasonically cleaned at my local Lucas dealers (look in Yellow pages). I had to drop them off and pick them up the next day. The results showed that one injector had a poor spray pattern. The flow rate improved by about 5% for all of them.
The fuel injectors are basically solenoid operated switches which open for a period of time decided by the ECU and hence meter the pressurised fuel. The standard ECU and system have a certain amount of leeway, say 20% before they reach their limit. If it is planned to raise power beyone this then there are a number of things that can be done. Since flow is proportional to the square root of pressure, it is possible to increase the injector flow by increasing the fuel rail pressure. The 8v engine runs at 2.5bar (2.5 atmospheres, roughly 35psi). It is possible to increase the pressure up to around 5bar. The limiting factor is that if it's raised too much then the injectors cannot open against the pressure. Taking 4bar, that allows a power increase of the square root of (4/2.5) which is 1.26. That means there is potential for about another 25% increase in power. There comes a point at which it is better practice to fit larger injectors and return the pressure to normal.
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Final drive ratio When the gearbox finally died I took the opportunity to fit a reconditioned gearbox with a lower final drive ratio. This improved the acceleration of the car from standstill but limited the top speed. It did not change the power or torque of the engine. The way it works is quite simple to understand. Lower gearing (ie: final drive ratio is a bigger number) means that the engine has to spin more quickly for a given road speed. This means that gear changes occur at lower speeds. It also means that the torque at the wheels increases in proportion with the gear ratio. It's like changing down a gear on a mountain bike - your effort produces more accleration but your legs have to spin faster.It also meant that in my case I could now hit the rev limiter in top gear, whereas before I would reach the power limited top speed at about 6400rpm, leaving me a 200rpm margin before hitting the rev limiter. By the way, seeing what mph corresponds to max rpm in top gear only shows you what speed you could acheive if your engine has enough power to get there. Most cars cannot hit the limiter in top gear because they don't have enough power to do so.
I spent a good deal of time with my acceleration calculater seeing what changing the final drive ratio would do to the 0-60 and 1/4 mile times. The reconditioners WTC had four ratios available. 3.55 (standard for GTEs), 3.7, 3.9 and 4.17. These offer 5%, 10% and 17% increases. Now at first glance the 4.17 ratio might appear to be the one to go for. However, I found that it actually made acceleration increments at higher speeds take longer. The reason for this is because you have to change gear earlier and each time the next gear is selected the torque at the wheels falls by another step. The choice was then between 3.7 and 3.9, with 3.9 offering better acceleration gains than 3.7. I considered the rpm per mph. At 80mph the 3.55 ratio requires 3800rpm, 3.7 4000rpm and 3.9 4200rpm. I felt that I could live with that. So I chose a 3.9 final drive. Top speed would now be reduced from 140mph indicated at 6400rpm to 128mph indicated at 6600rpm. I felt that I could live with this since acceleration in the 0-70mph range is more useful than license losing top speed.
The computer model showed a 0.2s improvement in 0-60 and 1/4 mile times when the final drive was changed from 3.55 to 3.9. It might not sound much, but that's a good result considering that the engine output and car weight are unchanged.
About fitting the gearbox | 0-60 timings.
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WeightwatchersTime spent playing with the acceleration model quickly showed that stripping weight from a car had a dramatic effect on 0-60 and 1/4 mile times. It is also an elegant solution for other reasons: it will improve braking effectiveness and cornering ability. It took me a long time to sum up the courage to rip the interior out. I was worried about noise mainly. But once I'd started then there was no stopping me. Every bit of extra weight was evil and stealing acceleration from me.
Pictures of the weight loss program. |1/4 mile results.
The previous mild Steel system had lasted well, but finally the weld to the back box fell apart. I decided that stainless Steel was the only way to go. None of the big names had a system for a MK2 GTE 8v off the shelf anymore, so I went custom. I looked at Powerflow and Longlife exhausts.
Now
the diameter of the exhaust caused a lot of heartache. Longlife recommended
a 2" system. My tuning books said 2.25" would be better. I phoned round a
few people. Janspeed, who make 4:2:1 manifolds amongst other things said
that their uprated system used 1.75" diameter anyway and that 2" would be
fine. Getting the exhaust diameter right is a balance between making it too
restrictive or making it too large and then the exhaust gas speed falls.
Decent gas speed means that the momentum of the gas pulses helps pull the
gas out of the manifold.With the new exhaust I noticed that the car seemed to pull more smoothly from 2,000 to 4000rpm. I was very pleased with the noise. A bit louder than the previous exhaust, but in the best way. Not droning, but burbling and occasional popping on the over run.
Dyno results. | 1/4 mile results.| More 1/4 mile results | More dyno results.
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ECUThe on board ECU controls the ignition advance and fuel injection pulse width using a built in map of data values. The engine speed and air flow rate are the primary input values, whilst air, oil and engine temperature are secondary inputs. The standard program is designed and tested by the manufacturer to satisfy a number of requirements. It also has a number of safety margins built in. By pushing into these margins slightly it is claimed to be possible to add up to 10% to torque and power. I used to believe this, but results I have seen show that on average, on a non-turbo car "chipping" with an "off the shelf" chip acheives very little. It might smooth out lean running between 1.5 and 3K and raise the rev limit a bit, but it is a very blunt instrument. It's akin to randomly turning the adjustment screws on a carburettor and advancing the timing a tad in the hope that it will make things better. My advice is to not bother with off the shelf chips unless you want to raise the rev limit easily. Info on chipping.
I considered Superchips, BBR Star Chips and the Dastek UniChip. The first two are more of a "one size fits all" design, whilst the Unichip allows a skilled technician to adjust the fuelling and ignition for maximum torque at a range of speed and load points. It's a "piggyback" chip in that it intercepts and alters the signals from the standard ECU.
I also looked at complete replacement management systems. Such as Alpha, Lumenition Emerald and MBE. The biggest expense of such a system is the actual mapping operation which takes about a day and a half of rolling road time. Originally I had planned of keeping the standard induction system, but if I was going to spend so much on the mapping then I may as well buy one per cylinder throttle bodies. Essentially fuel injected twin carburettors.
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CamNow people get all excited about chipping and camming their engines. A "fast road" cam shaft can indeed add 5-10% to the peak power output. It can add a good deal more if the engine is modified so that the maximum safe rpm is increased too. The general effect of fitting a power gaining cam shaft is that it moves the torque up the rev range. Since power is torque x speed then this increases the power. It also tends to increase the torque slightly, but this increase is at high revs. And, depending on how extreme the cam is, it will lose torque at the lowr end. Some cars noticeable come "on cam" as the revs rise. This can be fun, but good torque across the range is very useful and nice in a road car. On a race car that is kept in a narrow rev range pretty much flat out for short periods of time a narrow and peaky torque curve is acceptable.
On a pretty much standard bottom end then a cam swap is not necessarily worth it unless money is no object. With the 2.0 8v 130BHP engine the cam shaft is already a semi "fast road" item. It makes peak torque quite high up the rev range, though the torque spread is still very good. A replacement cam is agreed to add about 5-6BHP realistically with only a very slight loss in torque at the bottom of the rev range. In my case I deemed it better to wait until I had a safe 7250rpm limit and a suitable ECU. Then I could easily and effectively add 10% to the power.
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Engine tuning - Phase 3The next phase was aimed at building a solid platform for future power increases. The core of this was a 16v bottom end. The 8v head was mated to this. In the first instance the ECU and cam remained standard. The next step after that is toreplace the standard ECU with a fully mappable ECU, with Emerald being the favourite. It was hoped that fuelling improvements and removal of the air flow meter would allow an extra few lb-ft and up to 10BHP to be produced. Eventually a longer duration cam might be used to take advantage of the higher rev limit. Depending on the cam choice it is thought that around 160-170BHP would be possible. Finally full throttle bodies could be fitted. A similar engine with twin 45 carburettors made 180BHP at a rolling road feature in one of the car magazines. Since the 16v engine can make 196BHP with a similar set up it is hope that 180-185BHP will be possible with throttle bodies. Bearing in mind that the car weighs 880Kg and can do a 15.19s 1/4 mile with 145BHP then this should be plenty fast enough.
For months I had a spare 2.0 8v bottom end sitting on my driveway. However, when I went round to Maynard Engineering (local engine workshop) and got talking about what I wanted to do he offered me a 2.0 16v bottom end for £150. This was a very quick and convenient way of getting a clean bottom end and the uprated con rods or the 16v engine.
The spec for the final item was:
- 16v bottom end
- race spec bearing shells
- full balance
- ARP uprated con rod bolts
- lightened 16v flywheel (more fixing bolts so safer)
- Helix uprated clutch
- rebore from 86mm to 86.5mm giving 2.02 L (the largest size standard pistons. £35 each as opposed to £100 each for bigger ones)
- Pistons machined to lower compression ratio to 10.5:1
- new oil pump
- SBD machined oil pump gear
- SBD nylon pressure relief valve
- Oil gallery restrictor plug to mate to 8v head
- new water pump
This engine is safe for 7750rpm, though around 7250rpm will be the max used when the after market ECU is installed.I did some maths on the compression ratio of the 2.0 8v head on a 16v bottom end with 16v pistons fitted. It looked like the compression ratio would be somewhere in the mid 11s. This was way higher than the target figure of 10.5.The standard 8v Sri 130 engine is 10:1. Bill Blydenstein helpfully told me that his head lowers the combustion chamber volume from 47cc down to 43-44cc. This would make the compression ratio of the B+ head on the 8v bottom end around 10.5. Though it is tempting to pump up the compression ratio further , the fear was that I'd bolt my new engine together and it'd pink badly. Therefore the emphasis was on keeping things sane. Fitting a longer duration cam does mean that the real compression ratio will be lower than the geometrical compression ratio. However, I was running with the standard cam in the first instance. I did some calculations and worked out that removing 0.8mm from the base of the 16v pistons would take the compression ratio down to the required 10.5.Compression ratio calculations.
The new engine was built up over a long weekend.Rebuild pictures.
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4:1 Tubular Exhaust Manifold
I
originally bought a 4:2:1 manifold very cheaply. I think it's a
Janspeed item.
Sadly, this was thrown away by someone who thought it was
scrap. I lost interest for a while after that, especially
after SBD told me that the 4:2 cast manifold wasn't that bad
as long as you were using a decent 2:1 downpipe.About a year later I was offered a 4:1 manifold from an Opel enthusiast in Brazil who wanted some 16v engine parts in return. In the end this didn't work out cheap, the manifold essentially cost me £160. It did look good though and I was keen to fit it. My carb tuner had told me that he'd found that some 4:1 manifolds improve low rpm performance as well as high rpm. Most tuning books say that a 4:2:1 manifold is best for mid range torque, plus I'd had a very unfortunate experience with a PMC 4:1 manifold on my 1.3 Astra.
I was very pleased with the difference the manifold made. Low rpm pull was noticeably better. I couldn't feel any difference in the mid range. At high rpm it seemed to go a little better. Hard to tell really. It certainly didn't seem any slower. The noise was much improved. The carbs seemed to barp that much more crisply.
