The cheapest way to get more power from your Nissan Silvia S12 is by using a bleed-off valve fitted between the turbo and it's actuator. You will need to use silicone hose as the heat from the turbo will melt other types of hose.
An 8mm diameter plastic tee will also do the trick. Routing the pipe from the turbo through the straight part of the tee to bleed off, and coming from the tee at 90 degrees to the actuator gives the best results. A valve can be fitted to the bleed-off pipe to regulate the amount of boost. An up-rated actuator will do the job more efficiently without spiking, but they can be quite expensive. Other work is necessary before you attempt anything of this nature.

The Nissan Silvia S12 was never fitted with an intercooler! This should be your first modification. I have seen many different types fitted to the Silvia. The Volvo and the Saab do the largest ones, they are as large as the main radiator and involve moving or changing the radiator. The radiator cowl also cannot be returned as the gap between the engine and the radiator is reduced. Nissan fit a nice range of wing mounted intercoolers to the 300ZX. 200SX S13 and 200SX S14. These will fit the Nissan Silvia S12 with the 200SX S13 being the most awkward to fit.
Intercoolers with the side tanks separately fitted and held by a band of aluminium tabs are usually suitable for up to 14 psi of boost. The Ford Cosworth unit is much stronger and will withstand much greater pressures. All these units are relatively inexpensive, but you can spend a fortune if you wish. Many have!

On top of the inlet manifold and towards the rear of the engine is a safety valve. This is fitted to protect the engine from being boosted too high. It was designed to vent to atmosphere at 14 psi, but with age it can operate as low as 10 psi This valve can be removed and the head of a bolt welded inside the fitting, or a cap from the plumbers merchants fitted in place. The T2 turbo will not deliver much above 14 psi, so the safety valve is unnecessary.

You will need to fit a colder spark plug than the NGK BCPR6ES and this is the NGK BCPR7ES. The standard plug gap is also too large as boost pressures above standard blow the spark away whilst it is trying to jump the gap. In imperial the reduced plug gap is 25 thousandths of an inch.
The timing can be adjusted from the standard 15 degrees before top dead centre to 17.5 degrees to liven things up more.

A less restrictive exhaust system and air intake are also recommended. These alone should provide an extra 20 BHP. Modifying the air filter housing is easy and costs very little. The mesh is already there under the lid. All you have to do is remove the mesh and the sound deadening material and cut around the lid. Spot weld or glue the mesh back in, put a bit of paint on and plonk a Nissan badge on top.

The exhaust is harder to make especially if you increase the diameter. There is not much space over the top of the rear cross-member. Usually the front silencer is removed and a straight-through silencer is fitted to the rear.

To set the boost level a separate boost gauge is recommended. If you are still running the standard T2 turbo, your engine has been well maintained and your turbo is good then you may proceed. Wind the boost up to 10 psi and run the car for a while making sure that no detonation noise can be heard. If all is fine increase the boost to 12 psi and test again. If you are using the bleed off method don't go higher as you will get a 2 psi spike above your 12 psi. It is more than double what it is supposed to do including the spike!

Remember that you probably are near if not above 200 BHP now! The turbo is thrashing your oil and your engine is working the oil harder, so change it even more frequently than Nissan's recommended 3,000 miles. Reliability should not be any less if you bear this in mind.

If you are having trouble with detonation do not run the car until you are sure you have cured it. Basic unleaded fuel is totally unsuitable, so use super unleaded or other available higher octane fuels. The timing can be retarded, but this spoils the normal driving. Usually an efficient intercooler will solve this problem, but if the problem persists, all is not lost! There is a little trick that can be done. This involves using the detonation sensor wiring from the ECU. The circuit only becomes operational above 2,200 revs and the senor grounds the wire through a reed switch when detonation is detected. A variable pressure switch adjusted to operate at the required boost level can switch this wire to ground and retard the timing by 5 degrees. The pictures show a variable pressure switch fitted to an inlet manifold, a home made actuator saddled with a door pin switch that performs the same operation, and a suitable plumbing position, near the servo unit for one of these devices. The vacuum control unit feed for the automatic transmission is taken from here. There is a rubber blanking cap fitted to the manual transmission models. This is also a good place to run the small hose to the dump valve from.
Where automatic transmission is fitted care must be taken not to reduce the diameter of this pipe as this can cause the vacuum control unit to be less sensitive, and prevent an increase in output from the pump under hard acceleration. Slippage between gears will happen in this situation.

Above the region of 14 psi boost pressure is when the major expense starts, as the fuel pump and injectors will not deliver sufficient fuel to match the amount of air being rammed in.

Money Saving Tip:
I had a broken air-flow sensor in the garage, and as I never throw things away, I managed to find a use for it eventually. It is perfect for fitting an after-market filter too! A saw and a file and there it is. Fits both the Nissan Silvia S12 and the 200SX S13.
 

Improve Your Front Suspension:
Remove the struts from the front of the vehicle and remove the springs. Undo the top nut being careful not to loose the O ring below the nut. Empty the fluid from the strut and refill with the same amount of automatic transmission fluid. You will need to purge the air by carefully and slowly moving the piston up and down. When you have completed this and refitted everything you will now notice the front of the car is considerably firmer. This will cost you less than £5 but takes a while to do. More details at: http://silviaturbo.proboards30.com/index.cgi?board=how&action=display&num=1082743187

Cam Tweaks:
This is Shaun's pulley as modified by an engineering firm near him. If you want to know more you can find him on the SXOC forum under the name "S13eater". I am sure he will be pleased to help and answer any questions. This modification will help towards the 350bhp he will be achieving.

 

Coil Grounding:
Having given advice to others on this matter my car broke down the other day! Only for 20 seconds though! I scratched around the mounting bolts to the coil with my key, the engine fired and I drove home. I have fitted an extra earth strap to the power transistor side of the bracket, and from the opposite side where the earth for the tachometer is I have added an earth cable to the engine. I have also applied petroleum grease over the bracket to minimise further corrosion. I intend to repeat this exercise to the other vehicles and using stainless steel brackets in the future. Why did Nissan not provide a ground wire for this unit?

Air Flow Meter Improvements:
There are two wire elements on this unit. The first element in the path of the air is the hot wire the second detects the air temperature and sends a signal to the ECU. These elements, although titanium coated, eventually accumulate small particles of dirt. When dirty the unit will make the engine run a higher CO at idle and too lean under heavy load. To rectify this a jet of carburettor cleaner fired at the elements from both sides will restore the precise metering, and the original economy figures.

Wiring Problems I have found:
Sat on the driver's side chassis leg below the washer bottle are wiring loom plugs and sockets. The terminals inside the plugs after many years become corroded. It is advisable to check these out and clean them. They are very awkward to remove though. As our Silvias are not getting any younger it would seem that windscreen washer motors are beginning to leak. These drip directly onto where these plugs are located and can cause the car not to start as the ECU gets it's start signal via one of these plugs. Also the feed for the starter solenoid passes through here so check them before you change the starter motor. If you study the picture you can see the white plastic fitting with a cable looped over it. The plugs are clipped in behind here.

When the Horn stops working:
I have come across a few Silvias where the horn has stopped working! (None of mine I must add) On every occasion I have found corroded wires to the relay. The relay is located at the side of the battery and on every occasion two of the three wires have been bad. Riding around without a plastic arch guard will cause this fault.

When the lights won't go down:
I have only come across this one twice and this has been down to a corroded wire feeding the retract control relay. This relay is grey and is found at the side of the battery. Riding around without a plastic arch guard will cause this fault.

Headlamps won't flash:
This is a common fault in Silvias from late 1987 to mid 1988. Nissan must have used a poor batch of headlamp/indicator stalks. Sometimes there will only be one dipped headlamp illuminated. Try another stalk before you spend hours in the wiring and relays.

Silvia Water Pump:
The picture shows the front of the engine with the radiator, drive belts, crank pulley, fan, timing covers and water pump removed. The water pump is quite easy to replace, but there are numerous parts that have to be removed to gain access to all the bolts. It can be done without removing the timing belt. Having removed the cowl from around the radiator, you must remove the bolt from the centre of the crank pulley. The reason for this is that the engine is harder to turn with all the belts fitted, and if it is exceedingly tight, which is usually the case, you can lock the power steering pulley to get more force on the bolt. With a manual chocking the wheels and putting the car in gear will be of good use when attempting to loosen the crank pulley bolt. If you can't undo the screws holding the cowl to the radiator there is a section at the base of the aperture in the cowl that can be removed. Unclip this, the pipes attached to the radiator (two extra on auto) and the two bolts at either side of the radiator at the top and the radiator and cowl together can be lifted vertically up and away from the vehicle.
When you have removed the water pump make sure all remnants of the old gasket have been removed, I use a razor blade for this. Then using a block with fine wet & dry paper clean up the surfaces to be mated. Re-assemble using a Nissan gasket or and instant gasket silicone. Check for leaks afterwards and bear in mind that after refilling the system and running the engine to temperature any air locks will be forced through to the top of the radiator. When cooled down sufficiently you often find another half a litre may be required to return the level to the top. The job went well and only took two and a half hours.
All was not well though! The instant gasket only worked for two days and then drip, drip! I re-fitted the water pump with a Nissan gasket and fitted a new timing belt at the same time. I also found a split in the radiator cap seal and replaced it. No leaks at last! I thought! The new cap found a weak spot in the radiator and drip, drip! Before all this it was a water pipe going to the turbo! The radiator was second-hand when fitted, the turbo pipe was unpainted and rusty and the water pump could have had a fan belt too tight in the past. I can't blame the Silvia.

Uprated Actuator:
This picture was sent to me the other day from 'Datman' from Datsunworld and this is how he made it: "A tip I can pass on is a DIY adjustable actuator, weld a hook on the bracket, and make a clamp on the rod (I used a piece of carb, the bit that clamps the choke cable) run a stiff spring between the two and adjust the boost pressure by sliding the clamp up or down the rod". I wonder how the heat affects the spring but quite like the idea.

Clutch/Gearbox Change Tips:
Changing a clutch is a straight forward job, and here are a couple of tips. Support the front of the engine before removing the gearbox as the back end of the engine lifts when the box is removed. If the back end of the engine is higher than it should be it is impossible to line up when re-fitting. Use many extensions and a socket to get the bell housing bolts off and do it
from under the car as this is far easier than working in a tight space with a little spanner. Drain the gearbox oil first then you don't end up sliding about in gear oil when the prop-shaft is removed.  Make sure you can undo the level/filler plug before you put the box back so you can put fresh oil in it when it goes back. While you are under there replace the oil in the differential too, and as before see if the level/filler plug comes out first.
If you are changing the gearbox too there are a few differences in the floor-pan underneath between the pre-1987 and the post-1987 models. The mounting positions for the gearbox are nearer the front by around 75mm on the earlier models, the gearbox is slightly shorter and the prop-shaft is slightly longer. If you need to replace the gearbox and are unable to get the correct type then you must get the prop-shaft too. Everything will fit except for the gearbox mounting bracket, but two of the four bolts will fit. This will probably be sufficient to keep you mobile and the other two anchorage points can be attended to later with an added bracket and bolts. If you have to separate the prop-shaft at the centre joint for any reason put identification marks on first so that it can be put back together as before. The prop-shaft is balanced. If it is re-assembled differently there will be undesirable imbalance along with noise and vibration.

Uneven Idling of engine:
Things that can cause uneven idle on the standard setup I have found are:
Corrosion deposits on the distributor contacts and coil lead socket. Very old or non-Nissan high tension leads. Air leak on the charge piping or inlet manifold. Corrosion on the coil mounting bracket. Bad earths. Badly adusted throttle contacts. Accumulated dirt in the auxiliary air valve (auto choke thingy). Accumulated dirt in the IAA unit (the unit that houses the idle-up and FICD solenoids). Accumulated dirt on the wire elements of the air-flow sensor. Splits in vacuum hoses.
The obvious but sometimes overlooked are:
Timing out of adjustment. Plug gap/make (don't fit Champion spark plugs). Poor quality petrol. Non twin piston or diaphragm dump valves. A near death battery/alternator (metered at battery terminals the voltage should be over 14 Volts).
I occasionally put Redex down the plug holes in an attempt to remove carbon deposits off the valves, piston rings and the top of the bores as this can cause uneven idle in severe conditions. It is also fun if you drive into town belching out clouds of smoke. To check the rings remove the oil filler cap with the engine idling and there should be no drop in revs. If there is then Redex will solve this if the problem is not serious. I also add the occasional shot of injector cleaner to the petrol to keep the injectors in order.
My final thought on the matter is the plugs directly below the front windscreen washer motor attached to the chassis leg. They get corroded and can cause numerous problems (especially if the washer motor leaks) including non start problems. They are awkward to get at and work on, but all the ones I have checked have been suffering corrosion to the
terminals to some extent. Occasionally wires have come off their terminals during inspection and I have had to repair the wiring with new terminals.

 Rear Calliper maintenance:
To move the rear calliper away from the disc the handbrake cable must be removed first. This can be done by removing the vertical anchorage bolt seen when looking down from behind the disc. With the bolt removed the bracket attached to the cable can be turned through 90 degrees and pushed towards the rear of the vehicle so that the cable can be removed from the calliper. At this point it is recommended that the cable is checked for free movement within the outer part. If the movement is stiff the introduction of oil combined with back and forth movement of the cable should solve the problem. In severe cases the cable may be removed from the vehicle for easing it's movement.
If you are new to the Silvia S12 the rear pistons will not push in like the front ones, you have to screw them in clockwise as they use a ratchet mechanism for the handbrake. I use the tool for changing disks on an angle grinder for this. The pistons should turn quite easily and the dust boot should not move. Sometimes the dust boot sticks to the piston and as the piston is turned the boot gets ripped out from it's housing. If this happens the boot will not go back without the piston removed. I always break any adhesion between the boot and the piston before I turn it. A light smearing of grease can help.
Original pistons have 4 triangular recesses in them,  these recesses are designed to house a raised "nipple" found on the back of the pad. This prevents the piston from rotating when the foot-brake is applied. Check that the nipple will sit in one of these recesses when returning the calliper.
Where the calliper bolts are steel rods that slide in and out. Check that these slide freely when servicing. They should pull out quite easily with the rubber dust boot attached. Clean any hardened grease from them and apply new grease if necessary.
If the piston is difficult to turn it can be removed and inspected. Provided the surface is not pitted with rust the piston can be cleaned and returned. Do not use abrasive materials other than a fine rubbing compound. The piston can be removed by levering on the handbrake mechanism on the bottom part of the calliper.
Bleeding the rear callipers in position without a pressurised system is virtually impossible. To do this with pedal pressure I recommend that a wooden block is wedged in to prevent piston movement and the calliper is held up with the bleed nipple at the top. As the pedal is pumped all the air in the flexy pipe can be expelled successfully.
If you have no assistant the calliper can be tied up with wire and the nipple opened, a section of windscreen washer hose plugged on to the nipple with the non-return valve from washer system and the end of the tube in an empty Pot Noodle container with an inch of brake fluid in the bottom. A few gentle pumps on the brake pedal will expel all the air.

Automatic Gearbox Modification:
As standard the automatic transmission fluid is cooled through a small section in the bottom of the main radiator. This is not sufficient for above standard boost, or towing home another Silvia. The method shown in the picture is the perfect solution and totally eliminates the risk of contamination of the transmission fluid with coolant. This can happen with older radiators where the division between the two sections of the radiator corrodes. The only problem with this setup is that the radiator cowl can only be removed when the radiator is out of the car. However, there is a clip on part at the base of the cowl that can be removed. When this part is removed the radiator along with it's cowl can be removed easily with the fan still in place.

Heated Rear Window:
Nissan didn't put a relay in the heated rear window circuit! Another Except Europe thing. As a result of this our switches are getting hot and scorched! I suggest that there is a danger here! The switch obviously carries a large current, but this can be easily remedied using a relay. The circuit will then be switched by the relay and the relay switched by the switch.
The relay can be fitted on top of the fuse-box and the wire from the fuse cut and sent through the relay, and the live spliced and sent to the coil of the relay. The switch wires can the be joined together and an wire brought from the remaining terminal of the relay coil to the switch with the opposite side of the switch sent to ground.
A blue Nissan relay is used and will slide onto a slot above the fuse-box and click into place. The extra wires going to the switch can be fed behind the dashboard using a straightened metal coathanger.

The Ultimate Tweak:
A glimpse at Den's rather large turbo and custom manifold. This beast produces 430 BHP. The wastegate only opens at 30 PSI and vents through a separate short pipe to atmosphere making a wonderful growl. The acceleration is phenomenal. The differential is from a 300ZX with an S14 gearbox and a modified S13 engine. A massive intercooler cools the charge air being rammed into the engine.
Update:  Den is now well over the 500 BHP mark and still wants more!

Valve Clearances - Silvia S12:
Valve Clearance Hot. Intake and exhaust 0.30 mm (0.012 in) adjusting lock nuts 18 – 22 N/m (13 – 16 ft/lb)

Set No 1 cylinder at top dead centre on its compression stroke and adjust No 1, No 2, No 4 and No 6.

Set No 4 cylinder at top dead centre on its compression stroke and adjust N0 3, No 5, No 7 and No 8.

                            1        4        5        8

Camshaft front                                            Camshaft rear

                            2        3        6        7
 

Turbo Removal Explained:
In the picture are the modified tools needed to remove the turbo complete with the exhaust manifold. They are half a 14mm ring spanner, part of a 14mm open-ended spanner and a chisel with a 'v' cut in it. Other tools needed are a 10mm, 14mm 17mm socket and ratchet, mole grips, hammer, 10mm and 12 spanners,  a jack, axle stands, screwdrivers and a bucket to collect drained coolant. If a strut brace is fitted a 17mm socket will be required to remove it but the bolts must be returned before jacking the car. The car is jacked up for three reasons, one is to access the clip holding the oil return pipe and the 3 bolts attaching the exhaust to the down-pipe, the other is to make the job less painful on the back of the legs and lower back and the final reason is to make life easier to retrieve the spanners that inevitably drop in the process.
So, as stated jack and support the vehicle and drain the coolant into a bucket using the drain cock to the base turbo side of the radiator, remove the exhaust from the down-pipe held on with three 17mm bolts. I use a 'wobble drive' extension with a socket as one of the bolts can be obstructed by the exhaust when trying to get vertically on it. Put a rag in the exhaust as a friend dropped a spanner down it once during an engine change and it took ages to retrieve it. Undo the oil feed pipe, and the water pipes along with their brackets. Undo the clip holding the oil return hose where it attaches to the sump and twist the pipe a little to break any adhesion. Remove the charge pipe coming out of the turbo. Remove the induction pipe completely by disconnecting the oil breather undoing the clips at the air-flow meter and turbo. Remove the manifold bolts and withdraw the turbo along with its pipes, manifold and down-pipe. The oil return pipe should pull off in the process.

There are two variations to the oil feed arrangements for the uk engine, and these are as follows: Before 1987 models have the oil feed pipe coming from near the oil filter, this pipe is routed up to just below the cylinder head and then to the rear of the engine, round the back, then along the opposite side and into the turbo. The later models have a short pipe running from a drilling in the block below the distributor going only a short distance into the top of the turbo.
Nissan recommend that the engine is removed to change a turbo probably due to the restricted access available, but it can be done with the engine in place using tools similar to those shown.
The only difference between the two is that the oil feed pipe is attached to a bracket holding the lower water pipe and there is a compression joint in the oil feed pipe behind the engine above the bell-housing. This is where the part open-ended 14mm spanner and chisel are needed. This must be done before the pipe brackets are loosened as it keeps the compression joint secure. Balance the part-spanner on the nut and locate the groove of the chisel on the part-spanner, hit the chisel with a hammer and this should loosen the nut. The nut should then spin off by hand and when it is ready to be reassembled a pair of mole-grips clamped to the part-spanner should provide sufficient leverage for re-tightening it.
From memory there are two 10mm bolts holding a pipe bracket behind the engine on the turbo side and one on the inlet side along with a 12mm nut holding a bracket on the inlet side for the top water pipe. The water pipes are joined near the rear of the engine on the inlet side and it is easier if these are removed along with the turbo rather than attempt to remove the connections at the turbo.
The manifold has 4 bolts at the top and two underneath, three are straight forward whilst the fourth requires the half ring spanner for access to the bolt. You will find the awkward one under the manifold and closest to the bulkhead.
When you have fitted a replacement turbo it is recommended that an oil change is done at the same time and that the engine is turned over for 15 seconds with the coil lead removed. This guarantees that oil is present in the turbo before the engine fires.

Problems I have encountered/heard about are as follows:
Manifold bolts won't tighten due to stripped threads in the head. This can only be rectified correctly by drilling and fitting helicoils. Care must be taken regarding the depth of the drilling. Do not drill any deeper than the existing hole as the oil galleries are right behind.
Uneven surfaces caused by exhaust gasses blowing past joints. In such circumstances the mating faces need to be machined flat before reassembly. Manifold to turbo joints are the most common although I have heard of manifold to engine faces becoming distorted.
Studs snapping/stripping on the down-pipe where the exhaust attaches. These will need to be removed/drilled out and new studs fitted. I have seen the holes drilled out and nuts and bolts fitted but this makes future dismantling more difficult.
Water pipes to turbo difficult to bolt back due to excessive bending on removal. This is inevitable so try to bend any pipes as little as possible when removing a turbo.
It is essential that the lower water pipe is attached by it's bracket near where it connects to the rubber hose otherwise the pressure may blow it off.
Nissan recommend that new nuts and split washers are used when refitting a manifold and new locking tabs are used when bolting a turbo to a manifold or a down-pipe to a turbo. I have successfully attached a turbo to a manifold using a second set of nuts locking the first set in place.
I also recommend that the water and oil pipes are inspected thoroughly, any surface rust removed and the pipes painted with a heat-resistant paint such as Hammerite. If any pipes have deep pitting of rust they must be replaced otherwise you may have to remove the turbo again to replace a leaking pipe.

The method described is the method I use and I have found it to be successful. The last replacement turbo I fitted was on a pre-1987 model and it took approximately 4 hours from start to finish. It also included changing over the manifold and down-pipe.

If you are replacing the standard T2 turbo for a T25 you will need to modify the down-pipe for the exhaust, modify the charge pipe and usually send it through an intercooler, change the oil return pipe and grind a lug off the bell-housing. If this lug is not removed the manifold will not fit flush against the cylinder head.

Auxiliary Air Valve:
The auxiliary air valve is the unit that provides a signal along with the ECU temperature sender to tell the ECU to give an enriched mixture when the engine is cold. It is basically an automatic choke. It can be found near the front top of the engine on the inlet manifold. As it samples the charge air and the turbo can sometimes pass a little oil when driven hard, this unit can become dirty and clogged with oil. The unit will benefit from cleaning from time to time. There are two rubber hoses to loosen a plug to remove from the top and the unit is held in place with two bolts. To clean the unit pour a small amount of turpentine into it and shake vigorously holding a thumb an forefinger over each end then drain. Repeat until the turpentine drains out clean. The unit has a shutter inside that should be partially open when cold and closed when warm. The shutter position can be adjusted slightly by loosening the small nut that can be seen on the left hand picture and sliding the shaft of it's bolt away from the unit to open the shutter more when cold. The engine should idle at around 1200 revs when cold and drop to around 750 when warm. The idle speed for the automatic should be around 900 revs when warm as it drops to around 750 when drive is selected.

Chassis Mystery:
I have always wondered why the section under the floor runs from the front to the back on the drivers side whilst the one on the passenger's side stops under the passenger's front seat! I thought it would be a good idea to make a chassis section to fit in place where the missing part is and see if it improved the handling. I decided to try it out on Mrs. Silviagod's as she has on occasion carried large passengers due to her job, and I noticed a small patch of rust appearing on the back of the sill in the area. The floor pan of the Silvia is much stronger than that of the S13 200SX and the rear fittings for the seat seem adequately supported. However, I welded the chassis section in place and took the car out for a drive. I didn't notice any difference to the feel of the car and as I had Mrs. Silviagod at the side of me I was unable to throw it around. However I didn't hear any of the usual creaks from the sunroof and I am sure that in extreme driving the car will handle better and also carry large passengers now without a problem.
The only disadvantage I can see from doing this modification is that in the event of a heavy head on impact the cabin will not fold as easily on the passenger side. Then again, if you were going to be involved in such an impact it would be unlikely that you would walk from it.
I intend to carry out the same modification to mine next as I too have a creaking sunroof and it can get irritating at times.

More coming soon:

Extra space:
I have thrown up another little site with the intentions of improving it and adding more pictures. My web skills are only limited but I am trying to learn with the limited time I have available. Please have a look and feel free to offer suggestions.
http://www.angelfire.com/trek/silviagod/