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Converting a 4AGE 20V to Rear Wheel Drive

The 20 Valve engine is increasing in popularity as the choice of engine in rear wheel drive conversions in cars such as the AE86. However it does have some extra issues involved over a 16V in converting it to run in a north-south direction. The general conversion steps are listed that are shared with the 16V and of course the problems that are particular to the 20V engine.


Engine mounting:

For AE86 and AE71 equipped cars that came standard with 4AC powered engines the original mounts, gearbox and crossmember will suit all the A-series of Toyota engines. For the KE70 it is however more difficult as it needs to have the clutch converted to a hydraulic unit, new engine mounting and a different gearbox installed. To convert to the hydraulic clutch mechanism a different pedal box, clutch master cylinder, metal clutch line, flex line and slave cylinder need to be fitted. To make the mounting compatible the cross-member, gearbox, gearbox mount and rear half of the tail-shaft all need to be changed. Luckily all of the needed parts can be sourced out of either an AE71 or AE86 for the required conversion, although these are sometimes hard to find and hence sold for rather high prices.. It is of note that the AE86, AE71 manual and automatic engine crossmember are all identical.



Intake:


For Right hand drive: The AE101 20v "silvertop" engine featured a metal air-box with four plastic trumpets inside, while the AE111 20V "blacktop" features a visibly similar design it however had a larger volume air-box and trumpets which are made of a rigid rubbed in the place of plastic. The 20v air-box has the inlet facing to the rear of the engine which is not compatible with a Rear wheel drive(RWD) installation. Even with the air-box removed and just the trumpets installed by themself the fourth trumpet will foul agaist the clutch master cylinder on an AE86/AE71/KE70. However the trumpets can be bolted upside down without the air-box as a stop gap measure (see next section for more information). The air-box can also be chopped to change the shape however care must be taken so that the volume wont be reduced as it may effect the performance of the engine. Also of note the air-box is made from sheet metal steel approximetly 1mm thick which although is easy to shape needs some care so as to not blow holes through it during the welding process.


Left hand drive cars: For the Americans and others the left hand drive lets many of the firewall components be on the other side of the engine bay. Although unknown to this author it should be possible to bolt an unmodified bottom half of a silver or blacktop air-box into place. This is so would mean only the top of the airbox would have to be modified so that it faces towards the front of the car instead of the back.

An engine under no circimstances should be ran without some form of trumpets or without some form of radiused inlet otherwise power lose is gaurenteed. The most commonly used solution is to have 4 aftermaket trumpets with individual filters. This does however pose some problems such as the filter oil being suprisingly flamable which can cause an instant fire from even a breif backfire or the airfilters being suprisingly restrictive causing a power loss. Putting an air-box around aftermarket trumpets is possible however it is a difficult and time-consuming job. For those running a AE101 20V "Silvertop" ECU then there is no choice but to run some form of enclosed air box which is fed from the standard airflow meter.

Please see the article 'Multiple Throttle Intake Tuning' for more information.



Trumpet design:

As mentioned above it's is not possible to install the factory trumpets of a 20v engine in an ae86/ae71/ke70 even with the air-box removed because of the lack of clearence from the clutch master cylinder (may fit in the ae71 automatic). It is possible to run the factory trumpets in an upside down position however unless it is a buget upgrade this isnt recommended. In the search for increased power the standard trumpets should be discarded because not only do they all have a heavily cheated bends into the throttles which causes massive tumbulence but they also have a poor shape, a very crude flare on the entree instead of a bellmouth and are of an uneven diameter. An ideal replacement is a set of aftermarket or custom made trumpets that have only mandrel bends or no bends at all.

Caution must be used when changing the length from the standard sizes as it will affect how the power is delivered. As a rough rule the shorter the trumpets the more the top end power is increased at the expense of the bottom end and vice versa for longer trumpets. However it has been reported that the 20v does not behave predicatably to intake tuning and real world testing is needed for optimum results. Also problematic is that long trumpets cant be fitted if they arnt curved because it will foul against the brake booster. A trumpet should never get closer than the same as its diameter to the booster or be shorter than the rest of the trumpets. A possible solution is to have that trumpet curve away and then either have individual filters or a well constructed air-box. As a rough guide in air-box design the distance between the opening of the trumpet and the wall of the air-box should be at least the same as the diameter of the trumpet cross section, or for a 20v throttle approximetly 75mm (open to correction).

Please see the article 'Multiple Throttle Intake Tuning' for more information.



Headers/Extractors:

All 4AGE engines have the same exhaust port position and only the 20v engine has a difference with the mounting face. That difference being that on the 20v the two outer holes are place further outwards that its 16V equivolent. With the 20v engines readily gaining popularity off the shelf extractors are now much more common than previously. However 4AGE 16V extractors can easly be adapted to suit and vice-versa.

To adapt from 16v to 20v extractor flanges the most common way would be to extend the flange outwards on the two extreme edges with a simular material and redrill the flange. Another less preferable option would be to shave the outer edges of the flange and then use large washers to hold the flange in place with the outer bolts. Using this for-mentioned method it is possible to use the cast iron manifold off a Trueno.



Exhaust System:

From the headers onwards the exhaust system would be to the same specifications as that of a 16V engine. With that being 57mm (2.25 inch) as being the most accepted size for power for the majority of applications. The piping then ideally using mandrel bends where needed and the choice of mufflers/resonators/catalitic converter/etc.. depending on the owners personal preferance.



Accelerator cable:
 
For AE86 and AE71 equipped cars that came standard with 4AC powered engines the original throttle cable is too short. Although difficult to change the original cable out of a KE70 Corolla has the extra length to loop around and fit very well.



Cooling system:

Unless intended for a very low budget race only car the firewall should never be modified to suit the cooling system or the ignition system with a 20v conversion, there is no need with the right components. To convert the cooling system to RWD specifications due to its complexity has it own article, please refer to it for the required information.



Igniton system:
 
As mentioned above; unless intended for a very low budget race only car the firewall should never be modified to suit the cooling system or the ignition system with a 20v conversion, there is no need with the right components. The standard distributor on a 20v is placed on the rear of the cylinder head and can not be directly installed into almost all north-south engine bays because of clearence problems with the firewall, the heater core behind it and the heater hoses inbetween. The igniton system would have to be the single largest problem facing installers with a 20v conversion, for which there are a few options.


There are three ways to use the original ECU to run a RWD engine:

1- With an additional ignition module: Called a DLI module this custom part is integrated with the loom. Using this system the original top half of the distributor is removed and only the base is left, the base housing the crank angle sensor. From here the most common type of converter uses the signal from the original crank angle sensor and the ecu's single ingniton signal (one coil originally) and splits the signal into two sending it to either of two coils depending on the postion of the engine. This effectively changes the original single coil and distributor setup to that of a twin-coil waste spark setup, which effectivly removes the need for a mechanical spark distribution. DLI modules are also available in a form that splits the signal into four that then supports individual coil-packs per cylinder, however these are uncommon-common. The advantage of this setup is that it can be cost effective and can be a necessity to get a can engineered due to pollution standards. This is due to some states forbidding aftermarket ECU's without their programming being locked after passing the appropriate emmisions test.

2- Mechanically moving the rotor cap or the whole distributer: As above the cap can be taken off the distributer and leave enough room for heater hoses it is possible to just reloate the cap itself. A single prototype was made in this company that used the rotor button and cap off a 16V engine, it was found to not be viable due to the high amount of presice machining but the concept is sound. The other option is to take the whole disributer out, put a plug in it's place and run it off the front of the engine by a direct coupling or a belt drive. When driectly driven it spins in the reverse direction and it's reported to need the two wires for the crank sensor swapped.

3- Four coil-packs/COP's: This most unusual method shouldn't work but it's a proven solution. This involves using the coilpacks off late model Toyota's (See the Coilpack info guide) with built in ignitors and firing them all at once off the single output of the OEM 20V ECU. The reason this sounds impossible is because at any one of the engines strokes the fuel/air fix is being sucked in just as the coil is firing! However due to the short duration of spark, the lack of comrpession and in the overlap period there is no combustion. Some people use the original 20V coil in place to send the firing singal back to the ECU and run the tacho but some just use a single one of the coils to send the signal.

For more information on this see the forum thread: Alternative Ignition: COPs - batch fire



The other option is to use an aftermarket ECU, this can either pickup the signal from the original crank angle sensor or an aftermarket product. From here an array of options can be used such as individual coils with integral ignitors (Toyota echo coils suit a 20V), a waste spark system with a twin channel ignitors, etc. The advantage of this setup is that if tuned for high octane fuel a good power increase is guaranteed, this is due to the standard 20v ignition timing as being seen as conservative by tuners. Another advantage is that a duel map can be used that could for example be for a race day whereas a higher octane race fuel is used and the engine tuned for it.

Please see the article "Original Vs aftermarket ECUs'.



Fuel system:

For AE86 and AE71 equipped cars that came standard with 4AC powered engines the original fuel system is only designed for low pressure use in accordance with the original carberated fuel system. This causes problems in a few areas but is still quite solvable. Firstly all cars that originally have an EFI fuel system have no internal baffles or cups inside the fuel tank. This is needed because under G-force the fuel can move away from the pickup under certain circumstances, whilst carbies have internal floats and a function that inheritly allow for these fluctiuations and EFI fuel system definetly does not. Such a starvation imeadiatly causes air to be sucked in through the line, the fuel pressure to drop and then a potentially dangerous lean out condition. One option for AE86 owners is to fit an imported Trueno fuel tank, these have some form of intenal baffling however they are rare, expensive and there have been reports of that model still having fuel surge in use. Some people just keep the original tank, its all been reported that if the fuel is kept above a quarter then no fuel surge will occur. Professional modification of the original tank is also a possibility and lastly the most complex but the only definate way to not have problems with it is to run dual fuel pumps and have a surge tank. There is a good place to run a fuel tank in ae86's inbetween the fuel tank and the sunframe on the front drivers side, there is no need to have anything placed inside the vehicle unless easy access is required.

The fuel pump itself needs to be changed, a popular option for people running a single pump is to use the high pressure pump out of a Holden VL. If this pump is used its a good idea to use the original pump mounts as they incorparate a rubber mount which is good for isolating the noise of the unit. For people with a dual pump and surge-tank setup a primary pump is required to fill the surge tank and a secondary pump to suck the fuel from the surge tank to the engine. Again the Holden VL pump is ideal for the secondary pump however a low pressure pump is required as the primary.
 
Fuel lines also need to be changed, any fuel line that is on the outlet of a high pressure pump needs to be of the "EFI line" type. The original line likely would burst under the increased pressure. This is available in most auto parts stores.

Fuel clamps should ideally not be the serrated slot design but instead be proper "EFI clamps" which have a smooth inner and a ridged outer which the worm gear grips to. This is so when tightening the line is not damaged.

Notes on using a Holden VL pump: This pump is not designed to be a suction pump and will cause it to wear quicker and be louder if forced to do so. If used with a surge tank the pump can be placed much lower than the tank then the 'head' of the fuel will push the petrol into the pump.