The DOHC installation 'unspoken' details thread
Posted: Mon Dec 08, 2008 7:11 am
Lately there is alot of talk about DOHC heads. Either on 22T conversions or complete motor swaps. Everybody likes to say 'the heads bolt up', which is true. However there are alot of details that can make this 'bolt on' conversion a make-or-break proposition for many.
I intend for this thread to be an ongoing databank on DOHC swap information. All are free to contribute, but I ask that you keep it to facts. Please support your facts with proper documentation, such as pictures. Feel free to ask questions, of course.
There are three basic heads that seem to pop up in this forum the most. Legacy EJ20G heads, WRX EJ20G heads, and USDM (non-turbo) EJ25D heads. Early ('94-'98ish) Legacy twin turbo heads (EJ20h) are commonly discussed also, and can be considered the same as Impreza EJ20G heads. EJ20K and late twin turbo heads (Ej20r) are also completely compatable with anything stated in this guide, but because of thier value are rarely chosen by us 'old schoolers'.
This thread also only applies to phase I heads. Phase 2 DOHC heads have a different intake manifold bolt pattern. If your heads have an inline pattern then this guide will apply.
The pros/cons, performance, relability, and uberness of each head design is outside the scope of this thread. This thread is intended to catalog what it takes to install the various heads (as part of an assembled longblock) in a USDM BC/BF Legacy turbo.
This thread assumes you already have your longblock assembled, with cams in and cam covers on. Water and oil pumps each have thier own merits and are beyond the scope of this thread. As long as you have a turbo water pump you'll be fine as far as DOHC head installation goes.
Crankshaft position sensors
Both EJ22 and Legacy EJ20G sensors are the same and plug into the vehicles harness at the rear of the engine. The WRX sensors plug directly into the engine harness. The Legacy twin turbos use the same non-corded sensor as the WRX EJ20G. If your keeping the stock EJ22t wiring, use the corded sensor (stock BC EJ22).
Camshaft position sensors
Again, both EJ22 and Legacy EJ20G sensors are the same and plug into the vehicles harness at the rear of the engine. The WRX sensors plug directly into the engine harness. If your keeping the stock EJ22t wiring, use the corded sensor (stock BC EJ22).
Knock sensors
All early EJ Subaru knock sensors are compatable. Choose the best one you've got.
Rear engine connector bracket
This step mostly applies only if your installing a complete motor and needed to swap the above listed sensors to match your car's harness.
The Legacy bracket is designed to hold three conectors (Cam. crank, knock) while the WRX bracket only hold two (Multi, knock). Use a Legacy bracket for convience.
Basic sensors and bracket installed for installation in a Legacy.
Coolant pipes
The stock EJ22 coolant pipes cannot be used. They simply will not fit on/around the DOHC heads.
Legacy EJ20Gs and WRX EJ20Gs use the same coolant pipes. I do not have a set of EJ25D pipes to add to the photos, so at this point I do not know if they are the same as EJ20G pipes.
EJ20G coolant pipes installed on Legacy EJ20G.
Legacy twin turbo coolant pipe are routed very differently from other engines to avoid the second turbo.
Coolant crossover pipe
The main difference between the crossovers is the location of the two temp sensors.
EJ22s have the sensors on the opposite side as EJ20Gs. The engine harness for each version matches the crossover, of course. The WRX version also eliminated an insignificant casting 'bump'. I do not have an EJ25D crossover to add for comparision.
The Legacy twin turbo crossover has the sensors on the same side of the engine as the EJ20Gs, but they are located on the front side instead of the back. The contour of the pipe is also designed for the under-the-manifold turbo inlet.
The most often given advice is to use the EJ22T engine harness on your DOHC engine to make it plug-n-play. This is sound advice and will work, but there are a few things to look out for.
If your planning on using an EJ25D intake manifold you cannot use the EJ22T crossover. It interfears on the temp sensors.
If you plan on using an EJ20G intake manifold the clearance with the idle air pipe (to plug in the sensors) is very tight with the EJ22T crossover.
So, that leaves using the EJ20G crossover. Of course, that means modding the EJ22T engine harness to extend the temp sensor wires to the other side.
I hope to add info on EJ25D and twin turbo crossovers soon.
Oil pan and Dipstick
All the oil pans are the same as far as functional differences. While the dipsticks have a similier shapes the mounting tab prevents EJ20G and EJ22 from being interchangable.
Both Legacy EJ20G and WRX EJ20G dipsticks are the same. I can't confirm (yet) but I'm sure that EJ25D dipsticks are also the same.
Timing belt tensioner bracket
Other than a few casting differences, both styles of EJ20G bracket are the same. The EJ22 bracket does not have the 'ear' needed to secure the DOHC timing cover. The EJ22 bracket can be used with the DOHC covers, but may introduce a vibration or fatigue point.
Somewhere around '98-'99 Subaru redesigned the tensioner device. If you use the bracket and tensioner you can upgrade to the new style. Make sure you get one from a DOHC motor (such as the USMD WRX) so it has the 'ear' to secure the inner timing cover.
Inner timing covers
Left covers
The WRX EJ20G, twin turbo, and EJ25D covers are the same and will not fit the Legacy EJ20G heads. The Legacy EJ20G cover will not fit WRX, twin turbo, or EJ25D heads.
Right covers
Other than minor casting updates, all are the same.
Timing sprockets
Other than a few casting differences, crank timing wheels are all the same.
All cam wheels are all interchangable. Legacy EJ20G ones are metal, while WRX EJ20G, EJ25D, and Twin turbo sprockets are identical to each other and plastic.
Timing idlers
All the other idlers and tensioners are the same between all models. EJ22, EJ20G, twin turbo, and EJ25D.
Timing Belt
Obviously you can't use an EJ22 belt. Both Legacy EJ20G and WRX EJ20G use the same timing belt. Numerous posts indicate that the EJ25D belt is also the same.
Timing tensioner
Once again, all models are the same. Unless your upgrading to the newer style.
Outer timing covers
Broken record, but, other than a few casting differences all the same. Some say Turbo!! For the center cover, the SOHC and DOHC covers are even the same.
Next installment....intake manifold choices.
I intend for this thread to be an ongoing databank on DOHC swap information. All are free to contribute, but I ask that you keep it to facts. Please support your facts with proper documentation, such as pictures. Feel free to ask questions, of course.
There are three basic heads that seem to pop up in this forum the most. Legacy EJ20G heads, WRX EJ20G heads, and USDM (non-turbo) EJ25D heads. Early ('94-'98ish) Legacy twin turbo heads (EJ20h) are commonly discussed also, and can be considered the same as Impreza EJ20G heads. EJ20K and late twin turbo heads (Ej20r) are also completely compatable with anything stated in this guide, but because of thier value are rarely chosen by us 'old schoolers'.
This thread also only applies to phase I heads. Phase 2 DOHC heads have a different intake manifold bolt pattern. If your heads have an inline pattern then this guide will apply.
The pros/cons, performance, relability, and uberness of each head design is outside the scope of this thread. This thread is intended to catalog what it takes to install the various heads (as part of an assembled longblock) in a USDM BC/BF Legacy turbo.
This thread assumes you already have your longblock assembled, with cams in and cam covers on. Water and oil pumps each have thier own merits and are beyond the scope of this thread. As long as you have a turbo water pump you'll be fine as far as DOHC head installation goes.
Crankshaft position sensors
Both EJ22 and Legacy EJ20G sensors are the same and plug into the vehicles harness at the rear of the engine. The WRX sensors plug directly into the engine harness. The Legacy twin turbos use the same non-corded sensor as the WRX EJ20G. If your keeping the stock EJ22t wiring, use the corded sensor (stock BC EJ22).
Camshaft position sensors
Again, both EJ22 and Legacy EJ20G sensors are the same and plug into the vehicles harness at the rear of the engine. The WRX sensors plug directly into the engine harness. If your keeping the stock EJ22t wiring, use the corded sensor (stock BC EJ22).
Knock sensors
All early EJ Subaru knock sensors are compatable. Choose the best one you've got.
Rear engine connector bracket
This step mostly applies only if your installing a complete motor and needed to swap the above listed sensors to match your car's harness.
The Legacy bracket is designed to hold three conectors (Cam. crank, knock) while the WRX bracket only hold two (Multi, knock). Use a Legacy bracket for convience.
Basic sensors and bracket installed for installation in a Legacy.
Coolant pipes
The stock EJ22 coolant pipes cannot be used. They simply will not fit on/around the DOHC heads.
Legacy EJ20Gs and WRX EJ20Gs use the same coolant pipes. I do not have a set of EJ25D pipes to add to the photos, so at this point I do not know if they are the same as EJ20G pipes.
EJ20G coolant pipes installed on Legacy EJ20G.
Legacy twin turbo coolant pipe are routed very differently from other engines to avoid the second turbo.
Coolant crossover pipe
The main difference between the crossovers is the location of the two temp sensors.
EJ22s have the sensors on the opposite side as EJ20Gs. The engine harness for each version matches the crossover, of course. The WRX version also eliminated an insignificant casting 'bump'. I do not have an EJ25D crossover to add for comparision.
The Legacy twin turbo crossover has the sensors on the same side of the engine as the EJ20Gs, but they are located on the front side instead of the back. The contour of the pipe is also designed for the under-the-manifold turbo inlet.
The most often given advice is to use the EJ22T engine harness on your DOHC engine to make it plug-n-play. This is sound advice and will work, but there are a few things to look out for.
If your planning on using an EJ25D intake manifold you cannot use the EJ22T crossover. It interfears on the temp sensors.
If you plan on using an EJ20G intake manifold the clearance with the idle air pipe (to plug in the sensors) is very tight with the EJ22T crossover.
So, that leaves using the EJ20G crossover. Of course, that means modding the EJ22T engine harness to extend the temp sensor wires to the other side.
I hope to add info on EJ25D and twin turbo crossovers soon.
Oil pan and Dipstick
All the oil pans are the same as far as functional differences. While the dipsticks have a similier shapes the mounting tab prevents EJ20G and EJ22 from being interchangable.
Both Legacy EJ20G and WRX EJ20G dipsticks are the same. I can't confirm (yet) but I'm sure that EJ25D dipsticks are also the same.
Timing belt tensioner bracket
Other than a few casting differences, both styles of EJ20G bracket are the same. The EJ22 bracket does not have the 'ear' needed to secure the DOHC timing cover. The EJ22 bracket can be used with the DOHC covers, but may introduce a vibration or fatigue point.
Somewhere around '98-'99 Subaru redesigned the tensioner device. If you use the bracket and tensioner you can upgrade to the new style. Make sure you get one from a DOHC motor (such as the USMD WRX) so it has the 'ear' to secure the inner timing cover.
Inner timing covers
Left covers
The WRX EJ20G, twin turbo, and EJ25D covers are the same and will not fit the Legacy EJ20G heads. The Legacy EJ20G cover will not fit WRX, twin turbo, or EJ25D heads.
Right covers
Other than minor casting updates, all are the same.
Timing sprockets
Other than a few casting differences, crank timing wheels are all the same.
All cam wheels are all interchangable. Legacy EJ20G ones are metal, while WRX EJ20G, EJ25D, and Twin turbo sprockets are identical to each other and plastic.
Timing idlers
All the other idlers and tensioners are the same between all models. EJ22, EJ20G, twin turbo, and EJ25D.
Timing Belt
Obviously you can't use an EJ22 belt. Both Legacy EJ20G and WRX EJ20G use the same timing belt. Numerous posts indicate that the EJ25D belt is also the same.
Timing tensioner
Once again, all models are the same. Unless your upgrading to the newer style.
Outer timing covers
Broken record, but, other than a few casting differences all the same. Some say Turbo!! For the center cover, the SOHC and DOHC covers are even the same.
Next installment....intake manifold choices.