BACKGROUND
I have put in many aftermarket turbo and superchargers over the years, and repaired many hose routings of just stock turbochargers as well whilst working on those darn quattros. One of the biggest issues I have dealt with over the years is boost vs PCV systems. Especially in aftermarket add ons, it becomes a important issue to engine seal longevity. After seeing some familiar signs of PCV induced seal blowout on my Supercharged 80, I decided to look harder at the PCV design and possible modifications.
DESCRIPTION
The 80 uses a dual PCV system (1994 FZJ80). There is a idle PCV (IPCV) that goes to the PS of the valve cover then to the throttle body. Then there is a manifold runner PCV with valve (MPCV) that goes from the DS valve cover (with valve inserted) then routed to the manifold runner. In stock trim (no SC) the idle PCV drops vacuum from the tbody port with increase rpm. The vacuum in the manifold PCV then draws up the valve ball, and PCV function changes from throttle to manifold vacuum. As the manifold vacuum decreases, the ball in the valve seals back up, and the PCV function changes back to the TBody.
The reason for PCV, is to keep the crankcase and the head under vaccuum. This also allows blowby gasses and moisture to get recirculated into the intake manifold. Without PCV, the pistons would act as a pressure pump and start to blow out seals. With *inadequate* PCV this can happen too. Enter Forced Induction.
PROBLEM
TRD does not make any changes to the PCV routing. This means under boost, the MPCV will close the valve (from manifold pressure on top of the valve). The IPCV at the Tbody is closed, so now under boost, there is *no PCV* at all! Take a long enough run under boost with a closed valve, pressure builds in the crankcase and head, and seals start to seep oil. On my truck, the valve cover gasket, IPCV hose and the oil cap all are wisping oil (better there than at the rear main I suppose) from sustained crankcase pressure.
THE FIX
Cost me 22USD + 5 minutes
* New PCV valve and seal - Dealer 8USD
* 24in 3/8in trans/emission line - 3bucks
* 24in of 5/16 trans/emission line - 3bucks
* 1 set of vacuum caps - 3 bucks (you only need the 3/8)
* 1 5/16 vacuum T - 2bucks
* 4 hose clamps - 3 bucks
* R&R PCV valve (watch out the lower half of the seal wants to split and fall into the valve cover!)
* Install T fiiting with 3inches of 5/16 tubing between supercharger and hose to vacuum booster
* Install 3/8 vacuum cap over manifold runner port and use hose clammp
* Install 24inches of 3/8 tubing from PCV valve to T at vacuum booster clamp it down well onto 5/16 T (or get 2 x 5/16 to 1 x 3/8 T)
Have a beer, yer done.
Now, what happens is that during idle, the vacuum in the SC inlet chamber is low enough that the PCV valve ball drops, and the IPCV at the Tbody works as designed. When the SC is under boost, the prechamber (SC bypass valve closed) is under full vacuum, and the PCV valve will now be open under boost. This allows PCV function to be present during sustained forced induction engine load without crankcase pressure buildup.
HTH
Scott Justusson
94 FZJ 80 Supercharged
I have put in many aftermarket turbo and superchargers over the years, and repaired many hose routings of just stock turbochargers as well whilst working on those darn quattros. One of the biggest issues I have dealt with over the years is boost vs PCV systems. Especially in aftermarket add ons, it becomes a important issue to engine seal longevity. After seeing some familiar signs of PCV induced seal blowout on my Supercharged 80, I decided to look harder at the PCV design and possible modifications.
DESCRIPTION
The 80 uses a dual PCV system (1994 FZJ80). There is a idle PCV (IPCV) that goes to the PS of the valve cover then to the throttle body. Then there is a manifold runner PCV with valve (MPCV) that goes from the DS valve cover (with valve inserted) then routed to the manifold runner. In stock trim (no SC) the idle PCV drops vacuum from the tbody port with increase rpm. The vacuum in the manifold PCV then draws up the valve ball, and PCV function changes from throttle to manifold vacuum. As the manifold vacuum decreases, the ball in the valve seals back up, and the PCV function changes back to the TBody.
The reason for PCV, is to keep the crankcase and the head under vaccuum. This also allows blowby gasses and moisture to get recirculated into the intake manifold. Without PCV, the pistons would act as a pressure pump and start to blow out seals. With *inadequate* PCV this can happen too. Enter Forced Induction.
PROBLEM
TRD does not make any changes to the PCV routing. This means under boost, the MPCV will close the valve (from manifold pressure on top of the valve). The IPCV at the Tbody is closed, so now under boost, there is *no PCV* at all! Take a long enough run under boost with a closed valve, pressure builds in the crankcase and head, and seals start to seep oil. On my truck, the valve cover gasket, IPCV hose and the oil cap all are wisping oil (better there than at the rear main I suppose) from sustained crankcase pressure.
THE FIX
Cost me 22USD + 5 minutes
* New PCV valve and seal - Dealer 8USD
* 24in 3/8in trans/emission line - 3bucks
* 24in of 5/16 trans/emission line - 3bucks
* 1 set of vacuum caps - 3 bucks (you only need the 3/8)
* 1 5/16 vacuum T - 2bucks
* 4 hose clamps - 3 bucks
* R&R PCV valve (watch out the lower half of the seal wants to split and fall into the valve cover!)
* Install T fiiting with 3inches of 5/16 tubing between supercharger and hose to vacuum booster
* Install 3/8 vacuum cap over manifold runner port and use hose clammp
* Install 24inches of 3/8 tubing from PCV valve to T at vacuum booster clamp it down well onto 5/16 T (or get 2 x 5/16 to 1 x 3/8 T)
Have a beer, yer done.
Now, what happens is that during idle, the vacuum in the SC inlet chamber is low enough that the PCV valve ball drops, and the IPCV at the Tbody works as designed. When the SC is under boost, the prechamber (SC bypass valve closed) is under full vacuum, and the PCV valve will now be open under boost. This allows PCV function to be present during sustained forced induction engine load without crankcase pressure buildup.
HTH
Scott Justusson
94 FZJ 80 Supercharged
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