Thread: L26 swap PCM question

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  1. #1 Re: L26 swap PCM question 
    GTX Level Member wstefan20's Avatar
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    As an update, I'll be finalizing the hookup today, but while I was at the junkyard I took a look at a few supercharged 3800s. What I found was interesting. On the n/a 3800s (L26/L36) the crankcase vapors travel from both heads via the lifter valley to the front head where the gasses are routed to the pcv valve and expelled through the intake, while fresh air is drawn through the upper intake manifold either via the throttle body or vertical pipe.

    On the supercharged 3800s (L67/L32), the pcv is exactly opposite! The crankcase vapors travel through the lifter valley between the heads and the rear head expels the gasses up to the pcv valve while the front head is the breather that passes up to either the throttle body or vertical pipe!

    What this means:

    A few things. First, if you are going to re-route the intake to a breather, while on the supercharged engines you'll want to place a breather on the oil fill cap (front head), if you're going to block off the intake on any n/a 3800s (such as spacer with no provision for pcv, L26 and cap upper pipe, etc.) to achieve actual pcv function, you need a breather on the REAR valve cover!

    Placing one on the front of n/a cars actually completely bypasses the pcv!

    Also, drilling a hole through the vertical pipe as described in many famous L26 intake swaps is also negating the pcv system entirely as you are hooking your pcv intake to VACUUM! When you hook the intake to vacuum, you've now equalized the pressure between the manifold and the crankcase. Same thing as running lines from both valve covers directly to the manifold with no pcv valve!

    So for all those who have used this method, I would strongly advise for you to plug the hole you drilled and either route the intake to a breather, or to an inlet before the throttle body (remember anything after tb is vacuum).

    If this method works, both n/a, supercharged, and turbo cars alike can run catch cans and fully functioning pcv systems without having to run extra lines or breathers to accomplish the same thing!
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  2. #2 Re: L26 swap PCM question 
    GTX Level Member wstefan20's Avatar
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    Finally had the motivation to attempt the build. Now, this is far from a completed setup, and I will be refining this as I work things out, but essentially I've modified the map "cap" by running a hose through where the map is normally located and directly connecting that to pcv valve. "stem". This allowed me to bypass the normal vacuum source without modifying things where they can't be reverted easily. I then simply ran a t fitting out the top to the map sensor and the catch can. I already have a vacuum source pre-drilled on my throttle body spacer, but I have my doubts as to whether this is far enough away from the throttle body to create sufficient vacuum. I started the engine up and ran a preliminary test. Everything is idling smooth around 700-800 rpms, no check engine lights, no codes, and sprayed carb cleaner to verify no vacuum leaks. I'll be testing it for the next couple of days before I "commit" and finalize testing, but I'd call it a partial success for now!






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  3. #3 Re: L26 swap PCM question 
    GTX Level Member wstefan20's Avatar
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    *Update* well, if anyone comes across this thread, I mistook the port coming from the throttle body spacer as vacuum, and it is actually pcv air intake tapped! So the only modification to the above is to run a hose from the pcv air intake "nipple" if you have L26 or L32 to the throttle body adapter port, and either tap the evap port for the L26 or L32 for the vacuum attached to the catch can, or tap a port after the throttle plate on the throttle body for vacuum to the catch can. For L67 or L36, as long as you're using the stock throttle body, you're fine on the intake and you just need to tap a port for vacuum for the catch can, and Done!
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