8.1L in 78’ K10: Dual tank switch valve woes

[DirtyLarry]

Hello, I am new around here.

I just completed an 8.1L swap into a 1978 Chevrolet K10 running on an MEFI-4b engine controller and a frame mounted electric fuel pump. I am having an issue with the dual fuel tank switch valve causing a restriction on the fuel return side which results in extremely high fuel pressure. Once the switch valve is bypassed the fuel pressure runs normal (38 to 44 psi is normal for a MEFI-4 controlled engine).

Has anybody found an alternative dual tank switch valve other than the stock GM (Polluk) valve? Something about that valve is restrictive as all hell.

I am considering swapping the RH fuel tank for a 1987 tank and using an AC Delco EP241 in-tank fuel pump then running a frame mount pump to act as a transfer pump to move fuel from the LH to RH tank. The in-tank fuel pump would be more reliable any way. It just sucks to have to wire in a transfer pump if I don't have to.

Here is the beast....

[Shep]

Hello, I am new around here.

I just completed an 8.1L swap into a 1978 Chevrolet K10 running on an MEFI-4b engine controller and a frame mounted electric fuel pump. I am having an issue with the dual fuel tank switch valve causing a restriction on the fuel return side which results in extremely high fuel pressure. Once the switch valve is bypassed the fuel pressure runs normal (38 to 44 psi is normal for a MEFI-4 controlled engine).

Has anybody found an alternative dual tank switch valve other than the stock GM (Polluk) valve? Something about that valve is restrictive as all hell.

I am considering swapping the RH fuel tank for a 1987 tank and using an AC Delco EP241 in-tank fuel pump then running a frame mount pump to act as a transfer pump to move fuel from the LH to RH tank. The in-tank fuel pump would be more reliable any way. It just sucks to have to wire in a transfer pump if I don't have to.

Here is the beast....

I don't have an answer for you, but that's a helluva set up you have! Makes me want to get mine going sooner!

[HarleyDave]

I'm running the dual tank set up with no issues on return pressure. I have an ext. pump as well, but plan to go to an 87 tank set up later. The switching manifold is a little different than the <'86 and is rated for ~62 psi.

[DirtyLarry]

I don't have an answer for you, but that's a helluva set up you have! Makes me want to get mine going sooner!

Thanks Shep…

I am pretty much decided on ditching the dual tank switch valve and running an 87’ RH tank and a transfer pump to move fuel from the LH tank to the RH.
By the looks of your signature you are entertaining the thought of an 8.1L as well…From my experience I will tell you that the 8.1L is a much easier swap than the way too common 5.3 or 6.0L small block swap.

Everybody bad mouths the 8.1L due to lack of aftermarket support but that sucker makes a lot more out of the box stock HP and torque (TORQUE!) especially running on a Marine MEFI-4 controller and calibration than any stock 6.0L ever will. The 8.1L does not require any frame or engine mount modifications either and will fit right in the same exact engine mounts as an old school small block or big block did. In fact, I used my previous 454 exhaust manifolds and engine mount saddles on this 8.1L. No trans mods, no exhaust mods…just unbolt at 454 and bolt in a 8.1L. Pretty painless compaired to the BS of the GEN III small block route. Another bonus is on pre-GMT400 trucks (1988 and older) there is no need to hack up your frame to make room for the exhaust manifold or A/C compressor.

I agree with the masses that there is a lot more aftermarket support for small blocks if you are in the racing crowd but for what I use this truck for I feel Marine 8.1L HO calibration for 425 HP and 505 lb ft of torque should get the job done just fine in this expedition rig. I am happy with my results as the truck runs like a rapped ape on a poor cal file and will be even better once the cal files are dialed in.

HarleyDave,

I am not sure what you said….but I think you said something about running a frame mount pump and a dual tank switch valve. That is interesting. Tell me more about it please…..


YouTube - 8.1L 2

[carmstrongls1]

I am doing an 8.1 swap right now. Any tips? It is going into an 85 C20 behind a T56. I could use a few pointers if you have them Looks like yours went pretty smooth.