I have 16 psi boost on my 616 using a kkk26 turbo. No waste gate, I blocked it off and removed it.The kkk26 is stock on 617's. Garrett's are also used. VNT would be nice since you are starting from scratch.

Just pump adjustments and making sure the waste gate is not opening to soon(assuming stock turbo)will get 25 more ft pounds.

More compression does not help a diesel like it does a gas engine, in fact if you really boost it, like 40 psi then slightly lowering compression is good. Seems from what I have found that 40 psi and you start bending rods. I don't think you are looking for crazy hp.

I would balance the crank while you have it apart. Also enlargeing the burn holes in the pc's gives a benefit of lower egt's, so you can push fueling a little more. Otherwise just a basic rebuild will give you a good engine to work with for the smaller gains you seem to be looking for. I am pushing my 616 way past the factory limits and it is doing just fine, and the 617 has stronger rods, oil cooled pistons and some other goodies that the 616 does not have, so you basically you have a strong engine that can take a lot, and this leaves room for more power later. A little more is never enough, it is sort like an addiction.....

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1977 240D turbo