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Are you trying to just put N80's straight into an old "Low Block " 2-valve head 671 to upgrade horsepower?. I would think you will need to be running a 4- valve head, which is "high Block" with N80's and you would have to make sure you have the correct  injector rack, as from the HV- series injectors, they have a different offset than N80's , and then there is consideration about the type of liner you are using, with the different configuration on air-vent holes, as to get the right air-fuel mixture, as you are dumping more fuel into the cylinders, and also what compression ratio are you using, is this matched to the N80. In other words are you doing a complete strip and rebuild?, To give you a rough idea, a 2-valve head has exposed fuel line ( 2 ) and the 4-valve head are cast within the side of the head, so not externally seen ,Cheers Andrew.

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Hi I have rebuilt 6 6046 twin packs with 2 valve heads and dynoed 6 engines with the n80 injectors fitted in two valve head but all engines had the later bigger port liners run fine.

on a 4 hour full load run 245 hp 601 foot pound torque 2083 rpm blower pressure of 5.02 psi exhaust gas temperature 564 centigrade 1047 Fahrenheit.(each engine is nynoed on its own from a 6046)

n80 and 4 valve head gave more hp and torque

should have measured decibels in dyno room at full load that would be high!

As you say would not want to run n80s with the original liners small surface area compared to the modern ones.


the low block block does obscure the base of the new liner ports slightly but I have a military manual that says to grind the block to clear I have done this on a 6046 but made no difference on dyno results.

the injector arms if you grind/machine a notch to clear injector body works fine .

no external fuel rails is not a guarantee it is a 4 valve head 6-71  cylinder head casting number 5108548 has built in fuel gallery's and is a 2 valve head.

there is various mods that I do to the heads for more efficient cooling on the original 2 valve heads as recommended by  Detroit ,better as with n80s injectors will be getting more power =heat  than the ww2 setup.

if you like a visual clean exhaust then go for n65 injectors and 4 valve heads do not know what hp that will give you as have never dynoed that set up but did know of a gun carriage set up like that very clean exhaust.


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I had thought you had some good experience Hummermark with Detroits .I have run N55 on the 2 -valve head with elongated port holes with 17:1 compression ratio

making sure the return fuel line outlet elbow runs an .80thou hole, and is easy start and runs very clean around the 190- 200 HP, estimated, cheers Andrew.

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