Restrictive fuel fitting Detroit s60 12.7

You'd have no fuel pressure. That restriction is what regulates pressure

 

Yup that is what gives you pressure in the fuel passage in the head.

 

Top fittings the return line. Returns fuel to tanks. It’s 0.080 in. (2mm) Some swear by drilling them out to 0.090, Others claim you can drill it as much as 0.105 and still have adequate pressure in the head for injectors. The idea or theory is that by returning fuel faster, it stays cooler, and therefore burns or atomizes better. It’s probably the oldest and cheapest trick on a 12.7. I’ve never done it myself. Always wanted to try it though.

 

My dad had unlimited time and a dyno in the early 90's to do testing on engines, tuning them different ways to see how mechanical changes affected torque and HP.

On the 60's, he found a fuel pressure of 68-69 was pretty well optimal. He said even small differences of 3-4 psi were worth changing.

Most 60's from the factory were in the 75-80 range. And my most used bit for acheiving that 68 PSI was a .117.

I was just a dumb kid back then (not much change today), but dad taught me his methods as soon as i started. Folks came from all over for his tuneup procedure, which included very particular injector and valve settings. This was back before tuning ECM's were even a thing..

Back then, 80% of rated HP to the wheels was considered standard. The best i did and dynoed was a 500 putting 508 to the ground.