I know this sounds like a crazy idea but I'm hoping someone has tried it or has some information on it. I've got a 7.3 idi with a turbo from factory. my idea is I want to have the heads machined so they can hold Cummins 12 valve injectors and will protrude from the heads making it a direct injection 7.3 but it will still run off of the stock mechanical injection pump. If anyone knows anything that could be helpful to this project I'd be very fearful thank you

 

Not doable without spending waaaaay too much. It would require custom pistons, entirely different heads, and a ton of other work.
There is a company that offers a mechanical conversion for the 7.3psd for about $10-12k.

 

Yeah, I'd do this, if you want a mechanical direct injected engine. Or, just get a P-pumped cummins.

Really, you wouldn't gain anything by doing what you want, at all. The IDI design is a pretty good design, because you can use a very sloppy pump design like ours is.

I personally prefer an IDI design over a DI design because injector spray is far less critical. As long as the fuel comes out at the right time, you're good.
And even if it doesn't, it might create some smoke or a limp, but the engine will handle it.
On the other hand, a DI engine can melt a piston if an injector goes bad.

 

The only real downside to the IDI design is the loss of combustion heat through the pre chamber. That robs about 20% of efficiency on most IDI designs.

 

And yet, fuel economy doesn't seem to be 20% less.

 

The real question is... why would you want to go to smaller injectors? Besides that, what is it exactly you are trying to accomplish by "converting" to direct injection? Emissions not-withstanding, im not convinced DI is superior to IDI. IDI technology was to replace DI afterall. You do lose more heat to the head due to larger surface area, this can be mostly negated with heat coatings. Even so, the literature ive read puts it more around 10%. On top of that, DI pistons have a much greater surface area than ours. Instead of putting the heat in the coolant, youre putting the heat in the oil, but its still lost all the same, if not more so with DI, as aluminum absorbs / dissipates heat faster than cast iron or iconel.