What are the advantages and disadvantages of placing fuel injectors close to the head vs further back on the runners or even in the ram tubes on the ITB's.

closer, as in pointing at the back of the inlet valves is best for economy

further back pointing straight into the port and not at a port wall is apparently better for power as it cools the intake. obviously less efficient

And what about all the way back to the inlet of the ram tube on the ITB's.

Edit: Like in pre-throttle body/plate

i'd say even more power. thats how new M3s are and few actual race cars ive seen. but thats an injector just hanging in mid air squirting fuel straight into the ram tube

It's much easier to do that.

For maximum power, place it in the head, pointing at the valve.

Or in the head, pointing into the cylinder is 30% more power. But it require high pressure and precision timing (direct injection).

The injectors above and 'outside' the ram tubes/bellmouths (the trumpet shaped bit at the start of the tubes) will make most power, provided the cross section of the runners and the combination is 'right' for the rpm range you want to operate in. It cools the air and the furthrer from the engine it is (as long as you get the port shapes right) the denser the air getting into the cylinder, the more power.

But do it wrong (or try and run it at lower rpm or mid range 'cruising' rpms) and it'll have fuel drop out and terrible fuel efficiency/power delivery.

Incidentally this is why a lot of 2 valve v8 engines will make more peak power on a dyno with a tunnel ram intake and carburettors than vs efi with injector placement in the intake tract (rather that outside the top of it). They make more 'peak' power, but no carb can respond to changes in rpm/flow as quick as efi can, so even though they make a little more peak power carburetted, the efi engine will slaughter it in a real world scenario where rpms just soar up from off idle to redline, then get yanked back down again by each gearshift

Basically it really only 'works' for an engine that is kept buzzing in a relatively high powerband. They'll do 'ok' at part throttle, cruising behind a pace car under caution or whatever, but that is 'ok' as far as race needs go. Emissions and fuel economy will be nowhere near as good.

Generally speaking, it's _very_ hard to do better than stock/factory injector placement for any motor built in the last 20 years or so - for street applications (or even a street car with occasional drag strip or circuit race use.