I know many people have opinions if the aftermarket throttle bodies work or not, but suppose you were to make one from 1.5inch aluminum without the threads in the middle. Would it do anyhting on a fuel injection?
Well I don't think that it would be worth the time to make a new TB yourself. I'm not doubting your ability but it would not be so easy IMO. The aftermarket TB's work if your engine can use the air that a larger hole can give you. I'm new to the I6 but most people have said a stock engine it's a waist of money.
the TB isnt the restriction on a 300, its the head itself. the TB just lets air in depending on throttle position and a larger one is a) not worth the work and b) not gunna make a different besides a slight throttle inscrease. same thing w/ a TB spacer.
Are you talking about a new TB, or just a TB spacer? Either way, spend your time and money elsewhere. The TB spacers work nicely on carbureted engines and TBI engines. With port injection any benefit they provide has disapeared by the time fuel meets air.
how exactly does a throttle body work on fuel injection? I wouldn't see why there would be any difference?
Well this is how it works It controls the amount of air allowed to come in to the engine. If you removed the TB and started the engine the motor would rev out of control.
The TB is closed when you have you foot off the gas, the idle control is done with a small valve on the intake called the air idle control valve.
This is why there is no difference, if your air flow threw the head is max-ed out with the stock TB for sake of argument, then increasing TB size could not change the flow volume of air threw the head which was already max-ed out. If you ported the head to increase the max air volume flow then a after market TB could make more power.