Any downsides to doing such a large injector on a stock pump ?

Some say it's hard to tune the idle.
Otherwise I don't see any downsides to it ?

 

I don't see how the pump would relate to a tuning problem, if it's putting out proper fuel pressure then that's all you need it to do.

You will max out the fuel pump before you max the injector size that's for sure. If you aren't going to push that much power then it doesn't make much sense to run such a huge injector.

 

You will lose pressure long before the injectors reach their max, but the large injectors will help things stretch further. For example such a large injector may be able to fuel your motor as low as 30PSI fuel pressure where the pump is moving a lot more fuel than it is at our base of 58.

It's far from ideal.

 

But it needs to be adjusted to 30 or whatever base pressure and retuned.

 

Well yes and no... I mean if you lose pressure in a WOT pull. What youre talking about it absolutely the right way, but you can make up for that in your VE table. Thats how I got away with my 255 for so long. Again, its totally hack and far from ideal.