Does anyone know what the size/diameter of the stock y pipes are (ahead of the y) for a 95 F150 with a 302 in it.

 

small!!!I mesured mine to be a tick over 1 1/2" dia.

 

hmm
my '94 Aerostar has larger pipes than that, at 2" The 302 should have 2" pipes before the y-pipe. You should bump it up to 2.25 at some point after the y-pipe. I don't know why they used such small pipe for that year.

 

Not sure eather. I am custom making a Ypipe for mine using 2.5" head pipes, into a Flowmaster 2 into 1 collector.