Originally Posted by BillH
I have a '91 Sierra 1500 with a tired 305 and a 5-speed manual. I'd like to replace the 305 with a 350 for more power but need some guidance. It's a daily driver so mileage is also a bit of a consideration. First, which 350 should I order? Next, which EFI should I use? Thanks.
You will need to change the chip in the computer for a 350 with manual gear box. The program in the 305 chip which controls the on-off time of the injectors (yes the 2 injectors of the TBI do sequence) this controls the amount of fuel delivered to the engine since pressure is maintained at a steady amount sequencing the injector time on against time off is the only way to meter fuel against the engine's immediate need. The 350 is 45 cubic inches or 15 percent larger in size so the injectors will need to be turned on 15 perccent longer to get the added fuel required by the larger displacement. This is an over-simplification of what's going on but it is basically correct.
The 350 will in fact start and run on the stock 305 computer farily well but it will have a lean mixture in most operating zones which will result in surging and bucking and expose the engine to the risk of detonation and excessive heating of the exhaust valves. Another way to get more fuel in is to replace the TBI's non-adjustable fuel pressure regulator with an adjustable replacement. This works pretty well in a somewhat sloppy way, if you have to pass emissions this would not do it for you.
An alternative is to have custom chip made which may be the easier solution with the 5 speed since most 350s sat in front of an automatic. See this guy for chip <<< TBI CHIPS