I have an '89 GTU that has a street ported 13B. The primaries have barely been touched, however the secondaries have been ported. The rotating mass has also been balanced. Currently I have the stock injectors. I am contemplating 720cc injectors for the secondaries and keeping the primaries stock. Exhaust is RB header with presilencer and DynoMax mufflers...no cat, low backpressure. What size injectors would you buy and install? Also what would be your next upgrade? Thanks

 

for a normal aspirated motor, keep the injector size stock. Bigger injectors on the stock ecu will make it run too rich.

 

Contrary to what others on the forum will tell you, the stock injectors will support just over 200HP at 85% duy cycle.

 

720 is way too big. if you really need bigger injectors get the stock turbo ones which are 550cc, but unless you have a way to tune them in like a S-afc it'll run worse.