Originally Posted by darefugee
Hey guys I need more pointers. I'm preparing to replace my old tired 305 with a vortec-headed 383 I just finished building. Although I'll start with a quadrajet I already have, my guess is that I'll eventually want a 454 TBI to feed the 383. Assuming I get the 454 TBI and 454 injectors, what other different parts will I need to get?
The computer chip needs to know what size engine and injectors are under the TBI. Injectors are limited by duty cycle (time on as a percent of total time) which is about 80% max otherwise they overheat. The factory is usually very conservative with this, so 350 injectors can be stretched to feed a 383 but not a 454. 454 injectors would have excess flow capacity so when mounted on a 383 they wouldn't be on much at all, though TBI cycles twice per crank revolution but it's on time against off time we're measuring for injectors of differing volumetric capacities.
The cam comes into play, but with TBI cam's over 215 degrees of duration get to be a sensor sensitivity problem as the manifold vacuum falls with a bigger cam. So you end up with big flow changes for smaller and smaller vacuum changes till the sensors just can't discriminate the subtle vacuum changes that result in big mixture changes any more.
You will need a custom chip in the computer, check out these places that specialize in them.