CPI vs. TBI

[Jody Shapiro]

I've been on this list for almost 2 years now and I've learned a great 
deal.  I've also picked up a number of fuel-injection books and read a 
bunch.

However, I'm embarrased to admit that I don't know what the difference 
between Throttle Body Injection and Central Port Injection is.  I know 
what TBI is and how it works, but I don't know how CPI differs from it.

Case in point - GM has been using TBI on their trucks for years.  Their
recent engines are now CPI, but from pictures of the engines that I've 
seen, they still seem like TBI.

CPI has been described to me as there being one or two large fuel
injections in the throttle-body area; then there are runners from this
"Central Port" to each of the intake ports.  This sounds to me likes it's
fairly similar to a carbeurated manifold with fuel injectors in the
throttle body (instead of a carbeurator).  How is that different than
TBI?? 

Thanks,
-Jody