Actually....the cost of the aftermarket systems aren't that bad by the time you add up all the bells and whistles that are hidden expenses with a DIY type system.
Here's the biggest question, and the first to ask.
What kind of cam are you running and what kind of power is the motor going to make?
A lot of people forget the cost and hassles that people with OEM fuel injected cars face when building up from stock. So if your cam selection isn't somewhere near stock suddenly the aftermarket systems jump to a healthy cost advantage. These older, swappable OEM systems are fairly dumb and if you have to invest in programming capability to achieve driveability......you're typically rivaling the cost of an aftermarket control system that comes with software.
It's easy to say you're just going to send off ECMs for programming, but old performance cars tend to evolve. Now you need programming for gear changes. Transmission swaps. etc. And you're relying on somebody thru the mail. :down: A guy's just got to own that capability at home, and it's the hidden cost equalizer. First no-start without the capability, you'll be buying the capability.
GM TPI is an awesome system up to around 325 horsepower, then it's too small and EVERYTHING has to change to hit 400.
GM TBI offers flexibility up to around 400 hp using fairly stock stuff.
Aftermarket TBI/TPI goes from there.
One of the biggest benefits of adding an ECM to the vehicle is knock sensing, don't overlook the advantage of integrated ignition & fuel systems. With knock sensors you get what you pay for and that's important when the noise of hedders and aggressive valvetrain are added to the mix.
Many factory ecms are looking for a vehicle speed sensor that your transmission lacks. You can add them to the cable or you can program that out. Just one more glitch that's solved with money :laughing:
If you look around there's a fair number of intakes offered with injector bosses and universal fuel rails that a guy can fit together at home, old style or vortec style. Throttle bodies can be very low profile, allowing a taller intake under our low hoods. You can get ridiculously tight with the air cleaner, much more than with carbs. Really, it's only a couple hundred cost difference to have a more sophisticated system that not only makes more power with it's larger intake, but has growth room.
Typical TBI fuel systems are 15-30 lbs. TPI systems run 45-85. Pressure helps efficiency but has added complexity and cost. So what you're willing to do to your fuel system is another decision variable. The trend is to higher pressures, so if you want to be able to benefit from future injector technology, higher pressure wins.
Both systems will want a later CS style alternator or the voltage drop at idle will funk things up. Plan for it up front, don't chase the ghosts later. Low voltage is also hard on ECMs.
good luck with your cool project!