Manifold Mods
The only major modification to the manifold was the removal of the
EGR channel. I will not be using EGR so it is nothing more than an obstacle
to airflow from my perspective. The plenum area was smoothed slightly to
remove some of the casting imperfections and flashings which cause turbulence
and reduce overall flow.
Very minor grinding was done in the small-ish ports to remove casting
imperfections. The ports were designed small to increase velocity
and thus improve torque in the lower to mid RPM ranges for its native 350ci
engine. By keeping the ports practically straight from the plenum area
to the head, flow restriction is minimized. This CFI will have 20% fewer
cubes to fill than if it were on a 350. The longer rod length to stroke
ratio of my 283 should also help reduce cylinder filling inefficiencies
and keep the little 283 happy even in the higher RPM ranges.
The lid can be installed with a spacer to increase volume in the plenum
area. I opted not to do so, figuring that my small engine wouldn't require
the added work.
Mixers are located in the lid beneath each throttle body. The purpose
is to create turbulence and distribute the mixture to the runners farthest
from the TBI.
TBI Mods
Dis-assemble and clean everything.
In the OEM application, GM connected the fuel lines
in series. In other words, fuel was routed to the front TBI through the
return line and to the second TBI. From there a return line carried extra
fuel back to the tank. The front TBI unit contains an "accumulator" to
lessen fuel pulses as the injectors are turned on/off. The second
TBI contained the fuel pressure regulator.
This part of the TBI contains either the accumulator or the fuel pressure
regulator (depending on whether you're look at the front or rear assembly).
I disabled the accumulator and fuel pressure regulator in favor of an external
aftermarket regulator. This was done with a piece of 0.025" aluminum sheet
from Lowes. (It is probably also possible that the OEM regulator could
be made to be adjustable by drilling out the plug in the bottom of the
OEM regulator.)
I selected a pair of standard 350ci truck injectors (55#/hr) to replace
the differing OEM ones. After assembling the accumulator/injector unit,
it is ready to be installed back into the TBI housing.
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