There were a few things to do to the throttle body and throttle plates also. Short of getting the
UIM and LIM intake runners Extrude-honed to smooth flow I did want to improve the flow through the throttle
body itself. Looking at the throttle body, the interior aluminum had a rough sand cast finish and the
throttle bore separators were relatively thick and had almost blunt leading edges. Out came the Dremel
tool and I smoothed out all the throttle body bores and knife-edged the leading edges of each bore runner.
The interior was then polished to get the best result. I did NOT enlarge the bores, as this would have
meant new throttle plates. I just smoothed the flow into the throttle body bores. Will this net any power
increase, questionable, but it certainly can’t hurt. Oh and I polished the exterior of the throttle body
while I had the buffing wheel warmed up. A new Throttle body O-ring was fitted also. I had had the TB
off and on so many times before a new O-ring was in order.
The FD has two sets of throttle butterflies in the secondary intake runners. One set is to modulate
air intake via the gas pedal under large gas pedal movement (your traditional throttle plates found in the
throttle body) the second is to stop large amounts of air entering the engine when it is cold (which are
found in the upper intake manifold). This is a fail-safe device, called the double throttle control, to
stop Mr. Numbskull from going WOT on a stone cold engine and causing premature wear and possible mechanical
damage. These secondary butterflies, once the engine is up to normal operating temperature, stay wide open.
They serve no other purpose. In fact, it is another complexity that can be removed in the interest of
simplicity. Their removal eliminates a potential flow restriction or object that could introduce flow
disturbance in the intake flow. I would like to consider myself as not falling into the category:
Numbskull. Therefore the double throttle control had to go. This was as simple as unbolting the control
dashpot from the backside of the UIM, removing the throttle plates from the “axle” by unscrewing the small
brass screws, and sliding out the axle and attached hardware. I fabricated a block off plate (with a gasket) to cover the
axle hole in the backside of UIM where the actuator was. With the assembly removed the control solenoid can
be removed also and all the wiring for it was weeded and removed. Simple and clean.
The one thing I did keep, and some may call me foolish, was the throttle body coolant lines. In fact
I drilled and tapped the throttle body to accept braided SS lines to and from the water pump housing and the
rear block iron. I may just end up removing it later but for now it stayed.
For more specifcs on the reconstruction of Princess go to the following pages:
OUR "LOCAL7" COMMUNITY | THE WORLD OF THE RX-7
This page last updated March 19, 2009