|I have located a small problem with the previous 60mm throttlebody conversion writeup and haven't seen anyone else mention it yet, but this is something of importance you need to know.
In all throttlebodies, the butterfly shaft is sealed at both ends using a typical shaft seal to prevent manifold vacuum or boost from leaking through the shaft bore. The OEM twinturbo throttlebodies were designed for use in a boosted application whereas the 240SX (KA24DE) engines and the Stanza engine were not designed for forced induction.
I found a leak in my Z over the weekend and determined that it was coming from the shaft seals of the 60mm throttlebodies. It wouldn't leak at lower testing pressures of around 4-5psi, but it would show its face when reaching around 7psi. I pulled the throttlebodies off and disassembled them to inspect.
I had a set of OEM throttlebodies side by side to the 60mm throttlebodies and here's what I found:
Here's the shaft seal of the 60mm unit:
Here's the shaft seal on the OEM unit:
And the other side of the OEM unit:
It may not be clear what the difference is by the pictures, but here is the difference in the seal lip design:
Here is another image of the seals in comparison: (Top: OEM. Bottom: 60mm)
The OEM seal has a double lip design which will prevent both positive manifold pressure OR manifold vacuum from leaking past the seal whereas the 60mm unit was not designed for forced induction and the seal is a single lip design only intended to seal against manifold vacuum.
Fortunately the OEM shaft seals are the same ID and OD as the 60mm units so you can simply swap the seals over to the 60mm units during the conversion.
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