The 86-92 non-turbo rotor housings have a “splitter” (also called a “diffuser”) in the middle of the exhaust port. These are part of the casting of the sleeve insert, and are VERY hard metal. We do not do any porting on these rotor housings! If we are assembling a “ported” 86-92 6-port engine, we use the Turbo rotor housings, which do not have the sleeve.
When using the Turbo rotor housings (and for 84-85 13B rotor housings), refer to our Exhaust Porting FAQ.
 Non-turbo rotor housing is on the left, Turbo on the right – shows diffuser in the non-turbo housing sleeve. We have heard of shops grinding the diffuser out – you are welcome to do it. |
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 View from the rotor side – shows how hard it would be to work around the sleeve while porting. Port flow is terrible if the sleeve is left out – don’t do it. |
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 As above (N/T on left, TB on right), this shows the water passage into the intake manifold that needs to be plugged when using Turbo rotor housings in a non-turbo engine. We have freeze plugs available to do this, or it can be tapped and use a 1/2 NPT aluminum internal allen wrench plug. |