Comparative dimentions of the GM and MG throttle bodies

MG GM
TBdim_std_inlet.JPG (36720 bytes) TBdim_GM_inlet.JPG (42555 bytes)

Both the MG and GM throttle bodies use very similar inlet dimentions - as can be seen above. This means that airfilters intended for use on K-series engines should bolt straight on to the GM throttlebody.
TBdim_std_length.JPG (36152 bytes) TBdim_GM_length.JPG (37247 bytes)
The GM throttle body, as can be seen above, is significantly longer than the original MG item. Broadly speaking, if you are intending to use a replacement, aftermarket cone filter, there shouldn't be any installation issues - except possibly with the ITG maxogen, where the throttle body has been mounted on the MPi plastic plenum (larger than the alloy VVC plenum). [Note that the IACV and breather pipes enter the throttle body on the opposite side with the GM throttle body compared to the MGF item.]
TBdim_std_outlet.JPG (52223 bytes)

TBdim_GM_outlet.JPG (48936 bytes)

The outlet dimention does pose a problem. The outlet bore, as can be seen above, is 62mm versus the MG's 57mm. The MG plenums are obviously made to match the standard throttle body, which means that their inlet hole is 5mm smaller than the outlet bore of the GM throttle body. This discrepency would all but cancel out any advantage in fitting this throttle body to an MG, because the step in diameter is diasterous to airflow. Therefore, one would have to bore-out the plenum to match the 62mm bore of the GM throttle body to maintain the airflow, and get the advantage of the new larger diameter throttle. How easy this would prove to be, and whether this is a reasonable DIY propostion, I do not know, as this is not something I have ever personally tried.

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