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MG MGF Technical - 58mm throttle bodies

does anyone have any info on fitting 58mm throttle bodies as found on gm 2 litre cars and what modifications ie does it need re mapping
need doing

No mapping, look thru the archives and on dieters site ( But the advised wisdom is that going above 52mm give no performace advantages, and may actually diminish the gains seen by moving from 48 to 52.
Will Munns

Installation of the 58mm GM throttle body is not as straightforward as installing the Del'Orto 52 "Trophy" throttle body for some very simple reasons:
1. the throttle opens in the opposite direction
2. The hole centres for the mounting bolts to the plenum are different
3. The outlet diameter of the GM throttle is 5mm larger than the inlet to the plenum, introducing a nasty step in the inlet air stream.

These problems are not insurmountable - Dieter and others have been successful in managing to perform this modification in the past - but it isn't for the light hearted!

More details here: and
Rob Bell

Dieter is the guy you need (or at least his website).

Performance wise, it could be interesting for a VVC breathing engine, but it isn't really worth on an MPi. (IMO)

Could be a nice exercise, if you like that type of conversions.


Nice review page there Erik :o)
Rob Bell

This thread was discussed between 19/05/2004 and 21/05/2004

MG MGF Technical index

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