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mooney265 mooney265 is offline
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Join Date: Sep 2008
Location: New Orleans
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Originally Posted by JFairman View Post
That bottom left port on the 930 throttle body is the distributor vacuum retard port and looking at the counterclockwise rotation of your distributor and the vacuum pot connection position and shape of the vacuum pot and internal linkage rod it is going to pull the plate inside the distibutor in the same direction it is rotating and that will retard timing when intake vacuum is applied.

That TB port only has usable vacuum up until around 1500-1700rpms of throttle position when there is no load on the motor so it's not good for anything else other than retarding ignition timing at idle, deceleration, and the first few hundred rpms above idle to lower emissions.
If there is a catalytic converter the higher exhaust temps from retarded timing will heat it up more.

The top left TB vacuum port is for operating a blow off or compressor bypass valve and deceleration vacuum limiter valve if using one. It gets intake manifold vacuum combined with some TB venturi effect between the top edge of the throttle burrerfly and TB wall and vacuum port while it is partially opened because it's on the top side of the throttle body where the butterfly is opening downwards. Top right TB port is for the control pressure regulator boost signal.

If you've rebuilt carburators and studied the idle mixture hole and multiple idle to main jet progression holes (especially in Webers) next to it in the throttle body wall next to the downstream opening edge of the throttle butterfly they work on the same principal and it's easy to understand.
If I have no catalytic converter and can lower my idle as low as i wish with the idle screw, why would I need "vac idle retard?" Wouldn't the car run cooler at idle without it?? Thanks, Shannon
LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 09-07-2011, 11:19 AM
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