understanding ported vacuum link inside

[jono]

I've been trying to get my head around the theory and workings of vacuum and ported vacuums of throttle bodies. As far as the EA82T Series One I am sure the throttle body had three vacuum ports on the throttle body.

 

Series Two is the one I have been fiddling [butchered more like it ]with - has just two.

 

The middle one (as you can see where the third would be in the casting) rips straight into the throttle body airway just above the closed throttle plate/butterfly/valve

 

The other port pokes out directly where the throttle plate closes against the outer - "tunnel" in such precision that when closed just a quarter or third of the hole is exposed to whhatever pressure or vacuum is above the plate, so same as the other one, just that as the throttle plate opens up so too does the hole - throttle plate out of the way exposes whatever is driven by this port to full air flow.

 

Silly me starting altering a throttle body for my needs without thinking I need the correct port for the vacuum advance of the dizzy - no pick out a three vac port version.

 

Yet to find the three port version to see where the third port gets exposed to. Also suspect the missing port is for vac advance - [for good reasons]. I'd like to get it right so best to be able judge my performance mod - spider manifold on mpfi turbo heads on a carb block. Need to study the three port series one diagrams

 

thought I'd share this link for anyone curious - coz you don't just hook up a dizzy vacuum to the inlet manifold ports !

 

Well, actually, if you read this link, reckons vacuum is same except for no want vacuum at idle due to emissions etc. Though I have previously hooked up vac cans to manifold vacuum and got pinging on lightest of throttle from memory.

 

From this persons writings could use man vacuum for dizzy and also tinker with TPS to switch off vacuum to dizzy at closed throttle ??

 

 

http://www.lbfun.com/warehouse/tech_info/timing%20&%20vacuum%20advance/vacuum_explained.pdf

 

closer inspection of this two port throttle body shows each of the two ports has two holes into the air flow. Clever guys at Hitachi managed to drill two holes on the inside with just one bung plug of brass on the outside ! The centre port has similar equal sized drillings inside - one above and one below the throttle plate.

The other non middle port has a much smaler hole about 3mm above throttle plate and the bigger one right on the plate close position.

 

A curious dude may T piece a vacuum gauge into these ports one day. One gauge per port, line 'em all up and see what difference looks to be

Edited January 2, 2016 by jono