vacuum hose routing question Options

[L-Jet914]

I was installing my new ignition and FI harnesses today and I decided to look back at the vacuum hose routing diagram on Jeff Bowlsby's website. I knew my vacuum hose routing had been modified by whatever technician worked on my father's 74 914 1.8 years ago. I noticed that they teed the vacuum retard side of the vacuum advance into ported vacuum off of the intake plenum. According to the vacuum routing hose diagram, it's supposed to be connected to the rear port of the throttle body (which only gets vacuum after the throttle plate moves off idle). Would there be any reason the technician did this? I will end up rerouting the vacuum hose to the proper location. I'm just curious as to why it was modified for whatever reason. So would my 74 1.8 be considered a early or late 1.8? According to the late diagram and the throttle body that is in the car, the hose should route to the front port instead of the rear port.
The part number on the throttle body in the car 022133067C which fits either a Super Beetle 75-79, 76-83 Bus, or 83-84 Vanagon (two port t-body). According to the PET on AA's website shows two different throttle bodies 022133062L or 022133062S for California spec 1.8L 914s. The Porsche PET does not list a throttle body part number for the 1.8, only the 1.7 and 2.0s. Curious as to why someone would put the wrong part number throttle body on my 914, though it does have the 3 pin throttle position sensor. Port setup would be indicative of late 74 because the required port (front of throttle body pointing toward front of vehicle) is behind the throttle plate.

[wonkipop]

@L-Jet914

i looked up the PET i have on file and the version i have does list the 1.8 throttle bodies.



to assist in understanding this. essentially there are actually only two types of throttle body in terms of the basic design.

1. the 1974 EC-B. two vac ports. one beyond the throttle plate (facing forward in engine bay). one above the throttle plate (facing rearward in the engine bay).
the retard side of the distributor can (right side of can) connects to port below throttle plate. the advance side of the distributor can (left side) connects to port above throttle plate.

emissions outcome = less NOX at idle but higher head temps around exhaust valves.
no NOX clean up at cruise. but engine runs cooler and greater fuel economy.

2. the 1975 EC-b (california). has identical design throttle body to 74 EC-B. the difference is they connect the hose from port above throttle plate to an EGR device which is activated by engine vacuum when the engine is at cruise. (the diagram above you have posted for a 75 eroniously shows there is a T from the EGR connecting back to advance can on distributor - that was not the case. it did not connect to can. instead the hose from the can was simply tucked under the inlet manifold the same as for a 74 EC-A california). the reason it may have had a different part # than 74 EC-B was likely due to a minor design change somewhere on throttle body unrelated to these ports which led to it getting a letter at the end of the number sequence.

emissions outcome = less NOX at both idle and cruise. but EGR activated at cruise offsets higher head temps and returns some fuel economy at cruise due to exhaust gases mixed in.

3. the 1974 EC-A (california). may have had two vac ports like EC-B. but port above throttle plate was capped by a rubber plug. the hose which connected it to advance can on distributor was still there. all they did was not connect that hose at throttle body end and instead tuck the hose under the inlet manifold. a cursory glance at the engine would make you think it was no different to an EC-B

emissions outcome = less NOX at both idle and cruise. but higher head temps and less fuel economy at both idle and at cruise.

4. the 1975 EC-a (49 state) was essentially the same as the 74 EC-A california.
reason. 75 USEPA emissions standards were california standards from the year before.
the difference in throttle bodies was that the 75 49 states definitely did not have the port built into it for the position above the throttle plate. the port is omitted entirely.
the vac hoses hook up exactly as per the 74 californian.

emissions outcome = the same as 74 california with same disadvantages regarding head temps and fuel economy.


as to why would the throttle body been replaced with a beetle or other VW throttle body on your car - the answer is probably because it fits or works. though i would be curious to know how given the throttle cable activation comes in a full 180 degrees different due to rear engine application rather than mid engine like 914.

thinking further, the retard side of vac can (right side towards dizzy) will work connected to the inlet plenum chamber exactly the same way it would if connected to the port below throttle plate on TB. be the same. the only reason i can think that you would connect to plenum would be there was no port on T/B below the throttle plate on plenum side.