Vacuum advance vs EGR which should I use? Options

[SVG223]

The hose hooked to the EGR was stock config with the advance can unhooked. So I'm thinking cooler running on the interstate vs throttle response. If I understand this correctly.

[wonkipop]

i imagine this worked pretty much the same way for the 1.8s as it did for the 2.0s.

the EGR made up for the lack of vac advance as it helped with cooler running mixing in the exhaust gases at cruise.

its the ones without the egr that ran hotter. like the california 74 1.8s and the 49 state 75 1.8s. these had the vac advance not connected and no egr. only california 75 1.8s had egr - that kind of made them closer to 74 1.8s that had connected vac advance.

connected vac advance was a kind of standard vw thing world wide, even with carb cars and non usa / no emissions equipment. made then run cooler at cruise but also gave better throttle response and smoother running through part throttle opening driving.

only usa cars had the dual vac retard/advance cans on the distributors. meant they all ran hotter at idle due to action of retard side of can. and supposedly cleaner. but really cleaner only in the sense of reducing nox - main ingredient of photo chemical smog.

i'd probably connect up the advance can and disconnect the egr. but i say that only because i have a 74 1.8. i really think its close to a much of a much-ness if you have a functioning egr.

it was all about $ back then. the egr added to cost and complexity. so the cars without it kind of got sold short but conformed to emissions standards. ran hot at idle and ran hotter at cruise.

[emerygt350]

Personally, I would go with EGR. I really think the throttle response bit isn't a thing. Advance will give you better cruise mpg perhaps, but you pass through the 'zone' of the advance activation so quickly that I just don't think there is any other impact. For example, if you were going to accelerate as fast as possible you would go wide open throttle as soon as the clutch was engaged. That ported vacuum only sends a signal when the throttle is just barely open and soon as you depress the pedal to get any kind of meaningful acceleration you have turned off the advance.

Anyway, EGR is an excellent idea for air cooled engines with hot heads. I would definitely skip the advance and go with the EGR.

You can buy super cheap remote control vacuum switches on Amazon. I used them for testing the effect of advanced on my car. You could set up a simple system that lets you choose between advance and EGR at a click of a button.

I wonder how a t and using both would work?

[SVG223]

One vote either way so far. I like the idea of a remote vacuum switcher, I haven't found such a beast yet. One motivator for deleting the EGR is just removing clutter and complexity following the theme as I'm removing the smog plumbing; but in the Summer I'm very interested in keeping the engine as cool as possible. I'm not sure if there is enough throttle vacuum to actuate two diaphragms at once, but could work I'm not sure.

[emerygt350]

Here is the remote relay

https://a.co/d/iKw5wHP

And here is the vacuum switch
https://a.co/d/3r1Um0n

I might try the t first. Plenty of vacuum, not like it's going anywhere.

[wonkipop]

One vote either way so far. I like the idea of a remote vacuum switcher, I haven't found such a beast yet. One motivator for deleting the EGR is just removing clutter and complexity following the theme as I'm removing the smog plumbing; but in the Summer I'm very interested in keeping the engine as cool as possible. I'm not sure if there is enough throttle vacuum to actuate two diaphragms at once, but could work I'm not sure.

There is enough throttle vacuum don't worry.
if hooked up correctly to correct ports on throttle body.
the distributor was designed originally to have both hoses hooked up in the cars.
its only as emissions laws progressed that vw and porsche started doing the unhook the advance hose trick on later models to fairly bluntly and i think a little crudely conform with emissions laws.

@JeffBowlsby would know for sure, but i imagine that similar to the 1.8s and likely arlier 2.0s say in 73 or even 74 (49 states?) the advance hose was plugged into the throttle body to a port above the throttle plate while the retard hose is plugged in to t/b or intake plenum below throttle plate.

the way it works is retard only when idling. advance hose does not get engine vacuum, only retard hose has it due to throttle plate closed. acts on the retard can portion only of vac can and retards ignition at idle for emissions purposes.
engine runs hotter but less nox.

when at steady state part throttle plate opening (cruise) the advance hose receives engine vacuum. as well as the retard hose. the advance side of the can is much larger than the retard side and acts with a greater degree of influence. so its vac advance over mechanical advance (centrifigal advance in base of distributor) and the vac advance is total vac advance - lesser vac retard = actual vac advance. without the vac advance hose hooked up its only vac retard. so you get vac retard acting on mechanical advance which slightly retards the ignition while at cruise. hotter head temps at cruise speed. mainly around the exhaust valve area (that is unless you have an EGR, which whill counteract that).

the vac retard also influences distributor behaviour when you snap the throttle closed.
during that phase of engine braking/deacceleration the vac retard also acts to further retard the ignition than would be the case of just the mechanical advance declining.
this helped clean up the engines during deacceleration phases.

i think either way will work with your car.
either egr or hooking up advance hose.
but since you have intact egr, despite the "clutter" its not a bad thing.
egr was not really an emissions evil.
at least at that point in time with port injection.
(it is now with direct injection engines --!!!! (IMG:style_emoticons/default/sad.gif) , but thats another thing).

unhooking the advance hose and having no other compensation for the sake of emissions was a bad thing in my view and its what porsche and vw did in 74 and 75 to those cars without the egr. basically saved money, conformed with emissions, but made the engines run hotter at cruise.

the two superior set ups that are less compromised are, at least in the case of 1.8s, the 74 49 states and the 75 california. and it must be the same for the 2.0s?
but they do differ a little in terms of emissions conforming. the L Jets needed less extra stuff to conform. for instance no air injection (smog pump) was needed on the 1.8s. more accurate fuel metering (or more accurate enough) on L Jet. the smog pump did rob horsepower. maybe not much horsepower. but it did take some.

[SVG223]

Here is the remote relay

https://a.co/d/iKw5wHP

And here is the vacuum switch
https://a.co/d/3r1Um0n

I might try the t first. Plenty of vacuum, not like it's going anywhere.

What a cool idea, thanks for the links. I believe I will try using a T and hookup both, in that case.

[SVG223]

One vote either way so far. I like the idea of a remote vacuum switcher, I haven't found such a beast yet. One motivator for deleting the EGR is just removing clutter and complexity following the theme as I'm removing the smog plumbing; but in the Summer I'm very interested in keeping the engine as cool as possible. I'm not sure if there is enough throttle vacuum to actuate two diaphragms at once, but could work I'm not sure.

There is enough throttle vacuum don't worry.
if hooked up correctly to correct ports on throttle body.
the distributor was designed originally to have both hoses hooked up in the cars.
its only as emissions laws progressed that vw and porsche started doing the unhook the advance hose trick on later models to fairly bluntly and i think a little crudely conform with emissions laws.

@JeffBowlsby would know for sure, but i imagine that similar to the 1.8s and likely arlier 2.0s say in 73 or even 74 (49 states?) the advance hose was plugged into the throttle body to a port above the throttle plate while the retard hose is plugged in to t/b or intake plenum below throttle plate.

the way it works is retard only when idling. advance hose does not get engine vacuum, only retard hose has it due to throttle plate closed. acts on the retard can portion only of vac can and retards ignition at idle for emissions purposes.
engine runs hotter but less nox.

when at steady state part throttle plate opening (cruise) the advance hose receives engine vacuum. as well as the retard hose. the advance side of the can is much larger than the retard side and acts with a greater degree of influence. so its vac advance over mechanical advance (centrifigal advance in base of distributor) and the vac advance is total vac advance - lesser vac retard = actual vac advance. without the vac advance hose hooked up its only vac retard. so you get vac retard acting on mechanical advance which slightly retards the ignition while at cruise. hotter head temps at cruise speed. mainly around the exhaust valve area (that is unless you have an EGR, which whill counteract that).

the vac retard also influences distributor behaviour when you snap the throttle closed.
during that phase of engine braking/deacceleration the vac retard also acts to further retard the ignition than would be the case of just the mechanical advance declining.
this helped clean up the engines during deacceleration phases.

i think either way will work with your car.
either egr or hooking up advance hose.
but since you have intact egr, despite the "clutter" its not a bad thing.
egr was not really an emissions evil.
at least at that point in time with port injection.
(it is now with direct injection engines --!!!! (IMG:style_emoticons/default/sad.gif) , but thats another thing).

unhooking the advance hose and having no other compensation for the sake of emissions was a bad thing in my view and its what porsche and vw did in 74 and 75 to those cars without the egr. basically saved money, conformed with emissions, but made the engines run hotter at cruise.

the two superior set ups that are less compromised are, at least in the case of 1.8s, the 74 49 states and the 75 california. and it must be the same for the 2.0s?
but they do differ a little in terms of emissions conforming. the L Jets needed less extra stuff to conform. for instance no air injection (smog pump) was needed on the 1.8s. more accurate fuel metering (or more accurate enough) on L Jet. the smog pump did rob horsepower. maybe not much horsepower. but it did take some.

Thanks for this detailed information! I used to have a 1975 1.8 and it ran great, it got like 40mpg on the highway from what I can remember.