Hey all,
I posted this over at toyota3tc.com but haven't received any comments. Maybe someone here can point me in the right direction.
On both of the 3TC engines I have, there are two vacuum ports on the distributor. I'm curious if anyone knows about the function of each different vacuum port. One of them, I assume, goes to manifold and/or ported carburetor vacuum.
The other one, though...is it operated by a switched vacuum? Switched by load, or temp, or???
Basically, I'm trying to reduce about 5 lbs of vaccum hose from the system, and am trying to make sure I do it while still allowing optimum engine operation.
Is anybody familiar with these? I can just wing it, but figured I don't need to reinvent the wheel.
If I'm not clear enough (par for the course) feel free to dope-slap me and I'll clarify.
Thanks,
Clem
edit: photos forthcoming
I had an M10 318i where one of them was switched by temp. When the motor was cold to help start the car.
This one is a Ford piece but the operation is similar. The vacuum nipple (hehe, he said nipple) on the left side is for advance. The nipple that points up and to the right is for retard. Generally the retard side is to retard the timing at specific engine temperatures for emissions reasons and thus there will be a ported vacuum temperature switch on the engine somewhere that controls that side. More than one I have just disconnected that side entirely and run a hose to the advance side. If you do that, you want 'ported vacuum', that is you have no vacuum at idle but you do when the throttle is opened. Most carbs have that type of port at the base on the primary venturi side.
Sometimes it's set up so that the retard side goes to manifold vacuum. This retards the timing at idle because you have full vacuum. When you open the throttle, the manifold vacuum will drop and a spring inside the vacuum advance will advance the timing. Lots of British cars were done this way (typically British- ass backwards).
Excellent info...Thanks!
I'll trace the hoses back and ditch the "other" one, most likely.
I appreciate it, all!
Clem
why? You could probably run more base timing with it still engaged.
Well...you may have a point there.
Like I said, I'm looking to loose a bunch of the complexity in the engine compartment(s)...and will end up ditching a lot of the seemingly endless vaccum circuits that are there now. Both functions of the advance/retard setup are valuable, as it seems you think they are, I'll see about keeping them both.
Like I mentioned...I want to keep it running well and efficient, but eliminate a lot of the junk that's in there.
Thanks,
Clem
Usually a vacuum advance sorta 'fills in the space' between idle and when the mechanical advance comes in. On some engines this is not a concern, on others yeah it can lead to driveability issues.
Some engines have a situation where if you disable the vacuum advance and then set the ignition at full advance at an RPM where the mechanical advance has come in completely when you let the engine idle back down the base timing is high enough that it idles erratically and in some cases can be hard to start.
