vacuum advance and PCV with Offy

[Anonymous]

1. I've read where it's best to use a mechanical advance only when running an Offy because the manifold vac. drops to near zero when the outer carbs kick in. Why couldn't you just use ported vacuum? That shouldn't drop when the outers kick in, should it?

2. What are you supposed to do with the PCV line when using an Offy and you have an automatic trans.? Could those two lines be tee-d together?

 

[CobraSix]

1) You shouldn't use the ported vacuum for an Offy, should use the manifold vacuum. Or maybe I have the backwards...I can't remember anymore.

2) Get a PCV breather cap. looks cool, don't have to worry about t-ing anything. Personally I wouldn't T the PCV into the vacuum advance...too many chances of clogging.

Slade

 

[addo]

As the engine speeds up the manifold vacum drops away. As this speeding up corresponds to the opening of the extra carbs, there is little unusual in the behaviour. The best street use for vac advance sees it hooked to the manifold. "Off the line" acceleration is improved due to the extra advance under this loaded, low RPM condition.

You could consider a vacuum reservoir if you run boosted brakes.

Adam.

 

[Anonymous]

Thanks for the replies.

CobraSix,

What is a PCV breather cap? Where do you get one?

 

[Junk-Falcon]

i ppp

 

[CobraSix]

It's just a filter cap that kind of looks like a miniture air cleaner. They mount on the PCV opening. You don't have to run them anywhere. I've not run my PCV since I hooked up my Offy.

Slade

 

[addo]

Those push-in breathers are most common on the V8s. One side (one rocker cover) is fitted with one, the other has an oil cap with side pipe.

Some form of crankcase evacuation is a good thing. It assists slightly in engine cooling, and consumes inevitable (hopefully slight ) blow-by.

Cheers, Adam.

 

[Anonymous]

Hey Guys,

At the risk of seeming unkind, your concern over how / where to hook-up your vacuum advance is unnecessary. The vacuum advance system is not needed if the dual advance dizzy (68 - 73 mechanical + vacuum) is set up correctly.

The vacuum advance is used to overadvance the car during periods of low load, i.e., idle and running down a flat road at a steady speed. The overadvance condition is said to improve mileage and reduce emissions. Is this really an issue at this point. Given the mods you are making I doubt this is a concern.

As we are all well aware, these small sixes like a lot of advance at idle. It is also common knowledge that an initial advance around 15* does wonders for throttle response. A dual advance dizzy set up with an initial advance of 15* with an internal advance weight stop of 10* (20* at the crank - dizzy runs a 1/2 crank speed) will work extremely well with the vacuum advance system capped / plugged. I run mine this way. I have total control over the all-in advance. I use 16* initial and the mechanical advance brings in the needed 20 additional degrees by 2500 rpm. I would be happy to provide more detail if desired. So, do yourself a favor and stop trying to guess what is the correct thing to do with the vacuum advance. You don't need it. The following web site will provide some insight into this process. I will be hppy to provide more info if desired.

www.bob2000.com/dist.htm

Steve

 

[Anonymous]

Steve:

That sounds like a fabulous Idea... I have always wanted to eliminate the vacume advance on my 200...

However I am running a DruasparkII distributor.... are there similarities in them? Mine is a single vacum advance unit...

I am running the magnetic pickup off a MSD6... I would like to kill the vac advance line and run with everything dialed in at idle... just not sure how on this distributor? Of course I was not sure how on any distributor until I read this post....

 

[Anonymous]

Hi Jimbo,

The DSII is a dual advance dizzy. They were available with both a single and a dual vacuum advance. Sounds like you have the single. The important part is that it has a mechanical advance system. As a matter of fact the advance weight and spring system are very similar to the 68-73 dizzy. So, while the bob2000 site I refer to shows the internals for the distrubtor, the DSII is the same. Here again the process is to insure that you have 34 - 36 degrees of advance all-in at 2500 - 2600 rpm. A weight stop of 10* will allow the DSII / Dizzy to advance 20* crank degrees. You set the balance of the all-in advance needed with the initial setting. Remember, weight sets advance limit. Spring sets advance rate. I would not focus on the springs. Rate of advance will not be worth the trouble to change on most cars (even with the 2V and a cam). All-in at 2500 - 2600 will work well. You will be very happy with the control you will have after this change. By the way, the 10* weight stop was very common. You may not need to change the one you have. Also, there is no need to remove the vacuum system. Just cap the ports at the dizzy and the carb.

Check your PM, I will send a rather long post related to the process.

Steve