Guidance please: Setting up vacuum advance on webers using 280zx distributor

[PRW007]

Good Day!

 

I have just joined Hybrid Z and am unfamiliar with the site as far as searches or how posting goes, so apologies if I am missing the answer to my question if it's in FAQ or has already been discussed at length previously... If so, please direct me accordingly.

 

I have a 240Z with an L28 motor, N42 Head, Stage III Schneider cam, equal length headers and an essentially unrestricted 2.5" exhaust. I am also running triple DCOE 45 Weber carbs, Cannon intake manifold and the distributor off a 280ZX...

 

I am told that it is worthwhile to connect the vacuum advance to the intake manifold via a tube that connects the distributor to the middle of the intake manifold. I am advised that it is a fairly simple mod which requires 3 components: 1) hose/tubing 2) some sort of fitting/nipple to be drilled into the intake manifold 3) a regulator to be placed inline to limit flow/pressure.

 

My questions are....

 

Is this a worthwile modification, and why?

 

Where can I purchase the parts required?

 

Many thanks,

 

PRW

 

[luseboy]

Hello,

Search around as there are many great threads on here and classiczcars that cover this issue.  In short, the basic problem with running a vacuum advance with triples is that they don't have a ported vacuum port which is what the distributor uses, but only have manifold vacuum which reacts to changes in engine speed and throttle input in a different manner than the ported vacuum does.  You might still get ok results with manifold vacuum.  The other issue is that some believe that the triples don't pull enough manifold vacuum (well rather, they don't allow much manifold vacuum buildup) to even move the vacuum advance enough for it to do anything.  If I'm not mistaken, the 45 dcoe's only exasperate this problem compared to the 40's.  Some people have toyed with the idea of making a vacuum canister that pulls manifold vacuum from all six runners of the manifold, but as far as I know, no one has been successful at getting that to work properly.  Dcoe's are designed with racing in mind, and most racers don't mess with vacuum advance because once you get past 3k rpm it's already at full advance.  Read up more on it, you may learn something knew.  I never read too far into it because I'm running a 4bbl so I didn't have any real personal reason to find a solution.  Tony D or Leon on here are going to be your best resource, so maybe shoot both of them a message. Tony is the engine guru around these parts, and Leon knows a thing or two (maybe three, not quite sure) about side draft carbs (oh and Z cars too!).  

Good luck!

[bajcsi]

Howdy,

 

 When I built my motor with triples, I made a vacuum log that connects to 3 runners on the manifold.  The brake booster is fed off the back side of the log and the front side of the log has a .063" restrictor that connects to the PCV valve I installed in place of the pipe that exits the block.  In between the first and second runner port, I put a t-connector and fed my MAP sensor off that vacuum source for vacuum advance control.  

 

There is a post of mine on here that discusses it and TonyD and others chimed in.  By feeding it form the log rather than directly off a runner, it evens out some of the pulses, etc.  Seems to work well.

 

Bajcsi

Edited April 17, 2014 by bajcsi

[T-Bone028]

You can just leave vacuum advance disconnected, and set timing at all in. Have a friend with a timing light help you and set it at like 30-34ish total advance (depends on your CR and gas, pinging, etc). Just let initial timing fall where it may. I've been running fine for a year this way.

 

OR...check out 123ignition!!!! That's on my Christmas list.

[Lazeum]

With low engine load (i.e. low fuel mix inside combustion chamber), mixture burn rate is slower than at full load.

To run properly at partial load, you either need to get more fuel or get ignition occuring earlier than what a simple mechanical dizzy can do.

 

It is much more efficient to control timing than to compensate poor engine control with high AFR, hence vacuum advance system.

 

Bottom line, at WOT, you won't notice any change between pure mechanical advance based on rpm only & full engine timing control => no interest for racers.

Changes would be very noticeable at low load and transient states (which makes the engine more reactive - feeling more powerful).

Fuel economy will be much more efficient, you can get as much as 30% fuel economy with good timing. 

 

I'm controlling timing with TPS instead of MAP, difference on the street is night and day.

[Leon]

Properly-working vacuum advance is always beneficial to performance. Many times it's left off because there are no provisions for it and/or the distributor has too much vacuum advance, as some ZX distributors may.

 

What is the model number of your 45DCOEs? It will likely be either a 9 or 152. The good news is that the 45DCOE152s actually DO have provisions for ported vacuum! I was very surprised to see them when I got my 152s. You can gang up a few ports and have a decent signal. The possible not so good news is, as I mentioned earlier, that your particular ZX distributor may have too much vac advance for a non-EGR engine. You'll have to let us know the distributor part number off the body to be sure. It'll look something like "D6K8-xx" or a permutation thereof.

 

Otherwise, running manifold vacuum for advance will give you a lot of static timing, likely more than your engine wants. It can probably be made to work though if you really want to. As someone else mentioned up top, check out 123ignition. They're programmable distributor is a fantastic solution (or so I hope)!

[luseboy]

I knew you'd have an answer Leon.  That's pretty cool that the 152's have a ported source. FWIW, if you really want to get into it you can actually adjust the vacuum advance settings (http://www.zhome.com/ZCMnL/tech/ignition.html).  That said, it seems like a lot of trial and error, though I suppose these cars kind of work out that way anyways.  I would confirm that your vacuum advance actually works before going much farther.  It may not work, and hooking it up could just cause a vacuum leak if the diaphragm is broken/cracked.  You can simply put a short length of vacuum tube on the hose nipple, and suck on the other end with the cap off.  You should see the breaker plate move clockwise.  Hold it there for a few seconds to make sure it holds pressure, and you should be fine if that checks out. 

[Leon]

I knew you'd have an answer Leon.  That's pretty cool that the 152's have a ported source. FWIW, if you really want to get into it you can actually adjust the vacuum advance settings (http://www.zhome.com/ZCMnL/tech/ignition.html).  That said, it seems like a lot of trial and error, though I suppose these cars kind of work out that way anyways.  I would confirm that your vacuum advance actually works before going much farther.  It may not work, and hooking it up could just cause a vacuum leak if the diaphragm is broken/cracked.  You can simply put a short length of vacuum tube on the hose nipple, and suck on the other end with the cap off.  You should see the breaker plate move clockwise.  Hold it there for a few seconds to make sure it holds pressure, and you should be fine if that checks out. 

 

[steve260z]

i have an excel chart of different distributors if you want.

PM me