Dist. Advance Re-curve

[Wbulk]

Ken, exactly. You stated it well!

Wayne

[olddog]

Well I do not wish to argue the point in a thread that was so useful and well done. I'm sure Wayne has more hands on experience than me. I'm more of a theoretical guy.

[Rick Parker]

Lighter cars CAN accept a faster rate of advance (lighter spings), but ultimately the same maximum advance.

To quote Wayne:

I wonder why we spend so much time trying to make these primitive carbs act like something they can never be. It must be the challenge, you think........

It's just Mental masturbation

[r67cat]

Wayne, great write up and pictures. This is a task that anyone with a little ability, a timing light and some patients can tackle. I also agree with you that most of our Cobras would benefit from a vacuum advance. I scratch my head at the almost universal lack of vacuum on a car that spends 98% of its time at partial throttle. My 428 is set at 34 degrees of total advance, idles nicely at 750 rpm. and will provide neck snapping acceleration. Vacuum quiets the exhaust note at highway cruising and greatly improves drivability. Thanks again. Rick

[sexzsn8k]

Wayne, just a quick question. Why would you want to rotate the distributor 180 after repalcing the interior parts ? Wouldn't that put the vacumm advance to the rear ? Am I reading this wrong, and your just rotating the shaft only. Please expain.

Thanks

[Wbulk]

What we did was rotate the advance limiting slot inside the distributor from 18L to the 13L position which is 180 degrees off from where is was for correct timing. Since the dist. rotor slot (notch) in the top of the shaft is all part of that piece, you have to pull the distributor and rotate the gear that meshes with the cam 180 degress to get it back where it belongs. Look at the pictures that shows the advance slots. When you pull that up and rotate it you are changing the position of the rotor to.

If on the other hand you choose to remove the dist. and change the advance stops out of the car, when you put it back in with the rotor in the correct position, you would have actually changed the gears messing with the cam 180 degrees, but you may not have realized it.

If on the other hand, for advance slots that did not have to be rotated, but just springs adding, you would "not" do this.

Tell me if this is not clear enough and I will take a picture of my old dist. shaft I gave Jeremy with advance mechanism in the two positions so you can see clearly. Perhaps putting the rotor on will make it clearer.

The purpose of doing this was to help people that that were not familiar with the process. So ask any and all questions that will help so you understand.

Wayne

[Wbulk]

I just what to add that these concepts apply to most other distributors. Changing the degrees of advance in different brands varies on how that is accomplished. Some are easy to change, others are not so. Before you buy a distributor get the tech information on that distributor and find out what advance is built into the distributor and is it easily adjustable. Plus, does it come with various advance springs to change the rate of the advance. It is very important that you know what is built into the dist. so you know where the timing should be.

Since these cars are very hard to hear if they are pinging, it is more important that you get the timing in the ballpark or you can cause a lot of damage to the engine. In my opinion if you buy a distributor and just set the initial timing at idle without knowing what's in the distributor you could be making a big mistake. There are a lot of pretty billet distributors out there, but what's in it. Is it what you need for your engine, and the most important factor other that what engine, is what duration of cam you have in that engine. There are several other factors I mentioned earlier. Because of these variables of each engine a distributor you buy needs to be adjustable. Think about it.

Wayne

[El Gato]

Thanks for your help and kind words, I hade fun learning. The car is running better than ever my only regret is that I didnt come over sooner. I am going to order a new adjustable vacuum advance. I unhooked the one on there now because I think it is advancing way to much and causing some issues at cruze. it runs great with just mechanical but I would love to get the vacuum advance tuned in. your write up was a great refresher of what you taught me in your garage. you definitely know what you are doing and I am very fortunate that you are willing to teach me. cant wait to go through the carb.

[Wbulk]

I just wanted to do an update on this vacuum advance issue because I believe it’s important to cover all the issues. Jeremy and I talked this week and he was having a hard time finding an adjustable vacuum advance for his FE. I had not bought one for a few years so I did some checking. Crane or Accel don’t seem to make them anymore, but I remember reading that some after market companies were making the adjustable ones as standard, so I did some checking with a few auto parts stores. I found some Wells brand vacuum advance units come standard as adjustable. In checking part numbers I found a Wells brand unit FV945 for $21.00 that fits most Fords from 1959 to 1971, but it was not available locally. I called Wells tech people and they pulled one off the shelf. Sure enough it is adjustable.

I also found some mid seventies ones that were adjustable from AutoZone. I took my 3/32 Allen wrench with me to check and none of the parts guys had a clue that some were adjustable, and there was no instructions in the boxes. I checked the adjustment on one of them by inserting the Allen wrench in the end of the vacuum fitting. I found it was adjusted for full advance. I feel sorry for the guy that buys one and can’t figure out why his engine is now pinging and with a simple turn of a wrench it could be fixed.

So why is it important to have an adjustable vacuum advance on a street engine in a Cobra? When you change the centrifugal advance to make it come in sooner like we did, and you have a standard vacuum advance that could add another 20 crank degrees or more, the combination of the two at cruise or slight load can advance the engine too much and create some pinging. Remember we put in lighter springs so the advance comes in sooner. The combination of the two at lower rpms can be too much. To fix this you turn the vacuum advance down with an adjustable unit. Since it is hard to hear pinging with loud exhaust it would seem that 10-15 crank degrees may be in the ballpark, but each engine is different.

You can check and see what you have by checking your timing at idle with the vacuum advance disconnected, and then connecting the vacuum advance to full manifold vacuum and then seeing what your timing is. The difference is your vacuum advance. You may have to lower your idle at full vacuum advance to keep centrifugal from coming in and confusing the issue. In Jeremy’s case the stock vacuum advance was just putting out way too much advance. Hope this helps.

Wayne

[Ibr8k4vetts]

Wayne,
Thanks for the heads up!

[r67cat]

Wayne, what I did to determine how much advance I was getting was to check the timing at idle ( no mechanical advance and vacuum disconected), note the rpm, attach my Mighty Vac to the canister apply vacuum, the idle will increase. Then reduce the rpm back to what I had originally and check the timing. Subtract the first reading from the second and you know exactly how much vacuum advance the canister can add at partial throttle. Rick

[zrayr]

Originally Posted by Wbulk

"....... SBF engines can run a little higher, and in some cases I have seen them run 41 degrees.........."
Wayne

not just "some cases" as the standard specs for 289 Hi-Po's is 40 degrees (12 initial plus 28 mechanical).

nice write up of your experience.


Z.

[zrayr]

Originally Posted by olddog

"I disagree with one thing stated, and I have heard others state the same thing as well. I disagree that the engine can run more timing because the car is lighter. ...........

I don't remember the exact wording of the statement referenced, but the correct statement would be that a light car can take advantage of a quicker rate of advance than a heavier car can, but the weight of the car has no bearing on the overall advance.

Z.

[Wbulk]

r67cat, exactly. You covered that better than I did. Thanks for making that clearer.

Zrayr, you may be right but just for trivia sake I looked it up in my 1969 Motors Manual that has all the dist. specs. The most I could find was in 68 with 6 initial plus 14 in the dist. for 34 total. Manuals do vary. 65-67 were actually less.

An interesting point I forgot to mention was I have an Accel adjustable vacuum advance for my 302. It has ten turns min to max advance built into that unit. The Wells after market one had the same number of turns. Maybe the performance companies are not making them anymore since you can get the adjustable ones over the counter now.

Wayne