I think the ported vacuum signal is what you want to use going to the distributor. Let's agree to disagree.

 

No! I refuse to disagree!

Actually, I'm a "ported vacuum" guy from waaaaay back. But, on some carb's, like this one and David Branscomb's, the ported vacuum only goes to about a max of 8" of vacuum, which doesn't bring the advance on as it should. We tried all sorts of things on David's truck and finally gave up and used manifold vacuum.

But, normally I'll argue 'til the cows come home that ported vacuum is the only way to go. I like to tell folks about the endless loop of "dropping the auto tranny in gear lowers the RPM, which reduces vacuum, which lowers RPM, which reduces vacuum, which........."

Having said all that, according to our mutual friend you are the king of Ford inline 6's, so you'd know about the 8" of vacuum - right? Am I wrong on that? Is there a way to fix it? (Let's not get into plugging and re-drilling the port above the throttle plate as I doubt many of these guys would be up for that - although I would. )

 

Hmmm... mutual friend and admirer of both!

The vacuum port on the carburetor on my truck does as Gary described. I have been told that it is venturi-based vacuum. There is only one port on this Carter YF carburetor from a 1970 F350.

 

David - Let's rethink/relive the work we did and see if you might be a candidate for ported vacuum. And, if so, might Lightning23 also be?

First, somewhere in your Gas Mileage Recipe thread I found that the ported vacuum reached 11", although I can't put my finger on where I found that.

But, I do find in Post 7 of that thread we said that initially the advance started at 10" of vacuum and was fully in at at 16". Then we turned it 2 turns and it started at 8" and was fully in at 14". So, it appears that each turn drops the range 1" of vacuum. Right?

Then in Post 52 you stated that you've turned it a total of 6 1/2 turns, where it stopped adjusting - and you still don't have any pinging. So, if the adjustment is linear your vacuum advance should be starting at 3 1/2" and be fully advanced by 10 1/2". And, if that is true and if your carb really gives 11" of vacuum then you might be able to use ported vacuum.

However, you'd need to do two things:

1. Confirm that the advance is fully "in" by 10 1/2". I'm not sure the best way to do that, but if it was me I'd stick the advance hose in my mouth, with a vacuum gauge tee'd in and a timing gauge in-hand, and start pulling a vacuum and noting when the vacuum is all in.
2. Compare the two vacuum sources. This will take two vacuum gauges and a helper to record the differences.

Now, I'm not sure that you really need to go to ported vacuum since you have a manual tranny. And especially since I'm now thinking about another mod to your truck - additional vacuum advance. If we move the stop in the vacuum advance we should be able to get you more total vacuum advance, and that might let you find the limit where it starts pinging. And, all the advance between where you are and where you could be is money left on the table.

 

I do not know specifically how much your calibration needs. One has to balance what the engine wants at a certain speed/load vs what the upper detonation limit is at that speed/load vs what the hardware is delivering. As was suggested put a vacuum pump on the diaphragm and measure the advance at various vacuums and also find the total vacuum advance. You may be over sparking the engine, delivering negative work.

The thing I don't like about using manifold vacuum is at idle your vac advance is "all in". As soon as you step on the gas pedal, load raises abruptly, vacuum signal drops dramatically - maybe to zero - and the engine falls into a hole, accelleration wise.

 

You are preaching to the choir on the use of manifold vacuum. I fully agree that it is better for part-throttle acceleration to use ported. But, it appears that the ported vacuum may not be enough to get the amount of advance his engine can use.

And, speaking of "use", he's crept up on the amount of advance he has. This was done by running with a given amount of advance for several tanks of gas and documenting the MPG. Then he dialed in another turn or two and tested that. In each case the MPG got better - until he ran out of adjustment in the vacuum unit.

So, we don't know if he's at the optimum point on the advance. That's why I'm thinking we should grind off the shoulder of the advance arm to allow it to move further. Or, change to another can which goes further in stock condition.

The problem is that if we go too far then we'll either get into pinging or reduce the MPG due to "negative work", as you say. So at that point I think we have to replace the vacuum unit as turning the screw just changes where the range starts/ends and not total advance. And if we have too much advance we may not be able to move the range high enough to limit total advance.

Anyway, what are your thoughts?

 

Gary and The Frenchtown Flyer, I want to thank both of you for taking your time to consider what would be beneficial to me and my little red daily driver.


David

 

David - I would have taken this discussion to your thread had it not been for Lightning23's similar quandary. But, since this is all hijacking the DS-II thread, maybe we should? In any event, it would be nice to finally get our arms around what combination of carb jetting and ignition timing works well on these engines. And the part that seems to be still on the table is max timing with the carb that otherwise gives excellent results.

 

Will a six cylinder blue-grommet module work on an eight cylinder engine?

 

They are all the same.

 

Wanted to say thanks a million for this post, I read it, studied it and studied it some more finally got the nerve up up to do the conversion and am extremely happy with the results. I followed your procedure exactly. I didn't get to see your photos cause they dont show up for me and I have a couple questions About the actual removal of the computer and wiring under the hood. Not really sure how this forum stuff works for it's the first time I have ever been in one.

 

Yeah, the photos were on a hosting service known as ImageShack which was free once upon a time, bit no more (I had an account with them, too).

But thanks for replying, most folks aren't so appreciative.

 

Hi mceut,
Yeah, images on older threads can definitely be a gamble.
If you need any specific help, feel free to start a new thread with your questions. Plenty have done the DuraSpark II swap (myself included) and can chime in.
Pictures of what you're working on always help, and supermotors.net is a good, free image hosting site for automotive stuff. Once uploaded, you can copy the IMG tag and post it here, and your picture'll show up.

Welcome to the forums!