Engine: Ignition timing

[erik64]

Hi guys:

I just installed my new Edelbrock 1403. You guys are right; This is a nice carburetor right out of the box. Installation was a breeze, thanks to reading your posts on this subject. I do have a question on the vacuum advance on the Prestolite IGP4108. Which port do I use on the 1403? I think they are listed as ported and unported. One has full vacuum at idle. The other vacuum increases with throttle setting.

This brings me to another subject. Mike VanVeghten states that he never uses a vacuum advance and times by ear. Because of todays fuels, the 4 deg. BTDC is all wrong and actual timing will be much higher. Advance timing until pinging occurs on a hard pull, then back off. Did I read this right? It actually makes a lot of sense to me with todays fuels.

The reason for asking this; My vacuum advance is bad. If I am going to use this approach, then I won't replace my vacuum advance. And keep both ports plugged on the 1403.

thanks

[Mike Van Veghten]

Erik -

While I didn't write that way of obtaining a usable amount of ign. timing, yes, it is a good way to do it.
And by "back off"....try 2 degrees first, see how that works. It should do the trick, if pinging still occurs, back it off another 2.

Un-ported vacuum -
This will give you vacuum advance while crusing, and drop off when the throttle is applied. The harder the opening, the less timing.
Good for gas milage, not so good for power or driveability.

Ported vacuum -
Exactly the opposite from above. This will give no vacuum at steady state rpm, but will give timing when the throttle is applied.
Good for power and driveability, not as good for gas milage.

No vacuum -
No vacuum advance.
This leaves it all up to the initial timing amount dialed in at the crank with the timing light.

All three methods take a little different initial (at the crank) timing for optimum overall timing/tuning.

This is an interesting experiment if you like to play and learn.
The Stude (as all early cars did) ran un-ported vacuum if that makes any difference. It wasn't till the mid-late 70's or so that the ported vacuum came about.

Mike

[JoeHall]

Un-ported, a.k.a. "manifold vacuum" is probably preferable. But if you experience a problem in getting the idle speed to come down on the 1403, try ported vacuum. The constant vacuum at idle, with un-ported vacuum, keeps the Vac Advanc in full advance mode, which will kick up the idle RPM considerably.
The difference in MPG between ported and un-ported is negligible, as is engine temp and power.

ABSOLUTELY replace the vac advance, if it is not working. In order to compensate for its absence, you'd need to set the timing waay too far in advance, and even with premium gas, it still would likely ping. Forget all the race car info, and keep the vac advance

[Mike Van Veghten]

Joe wrote -
""The difference in MPG between ported and un-ported is negligible, as is engine temp and power.""

Don't agree...!
See my note -
""All three methods take a little different initial (at the crank) timing for optimum overall timing/tuning.""

Maybe my dyno's more sensitive to changes...!

Mike

[avantibngrant]

An adidition

Erik -

While I didn't write that way of obtaining a usable amount of ign. timing, yes, it is a good way to do it.
And by "back off"....try 2 degrees first, see how that works. It should do the trick, if pinging still occurs, back it off another 2.

Un-ported vacuum -
This will give you vacuum advance while crusing, and drop off when the throttle is applied. The harder the opening, the less timing.
Good for gas milage, not so good for power or driveability.

Ported vacuum -
Exactly the opposite from above. This will give no vacuum at steady state rpm, but will give timing when the throttle is applied.
Good for power and driveability, not as good for gas milage.

No vacuum -
No vacuum advance.
This leaves it all up to the initial timing amount dialed in at the crank with the timing light.

All three methods take a little different initial (at the crank) timing for optimum overall timing/tuning.

This is an interesting experiment if you like to play and learn.
The Stude (as all early cars did) ran un-ported vacuum if that makes any difference. It wasn't till the mid-late 70's or so that the ported vacuum came about.

Mike

i believe Studebakers used ported vacuum (taken from a port above the throttle plate at idle) for the vacuum advance. I know my Avanti does, with little vacuum at idle speed and increasing as the thottle is opened. If it was unported, they would have just plumbed it into the maifoild port the power brake uses. Instead, it is in a port on the front of the carburetor which is above the throttle plate at idle. That is where I would put it.
Also, I believe the only difference is when the throttle is near closed. With a partial open throtttle, the haracteristics will be the same with both ported and unported as they both are pulling vacuum from below the throttle valve - essentially maifold vacuum same as the power brake sees.
Regards
Neil

[Dick Steinkamp]

Lots of confusion and opinions on ported vs non ported vacuum advance.

Here's my two cents.

The only difference is that ported takes its vacuum source upstream from the throttle plate(s). This means, the distributor does not see a vacuum signal at idle. Non ported takes the vacuum source downstream from the throttle plate(s). It will see vacuum at idle. That's the only difference. Both will see vacuum at all other high vacuum conditions...like steady state cruising. Both are there primarily to add advance (about 15 degrees) during steady state cruising to improve fuel mileage.

Ported vacuum didn't originate until the 70's as a measure to improve emissions at idle.

You'll see little if any difference in drivability between the two systems...as long as you set your initial advance appropriate to each and as long as all other variables are equal.

[Bud]

I use ported vacuum on most Studebaker distributors as that is the way Studebaker engineers designed the original ignition system. Ported vacuum does not work at idle and full throttle conditions, but does work at part throttle increasing the ignition timing around 15 degrees which increases fuel mileage and decreases combustion temperature a bit. I don't believe I am smarter than the guys that originally designed Studebaker engines so I use ported vacuum on my cars and on the ones I service and have had good results for more years than I care to remember. Bud

[avantibngrant]

I use ported vacuum on most Studebaker distributors as that is the way Studebaker engineers designed the original ignition system. Ported vacuum does not work at idle and full throttle conditions, but does work at part throttle increasing the ignition timing around 15 degrees which increases fuel mileage and decreases combustion temperature a bit. I don't believe I am smarter than the guys that originally designed Studebaker engines so I use ported vacuum on my cars and on the ones I service and have had good results for more years than I care to remember. Bud

Right on in my opinion. I believe even my 47 takes the vacuum for the advance from over the throttle valve at idle. The non ported vacuum runs the wipers on it. At full throttle they should be the same - approaching zero when the wipers stop!
Neil
.0

[Dan Timberlake]

"Ported vacuum didn't originate until the 70's as a measure to improve emissions at idle. "

That sentiment is repeated pretty often these days, probably originating in GM production engineer John Hinckley's Corvette and Camaro tech articles, like this one.

http://www.corvette-restoration.com/resources/technical_papers/Timing101.pdf

(Note he is NOT this John Hinckley - http://en.wikipedia.org/wiki/John_Hinckley,_Jr.)

I think a good technical theory needs to support pretty much all reasonable examples without losing its balance and toppling over. Or, it should at least mention known exceptions, outliers and anomalies exist.

I'm not saying that ported vacuum did not become popular, or even widespread during the emission years. I have not dug thru any where near enough detailed tech info to know what every manufacturer did, every year after 1973.
I'm also not saying don't experiment with both ported and unported sources for vacuum advance.

BUT, the claim that ported vacuum is an emissions only technology seems to ignore some moderately authoritative info published well before the absolutely toothless Clean Air act of 1963.
1 - Attached is some info from an Audel's automotive theory book from the 1940s. "The most popular {type of vacuum advance} ... is the type in which the vacuum connection is made at the carburetor side of the butterfly valve, as shown in fig. 6."
2 - A page from the 292 V8 section of the 1958 Edsel factory manual is included. In addition to the description of using ported vacuum, improvements in part throttle performance, acceleration and fuel economy are claimed for vacuum advance.
3 - A page from an early 1950s Chevy shop manual describes the vacuum advance connection being uncovered only when the throttle is opened a little bit - NOTE - I would not stretch that info to assume all Chevrolets used ported vacuum.

[JoeHall]

Every 64 and earlier Stude I am familiar with came with un-ported (manifold) vacuum to the carb, and when disconnected the RPMs rise for a couple of seconds before the motor begins to stumble; but if you put your finger over the vacuum port/now vacuum leak, the stumble stops but the motor slows down, due to retarded ignition. There was not even a ported vacuum port to plug into. That is why the Shop Manual says to disconnect the vac advance before timing the ignition. (Think about it.)

Many modern aftermarket carbs (1970s and later), came with both type of ports to plug into, Most of those carbs run equally well from either port.

Back to the PO's original question about running a street car without a vacuum advance. While it would run, it would not run worth a darn. Anyone who cannot figure out why, probably would not be able to grasp an explanation as to why either.

[Bud]

All of the Studebakers I've encountered over the years use ported vacuum for the vacuum advance which goes back into the 40's. Some GM cars through part of the 60's and into the 70's use full vacuum on the vacuum advance. Ford and most Chrysler products also use ported vacuum and have for as long as I've been working on cars which dates back to 1959. I believe some people are confused with the difference between ported and full vacuum ports available on some carburetors. Without testing a distributor on a distributor machine, there is only information contained in the various shop manuals regarding the amount of advance and at what rpm and vacuum the distributor should have to arrive at the correct base timing for a particular engine. I will usually add a few degrees to the base timing on most Studebaker engines, But I will not just twist the distributor around because someone on the internet says it's good idea. My advice is to use common sense when dea

[Bud]

Something happened when I was finishing my last sentence which was to use common sense when dealing with ignition timing. Also keep in mind that detonation cannot be heard at higher engine speeds when the damage to internal engine parts can be serious. Bud

[Dick Steinkamp]

I think a good technical theory needs to support pretty much all reasonable examples without losing its balance and toppling over. Or, it should at least mention known exceptions, outliers and anomalies exist.

I stand corrected. Thanks for the examples and links, Dan.

One unresolved issue here (at least in my mind) is what did Studebaker do on production cars?

I'm with Joe. I would never say they don't exist, but I have not worked on a stock Stude with ported vacuum...they all used un-ported (manifold) vacuum. It is one of the reasons you have to disconnect and plug the vacuum line from the dizzy to the carb when you time the engine. For vehicles with ported vacuum, this step isn't necessary since the vacuum advance is not seeing vacuum at idle.

Anybody have a definitive answer on this one? Which Studebaker vehicles used ported vacuum and which used un-ported?

[JoeHall]

This issue is easy to settle: I just went out into the garage and looked at an WCFB off of a 56J. With the choke open, linkage against the idle stop screw, and butterflies completely closed, the slit for the vac advance port is just BELOW the bottom edge of the passenger-side, primary butterfly.

To double check for a possible high idle setting, I backed the idle screw out to where it would not touch the linkage, and the butterflies were stuck in the bores. (Mechanical interference.) At that setting, the slit was even with the edge of the butterfly, not above or below. With half a turn of the idle screw to un-stick the butterflies, the slit moved to the bottom edge.

Just to be positive the vacuum did not have an additional source, I used an air hose and blew into the outside connector fitting. The air comes out of that slit, that slit alone, and no where else.

So I am 100 percent positive 56Js are non-ported, and am willing to bet anyone who checks any other Stude carb through 1964, will find the same thing.

Anyone who thinks differently, maybe should look at the bottom side of an old carb, and put an air hose to it, to refresh memory.

[Bud]

A better way to check is to use a vacuum gauge on the distributor vacuum port on a stock Studebaker carburetor such as a Stromberg WW, Carter WCFB, AFB or even the older Carter WE used on the sixes. If there is manifold vacuum on the port at idle with the idle speed adjusted correctly, then the distributor vacuum advance operates with non ported vacuum. If there is no vacuum at idle and there is when the throttle is opened part way then the vacuum advance works with ported vacuum. Bud