single quad distributor vs. dual quad distributor

[cobravii]

Hi Giys, i posted this on V8 Buick and it is easier to post the link rather than re typing everything...

 

 

http://www.v8buick.com/showthread.php?297606-Single-4-barrel-distributor-vs-dual-quad-distributor

Edited June 1, 2015 by cobravii (see edit history)

[NTX5467]

In many cases, in general, the dual quad distributors (of most any manufacturer) had different advance curves in them than the more normal-use single quad distributors, or even 2bbl distributors in the same engine family.

 

Ignition "advance" needs of an engine are relative to the basic combustion chamber design of the engine (which is why the small block Chevy and B/RB Chrysler V-8s have an optimum desired advance of 38-40 degrees BTDC total at their power peaks, but the W-engine 348/409 Chevy V-8 only needs about 30 degrees BTDC total advance).  How effectively the cylinders are filled can also relate to the camshaft timing events.

 

In many engines, the 2bbl and base 4bbl motors will have similar camshafts.  The 2bbl V-8, of its nature, will not fill the cylinders as effectively as an up-option 4bbl version of the same engine (with or without the addition of dual exhausts), so those distributors will generally have more total advance than the similar 4bbl motors.  In the case of 2x4bbl motors, they usually have camshafts with longer timing events and can more effectively fill the cylinders due to their greater total potential airflow, hence the need for less total timing advance (in theory).  As these 2x4bbl motors will also usually have higher compression ratios than the 4bbl motor, it might also be necessary to decrease the total WOT timing to keep the motor from detonating on available fuels (unlike how modern vehicles can manage these things with sophisticated computer maps and still have the very high mechanical compression ratios).

 

In some cases, if the total advance is limited, then for the engine to operate correctly in more normal use, the initial timing spec can be increased (less total advance, but what's there will happen quicker), but still not enough to cause the motor to clatter on specified fuels at part throttle (might need a little less vacuum advance at part throttle, but not at cruise, which means a different spring in the  vacuum advance can and/or possible less total vacuum advance).

 

I believe you might have realized that the basic distributor housing is just that, a housing.  The stamped part/ID number relates to the timing mechanisms of the internal distributor weights/springs and also the vacuum advance con attached to it.

 

Somewhere, you might be able to find the distributor specs for each of your distributors in a MOTOR Manual or a factory Buick service manual for your model year of vehicle.  These would indicate the base timing at hot, base idle, when the mechanical advance will start (rpm) and what the total advance should be (higher rpm), plus similar items for the vacuum advance (minimum vacuum level to start the advance and the max vacuum advance at cruise vacuum levels).  For our purposes, add the initial timing setting and the max advance to get the total advance and the specified higher rpm level.

 

Depending upon the timing curve in the 2x4bbl distributor, you might need to experiment with the initial base timing setting you use to get the best driveability/performance from your engine.

 

In my explanation, I'm speaking in generalities of what I've observed over the years.  I probably need to do some research into Buick-specific issues of this nature, though.

 

Please keep us posted on your progress.

 

NTX5467

Edited June 1, 2015 by NTX5467 (see edit history)

[JohnD1956]

Thanks for the post.  ( And thanks for the engineering theory Willis!) That was an interesting visual comparison.  May I ask for a picture of the broken band with the ID?  Having never looked for one of these I just wonder what that looks like. 

[RivNut]

The easiest way to get the 12* advance that's built into the distributor used on the Super Wildcat engines is to use a distributor from a '63 or earlier 401.  They were timed at 12* advance just like the Super Wildcats.  

[cobravii]

Hey guys,

 

I will be starting  days off on Sunday and I am going to take more pics then. I will take pics of the ID bands, the slots in the advance and the numbers stamped on the same plate.

 

Thank you for your comments.

Edited June 4, 2015 by cobravii (see edit history)

[cobravii]

Ok, guys, all the pics are taken and this link: 

 

http://www.v8buick.com/showthread.php?297606-Single-4-barrel-distributor-vs-dual-quad-distributor

Edited June 12, 2015 by cobravii (see edit history)

[cobravii]

Thanks for the post.  ( And thanks for the engineering theory Willis!) That was an interesting visual comparison.  May I ask for a picture of the broken band with the ID?  Having never looked for one of these I just wonder what that looks like. 

Here are the pics: 

111058:

[cobravii]

Thanks for the post.  ( And thanks for the engineering theory Willis!) That was an interesting visual comparison.  May I ask for a picture of the broken band with the ID?  Having never looked for one of these I just wonder what that looks like. 

 Here are the pics of the single quad distributor,

111055;

 

Something to note is that when I took out the 111055 distributor I marked where the rotor was and where the vacuum advance was so I could place the 111058 distributor in the same place. When I tried to start the engine it turned over hard and puffed back through the carbs. i had to advance it significantly to get it to start and then set the timing after it was running.

Edited June 12, 2015 by cobravii (see edit history)

[NTX5467]

If you had to move the distributor about "1 notch", then I suspect the rotor was not completely clocked (when installed) as the prior one was when it was removed. Rotor position is independent of cap/housing positioning. Just my gut suspicion. Both are important.

NTX5467

Edited June 13, 2015 by NTX5467 (see edit history)

[cobravii]

Rotor lined up "exactly" from one distributor to the other. That isn't a reason for me having to advance the distributor.

[old-tank]

Points or electronic?  If points they should end up in the same position after the dwell is set the same and then the timing set the same.  My 55 has a different distributor, but after changing to Pertonix on one and setting the timing, the position was different.  Check that the lobes clock the same with the rotor.  Also check how the distributor gear is clocked, especially if it was ever removed from either distributor.

[cobravii]

Both distributors ave Pertronix electronic ignition. But that is a good point I never thought about.