289 High Performance Distributor

[BobbyB]

Why did the 289 HP not have vacuum advance?

Did any other factory v8s not have vac advance during this era?

[tenxal]

Did any other factory v8s not have vac advance during this era?

Yes.

[Walter R. Malik]

Why did the 289 HP not have vacuum advance?

Did any other factory v8s not have vac advance during this era?

Lots of high performance engines of that era did not have a vacuum advance mechanism.

[BirdMan]

Because it had 2 sets of points mounted a few degrees different on the open position to increase the dwell time which increased the spark capacity of the coil to give it more time to build the spark. This is with the same coil as std single point vacuum advance distributor used before the capacitive discharge, msd modules, coils like the big yellow Accel one which had a kick as spark.

When you installed new points you tore off a flap of cardboard and inserted between one set of points to set one of them and inserted in the other set to adjust the first set, then removed the cardboard and dwell should have been between 35*/37* instead of 30* as with stock single points distributors.

[frnkeore]

Why did the 289 HP not have vacuum advance?

This is just a guess but, I think it was because the HP engines, had lower, uneven vacuum and the plates were solidly mounted w/o the the VA, giving a more reliable, steady timing at higher rpm.

[piston guy]

+1 Ford HP engines 352-390-406-427-'67 Shelby 428 and 289 hipos all had centrifugal only distributors.

[PackardV8]

Because it had 2 sets of points mounted a few degrees different on the open position to increase the dwell time which increased the spark capacity of the coil to give it more time to build the spark. This is with the same coil as std single point vacuum advance distributor used before the capacitive discharge, msd modules, coils like the big yellow Accel one which had a kick as spark.

When you installed new points you tore off a flap of cardboard and inserted between one set of points to set one of them and inserted in the other set to adjust the first set, then removed the cardboard and dwell should have been between 35*/37* instead of 30* as with stock single points distributors.

Yes, agree as to the general details above, but disagree the dual points have anything to do with the elimination of vacuum advance. There were as many dual point distributors equipped with vacuum advance as there were without. GM, Mopar and Studebaker all equipped some performance engines with dual point vacuum advance.

[GerryP]

The more compression, the less vacuum advance contributes to improving fuel economy and overall light-throttle efficiency. The purpose of the vacuum advance is to raise cylinder pressure in those low-throttle situations. Beyond the Fords referenced, Chevy also had a centrifugal only on the 283 HP in the Corvette. I'm sure there were others. And it has nothing to do with distributor dwell.

[hoodeng]

GerryP is on the money, vacuum advance was for part throttle burn efficiency. In high vacuum situations [part throttle cruise] ignition is instigated earlier to propagate combustion earlier, hence fuel efficiency.

Performance engines did not have this requirement as they were either on the march or idling in the pits waiting their turn.[or hotrod performance street]

You could disconnect the vacuum advance on an engine and not notice any performance alteration, that was not it's purpose.

Cheers.

[Circlotron]

We know that if you give it (non-ported) vac advance at idle it will bring the idle speed up. Could this cause unstable idle speed under certain conditions, so that is why it was left off back in the day?

[Geoff2]

GM used vac adv connected to manifold vacuum. This not only improved part throttle economy/cooling/throttle response, it also improved idle quality. As noted above, when connected to a man vac source, timing at idle increases, & idle rpm increases. The idle rpm increase occurs because the engine is making more HP from the extra timing.
I suspect the 289 HP engine had low idle vacuum & adding VA might caused timing to fluctuate or be erratic at idle.

[piston guy]

Because it had 2 sets of points mounted a few degrees different on the open position to increase the dwell time which increased the spark capacity of the coil to give it more time to build the spark. This is with the same coil as std single point vacuum advance distributor used before the capacitive discharge, msd modules, coils like the big yellow Accel one which had a kick as spark.

When you installed new points you tore off a flap of cardboard and inserted between one set of points to set one of them and inserted in the other set to adjust the first set, then removed the cardboard and dwell should have been between 35*/37* instead of 30* as with stock single points distributors.

Yes, agree as to the general details above, but disagree the dual points have anything to do with the elimination of vacuum advance. There were as many dual point distributors equipped with vacuum advance as there were without. GM, Mopar and Studebaker all equipped some performance engines with dual point vacuum advance.

Jack ,
I fully agree that others had vacuum advance with dual points . The OP question was why the 289 Ford Hi Po didn't. FORD engineers didn't want it , feeling that pure mechanical advance was what they wanted. They did have a vacuum advance for the engine initially then went to centrifugal only.

[frnkeore]

Let me add to what I stated above.

1st, I'm 75 years old, i was 22 when I bought my first 271HP, 289, a factory '64 Fairlane 500, Sport Coupe, or as I called it, a Mini Thunder Bolt. I also had a factory Mustang 2+2 with the same combo, 2 years later and a 3rd engine, with 2 AFB's and headers. That just for back ground.

In those years no one in my age group or, under 35, cared anything about fuel mileage or how well a engine idled, gas was about $.28 per gallon. You could fill the tank for $4.

At that time, Ford distributors, were as good as they came, from the factory and trouble free. The only better options were W&H Dual coil (I have one) and magneto's. No race dist, had vacuum advance, as they were, of course, not needed. With the points plate mounted to the dist housing, nothing but the points can move, no worry about what vibration might do to the moving plate or springs that control the plate wearing out. You only needed right points with springs rated for the rpm.

Ford was very race oriented in those days, sold all the HP cars they marketed and had no reason to consider mileage until the gov, started requiring things, after the oil embargo's.

[piston guy]

I am 7 behind you and had to wait for my license to drive the '65 HIPO GT coupe my father bought in '65. I kept beating on it until I bought my first '66 GT350 in '72. You are correct about the quality of the ford distributors. I ran the transistorized points ( Ford called them "low inertia"in later years). That would allow 8,000 rpm use.

[HDBD]

The more compression, the less vacuum advance contributes to improving fuel economy and overall light-throttle efficiency. The purpose of the vacuum advance is to raise cylinder pressure in those low-throttle situations. Beyond the Fords referenced, Chevy also had a centrifugal only on the 283 HP in the Corvette. I'm sure there were others. And it has nothing to do with distributor dwell.

Chevy ZL-1 and maybe l-88 had a TI distributor that had a vacuum advance can with no nipple, a nub there, just locked the plate and used full mechanical advance.