Hei vs points.
Lets look at what we know.
(All timing and rpm values in this post will be in terms of crank degrees and rpms.)
Example he starts with is a smallblock magnetic pickup distributor. So its smog era.
Its intended for an early Barracuda. So no smog and possibly hot rodded engine.
On the distributor machine, the advance maxed out with 24* at 4000 rpm.
But he only took that one measurement.
We don't know even what rpm it starts advancing.
Finally he shows a slot plate stamped 15, indicating 30*.
After his modifications, which seem to include installing the 18 degree slot plate.
On the distributor machine, the advance maxed out with 12* at 1500 rpm.
Finally he tells us his goal is to install for 32* maximum, and 20* at idle.
So lets plot the before and after info on a graph using 32* as the reference.
Because this distributor started with its original springs we can sketch in a guestimate timing curve.
We can do that because idle speeds around 750 rpm were common in the early 70s and that typically LA engine combustion efficiency builds above 1400 rpm.
Likewise with just one sping stretched, and assuming the plate with shorter slots was installed, the new timing curve must actually look something like the red dashed line.
Would that work?
Yes.
except with vac advance its pretty much guarenteed to ping at part to mid throttle between 1800 and 3000 rpm :(
and
if you dont mind losing timing at high rpm.
and
if you're OK with timing at idle that changes with small changes in engine rpm.
Lets look at what we know.
(All timing and rpm values in this post will be in terms of crank degrees and rpms.)
Example he starts with is a smallblock magnetic pickup distributor. So its smog era.
Its intended for an early Barracuda. So no smog and possibly hot rodded engine.
On the distributor machine, the advance maxed out with 24* at 4000 rpm.
But he only took that one measurement.
We don't know even what rpm it starts advancing.
Finally he shows a slot plate stamped 15, indicating 30*.
After his modifications, which seem to include installing the 18 degree slot plate.
On the distributor machine, the advance maxed out with 12* at 1500 rpm.
Finally he tells us his goal is to install for 32* maximum, and 20* at idle.
So lets plot the before and after info on a graph using 32* as the reference.
Because this distributor started with its original springs we can sketch in a guestimate timing curve.
We can do that because idle speeds around 750 rpm were common in the early 70s and that typically LA engine combustion efficiency builds above 1400 rpm.
Likewise with just one sping stretched, and assuming the plate with shorter slots was installed, the new timing curve must actually look something like the red dashed line.
Would that work?
Yes.
except with vac advance its pretty much guarenteed to ping at part to mid throttle between 1800 and 3000 rpm :(
and
if you dont mind losing timing at high rpm.
and
if you're OK with timing at idle that changes with small changes in engine rpm.
