Matt Brannon - Midwest Bayless
Mad.Matt
All of this talk about vac advance / non vac advance, etc. has gotten me thinking a bit. What would be the best way to convert a 32 DMTR or 32 DATR to support a late-model Bosch electronic ignition advance mechanism?
On 74-78 US spec cars, as Tony K has told multiple times (and it's true!) the thing that looks like a vac advance module on the distributor is actually a vac retard mechanism. It gets its signal from either under the carb primary throttle plate, or the base of the intake manifold. It retards the spark at cold start, idle and then releases its effect as the throttle is tipped, going to zero effect when the engine is at max load.
On 79/80 carb cars, and on the later 80 1/2 - on FI cars, the vacuum signal is taken from just ahead of the throttle plate, meaning the effect is opposite. The strongest signal is achieved under maximum load and zero effect at idle or static operation. This is efficient for a number of reasons, namely ignition timing spikes at sharp throttle tip-in and full-on acceleration. If your set-up is running a bit rich, this will increase acceleration response.
So, back to the 32 series carbs. These things have no vac signal ports ahead of the butterfly. Seems fairly straightforward to drill a hole into the primary throttle bore at about the 4:30 position, relatively low in the bore right into the venturi area and swage a 4 or 5mm vacuum tap fitting.
Anyone have any success with such a solution?
-M
On 74-78 US spec cars, as Tony K has told multiple times (and it's true!) the thing that looks like a vac advance module on the distributor is actually a vac retard mechanism. It gets its signal from either under the carb primary throttle plate, or the base of the intake manifold. It retards the spark at cold start, idle and then releases its effect as the throttle is tipped, going to zero effect when the engine is at max load.
On 79/80 carb cars, and on the later 80 1/2 - on FI cars, the vacuum signal is taken from just ahead of the throttle plate, meaning the effect is opposite. The strongest signal is achieved under maximum load and zero effect at idle or static operation. This is efficient for a number of reasons, namely ignition timing spikes at sharp throttle tip-in and full-on acceleration. If your set-up is running a bit rich, this will increase acceleration response.
So, back to the 32 series carbs. These things have no vac signal ports ahead of the butterfly. Seems fairly straightforward to drill a hole into the primary throttle bore at about the 4:30 position, relatively low in the bore right into the venturi area and swage a 4 or 5mm vacuum tap fitting.
Anyone have any success with such a solution?
-M
