boost retard distributer

[ssnapz]

just an idea running through my head. is it possible to convert the vacuum advance into a boost retard pod. if vacuum can advance the dizzy why cant boost retard it. any thoughts?

[datzenmike]

Well the vacuum advance only works during part throttle. At WOT there is virtually zero manifold vacuum and thus zero advance and the motor is running only on the initial 12 degrees static timing PLUS any mechanical (centrifugal) advance depending on the RPMs you're at. There is no advantage to having the vacuum advance removed or not working if you drive at part throttle. This is because at part throttle the cylinder is not completely filled with air at atmospheric pressure because the throttle plate is partly closed. Only at WOT can the cylinder fill completely. A partially filled cylinder burns slower so in order for the burning gas and air to reach maximum pressure just after TDC (and to exert downward force on the piston) it needs to be lit sooner than the 12 degrees (plus any centrifugal advance). Without vacuum advance part throttle would be lit much too late and the piston will be too far down the cylinder and accelerating away from the expanding explosion.

 

So you need vacuum advance to get the most out of your gasoline when driving at part throttle. Racing is the exception.

 

Because of the design the vacuum advance starts at none, and moves only in the advance direction. I don't see how you are going to get it to go into a negative (retard) direction.

 

If you had a dual points dizzy you could set one side to be several degrees retard and cut them in when boosting. The trouble with any of this is that it doesn't retard in any relation to boost. In other words it retards the same amount on light or heavy boost.

[ggzilla]

Yes. That's how it works. Could it be modified to work as a boost retard? Maybe but Datsun already made a dual advance/retard unit, so no need to convert it.

[ssnapz]

where do i find this dual unit

[datzenmike]

Lots of old 510 L16s had the dual points on it. The retard set were 4 degrees of crank angle think.

[Kisor]

If you are going forced induction its prob best to upgrade ignition anyway. Just get a MSD 6AL-BTM. That way you can adjust from 1-3* per lb of boost.

 

https://www.msdignition.com/Products/Ignitions/Street/Strip/Analog/6462_-_MSD_6-BTM_Boost_Timing_Master.aspx

 

Search cl for a used one. Or eBay...

[DanielC]

Almost every Datsun with a L-16 (510, 521) had this dual point distributor.

The second set of points was retarded 5 distributor degrees, and was activated by a series of switches, on the clutch, throttle pedal, carburetor, two on the transmission, that if the truck was in third, part throttle, but not closed throttle, with the clutch fully up, the second set of retarded points was used.  

All these switches activated a relay, close to the ignition coil.  The normally open relay contacts kept the retarded points out of the ignition circuit.  When the relay was activated by all the switches, the second set of points was put in parallel with the advanced points.  When the advanced point opened, the retarded points were still closed, so nothing happened until the retarded points opened, 10 crankshaft degrees later.  The retarded set of points used a very small condenser, because the condenser for the advanced points was still in the circuit.

[ssnapz]

most likely what ill do, was just thinking if i could modify stock stuff with little money. i like building more then buying

[ssnapz]

i love the knowlage on this site

[ggzilla]

Dual point distributor could help a little. Instead of 34 degrees advance, under boost -- if if you used the retard set of points -- you'd have 29 degrees.

 

If you used the dual vacuum can it would be similar. You could use the full throttle vacuum signal that many Hitachis have to retard it about 5 degrees. The good news is this works with points OR with electronic ignition.

 

This is not enough retard for a serious boosted engine, but you could also rotate the distributor for more overall reduction.

[ssnapz]

thats more what im thinking of , i want a vacuum pod that works in reverse.  mechanical timing is enough for dd, and 8psi i can get away with no retard but if i could run more over all timing with a boost retard pod then low end drivability would be better. basicly im gonna make it work was just seeing if anyone haddone this or heard of it before. yeah im a stubburn fucker.

[ggzilla]

So do it. Use a stock Datsun dual-pod vacuum advance/retard can. I'll sell you one for $50 brand new, works Z-series 8-plug distributors.