Some ignition system confusion on my newly acquired 1975 308gt4

You have a small typo in the 5-8 stuff, but the conclusion is correct (and there is a "notch" in the top rim of the dist. housing as a more convenient target for the rotor end -- but should be as you said: "forward distributor [rotor end] should be pointing at #5 [terminal inside the dist cap])

Solid conductor spark plug wires can crosstalk to each other, and to the outside world, much more (especially if used with non-resistor spark plugs). Your timing light may be so sensitive that it is flashing with every firing event (not just the one that has the timing light pick-up on it).

 

Forgot to ask: Do you still have resistive extenders in place, or do the solid copper core wires go directly to the spark plugs? And are you using resistor or non-resistor spark plugs?

 

Correct.

For the spark plug wire -- look for a spiral (helically) wound fine-wire construction. Don't have any specific sourcing recommendation

 

That's the rather "cold" stock non-resistor spark plug (BP7ES). Unless you are really hammering the engine for extended periods (think AutoBahn), I'd suggest you move to BPR6EIX which is one heat range hotter for rational street driving and will have much better resistance to fouling.

Having the extenders is good, but they come in two flavor: with resistance (maybe 2K Ohms IIRC) and zero resistance, so you might want to confirm which you have - if zero ohm with solid wires and non-resistor plugs, you should be broadcasting to Mars

The stock 308 carb setup is:
spiral wound spark plug wires (has resistance of ~700 Ohms/foot and some inductance from the spiral winding form)
extenders with resistance
non-resistor spark plugs

with the idea that the overall system has some total resistance + inductance (i.e., some impedance) to keep the EMI emissions down (and on the later cars, with transistorized ignitions, to not blow up the output transistors driving the coil primaries). As long as you keep that in mind, you should be A-OK (for example, using the spiral spark plug wires with zero ohm extenders and the resistor BPR6EIX would be very equivalent to stock).

PS You might pull one wire out of the distributor cap to check the construction. The spiral wound wire construction can also be called "solid" since it is a continuous metal wire, but that's very different from just a straight non-wound copper wire core.

 

I don't think so on the street cars, but don't know for sure. The issue you might come up against is that most "modern" spark plug wires are 8mm OD; whereas, the 308 dist caps are designed for 7mm OD wires.

Yes, that's not right for a carbed 308 (they might be TR zero ohm extenders). However, using the resistor BPR6EIX plugs will compensate.

Correct, 7 deg BTDC (for a R1 only system).

 

why run resistor plugs? the Champion N7Y is solid non resistor plug, OEM spec. I've yet to come across extenders that are of the resistor variant. The spec on the BP7ES plug has a 0.9mm gap and the carb'd GT4 should be 0.4mm, that alone will cause some issues.

Steve where have you found the resistor extenders or recommendation of using resistor plugs in the 308's. Really curious about that.

Just check'd the GT4 WSM, the ground on the micro-switch provides the RF suppression.

 

Quick easy check, adjust the gap down to 0.4mm or ~.015" and see if that doesn't improve the starting and acceleration.

 

You don't remember this thread?:

http://www.ferrarichat.com/forum/threads/plug-extenders-differences.450474/#post-143176781

I'll admit now I can't recall whether it was the DigiPlex or carbed models that used the resistive extender, and, with both floating around, it's a bit like wheels -- any 308 could have either now .

With regard to resistor or non-resistor, the anti-fouling benefits of the EIX NGK plugs is so significant for a carb model that it's a no brainer for me to use them (EIX are not available in non-resistor).

The 308GT4WSM does show the (crazy) 0.4mm value for the spark plug electrode gap, but if you check later 308 OM (like the 1978), they increased it to a more reasonable 0.6~0.7mm. Regardless of how the plug are supplied, the gap can be readjust to any value.

 

I'm not that old, I do...

Depending on the overall resistance of the wires to the plug and the coils output charge/current saturation, resistor plugs can either work fine or cause issues. Too much resistance will decrease current draw and drop the voltage, severely in some cases, which would require closing the gap or getting a bigger coil, easier to adjust down the resistance of the circuit. I don't know the coil the OP has on hand but the first yrs of the GT4 had dinky little coils and given the RF suppression circuits they used it makes sense that it'd have a small gap. Doesn't hurt to double check and close the gap to see if it helps.

While not a Ferrari, my DD mercedes uses non-resistor plugs and was explicitly design by Bosch that way, resistor plugs cause all kinds of trouble. Have to import the buggers from Europe or Japan now.

Oh and on these older systems of coils and leads... avoid the platinum, blah blah high mileage plugs, copper, nickle or silver only. These old engines were not designed to run on that type (platinum etc..) of plug, the spark induced flame kernal doesn't develop correctly with these old engines as the energy is too low without CDI or COP to run them.

 

Oh too large of a gap will cause the spark to find another ground, usually thru the wire or extension boot. For those that didn't know.

 

Wires that fit into the cap will be a problem, most all are ~8mm in O.D as I recall vs the OEM 7mm. Many have simply shaved down the wire to fit and forgo the outer cover.
As to gap, manual specs are from 0.4mm~0.7mm, for 1974 it is spec'd at 0.4mm. Honestly I'd re-gap the plugs you have down and see what that does, if it improves things then you have a base point to start from. There is some speculation on re-gapping modern plugs as the metalurgy has changed a bit and the concern is that once at temp the metal memory will re-set to the original gap. Champion has the resistor version available, RN7YC pre-gap'd to 0.635mm, if you go with resistor plugs I'd recommend those.

This is going to get a bit more technical, Champion plugs use a SAC-9 resistor, it's a mix of strontium carbonate, aluminium oxide and copper oxide powders. It's not possible to measure the resistance of them with a std low voltage meter, it actually requires the use of a test set-up with high voltage discharge and induction meters. The resistor is designed for RF suppression. There is also 'wire wound' inductor "resistors", that would not be correct for coil and lead ignition systems and is labled with a 'Q', it's for CDI ignition.
NGK uses a fixed 5k ohm monolithic ceramic resistor, it's not recommended for older low output coils. Hence why I personally don't favor them in a stock ignition system like the GT4.

 

Magnacore still has 7mm plug wire

 

Yes!
https://www.magnecor.com/

 

As does Kingsborne

 

Carbon contact, like found in electrical motors but a bit more dense. If that was missing the entire time you'd have a dead bank. Very possible, is there arc tracings on the terminals on that one? just looked again, new cap or old one? there is ZERO arc tracing which means that bank was not running if that's the old cap.

 

do you have the cork gasket?

 

Time to check cam timing-the belts have been known to slip.

 

When the idle appears to rise on its own, on my previously owned 78 308 GTS, it was the floor mats sliding forward and pressing against the gas pedal. I learned from other 308 owners, it was a very common problem. A little Velcro fixed it.