Marelli distributor recurve

308 GTB 1979 CR 9.6 to 1 Euro cams 229/219 duration, twin distributors NGK BP7ES

Good information on this site about rebuilds so I will skip the hard work. https://www.ferrarichat.com/forum/threads/1979-308-gt4.105874/page-10

The teaser for me was the statement from Selmerpilot on the recent youtube Holley EFI 308 engine



“34 degrees by 3000rpm and full timing of 38-39 degrees by 4000-45000rpm or so”

Having just done this I have to fully agree what a spectacular improvement in drivability this does make in both light throttle ( cruise, fuel economy and sound reduction ) as well as lower speed engine performance.

It is almost a hybrid vac advance where you cruise with the advance you need, just don’t floor it in gears at less than 3000rpm.

Baseline

Spun up my distributor on the Heath Robinson tester and confirmed the usual advance curves noted. Static advance not included – distributor only.
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Engine RPM vs engine advance

1200 6 deg ?
2000 12 deg
2400 16 deg
4000 28 deg

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Advance with the S3 pin removed
1200 10
2000 16
2400 20
4000 28
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Note the full distributor advance available at an engine speed well over my test unit capacity ( electric drill ) is 36 degrees. This with a static timing of 4 degrees this gives you a total advance of 40 crankshaft degrees!




With S3 removed I now have 4 degree faster distributor advance curve which may well be better, but the total advance capacity in the distributor limits my static advance options so I have locked out the S4 pin with alloy spark plug ends, trimmed to the spring length ( 28 degrees max distributor advance )
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Currently running 8 degree static ( 8+28=36 total) and can’t be happier. Will update as the weather improves or any changes noted. I can pull away from a standing start in second gear and I had a vote of approval from my wife, “ this is a lovely car, we should use it more often.”

800km later and I can’t fault it.



I mounted both XR3000 triggers into the same distributor so I only have one distributor curve to manipulate. I used the strobe “distributor timer” to check the trigger separation angle. The setup lights on the XR boxes were within 1 distributor degree when setting the triggers by hand!

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Loctite and epoxy the trigger legs and screws units in place. The top bearing retainer unit touches and holds my triggers as well.

Cheers Rob
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Note: last image above is the original full distributor advance of 18 degrees - 36 degrees crank.