Dwell Angle on a V12

What would be the dwell angle on the Marelli distributors on a V12 e.g. a 275?

Thanks for your help!

Matthias

 

50 degrees total, 25 degrees on each point set.

 

Daytona ?

 

50 degrees plus or minus 2 and not built up by two times 25 as suggested by Motob.
Bart340

 

Each distributor with their respective points (R1/main on the U.S. Daytona) ?

Brian (or any one else with extensive experience), do You agree ?

 

Hmm... I understood, for the 275, they require 48-50 deg. on each distributor...meaning, ~25 deg on each point set. However, the Daytona is different as it has 6 lobes instead of 3 found on the 275. This results in a smaller dwell angle

 

European Daytonas, like my old 14009, had two three lobe distributors, with two sets of points each, just like the earlier twin distributor street V12s. On the road, so cannot confirm the dwell.

Taz
Terry Phillips

 

specifically, what engine are you asking, exact iteraation///
s85a is used on LOTS of engine families...not all with same specs...

 

The dwell angle for 2 3-lobed sets of points can be calculated, and should be around the 50- degree figure, or even a few degrees more.

 

As I said, factory information is 50 degrees plus or minus 2 (depending on the points gap), so 52 degrees can easily obtained. This is of course for a 3-lobe double points distributor.
Bart340

 

Digging up this old thread...

Can someone please explain how we have arrived at the 50 degrees total, 25 degrees per point set for the three-lobe, dual-points distributors? Thank you in advance.

john

 

John: The Marelli units are not like the American dual point distributors. On the Ferrari unit, each set of points operates independently and fires three cylinders. The American units link both sets of points together to increase the TOTAL dwell to get more coil saturation. I have never trusted dwell tachometers or Sun machines totally, so I adjust one set of points to a gap I like (usually about .015-.016" for the Marelli's) and then get a dwell reading for that point set. Then I adjust the other set of points to the same dwell reading. This procedure allows for variances in measuring methods and machines. By the way, the Marelli specs for the S85A distributor are 50 degrees PER SET OF POINTS for closing angle. This is NOT dwell. They also spec 10 degrees for the opening angle. Let me give you another example where Marelli actually gives spec for dwell. On a US Daytona with a six lobe cam, the spec is 32 degrees closing angle and 28 degrees opening angle for the primary set of points, yet the dwell spec is 53.5 degrees. Secondary points use slightly different settings. American six lobe distributors use about a 40 degree dwell setting. It is all about the shape of the distributor cam!!

 

Thanks for the explanation, Dyke. A .014" gap does produce a dwell of about 25 degrees on the distributor machine. Then, conversely, a dwell of 25 degrees does not necessarily give you a gap of .014" on the opposite set of points. As you said, the shape of the cam plays a part. It doesn't seem like the three peaks on the cam are exactly 120 degrees apart.

john