I see references to euro cars have a single distrib, and wonder why US cars are more complicated with two? Now, I fully understand that two distribs make each set of points think is only running half the RPM of an eight lobed distributor cam, and thus delay point float to a much, much higher RPM.. Did the later Euro cars get two dizzies also for high RPM reliability? What brought this up was was I was looking at the Black Stallion electronic conversion which uses a single distrib. Sorry for all the questions, but I have a need to know things like this. Once I get involved more in my car again in the rebuild, I will be able to answer questions also. Thanks, Doug
US cars required an ignition retard and it was just deemed simpler that way. It wasn't really but they were able to use off the shelf parts rather that go to the expense of having a subcontractor tool up and make something different for a small number of cars. Ferrari has in the past done many strange things in the name of being able to use off the shelf parts. The 4 lobe distributors were not meant nor do they have any less point float problem.
Why wouldn't the twin distributors have more RPM capability? The points open every 90 degrees ona four lobe vs every 45 degrees on an 8 lobed distributor, giving the points approx twice the length to return to base and allow electric flow back to the coil for re energization. Four, two lobe distribs should allow four times the RPM of a single 8 lobed distrib. The answer in an American V8 to point float was to use a stiffer point spring, which caused the rubbing block to wear faster and alter the dwell, thus requiring much more frequent point maintenance, and typically, high performance US point ignition systems didn't work much past 7K RPM new,a nd quickly degraded with the stiff spring, these Ferrari twin dizzies let my motor run to 8K RPM without ignition breakup, with no maintenance other than maybe checking them every 10K miles. Not looking for an argument, just looking to verify info. Thanks, Doug
Brian, maybe you can shed some light on this Peter and i have NOS japanese distributors S-159C's which are identical to the US version but have 1 set of points and a cam profile way more radical than the US cam. Why is this and what does it do to performance??? Image Unavailable, Please Login Image Unavailable, Please Login
yup. The single works but 2 will work better both for point float and coil charge time.....although the single works. The problem was worse when the electronic stuff came out as it just wasn't fast enough so 2 was the only answer as well as a basically off the shelf answer.
What confuses the issue is that some Euro cars had 2 distributors also. If I am not mistaken the euro set up had a four lobe cam with 2 points, each set working one 4 cylinder bank.
Because the single euro distributor also uses a 4-lobe cam with two sets of points physically mounted 135 deg (45 deg eletrical) apart firing two independent coils (i.e., even though it's all packaged inside a single distributor with a single "dual level" cap, it is still two separate 4-cyl ignition systems on the primary side). If they had used an 8-lobe cam with only one set of points and a single coil (like a 1960s US V8) then this would have had inferior high RPM action -- but they didn't. Here's a couple of shots of what's inside the single euro point-based distributor: Image Unavailable, Please Login Image Unavailable, Please Login
What Steve's saying is that that so called 'single' distributor is really electrically 2 distributors packaged co-axially in one case!!! About the only simplification over 2 distributors is that there's a single mechanical advance common to both banks.
Rob -- Can you give the dimensions A, B, C, and D for the two cam shapes? I believe the A/B cam is the "better" one from a performance view -- no discontinuity between the flat and the radius (although this area will be polished some to lessen on the C/D), and A/B has "steeper" opening/closing behavior, so the dwell angle changes less as the point block wears -- but the C/D shape is easier to make. With the numbers, we can plot/compare these shapes. Also, can you identify who is who (i.e., the A/B cam is from S-XXXX? and the C/D cam is from S-XXXX?) -- TIA. Image Unavailable, Please Login
Thank you for the pictures, that thought crossed my mind earlier on how to make a single dizzy allow dual points/dual coil by doing a double deck inside a single dizzy and leave enough coil saturation time for high RPM running, but I got over whelmed by how to mechanically design, and decided to not frustrate my brain. Doug
BTW, This is my other car. I know a lot about US V8 motors, but only basic fundamentals about Ferrari engines right now, which is why I am asking questions. This EFI small block Chev 427 CI motor I built last year (no, Chevy never made a small block motor that large), puts down 400 ft-lb of torque at the rear wheels at 1500 RPM, and 440 ft-lb at the rear wheels at 4400 RPM, and will run to over 7000 RPM. Doug
On a 308 GT4 I used to own, the previous owner had built a single dist. setup using one of the original Marelli cases. Inside he used a Mallory Unilite ignition and fit a Mallory 8cyl cap from an early Ford if I remember correctly. Tune up parts cost about $30 for the cap and rotor and $100 if the Unilite went bad. Here is a thread from a few years back. http://ferrarichat.com/forum/showthread.php?t=75853
And it still results in Ferrari rotors, caps, costing hundreds of dollars. Not to mention the dizzy itself costing an arm and half a leg. Amazing the cost reduction techniques that Ferrari went through on behalf of its car owners.
That is exactly what I just did. Here: http://ferrarichat.com/forum/showthread.php?t=245921&highlight=fuel+ignition+upgrades
This is unfortunately one of the downfalls to inductive style ignition. Long spark, but weak without proper charging to the coil (dwell) hence the extra set of points. High energy inductive systems correct this in a couple different ways. Electromotive's answer is to have a coil for each cylinder which gives a considerable amount of time for each coil to charge prior to being discharged. This arrangement also has considerable voltage going to each coil for an extra large bang. I personally like the high energy inductive systems which adapt to the existing distributors yet retain the inductive length of a spark as opposed to the uber short capacative discharge spark (inductive spark is 2-3 times longer). Mallory's IIIa is a high energy inductive spark like electromotive and the units are small enough to hide directly behind the coils. They work great and I retain a stock look even easier than the MSD users who have to hide the boxes in the trunk somewhere.
The Ferrari OEM "dual points" are not the same as high performance "dual points"....they are not splitting the work load. It runs on one set most of the time, and the idle set is used at low RPM only... HTH
Ferrari needed 2 sets of points in the early 1970s, the second to retard the spark at idle to even hope of meeting the emissions regulations. Most of the early V-12s also had two distributors because a 12-lobe cam would not provide adequate dwell to charge the coils. The early drawings (F106AB000 - 109379) and factory pictures show the 308 engine with two distributors. On a 2-distributor setup with 4-cam distributors (2 sets of points) the normal run points (R1) are set at 39° dwell and the idle run points (R2) are set at 34° I permanently enable my R2 points (ground the output to the microswitch) and adjust them to overlap and extend the dwell to 44° total. This extends the charge time for the coils by about 13%. I incorporated a switch on the ground circuit for the R2 points, so I can take them completely out of the picture (for timing purposes), and the car seems to pull better with the dwell extended. No dyno data, and I live at 5200 ft so carburetor jetting is a much greater factor, and I run a little rich. I have not had any plug fouling issues with the dwell extended, running NGK BP7ES plugs.
These distrib conversions have me thinking. Now, what if you took a 1960's Ford, or Chevy dizzy, which ever would fit best,and moved the breaker plate and the vacuum advance mechanism over to the Ferrari base. Use a Mallory Unilite for point replacement,and have all the benefits of electronic ignition plus the added low speed, part throttle,high vacuum, gas mileage improvements inherent with vacuum advance. Vac adv should be worth about 2-3 MPG at cruise condition. Having the US dizzy shaft machined and splined would cost something, of course, and I am not sure how vacuum advance would work on a car with no central manifold plenum, you would be pulling vacuum reading off only one cylinder intake port. Doug
