can anyone tell what type of vacuum advance I need? I have a 351 cleveland 4v in a 70 mach 1. I have the distributor but don't have the advance mechanism for it. I have the numbers on the side(d2zf)12127(ca). I can't seem to find the same numbers anywhere I can get a new one.I can find the d2zf but not the ca part. Can anyone tell me what type i need or a number.
Thanks Norm  

Not sure what your problem is nmdjr, my books list the D2ZF in 8 different Clevelands in 1972. There are 8 different configurations(CA,AA,EA, *** GA, HA, HB, JA)The 4V with manual trans is an EA. With automatic is a GA. The JA is dual point with dual advance in the HO.The 1970 used a D0OF-Z in both manual and auto.  You should be able to pick any one of these up at a parts dealer. Dont worry too much about the calibration level, the differences will be small.  

Thanks That answered my question. I wasn't sure if the different calibration levels would make a noticable difference.Thanks again  

Remember - vacuum advances are all adjustable.  Original equipment vacuum advances are adjustable via shims.  Aftermarket advances are adjusted via Allen wrench through the vacuum port. You have to tune them for them to work properly.

There are all kinds of schools of thought on how to tune a vacuum advance.  You can send your distributor to Ignitioneering or MCE Engines to have it curved, which includes centrifugal and vacuum advance.  Or you can tune it in your engine and road test.  Centrifugal advance and vacuum advance should work seamlessly with each other - with the vacuum advance handing off to centrifugal advance around 2500 rpm.  

Vacuum advance gets you started.  Centrifugal advance carries the ball at high rpm.  

For distributor tuning/curving, go to www.ignitioneering.com or MCE Engines at 323-731-0462 or MCEengines@aol.com.  

Yeah Jim nice to have you here in the forum. Someone with your expertise is great to have, I have seen many of your articles. So its with trepidation that I clear up one thing, vacuum advance is load dependent. Centrifugal is (intended anyway) the highest spark advance an engine can tolerate at wide open throttle. Thats why race engines are often built without part throttle advance(vacuum advance). Nowadays of course the computer maps it all anyway.  

I took my stock single point distributor and converted it using a Pertronix.   Then I installed one of those Adjustable Vacuum Advance Canisters I bought from Summit several years back.  I don’t remember if it was Crane, Mallory, or whatever.  But I installed it and cranked back the total advance while increasing the initial lead.  The more total advance the worse the spark knock.  So I’m probably only getting about 32 degrees total but have 16 initial advance.  That way I have good initial throttle response but don’t get the spark knock at the top of the gears.

Mine is a manual transmission (actually converted to a T-5 five-speed) so in fourth gear (or fifth) I can still get a little spark knock at low speeds and high throttle settings if I don’t down shift.  That is more a function of the lower octane fuel today vs 35 years ago than anything else.  It’s not a bad problem and knowing it, I can adapt my driving style.

Side note to above:
Welcome Jimbo, glad to see you getting your toes wet here.    

Couple of things there Bill. 16 degrees is pretty high initial, if your getting away with it, great. It usually degrades the idle at that much advance. Cranking back on your part throttle advance cant be compared to initial,,, they are apples and oranges. Your vacuum advance is dependent on engine load so when your load is the greatest say 4 inches of manifold vac,,,then there is no vac advance,,,, only whatever you have in your initial plus the centrifugal at whatever engine speed your at so if you crank back on the vacuum advance your hurting yourself at part throttle sutuations where the engine wants more advance. When we do a calibration, its a dance between octane and power. The power valve opens at ,,say 6 inches of vacuum and that tends to help octane and suppress ping so if the vacuum advance takes off at 8 inches then your pretty safe. Thats what you will find in most calibrations is a match between engine loads and power valve and vacuum advance and centrifugal. What you have found is what I tell most people, initial advance can solve most problems. If you take a look at the advance curves they vary a little bit one way or the other a few degrees here or there, but like you did, you just blew away the curves and upped them by 10 degrees(6 deg btdc is the factory setting) thru the whole range with initial advance setting that high. Most people would find the car pinging or idling poorly but your a careful driver and you can get away with it. More initial advance means more peak pressure so it always helps horsepower and efficiency,,,, the downside is when ping leads to detonation. Those two things are different, ping not usually damaging but detonation will do damage almost immediately. Sometimes the transition between the two is quick.  

mechanicalguy48,

While 16 degrees does seem (and is) a lot of initial you have to remember that’s what the stock setting was on the 1970 Boss 302’s also.  The 6 degrees a normal tune up calls for is a pretty conservative number with a lot of consideration of the car reaching it’s 5 years or 50K mile factory warranty back in 1970 burning regular fuel.  Most Fords/Mustangs back in that era could run more initial timing back then with a higher octane gas being used. I always ran my 302‘s (non Boss‘s) back then at 12 to 16 degrees initial with no problems.

I’ve also always used a vacuum gauge to tune my carburetors.  With my manual transmission I can get 16 to 17 inches of vacuum at a 800 rpm idle.  

One thing many people don’t realize is as a timing chain gets older and stretches slightly it retards your initial timing and people will keep advancing their timing to bring it back into specs not realizing what is really happening.  I had a timing chain that jumped a couple of teeth and wouldn’t start with about 110,000 miles on the motor.   Once I removed the cover is was a little loose but I didn’t think that much but went ahead and change it out anyway.  The car started immediately but the timing was running about 25 degrees initial.  It ran like crap and anything over 2,000 rpm would cause it to spark knock and rattle like a can full of rocks.   Once I reset it to 12BTDC again it ran like a champ for another 70K miles before I sold it.  Also if you’re are still running points in your distributor your initial engine timing will advance as the points burn and close slightly through usage and mileage.

I enjoy your commentary’s and advice, keep up the good work.  

Yeah Bill, go back and look at the original distributor on your Boss 302 because it had a dual diaphragm vacuum advance which retarded the spark at idle. A dual diaphragm unit was used for a number of reasons mostly because it helped emissions. I cant remember what the retard setting was, most of them retarded the timing 6 degrees. As soon as you come off idle it reverted to a normal advance unit.

But yeah I agree with ya and have been telling people to set timing based on how they drive and to advance it as much as they can and when you get ping,,,then back off a little. A little ping isnt a problem if its momentary. The car that pings constantly is a concern but the most advance you can get with your driving style/area/gas is the best. Heat is a factor also, we found that octane rating would rise by one number for every ten degrees rise in carb inlet temperature. Big reason why they all went to outside air ducting to draw cool air and lower the octane requirement of the engine.  

I believe 1970 was probably the first year for the dual diaphragm vacuum units.  Being the young "know-it-all hot rodder" back in those days (and I probably haven't changed much), the first thing I'd do was put a small ball bearing in the retard vacuum line to keep it from retarding the ignition.  I figured if it was good enough for the '69 and earlier guys it was good enough for me, so I guess I'm partly responsible for today's "Greenhouse Effect" (LOL).  

My first ’70 Mustang was a Grabber Package with 302-2V. I plugged the retard hose for a while and then bought a new ’66 Dual Point HiPo distributor from my local Ford dealer back then for $29.99.  I used it for years until figuring out vacuum wasn't necessarily a bad thing and bought an old single point distributor unit and converted it with a Mallory electronic kit in the early 80’s.

Heat is definitely a factor for spark knock and performance.   I have two Shaker mounted cars (1970 and 2003 Mach’s) and they both definitely love the cooler weather.