older electronic ignition and timing question

[coppertop666]

Im finally getting some time to go over my car since purchasing around the holidays and noticed a few things of interest. The distributor has some type of older pointless ignition system (WELLS?) and I am looking to get some more info on what is installed if possible (see pictures attached).

Also I have been doing a little looking around regarding ignition timing and I am getting a lot of mixed info. Before the Vair I had a bunch of ACVW's and the easiest (and best) way to set timing was at full advance between 2500 & 3000 RPM. Is this something that is a no go on the Corvair engine for some reason? Most info I see leans towards setting timing at idle, am I missing something?

Thanks

[Scott V]

The distributor has some type of older pointless ignition system (WELLS?) and I am looking to get some more info on what is installed if possible.

looks like a dale hei conversion. you can use the mopar electronics box like you have or a gm hei module if the mopar box dies & you want something smaller.

Also I have been doing a little looking around regarding ignition timing and I am getting a lot of mixed info. Before the Vair I had a bunch of ACVW's and the easiest (and best) way to set timing was at full advance between 2500 & 3000 RPM. Is this something that is a no go on the Corvair engine for some reason? Most info I see leans towards setting timing at idle, am I missing something?

the shop manual gives timing @ idle - so thats why you see that info. setting @ full advance can work but your going to have to know what full advance is & when it happens. like turbo engines are 24 btdc @ idle & full advance @ 4400.....do you want to be reving the engine @ 4400 trying to set the timing? lol

-Scott V.

[DAVECS1]

That is pretty cool, someone has retrofitted your vair with a chrysler electronic . Definitely a choice piece and should give you great performance for years to come.

[coppertop666]

Very Interesting...

Its a 319 Dizzy on a 110 - any tips from the experts out there regarding timing and or plug gaps etc? Also Brad Bodie noticed in a previous post that the vacuum advance was disconnected and plugged by the PO, is this something that was common for this type of conversion for some reason?

[bbodie52]

The breakerless ignition conversion eliminates the antiquated ignition points and condenser — a system that was difficult to maintain for accurate and consistent timing.

The first reliable battery operated ignition was developed by the Dayton Engineering Laboratories Co. (Delco) and introduced in the 1910 Cadillac. This ignition was developed by Charles Kettering and was a wonder in its day. It consisted of a single coil, points (the switch), a capacitor and a distributor set up to allocate the spark from the ignition coil timed to the correct cylinder. The coil was basically a transformer to step up the low battery voltage (6 or 12 V) to the high ignition voltage required to jump a spark plug gap...

...The disadvantage of the mechanical system is the use of breaker points to interrupt the low-voltage high-current through the primary winding of the coil; the points are subject to mechanical wear where they ride the cam to open and shut, as well as oxidation and burning at the contact surfaces from the constant sparking. They require regular adjustment to compensate for wear, and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations.

In addition, the spark voltage is also dependent on contact effectiveness, and poor sparking can lead to lower engine efficiency. A mechanical contact breaker system cannot control an average ignition current of more than about 3 A while still giving a reasonable service life, and this may limit the power of the spark and ultimate engine speed...

http://en.wikipedia.org/wiki/Ignition_system

New ignition points begin to wear out from burning and arcing as soon as they are placed in service. As the point gap changes with wear and use, the dwell and timing changes. In the Corvair (and other vehicles that utilize ignition points) the Chevrolet design engineers inserted a ballast resistor in the primary ignition circuit to reduce the voltage from approximately 12 VDC to a nominal 6-7 VDC. This lower voltage reduces the high secondary output voltage produced by the coil, but it is still considered adequate for normal operation. The reduced voltage reduces arcing and burning of the ignition points, which extends the expected length of operational service. The primary ignition circuit is also connected to a switched voltage output of the starter solenoid. Whenever the starter is engaged, voltage to the coil primary circuit is increased to a full 12 VDC for the duration of the engine cranking cycle. This boosts the high voltage spark output of the coil, to help promote engine starting. As soon as the engine starts and the starter is disengaged, the primary ignition coil circuit reverts back to the normal 6-7 VDC.

The ignition points system was found in cars from about 1910 through the 1970's. Electronic switching began to be phased in and modern cars no longer use ignition points. The electronic switching system is generally more reliable and is not subject to the continuous variations found with ignition points. As a result timing control is much-more accurate. As sensor-based computer control was phased in, centrifugal and vacuum advance mechanisms were also phased out.

Electronic control of the ignition coil was made available as a modification to the Corvair distributor decades ago, but the need for both centrifugal and vacuum advance in the Corvair ignition system remains.

The following explanation does a really good job of describing the need for both timing advance systems. I hope you will take the time to read it...

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

http://www.chevytalk.org/fusionbb/showt ... id/239321/

[coppertop666]

Appreciate all your info again Brad -

[LilRedDevin]

Just found this thread and wanted to say THANK YOU Brad for the info!

[bbodie52]

If your ignition system was any older it would probably be using vacuum tubes!