Recommendations for Distributor Vendor...

[Collin MacDonald]

Slowly but surely restoring my 63 coupe. I need to know some information about the distributor. I have got a 63 L-76 Engine. What is the proper configuration for the Distributor. The car's build date was on or about 24 Jan 63. I see so much about the matching numbers for parts, what would be the proper distributor, the cap etc. and the "lower band" that everybody talks about, what information should be on that? How much detailed are the judged upon? If I should want to replace my distributor, who is the best vendor to purchase one from, I hate to use Hemmings because you don't know who you are dealing with, and what is the cost for a complete unit, with proper numbers/dates fully restored?

Many thanks....

[John H.]

Re: Recommendations for Distributor Vendor...

Collin -

The '63 L-76 originally used a #1111024 distributor (that's the number on the band, doesn't show up anywhere else). '63-'67 carbureted distributors are essentially all the same, except for the autocam on the top of the mainshaft, the weights and springs, and the vacuum advance unit - those were "calibration items", and each of their many potential combinations resulted in a different part number. Your '63-'64 JG will describe what is expected for appearance of the cap.

[Collin MacDonald]

Re: Recommendations for Distributor Vendor...

Thanks for info....so the distributer does not really have a time date that I should be concerned about or a build date?

[Duke W.]

Re: Recommendations for Distributor Vendor...

L-76 for '63 used the same "024" distributor as base and L-75. The FI distributor has the same ignition advance map, but, of course, has a different housing for the injection pump drive.

1963 was the first year that Duntov-cammed engines received a vacuum advance and GM did not get it right! The Duntov cam only generates about 12" of idle vacuum, but the OE vacuum can requires 16" to pull to the limit. This is fine for the base and L-75 engines since they generate about 18" at idle.

For several years my L-76 suffered from idle instablility. The basic problem is that the ignition timing will vary due to "dithering" of the vacuum can in response to idle vacuum variation, which is somewhat inherent to SHP cams.

Once I realized the problem I installed a Delco "236" can, which was used on the '64-'65 SHP/FI engines. This can pulls the plunger to the stop at 8", which results in fixed idle timing and a stable (but slightly loping) idle. The engine will idle indefinitely without becoming unstable or overheating. With the original 16" can, it would often become unstable, get hot, lose revs and start chugging and sometimes even stall.

The above may not apply to '63 FI engines as it is my understanding they have "ported" vacuum advance, so there is no vacuum advance at idle. It's not clear to me why this is the case, however, it could be that Chevrolet found poor idle quality with FI and the 16" can, so they got around it by porting the vacuum signal line to above the throttle blade at idle. (Idle quality with FI was always a problem, and with the same cam, carbureted engines usually exhibit better idle quality.) This stabilized the idle, but increased heat rejection to the cooling system and increased idle fuel consumption. For most efficient idling these engines (and other SHP-cammed engines) need 26-32 degrees of TOTAL idle timing, which is satisfied by initial plus full vacuum, plus maybe a few degrees of centrifugal if the curve is quick.

GM got is right beginning in '64 when L-76/84 had distributors with 8" vacuum cans (and FI got full time vacuum advance) , and I recommend that an 8" can be retrofited to the '63 L-76. I also recommend the 8" can for '63 FI along along with conversion to full time vacuum advance. The '64-'65 SHP/FI engines also have a very quick centrifugal curve that starts at 700 and is all in at 2350. Since about 900 RPM is required for reasonable idle quality, the total idle timing includes a few degrees of centrifugal, which is okay. When I installed the 8" can in my '63 L-76 back in the late sixties, I also installed the companion '64-'65 SHP/FI weights and springs, and the improved the low end torque due to increased low end timing was greatly appreciated since my car is pulling a 3.08 axle through a CR trans.

L-79 also used the 8" vacuum can, but a slower centrifugal curve because it has a higher dynamic CR due to an earlier closing inlet valve. With today's fuels it's best to tune the centrifugal to your specific driving conditions - get all the centrifugal in as soon as possible, but the limiting factor is low rev detonation.

The generic replacement for the Delco "236" can is the NAPA/Echlin VC1810. Its overall appearance is essentially identical to Delco cans, but its stamped "B28" on the mounting bracket instead of "236-16" for the 8" Delco can. I believe the original '63 can was stamped "201-15", but it was replaced by a different (but nearly identical spec) service part by the seventies. Few '63s have the original vacuum can since they eventually stick or leak and don't last 40+ years. The first three stamped digits are the last three digits of the GM part number, and the second two digits are the maximum advance in crankshaft (not distributor) degrees.

During the 2002 National Convention judging in Monterey, I saw many "non-original" vacuum cans on '63s, but there was no mention of the proper markings in the JG. When I asked the National Team Leader about this he said: "If it's not in the book, we don't judge it".

Duke

[Doug C.]

Re: Recommendations for Distributor Vendor...

Duke, This is somewhat off-topic but you did mention the mapping of the mechanical advance. What is the proper mech. advance map for a stock 66 L-79? The GM service manual states 0 degrees @900 rpm, 15 @ 1500 and 30 @ 5100. The Sun Tune-up card for the same engine and distributor # states: 0 @ 450, 4.5 @ 600, 7.5 at 750 and 15 @ 2550. I would assume neither include the 10 degrees of intial ignitipn timing at idle. Am I comparing apples and oranges here?
Thanks - Doug

[Duke W.]

Re: Recommendations for Distributor Vendor...

Notice that the Sun numbers are exactly one half of the GM numbers. Sometimes data is specified in distributor degrees/ distributor RPM, but the GM data is typically given in crank degrees/cranshaft RPM.

If you are testing a distributor on a Sun machine (off the car) the data it reads is distributor degrees and distrbtuor RPM, so that's why Sun specifies the data in that context. If you check the timing map on the engine you will read crankshaft degrees and RPM.

This is a VERY important distinction that sometimes gets lost, but you always want to be aware of it and absolutely know the specification and test data context.

BTW, L-79 uses the same aggressive 8" vacuum can as '64-'65 L-76/84 with the 30-30 cam, but the L-79 centrifugal curve is more conservative because its earlier closing inlet valve creates a higher dynamic CR, so it won't take as much low rev WOT timing as the 30-30 cam engines. You can try quickening the curve to see if you can get a little more low end torque, and the limiting factor is detonation.

The 8" can is really more aggresive than necessary for L-79 since it will pull about 14" @ 800, so a 12" can will be okay.

If any L-79 owners have a transient detonation problem - a little rattle when you open the throttle, the less aggresive 12" can (NAPA/Echlin VC1765) should mitigate it. The 12" can is also okay for SHP BBs since they pull about 14" at 900.

If I had a L-79 I would install the 12" can, then quicken the centrifugal as much as possible to the ragged edge of detonation, and since the L-79 centrifugal maxes out at 30 instead of 24 as on the 30-30 cam engines, I would set the initial in the range of 6-8 before quickening the centrifugal.

Duke

[Collin MacDonald]

Re: Recommendations for Distributor Vendor...

Duke,

Many thanks. Another question, is this the reason many people are going to the electronic ignition systems in the mid years...I know that is almost a taboo subject here, but it seems if you just go to the electronic system you will eliminate the need and get much better performance...am I on the same wavelength or am I missing something?

[Duke W.]

Re: Recommendations for Distributor Vendor...

As far as why individuals install electronic conversions, you will have to ask them. Personally, I choose not to do it for the following reasons:

1. Ignition points are simple and reliable and almost never fail. If your distributor is assembled to spec with snug bushings, endplay, and a wobble free breaker plate, the high breaker arm tension points will provide a reliable spark to 7000 revs. For engines with redlines of 5500 or below, the standard breaker arm tension points are satisfactory. With a properly functioning point ignition that delivers design spark energy, there is no measureable performance improvement compared to electronic ignitions.

2. Given that most of our cars are driven only a few hundred to a few thousand miles a year, the nominal breaker point life of 30K miles means many, many years. A point resistance test and dwell angle check and adjustment, if necessary, should be conducted every few thousand miles. This is about a two minute job.

3. If a set of breaker points does fail, they can often be jury rigged or just replaced with a used spare set that you keep in the car along with a simple screwdriver. (Set the dwell to spec on an old set of points before you remove them, and keep them as a spare. They can be dropped in anytime an emergency occurs and will get you home. Been there done that! I've also been stranded twice by a failed HEI in my Cosworth Vega. (I now carry a complete HEI distributor in the spare tire drop center along with a 9/16" wrench to swap it out if it craps out again, so I am only inconvenienced a few minutes.) Then there were the two failures of the TI that I ran in my SWC for a few years and 50K miles. Both fixes were simple, but I sold the POS back to David Burroughs to reinstall on the "12-mile L-88" from whence it had come.

One of the true beauties of vintage Corvettes and other similar vintage car is that they are SIMPLE!!!

I can troubleshoot the entire electrical system with a twenty dollar Radio Shack multimeter, and don't need any technical documentation to do it.

In the last two weeks I have downloaded over 300 MB of technical and service information on my '88 MBZ 190E 2.6. Make no mistake, this car is BEAUTIFULLY engineered, but its complexity rivals some aerospace systems I have worked on and enough special test equipment is required to clean out your 401K. Once I absorb the system knowledge I need from all this data, I will be able to perform most diagnositics with basic electrical test equipment, but this is going to require considerable study and analysis.

Replace the points on my Corvette with some electronic black box? You gotta be kidding!!!

Duke

[Duke W.]

PS

"Gertrude" passed her CA emissions test today with the best numbers ever... no stinky butts on MY girls, but not without some consternation on my part as her past performances have been less than stellar. Continuous flow mechanical fuel injection systems are not the best for emissions performance, but 300 MB of tech data and the understanding it provides of the various systems can do wonders!!!

Duke

[Roberto L.]

Re: Recommendations for Distributor Vendor...

I think about the same on these cars. Recently made a long trip in the south of my country, more than 4K miles in my base 70. Imagine having a problem with the black box in the middle of nowhere... the points are reliable, easy to fix even in the road. When you reset a misaligned point set the car seems to revive with a good idle and low speed instability. Of course, my car climbs only to 5k revs or less, and very rarely. I'm not saying the other systems are wrong, quite to the contrary, but the old vettes are powerful and simple cars.

Roberto, NCRS #30019

[John H.]

Re: Recommendations for Distributor Vendor...

Collin -

"Electronic Ignition" is really a misnomer when talking about the conversions (Pertronix, Breakerless SE, Unilite, Crane, etc.); all they really are is an electronic switch for the coil instead of an electro-mechanical switch (points), and all they really do is relieve you of a five-minute annual job of setting dwell or a ten-minute job every year or two of installing new points.

Although they normally work quite well, try finding one of those "modules" in a parts store in the middle of nowhere when they take a dump. Most savvy folks that have one of the conversions carry a spare set of points in their "road box" for the occasion when the module dies without warning. There are few things simpler and more reliable than points.