Gregory - I also have a '63 340 hp and went down this road last summer. I had a '62 340 hp dist on the car - dual points, without a vacuum advance can. The car idled poorly, so I bought a correct distributor 1111024 from a guy in Chicago. This is a single point dist with a vac can. The car idled better, but fell on its face off the line. Duke Williams advised me to switch the van can with one that can be picked up at a NAPA store for 8 bucks. Part # V1810. Duke can explain why this works, I just know the car screams off the line with this small change.
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Re: 1963 Distributor C2
Duke- Please explain -
I should charge admission to my lectures
Vacuum advance is critical to obtaining proper idle and low speed TOTAL timing to achieve acceptable idle quality, good low speed fuel economy, and avoid idle and low speed overheating.'
Special high performance cams don't create as much idle vacuum as the medium performance cams, such as the "300 HP cam", so SHP engines require different vacuum advance specs.
Unfortunately, Chevrolet Engineering seemed not to recognize this until early in the '64 model run. The '63 and early '64 SHP/FI engines were equipped with a vacuum can that was not suitable to their idle vacuum characteristics. Of course, prior to '63, SHP/FI engines with the Duntov cam didn't even HAVE vacuum advance, so they were on a learning curve in '63.
The basic rule of thumb for selecting vacuum advance specs is that full vacuum advance should be established at 2" Hg. BELOW what the engine idles at because at idle we want total timing of about 25 to 30 degrees to achieve best idle quality, minimum fuel consumption, and MINIMUM EGT, WHICH IMPLIES MINIMUM HEAT REJECTION TO THE COOLING SYSTEM. We also want the vacuum advacne to be fixed at idle. If it varies, so will idle speed and this will degrade idle quality. With 16 degrees of vacuum advance and the typical 10-14 initial timing for SHP engines, total idle timing will be about 25-30 degrees, which is optimum, and this can be verified with a IR gun shoot of the manifold. It should be about 500 degrees F. If it's hotter, your total idle timing isn't right or something else is wrong.
The 340 and 360 HP '63 engines with the Duntov cam generate about 12" of idle vacuum at about 900. The '64/'65 365/375 HP engines with the 30-30 cam only generate about 10" at 900, so the rule of thumb tells us that the vacuujm can should provide full advance at 8". This is the vacuum can spec for the '64 second design 365/375 HP distributors that went into production fairly early in the '64 model year and carried over to '65. Very early L-76/84 '64 engines used carryover distributors from '63. The L-79 ALSO used the same vacuum can eventhough is will generate about 14" idle vacuum at about 750 RPM.
The bottom line here is that ALL SHP/FI engines and ANY engine that has a high performance aftermarket cam that generates less than 16" of idle vacuum should use the late '64/'65 SHP/FI vacuum can, and the Echin VC1810 provides the same vacuum specs as the original "236" Delco can, which is no longer available.
This vacuum can begins to pull at 4" Hg. and the plunger is fully pulled at 8" providing 16 degrees of crankshaft advance, so it will remain pulled to the stop with any Chevrolet SHP cam and most aftermarket cams that are remotely streetable.
Also bear in mind that this can must be connected to a FULL MANIFOLD vacuum source for it to be effective. "Ported" vacuum advance, which provides little or no vacuum signal to the can at idle is an emission control strategy and does not belong on a pre-emission engine!!!
The '63 model year SHP/FI engines use the same vacuum can and the 250/300 HP engine, which provides full vacuum advance at about 15-16". This is correct for the 300 HP cam, but is not suitable for a SHP cam that idles at 10" to 14".
When used on a SHP engine the 024 distributor should be "up-speced" to '65 SHP/FI specs including the NAPA/Echlin VC1810 vacuum can and as aggressive a centrifugal curve as your fuel octane quality will allow. Any used distributor should be disassembled for inspection following a check for bushing side play. If required, new bushings should be installed. A new snug fitting wobble free breaker plate should be installed and the upper bushing grease well cleaned and regreased. Upon final assembly the end play should be shimmed to two to eight thou, and don't forget to install the drive gear with the DIMPLE POINTING THE SAME DIRECTION AS THE ROTOR TIP. THE SHOP MANUAL DOES NOT SPECIFY THIS, BUT IF YOU INDEX IS 180 OUT, YOU WILL NEVER GET THE INITIAL TIMING SET BEFORE THE VACUUM CAN INTERFERES WITH THE MANIFOLD OR SHIELDING.
SHP engines should also use the high breaker arm tension points (28-32 oz.).
If you get the ignition advance map specs right and assemble it properly and run a spark plug with a heat range equivalent to a AC Delco "5" you won't need any aftermarket ignition stuff.
DukeComment
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Re: I should charge admission to my lectures
Duke - you probably should! I practically have a book ready for you now from all cut & paste I have done on your technical posts....it does need major organization skills though!...CraigComment
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