'65 Distributor components, 300 hp vs. 350 hp.

[Chris D.]

My car runs fine, I have simply gone off on a deep tangent and would enjoy more of the expertise I've read here on the subject of distributors.

The two units in question, 1111076 for the base engine and 1111087 for the 350hp, have slightly different mechanical advance curves. Curiously, they show the same part numbers for 1) main shaft w/ autocam, 2)weights, 3) springs, and 4)weight plate/points cam. If these parts are common, along with the vac canister (they all got '236 that year)why have different assembly numbers?

Either my service # source (1970 book) commonized the subcomponents, my advance curve chart is wrong, or (best odds) my understanding has a few major gaps.

Your insights appreciated.

[Tom H.]

Re: '65 Distributor components, 300 hp vs. 350 hp.

Without the advance curve specs my gut tells me that the springs for the 350hp should be lighter, the stop bushing larger and the initial advance higher than the 300hp. The vac can should be ported to full manifold at idle to improve fuel mileage and to maximize cooling at low speed and idle. Perhaps the exact curves are available in the archives.

[Duke W.]

Re: '65 Distributor components, 300 hp vs. 350 hp.

Check your '65 Shop manual supplement. There is a difference in total
centrifugal advance, and the vacuum cans are different for sure.

Only the L-79 had the "236" vacuum can.

Though all '65 engines were factory equipped with the standard 19-23 oz. breaker points, I recommend the 28-32 oz. points for all engines with redlines above 5500.

Duke

[Joe C.]

Re: '65 Distributor components, 300 hp vs. 350 hp.

Chris:

The base versus hi horse engines use different mainshaft/advance cam assemblies. I am not sure of GM part numbers, but if you look at some of the parts catalogs (e.g. LICorvette, Corvette Central, ZIP ,etc.) you will see 2 different part numbers listed for the 2 applications. The advance cams are noticeably different, with the hi perf unit having a flatter profile.
The vacuum advance cans, as Duke said, are also different. The "236" unit is specified for the hi horse motors.

Joe

[Chris D.]

Re: '65 Distributor components, 300 hp vs. 350 hp.

Joe,

Certainly the '236 has no business on a smooth idling, high idle vacuum engine. And yet Long Island has it listed as correct for 250-375 hp engines in '65 (typo maybe?). A better but still unofficial source, Colvin's Chevy by the numbers, says it was used on the 1111076 until 10/1/65. Doesn't really matter since nobody would recommend it on the low horse engines and my curiosity is really on the mechanical advance parts.

My '70 parts book specifically calls out shaft 1964925 for both "65-66 Corvette (327)(exc. Sp. H/Per.,FI,A.I.R)" and "65-66 Corvette (Sp. H/Per w/Hyd. lifters)(327)(exc. T. Ign.,A.I.R.)". Same engine pairing for the weight plate/points cam 1938116. Same for weights and springs. And yet, as Duke confirmed, they have different mechanical advance stats. Seems to me if these parts are the same the curves should match.

What am I missing?

[Joe C.]

Re: '65 Distributor components, 300 hp vs. 350 hp.

Chris:

You never specified the engine in question. Your profile says you own a '63 SWC, but your posts suggest that the car in question is a 1965, either 300, or 350 HP. Please clarify.

First, the easy part. My 1965 Shop Manual lists identical vac. advance characteristics for ALL 1965 small blocks. It would logically follow, that the same (236), vac can was used for all these. This assumption (??) is also in agreement with the parts listed in the LICorvette, Corvette Central, and Zip catalogs. I didn't check all my other catalogues, but I assume they will be the same (barring any typo's).

Next, the same 3 catalogs list the same "spring and weight kit" for all engines, 1963-67.

Again, back to the '65 shop manual. The centrifugal advance characteristics are listed as the same for 250/300/350/350with TI, which would suggest a common mainshaft/advance cam ass'y. The 365/375 both std, and TI have a common profile, and thus were fitted with a different unit than the others. This is NOT in line with any of the above three catalogs, but the 50 RPM difference in when the advance begins to ramp up should not be noticeable anyway.

Based on the above, if your car is a 1965, then the 236 can is used for all SB's. The springs and weights are all the same. The base motor mainshaft was used for both the 300 and 350 engine. This makes sense, because the 365/375 motors specified a higher idle speed.

All engines perform at their best, and provide optimum fuel economy at maximum spark advance (just short of detonation). Assuming that hydrocarbon emissions is not an issue, I would use a 236 can, a base (or, if you already have it) fuelie mainshaft in your distributor. I would set static timing as far advanced as the engine will tolerate without detonation.

Joe

[Chris D.]

[Duke W.]

Re: '65 Distributor components, 300 hp vs. 350 hp.

Here are the specs I have from Vol. 8 No. 2 Corvette News.

The 300 HP dist. is 1111076 and the ignition map is as follows:

0 @ 750

15 @ 1500

26 @ 4100

0 @ 6"

24 @ 13

The 350 HP distributor - 1111087 is speced as follows:

0 @ 750

15 @ 1500

30 @ 5100

0 @ 4"

16 @ 7"

The vacuum cans are definitely different, and the centrifugal is too, but the only difference might be the length of the slot in the autocam assembly.

My circa '80 GMPD parts catolog lists the 1964925 shaft assembly for 65-66 327 exc SHP.FI, AIR. This same shaft assy. is separately listed for 65-66 SHP w/ hyd lifters exc. TI, AIR.

Could be the Corvette News specs are in error, or they are correct, the '65 supplement is wrong, and GM consolidated the replacement parts. The fact that the engines are listed separately, but have the same part number indicates that originally different numbers were listed.

Joe might be able to determine the histories of these part numbers.

Duke

[Chris D.]

[Duke W.]

Re: '65 Distributor components, 300 hp vs. 350 hp.

I don't have a list of vacuum specs versus GMPD number. I just know a few of them. I believe the bushing on the limit pin is common to all single point distributors. Differences in total cent. advance are obtained by changes in the slot length on the autocam.

Don't know of any distributor specialists, but they are probably out there. If one desires to change the ignition map the aftermarket offers many options in terms of weights, springs, and vacuum cans.

Duke

[Chris D.]

Thank you all for the insights. *NM*