BB vacuum advance canister Question

[Domenic T.]

I just looked at the new vacume can on my distributor for my 435/427 and it was a B22. I checked the archives and it said the was for a SB. Again, the wrong parts. What did Duke or others recomend for the BB? The B22 is new and I am also building a 327/340 in the future. Is the B22 good for the 340HP? I am ready to install the distributor and I want the right one for my 427 distributor.

Dom

[Richard M.]

Re: BB vacume advance canister Question

Dom, It's really based if you're going to stay with ported vacuum or switch to full manifold vacuum on the L71.

[Duke W.]

Re: BB vacume advance canister Question

The B22 is essentially equivalent to the OE 201, but your engine was built with ported vacuum advance. If you switch to full time vacuum advance you must install a 12" B26 as the 15" B22 will not pass the Two-Inch Rule.

The '63 340 HP engine was also equipped with a 201 VAC and mine would not idle stably for any length of time and would stall unless you occasionally blipped the throttle. It took me a couple of years to figure out, but when I replaced the 201 with a 8" 236 (B28 is today's equivalent) circa 1966 the problem was solved, and that's how I came up with the Two-Inch Rule.

The B22 is suitable for manual transmission base engines or manual transmission optional engines that use the base engine camshaft, all of which should idle in neutral at at least 17". If these engines are coupled to an automatic, a B26 should be used because they idle in Drive at lower manifold vacuum.

Duke

[Joe L.]

Re: BB vacuum advance canister Question

I just looked at the new vacume can on my distributor for my 435/427 and it was a B22. I checked the archives and it said the was for a SB. Again, the wrong parts. What did Duke or others recomend for the BB? The B22 is new and I am also building a 327/340 in the future. Is the B22 good for the 340HP? I am ready to install the distributor and I want the right one for my 427 distributor.

Dom

Dom-------

There's no such thing as a "big block vacuum advance" and a "small block vacuum advance". Original vacuum advance controls, as appropriate, were used on both small block and big block applications.

[Domenic T.]

Re: BB vacuum advance canister Question

Thanks guys,
The B22 was the one they sold me at the time. I did give them the engine specs. As I understand it now, I need the B26 for either full time or ported vacuum?

Dom

[Duke W.]

Re: BB vacuum advance canister Question

The B26 is REQUIRED if you switch to full time vacuum advance. If it still has OE ported vacuum advance, either one will do. The Two-Inch Rule does not apply to ported vacuum advance applications - only full time.

Don't expect a parts store to necessarily sell you a functionally correct VAC. They will go with whatever is in their catalog and there are lots of errors in both GM and aftermarket parts catalogs. Some errors are due to parts consolidation in the past, and some like the '63 340 HP VAC were engineering errors in selecting a functionally correct VAC that was never corrected by GM. Also if a ported vacuum advance application is changed to full time, almost always a different spec VAC is required to meet the Two-Inch Rule.

They don't know what you engine idle vacuum is, and if you tell them about the Two-Inch Rule you will likely just get a blank stare back.

Given the idle instability problem on the '63 340 HP engine I'm surprised GM never even wrote a TSB on the problem. Everyone I talked to said the engine would never idle well with that "racing cam". So it was left up to a 19-year old second year ME undergrad to figure out and solve the problem, which was simply the more aggressive VAC that went into production on '64 SHP/FI engines. (About the same time he also figured out that the dimple in the dist. drive gear had to be indexed pointing the same direction as the rotor tip in order to get the proper initial timing before the VAC interfered with the manifold or coil brackets. All the "experts" told him to reindex the wires and other lame-brained solutions that just made the problem worse.)

The idle instability problem did not occur on the '63 FI engine because for some strange reason it had ported vacuum advance. This was the first year that GM used vacuum advance distributors on the SHP/FI engines and they clearly screwed up. The '64 SHP/FI engines idled at about 10", were equipped with an 8" VAC, and both had full time advance. They finally figured it out.

Duke

[Richard M.]

Re: BB vacuum advance canister Question

Dom, this is a 427 just built using the B26 and full manifold vacuum. Last one I setup the same way could idle all day long in 90* ambient temps at 180-190F. This one will act the same when I'm done with it.

https://youtu.be/8InATY5Na5s

[Domenic T.]

Re: BB vacuum advance canister Question

Duke,
Thanks for the detailed post.

Dom

[Domenic T.]

Re: BB vacuum advance canister Question

Rich,
Thanks, that was neat.

dom