Vac Canister B20

**Joe L.** · February 1, 2010, 11:27 PM

Re: Vac Canister B20

Originally posted by Andrew Papanicolaou (48361)

Hello,

I have been looking through the archives in order to use the correct vac canister for converting to full time vac advance. 71, 350(base), Auto.

What I have found is VC1765 which is stamped B20.

When I ordered this VC1765 through Napa, the can was stamped B26. The parts guy order 2 others and they both were stamped B26. Am I missing something here? Do I have the right number?

Any help would be greatly appreciated.

Andrew Papanicolaou 48361

Andrew-----

The B20 and B26 have virtually identical specs. In fact, I don't know why Standard Motor Products, the actual manufacturer of the "B-series" vacuum controls, ever made both of them. However, I believe they have now consolidated and the B26 has replaced the B20.

**Tom L.** · February 2, 2010, 08:47 AM

Re: Vac Canister B20

Last winter I replaced my VAC with the one you mention and it works perfectly.

**Duke W.** · February 2, 2010, 12:14 PM

Re: Vac Canister B20

What Joe said...

Over the years OEMs designed "new parts" when there was already something virtually identical in existance. Then there was an effort to consolidate mulitiple parts to only one number. As stated the B20 and B26 have virtually identical specifications, and they were consolidated under the NAPA V1765 part number. The details vary, but nominally both should be near 0 @ 6" and 16 @ 12", and figure 1-2" and 1-2 deg. tolerance.

I always recommend testing these with a Mighty Vac or equivalent before you leave the store, assuming you buy them in person. You can at least test the start and max vacuum points, but you will have to wait until it is on the engine to test the actual advance amounts, however, if the start and stop points are okay, the advance is probably reasonably in the ball park.

A friend recently order four B28s from gmpartsdirect using the Delco number. Two were in spec, one was out of spec and the fourth was stamped B25 and did not meet the B28 spec!

You chose the correct part. For base engines or optional engine with base cams and manual transmissions I recommend the 15" B22, However, since automatics don't pull as much vacuum in Drive, I recommend the B20/26 for automatics.

I would appreciate if you would measure idle speed/vacuum/total idle timing in Drive once you have everything setup, and post the data. Also any observations about driveability and engine temperature will be useful.

You should also experiment with increasing the initial timing to yield up to about 28 degrees of total idle timing (full vacuum plus initial) without exceeding 38-40 degrees total WOT timing (initial plus full centrifugal). You can also try quickening the centrifugal advance with lighter springs. I don't know your engine's centrifugal curve, but if you quote the specs from the CSM I can give you some guidelines. Optimizing the entire spark advance map will improve torque/power, throttle response, and fuel economy, and also reduce operating temperatures if they are high,

Also, understand that once you have everything set up for the full time vacuum advance and optimized the initial timing, you should go through the idle speed/mixture adjustment procedure.

Emission controlled engines generally have higher recommended idle speeds than their non-emission controlled antecedents, however, with full time vacuum advance, the engine should idle lower with acceptable quality.

You should be able to acheive good idle quality and minimum "creep" at about 450-500 in Drive, but it may take a little experiementation.

Let us know how it goes and your final settings.

Duke

**Andrew P.** · February 4, 2010, 07:32 AM

Re: Vac Canister B20

Thank you for all the replies!!

Once I get everything back together and have the engine running I will post some numbers.

Thanks,
Andrew

Vac Canister B20

Vac Canister B20

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