71 LS5 Distributor Vacuum Can

[Joe G.]

Does anyone have a reference for what is the correct unit for a late 71? The inoperable one that was removed is a 436-20. Autozone cross referenced it to a Wells DV1465, but could not give me any specs. Questions:
1. I am not sure the one I removed is original (a 20 degree unit)
2. Any information on ballpark figures for vacuum vs. degrees advance for calibration to check the new one.

Thanks,

Joe

[Joe L.]

Re: 71 LS5 Distributor Vacuum Can

Joe-----

The original distributor vacuum control used for your 71 LS-5 was GM #1973436. That's, apparently, the one you removed. The '436' coding confirms that.

This unit should generate 20 crankshaft degrees of advance at 17" vacuum.

I fully expect that the Wells brand unit specified is the correct replacement, but I can't confirm that. The GM #1973436 was just recently discontinued, but you might still find some of these around, if you wish to seek one out. However, it will likely be exactly the same as the Wells unit. GM hasn't made these controls in years. All of the ones available for the last 15 years, or so, have been "outsourced" parts packaged in GM/Delco boxes. They function perfectly, though. However, they do lack the stampings as seen on your original control and they have very slight configuration differences otherwise.

[Duke W.]

Re: 71 LS5 Distributor Vacuum Can

Your '71 has an ignition map that was set up for emissions and such maps typically have low initial timing, slow centrifugal advance with total WOT timing (initial plus full centrifugal) less than pre-emission engines),but more vacuum advance.

If you don't have to be emission tested, setting up your ignition map equivalent to a '66 390 HP big block should provide better performance, fuel economy, and less tendency to overheat. Early seventies emission controlled engines also typically have "ported" vacuum advance (no vacuum advance at idle) and/or TCS, which disables vacuum advance at all operating conditions other than when the engine is in top gear.

Duke

[Joe G.]

Re: Vacuum Can Results

Joe and Duke,

Thanks for the input. I found the Wells unit produced 3* at 8", 12* at 13" and 20* at 17".

Joe