Vacuum advance

[Donald O.]

I believe that a 1967 L79 (49 state version) uses a B28 vacuum advance but all I can find is a B26 unit.
Are the B28 units no longer available?
Is the B28 unit the correct one?

mine still operates nicely but I’d like to get an insurance one.

Don

[T P.]

Try Corvette Central for the B28 (#272033).
In a prior post by Duke Williams, he notes that "the OE L-79 VAC is '236 16" [B28], but it idles at 14"@750rpm; this VAC is too aggressive." So you might want to use a B26 instead.

[Duke W.]

The OE 8" VAC is more aggressive than necessary. If your L-79 has an OE equivalent cam idle behavior should be 750 @ 14-15", so a 12" B26 passes the Two-Inch Rule. The NAPA number is VC-1765 and any other parts store should be able to cross that to whatever brand they carry. I'm not sure who actually manufactures these VACs now, but all the major brands should have the same part and be stamped B26.

There are lots of stories of recently manufactured VACs being out of spec, so I suggest you buy locally and use a vacuum pump to check that the pin starts moving at 6' and is to the limit at 12".

To change the VAC with the distributor in the car pump it down all the way to expose the forward screw. With the screws removed carefully wiggle the pin out of the breaker plate. Pump down the new VAC and install in the reverse order.

Duke

[Donald O.]

Duke
I’m looking to keep my 67 L79 stock, repeat stock. My only deviation in 40 years of ownership was when I pulled the heads 35 years ago to replace a broken exhaust valve, was to pocket port and a 3 angle valve job. I also used the thin metal head gasket instead of the newer thick ones that are prevalent now. I h save timing set to factory specs, it doesn’t ping and I don’t use racing fuel, just the e10 93 octane here in Sillynois. It’s also not my first time replacing a vacuum advance can either.