C2: Vacuum reading on L36

[Dan Pepper]

I was dialing in the carb on my '66 L36 this evening and was curious about the vacuum reading I was getting. The car is set-up with a stock list 3606 carb (a.i.r. 427 with the smog pump nutered and holes blocked). I was getting a vacuum reading off of the AC/PB tee of 15-16" at 600 rpm idle. Based on past posts, this seems a bit high to me.

I'm doing my best to dial her in, but I am thinking the advance is kicking in too soon because of a high vacuum. The advance can is stamped "355MS". The distributor was set-up by a reputable performance shop, and they said they mached the curve to the can. Seems to run pretty good after my rookie tweaks, but always looking for more HP if possible.

Suggestions on settings?

[Joe L.]

Re: C2: Vacuum reading on L36

Dan-----

I think that 15-16" Hg is about right for an L-36.

[Duke W.]

Re: C2: Vacuum reading on L36

AIR means the OE vacuum advance is "ported" - no vacuum advance at idle. In fact the entire igntion MAP needs to be modified to non-AIR spec since the AIR ignition map was signficantly different on most AIR engines. The shop should have given you the map they set up. Without the numbers you are just stumbling around in the dark. Lack of vacuum advance at idle reduces manifold vacuum, increases operating temperatures and fuel consumption.

You can check for ported vacuum advance just by teeing your vacuum gage into the vacuum can signal line. If you don't read the same vacuum then your first step is to convert to full time vacuum advance by routing the vacuum can signal line to a full time manifold vacuum source.

You need to know the ignition map that was setup. Most shops IMO do not understand how to set up a complete ignition map. In particular, they don't understand vacuum advance and don't understand how to match vacuum advance to a specific engine configuration. If they reworked the distributor without documenting the map they created I would be highly suspicious of their competence and consider it unprofessional of them not to have provided you IN WRITING the ignition specs they set up, but that's SOP for "performance shops".

The OE non-AIR ignition map is a good place to start. The specs are in your CSM and AMA specs.

Duke