1966 L72 running hot

[Michael J.]

Re: 1966 L72 running hot

I would go with the B28, the B26 is one better suited for an L79, hydraulic lifter engine, not as much vacuum pull at low RPM. You need one that is all in early in the RPM range.

[Joe T.]

Re: 1966 L72 running hot

Thank you..... I really appreciate all the help I have received.

[Joe T.]

Re: 1966 L72 running hot

I have a timing light but not a vacuum gauge. Will look for one.

[Duke W.]

Re: 1966 L72 running hot

You can buy a vacuum pump/gage like a Mighty Vac or equivalent at Harbor Freight for about 25 bucks. It's an essential tool for any kind of engine tuning work.

Once you have measured normal hot idle speed manifold vacuum, apply the Two-Inch Rule to select the proper VAC. A 12" B26 is the best fit for the big block SHP cam, but if it has a higher overlap cam you may need an 8" B28.

Duke

[Richard G.]

Re: 1966 L72 running hot

A friend of mine chased an overheating issues for a couple years. He did many of the same things you already completed.

It was a stuck heat riser. I would confirm it is in the full open position and works as designed.

[Joe T.]

Re: 1966 L72 running hot

I will check the heat riser also. Where can I find a B26 or B28 vac can? My NAPA store does not stock them.

[Richard G.]

Re: 1966 L72 running hot

I found mine on Amazon.
Search;
Airtex Distributor Vacuum Advance 4V1053

[Duke W.]

Re: 1966 L72 running hot

The Airtex number is for a B28. I recently bought a B26 on Amazon, Standard brand, VC-181. You need to get a idle manifold vacuum before you decide which one is necessary.

Duke

[Leif A.]

Re: 1966 L72 running hot

I will check the heat riser also. Where can I find a B26 or B28 vac can? My NAPA store does not stock them.

Joe,
Rock Auto should have what you need. Below is a link for a B26.

https://www.rockauto.com/en/moreinfo.php?pk=45409&cc=1322143&jsn=635

[Joe T.]

Re: 1966 L72 running hot

I will purchase the vacuum gauge on Monday before ordering the can. I will also check the can number in the car now.
The comment on the heat riser has me thinking also. Mine are fairly new and can be moved. I may just wire them open since I only drive the car in the summer. Any suggestions or problems with wiring them open? Wow, after this, I should have completed everything to eliminate over heating..

[Chris H.]

Re: 1966 L72 running hot

Joe, also recommend you pick up a 1966 Chevrolet Service Manual. It will show you how to do a complete tune up for the L72 including valve lash, carb adjustment and ignition timing.

These motors are systems and everything needs to work in harmony for optimal performance.

No negative side effects for wiring open the heat riser.

[Joe T.]

Re: 1966 L72 running hot

I have a 1966 Chassis Service Manual, 1966 Corvette Assembly Instruction manual and the Corvette Technical Information and Judging Manual 5th edition. So is the manual you are talking about different?

[Chris H.]

[Duke W.]

Re: 1966 L72 running hot

Look in the specifications section for the vacuum and centrifugal advance specs. The original L-72 VAC ID is 360 12, but it may not pass the Two-Inch Rule if you have a higher than OE overlap cam.

Search the Web, my name, san diego, corvette, and download and read the tuning seminar to gain some understanding of how to optimize the spark advance map for better performance, lower fuel consumption, and cooler operating temperatures.

Duke

[Joe T.]

Re: 1966 L72 running hot

I have read your article twice. Very informative. I got a vacuum gauge. Had it with some of my tools from the past. At 850 RPM I got 9" and around 2500 RPM I got 18" with full manifold vacuum. I ordered a B28 (4V1053) from Rock Auto. Is that what you recommend with my vacuum readings? So, at idle with the vacuum plugged set the timing at 14 degrees? This should give me around 28 degrees with vacuum connected at idle. Am I going in the right direction?