Does a 30/30 cam produce enough vacuum?

[Rod R.]

Re: Does a 30/30 cam produce enough vacuum?

[Duke W.]

Re: Does a 30/30 cam produce enough vacuum?

I don't believe a new B28 should have a sleeve, but I see one is there. Is that from the old B1? Your post is not clear on this. Maybe someone else with a recently purchased B28 can verify whether or not the pin has a sleeve.

The B28 should start to pull at about 4" and be at the limit at about 8" with 16 degrees crank advance. You can test the start/stop points with a Mighty Vac before you install, but advance will have to be verified after installation.

If you know a little simple geometry, convert 8 degrees (distributor advance) to radians. (360 deg. = 2pi radians) measure the distance of the pin from the center of the shaft, compute how much the pin should move (radius time angle in radians) for eight dist. degrees and compare against measured pin movement between the limits.

Set total WOT timing at 38-40 (VAC disconnected and plugged). If the centrifugal is OE it's all in at 2350, so you can set a few hundred revs above 2350, but first verify that it is all in at 2350 or if not, when?

Then install the VAC hose and test total cruise advance at the same engine speed. It should be about 16 deg. more - about 54-56 give or take a degree to two.

To install the new VAC, pump down the currently installed B1 with a Mighty Vac to the limit of travel. Remove the VAC mounting screws and carefully wiggle the pin out of the breaker plate. It may take a little finesse.

The pump down the B28, wiggle the pin into the breaker plate and install the screws.

Once installed and connected, go through the idle/speed mixture adjustment procedure with a target idle speed of 900. Use an accurate test tach, not the in-dash tach. Best idle mixture will likely be about 1.5 turns out from the seat assuming an OE or OE equivalent carb.

You may also have to reset the hot fast idle speed to spec.

I'm assuming you have a 1964 Corvette Shop Manual and '64 Supplement that has all the specs and service procedures you need.

Duke

[Rod R.]

Re: Does a 30/30 cam produce enough vacuum?

Yes, I have the '63 Shop Manual and '64 Supplement.

Sorry if I was not clear. My new B28 VAC did not come with a sleeve. The sleeve/bushing you see in the photo on my new B28 was on the old B1 that I removed from my car yesterday. That bushing, was also on the original VAC (236 16) I removed almost 20 years ago. I transferred that sleeve from the original VAC to the B1 I just removed, if my memory serves me correctly. My car was never modified or "messed" with before I owned it. It was all original......I have owned it for over 33 years so my memory is sometime fuzzy on what I have done over the years in the restoration process.

It was challenging to remove the mounting screws from the B1 yesterday because the advance plate would not move when I applied vacuum from my Mighty Vac. So that was quite a revelation! The B1 VAC has not been working because the B1 will not hold a vacuum. That vacuum leak could also be source of my idle problems. My original VAC (236 16), which I have, see below, still holds a vacuum.

To get the mounting screws out I had to use a screw driver to pry the advance plate far enough to access the screws. That was challenging as the B1 spring is very stiff wanting to force the plate back. It took a third hand, my wife, to keep pressure on the advance plate while I removed the screws, without losing them!! What fun old cars are.

Anyway, I am hoping with this new B28 and no vacuum leak at the VAC I can achieve a better idle.

Another question: is there any recommendation as to a good dial-back timing light? My trusty old timing light does not have the dial-back feature.

Rod

[Duke W.]

Re: Does a 30/30 cam produce enough vacuum?

Like the B28, I don't think OE or replacement 236 16 VACs had a limit bushing, so I suggest you install the B28 without the bushing and check total vacuum advance on the car which should be about 16 degrees.

I have an older Acton dial-back timing light. I has a knob to set advance, which has too little friction, which can cause inadvertent changes and the cord falls off easily when moving it around.

Newer models have digital readouts and also show revs, which is a nice feature. Others may be able to offer specific make/model recommendations.

No doubt the leaky B1 was an issue in addition to the B1 specs not being suitable to the 30-30 cam. I'm sure the engine will run as it should when you get the ignition system issues solved and set up correctly.

Duke

[Leif A.]

Re: Does a 30/30 cam produce enough vacuum?

Rod,
I bought one of these about four years ago...love it.

https://www.amazon.com/INNOVA-3568-D...000EVU8J8?th=1

[Rod R.]

Re: Does a 30/30 cam produce enough vacuum?

Duke, I agree about installing the B28 without the bushing which I plan to do.

Upon close inspection of my OE VAC, it looks like the VAC did not have a bushing installed as there is corrosion where the bushing would have been. It has been at least 20 years since I replaced the original and cannot remember. I probably installed the bushing on the B1 based on a recommendation in a small-block rebuild book.

Thanks for the feedback on the dial-back timing light. I have read reviews about the loose friction dials as you reported.

Thanks for your help.

Rod

[Rod R.]

Re: Does a 30/30 cam produce enough vacuum?

Leif,

Have you used the dial-back (retard) feature on your timing light? It looks like a nice timing light with good reviews. Thanks for the link.

Rod

[Leif A.]

Re: Does a 30/30 cam produce enough vacuum?

Leif,

Have you used the dial-back (retard) feature on your timing light? It looks like a nice timing light with good reviews. Thanks for the link.

Rod

Rod,
I have used it several times and it, truly, is a very nice unit. Very accurate and very easy to use.

[Rod R.]

Re: Does a 30/30 cam produce enough vacuum?

Thanks Leif. Sounds good to me. I will be ordering one. I appreciate your help.

Rod