Does a 30/30 cam produce enough vacuum?

[Rod R.]

[Duke W.]

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

Typical 30-30 cam idle behavior is about 10" @ 900 with about 30+ degrees total idle advance. That would be initial plus full vacuum advance plus maybe a couple degrees centrifugal since it starts at 700. Use an accurate test tach, not the vehicle tach. There will be some lope and vacuum variation, maybe and inch or so.

Any typical automotive test vacuum gage in proper working order should be up to the task. The lower the idle speed the poorer the idle quality, which is why I recommend 900. Assuming the OE carb is installed best idle mixture should be about 1.5 turns out from the seat. Check that the installed VAC is stamped 236 16 or B28. It should start to pull at 4" and be all in at 8". A incorrect or non-functional VAC will result in poor idle quality.

Before conducting the idle speed/mixture adjusting procedure, one should always verify that the ignition system is functioning properly including vacuum and centrifugal advance, and initial timing is in the correct range. On 30-30 cam engines it is very difficult to set initial at "idle speed" because the OE centrifugal starts at 700, and the engine will usually not idle at that speed stably for long enough to get the job done. The best way is to use a dial back timing light and set total WOT advance at 38-40 at a little over 2500 because the OE 24 degrees centrifugal is all in at 2350. Of course, this must be done with the VAC signal line disconnected and plugged.

Also on a 50+ year old car that you haven't owned since new and carefully documented all service and modifications, who knows if it's all OE spec. That's why you should always use a vacuum pump/gage and dial back timing light to verify that the spark advance map actually conforms to OE specs published in service manuals and AMA specs or determine what it is. Most OE spark advance maps can be improved, but the 30-30 cam engines are about perfect as designed, so all you have to do is set the WOT advance as high in the 36-40 range as the engine will tolerate without detonation.

Duke

[Gene M.]

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

Your vacuum question answer is yes. Be sure to check all cylinders for compression pressure once you have valves set. Any valve that slightly leaks will cause false vacuum readings sometimes and be masked at higher RPM. Big overlap cams are lower readings but shouldn’t be as bad as you describe yours is “fast jumping a broad range”. You should get 9-10” steady at idle. Do a bit more investigation work.

[John D.]

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

Rod, The tighter the valve lash the less vacuum you have. I had three customers lasts year running 30-30 cams on their '64-'65 FI's. ALLL three of them had a tight valve lash. Don't remember the numbers. Now I am not an engine rebuilder but have suffered dearly because of the cams.
I told all three the same info. Set the 30-30 like the numbers say. 30-30 cold. All three FI units are running fine at about 900-950 RPM.
365 is same deal.
Story: I had a brand new '65 With a 365 engine. The valve lash must have been looser than 30-30 as the car sounded so mean going thru the Bob's Big Boy car hop. Everyone was looking. I absolutely loved it. It was soo noisy.
But my Dad didn't like it at all. He complained to the Chevy dealer and they reset the valve lash as I wasn't allowed to touch anything under the hood. (but I did). When the valves were tightened up the power dropped. Remember it like yesterday. John

[Rod R.]

[Rod R.]

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

Gene, thanks for you answer on the vacuum. I have compression checked all the cylinders and they are good. I am definitely doing more investigation. Thanks for your response. Rod

[Rod R.]

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

John,

[Mark E.]

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

John,
Interesting stories on the 30/30 cam engines. I set the valve lash (cold) according to the shop manual. This engine does have a great sound, now if I could get it to idle smoothly. I’ll try the 900-950 rpm idle range as you and Duke suggested. Thanks for your response. Rod

Search for a white paper by Hinkley and Duke about adjusting 30/30 cams. It goes through a method to adjust it cold/not running vs. the manual's hot/running. They claim the idle is much better if done this way.
L

[Leif A.]

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

Duke, Thanks for the good info and advice. My VAC is a B1, whatever that means. As you suggested, that VAC could be a problem. I’ll look into finding one of the VACs you suggested. The timing, dwell, and valves are set according to factory specs. I have not checked the WOT advance yet. I have not been able to get a good idle at 800rpm. I will try 900rpm. Thanks again for your help. Rod

Duke likes to call the B1 vac can a "boat anchor". It doesn't start pulling until about 15* and isn't all in until about 18*. If you can get 14*-15* of vacuum at 900-950 RPM steady idle, you need the B26 vac can (NAPA #VC1765). It's all in by 12* and meets Duke's 2" rule for your application.

[Rod R.]

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

Thanks for the tip Mark, I will search for the white paper.
Rod

[Rod R.]

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

Leif,

That is great. Thanks for the B26 part number. I will give it a try.
Rod

[Duke W.]

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

No, No, No! ALL OE SB MECHANICAL LIFTER CAMS NEED A 8" B28 VAC because they only pull 10" (30-30) to 12" (Duntov, LT-1) at a reasonable idle speed. (Read my first post in this thread.) They are getting tough to find, but search for an Airtex 1031V, which should have the B28 ID stamped on the mounting bracket.

You will not achieve acceptable idle quality until you get a B28 installed.

In addition to finding the Hinckley-Williams valve adjustment paper (Sept/08 revision) search my name San Diego 2012 tuning and download my tuning seminar. After studying it you should understand the concept of a "spark advance map" and also understand why SHP engines required a considerably different map than base engines. Both are easy to find on the Web.

Duke

[Leif A.]

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

In the original post, OP states that when he increases engine speed he gets a steady 14" of vacuum. If that's the case, the B26 would be the appropriate can. I guess we need to know (and, I asked) at what RPM is he getting the 14" of vacuum.

[Rod R.]

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

I was getting 14" vacuum at 1500 rpm. The engine would idle at 1000 a little rough. But, it is not a prolonged idle. If I do not work the throttle to keep it running the idle will begin to slow, get more rough and finally stall. Following are some rpm/vacuum numbers:
1000 rpm: 7-10"
1100 rpm: 10-11"
1200 rpm: 10-11"
1300 rpm: 13" w/slight needle vibration
1400 rpm: 13" w/slight needle vibration
1500 rpm: 14" steady
2000 rpm: 17" steady
2500 rpm: 18" steady

Bottom line is when letting off the gas if I don't work the throttle the engine will decelerate to a sub-idle condition, run rough, and stall.
Any more ideas?

[Gene M.]

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

I was getting 14" vacuum at 1500 rpm. The engine would idle at 1000 a little rough. But, it is not a prolonged idle. If I do not work the throttle to keep it running the idle will begin to slow, get more rough and finally stall. Following are some rpm/vacuum numbers:
1000 rpm: 7-10"
1100 rpm: 10-11"
1200 rpm: 10-11"
1300 rpm: 13" w/slight needle vibration
1400 rpm: 13" w/slight needle vibration
1500 rpm: 14" steady
2000 rpm: 17" steady
2500 rpm: 18" steady

Bottom line is when letting off the gas if I don't work the throttle the engine will decelerate to a sub-idle condition, run rough, and stall.
Any more ideas?

It shouldn’t do that. Something is loading up and or vacuum leaking. Should not see the fluctuations at those RPM’s. Check your carb for correct jetting, power valve, air blend passages, float level. Possible leaking seats, and correct setting on transition slots. Warp meter plates and housing should be checked with straight edge. Also the position of the secondary throttle plates is gotta be good. The idle should be a lope but go down to 800-850 no problem. The cam is not that radical. More work and time will sort it out.