Does a 30/30 cam produce enough vacuum?

[John D.]

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

Rod, Duke and others are 100% correct on the worthless B1 vacuum advance. GM is to blame for this as this what you got over the counter for a replacement 63 vacuum advance.
I royally goofed in old days. Bought a couple of dozen of them and was too dumb to know that B1 has the worlds strongest VA spring. I think I may have a couple around here yet.

Today someone asked me for the part number for the B28 from NAPA. And so I gave him the part number as he is my pal and like to tease him. But NAPA does not have it anymore (I think) VC-1810. Hope the VC is right. Anyhow a cheap place to buy it is Rock Auto. Duke mentioned a place also.

If anyone wants the real deal 236 16 VA Don Baker reproduces them They are dead nuts. John

[Rod R.]

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

John, thanks for the tip. I will try to find a correct vacuum advance. It will be a good start and go from there. I like Rock Auto, good prices and fast service. I checked with them and they only have the B1 VA.

I am not familiar with Don Baker. Do you have a contact number or link for him? Thanks for your help. Rod

[Rod R.]

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

Definitely more work and time to figure this out. Good ideas, some I have checked and others yet to do. Thanks, Rod

[Duke W.]

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?

That's what happens with a VAC and doesn't pass the Two-Inch Rule.

Duke

[Duke W.]

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

In a previous post I listed the Airtex number for a 8" B28 VAC, but it was WRONG!

It's Airtex 4V1053. Search that. Don't get picky about what retailer you buy from. AFAIK Airtex is the only brand that still has B28s, which have been out of production for several years, and they are getting very scarce. All the vintage VACs are manufactured by Standard Motor Products, but are available in many "brands" including Delco. It's the same part - just a different box and marketing channel. This applies to most vintage ignition, starter, and alternator parts.

The VAC is worth 3 points in Flight judging - two for originality and one for condition. If I see a B-number VAC when judging mechanical at chapter meets, I take away one point (OE replacement), and they usually get the condition point because the installed VAC is fairly new. These VACs can be bought for about ten bucks. I don't know what Don Baker charges for his repro 236 16, but the choice is your call.

Duke

[Rod R.]

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

Duke, thanks for the part number correction. I searched on line and found several vendors selling the Airtex 4V1053. Interesting, the vendors compatibility chart for the VAC indicated the 4V1053 is for 1973 Chevrolet's with 2bbl carbs. I guess our old 30/30 engines have dropped off the radar.

I ordered the VAC today. The correct VAC will be a start in achieving a good idle. There might be something else going on with the engine but at least the VAC variable will be eliminated once it is installed.

You mentioned in your other reply today about the "Two-Inch Rule." What is that rule? Thanks.

Rod

[Gene M.]

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

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The VAC is worth 3 points in Flight judging - two for originality and one for condition. If I see a B-number VAC when judging mechanical at chapter meets, I take away one point (OE replacement), and they usually get the condition point because the installed VAC is fairly new. These VACs can be bought for about ten bucks. I don't know what Don Baker charges for his repro 236 16, but the choice is your call.

Duke

The difference in the replacement is not even close to the original. First of all the configuration of the drawn metal is total different around the nipple face. Originals are flat not dished. The stamped part markings are total wrong. The plating is clear chromate treated that the original is just plain zinc. A knowledgeable experienced judge should not overlook these decisive totally different departures from typical factory original. Being not even a GM part it s/b a total deduct. Not the end of the world for incorrect part.

[Duke W.]

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

You mentioned in your other reply today about the "Two-Inch Rule." What is that rule? Thanks.

Rod

Search Duke Williams San Diego 2012 Corvette tuning. The answer is in the pdf of the PowerPoint presentation. After studying it you should understand the concept of a "spark advance map", why SHP engines need a significantly different map than base engines, and you should be sufficiently educated to design a spark advance map for any engine.

Be sure the Airtex 4V1053 is stamped B28, and test that the link begins to pull at about 4" and is at the limit at 8".

Duke

[Duke W.]

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

The difference in the replacement is not even close to the original. First of all the configuration of the drawn metal is total different around the nipple face. Originals are flat not dished. The stamped part markings are total wrong. The plating is clear chromate treated that the original is just plain zinc. A knowledgeable experienced judge should not overlook these decisive totally different departures from typical factory original. Being not even a GM part it s/b a total deduct. Not the end of the world for incorrect part.

It's only a total duct if there is no VAC, when the distributor should have one. Lots of OE replacement parts are not made by GM. Buy a "Delco" OE replacement VAC and it will be stamped with a B-number because it's the same part as Airtex, Niehoff, Standard, etc.

If you took full deduction for every functionally correct OE replacement or reproduction part, there would be very few Top Flight cars. That's why there are points for both originality and condition. So taking one point for a B-number VAC is a 50 percent deduction, but since it's not greater than 50 percent it gets the condition point as long as it looks fairly new.

Duke

[George J.]

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

Rod,
as Duke stated previously, don't use the tach in the car for taking these measurements. Mine is a couple hundred rpm high at idle. That makes all the difference. Also, you can turn the idle up to 1000 or even higher. Some engines like a slightly higher idle. Don't stress about 100 to 200 rpms. I think I remember somewhere that the tuning specs said "at least 900" for the FI cars.

[Rod R.]

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

Duke, found your presentation. Looking forward to studying the information, thanks. Rod

[Gene M.]

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

It's only a total duct if there is no VAC, when the distributor should have one. Lots of OE replacement parts are not made by GM. Buy a "Delco" OE replacement VAC and it will be stamped with a B-number because it's the same part as Airtex, Niehoff, Standard, etc.

If you took full deduction for every functionally correct OE replacement or reproduction part, there would be very few Top Flight cars. That's why there are points for both originality and condition. So taking one point for a B-number VAC is a 50 percent deduction, but since it's not greater than 50 percent it gets the condition point as long as it looks fairly new.

Duke

Being you have very little experience flight judging, more training and exposure such as observer judging would aid you in making a correct evulation to determine point deduction of incorrect parts. Missing part is not the only situation that denotes a total deduction. More familiarity with the judging reference manual and the CDCIF system is warranted. One can seek the judges training opertunities that NCRS offers.

[Rod R.]

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

George, I have an electronic tach/engine analyzer I always use. I noticed my car's tach is also off at least 100 rpm compared to the electronic tach. 1000 rpm is OK with me if it will maintain that idle. Hopefully, when I install the correct VAC there will be an improvement. If not, then at least one variable will have been addressed. Thanks, for your input. Rod

[Ralph S.]

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

Duke, Which VAC can would you suggest for a 1969 435hp Turbo-Hydramatic With 3:36 axle ratio it was always a dog off the line till the rev's came up.

[Duke W.]

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

The VAC doesn't have any effect on low end torque because if you open the throttle even halfway at low revs manifold vacuum drops enough to eliminate vacuum advance, but there are other issues with the VAC.

L-71 with a manual trans idle behavior is about 14" @ 900, so a 12" B26 passes the Two-Inch Rule. All L-71s have ported vacuum advance, so they should be converted to full time in addition to installing a proper VAC that passes the Two-Inch Rule.

I don't have any data on L-71 idle behavior with an automatic, so you will have to measure manifold vacuum idling in DRIVE, and apply The Rule to determine if a B26 is adequate. If it doesn't pass The Rule, you will need to install a 8" B28. I'd appreciate if you post the results.

After converting to full time vacuum advance with a functionally correct VAC you will need to go through the idle speed/mixture adjustment procedure and adjust the fast idle speed. Both will increase several hundred revs due to the increased idle advance because the engine is operating more efficiently.

Since your engine is emission controlled, the centrifugal advance is probably lazy. Specs are in your CSM and AMA specs. Lighter springs that bring centrifugal advance in quicker will improve low end torque. Also initial timing should be increased to achieve total WOT advance of 36-40, as high in the range as the engine will tolerate without detonation.

The best approach is to increase initial timing first, then try lighter springs.

You should also read my tuning seminar so you understand the reasons behind the changes I recommend.

Duke