W Guy

I'm trying to do some fine tuning and needed to get a different vacuum can for my 327 250hp engine with P/G. I tried ordering the following cans from NAPA and they all turned out to be for a 6cyl distributor:
VC1415
VC1420
VC1805

Since nearly everyone on the planet has a copy of his paper, I thought I'd post this information. It's possible that NAPA has changed their products under the same numbers that were complied originally, but if you order these numbers today, you'll get a 6cyl can.

Also, these numbers are no longer available through NAPA
VC1810 (everyone knows that already because they want the B28 can)
VC1675 (B13)
VC1801 (B21)
VC1650 (B12)
VC1725 (B18)
VC1804 (B24)
VC1807 (B25)
VC1812 (B30)

Verne

Powershift

Verne:

Thanks for the updates. Lars is still around, so you might want to send him an email with this info. I know he has updated his tech paper at least once, so it may already have this info in the latest version.

But I would contact him anyway. AFAIK his email address has not changed. It should be in the archives, or I can dig thru my files and get it for you.



Larry

Dr L-88

Lars' email:


V8FastCars@msn.com

W Guy

Thanks,
I just copied the post and sent it to him. Not trying to step on any toes here - just offering my latest experience.

I’m also trying to create a spreadsheet with the other retailers’ part numbers as a cross reference but it’s tough going. I don’t trust the auto parts stores “this replaces that” lists.

Verne

plaidside

Verne,
I have a small spread sheet that I made with the three most popular advances that I use.
It has the specs, NAPA and Standard Ignition's part numbers.
Send me your email and I will send you a copy.
Jo

QIK59

Why are you needing / looking for vac cans that have such low advance starting specs ?

Unless you are trying to run very little mechanical advance ?

A mild motor 250/300 hp 327 usually produces much higher vacuum.

W Guy

The car has a P/G trans. With it in gear at 600rpm I get 17"Hg. My current vac can still pulls advance up to 17"Hg. Therefore I was looking for a 10deg can (20deg crank) that was all in by 15"Hg. Or an 8deg can by 15"Hg and I can pull back the initial by 2deg. (which would also yield lower vacuum). I'm stuck on the edge.
Since I can't find the can I need, I'll probably just put a limiter bushing on the can rod. Stick shift cars make it easy but autos add another level, and autos with A/C add even another level to be concerned with. Each option creates a lower idle (and vacuum).

Verne

QIK59

You are trying to Mickey Mouse around the best / most effective and LOGICAL solution : a 10 degree vacuum advance stop.

I measured length of advance travel / slot , calculated length required and welded piece in vac can slot to act as a stop - simple and effective.

Lars now makes and sells vacuum advance stop plates for those who can't readily perform above solution.

As long as you're pulling ample vacuum (such as you are) : stick or auto, A/C yada yada doesn't make any difference !

lars

Please don't use or download versions of the Tuning Papers you find on the Internet. People posting the papers do not update them, and many of the papers are actually altered as well as outdated and obsolete. I update the papers as new info becomes available, and most of the issues you noted in the original posting above had been incorporated into changes made to the papers in the past several years.

Very few vacuum advance control units are limited to 10-12 degrees of vacuum advance. Testing done by Henry Olson and me during dyno testing and using an OTC 5-gas analyzer shows that current pump gas will not allow use of more than 12 degrees of vacuum advance if running the normally-recognized optimum 36-degree total mechanical timing curve. The key, then, is to find a vacuum advance control unit that meets your vacuum requirements (ref. "The 2-inch Rule" as outlined by Duke Williams), and then limit that control unit to 10-12 degrees of advance by welding the slot or by using the Vacuum Advance Corrector that Henry and I are offering.

Contact me, Henry, Duke or John Z if you need detailed info on this.

Lars

SWCDuke

[QUOTE=W Guy;1592949009]The car has a P/G trans. With it in gear at 600rpm I get 17"Hg. My current vac can still pulls advance up to 17"Hg. Therefore I was looking for a 10deg can (20deg crank) that was all in by 15

It should idle okay at 450-500 in Drive, but with less vacuum. If you want to keep the idle in Drive at 600 you need a B22 VAC, NAPA/Echlin VC1802, which is 0 @ 8", 16 @ 15".

I don't know where you came up with the idea for a 20 degree VAC. The '63-'64 OE 201 15 VAC specs for the 250/300 HP engines are 0 @ 8", 15 @ 15.5", but you didn't say your model year. In '65 GM did increase vacuum advance to 20 or 24 degrees for these engines, but that was a mistake and a TSB was written to go back to the previous 15 deg. VAC.

Try the lowering the idle speed in Drive, If you can live with it and vacuum drops below 14", install a 12" B26, VC1765. My recommendation for idle speed is "as low as possible commensurate with acceptable idle quality", so it's an individual choice.

If you have AC the compressor should be engaged when you measure vacuum/idle speed in Drive, and that reading should be used with the Two-Inch Rule to select a functionally correct VAC.

Congratulations for properly specifying idle behavior (It's a rare occurrence)- vacuum @ idle speed in Drive. Most guys just state a vacuum reading without stating the idle speed, or whether it's a manual (idling in Neutral) or an automatic (idling in Drive).

Without specifying the full context of idle vacuum data the number is meaningless!

What's the model year and number stamped on the installed VAC?

Duke

W Guy

Duke,
I appreciate your comments. You are correct; I should have had the A/C turned on (in gear) when I did my checks. I've tried to set the idle as low as possible and still be acceptable with it in gear and A/C on. I can set it lower without any hiccups but it starts to make "growling" sounds like it's laboring.
Unfortunately I didn't write sown the numbers on the original can and now I don't have access to the car. It's a '63 250hp.
Here are the numbers I got using a dial-back light:
Dwell was set right at 30deg before I started.
Vac adv:
start: 2deg @ 9"Hg
8deg @ 12"Hg
17deg @ 16"Hg
20deg @ 17"Hg
(I subtracted the 8deg initial)

Centrif Adv
11deg @ 800rpm
16deg @ 1600rpm
23deg @ 2000rpm
26deg @ 2600rpm (all in)

As I was increasing the rpm, the advance seemed to stall, then jump higher, so I know the distributor needs some maintenance. It would appear that the point plate has a bind or restriction somewhere in its travel. I'll check the weights too to make sure they move freely.

So right now I'm at 8deg initial + 26deg centrif = 34deg plus 20deg vac = 54deg. Just right or too much?

BTW, I'm pretty sure I know what I'm doing so the Mickey Mouse comment wasn't appreciated. (not you)

Verne

PS: With a full throttle stab (from a loaded up torque converter) it has a bad hesitation. I know the carb is right on the money.

QIK59

Fyi

W Guy

I noticed that in Lars' original paper, he recommended a max of 54deg but his recent paper (which he just sent to me) suggests a max of 46-48deg due to today's pump gas.
Remember that the 20deg of vac adv I posted is crankshaft degrees. That is 10deg dist adv. If you're suggesting a max of 10deg vac adv at the crank, then I'd need a can rated at 5deg and there are none available. To achieve the recommended 46deg max, I'd need to limit my centrifugal advance.
Also, to meet the two inch rule, I still need to find another VAC.

Verne

QIK59

Now you are starting to get it / understand !

Trying to find something that is virtually non-existant (5 degree can) or trying to compensate by changing initial or mechanical advance (from optimum values) IS Mickey Mousing around.

If you have a distributor machine (I do), a lot of weights, springs, and shafts and a LOT of time it might be possible to compensate for an incorrect vacuum advance.

Most effective way to deal with the vacuum over advance is a stop of some sort.

SWCDuke

It's real simple. With the engine idling in Drive and the AC compressor engaged, measure manifold vacuum and apply the Two-Inch Rule. Set the idle at the above conditions at the lowest you find acceptable and optimize the mixture. I don't know what you mean by "growling" - maybe it's the compressor - whatever, but I wouldn't worry about it for now.

The result will be either a 15" B22 or a 12" B26, and my guess is the latter, so maybe you should just buy one and install. They cost less than ten bucks. Both provide 16 max advance.

Your centrifugal curve has been quickened from OE, which is 24 @ 4600. The quicker curve is better, but it might be a little too quick, especially the 11 @ 800. It shouldn't start until 600-700 minimum. That's the first thing you need to correct before proceeding.

I have had no problem setting up aggressive centrifugal curves recently on a '65 L-76 and L-79 - both are running 39 total WOT advance with quick curves and a B28 and B26 VAC, respectively, so total cruise advance is 55! Neither exhibits any detonation, but we know the CR is lower than OE because they both have thick head gaskets. (The OE gasket was .018") Both owners are very pleased with how the engine run, and I was very pleased with my test drive.

Has your distributor ever had a blueprint overhaul? My bet is that it never has, so that's the place to start. If the shaft has any noticeable side play the bushings will need to be replaced, and that's best left to someone experienced in that procedure.

Then you can do the rest including shimming up the end play to the .002-.005" spec and verifying that the breaker plate fits snug over the housing and doesn't wobble. Bubba has obviously been in there, and trying to put bandaids on his damage won't work. You need to go back and start from scratch. See your '63 Shop Manual.

The distributor is the most overlooked component on old cars, but a properly functioning distributor with an optimized spark advance map is essential to achieve best performance and fuel economy. The difference can be amazing.

Duke

jerry gollnick

I've searched site, what is 2" rule?

SWCDuke

Search for threads started by me and download the pdf of my NCRS tuning seminar. (OP should do the same and anyone else who wants to learn how to set up an optimized spark advance map for any engine configuration.)

As a fellow UW ERC grad I will appreciate feedback.

Duke

W Guy

Thanks Duke,
I already have a copy of your paper and I understand it.

Now, I'll get back to Mickey Mousing around.

SWCDuke

You don't need Mickey to help out.

In the tuning seminar I discuss the 300 HP spark advance map and how it changed from '62 to '67, and this also applies to the 250 HP engine when it was base.

I've remapped several 300 HP engines, too. It's best to have the '66-'67 30 degrees of centrifugal, but bring it in quicker with lighter springs. If you do overhaul your distributor you can grind out the slot to allow a few more degrees centrifugal. That way you need less initial timing to achieve the optimum range of 36-40 at WOT and total idle advance with be in the ideal low to mid-twenties range for the 250/300 HP engines.

You don't really need a distributor testing machine, but it's nice if the guy next door has one. A distributor machine doesn't guarantee good results. You need to know the optimal specs for the engine configuration - or at least something close first - then you can set it up on the car or on a machine, if convenient.

I give baseline starting points for all OE configurations and guidance on how to setup something non-OE like if you have an aftermarket cam. If you can get close to them you are 99 percent there, and if you want to buy an hour of chassis dyno time and have a good test plan, you might be able to achieve a marginal improvement.

Duke

lars

If you drop me an e-mail request for the vacuum advance paper, it has Duke's entire narrative on the concept. I'll be glad to forward to you.

Lars
V8FastCars@msn.com