Don Terrill’s Speed-Talk

Approximately 16° initial wIth 16° centrifugal advance for your app,, most GM HEI distributors need modification to make that happen,,, (think 7000 rpm distubitor tester or verify on dyno) all in by 3400 if the springs are to week your idle will be compromised when the advance doesn't return to the initial setting, make sure the idle timing is consistent. Crane vacuum adv canister has good instructions in the box for set up,,,read them. MSD Pro billet HEI has nice centrifugal setup easy to make adjustments a bit pricey though.

Just my .02$

Belgian1979 wrote:

Walter R. Malik wrote:If it is not simply a race engine, then take the time to get it right and you will have a big smile while driving.

Agreed, but outside a dyno there is no much you can do than guess.

You don't NEED a dyno; as a matter of fact, a dyno does not tell you much about part throttle transients and manners.

Drive it for a couple days then change it ... drive it for a couple more days and change it again ... keep on doing this until you get it to where you like it and it doesn't detonate.

Firedome,
The Crane VA instructions are next to useless for modified engines. They do not take into account idle vacuum. This is the No.1 cause for the statement: 'Man vac adv didn't work on my engine.' If using MVA, timing needs to be steady at idle, especially with auto trans cars, & Crane instructions make no allowance for this. Great product let down by poor instructions....

Geoff2 wrote:Firedome,
The Crane VA instructions are next to useless for modified engines. They do not take into account idle vacuum. This is the No.1 cause for the statement: 'Man vac adv didn't work on my engine.' If using MVA, timing needs to be steady at idle, especially with auto trans cars, & Crane instructions make no allowance for this. Great product let down by poor instructions....

I'll review,,,,,always willing to learn thanks..

Geoff2 wrote:Firedome,
The Crane VA instructions are next to useless for modified engines. They do not take into account idle vacuum. This is the No.1 cause for the statement: 'Man vac adv didn't work on my engine.' If using MVA, timing needs to be steady at idle, especially with auto trans cars, & Crane instructions make no allowance for this. Great product let down by poor instructions....

This is the point I was trying to make. It apparently didn't come out right.

My Mercedes runs up to and over 60° timing advance when vacuum is high while driving, I haven't really checked it idling. Stabbing it with the throttle puts it at twenty something degrees under high load conditions. That's a relatively recent design multivalve v8.

Walter R. Malik wrote:If it is not simply a race engine, then take the time to get it right and you will have a big smile while driving.

Belgian1979 wrote:Agreed, but outside a dyno there is no much you can do than guess.

I had the mentality of ditching vacuum advance for a LONG time until I read one of David Vizard's books, I believe it was his second BBC book. In the chapter where he addresses ignition he completely smashed everything I ever thought about running vacuum advance with a nasty BBC equipped with long duration and tight LSA. In short, what I got from it is that vacuum advance will be beneficial to ANY engine, regardless of its performance level, if it's ever driven on the street. It seems the only time when it would be ok to ditch the vacuum advance would be on a trailer queen race engine (like you specified Walter) that only sees idle and WOT.

Gonna revive this thread as I have a project in the works that is relevant to vacuum advance tuning. My question is concerning adjustable vacuum units, Is there a difference between say the Crane unit v an Accel? Do they both accomplish the same thing? Do I understand correctly that they adjust the start up vacuum point and say the "all in" point. Thanks.

Hrdlx62 wrote:Gonna revive this thread as I have a project in the works that is relevant to vacuum advance tuning. My question is concerning adjustable vacuum units, Is there a difference between say the Crane unit v an Accel? Do they both accomplish the same thing? Do I understand correctly that they adjust the start up vacuum point and say the "all in" point. Thanks.

Crane units set how much by a adj. stop ,,and diaphragm spring by a Allen wrench.

We use a vacuum advance corrector - limiter we had made for us (since my welding skills are not all that good) to limit the travel of a General Motors point style vacuum advance unit to 0.120 total travel which limits the amount of vacuum based spark advance to 10-12 crankshaft degrees of advance. This 10-12 degrees of advance from the vacuum is what works best for us on an engine that has had the mechanical advance optimized for the needs of the engine. FYI, Standard Hygrade offers a part # VC302 vacuum advance for use with a HEI style distributor that has 10 crankshaft degrees that is all in by about 8 to 10 inches of vacuum.

Henry @ ole's carb

Favorite arguments against use of vacuum advance:
"I have no idea what it does"
"I don't know how to adjust it"
"It's just one more thing to go wrong"

Speaking of vacuum cans, it should be noted that cans for GM HEI and for older small diameter ones will bolt up to either type distributor, but an HEI unit will over-advance on a small diameter distributor and vice-versa.

olescarb wrote:We use a vacuum advance corrector - limiter we had made for us (since my welding skills are not all that good) to limit the travel of a General Motors point style vacuum advance unit to 0.120 total travel which limits the amount of vacuum based spark advance to 10-12 crankshaft degrees of advance. This 10-12 degrees of advance from the vacuum is what works best for us on an engine that has had the mechanical advance optimized for the needs of the engine. FYI, Standard Hygrade offers a part # VC302 vacuum advance for use with a HEI style distributor that has 10 crankshaft degrees that is all in by about 8 to 10 inches of vacuum.

Henry @ ole's carb

Sounds alot like the old solid lifter BBC vacuum cans of the past..

Hrd,

Simple answer to your question: yes there IS a difference between the Crane & other adj units. Some of them, I believe Accel & Mr. Gasket, have a spacer fitted inside the spring. With this USELESS design, it is possible to wind up the spring [ the Allen Key adjustment {AK} ] so that the unit locks up! Fixed, solid, does nothing, adds no vac adv!

The Crane is the best unit to get because it comes with the notched plate. The NP plate adjusts the TOTAL amount of vac adv added; the AK adjusts the spring tension which controls the RATE at which vac adv drops away. Once an engine is modified beyond stock, it is a waste of time trying to use a stock, non-adj vac adv unit because you will never get the best adjustment that is only possible with adjustable units.

We tend to avoid the adjustable vacuum advance units because for us either the adjustment moves on its own over time or the customer has gotten under the hood and adjusted it (even though he doesn't own a allen wrench).

the 2 points style vacuum advance units we use most are:

the old AC-delco d1312c (still sold by WELLS as # DV1810) marked B28 which starts advancing at 3-5 inches of vacuum and is fully advanced at about 6-8 inches of vacuum

or for a mild cam engine (if you are using manifold vacuum for the advance) Standard Hygrade # VC181 that is the equivalent of a B26 unit which starts advancing at 5-7 inches of vacuum and is fully advanced at 12 to 15 inches of vacuum. A clone of this unit is what comes in most of the MSD distributors that use a vacuum advance (other than their HEI distributors), we then use a limiter plate to limit the advance to 10-12 degrees of advance on both the B26 and B28 units.





Henry @ Ole's carb