Just installed a MSD 6AL.
Before installation, I was just running the MSD 8360 dist and a Blaster SS coil.
Now the engine is running very rich with the 6AL. I never touched the timing.
MSD folks are telling me I need to add some advance. :confused:

Why would that be? Would a multiple spark cause me to need more advance?
It is acting like it is retarded a bit.

(currently don't have a way to check timing. No timing tab. Can't find one to fit my mystery polished aluminum timing cover with the recessed allen cap screws, the Mr. Gasket timing tabs don't fit)
Before I changed the starter out, I used to just advance the timing till the starter labored a bit, then back it off and leave it. All was fine. But now I have this starter that is much much stronger. I'm not sure my old way of doing that will work now.
I'm still looking for something to give me a timing mark but in the mean time, why would adding an ignition box cause me to need more timing?

Thanks,

You need to know where TDC is. Nothing you do to tune your engine will be beneficial until you have a proper reference.
There. I said it. OK, is your timing cover that two piece unit from Summit? Just wondering because I found a timing tab on Summits web site just for that cover. I can send you a link if yours is the same. It wasn't available when I installed it two years ago.
Now, let's get you timed. Get a screw-in piston stop and find TDC. Place a mark on your cover for reference. Anything visible will do. I used a dollop of hugger orange paint. Hey, it matches the car. The amount of timing is determined with a Mr. Gasket harmonic balancer timing tape. And more orange paint at each 10° mark for a backup in case the tape fails.
When I place my next order with Summit, the timing tab will be included.
Edit; This just in. Summit just called about another back order. They are sending the timing tab and waving the shipping charge. Those guys are great.
http://www.summitracing.com/parts/SUM-G6316-8/

Why would that be? Would a multiple spark cause me to need more advance?
It is acting like it is retarded a bit.
why would adding an ignition box cause me to need more timing?


..because the timing was (probably) somewhat off to begin with, and now (in the lower RPM range) it's firing that second or third shot as the piston is stroking down, which calls for advance. setting the timing by ear or turning the dizzy til she runs best will work, don't get me wrong, but as we improve and upgrade items in the system, so does the requirement for accuracy of the adjustments. I'm surprised to see your complaint isn't "it's running hot" now....
you need a good timing light (I really like my dial-back) and definitely references on the cover and balancer. anything less, and you'll be chasing this from now-on.
take it from one who has been almost 4 years learning a hard lesson in timing and overheat issues, and I'm wayyy from graduating. :o

(Fred)
* Summit, along with everyone else, is hungry ,, and they want our business !
I ordered a thermal fan switch yesterday (regular freight) and got it today !
it's been that way for the last several orders.

You know, some of you guys really bring up my common sense factor. Why didn't I think of using paint as a marker after finding TDC?
And for that matter, paint on the balancer to back up the timing tape. I can relate to that because I put a MSD timing tape on mine and it came off almost immediately.

Now:
I did have a TDC indicator from Eastwood I think, that screwed into the spark plug hole. Only thing, it looked to me like it was going to bind in itself because it seemed like the thing would be at too much of an angle from the way the piston came in in relation to the angle of the sparkplug threads.
So got rid of it.
I can't really put a wrench on the center bolt, too many things in the way. So I'd need to bump the starter to bring it around.

That being said, what do you guys recommend for a tool to find TDC?

I have a neat little tool that whistles when its coming up on the compression stroke but its not all that accurate for finding exact TDC.

..because the timing was (probably) somewhat off to begin with, and now (in the lower RPM range) it's firing that second or third shot as the piston is stroking down, which calls for advance.

OK so help me with some theory....
Since its getting 2 more sparks, there is now fuel getting burned that wasn't before right?
And since the last spark is when the piston is stroking downwards, I thought that since its AFTER the compression stroke and the piston is heading downwards isn't that spark happening AFTER TDC? Now is that too much advance?
Or does the term 'advance' mean to happen advance of TDC or BEFORE TDC? Advancing the spark to happen sooner. (?)
I'm all confused now. Could you help me to understand this properly?
:o

Mike, forget all those sparks. They only insure that a short duration capacitive discharge spark has a chance of igniting the fuel air mixture. After 3,000 rpm or so, there is no time for the box to fire that many times (I forget how many times these MSD's 'multiple') so they revert to single sparks and work just fine.
Just remember that after the first spark successfully ignites the mixture, THE REST OF THE SPARKS DO NOTHING.
You set your timing normally with the light telling you when the first spark arrives. At idle you want about 10-12° (depending) BEFORE TOP DEAD CENTER. Simple. Just play with it. Not rocket science. Well, yes it is. Ever see the space shuttle engines ignite? That's one hell of an ignition system!

Fred's right; keep it simple and don't get confused.. there's much info on this on down in the Forum, and other places on the 'net.
but just for the record:
advance fires just BEFORE TDC, and retarded fires AFTER TDC.
too much advance lights the fire too soon before the piston tops-out, thus detonation, pinging, etc.
too much retarded lights the fire too late after the piston has topped-out, resulting in wasted fuel, low power, heat, and possible burnt valves.

you could also have a bad new MSD box. there seems to be a lot of discussion lately along those lines.

Fred's right; keep it simple and don't get confused.. there's much info on this on down in the Forum, and other places on the 'net.
but just for the record:
advance fires just BEFORE TDC, and retarded fires AFTER TDC.
too much advance lights the fire too soon before the piston tops-out, thus detonation, pinging, etc.
too much retarded lights the fire too late after the piston has topped-out, resulting in wasted fuel, low power, heat, and possible burnt valves.

you could also have a bad new MSD box. there seems to be a lot of discussion lately along those lines.


Why do people tell me that I'll get a little better performance with more advance or as its been put to me, as much advance as I can get?

Also, how do I know if my box is bad?

Why do people tell me that I'll get a little better performance with more advance or as its been put to me, as much advance as I can get?

Also, how do I know if my box is bad?
Answer=time. More advance = more time for the fuel-air mixture to burn INSIDE the combustion chamber to make more power pushing the piston down instead of being expelled to the exhaust port. Now that's simple.;) Not like that real rocket science.

The test for a bad MSD box is in their instruction sheet. It involves touching the white wire to ground. You'll find it with their paperwork or on line.

Answer=time. More advance = more time for the fuel-air mixture to burn INSIDE the combustion chamber to make more power pushing the piston down instead of being expelled to the exhaust port. Now that's simple.;) Not like that real rocket science.

The test for a bad MSD box is in their instruction sheet. It involves touching the white wire to ground. You'll find it with their paperwork or on line.

So the more advanced the timing the sooner it happens BTDC? So if it was REALLY advanced, it would be sparking as the piston is still coming up the compression stroke? Or am I wrong?

Mike it's called timing for just that reason... Not enough or too much will both equally impact how your engine runs. I think you understand TDC and the 4 strokes (intake, compression, power and exhaust) of a piston. Think of the power stroke and pushing a child on a swing. If you push the swing and don't step back to prepare for the next push the swing is going to clobber you as it returns because you are before top dead center or too advanced. Now you step back and get ready for the swing but as you are getting ready to push the swing again you get distracted and have to rush forward to catch the swing if you want to push it. You are now retarded and way after top dead center and the swing doesn't pick up any speed from your push. If you are paying attention, stepping back and catching the swing at the right moment all your effort is rewarded and the kid in the swing gets a big boost and goes higher than ever... That's timing, you are the spark and the swing is the piston.

Every engine is a bit different, compression, cam, rod length etc. This effects what proper timing should be. As well as the load on an engine changes and the rpm increases the timing is going to need to change. The time it takes the spark to get from the coil to the dist and then on to the plug is consistant. How fast the piston gets to TDC depends on the engines RPM. In a drag strip application where WOT is all that matters it's common to set and lock out the timing curve. For street use it's important to have the timing change to meet the conditions set. The first thing is to find what total timing your engine likes at WOT and find out what rpm it likes to be all in at. Then you need to figure out how much timing your engine wants at idle so it doesn't generate heat, diesel when you shut it off and over comes the lump of the cam and holds a steady idle. The mechanical curve is then either brought on faster or slower depending on the engines needs using heavy or light springs as resistance. Last you toss in the ability to turn on and off some more timing using the engines vacuum with vacuum advance. This will benefit you when cruising at hwy speeds and is another way of making sure the engine gets the spark at the proper time.

Mike it's called timing for just that reason... Not enough or too much will both equally impact how your engine runs. I think you understand TDC and the 4 strokes (intake, compression, power and exhaust) of a piston. Think of the power stroke and pushing a child on a swing. If you push the swing and don't step back to prepare for the next push the swing is going to clobber you as it returns because you are before top dead center or too advanced. Now you step back and get ready for the swing but as you are getting ready to push the swing again you get distracted and have to rush forward to catch the swing if you want to push it. You are now retarded and way after top dead center and the swing doesn't pick up any speed from your push. If you are paying attention, stepping back and catching the swing at the right moment all your effort is rewarded and the kid in the swing gets a big boost and goes higher than ever... That's timing, you are the spark and the swing is the piston.

Every engine is a bit different, compression, cam, rod length etc. This effects what proper timing should be. As well as the load on an engine changes and the rpm increases the timing is going to need to change. The time it takes the spark to get from the coil to the dist and then on to the plug is consistant. How fast the piston gets to TDC depends on the engines RPM. In a drag strip application where WOT is all that matters it's common to set and lock out the timing curve. For street use it's important to have the timing change to meet the conditions set. The first thing is to find what total timing your engine likes at WOT and find out what rpm it likes to be all in at. Then you need to figure out how much timing your engine wants at idle so it doesn't generate heat, diesel when you shut it off and over comes the lump of the cam and holds a steady idle. The mechanical curve is then either brought on faster or slower depending on the engines needs using heavy or light springs as resistance. Last you toss in the ability to turn on and off some more timing using the engines vacuum with vacuum advance. This will benefit you when cruising at hwy speeds and is another way of making sure the engine gets the spark at the proper time.


Thank you.
I needed that explanation.

Now somemore questions,

How can I adjust initial timing and not effect total timing or can that be done?

How do I figure out what total timing my engine likes under a load at WOT? Can that be done without knowing the cam specs?

Thanks for all the info so far....

Originally Posted by mkpatrick
Why do people tell me that I'll get a little better performance with more advance or as its been put to me, as much advance as I can get?

Because they still believe the old timers" who through some meraclious instinct that doesnt exist, could time an engine by ear.

As an engine gets over advanced, it has a slightly different sound, get a bit deeper....a sound ppl like, and gives the impression when driving there is more power, when in fact the power hasnt changed significantly ....the NOx gas levels increase also....
Eventully its starts to detonate auditably...but detonation starts well before it ever become auditable.
When one retards, the power/economy drops of real fast in a couple degs, when advanced drops off slow over 10 or 15 degs and is not noticed.
Generally find the piont retarding, drop off of power at a given rpm, and add a coupe degrees.
Do this at 1500, 2000, 2500, 3000, 3500...upto when the cent is all in.
Then graph the results, then dupilcate this graph changing springs/weights

Thank you.
I needed that explanation.

Now somemore questions,

How can I adjust initial timing and not effect total timing or can that be done?

How do I figure out what total timing my engine likes under a load at WOT? Can that be done without knowing the cam specs?

Thanks for all the info so far....

You're welcome...

The initial and total are fixed to each other by the amount of advance built into a dist and the curve between them is centrifically controled. You can alter the amount of advance with different shaped weights that won't allow as much travel or you can replace the bushings with ones that limit the overall movement.

As for finding the correct total timing, there is no set formula, mostly it's making test runs and adjusting the timing up and down in small changes (maybe 2 degrees at a time). There are some basics where longer stroke engines want less than short stroke engines, most will agree that about 36degs total works as a starting point for most small blocks, a 383 (stroked 350) or 400 small block seems to like a bit less so 34degs is a good start there. I'm not really a big block guy but I believe 36 - 38 degs is a good starting point for most of them as well...

Awesome thanks!:thumbsup:

Now I just need to go buy a light.

:)

Well I installed the timing pointer, its adjustable. The only one I could find that would fit my timing cover.
So I didn't know where to put it for TDC. I have a little gadget that whistles when I come up to TDC on the compression stroke. The closest I could get it was within about 1/4" of the mark.
I adjusted the pointer to as close as I could get but even with my little whistle device, I couldn't tell if I was EXACTLY at TDC.
Later, I will buy one of those TDC indicators and turn the motor by hand and set the pointer exactly.
I put a timing tape on the balancer too.
This pointer rides extremely close to the balancer. So close that where some of the timing tape was bumpy, it skinned it right off.
I was able to see with the timing light that it was pretty retarded. So I advanced it about 7 degrees. (Once again, its not exact cuz I don't exactly know where TDC is)
When I advanced it, the idle decreased. Normal?
Also, the richness I complained of earlier stopped.

So now it was time to take it out and drive it. First time its been on the road in months.
I live near a country road that has a 60 mph speed limit, when I turn onto it, I'm clear for acceleration to 60 and I use this as a bench mark to 'feel' any performance issues.
Normally, before this 6AL box, it was like this. Get straight on the highway and from about 15 mph, roll on the throttle. Not necessarily punching it but accelerating with authority.
This time there was NO doing that. It instantly broke the tires loose.

So I tried again at 40. I figured with a bit of momentum, the tires would maintain adhesion.
They didn't. They broke loose like I was on a wet street.

So now I can't use my bench mark road anymore. Breaking the tires loose on the street can get you a BIG ticket.
So it looks like now, its time for a trip to the track.

:thumbsup:

BTW- The timing tape? Gone after my first drive.

Instead of tape, I have punchd marked my balancer
Used a tape to measure the circumference in mm, divided by 360, x 10 to give distance of 10deg
Then on TDC and each 10 deg used a small coal chistle to tap a line, and a center punch for the 5 deg inbetween.....up to 50 degs

When one gets up around the 25 /35 degs it is easy to 'loose which mark is which, so I have stamped the 10 deg marks with appropriate 1 . 2 , 3 ....

Wiped some white paint over , wipping off the flat so it remains in the punch marks

If doing it on the car, ir is easier to stamp from underneath.

somewhere along the line, it was advised to advance the timing.?.. :rolleyes:
keep playing with it man ,, you'll find the right combination that works .. :thumbsup:

fwiw: the funky thing about timing on a modded engine,, is that they will have inclinations to run (perform) and idle as well timing-retarded as they do timing-advanced. especially SBCs.
it just takes a lot of tinkering and patience to find that "sweet~spot". :yes:

somewhere along the line, it was advised to advance the timing.?.. :rolleyes:
keep playing with it man ,, you'll find the right combination that works .. :thumbsup:

fwiw: the funky thing about timing on a modded engine,, is that they will have inclinations to run (perform) and idle as well timing-retarded as they do timing-advanced. especially SBCs.
it just takes a lot of tinkering and patience to find that "sweet~spot". :yes:

Well it was running extremely rich. When I did finally put a light on it, it was pretty far back there. Advancing it a bit, made the idle decrease but the richness went right away.

Not sure why the performance increase. Not sure if thats from the advance in timing or the new 6AL box or a bit of both.

Instead of tape, I have punchd marked my balancer
Used a tape to measure the circumference in mm, divided by 360, x 10 to give distance of 10deg
Then on TDC and each 10 deg used a small coal chistle to tap a line, and a center punch for the 5 deg inbetween.....up to 50 degs

When one gets up around the 25 /35 degs it is easy to 'loose which mark is which, so I have stamped the 10 deg marks with appropriate 1 . 2 , 3 ....

Wiped some white paint over , wipping off the flat so it remains in the punch marks

If doing it on the car, ir is easier to stamp from underneath.

If its an 8" balancer, can't I just get the circumference that way?

So the only reference you used for this was the TDC mark on the balancer only?
Because this sounds like a good idea.

Because this sounds like a good idea.
Its not a bloody idea....I have been doing this for yrs...and that is basically what sticking a tape on does...
And DONT say for example 10 degs = 5mm then measure with dividers 25mm for 50 degs...it will be wrong because thedividers measure a straight line...the shortest distance between 2 points, ....the 5mm per deg example is on a curved surface

If its an 8" balancer, can't I just get the circumference that way?
Well convert to mm and calc the circumference OR grab the missus sewing tape and wrap it around.....

Its not a bloody idea....I have been doing this for yrs...and that is basically what sticking a tape on does...
And DONT say for example 10 degs = 5mm then measure with dividers 25mm for 50 degs...it will be wrong because thedividers measure a straight line...the shortest distance between 2 points, ....the 5mm per deg example is on a curved surface




It must be somebody's idea, it originated somewhere but anyways.....

What you explain above must be why you use a measuring tape on it, so you can get it correctly on the curved surface.
Is this essentially what one of those fancy balancers with all the degree marks on them do for us?
(Just about a hundred $ cheaper right?)

Is this essentially what one of those fancy balancers with all the degree marks on them do for us?
(Just about a hundred $ cheaper right?)

Yes...except we used to do it on our boy racer cars 30/40 yrs ago... when pre marked balancers/pullys where not avalible.

Well it was running extremely rich. When I did finally put a light on it, it was pretty far back there. Advancing it a bit, made the idle decrease but the richness went right away.

Not sure why the performance increase. Not sure if thats from the advance in timing or the new 6AL box or a bit of both.

you're on the right track now.. just keep tinkering,, it'll all come together :thumbsup:

One thing. I just want to make sure you were using the timing tape correctly before it flew off. Looking at the balancer from the front of the engine, the tape numbers go from zero to maximum TO THE RIGHT. It's easy to get it wrong if you're not used to this stuff and don't have a reference. Hell, it's easy to get it wrong if you're a wrench! The fact that your engine slowed when you advanced has me wondering. Most speed-up.
Anyway, now I feel bad. You installed your pointer and mine is just sitting on top of the work bench. Off I go. It's time.

Try this as a "primer" on ignition and advance systems: :)

TIMING AND VACUUM ADVANCE 101

John Hinckley


The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

:beers:

Try this as a "primer" on ignition and advance systems: :)

TIMING AND VACUUM ADVANCE 101
Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

:beers:

Will that vacuum can work on a MSD distributor? Maybe MSD has an equivalent. My cam gets me about 7-8 inches of vacuum at idle.

When I do run at the dragstrip, I disconnect and plug off the vacuum advance.