Y-block 292 Timing question

[smtichy]

I have a '55 Sunliner, with a 292 (casting no. shows it as a '59)

This weekend I did a tune-up and hit a bump when checking the timing. The timing pointer on my car is different than that shown in the shop manuals. [See thumbnails attached at bottom, double click to enlarge].

The timing pointer has 4 points marked clockwise 10, 6, 3, 0.
Anyone familiar with this type of pointer on the Y-block?
If so, which point matches the standard pointer and should be used to set timing?

The damper is stamped TDC followed by 6 marks. The timing light shows the point on the pointer labled "10" between the 4th and 5th marks on the damper.

FYI in doing the tune up, I checked points, plugs, idle, dwell, vacuum, etc. None were within proper specs but now they are sorted.

I've had this car for about 6 months now and have been getting it into good shape thanks to all the knowledge you all have shared with me.

Have a great weekend!

p.s. - a picture of a similar pointer below:

[Y-Blockhead]

There are two different "sets" of timing marks used on Y-Blocks.

One has the pointer with the scale on it like yours with only one mark on the damper. This is the early style.

The other has a single pointer and graduated marks on the damper like yours. This is the later style.

Appears to me you have a combo of each "set".

I would use the "0" on the damper as your TDC and time to 10° BTDC on the tab. Make sure that the "0" is a true TDC. Sometimes the damper spins in the pulley, throwing off the mark.

Hope that helps...

[Y-Blockhead]

Or you could use the "0" on the tab as TDC and the scale in the damper. either way you need to establish TDC. Or locate the correct pointer.

[Ole Don]

Where you want the initial timing depends on the grade of fuel you get. Here in the US, we have several grades. The more you want to spend, the better grade you get, and the motor will respond to each. The best way to time an engine is with a vacuum gauge, with the fuel it will be using. With the vacuum gauge reading manifold vacuum, advance the ignition to the maximum reading, then back off just a bit, maybe 1/2 inch of vacuum. Test drive, lug the engine and if it pings, retard a bit more.

[scicala]

Originally Posted by Y-Blockhead

There are two different "sets" of timing marks used on Y-Blocks.

One has the pointer with the scale on it like yours with only one mark on the damper. This is the early style.

The other has a single pointer and graduated marks on the damper like yours. This is the later style.

Appears to me you have a combo of each "set".

I would use the "0" on the damper as your TDC and time to 10° BTDC on the tab. Make sure that the "0" is a true TDC. Sometimes the damper spins in the pulley, throwing off the mark.

Hope that helps...

I recently worked on a '54 Mercury 256 Y Block, and it had a pointer mounted to the engine, and the TDC with notches up to 10 degrees was on the damper ring. Maybe they were all over the place.

[Y-Blockhead]

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Originally Posted by scicala

I recently worked on a '54 Mercury 256 Y Block, and it had a pointer mounted to the engine, and the TDC with notches up to 10 degrees was on the damper ring. Maybe they were all over the place.

And lotsa things get changed by all the "Mekeniks" over the last 60 years...

[smtichy]

Thanks everyone, your input set me on the right track. I pulled the #1 plug and made a quick check with my finger where TDC is.

It looks like it is close to the timing pointer marked 0°, just a little off. Anyway, that means the current timing is at about 12° BTDC vs. the specified 3°. I'll give a go at timing with the vacuum gauge, and then after seeing the result try and find the precise TDC later.

Ole Don, the fuel here is generally pretty good. I use the mid-range Euro Natural 95 which is equivalent to about 85-86 octane US (similar to that available in '55). At the better fuel stations such as Shell, OMV, and Agip it contains about 3% ethanol. I've had that car sit for a couple weeks and fire right up with the fuel in the bowl.

[Y-Blockhead]

Steve, Y-Blocks like a little advance. I wouldn't set it at 3°.

With the cam I have in my 318" I also set it with a Vacuum gauge. When I check mine with a light after setting it with a gauge it is ~16° BTDC so don't be surprised if it is advanced a bit.

Not saying yours will be 16°, that's just where my engine likes it.

[smtichy]

Once again thanks for the tips. Here are the results. Top vacuum was around 24 in.Hg and over a range of about 10°. I put it on the lowest advance in that range and then retarded by about 1/2in. Hg. Took it for a drive, and it was sluggish and missing so advanced a bit further. Did some tests, lugging on a steep hill in 3rd at about 20mph, no pinging, so fixed it there.

End result is an estimated 14-16° advance, which surprised me for a stock setup. We'll see how it goes. Thanks again.

[Hot Rod Reverend]

Ditto on the Y blocks and giving them a little more initial advance than normal... wakes 'em up quite a bit.

[Ole Don]

Where I live in the corn growing part of central US, our fuel is 87, 89, or 91. If my car is tunned for best performance, it requires 89. It all has about 10% ethanol. It evaporates out of the carb in about three days. I have mounted an electric fuel pump near the front of the tank, with a relay and a swich under the dash. If the car sits more than a few days, I run the pump for several seconds prior to trying to start it. Neither fuel pump seems to mind the other one in the system.

[smtichy]

Pardon my dragging out this post, but I took the car out for a good drive today, slower speeds, with some starts and stops, plus hotter weather. Note I have a manual transmission, and I noticed that in 1st it would loose considerable power, almost stutter, at higher rpms, and backfire more letting off the throttle in mid-range speed in 2nd. I'm assuming I might need to back the advance off a bit. Any thoughts are appreciated. [It might be the timing on the car was fine as it was , oh well that's how you learn].

Ole Don, I grew up in Nebraska and remember back in the late 80's we too were running 10% ethanol. The higher octane from the ethanol sure squeezed more power out of the Ford turbo 4 banger I had in those days.

Also Ole Don, coincidentally my car had a mystery toggle switch below the steering wheel that some "mekeniks" installed. I traced it to an electric fuel pump that is mounted on the frame by the rear axle, but seems to be frozen-up and non-functional. It's been Ziebarted over so I haven't been able to figure out what era it came from but I think it was before a general restoration done on the car in the 80's. Surprisingly the non functioning pump doesn't seem to obstruct the fuel line (ie. same situation as you have).

BTW, I'm sure I don't need to tell you all this but never Ziebart a classic car, it makes a nice sticky mess to manipulate around!

[Y-Blockhead]

Steve, check your total advance. When you have 16° initial advance you may be over advanced at higher RPM. I had to limit my mechanical advance for 38° total advance.

[Talkwrench]

You will be over advanced . If you want higher initial advance you will need to modify your timing slot [shorten it] I don't think you should be going over 35 degrees total, but then I don't know your corn fuel.. I would say for your engine [manual trans]everything being in tip top condition you should be idling on 21 Hg. This info without Vacuum advance hooked up.

[Ole Don]

The racers in the Y block magazine say to time the engine at 3600 RPMs for a total of 36 to 38 degrees. I ran about 37 - 38 with 100 LL fuel for one mile at Bonneville.

[smtichy]

Considering the comments on vacuum / mechanical advance, one thing occurred to me that I need to research.

My motor is a '59 and the dizzy appears to be '57-59 as it has a 12200-B type rotor in it. The vacuum advance is hooked up to a "ported" pickup on a '55 Holley 4000. Some research a friend of my forwarded to me seems to indicate that the "newer" dizzy has a different advance system and might need the vacuum hooked to a non-ported source . With the other stuff I've found, I would be surprised it the old "mekenik" got it wrong .

Let me know if you think I'm on to something here with the ported vs. non-ported pickup? Tomorrow evening I'll try to get over to the garage and see if I can identify the type of distributor I have to be sure.

[Y-Blockhead]

The '55 carb is set up for the Load-o-matic distributor and visa versa. The later distributor will not work properly with it nor will the Load-o work with a later carb.

Later Holleys (AFB's, Edelbrocks, etc. have ported vacuum for the vacuum/mechanical distributors ('57 up).

Some have run with manifold vacuum with success but it is best to run the correct combo.

[scicala]

Originally Posted by smtichy

Considering the comments on vacuum / mechanical advance, one thing occurred to me that I need to research.

My motor is a '59 and the dizzy appears to be '57-59 as it has a 12200-B type rotor in it. The vacuum advance is hooked up to a "ported" pickup on a '55 Holley 4000. Some research a friend of my forwarded to me seems to indicate that the "newer" dizzy has a different advance system and might need the vacuum hooked to a non-ported source . With the other stuff I've found, I would be surprised it the old "mekenik" got it wrong .

Let me know if you think I'm on to something here with the ported vs. non-ported pickup? Tomorrow evening I'll try to get over to the garage and see if I can identify the type of distributor I have to be sure.

There is a procedure for making the Holley 4000 work using ported vacuum from the carb instead of using the loadomatic (AKA: BS system) distributor.

I can try to dig it up if interested. The Holley 4000 does have a ported vacuum hole in the right front bore. Just need to block off the part that uses venturi suction for the loadomatic system.

[smtichy]

Originally Posted by scicala

There is a procedure for making the Holley 4000 work using ported vacuum from the carb instead of using the loadomatic (AKA: BS system) distributor.

I can try to dig it up if interested. The Holley 4000 does have a ported vacuum hole in the right front bore. Just need to block off the part that uses venturi suction for the loadomatic system.

Hi Scicala, hold up on the digging, you're note gives me a lead and I will first flip through my Holley manual, and get an ID on the dizzy. My vacuum advance is hooked to a ported vacuum hole, if I follow what you noted above, maybe it is set up right?

My confusion / question is related mainly to the dizzy. Do the '57 - '59 distributors with centrifugal advance need to be connected to a ported vacuum source or a manifold vacuum source?

[Y-Blockhead]

Ported, but the ported vacuum in not the same on later Holley as on your Holley 4000 unless you modify the 4000 as scicala suggests. That's where a lot of guys get confused.

[scicala]

Originally Posted by smtichy

Hi Scicala, hold up on the digging, you're note gives me a lead and I will first flip through my Holley manual, and get an ID on the dizzy. My vacuum advance is hooked to a ported vacuum hole, if I follow what you noted above, maybe it is set up right?

My confusion / question is related mainly to the dizzy. Do the '57 - '59 distributors with centrifugal advance need to be connected to a ported vacuum source or a manifold vacuum source?

Smtichy, like Y-Blockhead mentioned, ported vacuum is correct and not straight manifold vacuum. There should be no vacuum to the distributor advance when at a warm idle speed. When you crack the throttle open slightly you should get vacuum there because you expose the ported vacuum hole in the throttle bore to manifold vacuum (below the throttle plate).

Here is a link to the article on how to convert you're 4000 carb for '57 and later distributors.

Sal Cicala


http://www.eatonbalancing.com/blog/2...-distributors/

[smtichy]

Sal, Many thanks for that link. Now I get how it works!

I think my advance problems started from my cleaning up the incorrectly hooked up vacuum tube which was plugged up ... Geez. I'll probably run it with the vacuum advance disconnected for now, and see how it goes.

If that does the trick, I'll make this an Autumn project as I don't think my wife will be pleased with my putting the car out of commission just after I've told her it's purring like a kitten and all ready for the season.

Guys, as always thanks for the pointers.

[scicala]

Steve,

You should be OK running without the vacuum advance for now. As long as you have centrifugal advance, the engine will get what it needs to run good when the RPM gets up higher. Only thing it will hurt is not enough spark advance at light loads which will hurt the fuel economy a little bit and slightly higher exhaust temps. Good luck, Sal

[RooDog]

Here's something to think on. I believe it to be true and correct. I run manifold vac on my street built 357 Ranchero engine....RooDog
Re: Ported vs manifold vacuum advance
March 21st, 2012, 09:36 AM
This was the post I found on a MOPAR forum during a google search.

This was written by a former GM engineer as a response to a similar question on a Corvette board:


As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

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.

PS: The combustion chamber don't care what name is on the valve covers....

[scicala]

Originally Posted by RooDog

Here's something to think on. I believe it to be true and correct. I run manifold vac on my street built 357 Ranchero engine....RooDog
Re: Ported vs manifold vacuum advance
March 21st, 2012, 09:36 AM
This was the post I found on a MOPAR forum during a google search.

This was written by a former GM engineer as a response to a similar question on a Corvette board:


As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

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.

PS: The combustion chamber don't care what name is on the valve covers....

So why then did all American auto makers design engines to run using ported vacuum ? Also done by competent engineers. In my eyes it doesn't really matter since you get full manifold vacuum advance as soon as the throttle is touched the slightest amount. I'm also aware of how it all works from many years of working in engineering doing dynamometer work and calibration.

[RooDog]

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And why then did competent engineers install a thermal, water temperature, sensing valve on the radiator side of the thermostat to direct manifold vac to the other side on the vacuum diaphram in opposition to ported vac?
In the article above he speaks of retarded timing to heat the exhaust to make the air injector more efficient for emmission reasons. Read it again, most things are explained. I do know that more advance leads to a smoother idle & higher vacuum meter readings, but the tuner must contend with starter kickback. Ever deal with an old lick start Harley Panhead? If so the effects of retarded vs advanced timing during starting can be painfully obvious. There is another writeup, on the web somewhere where, the author drove with dual vacuum gages, ported and manifold, and once under way they read the same, only at idle was there a diff. Choose you own poison and draw your vacuum advance from where it feels best to you and your engine.....I'll take mine straight, but bourbon and branch is OK too....RooDog

[[email protected]]

Hi Scicala: I saw that you had recently worked on a 54 Merc 256 ci with the Teapot Carb. I've got a problem with mine that I don't understand. I have to unplug the vacuum advance to keep the engine from back firing continuously. After much adjustment - checking valve lash, timing chain (new), distributor (rebuilt by Concours) Carburetor rebuild by professional, I'm not getting anywhere. Vacuum at the carb is about 4 in. Manifold vacuum is 17 plus in. Timing is advanced beyond the pointer. Any ideas anyone?? Thanks Timmy D, C'ville, OK

[dmsfrr]

Originally Posted by [email protected]

... a 54 Merc 256 ci with the Teapot Carb. I've got a problem with mine that I don't understand. I have to unplug the vacuum advance to keep the engine from back firing continuously. After much adjustment - checking valve lash, timing chain (new), distributor (rebuilt by Concours) Carburetor rebuild by professional, I'm not getting anywhere. Vacuum at the carb is about 4 in. Manifold vacuum is 17 plus in. Timing is advanced beyond the pointer. Any ideas anyone?? Thanks Timmy D, C'ville, OK

timd63, resurrecting 5 year old posts usually causes confusion with following replies, you may get responses related to the old original post.

What carb and distributor does it have? An original '54 'teapot' and Load-o-matic or something else?
At first glance they may look much like the '55 versions. Are there part or casting #'s on them?

Is there an EBY prefix casting number on the block at the base of the distributor, on the heads and across the rear of the intake manifold?

What is the vacuum line for the distributor connected to, a carb port or the intake manifold?
A Load-o-matic timing advance operates on 0 to 5 inches of vacuum, intake manifold vacuum will be way too high.

If the timing marks are on an old original crank pulley damper ring a common problem is for the ring to slip, then the timing marks don't line up any more. Can you post a photo of the crank pulley & timing pointer?

Not sure it would run even as well as it currently is, but...
was the new timing chain installed properly? .(photo 1)

IF, either of these things has happened you may need to re-confirm #1 TDC (compression stroke) and/or valve & crankshaft timing.
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