Mileage Quest 2011!

[Happy_Camper]

Manifold vacuum is backwards for the vacuum advance. Manifold vacuum vacuum is highest at an idle and drops when the throttle plates open. Ported vacuum (where the vacuum advance connects) is very low at idle and increases when the throttle plates open. If you hook the vacuum advance to manifold vacuum you will get full vacuum advance when the engine is idling.

Good point QC,
This is a really good topic in and of itself.
The idea of ported vacuum is that a lean mixture burns slowly, as the distance between molecules is greater. So at part throttle cruise (where ported vacuum comes in to effect), the timing could be advanced so that efficiency at this point is maximized. Right time to start the burn to get maximum expansion pushing the piston down, with greatest affect.
This principle can be taken further, in that under heavy load there is a dense rich mixture, which burns quickly so the timing should be retarded to maintain maximum efficiency.
Idle time is anti-efficient, as it represents 0mpg. so realistically, we want as lean a mixture as we can get away with... lean needing additional timing.
So, if the distributor uses vacuum advance instead of vacuum retard, then manifold vacuum can be a good way to maintain efficient burns. reprogramming the timing curve (weights and springs), and setting max-min limits, can be a pretty efficient way to increase fuel mileage.
I remember back when the Sun distributor machine was a staple in most shops. Spent a lot of time working with "dual point" distributors on one of these machines.

Scott

Another item that helps fuel mileage is an efficient EGR system.

[woods]

I think there is some misunderstanding about vacuum advance and what port does what. Here is how it reallly works and why it was ever hooked to ported vac in the first place.
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.

[fomocoguy]

I just put a 180 stat back in and my next mod will be hooking my vacuum advance up to full manifold vacuum and maybe adding a few degrees static. Its at 12 now; I'll probably push it up to 14 and see if she pings.

I'm glad everyone is having fun and maybe learning something from this thread!

[woods]

And now for a long dissertation on the industrial revolution.

[wildcard]

[cdeal28078]

Well, I guess next time I am bored I'll try the full manifold vacuum route again. I don't think it'll make much difference except at idle though. Once the throttle blade open it's all the same right?
clint

[67 428 F250]

Like I have said before, it doesn't matter if you use ported or manifold vacuum, just adjust initial, mechanical and vacuum timing and you will achieve the same performance. (Ported gives you a better sound at idle)
Will

[390bump]

woods - great post! Many moons ago I worked at Standard Motors and we used to test all OEM distributors and replacement parts to catalog replacement parts. Spent a lot of time with a Sun distributor machine, vacuum and flow benches. Your post is very accurate and brought back a lot of memories! The distributor vacuum advance canister was sold as a replacement part as it would sometimes fail. If in doubt I would run a timing light and with the engine at idle pull off the vacuum hose and see how much the timing changed. Then rev up the motor to see how well the mechanical advance is working (the plates could use some shots of WD-40 if old and rusty).

But even with all the testing and specs we analysed our most effective technique to set the timing was on a coworker's van. We would remove the cover inside the van exposing the motor and take it for a drive. With the distributor hold down bolt loosen a bit the driver would have one hand on the steering wheen and the other on the distributor. He would advance the timing under accelaration until the motor started to knock then back it off just a bit... Later on knock sensors and computers came out and did the same thing. On a bump, if you want the maximum efficiency, you can try more advance - take it for a drive to see if it knocks or not...

And I agree a lot of "race" or high performance parts sold were crap. Some were designed improperly and some were poor quality. A great example is the "super coils" (Accell) we used to test. They put out a hot spark at low RPMS but were unable recharge fast enough at higher RPMS... Couldn't run past 4K RPMS but were sold as race coils.

[woods]

woods - great post! Many moons ago I worked at Standard Motors and we used to test all OEM distributors and replacement parts to catalog replacement parts. Spent a lot of time with a Sun distributor machine, vacuum and flow benches. Your post is very accurate and brought back a lot of memories! The distributor vacuum advance canister was sold as a replacement part as it would sometimes fail. If in doubt I would run a timing light and with the engine at idle pull off the vacuum hose and see how much the timing changed. Then rev up the motor to see how well the mechanical advance is working (the plates could use some shots of WD-40 if old and rusty).

But even with all the testing and specs we analysed our most effective technique to set the timing was on a coworker's van. We would remove the cover inside the van exposing the motor and take it for a drive. With the distributor hold down bolt loosen a bit the driver would have one hand on the steering wheen and the other on the distributor. He would advance the timing under accelaration until the motor started to knock then back it off just a bit... Later on knock sensors and computers came out and did the same thing. On a bump, if you want the maximum efficiency, you can try more advance - take it for a drive to see if it knocks or not...

And I agree a lot of "race" or high performance parts sold were crap. Some were designed improperly and some were poor quality. A great example is the "super coils" (Accell) we used to test. They put out a hot spark at low RPMS but were unable recharge fast enough at higher RPMS... Couldn't run past 4K RPMS but were sold as race coils.

Yeah, guys like you who have set up a lot of distributors or do it for a living really understand how important a proper set up distributor and proper timing are. The cool thing about this is everyone can try it for themselves, it's free and easy. Take your truck for a drive. Every time you take off from a light or stop sign, you will notice how much stronger your car feels from that instant it starts rolling. A lot less effort.
Much like when you free rev your engine. If you are hooked to ported vac, you will notice that it revs faster if you ever so slightly crack the throttle blades first before you rev it. This slight crack in the throttle is giving you full vac at your distributor, which is why it revs faster and crisper that way. With it hooked to full, your engine will hit like that right off idle with the throttle closed. Now think of how many times your truck or car is at idle during a day of town driving (stop and go). The difference is a cooler running engine when sitting in traffic and a real difference just getting rolling. Give it a whirl, nothing to lose. If you don't like it, no one is forcing anyone to make their engine run to it's potential, you can put it back to ported in a few seconds.
I have always been into making something run as good as possible, been doing it for a living for quite a while. Full vac is how all my normal street driven cars and trucks are hooked up and I would never go back to port unless I have to run it through a smog check.

[Ranchero50]

I think there is some misunderstanding about vacuum advance and what port does what. Here is how it reallly works and why it was ever hooked to ported vac in the first place.

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.

I question this. From experience my '68 302's in the fairlanes ran best if I free revved them to 3500rpm or above and they had 34-36` with the vacuum advanced hooked up. Any more and they detonated. Of course free revving them the vacuum was higher than normal because the throttle plates weren't wide open. The mechanical was all the way advanced at 3500rpm (timing didn't change revving higher). So the vacuum advance setup was 15` BTDC at 800rpm no vacuum, double check the high mark (33-34) with the vacuum hooked up and away I went, no drama. My EFI 302's are about the same, initial at 15` no detonation, free rev to 3500 and the timing was around 35`.

From what I've always read and understand the only reason you have centrifigal advance was so the spark fired as close to the pressure spike in the cylinder as the RPM increased (had to fire earlier as the RPM climbed because the coil disharge time stayed the same (or went up if you ran Accell stuff). The vacuum advance controls the drivability of the engine so I have no idea why you would want it hooked up backwards. Ford kept it like that for 50+ years so I'm pretty sure they knew what made the engines run best...

I've also experienced and read that engines run much more efficient on the lean side of stoich vs. the rich side, the power loss curve is much flatter on the lean side vs. the rich side of Stoich. Read the Probst book on Ford EFI, very informative.

Jamie

[woods]

I think there is some misunderstanding about vacuum advance and what port does what. Here is how it reallly works and why it was ever hooked to ported vac in the first place.

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.

I question this. From experience my '68 302's in the fairlanes ran best if I free revved them to 3500rpm or above and they had 34-36` with the vacuum advanced hooked up. Any more and they detonated. Of course free revving them the vacuum was higher than normal because the throttle plates weren't wide open. The mechanical was all the way advanced at 3500rpm (timing didn't change revving higher). So the vacuum advance setup was 15` BTDC at 800rpm no vacuum, double check the high mark (33-34) with the vacuum hooked up and away I went, no drama. My EFI 302's are about the same, initial at 15` no detonation, free rev to 3500 and the timing was around 35`.

From what I've always read and understand the only reason you have centrifigal advance was so the spark fired as close to the pressure spike in the cylinder as the RPM increased (had to fire earlier as the RPM climbed because the coil disharge time stayed the same (or went up if you ran Accell stuff). The vacuum advance controls the drivability of the engine so I have no idea why you would want it hooked up backwards. Ford kept it like that for 50+ years so I'm pretty sure they knew what made the engines run best...

I've also experienced and read that engines run much more efficient on the lean side of stoich vs. the rich side, the power loss curve is much flatter on the lean side vs. the rich side of Stoich. Read the Probst book on Ford EFI, very informative.

Jamie

But, did the 302 rev the same from a dead idle, or did it rev faster after giving it a touch of throttle first?
As far as reading that they run better lean...I run and own a dyno and with a wide band...The bigger percent of naturally aspirated engines give more power and flatter torque curve at around 12.5, not 14.7. There are some ecxpetions on newer better build combustion chambers. It's easy to figure this out first hand. Buy or rent a wide band tuner that tells you your exact mixture, take it for a drive and look at it. Make your engine run higher than 14.7 and see what you personally think about how it runs...that's the important part right? I can save you a little time on that if you would like...an older style engine (even running 14.7) will run poorly at best. Of course, the right thing to do is to not take mine or anyone else's word for it, the right thing to do is to try it yourself and make an informed decision on person experience.
So you can never make an engine run better than factory did? I for one have never understood this point of view. There are classes in racing that don't allow any aftermarket parts, but we can pull all sorts of extra power out of them by just blueprinting what the factory did not. How about the retarded camshaft Ford put in engines, that can be very improved by just setting it straight up. A lot of thing were done that were not perfect (far from it). That includes timing. Nearly everyone who runs a bit more initial timing than factory notices an improvement in drivability, looks as if you change the factory setting too.
The vacuum advance is really nothing more than a load sensing device. It senses load (due to loss of vacuum) and pulls out some timing, but runs it advanced when it's under light load.
Below the throttle plates or above is the same when cruising, it gives a lot of timing when under light cruise, nothing changes other than it will idle smoother, cooler and respond better right off idle.

[Ranchero50]

Honestly, the engine runs great. It's a 48k mile 289 /C4 with 2.79 gears in a '68 fastback Fairlane. The only thing done to it is a Mallory optic conversion kit and unhooking the manifold retard on the dual advance distributor. It will pull down 20+ mpg at 60mph smooth a silk. It still has the Ford stamped belts and hoses on it.

I agree that Ford left a lot on the table mechanically but they kept this carb ported advance strategy up until the EFI's came out, must have been some reasoning to it.

I'm still going to dissagree with your last statement, below or above the throttle plates will be opposite at idle and low throttle settings. Throttle closed it'll be high below and low above, not the same.

[woods]

I think we may have a misunderstanding, Which is easy in nothing more than typing. Do you think there is no difference between ported and manifold vacuum aside from idle? Just help me out with what your saying. Do it like you're teaching me something (really, not being a jerk, it's easier for me to get a grasp on what you're trying to say) because I really think we agree but not getting it across right.

[Ranchero50]

I know there is a difference between the ported and manifold vacuum readings at idle and most throttle settings. 95% of warm cruise driving is low throttle setting so there shouldn't be much if any vacuum advance on the distributor unless your air cleaner is clogged solid. The whole purpose of the vacuum advance is to goose the engine timing at low load mid throttle so it feels more responsive.

According to my OEM '68 Cougar Fairlane Etc Etc shop manual the engines with the dual vacuum distributor on the Imco emmisions engines use the manifold vacuum retard function only during idle and closed throttle decelleration and most of the plumbing diagrams show the manifold vacuum being routed through a thermostatic switch that only allows manifold vacuum during overtemp conditions purely to reduce HC emmisions. The book shows the retard function was good for 5-6` and the vacuum advance was good for around 7-21 depending on the distributor. Most centrifigal advance was around 7-15` @ 2000rpm and total advance veried from 21-43` depending on the setup.

No where does it say running manifold vacuum to the vacuum advance is good for economy or to make the engine run cooler. If anything it seems running the timing too far advanced at idle and low throttle settings will just cause the engine it run warmer and on the verge of detonation. I know Chevy does it but since I usually don't play with orange engines I never looked into their timing curves to figure out how there vacuum advance modifies the timing curve. I did swap the lines on a friends 454 '71 Chevelle and it seemed to drive better SOTP but all the Chevy guys flipped out about it so we swapped it back just to comform.

Jamie

[woods]

I know there is a difference between the ported and manifold vacuum readings at idle and most throttle settings.

I think this is where we are getting off track. No, there is ONLY difference at idle. This is one of those things that you don't have to take my word for and is easy to prove to yourself. Take your vacuum gauge, put it in your car and drive around, notice where it's at at what throttle position, then hook it to ported, it will be the same reading. Done it a lot, it's the same.

95% of warm cruise driving is low throttle setting so there shouldn't be much if any vacuum advance on the distributor unless your air cleaner is clogged solid.

No, this is where you have a lot of vacuum. That is one of the reasons the vacuum advance is there, to give you a lot of advance when NOT under load. It's a lean fuel mixture, lean mixture in harder to light. At cruise is where you want the very most timing available. Timing is advanced during this time because an engine can get away with it. You sure in the heck can't run 50 degrees of advance under load or pulling hard. You know this. Of course, this is another thing you don't have to take my word for, just hook a vacuum gauge to your ported vacuum and watch it while you drive. It will put out the highest reading under low load, light throttle. It's the way the factory set up most cars, this is just a fact. The vacuum advance is there to give you a bunch of timing at cruise and to pull out timing when vacuum drops because of heavier load on the engine. This keeps it from pinging.

The whole purpose of the vacuum advance is to goose the engine timing at low load mid throttle so it feels more responsive.

Well, this is a "kinda" area, but really, no, it's not. It's a load sensing device plain and simple. It give you a lot of timing when you're not under load (due to the high vacuum not under load) when you put a load on the engine, vacuum drops, the vacuum advance sees the drop and pulls out timing. Pretty simple really. The reason I said "kinda" is because when you goose the engine, from light load mid throttle, the vacuum advance does make it more responsive. Know why? Because it has advanced your timing at low load part throttle, due again to the high vacuum. Advanced timing makes an engine more responsive. So in a way, you're correct. But, it's because the advanced timing that it's responsive. Much like if you had it hooked up to direct manifold vacuum at idle, more responsive. I am assuming you know that advanced timing is why a motor responds better correct? If not, this is another thing you can prove to yourself. Lock your distributor at 6 degrees with no vacuum hooked up and see how it responds at ANY rpm. Yes, terrible, because it needs advance. Many cars run 50 degrees of timing under light load cruise, some newer cars even more, it's just the way it works.

According to my OEM '68 Cougar Fairlane Etc Etc shop manual the engines with the dual vacuum distributor on the Imco emmisions engines use the manifold vacuum retard function only during idle and closed throttle decelleration and most of the plumbing diagrams show the manifold vacuum being routed through a thermostatic switch that only allows manifold vacuum during overtemp conditions purely to reduce HC emmisions. The book shows the retard function was good for 5-6` and the vacuum advance was good for around 7-21 depending on the distributor. Most centrifigal advance was around 7-15` @ 2000rpm and total advance veried from 21-43` depending on the setup.

This is just what I said before. Retarding the timing (which is what that is doing at closed throttle) is nothing more than an emissions Band-Aid. Retarded timing burns the fuel mixture later than sooner, it makes a lot of your usable power burn in the exhaust manifold and not the combustion chamber, thus keeping your engine from idling like it should or responding like it should. Anyone who has ever driven a car with timing too retarded knows what can happen here. The manifolds or header will start to glow red. That is all heat that should have been used to power your engine, instead it's heating your exhaust. This cuts down on emissions at idle and deceleration. It's not operating to it's potential in those conditions, just burning excess emissions with a red hot exhaust. It was the early version of a catalytic converter. The heat from it was a Band-Aid to pass emissions, nothing more.

No where does it say running manifold vacuum to the vacuum advance is good for economy or to make the engine run cooler.

So the shop manual for a Ford car does not tell you to change what Ford did to help with emissions? You are surprised by this? Whether the book says it or not, it does not change the laws of physics. Yet another thing that guys can test for themselves. Fire up your car in the driveway and let it idle. Pull your timing down so it's idling very retarded, you may have to turn up your idle. Now after a little while of idling, watch the temp. Your car always ran cool before, but now it's running hot. If you have one of those temperature guns, point it at the exhaust manifold, you will almost faint at how high the temperature is. This is unused heat that could have been made into energy to power your engine. But instead, it's just heating it. Like I said though, there is no reason to take my word for this, you can try it yourself. The proof is not in what I say, but rather what really happens in front of your own eyes and I fully encourage everyone who has doubts to try these things. Only one really good way to learn is to do. I can go into a very long explanation as to why retarded timing causes heat, but I feel someone should know for sure that it does cause it before reading an explanation on the dynamics of it.

If anything it seems running the timing too far advanced at idle and low throttle settings will just cause the engine it run warmer and on the verge of detonation.

The "verge" of detonation is where your engine runs cooler and better. It's why many guys will time their cars without a light. They will run it up until they get some pinging and then back it off a little. As long as the advanced timing does not hinder starting, then they are good to go. I know a few guys in here do it this way and swear by it. Advanced timing does not cause excess engine heat. Retarded timing does. Again, something you can prove to yourself.

I know Chevy does it but since I usually don't play with orange engines I never looked into their timing curves to figure out how there vacuum advance modifies the timing curve.

Same as Ford, they are both just an air pump. They have a hole in the top and 8 round things that pump air, the same laws of physics apply to piston driven engines, even if they have different firing orders or a different valve train. Retarded timing has the same effect on your mower as it would have on sprint car engine, it builds heat and does not using it to push the vehicle forward.

I did swap the lines on a friends 454 '71 Chevelle and it seemed to drive better SOTP but all the Chevy guys flipped out about it so we swapped it back just to comform.

Yep, you will find guys reluctant to change in every venue. Ford guys, Dodge guys and Chevy guys, they all read something wrong or are repeating info they got from someone else and stating it as fact. It ran better is the fact, never conform when something runs better. There is such a mass of ill information around. The problem is, some of it is good info and some is terrible and has been passed down from generations. So if you're not in my particular line of work, it can be hard to tell which is right and which is bogus. The right thing to do is to check it for yourself and make an informed decision on your own personal findings, this is what I strongly encourage for everyone.