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Old 10-05-2006, 04:51 AM
72NOVA454
 
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454 Ignition Timing Question

Help

I just had a engine builder tell me over the phone that my 454 setup should have about 10-12 deg initial timing advance, with maybe 35 deg total advance. So.........I went and hooked up a timing light, warmed her up, put her in gear, at idle (about 800 rpm) no vacuum advance, and checked timing. She was "off the board" and running about 24 deg initial advance!!!!!!

what the heck is going on? Now I'm afraid I'm going to blow her up, or I somehow dont have TDC set properly on the timing mark. I just rebuilt her last winter. I'm sure I did it right though. She runs good the way it is now. If I go down to like 10-15 deg initial timing she won't idle. I also have the MSD distributor with adjustable everything. I currently have the "fastest" centrifugal advance spring in there, and the bushing which allows the "greatest" amount of advance. Will I damage the car this way? She seems to run pretty good though througout the rpm range. The engine builder dude told me that timing is set more by compression ratio and not valve timing (cam) I told him I though my comp ratio was like 10:1.

It's a 454 motor (.060 overbore) with 101cc iron oval port heads, slightly domed pistons, long duration cam (comp cams 11-250-3) dual plane intake, holley 4 bbl, etc.

thanks.

Lee

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Old 10-05-2006, 05:44 AM
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454 Timing

Do you hear any indication of pre-ignition (knocking)? Also, how are you reading that much of advance? Does you tab over the balancer read that high? Is it an after-market tab that might not be the correct one?

Alan
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Old 10-05-2006, 05:58 AM
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Quote:
Originally Posted by scs2rescue
Do you hear any indication of pre-ignition (knocking)? Also, how are you reading that much of advance? Does you tab over the balancer read that high? Is it an after-market tab that might not be the correct one?

Alan
No, there is no pinging or pre-ignition. I am sure of that. It is not an aftermarket tab. I am just eyeballing, guessing on the timing reading because it is "off" the tab.
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Old 10-05-2006, 07:04 AM
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Quote:
Originally Posted by leejoy
I went and hooked up a timing light, warmed her up, put her in gear, at idle (about 800 rpm) no vacuum advance, and checked timing. She was "off the board" and running about 24 deg initial advance!!!!!!

I currently have the "fastest" centrifugal advance spring in there, and the bushing which allows the "greatest" amount of advance.
By the "fastest" centrifugal advance spring(s) installed, I assume you are talking about the lightest tension springs. If this is the situation, it could be that your mechanical advance is operating at idle causing the 24 (your estimated figure) degrees of initial advance. If you can't lower the idle in drive to around 650 RPM to check the initial advance at that lower idle speed, then try one or both slightly heavier advance springs. This will prevent the mechanical advance from beginning at too low of an RPM. You might also check to see that the mechanical advance plate is not sticking. Look for light corrosion and/or dirt buildup.
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Old 10-05-2006, 09:01 AM
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Quote:
Originally Posted by Frisco
By the "fastest" centrifugal advance spring(s) installed, I assume you are talking about the lightest tension springs. If this is the situation, it could be that your mechanical advance is operating at idle causing the 24 (your estimated figure) degrees of initial advance. If you can't lower the idle in drive to around 650 RPM to check the initial advance at that lower idle speed, then try one or both slightly heavier advance springs. This will prevent the mechanical advance from beginning at too low of an RPM. You might also check to see that the mechanical advance plate is not sticking. Look for light corrosion and/or dirt buildup.
interesting thought..........I'm sure it's not sticking because it is all shiny new and recently installed, and the timing does change with engine speed - I checked that.

as far as the lightest spring being in there and advancing the timing even at idle: you may be right on that. I will try the next spring. I still have them all. thanks for the idea.
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Old 10-05-2006, 12:44 PM
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I recently setup my timing on my 454 using manifold vacuum on the vacuum advance and I like the way it runs. This method was recommend by the tech at Racer Brown Cams.

Here is how I did it.

Set initial timing to 15 degrees and total to 35 without vacuum advance. Then connect the vacuum advance to manifold vacuum and set the vacuum advance give another 15 to 20 degrees advance at idle vacuum. If you have low vacuum at idle then you need to install an advance canister with a lighter spring (kendricks automotive, TX). Then set the idle speed and adjust the idle mixture for best idle.

So, initial timing at idle will be 30 to 35. Sounds high but it works great. It allows the engine to idle with very little throttle blade opening. This also increases vacuum at idle by 2 to 3 inhg and it reduces the idle drop when put into drive. Throttle response is better and the idle mixture seems a lot less smelly. The starter can crank the engine over easily because the vacuum advance doesn't come in until the engine starts.

When driving down the highway with a light engine load (high vacuum) the timing will be about 55 degrees (35 total + 20 vacuum). This will increase gas mileage! When the throttle is opened, the vacuum advance will drop out and give 35 degrees (total timing).

Give it a try.
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Old 10-05-2006, 01:06 PM
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Quote:
Originally Posted by 454C10
I recently setup my timing on my 454 using manifold vacuum on the vacuum advance and I like the way it runs. This method was recommend by the tech at Racer Brown Cams.

Here is how I did it.

Set initial timing to 15 degrees and total to 35 without vacuum advance. Then connect the vacuum advance to manifold vacuum and set the vacuum advance give another 15 to 20 degrees advance at idle vacuum. If you have low vacuum at idle then you need to install an advance canister with a lighter spring (kendricks automotive, TX). Then set the idle speed and adjust the idle mixture for best idle.

So, initial timing at idle will be 30 to 35. Sounds high but it works great. It allows the engine to idle with very little throttle blade opening. This also increases vacuum at idle by 2 to 3 inhg and it reduces the idle drop when put into drive. Throttle response is better and the idle mixture seems a lot less smelly. The starter can crank the engine over easily because the vacuum advance doesn't come in until the engine starts.

When driving down the highway with a light engine load (high vacuum) the timing will be about 55 degrees (35 total + 20 vacuum). This will increase gas mileage! When the throttle is opened, the vacuum advance will drop out and give 35 degrees (total timing).

Give it a try.
Ok, I kind of get all that. One thing though. I do not use vacuum advance. I removed it from my MSD distributor. Having said that, I wonder if there would still be some benefit of installing a vacuum canister to improve idle and "off-idle" performance and get rid of that stinky exhaust smell at idle.
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Old 10-05-2006, 01:15 PM
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Yes, put it back on and try it.

Here is a little copying and paste that I got off this site: Do a search, there has been a lot of discussion on vacuum advance and timing.

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.
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Old 10-05-2006, 04:33 PM
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454 Ignition Timing Question

I also have a 454 Big Block LS-6 in my car with a fairly big Comp solid roller cam and I use a MSD distributor.The best combo that I have found is 16-18 degrees initial timing,the heaviest springs,the bushing that allows the least amount of advance,and no vacuum advance,and this gives me a total timing of 36-38 degrees.Dont put too much faith in what you hear or read about vacuum advance,it is not necessary in every case.When I still had it hooked up there would always be a slight stumble and pinging at part throttle tip in.I unhooked it and that went away,gas mileage didnt suffer,spark plugs last just as long.I experimented with different weight springs and found that mine liked the heavy ones best.Do what works best in your situation.
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Old 10-05-2006, 07:44 PM
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Good stuff, but don't forget the confusion that computer sustems added to the mix. Also most of these guys are trying to tune cars that are made up of piles of the cheapest parts they could buy (or the previous owner could buy) from garage sales and swap meets.

With all this confusion, the best thing I can tell them is that it takes around 5 to 10 degrees initial advance to start an engine. Most (not all) engines will run pretty well with 35 to 38 degrees total advance. They can find a good timing maxium (that is if all the timing advance is full in) by driving the car in high gear with a slight load like up a gradual hill and adjust the timing until there is a slight pinging under this part throttle load.

Manufacturers have stepped on themselves for years trying to engineer a vacuum advance that will provide smooth power and low emissions. What they have acheived is neither. Trying to balance the vacuum advance in an unknown distributor plus mechanical advance is beyond the abilities of most modern mechanial engineers much less some poor hot rodder trying to get his car to run half way decent so it will get him to work.

If you can't get it to run to your satisfaction, try to keep it simple. If you are willing to work through it, there is enough information here to make it work.

Quote:
Originally Posted by 454C10
Yes, put it back on and try it.

they don?t understand it, they're on commission, and they want to sell "race car" parts.
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Old 10-06-2006, 08:16 AM
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I have the Mallory Unilite vacuum advance distributor on my 427 and I have a 36 degree mark on my harmonic balancer.This is what I ended up doing.I set my timing(using stock mechanical advance springs)with a timing light and the vacuum advance disconnected so the 36 degree mark on the harmonic balancer was at the 0 on the timing indicator at (approximately)2800 rpm.This gave me an initial timing of 10 degrees.Then I hooked the vacuum line to my distributor and checked what my timing was with full vacuum advance.This put me at 60 which was too much so I used a Allen wrench up inside the vacuum canister and turned it till when at full vacuum it advances to 52 degrees.I use manifold vacuum not ported as it gives me that street friendly idle for this high compression daily driver.It took me a long time and many different combinations to come to this best combination for my engine.Good luck on your quest for what works best for your engine.
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Old 10-06-2006, 08:36 AM
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Why is it that most guys will describe their mechanical advance system using words like initial, total, rpm, curve, springs, bushings, and weights yet describe their vacuum advance system as simply 'vacuum advance'? Every vacuum advance can has a vacuum point that starts the advance, a rate of advance per unit of vacuum, and a limit to the advance. If you simply try to put a stock vacuum advance can on a modified engine it's not going to work very well. You need to tailor the VA curve with the same concern that you put into the mechanical curve. Lars Grimsrud has a part number listing of vacuum advance cans, specifications and applications that make selecting the proper VA can a little easier.
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Old 10-06-2006, 09:02 AM
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Quote:
Originally Posted by 454C10
Yes, put it back on and try it.

Here is a little copying and paste that I got off this site: Do a search, there has been a lot of discussion on vacuum advance and timing.

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.
dear 454 dude

I just told my boss I have to take a day off work to ready the latest response you wrote. He said no problem. He is a gearhead also.

Just kidding buddy. thanks for all your help. I'll have to read it a few times though. May need a couple beers to help me out.

I love it.

Lee
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Old 10-06-2006, 09:36 AM
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Guy, I beg to differ with what you said. If you are driving on the steet you want vacuum advance. That long post was an excerpt written by a gentleman who designed and worked on GM igintiions. An engineer I do believe. I can't believe anybody would actually question what this guy has to say. It's all there in black and white, theory, cause and effect, etc. By all means experiment with different vacuum cans but run manifold vacuum on a STREET car.
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Old 10-06-2006, 09:56 AM
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Quote:
Originally Posted by cool rockin daddy
Guy, I beg to differ with what you said. If you are driving on the steet you want vacuum advance. That long post was an excerpt written by a gentleman who designed and worked on GM igintiions. An engineer I do believe. I can't believe anybody would actually question what this guy has to say. It's all there in black and white, theory, cause and effect, etc. By all means experiment with different vacuum cans but run manifold vacuum on a STREET car.
OK, OK. I'm convinced.

throw me in jail with only stale bread and water for a month. I goofed up. I should be put on trial and punished for my actions.

but then again, that's one of the best ways to learn things unfortuneately, is to do them wrong initially, then correct your mistakes.
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