[BillsNogo]

Anyway, I used my dial back timing light because that is what I have, and because other than TDC and a mark at 35 degrees, there are no other marks on the balancer The car had a rediculous amount of initial timing, close to 30 degrees plus the 20 degrees of mechanical advance. It is amazing to me it ran as well as it did. I backed it down to 20 degrees initial and 40 total. MUCH better, part throttle surge GONE, runs great especially after I adjusted idle mixture after the timing change. My wife is taking it to town today, 30 miles each way, to see if the running hot problem has gone away as well.

I hope you didn't hurt it with 50 degrees of advance.

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).

Please bare with me as I am really trying to learn the correct way to time an engine, and to do that, I need to know why you need to do what is needed. Does that make sense?

Anyways, why would the guy running 50 degrees mechanical advance (30 initial and 20 centrifugal), be hurting the engine, but when using 50* timing with the vacuum advance in addition, it is okay.

Lets say I set mine at 16* initial, and the centrifugal advance from the HEI adds in 20* in by...lets say 2800rpm.

Assume my car cruises on the highway at 3000 rpm (4.10 gears with 28" tires). To cruise on the highway I do not need to have it at WOT, so would there not be vacuum advance added in to get me close to 50* timing?

Is it only because there is no real load on the motor? I just don't see why 50* at 3000rpm in one situation is worse than another.

Next edjucation I need is to read up on tuning a carb with a vacuum gauge

bill (back in class studying :yes: )

 

[chevyIIheavy]

actually with the vacume advanced hooked up it would stop advanceing at lets say 3000 rpms so you would be at or near total advance ( initial+centrifigul+vacume= total timing ) if you had lets say 50* of advance the motor would be real responsive but have no power to pull it through the rpm range and it would start noseing over or fall on its face or blow up with a vacume advanced dizzy you have three points of timing ( initial , centrifugal, and vacume ) these all have to be added to get the total timing at say 3000 rpms
example: 8* initial ( idle timing )
+
12* centrifigal ( distributer advance , usually from the factory )
+
10* vacume advance ( little vacume canister on dizzy )
-------------
30* of total timing ( all in by 3000 rpms )

 

[The Big Al]

actually with the vacume advanced hooked up it would stop advanceing at lets say 3000 rpms so you would be at or near total advance ( initial+centrifigul+vacume= total timing ) if you had lets say 50* of advance the motor would be real responsive but have no power to pull it through the rpm range and it would start noseing over or fall on its face or blow up with a vacume advanced dizzy you have three points of timing ( initial , centrifugal, and vacume ) these all have to be added to get the total timing at say 3000 rpms
example: 8* initial ( idle timing )
+
12* centrifigal ( distributer advance , usually from the factory )
+
10* vacume advance ( little vacume canister on dizzy )
-------------
30* of total timing ( all in by 3000 rpms )

I don't mean no harm but this is incorrect!

Sorry
Al

 

[The Big Al]

You have to understand that a Vacuum advance is used when the engine is not under a heavy load.

It is based on engine intake vacuum. intake vacuum is very very sensitive to load and throttle response.

You have initial timing for easy cranking and smooth low RPM operation.

The total mechanical advanced timing is the best factor for best performance.

example!
you have 12 initial
You have 36 total at full mechanical advance

Then on top of this you have a vacuum advance, the advance (In most cases) gives 12-18
This could be 48-54 at cruise.

Understand when the engine is under acceleration and vacuum drops the vacuum advance is not a factor.

I suggest anyone want to learn more about how this works and how there engine operates get a vacuum gauge and mount it in your car.
This gauge can tell you more about the engine tune than any other gauge.

Oil & temp tell you engine condition. Vacuum can show you a vacuum leak, a mis-fire, and you can learn how to drive leaner saving fuel.
This is not a rumor, this is a REAL TOOL!


IMO
Al

 

[ALLT4]

This place really needs a dedicated tuning section. No offense Bill but I've posted information on timing as well as others and they just get lost in the mix of "Which cam should I buy"

Then you have to run the gamut of folks that tell everyone they can just lock it all out and be happy. We get tired of it. They don't even know what your combo is, what heads you have, what gears you have, what converter you have, what your pusrpose of the car is or anything.

I'm going to try to come up with my own thoughts and the way I do things in a clear easy to understand write up at some point so I can reference it when these questions come up.

 

[BillsNogo]

This place really needs a dedicated tuning section.

I would love that! I have been searching this and other sites for the last three days and am definatly learning the basics, but still run across post that SEEMS to contradict each other, and need to know why there is a difference to I can grasp the reasons, that is why I have you guys

sorry if I am babbling, I just woke up

edit: Nevermind (in the voice of gilda radner)
I think it just clicked. The example of 50* with vacuum advance at 3000rpm is not unsafe since the vacuum advance timing would be pulled out when engine vacuum is going down (already knew that), but the other guy with 30 initial and 20 centrifugal will have 50* when under hard acceleration or any condition when it is above rpm his fully advances since it is ALL mechanical advance.

bill (babble, babble, uh..... babble)

 

[Paul Wright]

Have you read "vacuum advance 101" in Best of... Archive?

 

[ALLT4]

Paul I think he did read it, one of his original quotes looks like it's from that sticky.

Just keep in mind vacuum advance plays no role under load or heavy load. It's only added when vacuum is high under light load bringing the engine back to peak efficiency. Vacuum advance is NOT RPM dependent what so ever. It only responds to vacuum.

Nobody that I know of runs 30° initial timing then adds in even more with centrifugal. What you're saying Bill, is that some use 30° initial and then add in 20° more making 50° centrifugal. Not so, that would kill an engine with detonation under load.

Here's how it usually goes; take out the vacuum advance for minute. We aren't even going to bring it into the equation yet. You have a dizzy that has a 20° centrifugal advance slope or range it can travel. The initial timing is set for example 12 degrees. When the engine RPM climbs so does the centrifugal advance up to that 20° range, at 3000 RPM or so it should be full through it's travel and reach 32 degrees advanced. 12° + 20° of centrifugal swing = that 32° There's your FULL total mechanical timing.

People that have problems with sluggishness more than likely have springs that are too tight not allowing full mechanical advance soon enough and toss everything locking it down causing other problems that need band aided like ignition kill switches so they can start their engines without that grunting of the starter. When all it would take is lighter springs and no band aides.

Well now that there's the full mechanical advance most engines that don't live in a black hole can use even more than that 32° of mechanical advance but only under light no load situations with vacuum advance. Keeping the engine at PEAK efficiency. It has nothing to do with being an economy device, losing power, or any of that hogwash you hear. Isn't an engine that's running at peak efficiency an engine that is making the most of fuel and making the most power? You bet it is, you can feel it in acceleration cruising when stomping it, throttle response is greatly enhanced with it.

Back to that theoretical engine with 32° of mechanical advance. Since most engines can use more under light load up to 50° advanced or so, real world it's less depending cylinder heads, cam and many other factors. Let's just use 50° since you seem to be stuck on that. We would need a vacuum advance can that bring in up to 18° of additional advance under light load. 32° of mechanical advance + 18° of vacuum advance = that magical number of 50° you're talking about.

The vacuum advance will swing a lot during throttle position, load and what not trying to always keep the motor at peak efficiency. If you have your foot fully in it from a launch it has absolutely zero effect because vacuum is like null, only the mechanical will be reacting up to that 32° until load levels out vacuum goes back up and then the vacuum advance starts coming back in.

Is it hard to get all right? Hell yes it took me weeks to get it all spot on. The trick is to get it somewhere just below ping at all conditions. Gas, throttle position, load changes, weather everything considered.

I don't know if any of that helps or confuses more.

 

[danthegeek]

I don't know if any of that helps or confuses more.

I just want to add one more thing. To understand why an engine needs an advance in timing you have to understand how it works. Fuel takes time to burn and depending on the conditions that amount of time changes. A rich mixture will burn quicker then a lean mixture. Also, a more efficient combustion chamber (such as newer cylinder heads) are better at "mixing" the fuel and have a better flame travel. This means the mixture can burn in the cylinder much quicker then a old or less efficient combustion chamber design. So they need less advance in the spark. The opposite is true for less efficient designs in combustion chambers, they need more advance to burnt he mixture completely. Also a higher compression ratio is more efficient at mixing the fuel in the cylinder then a lower compression ratio. This also means a higher compression ratio should require less advance in the spark then a lower compression ratio.

All of this effects the amount of time it takes for the mixture to burn. When the mixture begins to burn and starts to create pressure, that is where the power your engine creates comes from. This cylinder pressure will peak and you want this peak in cylinder pressure to happen between 10-15 degrees after top dead center. If the peak in cylinder pressure peaks to soon, it can cause detonation and harm to your engine. If it peaks to late, you are loosing power and efficiency.

The "pinging" you hear when the you have a little to much advance in the timing is the peak in cylinder pressure happening to soon. The effect on the piston is the same as hitting it with a hammer and can cause damage such as pitting of the surface over time. Usually a few degrees less in advance will put the peak cylinder pressure in the right range (10-15 degrees after top dead center) to create the best power and efficiency.

So, its going to take some trial and error to find what your engine likes. Going to the drag strip to find how much total advance it likes is the safest and easiest way. Thats were i would start first. Then work on the rest like initial and vacuum advance on the road like "ALLT4" suggested.

-Dan

 

[Paul Wright]

Here's another Best of Thread that has timing info buried in it.
http://www.stevesnovasite.com/forums/showthread.php?t=44524

 

[BillsNogo]

Have you read "vacuum advance 101" in Best of... Archive?

Yep, that is where my third quote came from

Here's another Best of Thread that has timing info buried in it.
http://www.stevesnovasite.com/forums/showthread.php?t=44524

That one is where I got the first two quotes from and confused me a little. It is all making more sense now, so thanks to all who tried to help me, as it sinks in slow for me

Now on to search about tuning carbs :slap: oh, and maybe spark plug gaps opcorn:

thanks again

 

[Baddbob]

It takes awhile to figure out what each combo likes. The same engine installed in your nova would need a totally different curve if installed in a heavier vehicle, gearing also plays into the combo. If you're running the combo that's in your sig: 454/th350/2800stall/4.10's in a third gen nova and can provide all the engine specs I bet the members here can come together and give you a fairly accurate guess at what curve it will like.
tuning for just below ping through the entire rpm range is the most ridiculous thing I've ever heard!

 

[RED67]

What happens to the "Ping Factor" when you "lift off" a high compression engine in gear at the end of a drag strip run with a vacuum advance ?

 

[Paul Wright]

tuning for just below ping through the entire rpm range is the most ridiculous thing I've ever heard!

No....

Leaving the distributor hold down clamp slightly loose and running the car at WOT down the road, "allowing" the timing to "find its own place"

is the most ridiculous way to set timing I've ever heard!

 

[ALLT4]

I love you guys, you shoot other people down and disagree but offer nothing of your own in your own words. How about when you disagree you explain why and offer some help instead of just being argumentative?

 

[danthegeek]

tuning for just below ping through the entire rpm range is the most ridiculous thing I've ever heard!

Yes, you dont want to tune "just below" pinging through the entire RPM range. If there is pinging, you know you have to much advance. You can assume somewhere close to that peak efficiency is occurring. That could be 2... 4.. 10.. degrees less in timing and you have to find out what it is.

Start with total mechanical advance and to see where the most power can be made during WOT. This should be done at the track so you can get concrete evidence (time slips) that you are making more power. Read the plugs, they will tell you more then your ears ever will. If you see any silver or sparkles on the plug, you are experiencing detonation. Those little bits are pieces of the pistons because they are getting pounded on by pre-ignition. Once total timing is done, tune the initial timing and the timing curve for best throttle response off the line when going to WOT. Make some runs and check the plugs again. If all is good, move on the vacuum advance and a good article for this is the article in the Best Of tech that Paul suggested.

Another good article and will probably be more benificial then my rambling on...

Finding Fuel Efficiencies and Peak Power By Sam Moore

 

[ALLT4]

I pulled this right from the article, how ridiculous!

The ideal ignition timing for power occurs just before the point where detonation or pinging takes place.

It's all you can do to use your ears barring a dragstrip or knock sensor. Two things that aren't readily availble to the guy scratching his head in his garage in the suburbs.

Someone please correct me. I'm serious.

 

[chevyIIheavy]

sorry guys i sometimes post the wrong or misleading info...... i to dont fully understand how vacume advance works i was just trying to help ( im a shade tree mechanic :yes: ) this is one reason why i dont have it on my car same goes with vacume secondary carbs ........ in my opinion there sh** and it takes to much time under the hood to fittle fart around with what works and what doesnt ..... so i run my dizzy locked out and a mechanical secondary carb on my street/strip 360 c.i. pump gas motor .... i know how to set the timing with it locked out and if i go to the track i read the plugs to see what its doing ( a/f mixture , timing , etc... ) ........ please dont take this the wrong way im not here to bash or critisize im not trying to be rude either i repect all of you guys on this site and most if not all of you have very good info for me and others im here to learn so i can one day help other as you guys have helped me :yes:

 

[BillsNogo]

It's all you can do to use your ears barring a dragstrip or knock sensor.

And unfortunatly, the nearest drag strip is about two hours away in any direction, and I have no trailer. Too far to drive it to the strip, at least until I get OD.

thanks again guys

 

[Paul Wright]

I love you guys, you shoot other people down and disagree but offer nothing of your own in your own words. How about when you disagree you explain why and offer some help instead of just being argumentative?

Here's why:

If you put a degree wheel on a short block and a dial indicator on the piston at TDC, you'll see there is about 15 degrees sweep of crank movement around TDC before the piston/rod has moved far enough to have leverage on the crank throw.

An engine will make the most power when peak cylinder pressure occurs the piston is 12-15 after TDC when the piston is beginning to descend. Before that the piston and rod are near vertical and the force will be transferred as a hit into the bearings. Peak pressure occuring much after that, the piston has descended too far for complete combustion and power wasted.

For peak pressure to occur at the optimum crank angle, it is necessary to initiate combustion, before TDC. Pressure is builds as the flame begins at the spark plug and burns fuel across the chamber. The piston is rising against the increasing pressure causing a loss in torque (negative torque).
This is an acceptable loss because when peak pressure occurs at the right crank angle after TDC, the positive torque is much greater.

Let's choose a particular engine combo that has been proven to make the most power at 38 degrees total timing.

Fill the tank with 87 octane. Twiddle the distributor until it knocks, back it off 2 degrees. Check the timing and it's 33 degrees.
Drain and fill the tank with 110 octane. Twiddle the distributor until it knocks, back it off 2 degrees. Check it with a light. 45 degrees.

If you tune your engine without a timing light and based solely on audible spark knock you are not going to get optimum timing. You may luck out and it may be close, or.... it could be way off, waste power and damage the engine.