Total timing?

[red82gt]

I just did some reading over at Fordmuscle.com and I think I now know why my car's been a bit of a disappointment. I've been running 32* total timing on my car and my CR is only about 9.0:1 . According to them I should have my total timing between 38-42*! One of their project cars picked up 30rwhp and a boatload of torque by going from 30* total to 42*!
Anyways, my initial timing is 14* and it only seems to advance 18* (even though it's on a 10L weight) so I think I need new weights and probably a spring with less tension.
Anyways, what does everyone else run for advance? What should I use as my starting point?

[PKRWUD]

42 sounds a little high to me, but hell, there are dozens of factors that play into it. That is also the reason that you shouldn't set your timing to a specific setting based on something you read in a magazine, or online.

You are going to have to experiment. Buy a recurving kit for your distributor, change the weights, and try one think spring and one thin spring, and see how that feels. If it's better, try two thin springs, etc. The recurve kits usually come with 3 different sets of springs, and by mixing and matching them, you can alter your curve. Don't forget about vacuum advance, too. The factory units have differ in the amount of advance they permit. Some only allow 8 degrees, while others go as high as 16.

Experiment. That's the only way to find what will work best for your combination of parts and geographic limitations.

Take care,
~Chris

[RoadWarrior]

I agree that 42 sounds pretty high. Maybe the gas up here isnt as good but i probably wouldnt run it past 36 otherwise a bad batch of gas could wreak havoc. But PKRWUD is dead on. Do some trial and error and find what works best on your engine. And just work your way up. Dont just crank it to 42 and risk damaging things. Try it in 2 degree intervals and see how it goes.

[red82gt]

I also thought 42 seemed a little high. I'm going to start at 36 and go from there. I'll worry about the vacuum advance once I get the mechanical curve I want. My car has the adjustable vacuum advance so I can change it, I'll adjust it by driving it up a steep hill and see how it behaves.
I think my car does need a fair bit more timing because it seems to be out of where the powerband for this motor should be at the track. I get my best times and MPH by running it up to 6300+ rpms and it bogs out of the hole bad (2.0 60' times on sportsman pros) even with a 4000rpm launch, saying to me there's no torque down low.

[PKRWUD]

If you ignore your vacuum advance now, your curve will be way off. When you're at WOT, your vacuum advance is at it's maximum, but when you're cruising, it's hardly used at all. You need to include it in your calculations for racing, and can ignore it if you want to figure a curve for highway cruising.

Take care,
~Chris

[red82gt]

I thought that at WOT there was virtually no vacuum at the spark port? When I crack the throttle open from idle with the vacuum guage hooked to it it stays at 0, if I hold the engine at say, 2000 rpm, it settles to about 20" and back at zero at idle. Also everything I've read says the same thing, I think you've just mixed yourself up today PKRWUD, everthing else you've said makes sense to me except this.

[302 LX Eric]

I'm running 33* with my 331. Still need to experient though.

Also, vacuum under WOT should be zero and at idle I'm at ~11 or 12 in. hg.

E

[red82gt]

At a full vacuum port my car pulls 14" at idle, it's only zero at the timed port, sorry I didn't clarify that.

[PKRWUD]

Originally posted by red82gt
I thought that at WOT there was virtually no vacuum at the spark port? When I crack the throttle open from idle with the vacuum guage hooked to it it stays at 0, if I hold the engine at say, 2000 rpm, it settles to about 20" and back at zero at idle. Also everything I've read says the same thing, I think you've just mixed yourself up today PKRWUD, everthing else you've said makes sense to me except this.

Vacuum advance operates on PORTED vacuum, not MANIFOLD vacuum. You seem to have them backwards.

Check your ports yourself. Oh wait, you mention that in your last post. So you understand you were mistaken, and how important it is to calculate in your vacuum advance. Good.

You had me worried for a minute there.

[gofastmercury]

Sh*t, I'm sorry Chris. Isn't there no vaccumm at WOT? Maybe 1?
Maybe your just testing us?:D Right Jim?

[PKRWUD]

Actually, as I read that, I don't think you have a clue about PORTED vacuum (the vacuum source for your vacuum advance).

Manifold vacuum is what exists underneath your throttle plates. When they are closed, manifold vacuum increases. If your vacuum advance was hooked up to this source of vaccum, you would be fully advanced at idle, and the timing would retard as you accelerated. This won't work. So, the engineers needed to figure out a way of having the opposite effect, but that meant creating vacuum as the throttle opened, and lessening it as the throttle closed. Quite a paradox. Until someone realized that the transfer slots, the grooves that are cut into the venturi above and below the throttle plate, worked on a similar principal. Rather than depending on the vacuum created when the throttle plates are closed, they used the vacuum created by the air rushing by a small port at the narrowest part of the venturi. The faster the air would rush by, the more vacuum would be created. So, at closed throttle, there would be no PORTED vacuum, whereas the farther the throttle was opened, the more PORTED vacuum there would be. It's just like a minature fuel feed, except it goes to the ported vacuum port instead of the bowl.

Get it?

Take care,
~Chris

[PKRWUD]

gofast-
That wasn't aimed at you, but the explaination is still accurate.

:)

Take care,
~Chris

[CB93LX]

I dont know if Im reading this correctly, but I dont think there is any vacuum advance at WOT.

[gofastmercury]

You know, I never knew that. That seems to make alot of sense. explained well too.......

[PKRWUD]

In a nutshell, ported vacuum and manifold vacuum react opposite to the throttle opening.

Think about it. If the vac advance was hooked to mani. vac., you'd be phucked!

Thanks gofast, I try.

:)

Take care,
~Chris

[PKRWUD]

Originally posted by CB93LX
I dont know if Im reading this correctly, but I dont think there is any vacuum advance at WOT.

Yes, there is. In an engine with vacuum advance, the TOTAL advance is made up from three sources:

max vacuum advance
max mechanical advance
base timing

C'mon guys, carburetors weren't that long ago! you guys are making me feel old.

[CB93LX]

Ive been wrong before, and I may be now but I was sure vac adv was 0 at WOT. Only mech and at WOT. Ive had a few and still own a carbed. As far as how it all works and the way you explained it is correct and it makes since to think there would be vac adv at WOT but I beleive there was a reason that there wasnt any. I used to run my truck 73 F100 at the track with no line hooked to vac advance. Later down the road I started driving it daily and put a line on it. Got better gas milage but no improvement in times at all with the same base timing. I believe it only works at part throttle.

[red82gt]

I'm confused? Howcome my car hasn't detonated itself to death then? With the vacuum advance hooked up my car goes to about 50* advance @2500 and it doesn't ping but if I crack the throttle wide open with the light on it, the timing falls to my original 32* mark? Vacuum advance is mostly for fuel mileage, otherwise why would a lot of performance distributors not have it? This is the website I've been reading... www.fordmuscle.com/archives/2000/03/timing/index.shtml

[PKRWUD]

Originally posted by red82gt
I'm confused? Howcome my car hasn't detonated itself to death then? With the vacuum advance hooked up my car goes to about 50* advance @2500 and it doesn't ping but if I crack the throttle wide open with the light on it, the timing falls to my original 32* mark? Vacuum advance is mostly for fuel mileage, otherwise why would a lot of performance distributors not have it? This is the website I've been reading... www.fordmuscle.com/archives/2000/03/timing/index.shtml

Ahhhhh! I now see why you are confused. That article is incorrect. If you read the sidebar right next to it, where it says "Tuning Vacuum Advance", you will see that they contradict themselves. The sidebar is correct, the article is mistaken.

The reason that you setg the base timing with the vacuum disconnected is so thet you can accurately set it. If the vac was hooked up, you wouldn't know how much of your advance was mechanical, and how much was vac. BUT, you MUST include the vacuum advance in your calculations.

Hope this helps.

Take care,
~Chris

[PKRWUD]

Originally posted by red82gt
Vacuum advance is mostly for fuel mileage, otherwise why would a lot of performance distributors not have it?[/url]

I missed this part, sorry.

When it comes to racing, you are rarely at speeds of less than 2500 rpms, and since that is where the timing is usually fully advanced, there is no point in having a vacuum advance.

This may be slightly different in some Ford applications, because for a few years, they had vacuum advance units that had two ports on them, and had two different vacuum sources to help control the advance, to reduce emissions. Those are useless, when it comes to performance.

[PKRWUD]

One more point to keep in mind is that distributors that have a vacuum advance unit usually have a smaller range for the mechanical advance.

[PKRWUD]

Last point to keep in mind. Hopefully this will answer your questions as well. The vacuum advance and mechanical advance do different things to create the advance. The mechanical uses weights and springs to advance the rotor beyond where it would normally be, in relation to the driven shaft. The vacuum advance actually moves the breaker plate, or in electronic ignitions, the pole plate, where the magnetic ring is. Both forms of advance work independent of each other, and must be added together when determining your total advance.

Want me to take some pictures for you?

[red82gt]

I'm gonna need the pictures, I know how it works, except the part where you say that the spark port keeps pulling harder as the air moves faster, wouldn't this mean that both advance mechanisms are doing the same thing, increasing with rpm?
The spark port pulls a vacuum that is proprtional to the load so it'll pull it's hardest under the least load once the throttle blades are opened. I also have an article in HOT ROD that says the exact thing as the FordMuscle article and I think if it was incorrect, it wouldn't have made it into print.

[gofastmercury]

Gees man, just because its in Hot Rod , don't mean its true!
I've seen LOTS of stuff in there thats wrong.

[gofastmercury]

Oh and by the way. This explains ALOT of timing problems I've had over the years. Good to gets these out of the way before I hit 30!

[CB93LX]

Everything PKRWUD is saying is correct as far as figuring total advance, but , Vacuum advance doesnt apply to WOT.

[PKRWUD]

Originally posted by red82gt
I'm gonna need the pictures, I know how it works, except the part where you say that the spark port keeps pulling harder as the air moves faster, wouldn't this mean that both advance mechanisms are doing the same thing, increasing with rpm?
The spark port pulls a vacuum that is proprtional to the load so it'll pull it's hardest under the least load once the throttle blades are opened. I also have an article in HOT ROD that says the exact thing as the FordMuscle article and I think if it was incorrect, it wouldn't have made it into print.

This is from your article:


Vacuum Advance: Most Ford distributors include a vacuum advance mechanism. This consists of a diaphragm vacuum canister, an arm from the canister to the breaker plate, and a hose connected to an engine vacuum source. The purpose of this mechanism is to provide spark advance when the engine is not spinning fast enough to create the centrifugal advance talked about earlier. In other words this is an engine-load dependent advance. This would be a typical situation when climbing a steep hill, or driving at low rpms, light throttle, conditions. In these conditions there is high engine vacuum, so the vacuum signal applied to the diaphragm in the canister, via the hose, will cause a 'pull' effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there is very little engine vacuum, and thus the vacuum advance does not contribute to total advance.

Have you ever driven up a steep hill? Your pedal is to the floor, and your manifold vacuum is at zero. The last line is completely false. If manifold vacuum and spark vacuum were in fact the same, then it would be correct, BUT THEY ARE NOT. They are the opposite. if they were the same, it wouldn't matter where you got your vacuum from for the distributor.


Vacuum advance is tricky to tune because there is no direct measurement like total. In fact, the reason you must measure initial and total timing with the vacuum hose disconnected is because when the engine is in neutral there no load, thus the vacuum is high, and if the hose were connected you'd see as high as 60 degrees advance and think something is really wrong! The only way to tune vacuum advance is on the road, by feel, and AFTER the initial and total are adjusted.

This is simply false. Check the vacuum at the spark port when you are idling. There is none. The vacuum increases as the throttle plates are opened.

I'll take some pictures for you. Do you understand the venturi principal? You need to in order to understand this. I'll be back in a few.

[PKRWUD]

This is from the side bar on that same webpage. Read it, and you will see how they contradict themselves.


Tuning Vacuum Advance
The last step, after the total advance curve is set, is to dial in the vacuum advance if you have one. There should be a vacuum line connected from the carb, or the manifold, to the vacuum canister. There are two types of vacuum sources that you should be aware of. One type is known as "full" vacuum or "manifold" vacuum. This is a direct connection to the manifold, and if the hose is connected to this port you will get vacuum in the line at idle. The other port is a "timed" port, which only yields a vacuum above a certain rpm. At idle the line will have no vacuum. Most carburetors have both ports. On Holley's the timed is above the throttle blades, and the "full" is below, near the base. On Carter/Edelbrock carbs, the timed port is on the passenger side and the full is on the driver's side. The easiest way to confirm what port you have is to hook up a vacuum a gauge and check for vacuum at idle. The preferred vacuum source is the timed source. This way there is no effect on the initial timing setting.

[PKRWUD]

This picture shows where the vacuum advance port goes to. It is above the throttle plate, which means that manifold vacuum does not apply to it. As the throttle plates open, the air rushing by creates a vacuum in the carburetor. This is how the fuel is sucked from the bowls, and is how vacuum is created at the spark port. The more air that rushes by, the higher the vacuum.

If this doesn't explain it, I quit.

Take care,
~Chris

[CB93LX]

I dont think you are getting it now PKRWUD, those articles sound correct to me. At WOT it is the same vacuum above or below the throttle blades. Vac advance is only there to bring in more advance at part throttle wheras mech advance works all the way to WOT. Same total advance with or without vac advance at WOT.

[PKRWUD]

Okay, let me clarify something, for the purposes of explaining this, I have referred to WOT when I should have been saying 2500 rpms, or whatever engine speed the full mechanical advance is tuned to comes in at. To be specific, yes, at WOT, the ported vacuum source is zeroed out, but prior to WOT, at common driving speeds, both the vacuum advance and the mechanical advance can and do simultaneously reach their peak, so if you don't account for this, you will have detonation problems. That was the whole point I was trying to make here.

I disagree about the article, though. They are mistaken.

[red82gt]

I went to the carbed ford message board and the corral and so far I've got about a dozen people that say the same as I do and I've even got a test for ya. Hook your vacuum guage up to the spark port with a T and go for a drive. 0 at idle, goes up cruising at 2000 and a little more as you go up in cruise rpm. Put the throttle down a bit and the vacuum will drop to 3-4" meaning it's dropped some of the advance, go to WOT and it's at about 1", go ahead and try it.

[red82gt]

PKRWUD, I already had my vacuum advance adjusted so that it wasn't pinging at part throttle, we could've ended this debate a long time ago. I did in fact know that the vacuum advance added timing at part throttle but that wasn't my problem, it was top end track performance at WOT that I was concerned with. Oh well, just glad it's settled.

[HotRoddin]

Originally posted by red82gt
0 at idle, goes up cruising at 2000 and a little more as you go up in cruise rpm. Put the throttle down a bit and the vacuum will drop to 3-4" meaning it's dropped some of the advance, go to WOT and it's at about 1", go ahead and try it.

yep ... now let the RPM come up and watch it go back up again ... its load dependent, its affected by both throttle position and RPM. Either way, whatever vaccum advance you have is added to the mechanical advance you have which is added to the initial advance, so you can't just discount vaccum advance. Well you can but you're gonna end up with more advance than you bargined for :eek:

[CB93LX]

Looks like everyone is on the same page I guess our wording and interpetations of posts just werent on point. Oh well.

[PKRWUD]

Originally posted by red82gt
PKRWUD, I already had my vacuum advance adjusted so that it wasn't pinging at part throttle, we could've ended this debate a long time ago. I did in fact know that the vacuum advance added timing at part throttle but that wasn't my problem, it was top end track performance at WOT that I was concerned with. Oh well, just glad it's settled.

Great! As long as you understand that you need to include your vacuum advance when calculating your total timing, my job here is finished.

:)

Take care,
~Chris