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Discussion Starter #1
Just a quick question to those of y'all who've ever run a high-compression 429, where should the timing be on those? I'm looking for best fuel economy and low-end torque. I'm currently running 12*BTDC initial and I'm fairly happy with how the truck accelerates and maintains speed, absolutely no pinging on 87 gas either, but I was wondering if I can do better while still on regular gas? My 350 Chevy I had at 14*BTDC but that was a regular compression engine, I've never had a high-compression or even a big block before so I figured I'd ask y'all before I go and do something stupid. Thanks!
 

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Discussion Starter #3
Tis a '69 engine, so supposedly 10.5 compression. And yes, dizzy is all stock, short of new rotor and cap.
 

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A stock points distributor that came with it? Or just a regular duraspark from a 460?

The stock advance springs are very heavy and don't give you much advance at everyday driving around RPM levels.

if you set it at 12 by the time you hit 2000 rpm you might only see 16 or 17 degrees. Some of the stock spring setups wont give full advance till almost 5000 rpm's

Normally with a 10.5 to1 compression engine you would be running 100 octane back in 69 and might want something like 4 degrees initial timing and 44 degrees or so total timing with the lightest spring you could run that wouldnt allow the advance weights to bounce and cause spark scatter.

having all the timing in by 2200rpm or so would be great but you wont be able to do that on pump gas at 10.5 to 1 .

I don't think its possible to run more than 32 or so degrees timing on super unleaded with 10.5 to1 compression.


Are you using the original cam that came with the engine?

they had shitty valve springs back then so they tended to make cams with long duration and low lift to make power and not have valvetrain problems . Cams like that bleed off a lot of static compression, so the 10.5 to1 compression isnt as much of a problem as it would be with a modern cam design.

If you have a newer cam you need to be very careful because higher lift shorter duration cams will build very high cylinder pressure in a 10.5 to 1 motor .
 

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My stock 70 429 is set at 12 before. I am running the stock 78 400 ignition system. I only run 91 octane fuel. If I go below my present altitude (8K), I put in 1 or 2 cans of octane booster.

I have loud exhaust system, so I am very paranoid about pinging, and not hearing it. So far, even crawling around at Moab, I have not heard any pinging.
 

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Discussion Starter #6
I guess then my setup is very similar to what 7LBronco is running - stock '69 429 with stock '78 ignition system. I'm not planning on doing any cam swap any time soon, as the engine is plenty powerful as is, so I should be good on the cylinder pressure thing?

Those 32 degrees you mention, that's initial + centrifugal advance, right? I can probably limit the amount of centrifugal advance by flipping that thingie in the dizzy to the shorter slot, so that way I know there's no way I over-advance even at higher rpms (which my truck rarely will see). So for regular gas what total timing would you recommend, and by what rpm? I mean those [email protected] you mentioned are for super unleaded, how about for 87 gas? And how does vacuum advance factor in the whole equation, my engine pulls like 20" vacuum at idle and about 15" at cruise, so I bet the can on the dizzy is near maxed out for the most part, wouldn't that mess up the whole advance calculations?
 

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My stock 70 429 is set at 12 before. I am running the stock 78 400 ignition system. I only run 91 octane fuel. If I go below my present altitude (8K), I put in 1 or 2 cans of octane booster.

I have loud exhaust system, so I am very paranoid about pinging, and not hearing it. So far, even crawling around at Moab, I have not heard any pinging.
The stock 78 400 distributor pulls all the advance in way too fast for a 429, and even too fast for a 460 in my opinion. If you got a 460 distributor it should run 12* initial, 32* total with 87 octane.
 

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Discussion Starter #8
How much centrifugal advance is a 460 or a 400 dizzy good for? Assuming tis a stock unit that is.
 

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Discussion Starter #11
Generally 30 to 35 degrees, 10 more for the vacuum advance. The rpm of the maximum advance is as important as the actual advance degrees.
So I'll definitely need to flip that plate inside the dizzy, as I only need no more than 20 degrees centrifugal (12 initial + 20 centrifugal = 32 total)? Or is the 10 degrees of vacuum also included in the equation (so 12 initial + 10 centrifugal + 10 vacuum = 32 total)?
 

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look at which advance plate is in the distributor . Whatever its marked double it to get the centrifugal advance and knock off a little if there is a plastic bushing on the stop post.

If you want 32 total and you are using a 10 degree plate then set the initial at 12 .

if you are using a 15 degree plate then you will have to set the initial at 2 degrees.

Always work off your max timing and let the idle fall where it may. If it winds up at 2 degrees then put the vacuum to it at idle if it winds up at 14 then use ported vacuum.



Whichever plate is in the distributor you can always flip it to have at least 1 option.

Just remember if you flip it without pulling the distributor your timing will be 180 out .

The 10 degree and 13 degree slots work best with low compression motors For higher compression 15 or 18 might be your best bet to give you a good spread between ease of starting and your max timing that you want .

As for stock curves its difficult to tell I've seen 21 degree slots in a few 79 broncos I've also seen 15 or 18 who knows whether the randomness is from a Ford mistake or a different distributor being swapped in .

With a 21 slot you'd have 42 degrees centrifugal added to 14 or so initial it would put you at 56 . If you ever put a light spring in that setup your engine would be toast.


The best tool you can have is a good dial back to zero timing light. Its much easier to mark the zero and just dial the light to what you want to set your timing at.


Its also the only way to see what amount of timing the vacuum advance is putting in. Some of them will add 40 degrees before you adjust them. Some of the vacuum advances wont stay put either I have seen the screw move over time and change from 10 degrees to 30 over a 6 month period.
 

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Discussion Starter #13
I was under the impression that the plate can be flipped without the firing order ending 180deg off? At least that's all I've been told by a few other Ford folks, that the plate gots two vertical slots for the rotor? As for the vacuum advance, how's that adjusted as far as max travel goes? With the Chevy HEI we throw in a kit by Crane that has a cam-looking plate that allows to lock out as much advance as you need up to 12deg, which means the stock 22deg vacuum advance can be made to pull only 10deg at max vacuum, is there something like that available for the Fords? Sorry if that question seems silly, tis just I've never messed with a Ford dizzy before.
 

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If its at TDC when you start and the rotor is pointing to 1. When you flip the plate the rotor winds up pointing to 6.

There is only 1 notch that locates the rotor.


Adjust the vacuum with an allen through the hole where the hose plugs on. They use a few different size allens depending on who made the advance. There are 2 types of advance but the one you see most when you adjust it you are changing the total advance limit. its basically a stop screw. It moves a little at 1 or 2 inches of vac but by 6 or so inches of vacuum it goes to max whether thats 10 degrees or 40.

Accell used to make a nice one where the screw adjusted a spring so you were changing the amount of vacuum it took to get a certain amount of advance. You could say have 10 degrees at 10 inches of vacuum and by loosening it have 10 degrees at 5 inches. or tighten it and go the other way.
 

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Discussion Starter #15
Well, that's kinda silly, so the vacuum advance on a stock dizzy runs at 100% pretty much all the time except when you floor it? Ain't that thing supposed to be load-sensitive, if it does indeed max out at such a low vacuum reading that's like an on/off switch for the timing more than anything else!

How do you adjust the stopper screw in the vacuum can, let's say turning it clockwise does what, reduce max vacuum advance, or increase it? Also if I drop it down to 10deg from the 20+ where it's at now (I got a lot of marks on my balancer, that's how I know), will that turn the whole shaft too and require me to reset the initial again? That's just what happens with the Crane kit for the HEI, when you limit the vacuum advance it turns the whole mechanism inside the dizzy and advances initial timing by whatever amount you're locking out from the vacuum, will the Ford do something like that too?
 

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the stock vacuum cans are like a on off switch for the most part. But it doesnt run that way stock there are a whole pile of little vacuum doohickeys that affect it .

Over the years most get tossed or break .

now you basically have 2 choices direct manifold vacuum or ported off the carb. ported will be off at idle then become manifold vacuum at above idle.


vacuum pulls the diaphragm towards the front of the truck so turning the screw in would decrease the vacuum advance

Its getting late here so i might have wrote that backwards:toothless

Adjusting the vacuum advance won't affect base or centrifugal timing. If you set the base timing it will stay put.

The adjustment is pretty fine grained 1 turn is 4 degrees or so depending on the pitch of the screw they used on that unit.
 

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Discussion Starter #17
Mkay, makes sense, will turn the screw in a bit tomorrow evening after class and watch what happens. Should I be shooting for 10deg of max vacuum advance, or you'd recommend a different value? Also is there a chance of stripping the screw, or tearing the diaphragm?
 

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Good postings on timing and effects of vacuum advance.

I've always thought of that VA screw adjustment as changing the 'sensitivity' of the vacuum can; and that increasing the spring tension on the diaphragm decreases the sensitivity and gives less timing advance at cruise speeds (for any given manifold vacuum). Conversely, decreasing the tension would increase sensitivity and give more vacuum advance at cruise (and better fuel economy).
If the screw is turned more CW (tightened?), then there would also be a poiint where the vacuum couldn't overcome the diaphragm spring resistance and the total vacuum advance would be reduced. At least that's the way I understand it.....

On my 78, the VA hoses are routed through a temperature vacuum switch mounted on the thermostat housing. This switch feeds manifold vacuum to the VA when the engine's cold, and switches to ported vacuum after operating temp is reached. Now I don't know if Ford did this to reduce emissions or for better driveability, but it does seem to run better when cold with this setup.....
 

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That was all done for emissions. Prior to that the VA from the dizzy was plumbed directly to the carb.

I think I run the 429 in the 250 at 10 degrees.
 

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I believe mine is set at 8 degrees and my current elevation is 1100 feet. I haven't played with it much to see if there is a better setting.
 
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