What is the total advance btdc 1974 460 with edelbrock preformer plus cam#2167 260/280 duration 460/480 lift stock timing chain.
Procomp dist. non vacume advance stock maniflods and stock carb.
seems to labor and backfile at 1000 to 3000 rpms?
ive been told to set the total advance with the rpms at 2500-3000 rpms?

 

For most Ford motors, 38° BTDC is the max mechanical advance you can run. That would be with a clean healthy motor and real good gas Good luck with the gas part). Normally anymore than about 36° is the most you will want to try running. If the engine pings or rattles under heavy load, you will want to retard until it stops doing it. From you description of your problem I would guess you need to re curve you dist. so you can have the advance you need. Not running vacuum advance is killing any gas mileage that was possible with the engine.

 

If you care about the motor having good performance you should get a vacuum advance and tune it right with an adjustable vacuum can.
The problem your having probably stems from not having enough timing, whitch will cause a loud exaust note and a lack of torque. Once again get a vacuum advance distributor.

 

Interesting statement considering true race motors don't ever use vacuum advance and have plenty of torque. Where did you come up with the loud exhaust thing?

 

He said nothing about this being a drag car, he did say stock manifolds and carb. I kinda thought this was a truck forum. Sure drag cars don't have any use for a vacuum advance. But if the engine is ever used at part throttle it will benefit greatly from a well tuned vacuum advance.

I came up with the loud exaust thing from years of tuning performance engines. And cause it's true, think about it. The later the timing the more the combustion finishes in the exaust. A well tuned ear can hear the differance. I trust my ear more then my timing light. It's just like being able to hear a ping or a bad valvetrain.

Once again there wasn't much info on what's going on with his motor. I'm just throwing out my best advice based on what I know.

 

But his off idle bog problem is not gonna be caused by vacuum advance unit, ever. Vacuum advance is a mileage improver, not an performance item. This is either a carb problem, a initial timing problem and a mechanical problem in the engine itself.

 

Where in the above quote did he say anything about an "off idle bog" are you a little confused?

So you state it could be a "timing" problem but somehow not a vacuum advance "timing" problem, your logic has failed you. Just like sticking with a lame black powder cartrage like the 45/70.

How does one improve mileage? You increase efficency witch has a nasty byproduct of also increasing power ond drivability.

Once again if there is an "off idle bog" a vacuum advance is very much the way to fix it. The engine needs more timing to run efficently then you can get away with in the inital timing and still start the motor. The stater can't crank past TDC when the ignition fires to far before TDC this causes the engine to kick back during cranking as soon as one of the cylinders fires. But if you have the engine running and only change the timing you will find you get the fastest idle at about 20deg. That timing in witch you get the fastest idle is the best timing for that rpm and throttle. But you'll have a hard time starting the engine with a 20deg inital. The solution VACUUM ADVANCE let the engine have a stable idle at your inital timing and as soon as you touch the throttle before the carb has deliverd any more fuel, the timing is advancing giving you more power and rpm. It works try it.

 

Bear you must undersstand this better then you demonstrated here. I came across this post https://www.ford-trucks.com/forums/7...ce-sought.html asuming you read what was being said as you contributed to the discussion, or do you jest refuse to learn anymore?

 

I'll add my two Cents here to point out that Opossum has a point since most people fail to realize that the vacuum advance runs off of Spark Vacuum that is taken from the venturi in the carb and increases with engine RPM. And yes, I ran a drag car/street car with a 351 4V Cleveland and a recurved DSII, MSD 6A and Vacuum advance; gotta have it!

 

Bern--That's a good looking carb in your sig. Looks like a Barry Grant? I haven't before seen a secondary throttle plate that cool on a Holley type carb.

Bern I apreciate the validation but just want to point out a couple small myth's in what you said:

The spark/ported vacuum dosen't really come from the venturi (though I see how it might seem that way) and does not increase with RPM.

The ported vacuum comes from a small hole that is coverd by or just above the throttle plate at idle. On the holley in the picture it will be a rectangular slit just above the small idle fuel feed holes that you can see in the pic. This slit is uncoverd by the throttle plate at tip in allowing the vacuum advance to provide some extra responce. After the throttle plate passes the ported vacuum passage ported vacuum is equal to manifold vacuum there after.

The port in the base is to far down the bore to be effected by the venturi in the body, and because the port is 90 deg to airflow it is not effected by air speed.

The manifold vacuum will go down with increased throttle decreaseing timing with increased throttle. Manifold vacuum increase and therefore port vacuum increase during high throttle with RPM is entirely a function of carb size and an increase in timing, an increase manifold vacuum at high throttle high rpm is a good thing, as manifold vacuum drops cylinder pressures drop allowing/requiring for more timing.

 

So how come a real honest to God racing engine will never have vacuum advance. But by your theory is won't preform well because of no vacuum advance. My response is, you don't know what you are talking about.

 

OK Bear I'll answer this one for ya, pay attention.

First, these days a real honest to god racing engine won't have a vacuum advance because it uses a computer to control the timing.

Back in the day before computer controlled timing, race engines didn't (NASCAR still dosen't) have a vacuum advance for reliability, because it has very little effect on the performance there looking for, and would be to hard to make work well (the throttle is open to far at idle, and these engines produce very low vacuum). Many race engines are designed and tuned only with full throttle performance in mind. At full throttle the vacuum advance is irelevent because there is very little vacuum.

These engines also don't idle well, produce good low end torque, have good throttle response, or get good mileage.

They also don't use power valves, vacuum secondaries, hydrolic lifters, pump gas, or streetable torque converters.

There not asked to drive around in heavy traffic, haul heavy loads, deal with low stall converters, and drive power stearing and A/C pumps.

Hope this helps Bear but I suspect it won't.

I've been doing this for a living for a long time and have been fortunate enough to work shoulder to shoulder with many professional racers including a top fuel funny car champion. My personal passion and business is built around providing my customers with the most capable street cars and trucks, to fit there needs much better then any factory can provide.

Ya know if you didn't have that pic I'd think you knew better and were just being argumentative.

When I look at the picture in your sig it is obvious that you are confused. I see a tri power, these were never a good idea and you will never see any honest to god racing engines running a tri power. And I see a very cheap ignition system. How do you even get that thing started? I could go on but those are the biggies and tell me all I need to know about wether or not you know what your talking about.

From what I've read in other posts your very knowladgable on classic fords and probably know more than I do when it comes to restoring a factory ford. At least when it comes to what came with what, but I'll still make it run better.

Now your wondering, what's wrong with tri-power? The problem really isn't tri-power per se, it's the fact that there is (no one has been able to do it yet) no good manifold to make it work well. For a street engine you need a good dual plane manifold. This is to hard to do while providing for the three carbs. It in theory can be done but the manifold would be rather tall and complicated, making other options like dual quads a better choice. Or my favorite a big single 4V with four corner idling on a medium height dual plane manifold with a large volume.

I'll be in the Union area the weekend after thanksgiving, if you would like I could stop by and make your vehicles run better?

 

opossum---I was just thinking about something after reading the last few posts. Just a suggestion, but there may be something to this idea of using venturi vacuum for advance purposes that bern talks about.
I have a 70 Mach in the garage w/351C 4bbl heads, FMX (I hope its still there). Its been a while since I looked at it carefully, (engines out anyway). So, this is kinda just a question . Didnt they use venturi vacuum to perform some advance function somewhere around the late 60's? Is that what they used on the double diaphram distributor to pull advance out as the engine speed increased? That would have offset the manifold vacuum to the dist and acted as a retard feature or more correctly pulled the advance back to a power range at speed. Remembering that all vacuum (ported or manifold) is the same value at off-idle.

I swapped out a tri-power setup on my 67 427 vette, years ago for an edelbrock DP with a 780 squarebore, vacuum secondaries. I picked up noticeable perfomance below 4000 with only a small loss above that. Overall, it was stronger--! I even tried the Segal progressive mechanical linkage for the tripower----whatta waste, should have stayed with vacuum pull-in.

I cant help but notice you are having trouble getting the message out about vacuum advance for street (that would be non-racing) performance vehicles. Dont be discouraged, most of us understand!!

Now get busy figuring out how I can adapt FI to a 434 in my mach

 

Easy.

A real honest race engine will not be in a car that is driven on the street.... Not on the street, no need for a vacuum advance.

A little off topic, but your reasoning seems pretty out of whack... someone of your integrity might respond with:

If transbrakes work so well in race cars, why arent new cars manufactured with them?

How come i have never heard a car leave a stop light off a 2-step?

If slicks provide enough traction for race cars to run 4 second 1/4 mile passes, why dont we use slicks instead of snow tires?


Darren, With your truck being a 1974... Im guessing it has a points distributor? The backfiring and lack of power in that RPM range could be because your point gap is set wrong.... Sorry if you have a duraspark ignition... But if i remember right, 1974 trucks with 460's had points ignition system

 

To make mechanical linkage work on 3X2 setup, you need to have accelerator pumps on the end carbs. Just like the 390 and 406 3X2 set up had.

On my 1969 428CJ going from the stock 4V to the 3X2 made for a dramatic increase in ET and top speed.