Vacuum advance does not affect the "haul *** quotient", correct?

[moparedtn]

Real quick, the particulars on my car:
'68 GTX with a mild rebuild 440 with a 484 Purpleshaft in it. 4 speed, 3.55 SureGrip.
Edelbrock 1407 750cfm carb, right out of the box set up.
Everything is fresh, including Centerforce Dual Friction clutch.
Car actually runs and drives very nicely. Mixture screws set for best vacuum and the car likes the accelerator pump on the furthest out hole/setting.
Mopar electronic ignition conversion. Timing is set to give me a mechanical advance total timing of 36BTDC which comes in around 2500rpm or so; that gives me an initial idle setting of about 13BTDC. Vacuum advance disconnected for now - it gets jittery/surges on part-throttle acceleration if it's hooked up, which I know I need to play with/adjust eventually.
Car idles just fine at 800rpm, too.

Now that the combination has gotten some miles on it, it's time to tune it more.
It pulls just fine as it sits, but I feel that it's not pulling as hard as it could/should based on my past experiences with other 440s.
Don't get me wrong - it doesn't stutter or fall down or nose over or anything, it's just not as hard a puller as I think it should be.

Before I start playing with the carb to richen things up (which I know it needs because it flat hates it if I move the accelerator pump rod at all towards leaner), I just wanted to make sure that the timing is pretty much a done deal?
FSM says to get 38BTDC so I'm pretty close with that now.
Does the vacuum advance actually do more than make for better part-throttle cruising fuel economy?

 

[440beep]

Yes, the vacuum advance only comes into play while doing a steady cruise while the motor is generating vacuum. Once you nail it, vacuum advance goes away.

You might want to mess with the dizzy and take out some mechanical advance so you can put more initial timing in. Seems the consensus is the 440 likes more initial timing.

Also, you're comparing your 440's pulling power to other 440s you remember; what gear ratio was in those cars? Might the 3:55 gear be affecting the pull power sensation?

 

[khryslerkid]

Seems like I've read about you working on this car before?

Glad to see you're at the point of fine tuning her!

Do you know what the compression ratio is of this engine? How about your vacuum numbers?

 

[moparedtn]

Yes, the vacuum advance only comes into play while doing a steady cruise while the motor is generating vacuum. Once you nail it, vacuum advance goes away.
You might want to mess with the dizzy and take out some mechanical advance so you can put more initial timing in. Seems the consensus is the 440 likes more initial timing.
Also, you're comparing your 440's pulling power to other 440s you remember; what gear ratio was in those cars? Might the 3:55 gear be affecting the pull power sensation?

I could on the initial timing, sure but the 13BTDC is already more advance than I ever remember running on one in the past. Seems like they "used" to like around 10BTDC stock back in the day?
'Course, gas was a whole different critter back then, too....

The 3.55's might be a partial cause, sure. Thinking back, I remember running 3.91's in a few and 4.10 in one in particular that never saw a highway (for obvious reasons).

 

[moparedtn]

Seems like I've read about you working on this car before? View attachment 503280
Glad to see you're at the point of fine tuning her!
Do you know what the compression ratio is of this engine? How about your vacuum numbers?

Who, me?

No idea what compression it's running, but I haven't been able to get it to knock yet and it registers 145psi on a compression test, however that translates.
Vacuum is about 11-12hg at idle.

 

[wagonman]

Real quick, the particulars on my car:
'68 GTX with a mild rebuild 440 with a 484 Purpleshaft in it. 4 speed, 3.55 SureGrip.
Edelbrock 1407 750cfm carb, right out of the box set up.
Everything is fresh, including Centerforce Dual Friction clutch.
Car actually runs and drives very nicely. Mixture screws set for best vacuum and the car likes the accelerator pump on the furthest out hole/setting.
Mopar electronic ignition conversion. Timing is set to give me a mechanical advance total timing of 36BTDC which comes in around 2500rpm or so; that gives me an initial idle setting of about 13BTDC. Vacuum advance disconnected for now - it gets jittery/surges on part-throttle acceleration if it's hooked up, which I know I need to play with/adjust eventually.
Car idles just fine at 800rpm, too.

Now that the combination has gotten some miles on it, it's time to tune it more.
It pulls just fine as it sits, but I feel that it's not pulling as hard as it could/should based on my past experiences with other 440s.
Don't get me wrong - it doesn't stutter or fall down or nose over or anything, it's just not as hard a puller as I think it should be.

Before I start playing with the carb to richen things up (which I know it needs because it flat hates it if I move the accelerator pump rod at all towards leaner), I just wanted to make sure that the timing is pretty much a done deal?
FSM says to get 38BTDC so I'm pretty close with that now.
Does the vacuum advance actually do more than make for better part-throttle cruising fuel economy?

Pretty much for fuel economy. My setup is close to yours except 3.23s Auto trans Comp XE268-10 and a Holley 750 DP. Has an old Eddy TM7 with a 1/2 in spacer. Belive it or not got 14.7 on a recent trip and that was at 70 to 80 mph up I-5. 10.2 gallons in 158 miles aint to shabby for a warmed 440. Has a very slight surge at about 45 but I can live with it. Hook it up to ported vaccum and she what it dose. You might be cruisin with a big grinn like Me.

 

[moparedtn]

Pretty much for fuel economy. My setup is close to yours except 3.23s Auto trans Comp XE268-10 and a Holley 750 DP. Has an old Eddy TM7 with a 1/2 in spacer. Belive it or not got 14.7 on a recent trip and that was at 70 to 80 mph up I-5. 10.2 gallons in 158 miles aint to shabby for a warmed 440. Has a very slight surge at about 45 but I can live with it. Hook it up to ported vaccum and she what it dose. You might be cruisin with a big grinn like Me.

Oh brother, trust me after all the car and I have been through these last 6+ years, she's a joy to get into and go driving.
I'll eventually fool with the vacuum advance on the Mopar distributor; just have to get out the little allen wrench and play with settings until the jitteries go away is all.
Another fight for another day.
Thanks!

 

[lewtot184]

those 1407's are butt ugly rich on the primary main metering. the 284/.484 isn't cast exhaust manifolds friendly.

 

[moparedtn]

those 1407's are butt ugly rich on the primary main metering. the 284/.484 isn't cast exhaust manifolds friendly.

I have Hedmans on it. Inherited them with the car. Big ol' headers.
3" duals all the way out the back, single chamber Flowmaster looking thingies.

 

[oldbee]

Just an idea but I'm going to side with lewtot on this one. If ur at the outer most hole on pump then that's the leanest(less pump shot) there is. So if u go inboard on a hole ur going even more rich with the throttle movement. Check spark plugs I bet they're kinda sooty!

 

[moparedtn]

Just an idea but I'm going to side with lewtot on this one. If ur at the outer most hole on pump then that's the leanest(less pump shot) there is. So if u go inboard on a hole ur going even more rich with the throttle movement. Check spark plugs I bet they're kinda sooty!

You are correct sir, at least on the accelerator pump. From the manual:
"CALIBRATING THE PUMP
If you encounter any hesitations or stumbles that do not seem to be related to the basic metering or have not responded to changes in the basic metering, move the pump drive link to one of the holes closer to the carburetor body. This will increase the stroke length of the plunger and result in more pump delivery."
My having to run it on the outermost pump rod setting then means I have to run it on the leanest pump setting then, because it does make a noticeable difference when it's on the middle hole for sure - there is a noticeable hesitation.
If that's too rich on the pump, then that probably means the primaries are already too rich.
Ok, I understand that, thanks.
I was thinking ***-backwards on that, probably because I'm used to chasing down too lean a carb usually.
Book says to change rods first on that, then mess with jets beyond that.

Reckon I best fetch a kit for this carb - the one I have is for the 1411, none of which works for the 1407 at all (of course!).
I just wanted to make sure that I was about done playing with the timing first.
Thanks again, y'all!

 

[Kern Dog]

That 284 cam is sort of an oddball. It should make more power than the 280/474 and less than the 509 but my experience was that it idled as bad as the 509 with less power.
The 284 and 292/509 really like lots of initial timing. I ran 17 initial and 31 total (Instead of a more common 35 degrees) because at almost 11 to 1 it wanted to rattle at anything over half throttle. The MP distributor has an adjustable plate to widen or narrow the advance range. It is possible to run it tighter than I did if needed.
The Edelbrock is not the easiest to tune as compared to Holleys or the Holley based Demon/Proform, etc carbs.
As stated, vacuum advance should be only in effect at part throttle. If the vacuum line is connected to manifold vacuum, it puts the vacuum advance in from idle on up. That is not the correct use of the vacuum advance and will contribute to an unstable idle, especially with a lumpy camshaft. Think about it...The engine is running with loads of timing at idle, you lean on the gas a bit then floor it and half of the timing backs off. That is not going to give the best performance. It is better to set the initial and total advance THEN use the vacuum advance (Connected to a PORTED source) to improve mileage.

 

[HALIFAXHOPS]

PM the dist number and I can give you the factory specs at least to start with to get a baseline. Remember specs the total is mech adv + vac advance = total advance.

 

[Dragon Slayer]

PM the dist number and I can give you the factory specs at least to start with to get a baseline. Remember specs the total is mech adv + vac advance = total advance.

Doesn't initial Advance count towards total?

 

[HALIFAXHOPS]

Yes that is the mechanical, the vac usually does not kick in until around 7"hg or so on average, when I run them on the machine I do mechanical first then add the vac to get the total at rpm. Here is a example of the specs if you can read it, some times easier to see it.

 

[Dragon Slayer]

Understood, but your post can be misleading as your combining initial and centrifugal as mechanical. If your worried about performance at WOT, to help determine where you put initial timing, you have to factor that in separately. Initial Timing + mechanical advance of distributor weights + Vacuum Advance = Total Advance. Spring tension, and vacuum curve effect all this. I know you know this, just think as stated may not help those not as knowledgeable on how it all works. Seeing it on a distributor machine helps you see how it all works.
Finally, too much initial with light springs and the car may be hard to start.

 

[HALIFAXHOPS]

Totally agree just going to throw easy numbers out the timing at idle on the balancer is set at 10 btc, then it has 20 mechanical advance at 2000 rpm and the vac advance is 10, then total timing is 20 positive. Hope it helps someone.

 

[HALIFAXHOPS]

I just had a hard start with my 440 in my dart, had a cheap two wire in it I bought when I first started building the car to get it moving (marine 440) the springs were way to light, broke two starter noses off (mini starters). It would advance way to far initially at crank, and if I set it where it would start right it was way to retarded at 3k it almost bogged down. The start problem was when it was hot I should add. Finally got a distributor I wanted (Mallory mechanicle) that is totally adjustable, Runs great now.

 

[HALIFAXHOPS]

Getting back to the original question yes a vac advance does affect the haul *** right @green 66

 

[TxDon]

When it comes to advance curves everyone's experience is as different as the equipment on their cars. My car came with an unknown cam that sounds a lot like yours, same carb, and an MP distributor with about the same timing settings as yours. It would not run right with vacuum advance connected just like yours and seemed to not pull as hard as I thought it should. I ended up limiting the centrifugal advance to 16 degrees and bumping the initial to 20 degrees, it made a big difference in all around running and it pulls more like it should without any negatives. I have not tried using the vacuum advance since I did this but I will at some point.