Locked advance

[roccodart440]

I'd like to toss this out there for input and discussion

I run an MSD Billet Dizzy with a 12 degree bushing. 26/28 in at 2500

I don't really see, since the Digital 6 has a 20 degree start retard, why you couldn't lock the dizzy at 34-38 range. The car is light, 4.10 gears and a [email protected] cam cut on a 112, and a 4500 stall.

 

[rmchrgr]

Dedicated race car? Lock it.

On a street car it's good to have a curve with tuned vacuum advance because you're spending most of the time at part throttle operation. Just have to ask yourself if you need/want full ignition advance all the time. Your idle will be higher and you will have to tune it to suit the extra advance. Check your vacuum before and after you make the change.

I briefly drove a car with a solid roller and locked timing on the street. I didn't think it was necessary.

On the other hand, there isn't that much difference between locked timing and a very quick advance curve, especially with a digital MSD. The multiple sparks supposedly help combustion at lower RPM. YRMV.

 

[roccodart440]

Dedicated race car? Lock it.

On a street car it's good to have a curve with tuned vacuum advance because you're spending most of the time at part throttle operation. Just have to ask yourself if you need/want full ignition advance all the time. Your idle will be higher and you will have to tune it to suit the extra advance. Check your vacuum before and after you make the change.

I briefly drove a car with a solid roller and locked timing on the street. I didn't think it was necessary.

On the other hand, there isn't that much difference between locked timing and a very quick advance curve, especially with a digital MSD. The multiple sparks supposedly help combustion at lower RPM. YRMV.

Street car

There is no vacum advance on the MSD pro billet dizzy I run.

YOu have a good point, the mopar performance dizzy is full in at like 1200 or something

 

[rmchrgr]

Street car

There is no vacum advance on the MSD pro billet dizzy I run.

YOu have a good point, the mopar performance dizzy is full in at like 1200 or something

I think that’s where this question usually comes up. If the engine wants to idle at say 1,200 rpm because of the combo and the advance curve is “all in” around the same rpm then theoretically there is little to no advance curve anyway.

No way to know if there is any benefit to locking the timing without trying it. I believe it’s pretty easy to do on those distributors so give it a shot and let us know how it works out.

 

[Bewy]

Rocco,
There are onoy two reasons that you would not run a locked dist & reap the benefits:
- starter may have difficulty cranking
- may get detonation with locked timing. That is why MVA is so good: the timing reduces under load.

Good on you for experimenting.

 

[mderoy340]

I'd like to toss this out there for input and discussion

I run an MSD Billet Dizzy with a 12 degree bushing. 26/28 in at 2500

I don't really see, since the Digital 6 has a 20 degree start retard, why you couldn't lock the dizzy at 34-38 range. The car is light, 4.10 gears and a [email protected] cam cut on a 112, and a 4500 stall.

Since you have the 20* start retard, I would simply compare idle quality between 26/28 and 34/38. 3rd gear low rpm acceleration will be the range to much timing will show up on a street car.

 

[AJ/FormS]

If you are running a carb;
a large amount of Idle advance will usually negatively affect the transfer slot fuel delivery, usually causing a tip-in sag/hesitation. But with a 4500 stall, Ima thinking you may not notice it, However, it will still create a stink in the exhaust at idle.
Briefly, I ran the 292/108 Mopar cam, that I measured at [email protected], and that was when I learned how to tune. But I was running a manual trans, so parading with 3.55s, required the idle-speed to be quite low, lol, which demanded a retarded Idle-timing. Yeah, that took me a long time to figure out.
I got her down to 550 in gear and pulling herself. Using a modified factory Mopar distributor. I get 22 degrees out of the modified Vcan, for a total available Part-Throttle Timing of
up to 12/14+22+22= 58* after 3400 rpm. Which translates to
up to 12/14+14+22= 50*@2800..Cruising at 65= 2240 in overdrive, is
up to 12/14+10+22= 46* which is not optimum, so I have a dash-mounted, dial-back, timing module with a range of 15*, that I dial up, for up to 6 more, for up to 46+6= 52*@2240
With 3.55s, 2800 in Second gear is ~33mph, and with 50* is so smooth, and the exhaust sound is so sweet, and at Part-Throttle the lil 367 pulls so hard, that around town, that is my upshift cue .
But I pulled that big cam after a few months. I ran it just long enough to be frustrated by the lack of torque at take-off, with only 3.55s. Being a dedicated DD, with lots of hiway miles; that was all I wanted to run.
The next cam (223/110), was a whole new engine.

What I'm saying is that VA is the bees knees.

 

[roccodart440]

Since you have the 20* start retard, I would simply compare idle quality between 26/28 and 34/38. 3rd gear low rpm acceleration will be the range to much timing will show up on a street car.

I have a manual VB and (most likely) wouldn't be in 3rd gear under mid 2k rpm range, where I already have full advance.

 

[roccodart440]

If you are running a carb;
a large amount of Idle advance will usually negatively affect the transfer slot fuel delivery, usually causing a tip-in sag/hesitation. But with a 4500 stall, Ima thinking you may not notice it, However, it will still create a stink in the exhaust at idle.
Briefly, I ran the 292/108 Mopar cam, that I measured at [email protected], and that was when I learned how to tune. But I was running a manual trans, so parading with 3.55s, required the idle-speed to be quite low, lol, which demanded a retarded Idle-timing. Yeah, that took me a long time to figure out.
I got her down to 550 in gear and pulling herself. Using a modified factory Mopar distributor. I get 22 degrees out of the modified Vcan, for a total available Part-Throttle Timing of
up to 12/14+22+22= 58* after 3400 rpm. Which translates to
up to 12/14+14+22= 50*@2800..Cruising at 65= 2240 in overdrive, is
up to 12/14+10+22= 46* which is not optimum, so I have a dash-mounted, dial-back, timing module with a range of 15*, that I dial up, for up to 6 more, for up to 46+6= 52*@2240
With 3.55s, 2800 in Second gear is ~33mph, and with 50* is so smooth, and the exhaust sound is so sweet, and at Part-Throttle the lil 367 pulls so hard, that around town, that is my upshift cue .
But I pulled that big cam after a few months. I ran it just long enough to be frustrated by the lack of torque at take-off, with only 3.55s. Being a dedicated DD, with lots of hiway miles; that was all I wanted to run.
The next cam (223/110), was a whole new engine.

What I'm saying is that VA is the bees knees.

Tough to compare these, but your post is valuable info.

My cam is [email protected] 112LSA, 4.10 gear, 4500 man vb auto.

My idle is about 900. I can get it down a touch lower, but why would I. It likes 900.