Distributor changes

[RustyRatRod]

I'll take your word for that. Good people can be wrong sometimes. Sometimes bad people can be right. Heck its easy enough to be right or wrong and not know why - so we take a guess that seems reasonable.

PM incoming.

 

[Abodysrule]

Thanks Mattax, that was very clear. For the 32 degrees at 2800 mechanical, I guess how that 32 is applied will depend on the build, right? This 360 mag will have a cam that isn't lopey, but somewhat aggressive I'm told (I'll see if can get the specs from the builder).

Let's see if I understood you. So, as a first approximation, I have the FBO limiter plate and spring kit. Many posts I've read say throw out the heavy stock spring and put a light one in it's place. The kit comes with gold (strong), silver (medium) and black (light) springs. Good guestimate of which I might try first? Then the limiter plate slots appear to limit travel of the weight pins in both directions, not just at one end of the slot, but both, so keeps more initial timing and limits total under acceleration. Good guestimate of a first slot to try? Say I choose 16 degree slot, and the springs allow the full 16 degrees at 2800 rpm, then I add 16 by advancing the dizzy at that rpm. As you say idle is what it is after that's done, I usually set my idle at 800-900 rpm. Then I do the vacuum method and figure out any vacuum can adjustment based on vacuum to get me to 50 degrees. Correct?

brian

 

[AJ/FormS]

My best advice is;
1) to get a dash-mounted, adjustable, timing knob, and start with roll-ons to find the spark knock limits of your fuel at various rpms, and then build your advance curve just once..
2) My second best advice is install closed chamber heads, crank up the Squish with flat-tops, and reach for a Dynamic Compression Ratio of over 8.2:1 with iron heads, and minimum .8 more with alloys. You will not be sorry.
3) My third best is to not install any cam with more than a 110 LSA. a 107/108 would likely be best. This, depending on the overlap, may somewhat limit how slow you can idle down the hiway and still get decent fuel-economy. But it will help to pump up your cylinder pressure, and that means .... torque
4) As for the advance cans, the screw inside them just delays the onset of advance. But every can in my collection has stops on the arms, that you can file down to transform it from whatever it is, to whatever you want it to be, up to a max of 22>24 degrees.
5) On the street, with street gears and tires,
torque is king; so forget about chasing Power, which is nothing but bragging rights. Build for torque and the power will come right along with it.
6) To work within the limitations of your Transfer slot sync you will most likely need a two-stage timing curve.

Opinions;
>if you install open chamber heads with no squish provision, you will be sorry. see note-1
> If limit your Static Compression ratio to 9/1 as some do, you will be sorry. see note 2
>If you install a big cam, into your lo-compression open-chamber heads, you will be very sorry; see note-3

note-1
such a chamber will be detonation prone at WOT, and often even at Part-Throttle, with almost any compression ratio, and any pump-gas; don't do it!
note-2
static compression ratios of 9/1 or less, with street cams, will lead to low Dynamic ratios, and low cylinder pressure, and a sucked out bottom end that needs a higher than stock stall, and higher than necessary rear gear ratios.
note-3
If you do this, your low-rpm torque will take a big hit. If you have to install a 3000 TC into a street 360, or anything higher than 3.55s, in an A-body, at 1000ft elevation or less, you did something wrong, and I can almost guarantee you that your cylinder pressure is weeeeeeeeak.
note-4
A streeter is a two gear car at best. and
your engine saddled with 3.23s and 27' tires in Second gear, it will
hit 65=3800 at zero-slip, say 4100 on the tach.
So then, that engine better have some grunt when it gets there; and it absolutely does not care how much power there is at 5500.
If it spins the tires all the way, well, that is different situation, lol.

Happy HotRodding

 

[Mattax]

For the 32 degrees at 2800 mechanical, I guess how that 32 is applied will depend on the build, right? This 360 mag will have a cam that isn't lopey, but somewhat aggressive I'm told (I'll see if can get the specs from the builder).

Yes it will vary a bit with cam, compression, heads etc. The 32* is at 2800 is a starting point that ought to be close.

So, as a first approximation, I have the FBO limiter plate and spring kit. Many posts I've read say throw out the heavy stock spring and put a light one in it's place. The kit comes with gold (strong), silver (medium) and black (light) springs. Good guestimate of which I might try first?

As a first approximation, run it as you bought it. Install it per instructions (with vac advance plugged).
Measure timing versus rpm from as slow as it will go to as high as you feel comfortable.
If its like the old Chrysler built ones, the curve will look something like this

Then the limiter plate slots appear to limit travel of the weight pins in both directions, not just at one end of the slot, but both, so keeps more initial timing and limits total under acceleration. Good guestimate of a first slot to try? Say I choose 16 degree slot, and the springs allow the full 16 degrees at 2800 rpm, then I add 16 by advancing the dizzy at that rpm. As you say idle is what it is after that's done, I usually set my idle at 800-900 rpm.

That's interesting. Depending on the original governor's slots begin and end, that could be so. I alsways recommend measuring the distance between the slots as well as their lengths before making any changes. Chrysler had a number of ways they could set up the curve and while it seems all those similarly stamped ought to be the same, can't be sure what you have unless you measure it.

Anyway, do not limit the timing to 32 at 2800 rpm. That's the reference point, thats all. Timing should continue to advance slowly with rpm for a few reasons.
The heavy spring is special because of the long loop. This delays engagement for X number of degrees allowing a quick advance, then a slower advance. In general Chrysler timing advances very quickly from idle to 1400-1800 rpm. Then advances slowly with increasing rpm.

The secret advantage of the heavy spring for high rpm when using electronic ignition.

Since you are begining with a MP distribiutor (or copy) you shouldn't have to mess much with the springs.
If you do, this thread has a good example of trialing different springs and making other adjustments.

Distributor curve help needed

I just checked the curve of my stock distributor (ported vacuum blocked) and need some help to optimize. Car is a 70 Duster with a stock 360, stock converter, 3.23 gears, 28" tires. Distributor currently has FBO black & gold springs with no limiter plate. 500-24* 1000-24* 1500-25* 2000-27*...

www.forabodiesonly.com

Then I do the vacuum method and figure out any vacuum can adjustment based on vacuum to get me to 50 degrees. Correct?

Yes.

 

[Hysteric]

Timing should continue to advance slowly with rpm for a few reasons.

What if the continual advancement is required because of left over CO in the chamber.........I'll let you figure who said that.

 

[Abodysrule]

Thank you Mattax. It is a mopar performance distributor from Mancini Racing, part number MOP440-430. The heavy spring doesn't appear to be as thick as some stock units I've seen, so I'll take your advice and start with it "as is" and go from there.

 

[Hysteric]

Try Halifaxhops here on the forum he should be able to furnish you with the right springs to get the advance you want or need.

[SOLD] - Refurbished Mopar only distributors.

 

[Brooks James]

LOL there was just a similar thread. The basics:

1...ALL factory distributors for these are "smogger" distributors, with a long slow advance. Even 340 "performance" distributors in 68 were somewhat smogged as federally "that is when it started." And they got worse every year. ANYTHING 360 OEM is gonna be a "smogger." You can braze up and file the slots for advance limit, find some springs and modify the advance rate
2....Install a performance distributor, preferably with an adjustable advance system
3.....Buy the FBO limiter plate kit.

MP dizzy with a bronze shaft

 

[Abodysrule]

Correction: I looked more carefully, the limiter slots in the FBO plate in fact do line up with the governor slots at the end closer to the center shaft, I was mistaken.