Proper advance

[Dobber]

I am looking for some guidance on whether or not this distributor is going to work with the setup that the P.O. had in place. I have read Walter Moores' post and can not find my dist. number on any list. I have a D612-53, with a 12 deg. T bar. I see D612-52 and D612-54, but no -53. My distributor is from a 1971 S30 and has been converted to electronic ign. ( Crain XR3000 )

Engine config. is an F54 block, N42 head with a .450/.450 238/238 @ 0.050 cam, 6-2-1 header 1972 carbs with Z Therapy SM needles and stock air box, with cold air intake.

My question is, IF this distributor falls in the same category as the D612-52 and the D612-54 with the wild centrifugal and the vacuum adv. of 18 deg. for something in the neighborhood of 32-34 initial advance ( yes, the vacuum adv. works ) and aprox. 45-47 total, work with this engine config. I am leaning more toward mid. range power. Than you for any insight on this.

[John Coffey]

SUs work better with a less static advance then a set of Webers. Maybe 10 to 12 static then ramping up to 20 at 2000 and 36 by 3500. That faster you can ramp up the curver the better mid range response you'll get, if your fuel can handle it. IMHO, throw away the vacuum advance if you drive in a spirited way.

[Dobber]

Thanks for the input John. So if my dist. is in the same ball park spec wise as the D612-52 and the D612-54 ( mine is the D612-53 ) I would not be able to achieve those numbers? I would go from 5 - 7 deg. static to 12 deg. and disconnect the vacuum advance, would I be able to stretch upper end advance? The chart shows 29 and 31 for full throttle advance with no vacuum. It also shows that at 2830 rpm ( with active vacuum adv. ) there is a whopping 47 - 45 deg total adv. It seems to me that this distributor in its current curve config., is just plain wrong for my setup. ? ?

[Walter Moore]

The 12 on the T-Bar indicates 12 degrees of centrifugal advance at the distributor, which translates to 24 degrees at the crank. If the vacuum advance is attached to the front carb, it will only work at part throttle which is how it was designed. If you hook it directly to the manifold, as I have seen suggested on some sites, it will basically work all the time. (this is bad)

The 47 Degrees of total advance that I showed on the chart is the theoretical maximum and only meant as a comparison to other distributors. I doubt that you would ever get that much advance because the vacuum wouldn't be available in the carb at that engine speed under most conditions.

Even with the vacuum advance disconnected, if you set the static timing to 12 degrees BTDC as you suggest, you will end up with 36 degrees of total advance at high RPM which is probably too much for pump gas. I started down the road of looking up the distributor specifications because I set my car up almost exactly as you describe, and had excessive spark knock at speed.

If you want to get more advance early with your existing distributor you will need to get it re-curved.

Have you checked the condition of the bearings in your distributor? If it needs work anyway, that may be an excuse to do something else.

[Dobber]

Thanks for your reply Walter. What specs did you end up with? Do you run with the vacuum adv. connected? Mine is running off the carb, not the manifold. The shaft is very as new stable, no play. I also have a D6F4-01, but I am sure this was off of an injected 280z. The numbers seem to be a little closer to what I am looking for though. Would this be a viable alternative?

[John Coffey]

Remember that the factory non-emissions static timing number is 17 degrees BTDC at the crank. A "typical" 240Z distributor will get you an additional 21 degrees of advance at the crank for a total of 38 degrees by 3,500 to 3,700 rpm. That was all designed for leaded fuel.

Realistically on today's pump fuel you're lucky if you can get by with 32 degrees total at 3,500 to 3,700. That brings the static number back down to 10 or 11 degrees BTDC assuming the same advance curve.

All of the above is without vacuum advance.

I'm actually in the process of rebuilding and recurring a 240Z distributor as part of a little project. I'm going to try a build a digressive curve (more in earlier - starting at 1,500) and get 24 to 26 degrees of advance by 3,500 rpm (plus whatever static). So if you start with 5 static you'll get 31 total and if you start with 10 static you'll get 36 total.

Luckily the Porsche shop across the alley from mine has an Allen Synchrometer distributor dyno. :-)

EDIT: When I mean "typical" 240Z distributor, I mean ones that are 40 years old. I've tested a half a dozen and the actual advance curve is different then what's plotted in the FSM due to age, wear, gunk, etc. If you got to the trouble of tearing it apart, cleaning, media blasting, lube, etc. you might be able to get back to what the FSM says.

Edited May 4, 2011 by John Coffey
added a comment

[Dobber]

I would be very interested in hearing how that turns out John. Even if I could find a shop with a dyno, I am sure they would have little experience with six cylinder Datsun's. My dist. is in very good condition, so would be great to use. Are you running points or electronic?

[John Coffey]

Electronic (XR3000) and I'm also working with Pertronix to have them build an Igniter2 for the Datsun distributor.

[John Coffey]

BTW... there's nothing special about the Nissan L6 when it comes to timing and the advance curve. I'm just experimenting and its most likely that I will end up with a linear advance curve that's remarkably similar to the advance curve for a Porsche 4 or 6 cylinder, BMW 6 cylinder, the stock Nissan L6, or most any other automotive IC engine's advance curve.

[Dobber]

I wondered about that non linear advance. The only way I could see something like that working, would be with a variable pivot point on the centrifugal weights. Just me.

As I do not live in gear head utopia, ie: Distributor dyno across the alley, can you recommend a weight or spring swap for my current setup that would put me firmly in the ball park of a tunable system. Thanks for your help John.

[Dobber]

OOPS! Sorry John you already answered my question with your first reply. Will stay with the 12* T bar and set static to 10* and disconnect vac. and start from that point. I think I'm awake now. Thanks for the help.

[MY1PATH]

I know this is an old thread but I thought I would add a finding...

My '74 260z auto came with a D6F3-02 But the T-Bar had 14 stamped on it for 28 Degrees of mechanical advance. I think thats a new High and maybe a little scary.

I am currently rebuilding an electronic D6K80-03 out of an '81 280zx (17 degrees advance)

I'm guessing with fuel injection flame fronts moved faster and that's why less mechanical advance was used from '75-83