Tuning my distributor

[AcampoDave]

Now that my drivetrain is the way it's going to stay, I thought I'd take it up a notch and check my timing curves.
First the deivetrain: 283 bored .60 over with a .442/.444 lift and 204/214 duration. The heads are #416 from a 305 H.O. and they've been ported and polished. Its got a performer eps intake and a 500cfm Eddy carb and ramhorn duals. The carb is reponsive and doesn't seem to run rich.
The rear gear is a 3.08 and its mated to a muncie with a 2.98 first gear giving me a modest launch ratio of 9.2
Now the distributor: as checked by using a balancer degree sticker my static timing is currently 15 btdc and the mechanical advance adds in antother 14 giving me a total of 29. The "all in by" is still unknown because i am working alone and cannot read my tach and my balancer simultaneously. I did try advancing to 18 degrees static to shoot for a total of 32 "all in" but had to feather the clutch a bit too much on hard launches so as to avoid an off idle ping. Also, moving my advance line to manifold vac made the static timing 34 degrees and the idle got rough. It started quickly but stunk like it idled rich so I put it back to the ported side.
The truck does get hot rodded sometimes but its normal duties are more in line with touring the back roads of California while running the A/C in summer. I need to keep the distributor curve consrvative enough for real world triple digit summertime driving over a wide variety of conditions including mountai grades, on regular unleaded.
Distributor tuning is becoming a bit old school these days and whereas I am 53 years old and I understand how they work, I've never tried to take it up a notch before.
I would be very interested to hear some insight from you guys. Edit: my distributor is a Proform HEI style.

[geezer#99]

Couple things.
Have you confirmed your timing tab/balancer are accurate using a piston stop? Not a straw, pencil or screwdriver but an actual piston stop.
Easy to find your all in rpm. Just keep turning the idle screw up until timing quits advancing then quick like a bunny check your tach. Plug off vac advance off course.
You can limit your vac advance with a simple little tab made by Moroso.
Here’s a link I like on timing.

https://www.badasscars.com/index.cfm...&product_id=76

Here’s the Moroso tab in here.

http://www.crankshaftcoalition.com/w...EI_distributor

What’s your idle rpm is another question?

[AcampoDave]

Originally Posted by geezer#99

Couple things.
Have you confirmed your timing tab/balancer are accurate using a piston stop? Not a straw, pencil or screwdriver but an actual piston stop.
Easy to find your all in rpm. Just keep turning the idle screw up until timing quits advancing then quick like a bunny check your tach. Plug off vac advance off course.
You can limit your vac advance with a simple little tab made by Moroso.
Here’s a link I like on timing.

https://www.badasscars.com/index.cfm...&product_id=76

Here’s the Moroso tab in here.

http://www.crankshaftcoalition.com/w...EI_distributor

What’s your idle rpm is another question?

Geeze,you linked that before, and I saved the page. It's kinda what kickstarted all this. The mark was confirmed by the the builder of the engine. He used an inkpen on one of two hashmarks that came on the new balancer. I just trusted his mark. I'll do the "bunny check" tomorrow. Thanks for that one btw. Do you think my vac can pulls too much? Is it pulling 20 degrees if it jumped my static from 14 to 34 btdc? Edit I've not paid attention to idle rpm, but I will. Its usually a bit high in summer for the AC and i drop it to a smooth rumble the rest of the year.

[geezer#99]

Idle rpm can effect your initial timing readings. If idle gets close to where the mechanical timing starts then your initial number may not be accurate. Mechanical can start at 750 rpm.
Best to get idle as low as possible for initial timing checks.
Seems your vac pot does add 20 degrees.
A limiter is cheap to buy or make one yourself.
I usually adjusted them to give 10-12 degrees.

[Wrenchbender Ret]

It seems you have done your arithmetic & have it pretty well dialed-in. You could put a limiter on the vacuum advance & hook it to manifold vacuum but if it is working good you can run it like that. You still get the fuel mileage advantage with it hooked to ported vacuum. I like to get an adjustable vacuum chamber & it comes with the limiter.
George

[68 P.O.S.]

I looked up the Proform website and all of their HEIs provide 22 degrees of mechanical advance. Since Chevy’s run best around 36 degrees total timing, subtract the 22 degrees of mechanical advance from the total timing, and this shows your initial timing should fall at 14 degrees btdc: 36-22=14. It’s best to set your total timing and let the initial timing fall where it may. In your situation, the easiest way to set total timing is to take out the advance springs. Without advance springs, the weights fully advance the mechanical timing at a much lower rpm, like 1000. I prefer this method because it ensures the advance weights are fully deployed and you don’t need to have the engine screaming at high rpm while your head is under the hood. Once you set the total timing to 36 (with vac advance disconnected and plugged), you can add springs that allow the timing to be all in between 2500-3000 rpm. The Crane Cams springs are the best to use (1 blue and 1 silver) and allow full advance at about 2700 rpm. After that, move on to the vac advance.

The vac advance should be restricted to provide no more than 10 to 15 degrees of advance, no more. The aforementioned limiter is a great way to do this. Then, connect it to manifold vacuum and you’re all set on the ignition side so you can move on to the carb.

The carb transitions slots need to be set as shown in Geezers HEI link. Then you can use a vacuum gauge to set the idle mixture screws for best vacuum. Also, Edelbrock carbs are notorious for flooding and percolating fuel so make sure you address that as well.

[AcampoDave]

Great, so it does indeed look like 14 static is my number. I checked the "all in by" today and came up with 2000 r.pms on my old Suntune mini tach. I also confirmed that the weights are not advancing at an idle. Strange that my results seem to put the amount of Proform mechanical advance at about 14-15. Guess I'll pop the cap in the near future and take a peek in there. I will also pull the springs and see how much I get without 'em at high r.pm. That's good trick.

[AcampoDave]

When I increased the initial from 14 to 18 the motor pinged upon engaging the clutch unless I brought the rpms up a bit more and eased out a bit more gently. (A bit too much for practical clutch engagement during congested city driving. ) Would that ping be aggravated by the vacum advance? Also, I fiddled with the wieghts and springs, just made sure it was all free and clear and that the springs were secure and without slop. It was all good, and when i buttoned it up, the mechanical advance had picked up the extra degrees carrying the "all in number" to 32 with my crank at 14. Im good with that. My vacuum advance still pulls 20 more on ported taking me up to around 50 but i never feel it surging on open roads. Maybe the Proform distributor is set up pretty decently,

[AcampoDave]

I figured Id wrap this project up by checking my longbed truck too. It's an otherwise stock 283 with a new HEI from O'Reilly's. After installing the timing tape, I found my inital to be 14 and my mechanical added another 14 for the all in of 28 degrees at 2000 rpm. The advance can pulled another 22 degrees on ported. An all in of 28 degrees seemed low so I added 2 more to the initial and verified 30 all in. It did make some difference and I had to back the idle off prior to hitting the road. The power band used to fall flat in second gear at around 3500 rpm, but now it pulls smoothly up to 4k which is as high as I ever go. It also starts quicker and the midrange feels punchier too. The extra two degrees seemed to not bother anything at cruise when the vacum advance brings it up to a total of 52 degrees. I thought about going for more initial still, but it gets really hot around here in the summer so I opted to leave it alone.
Thanks for reading.

[crazy longhorn]

It sounds like you have it pretty much on the run.....but I will add a couple thoughts. You might remove one spring on the mech advance/& or put one lite spring on, & check it all in? I like the all in spot around 3000 rpms on a street motor. You may have to tailor the vac advance a tad to compensate....but 32-34 (mechanical+ intitial), is not far off. With the vac hooked , on your app, I would suggest around 48-50 degrees(all 3 in). I like the vac advance hooked to manifold vac source. Not carved in stone, as they all tune differently. Best of fun,crazy longhorn