Ignition Timing

[Classics Fan]

Originally Posted by SeventyOne

Why do you say the Black springs are too light? To me that curve seems to be what you need for a stockish build. You'd have 16 initial timing and ~20 mechanical advance. Depending on what RPM this maxes out at (hopefully you get around 36* at 3000rpm.)

If you get pinging drop your initial timing to 14 and total advance will be 34. You can also mix/match the springs. IE one black and one silver to get somewhere in the middle between the two curves.

Lastly I'd hook your distributor up to full manifold vacuum. It will help immensely with the sluggishness you are experiencing and the engine will run cooler. Not to mention you can lower the initial to help with starting but still get the advanced timing right away to be more in the right torque range.
You may need an adjustable vacuum canister to dial in how much max timing the vacuum can adds at cruise. Run as much timing as you can during cruise without inducing pinging.

One more thing. I ran a Progression Ignition HEI for awhile and it was super awesome to be able to set my own timing tables from my phone (connected with bluetooth) without having to mess with any springs or weights at all. It's pricier that a standard HEI unit but so worth it.

https://progressionignition.com/

Thanks for the reply and info. The black springs were coming in at 900 RPM, below the idle RPM I had set at the time and I could only get 12 degrees mechanical at 2200 RPM, not 20 as shown on the chart. Maybe the black/silver combo will get me more at a little higher RPM since I’ve since reduced idle to 850, but it doesn’t seem like enough.

I’ve read a lot of debate on ported versus manifold vacuum. I know by going to manifold I could reduce initial, but wouldn’t that defeat my quest for more total?

The Progression looks like a nice unit and would no doubt be fun to play with. However I’d rather not spend hundreds on a distributor right now and besides, I’m having too much fun learning and playing with the old-school analog one I already have.

Thanks again.
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[SeventyOne]

Originally Posted by Classics Fan

Thanks for the reply and info. The black springs were coming in at 900 RPM, below the idle RPM I had set at the time and I could only get 12 degrees mechanical at 2200 RPM, not 20 as shown on the chart. Maybe the black/silver combo will get me more at a little higher RPM since I’ve since reduced idle to 850, but it doesn’t seem like enough.

I’ve read a lot of debate on ported versus manifold vacuum. I know by going to manifold I could reduce initial, but wouldn’t that defeat my quest for more total?

The Progression looks like a nice unit and would no doubt be fun to play with. However I’d rather not spend hundreds on a distributor right now and besides, I’m having too much fun learning and playing with the old-school analog one I already have.

Thanks again.
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Next question is why is your idle set so high? I've got a street/strip cam in my 383 and it idles at 800 when hot. A tamer build with an RV cam ought to idle fine below that...

And you dont have to reduce the initial w/ manifold vacuum but you had mentioned you were coming into starter issues at 16. It just allows you to run lower initial but with the vacuum advance in play AT idle you will have a peppier engine.

If you cant get the advertised 20* in the chart i'd try another product, personally. That's your true issue. Unless for some reason you have limiter bushing in place that should be smaller to allow for more mech advance...

[Classics Fan]

Originally Posted by SeventyOne

Next question is why is your idle set so high? I've got a street/strip cam in my 383 and it idles at 800 when hot. A tamer build with an RV cam ought to idle fine below that...

And you dont have to reduce the initial w/ manifold vacuum but you had mentioned you were coming into starter issues at 16. It just allows you to run lower initial but with the vacuum advance in play AT idle you will have a peppier engine.

If you cant get the advertised 20* in the chart i'd try another product, personally. That's your true issue. Unless for some reason you have limiter bushing in place that should be smaller to allow for more mech advance...

Yeah, idle was too high for sure. I have it set at 815 now, could go much lower and idle fine in Park but Drive brings it down 215 to 600.

My starter problems begin at 18, no problems so far at 16.

I haven’t seen anything that should limit distributor travel. I am going to try a different product. Morosso seems to make a quality kit. I’ll look deeper. Appreciate your help!
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[SeventyOne]

Originally Posted by Classics Fan

Yeah, idle was too high for sure. I have it set at 815 now, could go much lower and idle fine in Park but Drive brings it down 215 to 600.

My starter problems begin at 18, no problems so far at 16.

I haven’t seen anything that should limit distributor travel. I am going to try a different product. Morosso seems to make a quality kit. I’ll look deeper. Appreciate your help!
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Oh gotcha. I was thinking you were in drive at that idle number. That make way more sense. I'd aim for a 600-650 idle in drive. I assume you have a carb as well? We're getting off topic (I like tuning talk haha) but when you tune the idle circuit for best manifold vacuum do it in drive with someone pressing the brakes.

[Classics Fan]

Originally Posted by SeventyOne

Oh gotcha. I was thinking you were in drive at that idle number. That make way more sense. I'd aim for a 600-650 idle in drive. I assume you have a carb as well? We're getting off topic (I like tuning talk haha) but when you tune the idle circuit for best manifold vacuum do it in drive with someone pressing the brakes.

Yeah, Quadrajet. I’ve only tuned an idle circuit once, on a 72 Pontiac 350, but did it in Park. Why Drive? I wasn’t planning on tuning this one since I know it’s pulling 15” vacuum at idle, and there’s virtually no exhaust smell in the shop when the door is shut and the truck’s running. I’m a novice at tuning but am finding it enjoyable. Just ordered a Moroso kit, should see it before the end of the week.
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[SeventyOne]

Originally Posted by Classics Fan

Yeah, Quadrajet. I’ve only tuned an idle circuit once, on a 72 Pontiac 350, but did it in Park. Why Drive? I wasn’t planning on tuning this one since I know it’s pulling 15” vacuum at idle, and there’s virtually no exhaust smell in the shop when the door is shut and the truck’s running. I’m a novice at tuning but am finding it enjoyable. Just ordered a Moroso kit, should see it before the end of the week.
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So just a little 101 on tuning:

First for your carb you want to make sure the idle set screw is set so that your transfer slots look like squares when viewed from the underside. If you've played with this screw to set your idle speed you may induce an off idle stumble if the transfer slots are overexposed.

Then set your initial timing to achieve the idle rpm you want. Larger cams will need more initial.

Then you set your idle mixture screws in drive simply because that's where you need the right mix, in drive ready to drive the car, with a load on the engine from the torque converter.

Then set your idle mixture screws for best/highest vacuum.

All of this has less to do with exhaust smell and more with optimizing the AFR at idle and this is how you do that short of an AFR gauge.You may very well have the right tune on your carb/distributor but this is how you do it from square 1.

[Classics Fan]

Originally Posted by SeventyOne

So just a little 101 on tuning:

First for your carb you want to make sure the idle set screw is set so that your transfer slots look like squares when viewed from the underside. If you've played with this screw to set your idle speed you may induce an off idle stumble if the transfer slots are overexposed.

Then set your initial timing to achieve the idle rpm you want. Larger cams will need more initial.

Then you set your idle mixture screws in drive simply because that's where you need the right mix, in drive ready to drive the car, with a load on the engine from the torque converter.

Then set your idle mixture screws for best/highest vacuum.

All of this has less to do with exhaust smell and more with optimizing the AFR at idle and this is how you do that short of an AFR gauge.You may very well have the right tune on your carb/distributor but this is how you do it from square 1.

I knew most but not all of this. Great explanation and step-by-step. I’ll post back after I receive and install the Moroso kit. Thanks!
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