We have installed a 'stock' HEI on my brother's 383, and mechanical advance is set up at 10 initial, 30 before 3600 (it has fastburn heads).

The vacuum advance can is adjustable, but we cannot seem to get it below 22 added at high vacuum (0 at curb idle). This gives 52 total. Seems high to me, for this engine, and I'd like to go lower (maybe 40 total, I'm not sure what most people with carbs/fastburns run at cruise?)

So the question is, does the crane kit (or any other) offer adjustability below 22 advance minimum on the vacuum can?

Also going to throw this in, these distributors do continue to add spark above their 'cutoff' points right? Or is there a mechanical limit you can set inside (there was on the MSD mechanical adv. dist. we were using before). I haven't cracked this one open and would rather not if I can help it.

Thanks for the help, I'm a FI guy, I just punch my stuff into a table

-Ben

 

With the Crane kit, you can have pretty much any amount of vacuum advance you want, from 0 to full-travel.

If the engine doesn't ping though, keep the extra advance. Even with fastburns, you should be able to bring all the centrifugal in well before 3600.

 

Yep, 30 is total mechanical advance and it is in before 3600.

I want to bump initial to 14 giving about 32 total mech. But this will give 52-53 at high rpm cruise.

This does not seem like a lot?

I guess we can give this a try and see how it runs. I'll keep crane kit in mind tho, thanks for the info.

 

that is way to much... i have found about 27* total to be best with mine most are around only 29 total for fastburn heads... any more than 27* for me and stuff starts to rattle...

 

I think Apeiron meant earlier than 3600, ie, 2800RPM have all 30* in by.

You can buy a little limiting tab for your HEI, or just buy the crane kit, it comes with this tab. The tab basically lets you lock in (lets say) 10* of your vacuum advance, only leaving 12* left. So you have 10* more initial, so you back off your distributor back to where you were. Kinda gives you a "head start" on your vacuum advance - that's how it works.
Then you can adjust how much vacuum it takes to bring it in, using the little allen screw into the vacuum hole. It's a nifty piece, i'm running the crane cam myself.

 

And the benefit of doing that would be ...... ???

According to GM (not that they would know anything about their product, but just for reference) those heads want about 30-32° of "total" timing. That's "static" plus "centrifugal", BEFORE vacuum is added. The portion of that 30-32° that's static, vs the portion that's centrifugal, and the RPMs that the centrifugal operates at, will be primarily a function of the cam you're running; the bigger your cam, the more static you'll want and the less centrifugal, and the lower the RPM at which you'll want the centrifugal "all in" at. For a typical hot street cam with an intake duration in the mid 220s, you'll probably want 15-18° of static, and 12-16° of centrifugal on top of that, such that they add up to that 30-32°; and you'll want the centrifugal to start "coming in" at about 1100-1200 RPM, and you'll want it "all in" by about 2800-3000. Then you'll want AT LEAST 15° of vacuum advance on top of that, for cruise gas mileage; basically, give it ALL IT WILL TAKE, without pinging going up a hill in high gear at a low cruise speed (say, 50 mph or so, whatever the lowest speed is that it will stay in high gear with the TC locked) fully warmed up on a hot day with crappy gas. You'll probably want the vac adv hooked to straight manifold vacuum.

This is no different from FI. It's all air, fuel, and spark. Once all of that gets past the intake valve, the engine doesn't know, can't tell, and couldn't care less how the fuel got there, or what mechanism is controlling it. Put that "FI vs carb" stuff out of your mind. They are no different.

 

Sofa, whoa slow down. I have no FI vs Carb stuff in my mind, other than they are different in how you set them up.

I think what you said is pretty much what I have set up. I know the engine could care less about FI vs carb, I'm just not as experienced with getting what I want with a mechanical distributor is my point. For instance, I run my FI setup at 20-22* at idle, and it doesn't seem that I can get that with a mech. type distributor being that there is no vacuum advance at idle, (well, I do if it's straight hooked to manifold vacuum, but is this ok to do...there's a reason they have a timed spark port on the carb? See, I don't know this, why WOULDN'T you want full manifold vacuum?)

SO...I guess you run with less timing at idle than what I would with my FI simply because it's not feasible, but how much is the question, see I don't know...kind of like making due with what you have?

I was recalling from memory what we had it set at in the first post, and it was slightly different if you noticed in my second. The final answer is, we have it at 10* initial and 28* total before 3600 (now correct, as opposed to 30 I said before).

So I want to bump it 4* initial giving 14*/32*. This is as I said above. I think we agree on the mechanical advance, and we could try a different slope (bring it in sooner), that is not a problem, but I wanted to start off conservative if anything, and we didn't have a lot of time to play around with it last time I was there so that is why it is where it is. There is no knock at this point, under high loads, it's been tested.

So basically, that leaves us at the vacuum advance, which was really the whole point of my post. Sofa, you say at least 15*. This is about what sounded good to me (although this is way more than I am, and more than I can run on my FI, so I am in unfamiliar territory here). This gives a total of 47. The least amount we can get, setting vacuum canister all the way down is 54 total (total mechanical + total vacuum = 32 + 22 = 54). Hence the reason I ask, is that too much because it sounds like too much to me. I wanted to bring it down to around 32 mech + 8 vacuum = 40, to start off and test, or if there is a suggestion contrary I'll hear it. I said 40, Sofa said 45, I don't see a gigantuous difference there, at least to be scratching heads over...I like to be conservative when I am unsure, at first. 45 would be great, but how do you get there, without the crane kit. Guess we need it. Question answered, right?

Sofa, you say straight manifold vacuum is ok for vac signal. I don't know how the timed spark port works exactly, would you or someone else care to clarify the difference. What I understand is that the timed spark port gets full manifold vacuum right when the throttle blades are cracked, in which case I ask myself why not just use full manifold vacuum so that we can idle around 20+* with the extra vacuum advance. I guess I'm just not sure why you wouldn't default to the full manifold vacuum port, and why you would want the timed vacuum port. I'll tell you, it seemed like it idled better with the extra vacuum advance, when I had it on full vac. port, at idle.

Sorry for the length, and Sofa, sorry if I'm defensive, maybe I'm not as clear as I think I am (wait, of course I'm not). I'm tired and shoulda put this off until tomorrow but I just happened to visit the board and noticed replies (which, I haven't been getting email notif's lately and I'm not sure why).

Anyhow, thanks again for the help.

 

Usually you don't want to exceed 51deg of combined advance at part throttle high vacuum cruise. You can limit the vacuum advance travel by removing the vacuum advance assembly flip it over and welding a metal tab across the linkage arm to limit the rods travel. If you have 22deg now, limit the travel of the linkage rod by just less than 1/2.

What camshaft is in this motor?

 

No, THEY ARE NOT; that's exactly my point. They are EXACTLY THE SAME in how you set them up. They're both just air, fuel, and spark; no more and no less. The ENGINE requires the same amount of air, the same amount of fuel, and the same spark timing for "best" operation, regardless of the control system that delivers those things. So, put the whole "I don't understand carbs, all I know is FI" out of your mind; THERE IS NO DIFFERENCE, all you are doing by maintaining that attitude is making your own life more difficult. You're working toward the EXACT SAME GOAL, you just get there by a different procedure; you use various mechanical means instead of electronic. Kind of like your old TV vs the one you have now; used to be, if you wanted to watch Channel 12, you had to get up and walk across the room and click the dial to 12, where now you just push the buttons on the remote. Mechanical control vs electronic. However, Channel 12 is still Channel 12.

Moving right along:That's a pretty typical stock FI setup. Too little for a typical "hot" street motor.

However, if you look at the #s I gave you, you'll see that running full mainfold instead of the ported source, will give you your static timing (15-18° or whatever), PLUS your vacuum advance setting (probably another 15° or so); so you could very easily see 30-some-odd degrees of advance at idle.

You're right, the "ported" source comes from a spot in the throttle bores that's just above the blades when they're at their curb idle position. That way, the port is at atmospheric (no vacuum) at idle since it's above the blades then, but whenever the blades are opened a bit, as they might be when cruising for example, the port will be exposed to manifold vacuum. This was actually a "hack" that most all the factories applied to engines back in the early early days of emissions; given the other features of engines at the time, it was the only way they could get the NOx emissions down to acceptable levels at idle. Before emissions, full-time vacuum was usually used; and since the advent of computer cotrols, even before FI, it also hasn't been necessary. CC carb systems have about that same 22ish advance at idle.

Like F-bird is hinting at, most "street-strip" distributors you buy, have too much centrifugal travel built in. I.e., the actual engine requirement is NOT some "static" value; but rather, whatever it needs at full load and full RPM, known as the "total" value, 30-32° in your case. The static value you're looking for is therefore that necessary "total" value, MINUS some amount so that it doesn't ping as it comes off idle or putts around town in too high of a gear on a hot day. So, to get your engine to REALLY run right, you have to limit the travel from the 22-24° that they typically have, to the 12-15° that's actually appropriate.Again, put that sort of "I can't do this" out of your mind; the surest way to guarantee that you can't do something, is to tell yourself that you can't do it. If you want to TUNE your car, which is what this is, then this is how it's done. People from all the way back in the Stone Age, like me, have been doing this, with rocks and sticks basically, for all these years before computers came along; it's not "hard"; you can do it to. Trust me on that.

Note also that both he and I referred to the cam. As I said, the cam you use will determine the optimum "static" timing, and the curve at which you want to introduce the centrifugal advance. The lower the low RPM cyl pressures (the "hotter" the cam), the more "static" timing the engine will want, and the lower the RPM at which it will want to reach its "total" timing.

What cam do you have?

 

Can you build me this exact curve, below (if that's what was desired, for whatever reason).

You are correct, with full vacuum port, at idle, we get 26*. Otherwise, it's 10*. It likes the 26 better, but as the car is not mine and being that I was not sure on the difference at that time (ported vs unported, I read up on it a little AFTER that day), I decided to be safe and leave it as per the instructions, for the time being. Yes, I could have verified the points on the rest of the curve, with throttle blades cracked, with the timing light but as I said, I have very limited time to do this and the day was nearing an end.

You under-estimate me. By not wanting to crack it open I simply meant that there are other things that needed addressed in the very short amount of time that I have to help him out, when I'm there (once a month). I can do most anything I put my mind to. We have decent settings now for mech., and is pretty much what everyone here states, I have no argument to that, so I don't know why we are going round and round about the mechanical advance settings....

Thank you for the confirmation on ported vs unported. I will have him switch it back.

I wrote all that and got to the cam part. I don't know off the top of my head, and I have to leave here, I'll post back later with the cam specs. It's not radical.

 

Forgot pic

 

The cam is the lunati voodoo 268. Specs: duration 227/233 @ 050, Advertised 268/276, .489/.504 lift, Lobe seperaton 110.

 

I ran that cam briefly, I liked it. Definately needed 24*+ timing at idle to get it running smooth.
I welded my slot to get 12* mech advance.
You could always set advance at 3000RPM to 32*, then just run manifold vacuum and you're done.

I'd just do that.

 

I think you got some good advice early on in this thread- using the Crane kit (or some equivalent means) to limit the maximum amount of vacuum advance the canister can supply.

22* is typical for a stock can. And WAY too much once you have the intial and centrifugal properly dialed up for maximum WOT scoot.

You need about HALF that much vacuum advance. Typically about 12* (maybe ~16* if you run a functional EGR system). On most small blocks you don't want or need any more than about 45-46* total maxium advance (intial + centrifugal + vacuum).

A typical "baseline" total would look like this:

14* intial + 20* centrifugal (usually all in no later than 3000 RPMs)= 34* max WOT advance
Then add in another 12* of vacuum advance = 46* max total advance

As for ported vs. full manifold vacuum to the vacuum advance....... try it both ways. There are no real hard and fast rules here. Remember that from about 5-10% throttle on up, a ported vacuum source supplies vacuum just like a full manifold vacuum source.

 

Thanks all for the replies, my question has been answered and most everything stated is congruent with what we have set up (well except for the vacuum adv obviously, because of its limitation, or lack of limitation really).

Thanks