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In the instructions for setting the rev limiter, it says "Setting both rotary dials to '1' will activate a special function explained below." Well below it tells you how to program the box to show you the rev limit setting on your tac before starting the engine. This can be done without turning the two dials to "1", so that's not it. Just what is the special function?
I have MSD 6AL boxes on my 55 and 3 of my Camaros and no rotary dials, they all rely on rpm chips. Are you sure you have a 6AL .
Checking the rev limit is the special function. Once the function is activated, it stays on until you go through the procedure to turn it back off. Sounds like yours is activated.
Mark - he has the digital unit. The rotary dials are under the cover marked Rev Limiter on the front of the box. We have one in our Camaro which replaced our aging analog 6AL - works really well.
Seems like something is missing. Checking the rev limit is turned on and off by the grounding of the tac wire procedure. It doesn't mention the two dials. I just turned that on without touching the two dials.
What got me looking is that I was messing with my timing and it seems like I can start the engine with the timing advanced really far with no engine bucking. I was looking to see if it has a retard function while cranking but I don't see that anywhere.
Tony - there are multiple versions of the 6AL - I believe a programmable retard and a separate start retard is on the MSD 6AL - Plus version.
Maybe you can help with my other question, when not using vacuum advance, around what do you set your initial timing at?
I had it way advanced till it pinged but it only did it immediately upon acceleration then stopped. I'm thinking that may be due to the vacuum advance period when it is *falling off* (manifold vacuum). If initial is often 18 advanced and vacuum is close to 12 more advanced, then since the engine doesn't buck set at 30° advanced with no vacuum advance, that may be a starting point. Or am I way off?
Oh, and my box is a 6425 which Jegs and Summit lists as no retard function? So why doesn't it buck at 32 advanced initial?
Today I set the initial to 25° and kept the vacuum advance on. The test drive went well, I didn't hear any ping at all. On the highway it chirped 3rd every time. Now when it gets really, really hot, I'm getting a random miss that I can feel when going up my steep driveway at 5mph. I may have to swap distributors again to see if the pickup in this one is also bad. It's nothing like it was with the RTR circuit board in it, much much less. Not noticeable at WOT. Temps around 90 and the engine as hot as it gets.
Back to my post about the "special function" when setting the switch dials to 1 and 1, I called MSD and luckily got someone who sounded intelligent. He said the special function is only used if you have a power grid setup. Something to do with the power grid limiting the rpm's.
Asked if maybe the later 6425 box's might have a timing retard for starting and he said no.
Also asked how much a pickup costs and it's about $98. He said it's cheaper to send the unit in for repair, but I really don't know about that when adding shipping both ways. And with that I explained how I removed the faulty circuit board and am running just the pickup, would they work on such a distributor and he said yes, a lot of people have done the same thing.
You are not treating the vacuum advance correctly when setting the timing. You seem to be trying to tune for WOT so let's start there. Your distributor has mechanical advance also which adds timing as rpm increases. Do you know how much advance and what rpm that it maxes out? Typical timing for a big block would be 32-36° advance total, all in by 2500-3000 rpm. When I say "total", this is the sum of initial advance + mechanical advance (no vacuum yet), at an rpm where the mechanical advance has quit increasing. So let's say for discussion sake that you have 16° initial timing and 36° total timing. The mechanical advance would be 20°. You can adjust the mechanical advance with springs and stops.
Are you setting the initial timing with the vacuum advance hose disconnected and plugged? That's the only proper way. (I suspect you haven't been.) Also, your engine does not make vacuum at WOT, so you could actually disconnect it at the track and it should make no difference.
Vacuum advance is only useful at part throttle - when the engine actually makes vacuum. More ignition advance at light loads/high vacuum is useful for throttle response and fuel economy. In an engine with high compression or marginal fuel, you may have to limit the amount of vacuum advance with a stop to avoid pinging.
So again, to tune for WOT concentrate on initial and mechanical advance, and disregard vacuum advance entirely.
I suggest you go do this - disconnect and plug the hose for vacuum advance, hook up the light and see what the timing is at idle - that's your initial advance. Then slowly rev the engine past 3000 rpm while monitoring the timing. When it quits increasing, that's your total timing. Report both back here and we can discuss.
Sent you a PM.
Rick, I appreciate your help. In the scenario I gave I did indeed have the vacuum advance disconnected. With the amount of timing advance it has I am baffled as to why the engine doesn't *buck* when trying to start it and why it isn't pinging. Just now I rechecked the timing with the vacuum disconnected and plugged (although I don't see any need to plug the vacuum hose unless your engine won't run with the vacuum leak). The initial is 22° advanced and the total is a whopping 50°. Two different timing lights both give the same reading on the balancer on the tape, not using dial back. That centrifugal advance shocked the shit out of me, but it ran great and didn't knock or ping. After some thinking, I believe the centrifugal is so high because I borrowed the advance stop bushing for my other distributor and forgot to put it back on this one. I'll be back in a few days.
Doesn’t that 50 degree-22 degrees initial=28 divide by 2 for distributor speed =14 degrees put the rotor way off position with the distributor contacts? Unless this is total electronic fixed distributor (which I assume it is not) doing phase compensation there is big spark gap.
Rotor phasing is the least of problems with what's been described. 22° initial advance is WAY too much for almost any engine, especially a BBC, unless running fixed timing. I suspect it's not being checked properly either (vacuum advance may be connected) because the engine should have hot start and pinging problems with 22° advance. Another possible situation could be that the timing mark is off, and until it is, everything seen or reported is just garbage as far as the numbers.
But, if the engine could really run that timing successfully, rotor phasing might be off - but maybe not enough to be a huge problem.
Rick, he did say the vacuum was plugged. But as you say 22 is too much initial. The only condition that could work is on drag strip without power adders. But the all in shouldn’t be 50 degrees. Your suggestion the timing mark must be off position is most plausible.
14 degrees on a small diameter distributor is a rotor displacement of about 3/8”.
Didn't realize this was about me. I've had the strangest things go on with timing and this motor. Before the rebuild it was reading off the charts, as if the light was clamped on the wrong wire. Two of my lights and a third at a garage did this. Then suddenly it started reading correctly. The balancer key is in line with the 0° mark. Since then everything timing wise has been changed and still I sometimes get crazy readings. If I increase it until it slows down then back it off again, how far back should I go?
Quote:
Originally Posted by 55 Tony
Something had to change for it to start reading correctly maybe the pick up is screwed up. If it is it will cause everything to be out of wack even the rotor phase to the cap. Electronic stuff is sometimes difficult to trace out.
try another module or go to a points set up. Do switching when it is screwed up, one piece at a time. i put my money on the magnetic pick up. I had a similar problem with Pertronix piece of crap, put the points back in, ........problem solved.
Run it without the MSD box no telling if something weird is going on there.
First time it did it was with a very old msd distributor with no 6AL box. If it were actually firing light the timing light showed, no way could it have run. Did it with a different msd distributor, and a different balancer. Right now it's running the 6Al box and it's working properly ... that is if I hold the clamp on pickup @ 90° to the rest of the wires. I think it's possessed.Quote:
Originally Posted by Gmvette
Tony, I don’t follow what you mean by “that is if I hold the clamp on pickup @ 90° to the rest of the wires. I think it's possessed.”
Are any of the wires in bad shape?, grounding out?
Generally the wires coming out of the distributor “they” recommend twisting them together so nothing is like a single strand. Something about RF interference. Worth a try.
I've heard a lot of timing lights don't like msd 6AL boxes. This is what I do to make it work. This I believe is just good for the msd box wackyness, nothing to do with the other weird readings I sometimes get. Wires are good. I know they say #5 and #7 wires should not run touching each other parallell, if they need to cross, try to make it at a right angle.Quote:
Originally Posted by Gmvette
It makes me remember that I didn't have that much trouble with the 2 427ci engines I built 46, and 48 years ago, that pulled smooth, and hard to 6500rpm with just points. I could lift the left front wheel on my 68 Chevelle in second gear with G60-15 tires on the street. I had both of those engines machined at
Speed-O-Motive in 73, and 75 while I was in the Navy in Long Beach. I just had a POS timing light back then...
To me that's an indication something is wrong, rather than it being a solution.
I can't say this for a fact, but your "fix" may be telling you want you want to see rather than the correct timing.
The trouble with MSD boxes and timing lights is when you use a dial back light (hope you aren't doing that). The only dial back light I've seen that works with an MSD box is a Snap On, though there may be others. Using most dial backs on MSD ignitions results in totally erroneous readings. That includes using one with the dial on "zero".
In fact, the timing you've been reporting should have blown your engine up by now.
Haven't we already discussed dial backs?
Hint: MSD stands for "multiple spark discharge". That alone would freak out a timing light. I have timed an engine by sound, and feel which is a better approach than what you are dealing with.
That's a recipe for one of two things. 1. Disaster. 2. Leaving lots of power on the table. Use a freaking timing light, non-dial back, and get it right.
Yes Rick_L, I have a dial back but I am using my newer non dial back light. I know it would have blown my engine, all I can do is to time it by ear, which has been working just fine. Tried in the past to have a mechanic adjust it but his Snap On light gave erroneous readings also, and that was before the 6AL box.
Yes I know what MSD stands for. In fact the company is actually "Autotronic Controls" doing business as MSD. They changed their operating name to MSD after their multi spark boxes took off. Right now it is timed by advancing it until it bucks when starting, then turned back some. Then I tuned it a little better at the track going by times. Right now I'm running an Autotronics Controls distributor with it's electronics unplugged and just using the pickup coil to trigger the 6AL box.Quote:
Originally Posted by 55 Rescue Dog
If that is pick up for your timing light you are putting it in a bad area. Hook it up down close to the #1 plug.
your plug wires look ok. I’m refering to the wires to coil and MSD box be twisted not plug wires.
You are right, I don't know how I got into that habit, probably from removing the clamp after it was resting on a header tube. Ouch! I suppose I could try mechanics gloves. I think I remember twisting those coil wires but I'd have to look again. Commonly known in electronics as a "twisted pair" to shield from outside interference. The one wire is normally a ground, but neither of the wires to the coil are ground. Not sure if it would also help reduce them from emitting RF noise.Quote:
Originally Posted by Gmvette
Yep you got it right. Personally I have never seen a bit of difference with the clamp-on lights whether it was near the plug end, in the middle of the wire or near the distributor cap. I have seen a difference on a dial-back light if you did not have the clamp orientation correct. I have mine marked with a yellow paint dot towards the plug - makes it a bit quicker in the pits.
And as to the timing, I have seen BBC engines with a huge amount of compression run at high timing numbers. My 555 engine has a bit over 14.6:1 but I run Alcohol and a-b-a testing has shown us that this engine is perfectly happy with a total of 30 degrees. I gain nothing except a harder starting engine moving the timing up. And btw this is a locked crank-trigger distributor. 30 degrees at start up. For STREET engines, I would normally tell someone to start with 8-10 degrees of initial and another 15-25 in mechanical advance for a total of of 33-35 somewhere around 2800-3000 rpm. That's a good start but it's up to the tuner to find out what that engine and it's combination of parts works best at - I like to call it a happy engine when you get it figured out. But this car magazine nonsense of 12+24=36 has to be understood as a starting point, not something that is written in stone! If Tony's engine runs it's best with the numbers he has then that's what that engine wants whether you agree with it or not.