My car has been a little sluggish lately, checked the timing only getting 24 total. This is an HEI distributor.
On the dyno I got my best power and torque with 28 total and my best idle and starting with 16 initial. As I'm on the edge of detonation I disconnected the vacuum advance. In order to get 16* initial and 28 total at 3200 rpm without the vacuum at idle, and keep my advance curve, I welded the distributor plate on the low side to keep the mechanical slightly on and have the desired 16 idle. Worked well and stopped the partial throttle up hill pings I was getting with the vacuum advance.The vacuum signal does not drop to zero on partial throttle pulls.
I checked the advance mechanism and everything seems to be in order, no rust or debris to stop it from reaching the previously set 28 degrees. I can see the springs going soft and getting more total or total at a lower rpm but can't think of why the initial would stay at the previously set 16 and the total would drop to 24. Any way the module would cause that? I've had a few that just stop working, like turning a light switch off one second working and the next junk, but never heard of one doing this.
So just the mechanical adv has changed? Must have to do with the way the weights are swinging out. Must be hanging up somehow. Check the pivot points. Maybe rubbing on the under side of the rotor? Gotta be something. Seems like the modules either work or they don't. Doesn't sound like it would cause that anyway.
I took the distributor out today and took it apart. The mechanical advance is clean, free of debris and operating as normal. Cap is clean and no carbon tracks, rotor is good, plates, advance cam, weights, springs, everything looked good. Then I grabbed the reluctor/stator and it moved up,down and tilt. Seems my billet distributor has a mickey mouse bracket and a snap ring so thin the reluctor was moving up and over the snap ring. Hmm, I wonder where that was made. I don't know if that is what is causing the timing discrepancies or not but that has to go.
I took out the two GM HEIs I have and swapped a bunch of parts around to get one with the best internals out of the two. Played around for a while and got 10 at idle and 28 at 32000. I have an Accel adjustable vacuum can that is supposed to give 9 degrees of engine advance with just under 10 inches of vacuum at three turns. It gave me zero degrees at 12 inches and three turns, Hmm I wonder where that is made. I hope to get close to what I want with this distributor, I'm not looking forward to taking the thing out another 18 times to weld and file the stops to get the curve and advance I want.
All these adjustable advance cans just stop the movement at a specific setting, goes up so far then stops. Too bad someone didn't have one that actually changed the amount of movement by altering the pull of the diaphragm . One could have no movement until the vacuum signal was at the desired point.
I've lost count of how many times I've taken my distributor out. I have a unilite and a spring kit and had to experiment quite a bit. I've had the best luck with 34-36 total timing; your 28 may not be enough. I found these to be a good read: Distributor Advance Explained Timing 101
The issue i had at cruising speed [low rpm] is the ported vac increased and I'd get a ping. I ended up running without the vac can; unfortunately Mallory doesn't make an adjustable can for the unilite. After reading the article above I'll try manifold vacuum...
Can't go to 34-36, I get ping and my best power and torque is at 28 so that is the target. Hard to get without running the initial above 8. If I wasn't close to detonation I would start with 12-14 initial and go for 34 total then have the vacuum can connected to manifold for an additional 15-20. If!
I've had my distributor out many times as well. I've knocked the drive gear off so many times I bought a dozen roll pins just to keep them tight. Yesterday I adjusted the vacuum can to give me about 16 at idle but I started to get pinging again while driving around the island. I'll have to do the weld, test, file routine with this distributor as I did with the billet one. Unless the shaft and plate from the billet will fit the stock unit,.Hmm.
The best I can get around here is 94, sometimes 91, I add a booster. I long for the days I could buy 100 with real lead for 25 cents a gallon and no corn, grain or other green, eco, bio [censored] in it. Heads are Aluminium KRE with CNC machined heart shaped 85 cc fast burn combustion chambers. Flow is 310/220 at 0.055". Compression is 10.5:1 static and 8.1:1 dynamic. After I welded the distributor plate every thing was great for about 8,000 miles until just a month or so ago when it seemed dogish. I'm sure it is the loose reluctor/stator in the billet distributor. I will weld the plates in the stock one or swap the shaft from the billet.
The shaft out of the billet distributor fit in the stock one, although I had to use three shims to get the end play down. I set it to 28* at 3200 rpm and got the 16* at idle I had before. It was the reluctor stator assembly sliding up over the round snap ring in my billet distributor that was causing the timing change, the stock ones use a flat snap ring.
Now I have four modules and three coils. Performance coils can supply high voltage at a much higher rpm than the old stock ones but should have a matching module to operate correctly. After seeing the innards of my so called performance distributor become dislodged, I suspect the coil is of the same low quality. Any suggestions on a good quality performance set?
I have had strange problems with HEI modules. Strangest being setting initial timing at 20 degrees while running an engine on the dyno and the engine started running bad so I check the timing and its retarded 20 degrees. Replaced module and all was good. Testing these HEI modules on an oscilloscope you can see the power start droping off at 4200 rpm. With a good aftermarket coil you do get a more powerful spark but the power does still drop off at 4200 rpm and by 6200 rpm it really gets too random to get a good spark. The cure is a good ignition box like MSD. Then you get full spark power to 6500-7000 rpm no problem.
I'm running a cheap eBay billet( procomp I think) and MSD 6AL box( no module needed) and a remote coil mounted to the firewall. It all seems to work pretty well. I like not having to worry about a module crapping out. I had an in cap coil and after one particularly hot road trip it fried. Try diagnosing a bad coil when your on the side of the road. Not fun. Live and learn.
Mine seems to drop spark at about 4,000, the timing light gets erratic. Trouble with the gm module is there are quite a few different part numbers and each one has different characteristics such as dwell. The first one I tried this time around was from a smog 455, 73 I think, I put in another and got better results. Can't seem to find a chart showing what each different module does. I also set the initial to 16 degrees, ran it up a couple of times and had an initial of 24? The distributor is tight and the advance is working.
Is your ebay procomp an HEI? If so do you by-pass the module with the MSD box? Can the ignition box be used to modify the advance or is it just to give a consistant hot spark? I looked at MSD distributors with the adjustable timing stops but The largest stop bushing will only limit the mechanical to 16, I need to limit mine to 12.
That in cap coil gets pretty hot, especially with a modified engine and tubular headers. The one I took out of the HEI when I bought my car really showed signs of heat damage. I'm surprised it worked at all, most likely wouldn't for long..
Yup, HEI. You just remove the module altogether. The box only uses the pickup as a trigger. I think if you want to use the box to adjust the adv you have to go with something digital. More of a ECU setup. I did drill the dist housing awhile back and installed a zerk so I could occasionally lube the shaft from the top. I've been tempted several times to pull the trigger on a ready to run MSD dist. But then I hear about somebody that bought one and it went to crap right away and they had to send it back for work. Seems like their QC isn't what it used to be. That same trip when my in-cap coil went out my buddy's coil crapped out as well 2 days later. This was my solution.
How did you get the coil wire to mount on the HEI cap, they don't have a coil tower like the points caps? Or does a modified cap come with the ignition box?
I also bought a ready to run distributor a few years back, couldn't adjust the mechanical as much as they stated and the vacuum was more than twice that advertised. I sent mine back for a refund. Still have the gear I bought for it to match my roller camshaft, couldn't use the one off my GM HEI as the shaft diameter is a different size. Not happy with it at all.
I bought a special cap set up with a connector for the coil wire. Cap seemed kind of Hokies when I looked at it but it seems to work fine. Also bought a low something or other bushing for the center of the cap.