I have tested 36* + 10 = pings when kickdown 33* + 10 = pings when kickdown 31* + 10 = no pings I think the car is weak when I accelerate with 31*. I had my family with me and I tried to show them a burnout, but the car did not make it. Which is better ~34-35* + 8 vacuum advance. ~33* +10 but slower vacuum advance.
Disconnect the VA and make full throttle runs to see what feels best with NO PING. Once you have that, add in vacuum advance. You may have to reduce it down from 10*, to 8. Increase of spring pressure in the canister to pull the vacuum advance out faster will help with part throttle ping.
[h=2] Timing degrees and distance on harmonic balancer[/h]Came up with a spreadsheet to determine timing degrees in relation to distance on the balancer. Unfortunately, I think I can only upload this jpg image. This one is for a 6.75" diameter. The spreadsheet allows you to change the diameter and calculates the distances below.
Question, What would be the ideal advance curve for the mechanical advance from the attached Mallory chart? figure 1 - 2 or 3 I have it set now for two stage (figure 1) with purple and brown spring and I bent the tab a little to bring it in quicker than the stock setting. I've been running this for awhile now with no real problems but, I thought I would ask to see if there was a better option other than the curve I currently have set. http://static.summitracing.com/glob...AA-yh_series_mechanical_advance_kit_29014.pdf Tony
Tony, Trial and error. What works for one car might not be good for another. There really is no better for all cases. Hopefully, you have no more than 24* (Mallory factory limit). Try bringing it in sooner or later and see what feels best.
Sounds good, I think just for piece of mind I am going to try a set up from figure 3 and see what the responce is. as far as the mechanical advance, I used the 12* shims in the distributor and then set the total at 34* and I have not yet adjusted for that extra 2-3* I was telling you about when you blip the throttle at the higher rpm range. (I am below the recomended amount of advance) but it seems to run better with more intial advance. The other thing I was thinking was to put the 16* in the distributor and then have some of the mechanical advance be ithere at idle with different spring set up. First I'm going to bend that tab a little more to bring it in a little faster to see if that corrects the additional timing degrees and then set the total back to 34* and hopefully have no extra advancement at the higher rpm range. Tony
What is best: mechanical pointset or unknown ignitor conversion kit? Can i controll test the electronic one?
Electronic ignition is more accurate especially over time. Points get the job done. Petronix can be problematic, experiences VARY WIDELY.
I was with my friend and adjusted his dwell to 30 with a digital tool. (coil + terminal and ground) If I connect his tool in the same way on my engine, should it read ~ 30 on my engine also in case the electronic work? Or do they give completely different values compared to mechanical?
From this page, http://www.jetav8r.com/Vision/Ignition/CDI.html "Dwell time refers to the time the distributor points are closed. The dwell angle was the amount of rotation of the crankshaft that corresponded to the points being closed. This affects the charge time of the coil. Dwell was important then because at higher RPM the dwell time (points are closed to charge the coil) was not enough to fully charge the induction coil. That meant less voltage spark at higher RPM (...BAD). There was also the problem of how fast a point could open and close without "floating" (a problem you have with valves also). There was a real balance between dwell time at high RPM, how much voltage you needed for high RPM spark, how much voltage you could actually push thru a point without burning it up, and then what would happen at low rpm (long dwell times) when all that voltage was just heating up the coils. In newer CDI systems this term is near meaningless for several reasons. Solid state transistors control the discharge pulses electronically with near instantaneous timing in the nanoseconds. So the dwell times can be finely controlled to achieve the best coil output. Transistors can handle a LARGE amount of voltage/current (compared to points). And, newer generation coils are extremely fast with charge "saturation" times around 1milliseond. Their coil pulse "voltage rise time" to the plug is VERY fast at around 6 microseconds. So charge / discharge times are not a huge factor (unless racing). Newer racing ignitions (like MSD) are NOT producing bigger sparks with long durations but in fact getting more efficient burn by producing very controlled multiple short duration sparks to the plug."
I've been reading this thread for days and I'm just about ready to roll my sleeves up and get into the advance curve. Pretty sure everything I need to know is already here so I'm going to dive in and post my results without asking a bunch of questions. But I do have one related question that I don't see covered here. Is an advance timing light any more accurate or am I just paying for convenience? My builder scribed a nice clean 30* mark on the balancer and I have several old standard timing lights. The problem is that I see bad reviews for the cheaper advance lights and I just can't see spending $100+ for a tool that doesn't really do anything I can't already do. However, if accuracy or some other factor plays into it, then I guess my motor is worth it. Appreciate any and all opinions on this. David
Both methods work equally well, but the biggest variable will be the accuracy of your 30* mark. 1.76" = 30*, 2.0" =34*. .059" =1*
That's what I was hoping to hear. Thanks for the quick reply and for all the patience and knowledge throughout this thread. David
Ok, so here's my deal. Car: 68 Wildcat 2dr w/original torque converter/trans/rear end. Motor: Fresh 68 430 .030 over. Rebuilt heads, Lunati Voodoo "GS Club" cam, TA shorty headers, stock intake, rebuilt Q-jet, recurved HEI w/Pertronix Ignitor/adjustable vacuum advance. Yes, I know what you're thinking. That motor was built for a much lighter car with taller rear gears. In fact it was built for a 70 Skylark GS and from my initial runs around town I have no doubt that it would make a 3200lb car get up and fly. However, I knew before I bought the motor that I would face challenges taming it to suit my 4000lb 'cat. And that's where this thread comes in. I know the real change needs to be in the torque converter/trans/rear end situation, and my intent is to put a switch pitch trans/converter next spring and see if I really need to get into the rear gears after that. But before that stage I want to get everything I can out of tuning this motor and see where I stand. Btw, this is just a street cruiser, I'm not looking for track times, just good times cruising. Anyways, from both street runs and studying the power band curve of the Lunati cam I know that low end has been traded off for mid and high end. And there is an absolute boatload of power being produced up there. The distributor was curved to match with a 20* limit and fairly stiff springs. My challenge was pretty simple, bring the curve in a little earlier with lighter springs and set the total and total+vacuum in hopes of restoring a little low end and drive-ability. Set initial at 12* with stiff springs, total was coming in around 32* but at fairly high rpm. Put the black springs from Mr Gasket in (wimpy little things) and got the curve in at 1000rpm, all in by 2000. Set total at 34*. Then I replaced one black spring with a gold and got the curve starting at 1200rpm with all in by 2200. This is based on a post by someone in this thread who used lighter springs on an Electra. I'm going to play with more combinations and try more advance but at this point I'm pretty happy. Still lacks a bit off the line but pulls like a runaway freight train once it launches. The power band is pretty darn impressive and seems to never let up. I ran into a little trouble with my secondary air door cam that I need to fix before I can really tweak it but I'm very pleased with where I'm at. One thing I will say. Running a big car with a big cam and stock gears w/no vacuum advance will open your eyes to the need for vacuum advance. I can feel the motor struggle through transitions. I have my Pertronix can pulled back to 10* but still need to play with it some after I get the carb sorted out and settle on springs and total timing. I'm still a little confused about the vacuum can. My situation is complicated by the fact that I get very low vacuum at idle, about 12" in park and much lower in gear. Again, this was to be expected, I'm just not really sure how the vacuum can plays into this. Idle is nice at 800 but drops below 500 in gear, although she never, ever stalls, just chugs and chugs. When I get into the vacuum can I will try both ported and manifold. All in all I'm extremely pleased. If anyone has suggestions or tips I'm all ears, but at this point I know I am close and that's all thanks to this thread and other knowledge gleaned mostly from this board. I also know that all the info I need to understand vacuum advance is somewhere in this thread. Thanks Larry and all, David
As long as you are sure there is 20* of mechanical advance in that distributor, you can just vary the amount of initial advance to adjust your total advance. Mixing and matching the springs can get your total advance in earlier or later. Usually with a big heavy car, you need to play with that to avoid detonation/ping when accelerating at WOT from low speeds, sometimes the motor won't tolerate it with the available octane. I always advise leaving the vacuum advance disconnected while you do this. Get the advance in around 2500 RPM or so, and determine what total advance you want to run, and you should be in good shape. Once you have that set, then work with the vacuum advance. Some adjustable vacuum cans are adjustable for both amount of degrees and rate of advance. If the rate is adjustable, you can get the advance to start at lower vacuum. There is a spring in the canister that opposes engine vacuum, so the engine vacuum must overcome that spring before the canister can advance the timing. That same spring is responsible for pulling the advance out when vacuum drops off (at larger throttle openings including WOT). If the vacuum advance does not drop out quick enough, you will get part throttle ping when accelerating from cruise or part throttle. You generally want your total advance at cruise to be 40-45* for best gas mileage. If all your mechanical advance is in at your typical cruise RPM, then all you need the vacuum advance to add is 8-10* more. If you add too much, the engine may surge and/or ping. As far as ported or manifold vacuum goes, realize that at part throttle, both will be the same. At WOT, they will both be at or near 0. The difference will be that manifold vacuum will enable you to advance the timing at idle and low speed assuming you have enough vacuum for the canister to work. If so, the additional advance can make a difference in coolant temperature during stop and go traffic. Manifold vacuum will drop off quickly as you load the engine. Ported vacuum is non existent at closed throttle and increases rapidly as you open the throttle. again, at part throttle, ported and manifold vacuum will be equal.
I get a steady 20* difference no matter where I set the initial or total. It looks to me like this was done with weights and center plate, the center is a 368 and weights are 053 with the plate underneath stamped 126. No sign of welding or screws added. I use 93 octane and haven't heard any pings yet in my limited tests, but with headers and loud mufflers it's hard to sort out what I'm hearing. This weekend I'll push the total forward a touch and test some more. The early curve seems right but I may try to push it back some with spring selection and see what feels best. I still have the vacuum can unplugged, but I tested the port adjustment to make sure that it actually limited pin travel, then I backed it out 3 full turns to subtract 6* from the factory 16* setting, giving me 10* for a start point when I'm ready to dial that part in. I do understand how the vacuum advance affects drive-ability, but I'm still curious about the effect a manifold source can have on idle. Was it here that I read it can smooth out a choppy idle caused by a big cam? If I recall it needs to be 2* below minimum idle vacuum. I can achieve that at idle in park, but even limiting the can to 8* won't get me there in gear yet. Still got some fiddling and studying to do on that end, and I may even get a little more vacuum at idle from advancing the total and resetting the idle mix screws. On a side note, my trigger finger is itching to hit "buy it now" on a rebuilt long tail switch pitch and converter out of a 66 Caddy.
You lost me there. I think what you read is that a bigger cam will like a lot more initial advance, at least 20*. That can tame the idle a bit and maximize engine vacuum. Locking out the mechanical advance and running constant timing is the ultimate solution, but it requires you use a start retard so you don't have hard cranking when the engine is hot. I ran a switch pitch transmission for many years, it's an awesome transmission. I have now switched to a fixed pitch transmission with a custom 10" converter. I paid more for the converter than I did for the transmission, but a custom built converter is the way to go for the very best performance. That costs though, you can't get there with an off the shelf converter.
Hmm, interesting. So to get up near 20* initial will still require some modification to the distributor to bring the mechanical advance down to about 14-16* if I'm reading that right. Sounds like I've got more work to do. But if there's that much wiggle room and this engine will be happier then the extra vacuum at idle will just be a bonus. Thanks again Larry, I don't know how you guys did it before the internet. uzzled: David
Using a small machine screw similar to what Andy did on page 2, I limited the mechanical advance from the distributor. Put light springs in and set total to 34*, checked with heavier spring and getting around 18* initial. Grrrr :af: guess I may as well tinker more to get it down a few more degrees before test driving. Figure if I'm in this far I may as well give myself all the options. Wondering if anyone has had any trouble down the road using the screw method permanently. I'm thinking that if I can get the limit where I want it I'll install a second screw and give them both a dab of blue loctite.
For what it's worth, I measured my stock springs with a micrometer. The spring constant, k, should be about 54 pounds per inch. The aftermarket spring kits range from about 20 and down to 8 or 9 pounds per inch in the springs. I can see how the mechanical advance is tough to get all in with stock springs. The heaviest Crane and Mr. Gasket springs are less than half of my stock springs. Plus if I had to guess, it looks like my weights are small, so it's hard for them to pull those tension springs. Something to be said about having the right distributor to start with that has heavier weights and a lesser slot for advance.
