I have done many searches on the board here to find the answers and I am still unclear about some issues regarding the timing of the motor. Anyways... Yesterday I tackled my timing on the 350 in the 5000 lb LeSabre and I think it has improved performance but can I do better? As of right now I altered the vacuum can and put a limiter plate in but I think I have to do some more readjusting. The limiter plate was made as such from the photos that ignitionman have provided. My initial timing is 17 and reaches 32 degrees at 3000 rpms with no vacuum. I put in the lightest springs that were in the moroso kit and also installed the weights that came with as well. The little instruction sheet that came with the kit were right on target when they said about full advance at 3 grand. Now when I plug back in the vacuum line which is currently attached to the ported side of the carb, my initial jumps to 18 and at 3000 rpms, I am hitting 48 total degrees. As it stands, the engine sounds healthy with no pings... Not sure if my math is correct, but with the above numbers, is the vacuum can making the 16 degrees difference between the non vacuum numbers and the numbers with the vacuum attached? Would it be safe to up the total to 34 with no vacuum or would I be pushing the initial too far? Also, I have heard many opinions about using the ported and the full vacuum. For my situation, would I be better to stay with the ported side? ---------------------------------------------------------- Today, after some further investigating, I decided to do some vacuum readings on both the ported and the manifold. On the ported side, at idle it might be pulling 1 psi but when I give it a rev to open up the mechanical to 32 degrees, the ported vacuum jumps to about 18 psi. On the manifold vacuum, I get roughly 23 psi at idle and with a rev, it will drop quickly to about 10 psi then rebound quickly back up to 23 psi. Now if I hook up the distrubutor to the manifold side and if my limter plate was set to only allow 8 degrees, I would have 25 (17 initial with no vacuum) for inital and 40 degrees (32 with no vacuum) full advance correct? Going this route wouldn't my initial be to high? Using the ported side, it keeps my initial down but when I get on the gas it also increases the advance. So what are the benefits to using the manifold side? o No:
I use a vacuum stop and manifold vacuum as per former member ignitionmans specs. In my LeSabre I have the initial timing at 10 degrees, then 10 more degrees of vacuum as soon as I fire it up. So I idle at 20. Then springs and weights take me too around 32 degress. I really need timing tape, but I made a new mark that works pretty good. I found the lightests springs in the Crane kit (which seemed kinda generic) were to light. The next springs up work really well. This take some experimenting, but you'll get it. The idea for using manifold vacuum and a stop is so that you'll have more timing there when you punch it. Rather than locking your timing in, the ten degress of vacuum you get with manifold vacuum and the stop allows your engine to still start easy. But be advised, these sorta mods will flunk you on Emissions testing! So if your car needs emissions, you'll wanna run very little advance at idle for the test. I've also been told that manifold advance to the distributor is not good if you are running an EGR valve, although I don't know why. Nothing a golf tee in a vacuum line won't cure.
John, Sounds to me like you have 16* of advance in the cannister. You need to limit it more. A stock Buick distributor, usually didn't allow full advance until 4000 RPM or more. As a result, only part of the mechanical advance was in at typical cruising speeds. The vacuum advance made up the rest, by adding 14-18*. Buick motors usually run best with the total advance(no vacuum) set to between 30 and 34* Every engine is different. If you have all your advance in early, at cruising speed, you only need to add another 8-10* of vacuum advance. An engine will tolerate more spark advance at light loads. You can run 40-44*(initial+mechanical+vacuum) for increased economy. Again, some experimenting is needed to see what your engine likes, and will tolerate. Plugging your vacuum advance into manifold vacuum will give you all the advance in the cannister. When you punch the gas, manifold vacuum should drop close to zero, and the vacuum degrees should go away, leaving you with just the initial+mechanical. Ported vacuum should be nill at idle, then increase as you open the throttle, then go close to zero at wide open throttle. An engine with a healthy cam will like a large amount of initial advance, coupled with a shortened mechanical advance curve. The extra advance helps the bottom end power, that suffers somewhat with a bigger cam. Manifold vacuum advance gives even more initial advance at idle, that goes away at wide open throttle, where you neither want or need it. I've posted this before, but I'll say it again. The Crane adjustable vacuum advance, comes with the best springs I've seen on the market. You can benefit by getting your advance in by as early as 1600 RPM, or as late as 3200 RPM, and everthing in between by mixing springs. The cannister is adjustable for rate and amount of degrees. It is much more versatile. Just my .02
And they are less than $23 from either Jegs or Summit (part # CRN-99601-1). Based upon Larry's advice, I ordered mine today from Summit (along with my new MSD Super Conductor BBC wire set ($69.95 (# MSD-31373), with free wire separator set!) and my Walker Dynomax Ultra Flow 17749 muffler's (# WLK-17749 - $42.88 each). thanks for all the advice Larry, pretty soon all have most of the goodies in your signature!:grin:
Another little trick with the advance springs. You do not have to use them in matched pairs. It is the total spring tension that determines the advance rate. You can use a dial back timing light to determine your advance rate. To do this take a reading at say 1500 rpm by turning the dial until you have zero on the timing mark. Repeat at 2000, 2500, 3000. This should give you a good idea of your "curve. "
A couple of comments from a 462" Buick powered roadster guy. Some good advice here on the curves etc. If you have an MSD or other ignition amplifier box, you shouldn't use a dial back timing light. They will not show the correct timing figure where the regular timing lights will. This with the dial-back set at zero fwiw. Both timing lights Penske's from Sears fwiw. I've found - as have a whole lot of SBC guys - that selecting the vacuum advance source to ported vacuum results in overheating at idle. Usually in traffic and like always, the hot days are the worst. The overheating problem is almost always cured by selecting the vacuum advance to full time manifold vacuum source. GM engines like a lot of advance at idle. My Unilite distributor is set at 8 degrees initial - all figures BTDC. All in at about 2700-2800 rpm and 32 degrees total. Add another 16 degrees of vacuum advance and it reads 48 degrees advance at just under 600 rpm. The engine has a mild Crower cam - about 262 degrees advertised duration - and 9/1 compression. The car never gets over 205 degrees on a hot summer day and that's extensive idling in traffic. Most times it runs around 198 degrees in summer traffic. (100 degrees + in my neck of the woods.) With the 32's small engine compt. - running either the SBC or the big Buick - overheating is a concern in these little cars, but setting up the correct timing usually cures it. It's my considered opinion that running the race-o, centrifugal only distributors on the street is not the way to go.
Don't you mean 48 degrees at 2800 rpm? so with you using the manifold vacuum, you are getting 24 degrees at idle, right? Question... changing the weights to either lighter or heavier ones, do they have any affect on the tiiming?
I have to disagree with you. Both my Sears, and Snap on light work with my MSD Digital 6. If I use the dial back feature to set my initial at 12*, and then dial back to zero, the mark is right at 12* on the timing tab. I also have a plain Sears light that I bought 20 years ago and that agrees with the newer lights I have.o No:
I can't argue with your personal experience, but the dial-back didn't work right for me and the regular light did. MSD 6AL fwiw. I mentioned this on another board and had several guys agree with me that the dial-backs could be a problem when an ignition amplifier is in use. Which pretty much answered my question about the dial-back light being defective. Kinda sorry too, the dial-backs sure look like a good way to go.
Umm, That's interesting. Can you go into more detail about how it didn't work for you? Did anyone tell you why it wouldn't work? I have heard this before. Someone mentioned the multiple sparks, as one reason. I'm really curious about your experience. The dial back is a really neat feature. I think I'll ask the MSD tech line. Maybe they can shed some light on this. Just for kicks, I went out to my car and put all three lights on it. I have 16* initial, 32 * total, retarded 2* from 4400 RPM and up, and 10* of manifold vacuum advance. All the lights were extremely close, less than 1* if that much difference.
I've heard the same thing. One of the guys that said it was the ignition man but I have not seen it with my Sun dial back light. But I timed my system with the dial back and set at 0* and timed on the balancer and see no diff. I use a GM HEI with Crane HI-6S. Would love to hear from an electronics engineer.
I posted this question to the MSD tech people. Let's see what they come back with. I remember Dave saying this, but he never explained why. I need to know why. I'm just really curious.
If I remember right it ended up showing about 10-15 degrees retarded. One of the guys - who writes auto electric books among other things - on another board thought it could perhaps be related to the multiple spark discharges during the 20 degrees of crank rotation. Maybe, seems to me the strobe should trigger when the spark impulse is first picked up and not have to wait for the spark impulse to die off to trigger the strobe. I did pretty much what you did when you checked your timing lights. Hooked up the new one, shot the timing, saw that it was off and realizing the car was running ok, hooked up the old timing light and saw the initial timing sitting there at 8 degrees BTDC. I did check the dial-back knob for zero several times. Now you got me tempted to try another dial-back. Maybe the one I had was defective, but I've heard the dial-back vs. MSD story from several different sources.
Thanks C9, I'll post back, when I hear from MSD. If you know anyone with the Sears dial back, see if you can borrow it, and try it. That is one nice timing light, and it works great for me.
Thanks all for your help! I got it switched over to manifold vacuum and I get 19 initial and 42 at the other end. I need to bump it up a little but so far its working pretty good. Couldn't have done this without the v8 board!:TU:
Well I heard back from MSD Tech, this is what they said: Dear Sir; We normally don't recommend using digital or dial type timing light with our ignition systems. The reason is that the digital circuitry can pick up interference from the ignition and can cause erratic timing readings. This can sometimes be as much as 1 degree per thousand RPM. It may not happen all the time, but we have seen it before. An analog type will be much more accurate. Thank You, MSD Tech -----Original Message----- From: [mailto:Larrymta@aol.com] Sent: Friday, June 04, 2004 8:55 PM To: Joe LaPille Subject: Tech Question from Larry Hymowitz I have heard from some people that dial-back timing lights will not work with MSD ignitions. No one seems to be able to tell me why, they just say it is fact. I have my doubts about this. I have 3 Timing lights, a Snap-on digital dial-back, a Sears dial back, and an old Sears standard light. They all seem to work just fine, and agree with the timing tab and marks on my 70 Buick 455 Stage1 motor. BTW, i'm using your Digital 6+ ignition, and I love it. If the lights are prone to inaccuracy, how much off would they be. Any info you can provide would be appreciated. Thanks, Larry Larry Hymowitz 69-42 213 Street Oakland Gardens, Ny 11364 USA Larrymta@aol.com Apparently, this doesn't happen all the time, but it can be a factor. For now, all 3 of my lights agree, but it is good to be aware of this potential problem.
When is using manifold recommended? I've been running the car on manifold for a couple days but decided to swap back to the ported side for a test. With my LeSabre, the preformance is much better on the port side. I also noticed when the car was on manifold vacuum, it didn't really like the 19 degree initial advance. After thinking about this, I don't understand the benefits of manifold vacuum. With the ported side, you can keep the initial where it needs to be and when you open the car up, it will open your advance up as would the manifold side.
