I have a 67 Skylark with a stock 340-4 in it that I am trying to get going again. It runs well after rebuilding the carb but I would like to optimize it for a nice little cruiser. I'm considering having the distributor gone through and recurved on a distributor machine. I has a Pertronix in there now that has worked well and I was planning to keep it. Per Larry's guide, I am planning to use the Crane vacuum advance kit but wanted to get some input on approximately what range I should be targeting for the advance. I'm new to the whole performance timing and since the engine has 10:25:1 compression, I don't want it to start pinging unnecessarily. I'd love to get some thoughts from those that have far more experience than me on this subject. Thanks!
Good to see someone else tuning up a 340! It will come down to a lot of trial an error. The timing thread is excellent and very helpful. The main thing is to keep if from pinging and that involves sneeking up on the timing. I have the crane kit and did some messing around with it last year but never got it perfect before I needed to take a long trip and back it off a bit. What gas do you have available and what octane will you run??? Do you have a dial back timing light?
I have never used a 340 so take my info for what it is... I find my 350s like 14 degrees initial timing, 34 total timing all in by 2400 RPM, and 10 degrees of vacuum advance. I would start by eliminating the points if you have not already... Then use a mr gasket bushing to limit the mechanical advance and a spring kit to get the timing in earlier... I have to limit the vacuum advance to just 10 degrees. Use the highest octane fuel at the pumps for sure and try to always fill up at the same place for consistancy.
MY 340 has been operational for about a year now but unfortunately I can't do much more than confirm Sean's recommendations at this point since I'm still sorting out the transmission. It should be clear to all by now that if it is possible to go to electronic control of the timing it gives greater accuracy and flexibility, but it seems by and large that Buicks are fairly uniform in their timing demands, and reasonably tolerant also. So while a map will let you get very exact, it will also exceed requirements, and the general recommendations are going to be just fine 90% of the time. However, in any engine where you approach the limits of the particular build you need to watch the max advance, and this applies whether it's at WOT or just a ping under light load. Both ends should be right, and then you can go for best behavior at idle. I know it's usually done the opposite way but just consider what's most important to you. Tuning advance at WOT is not easy. You can tune to a number but that only gets you in the ballpark, usually in a safe zone. Beyond that are things like dyno pulls, dragstrip days, O2 sensors, EGT gages, coolent temp and vacuum. It takes a lot of thought and effort to get it right. That's where a map is handy, because you can tune each area without changing the others. The order of priority rightly should be Power, Economy, and last, idle quality. But physical limitations with a distributor often reverses the order. Part of the problem is that idle requirements can change as the engine breaks in and then as it wears also. Part is that your idea of what constitutes the best idle can also change, and part is that you may modify things that affect the idle like carb tuning, egt and pcv. If your WOT timing anchors your idle timing, as it does in distributor systems it restricts your ability to tune idle, handicapping your overall tuning efforts. This is why electronic control is a good thing. Relatively inexpensive options such as MegaJolt allow the flexibility to tune the map just in the area where it is needed. Jim
67skylark27, Sean and Jim, Thank you for your suggestions and recommendations. Looks like I may need to play around a little with it and see what works best but at least now I have something to go by. Here in AZ I can get 91 octane at the pump. I've been running 89 successfully if I don't floor it. I may have to grab a cheap dial back timing light from HF. 67skylark27, how do you like that 2004R behind your 340 with the 3:36 gears?
The stock 1967 340 distributor was 1111159. It had 26-30* of mechanical advance, and stock initial timing was 2 1/2* BTDC. First thing to do is to see if that distributor is the one currently installed. If so, you will need a bushing to cut back the mechanical advance if you want to run more initial timing.
I love the transmission swap! Even when I had the 300-2 in there it made a huge difference in performance (gas mileage was excellent too). It took me awhile to get the rear gear swapped out and that only made it better. Now it all matches up, the rpm's are where they should be and the shift points are right on. As far as timing goes, if I remember right, I'm at 10 degrees initial and have a medium and heavy spring on for now, and no limiter. I don't have any ping with 89 or 91 ethanol free gas so I know I can go a little more on total timing, just have to spend the time doing it! In case you have't run across this, here's my write up of the changes I've made: http://www.v8buick.com/showthread.ph...ing+completion 67skylark27, how do you like that 2004R behind your 340 with the 3:36 gears?[/QUOTE]
As Larry said above, you will need to put a timing limiter in the distributor. That's my next step after messing around with the springs etc. Car is great on 12 degrees initial but ends up pinging under heavy load. So I'm at 8 initial for now and have the stock heavy springs in.
Sounds like you need a MR gasket bushing to limit your mechanical advance so you can run more initial timing and not have too much on the upper RPM....
Hi All, I have an issue with the timing on my 1967 340 4 and I hoped someone may have experience in sorting the problem. I decided to install a new CRT branded electronic distributor as original distributor was in bad shape and now I’m having issues with pinging under load. I’ve set the timing at 2.5 btdc with vacuum plugged as per factory spec but motor pings under moderate acceleration though it seems to disappear when under hard acceleration. I presume I have too much advance which is causing this issue? When I disconnect the vacuum it stops pinging but seems sluggish. I noticed that the timing jumps to 10 btdc at idle when I reconnect vacuum and I’m unsure if this is correct, it seems a lot? Not sure what to try next so would appreciate any advice. Thanks.
The original distributer runs manifold vacuum meaning it has advance at idle. But having ping at 2.5 degrees of advance seems like a problem. You may need to decarbon the Pistons and combustion chamber. Or carb may be too lean. I never heard of crt distributer. I would double check your spark plug wires. And double check your directions. Is that distributer supposed to run on 12 volts? The points distributer runs on 7 . You would need to remove resistance wire from wire harness. And replace with regular wire. 10 advance is fine and removing it will make it sluggish. So yes it’s normal. But distributer may not be designed to work that way. Most aftermarket distributers run ported vacuum.
The problem is you installed a non stock distributor and you don’t know the specs on that distributor. That was your first mistake. Your second mistake was setting the initial timing to the stock 2.5* BTDC. That no longer applies because you no longer have the stock distributor. The only time an engine runs at the initial timing is at idle. You step on the gas and the mechanical and vacuum advance add timing. What you need to do is disconnect the vacuum advance and set the maximum timing to 30-34*. The initial timing will take care of itself. Make some full throttle runs and check for ping. Reduce the maximum timing if it pings. If you have to reduce it much below 30*, suspect other causes. Once you set up the max timing, then connect the vacuum advance. If it pings, reduce the amount of vacuum advance until you eliminate the part throttle ping. As mentioned, the HEI type distributor requires battery voltage. If you were using points before, you need to remove and replace the resistance wire. http://www.v8buick.com/index.php?th...ystem-function-tests-and-modification.248990/ http://www.v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/
OK thanks, how many rpm should I use to set to max advance of 30-34? Is 2500 rpm ok? I am using the original wire plus have added another wire direct from the fuse box to the hei distributor? Could this be causing an issue? I am also using the Carter carby port for the vacuum, is this correct for hei distributor or should I be running from manifold? Thanks for your assistance, it is really appreciated. Regards, Phil
The mechanical will max out at a certain RPM. That RPM will DEPEND on the tension of the springs holding the weights back. You want to set the maximum timing when the weights are all the way out. That may be more than 2500 RPM. There is no way for me to predict that. There is no sense in setting the maximum timing if the weights haven't swung all the way out yet because the timing will advance beyond that. What type of timing light do you have? Is it a dial back type, or a standard timing light? That will determine your method. Your 67 engine probably used manifold vacuum. You have the option to use ported vacuum. If your initial timing ends up being low, that can cause the engine to run hot when at idle and stop and go traffic, especially in warm weather. Using manifold vacuum can boost advance at idle and low speed to help the engine run cooler. If you use ported vacuum, you will only have vacuum advance when the throttle is open. The advance will be the same at part throttle. I do not know what the specs are for the CRT distributor. Their page on the net doesn't help. Set the max timing to 32* and see how it runs WITHOUT vacuum advance. Read this thread, http://www.v8buick.com/index.php?th...ystem-function-tests-and-modification.248990/ I describe the right way to swap out the resistance wire. I don't think this is your problem. If you wern't getting battery voltage to the distributor, the engine would be hard to start or run very poorly.
Ok Cool, appreciate the help. I’ll have a play with it on the weekend and see how it goes. I have an old timing light with no dial back so will be a bit of trial and error. I might try and buy a new one, maybe an early Xmas present.
OK, what you do then is make a 30* mark on your balancer. Standing in FRONT of the car, locate the factory mark. Measure EXACTLY 1 3/4" CLOCKWISE from the factory mark, and mark that point. Make sure you can differentiate it from the stock mark. When you use the timing light, that 30* mark will be below the timing tab. As you slowly rev the engine, that 30* mark will begin to move up. When the weights swing all the way out, the 30* mark will STOP moving up no matter how much higher you rev the engine. At that point, the 30* mark should be aligned with some part of the timing tab scale. If it aligns with the 4* on the scale, that would mean you have 34* total timing. With the 2*, 32 ect. If the 30* mark never makes it high enough to reach the timing tab scale, it means you need to advance the timing. If it goes beyond the tab, you have too much advance and need to retard the timing. If you loosen the hold down bolt just enough so you can move the distributor, you can adjust it right then and there. Rev it until the 30* mark stops moving, then hold that RPM, and turn the distributor to line that 30* mark with the scale. Turning the distributor clockwise retards timing, counter clockwise advances the timing. Remember to disconnect and plug the line to the vacuum advance.
