Distributor / Ignition tunning info
11-16-2013, 10:05 AM
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Distributor / Ignition tunning info
Since there are constantly threads going that require distributor tuning info, rather than keep repeating everything I thought I would try and make a sticky for it.
Any comments are welcome.
Ignition / Non computer controlled distributor tuning sticky
First the most important thing is to make sure you balancer and tab are actually reading correctly. This is a very common issue with old balancers when the outer ring has spun and even on inexpensive new balancers. I recently have seen a brand new balancer 9 degrees off.
The easiest and most accurate way to do this with the heads on the engine is with a piston stop. Here is a video showing how to do that.
www.youtube.com/watch?v=PD0ZRc7Dy28 (I have no affiliation with the guy who made the video. Just found it on youtube.)
Next is setting up the distributor. I will break this down with standard hei style and msd style distributors.
HEI Style (this includes stock and all aftermarket hei distributors)
If you have a vacuum advance, make sure it is disconnected for this step.
For this example we are going to set the total timing for 36 and pretend we have an msd non hei distributor with an 18 degree bushing in it.
Have a helper hold the rpm at around 3300. Now time the engine to 36 degrees and lock the distributor back down. Now at idle you should have approximately 18 degrees.
Here are some general sbc timing numbers for pump gas you can start at. Note these are just general guidelines. Every setup is different and may require numbers outside of these.
Vortec or modern aluminum heads 32 – 34 degrees
Stock iron or old aftermarket iron 34-38 degrees
Now for vacuum advance
First I will say that it has absolutely no adverse effect on performance at all and in a lot of cases will improve light throttle acceleration. It will also increase you cruising fuel economy by 2 – 4 mpg and depending on what vacuum source it is hooked up will improve idle quality.
Any street car should have the vacuum can at least hooked up to ported vacuum at a minimum. It will improve fuel economy and in most cases a smoother cruising engine. There are no adverse effects.
Now for the hot debated part. Hooking the vacuum can up to full manifold vacuum.
For people who have stock or small cams hooking the vacuum can up to full manifold vacuum really isn’t needed since the added timing at idle isn’t really going to make much of a difference, but you can still do it and usualy works just fine. But for people with bigger cams it can make a huge difference. I have seen big camed engines like as much as 50 degrees at idle.
Now the correct way to set this up is to get an adjustable vacuum can and get a vacuum reading at idle with the carburetor properly adjusted and the vacuum can disconnected. Let’s say it is 10 inches at idle, then adjust the can so that it gives full vacuum advance at 9 inches. (The easiest way to do this is with a hand vacuum pump like a mighty vac) Now you can have 10 to 15 degrees more timing(depending on the can and advance stop) at idle with no adverse effect.
Now say you don’t have an adjustable can. Can you still use it on full manifold vacuum? Yes and no!
If you hook the can up to an engine that has say 8 inches of vacuum at idle you will still get some advance from the can but not full. And yes ever little bit helps. But here is the catch. From my testing what I have found is on an automatic equipped car this setup works well and had no idle issues at all. But on a manual trans car this does not work well and can cause the idle to drop and be rough. I think this is due to the fact that when you let the clutch out you can wind up going below normal idle rpm and this in turn creates less vacuum to the can which causes the can to drop the timing down. So now you may have an engine that was tuned to idle at 850 rpm with 20 degrees of timing now at 600 rpm and 10 degrees and it kind of gets stuck there until the engine is reved up.
Here are a couple good articles explaining mechanical and vacuum advance in detail.
http://www.hotrodders.com/forum/dist...1-a-59033.html
http://classicinlines.com/spark.asp
Any comments are welcome.
Ignition / Non computer controlled distributor tuning sticky
First the most important thing is to make sure you balancer and tab are actually reading correctly. This is a very common issue with old balancers when the outer ring has spun and even on inexpensive new balancers. I recently have seen a brand new balancer 9 degrees off.
The easiest and most accurate way to do this with the heads on the engine is with a piston stop. Here is a video showing how to do that.
www.youtube.com/watch?v=PD0ZRc7Dy28 (I have no affiliation with the guy who made the video. Just found it on youtube.)
Next is setting up the distributor. I will break this down with standard hei style and msd style distributors.
HEI Style (this includes stock and all aftermarket hei distributors)
As long as you don’t have a really heavy car you want to set up a quick curve to get the timing in pretty fast. I will usually use the Moroso hei advance kit 72300 with the med or light springs. The light springs will make a bit more torque down low, but may cause idle fluctuation and or low rpm knock do to the springs adding advance at idle and in full by about 2100 rpm. Try it and see which ones work better for you.
Note: I do not recommend using an hei style distributor (factory of aftermarket) on any reasonably sized camshaft do to the fact that you cannot control the total amount of mechanical advance which will usually not give you enough timing at idle for it to be smooth and properly burn the fuel so it does not smell of fuel out the exhaust and foul the plugs. With and hei distributor using the moroso med springs if you set total timing to 32 degrees then your idle timing will be only 9. That is no way near enough timing for it to idle properly. Now there is a work around using the vacuum can I will get to later.
MSD (non hei)Note: I do not recommend using an hei style distributor (factory of aftermarket) on any reasonably sized camshaft do to the fact that you cannot control the total amount of mechanical advance which will usually not give you enough timing at idle for it to be smooth and properly burn the fuel so it does not smell of fuel out the exhaust and foul the plugs. With and hei distributor using the moroso med springs if you set total timing to 32 degrees then your idle timing will be only 9. That is no way near enough timing for it to idle properly. Now there is a work around using the vacuum can I will get to later.
For most aftermarket street cams Install the black 18 degree bushing. For stock cams you can just leave the one in that came with it or the 18. It doesn’t really matter. For larger cams I recommend purchasing a 10 degree bushing. You can find these on ebay for under $10 shipped.
Note: For guys running larger cams I highly recommend the 10 degree bushing. It will make a huge difference in idle quality, vacuum, smell, plug fouling, and off idle response and drivability. This is due to the increases timing at idle. For example if you set the total timing at 36 then your idle timing will be at 26 with the 10 degree bushing. With the black bushing you would only have 18 degrees at idle and with an hei you would have about 13 degrees at idle.
Next As long as you don’t have a really heavy car you want to set up a quick curve to get the timing in pretty fast. Install one light silver spring and one light blue spring.
Now it is time to set the timingNote: For guys running larger cams I highly recommend the 10 degree bushing. It will make a huge difference in idle quality, vacuum, smell, plug fouling, and off idle response and drivability. This is due to the increases timing at idle. For example if you set the total timing at 36 then your idle timing will be at 26 with the 10 degree bushing. With the black bushing you would only have 18 degrees at idle and with an hei you would have about 13 degrees at idle.
Next As long as you don’t have a really heavy car you want to set up a quick curve to get the timing in pretty fast. Install one light silver spring and one light blue spring.
If you have a vacuum advance, make sure it is disconnected for this step.
For this example we are going to set the total timing for 36 and pretend we have an msd non hei distributor with an 18 degree bushing in it.
Have a helper hold the rpm at around 3300. Now time the engine to 36 degrees and lock the distributor back down. Now at idle you should have approximately 18 degrees.
Here are some general sbc timing numbers for pump gas you can start at. Note these are just general guidelines. Every setup is different and may require numbers outside of these.
Vortec or modern aluminum heads 32 – 34 degrees
Stock iron or old aftermarket iron 34-38 degrees
Now for vacuum advance
First I will say that it has absolutely no adverse effect on performance at all and in a lot of cases will improve light throttle acceleration. It will also increase you cruising fuel economy by 2 – 4 mpg and depending on what vacuum source it is hooked up will improve idle quality.
Any street car should have the vacuum can at least hooked up to ported vacuum at a minimum. It will improve fuel economy and in most cases a smoother cruising engine. There are no adverse effects.
Now for the hot debated part. Hooking the vacuum can up to full manifold vacuum.
For people who have stock or small cams hooking the vacuum can up to full manifold vacuum really isn’t needed since the added timing at idle isn’t really going to make much of a difference, but you can still do it and usualy works just fine. But for people with bigger cams it can make a huge difference. I have seen big camed engines like as much as 50 degrees at idle.
Now the correct way to set this up is to get an adjustable vacuum can and get a vacuum reading at idle with the carburetor properly adjusted and the vacuum can disconnected. Let’s say it is 10 inches at idle, then adjust the can so that it gives full vacuum advance at 9 inches. (The easiest way to do this is with a hand vacuum pump like a mighty vac) Now you can have 10 to 15 degrees more timing(depending on the can and advance stop) at idle with no adverse effect.
Now say you don’t have an adjustable can. Can you still use it on full manifold vacuum? Yes and no!
If you hook the can up to an engine that has say 8 inches of vacuum at idle you will still get some advance from the can but not full. And yes ever little bit helps. But here is the catch. From my testing what I have found is on an automatic equipped car this setup works well and had no idle issues at all. But on a manual trans car this does not work well and can cause the idle to drop and be rough. I think this is due to the fact that when you let the clutch out you can wind up going below normal idle rpm and this in turn creates less vacuum to the can which causes the can to drop the timing down. So now you may have an engine that was tuned to idle at 850 rpm with 20 degrees of timing now at 600 rpm and 10 degrees and it kind of gets stuck there until the engine is reved up.
Here are a couple good articles explaining mechanical and vacuum advance in detail.
http://www.hotrodders.com/forum/dist...1-a-59033.html
http://classicinlines.com/spark.asp
11-21-2013, 05:02 PM
#3
Supreme Member
Re: Distributor / Ignition tunning info
I've more or less followed that formula and have had some excellent results improving the idle quality, performance and mpg.
I've limited the mechanical advance in my MSD using the black (18°) bushing and adjust my initial for a 32-34 total in by around 3000. I'm a little timid on having it come in any sooner as A) the car is quite heavy at 3700lbs and B) I'm running a lot of compression with iron heads and a short cam (cranking pressure is 200 psi plus) and I'd rather err on the side of caution.
I've really experimented with the adjustable vacuum can using the hand pump method you've described. Plenty of trial and error with either type of vacuum source although currently, I have my maximum vacuum advance all in by 9"-10" as I idle around 11" using full manifold vacuum. I have an adjustable vacuum unit as well as the Crane Cams kit for changing the amount of vacuum advance available. Although a little excessive at the moment with 20-22°, it brings my idle timing to as much as 36°. That's improved the idle quality a great deal and solved the temperature climb I'd see if the car idled for any length of time. Mileage is excellent also at well over 20 mpg hiway.
I've limited the mechanical advance in my MSD using the black (18°) bushing and adjust my initial for a 32-34 total in by around 3000. I'm a little timid on having it come in any sooner as A) the car is quite heavy at 3700lbs and B) I'm running a lot of compression with iron heads and a short cam (cranking pressure is 200 psi plus) and I'd rather err on the side of caution.
I've really experimented with the adjustable vacuum can using the hand pump method you've described. Plenty of trial and error with either type of vacuum source although currently, I have my maximum vacuum advance all in by 9"-10" as I idle around 11" using full manifold vacuum. I have an adjustable vacuum unit as well as the Crane Cams kit for changing the amount of vacuum advance available. Although a little excessive at the moment with 20-22°, it brings my idle timing to as much as 36°. That's improved the idle quality a great deal and solved the temperature climb I'd see if the car idled for any length of time. Mileage is excellent also at well over 20 mpg hiway.
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