I struggled for a long time trying to get my Accel distributor setup right from timing curves to initial and vacuum advance. Then I switched to the MSD 6AL-2 Programmable Ignition and became making curves via my laptop computer. I will detail my results here:
I haven't driven my car but a few times in the last year because it was having bad pinging and detonation problems. I finally had some time lately and applied some of my latest knowledge acquired from my time in the university I been going too (studying theoretical physics). I did some math and calculated the octane rating that I needed for my engine and determined the proper mix of E85 and 92 octane pump gas needed to prevent detonation. I mixed it up and and setup the carburetor to provide the proper amount of fuel. Again I had calculated the increase in fuel required to compensate for the E85 and found it to be doable with just a jet change. But I was still getting detonation.
I will add here this is no easy feat. This requires knowledge of geometry of a circle and trigonometry. As well as all the variables of your engine like the rod throw length from the crank, rod lengths, and your total cylinder volume from bottom to top during a full cycle. It is my recommendation that unless your 100% confident in these skills and/or not building a competition motor, that you just stick the the recommended builds by other hot rodders that have proven engine combinations as I have a few years into my project before finally getting it running right.
At this point I have finally convinced myself that it wasn't the fuel mixture as I was confident in my math and other calculations. I knew it was timing curve but even after checking it several times, it seemed to show it was correct. Having my doubts still, I removed my Accel 300+ ignition and replaced it with a nice expensive MSD AL6-2. Me, being more comfortable tuning a computer than a distributor recurve, the programmable MSD ignition seemed to be a good investment.
This wasn't the only reason I chose the programmable ignition. I have an Accel billet distributor and the only way to access the screw to adjust the total timing and advance springs was to remove the distributor, pull the gear pinion from the distributor shaft, remove the magnetic pickup, basicly a full dissemble. A 25-30 minute process that I have done a few times before trying to set how much advance it would do and change the springs for different curves. I did this last friday but this time I set it up so that the distributor couldn't change timing at all and removed all the advance weights and springs since now my programmable ignition would take over the timing curve.
After 4 attempts I finally got the distributor splined just how I needed. After designing a few curves I finally got it idling better then I ever heard it idle. But only estimated the curve needed for WOT. The AL6-2 is backwards to what a distributor does by pulling in more advance as RPMs go up. With the MSD since its not part of the distributor it can't advance timing any more than when the distributor sends the trigger signal. So instead, you set your distributor (for example) to 16+ degrees advanced to start with, don't forget to add some more for the initial timing you want (your distributor my end up being 28+ degrees or more advanced at this point). Then you program the MSD to take out timing (retard the timing). So for my case I have the 600-1000 rpm set to take out (retard) the timing 16 degrees. Putting a timing light to the damper shows I'm at 12 degrees initial advance at idle. Then I put another dot on the MSD map for 3000 RPM at the 0 retard mark and it draws a straight line from 1000rpm -16degree retard all the way to 3000 rpm 0 degree retard. So this IS your advance, 16 increase from 1000rpm to 3000 rpm (if you start at -16 and go to 0, its a positive 16 degrees, get it?
). By pulling out less retard as you rev up, your essentially advancing the timing. Backwards eh? It works though once you realize its the same thing just slightly different way of looking at it.
BTW, this ignition has a map sensor plug that works just like the paragraph before. It can monitor manifold vacuum and adjust your timing based on that too. Again its also backwards. At max vacuum your map sensor will read almost zero pressure. When you have no vacuum (WOT) the gauge should read close to 14.7psi (standard atmosphere pressure). So like before you, you set your distributor advanced however many degrees of vacuum timing you want. Then on the MSD program you set it so at near 0 psi you retard the timing by the amount you had added to the distributor which brings you back where you where in timing before you added the extra for the vacuum portion. And when you reach max psi (in non-turbo/boost, this will be around 14.7psi) you set your vacuum (on the MSD its called Boost/Run) to pull out 0 degrees. Since your not retarding the timing with the map sensor anymore whatever extra advance you set on the distributor is now vacuum advanced. It makes perfect sense to me, but I think backwards the most people anyway, so ask questions if your still confused and I or someone else can maybe explain it better if it still makes no sense. I should note here that I haven't tried the map sensor yet, been a busy couple of days but I did look at the situation and confident I can set it up. I will add a post after I get that setup.
THE FUN STUFF:
It was at this time my dad arrived from 700 miles away for a once per year visit so I offered him a ride. Giving him the disclaimer that I had just installed this new ignition and the timing might not be right. So with my laptop in hand we jumped in and went for a ride (straight for the nearest highway). I could already tell it was running good even while it was warming up.
We made it to the on ramp to the freeway so I eased into it smoothly but quickly. Rolling at about 35mph already, the rear tires lit up and I finished pressing the gas pedal to the floor and got ready to shift again, meanwhile I was steering the car trying to keep it as straight as possible. A couple seconds later we where successfully cruising on the freeway slowing down for the cars we where catching.
Looking over at the father was a total astonishment and what he just felt on his seat. And the following priceless comment "In all my years of wrenching and riding in hot rods, this is the most powerful car I have ever been in".
And he went on to recount the fact the the Impala didn't hesitate to rip the tires free so easily while already at 35mph without downshifting.
Now for the best part. Not a single ping or sign of detonation.
Maybe now I can work on finally tuning the carb properly and working on dialing in the best timing curve. TBH I have no clue how much timing to use when it should be all in by and for how long. Tomorrow I am installing a map sensor that I received so I can replace the vacuum advance on the distributor (the only thing left on the distributor that has any control). Its only pulling in around 4 extra degrees at the moment.
More details and hopefully pictures coming soon.
I haven't driven my car but a few times in the last year because it was having bad pinging and detonation problems. I finally had some time lately and applied some of my latest knowledge acquired from my time in the university I been going too (studying theoretical physics). I did some math and calculated the octane rating that I needed for my engine and determined the proper mix of E85 and 92 octane pump gas needed to prevent detonation. I mixed it up and and setup the carburetor to provide the proper amount of fuel. Again I had calculated the increase in fuel required to compensate for the E85 and found it to be doable with just a jet change. But I was still getting detonation.
I will add here this is no easy feat. This requires knowledge of geometry of a circle and trigonometry. As well as all the variables of your engine like the rod throw length from the crank, rod lengths, and your total cylinder volume from bottom to top during a full cycle. It is my recommendation that unless your 100% confident in these skills and/or not building a competition motor, that you just stick the the recommended builds by other hot rodders that have proven engine combinations as I have a few years into my project before finally getting it running right.
At this point I have finally convinced myself that it wasn't the fuel mixture as I was confident in my math and other calculations. I knew it was timing curve but even after checking it several times, it seemed to show it was correct. Having my doubts still, I removed my Accel 300+ ignition and replaced it with a nice expensive MSD AL6-2. Me, being more comfortable tuning a computer than a distributor recurve, the programmable MSD ignition seemed to be a good investment.
This wasn't the only reason I chose the programmable ignition. I have an Accel billet distributor and the only way to access the screw to adjust the total timing and advance springs was to remove the distributor, pull the gear pinion from the distributor shaft, remove the magnetic pickup, basicly a full dissemble. A 25-30 minute process that I have done a few times before trying to set how much advance it would do and change the springs for different curves. I did this last friday but this time I set it up so that the distributor couldn't change timing at all and removed all the advance weights and springs since now my programmable ignition would take over the timing curve.
After 4 attempts I finally got the distributor splined just how I needed. After designing a few curves I finally got it idling better then I ever heard it idle. But only estimated the curve needed for WOT. The AL6-2 is backwards to what a distributor does by pulling in more advance as RPMs go up. With the MSD since its not part of the distributor it can't advance timing any more than when the distributor sends the trigger signal. So instead, you set your distributor (for example) to 16+ degrees advanced to start with, don't forget to add some more for the initial timing you want (your distributor my end up being 28+ degrees or more advanced at this point). Then you program the MSD to take out timing (retard the timing). So for my case I have the 600-1000 rpm set to take out (retard) the timing 16 degrees. Putting a timing light to the damper shows I'm at 12 degrees initial advance at idle. Then I put another dot on the MSD map for 3000 RPM at the 0 retard mark and it draws a straight line from 1000rpm -16degree retard all the way to 3000 rpm 0 degree retard. So this IS your advance, 16 increase from 1000rpm to 3000 rpm (if you start at -16 and go to 0, its a positive 16 degrees, get it?
). By pulling out less retard as you rev up, your essentially advancing the timing. Backwards eh? It works though once you realize its the same thing just slightly different way of looking at it.BTW, this ignition has a map sensor plug that works just like the paragraph before. It can monitor manifold vacuum and adjust your timing based on that too. Again its also backwards. At max vacuum your map sensor will read almost zero pressure. When you have no vacuum (WOT) the gauge should read close to 14.7psi (standard atmosphere pressure). So like before you, you set your distributor advanced however many degrees of vacuum timing you want. Then on the MSD program you set it so at near 0 psi you retard the timing by the amount you had added to the distributor which brings you back where you where in timing before you added the extra for the vacuum portion. And when you reach max psi (in non-turbo/boost, this will be around 14.7psi) you set your vacuum (on the MSD its called Boost/Run) to pull out 0 degrees. Since your not retarding the timing with the map sensor anymore whatever extra advance you set on the distributor is now vacuum advanced. It makes perfect sense to me, but I think backwards the most people anyway, so ask questions if your still confused and I or someone else can maybe explain it better if it still makes no sense. I should note here that I haven't tried the map sensor yet, been a busy couple of days but I did look at the situation and confident I can set it up. I will add a post after I get that setup.
THE FUN STUFF:
It was at this time my dad arrived from 700 miles away for a once per year visit so I offered him a ride. Giving him the disclaimer that I had just installed this new ignition and the timing might not be right. So with my laptop in hand we jumped in and went for a ride (straight for the nearest highway). I could already tell it was running good even while it was warming up.
We made it to the on ramp to the freeway so I eased into it smoothly but quickly. Rolling at about 35mph already, the rear tires lit up and I finished pressing the gas pedal to the floor and got ready to shift again, meanwhile I was steering the car trying to keep it as straight as possible. A couple seconds later we where successfully cruising on the freeway slowing down for the cars we where catching.
Looking over at the father was a total astonishment and what he just felt on his seat. And the following priceless comment "In all my years of wrenching and riding in hot rods, this is the most powerful car I have ever been in".
And he went on to recount the fact the the Impala didn't hesitate to rip the tires free so easily while already at 35mph without downshifting.
Now for the best part. Not a single ping or sign of detonation.
Maybe now I can work on finally tuning the carb properly and working on dialing in the best timing curve. TBH I have no clue how much timing to use when it should be all in by and for how long. Tomorrow I am installing a map sensor that I received so I can replace the vacuum advance on the distributor (the only thing left on the distributor that has any control). Its only pulling in around 4 extra degrees at the moment.
More details and hopefully pictures coming soon.
