HELLTRIX
POSTED THIS INFO, and it looks impressive
"So I thought I would share my latest success. 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.
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 and or my curve but even checking it, that seemed to show it was correct. Having my doubts 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 a good investment.
This wasn't the only reason. I have an Accel billet distributor and the only way to access the screw to adjust the total timing and advance spings was to remove the distributor, pull the gear shaft, remove the magnetic pickup, full dissemble. A 25-30 minute process which I just did today but this time I set it at 0 advance 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. (needed to be really advanced so the MSD could pull out timing for the curve). 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.
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. At about 35mph the rear tires lit up and I finished pressing the pedal to the floor and got ready to shift again, meanwhile steering the car 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.
So I will be in search of tuning advice.
Sorry for such a long update and/or excitement spew about my recent success.
It has a "Running Retard".
Its 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. So instead, you set your distributor 16+ degrees advanced to start with add some more for the initial timing you want (your distributor my end up being 28+ degrees advanced at this point). Then you program the MSD to take out 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 and it draws a straight line from 1000rpm -16degree retard all the way to 3000 rpm 0 degree retard. So this IS your advance. 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.
The only issue I have right now is the timing below 1000 rpm is not exactly right. This is because I don't really know enough about engines to know this. For instance a big engine with a rough cam, what kind of idle timing do the like? 8,10, 12 degrees initial? I think they like lots of initial but there becomes a point where your starter can't really handle too much initial.
This is where I setup my 0-300rpm to pull out a few more degrees, then as it passes 500rpm it bounces up the timing to slightly above my idle initial thinking that maybe the extra initial at that point might help keep the engine from stalling. The problem with this is sometimes the engine doesn't quite start up before hitting the extra timing and really makes the engine rattle. Sometimes starts other times stalls.
Finally once its started up the idle floats around the 850-900 rpm in neutral where in this range the engine is at 12 degrees initial which includes my 4 degrees vacuum. Although I should have more like 14-15 inches on my vacuum gauge and when I checked it I only had 9-10 telling me I probably need to work on the timing a bit more. Though I'm not sure its been 2 years since I last checked the vacuum and don't remember what I had for good vacuum.
My latest idle mapping I made reduced the timing at 500rpm to bring it closer to same timing as the 800-1000rpm setting to maybe allow the engine to start up better.
Let me ask this, am I dreaming to think I can get this engine to idle at 850rpm in neutral, then pull it into drive and have the car still idle? Right now I gotta feather the throttle a bit to keep it idling while in gear. (2800rpm stall converter).
"
