I understand the basics of timing with respect to tuning pretty well. Setting desired overall timing is no problem at all. I simply increase the timing until I hear detonation and not that as my max timing. I then install a timing advance stop so that my initial timing plus the advance gives me my max total timing with no detonation. I generally shoot for 10* or so of initial timing but basically try to put as much initial timing in as I can without starting issues. I assume this is right...

My question is with relation to the timing curve. At what point do you want the total timing advance to come in? I recently read an article in Car Craft that implys that timing advance should be fully in before the motor reaches peak torque. Do you guys have any thoughts on this? How fast should timing come in? I know this will change based on the car weight and available torque, etc, but for a performance/race motor in a mid size car like a classic mustang, what is a good rule of thumb?

Right now, I have a tad too much total timing in my car for the current tune. I get some pinging under WOT when it is hot and it is only slightly noticeable when it is cool in the mornings, so I know it is just a degree or maybe two high on the total. I still need to take the jets down one on the secondaries because I am at 12.0-12.5 AFR and should be at 12.5-13 for optimum power. My next step is working on the timing curve and when it should come in.

As always, thanks for the education.

 

1 degree retarted is better than 1 degree advanced. So i'd say the first thing to do is to retared 1-2 degrees when you can hear pinging (no matter what condition).
I usually disconnect the vacuum advance completely, start revving the engine quicker and quicker and see where the mechanical advance stops. in my distributor that is at around 3200rpm (no restriction in place). I then turn the distributor at that rev to get 34 degrees.
This gives me a max of 34 at 3200 at WOT.
then I go back to idle and hopefully it will be around 12 degrees for my engine. if not i start messing with the mechanical advance.
If I have that I plug the vacuum advance to manifold vacuum at carb.
Turn curb idle screw to idle rpm, quickly set mixture.
The idle is usually at 20+ degrees than with that vaccum fully in. I then adjust the vacuum advance toi give me 12 degrees max. So I end up at 24 degrees initial.
it's a lot but as soon as you put the foot anywhere near throttle it drops instantly.
hard start is not an issue as the vacuum is not fully there during start.

now to the question on when the mechanical advance should actually kick in. I believe it should gradually increase from idle to 3200max. but sometimes I get driveability issues when it kicks in before 1200 (light springs). I messed around with it a lot, but I'm best off with the pertronix factory preset

ince that's all done I doublecheck the idle mixture and that's my timing done.

I'm not saying this is how it's done, but I thought I throw it in for discussion :-)

PS: I ordered the plug reader and DVD that 67m302 mentioned and I'm full of hope for a steep learning curve as far as ignition timing goes

Kalli

 

I should have mentioned that I am running a MSD mechanical advance only dizzy. I have changed the timing stop and spring from stock. Currently the total timing advance is about 24* (silver stop) and totally comes in by 3300 rpm (2 blue light springs). The stock config was 21 total advance (blue stop) by 4000rpm (2 silver heavy springs).

 

wow. wonder how it is too drive without vacuum advance. doesn't sound like a good idea on a car that sees street more than track.
24 on advance with 12 initial is 36. If you want to keep the 12 initial i'd make sure to end up with less advance at 3300. Any chance of castrating the advance by two degrees but end at 3300 as well ?
maybe just retard the initial by 2 degrees and you'll be golden up top ?
when does it actually start to kick in? at idle, at 1000, at 1200 ... ?

and just for the fun of it, can you take a good pic of spark plug ? maybe someone capable of reading them might join the discussion

kalli

 

I am idling at 900-1000. According to the MSD timing chart, not much advance is added below 1400. Best guess, my peak torque is between 4000-4500rpm.

According to what I have read, putting full timing in too early can generate too much cylinder pressure which will actually fight the engine, even if detonation is not an issue. Too little timing will cause the fuel to not be burned efficiently.

I guess my main question is philosophically, when should total timing be achieved with respect to the torque curve of the cam, intake, and heads? Do you want total timing 100rpm before peak torque, 500rpm, 1000, or maybe after peak torque??? If you have a delayed peak torque due to a single plane intake and a large duration cam, I would think you would need a longer more delayed timing curve.

 

that's a good question. only thing I ever hear is max at 3200-ish

I always thought that from tehre everything goes so quick that you don't want to advance any further. it's not scientific, just a thought :-]

 

I believe you, but why would the stock MSD curve and stop setup put total timing at 4000 if 3300 was normal for most applications...

This is why the title of this thread includes Philosophy...I believe that 3300 is about right for most stock stuff but what is the theory behind that and what do you do when you do not have a stock application?

It is so strange that MSD puts a slow timing curve in stock. For many stock applications, the motor might never see full timing under regular operating conditions.

Edit: Several articles on the web talk about dyno tuning the timing where you can set an rpm and then adjust the timing until torque is maxed. You do this in small increments or rpm and then pick a curve that matches as close as you can. I guess that will work, but I had hoped to have the AFR tuning and timing pretty dang close before I headed to the dyno.

 

It totally depends on the build and what it's used for. The more cam the more aggressive the curve, better heads, better detonation resistance, lighter car with more gear all tolerate more timing.

Ultimately though you need to check plugs for total timing. Get the fuel right, and do WOT runs, shut down at the end of the run and pull plugs. The ground strap should show color change on it, ideal timing has the color change at the apex of the strap, closer to the plug body is too much timing, closer to the ground strap end is too little timing. Curve is based on a mess of variables, but once total is correct, give it as much curve as it will tolerate that gives the best performance.

 

sounds sooo simple :-)

 

LOL, yeah.

Everything does until you start doing it I suppose.