2.4 T, E, and S: same advance curve?

[Plays with cars]

I am in the process of building a motor but don't have a distributor for it so I need to either find the right one, recurve the 2.7 distributor I have, or go to a crankfired system (leaning toward MegaJolt Jr because I can't justify new Electromotive cost and haven't found a used one at a low enough price). In a nutshell the motor will be a 2.4E w/ 2.2S pistons, sightly advance cam timing, and MFI to be used in a 914-6.

So, I've been doing my research on advance curves to see how far off the 2.7 curve would be for the 'E' cam and higher compression that I will be running. But I've managed to confuse myself.

In this chart it appears that the 'E' and the 'S' have the same profile, but the 'E' starts advancing sooner and has more mechanical advance.



But then I saw this chart and interpretted it to say the 'T' and 'S' have the same curve, but the 'E' was unique. That the 'E' starts advancing later and has less overall mechanical advance. (kind of backwards from the first chart)



This got me scratching my head; didn't really make sense. So I started thinking maybe they all are the same and the two curves represent the boundaries of acceptable variation. i.e. + 6 degrees? But this seems like a pretty wide range.

Then this chart kind of confirmed that since it is for a single engine variant but still indicates a range.



So, am I right? The 'T','E', and 'S' distributor curves are the same? Whether I re-curve a distributor or build a DIS system I need to figure this out. Any sage advice you can provide would be appreciated.

[Steve@Rennsport]

Mark,

JMHO, but the distributor you use should be curved to the configuration of YOUR engine and the local octanes.

I would not use a DIS on an MFI engine: a good distributor and MSD system runs FAR better.

[Plays with cars]

Yes, ultimately that will be the answer but I'm trying to figure out a reasonable starting point and/or strategy. If the 2.7 distributor is close, I can use that to get the motor started and use it as the basis to build the final distributor.

Curious about your comment on using a DIS system on an MFI engine. What about MFI makes it sensitive to the ignition type? Certainly the advance curve can be tuned to be the same regardless of whether I use a distributor or go distributorless. Everything I've read indicates that a DIS system gives a long spark duration, similar to what MSD is achieving by firing multiple sparks below 3,000 rpm. The supposed advantage of DIS is that it continues to give a hot/long spark above 3,000 because of the extended dwell time enabled by using multiple coils.

Besides the long duration vs multiple spark strategies, the other difference is that the DIS systems typically fire the plug on the compression as well as the exhaust stroke. Not sure what impact this could have on the induction system.

[BURN-BROS]

[QUOTE=Plays with cars;4907771]

But then I saw this chart and interpretted it to say the 'T' and 'S' have the same curve, but the 'E' was unique. That the 'E' starts advancing later and has less overall mechanical advance. (kind of backwards from the first chart)


QUOTE]

The curves are the same. The model designations that you see on the chart refers to the rev limiting rotor for each model. The two lines are the acceptable range of deviation.

[Plays with cars]

Excellent! Makes finding the "right" (interpret as starting point) distributor much easier.

[Sigurd]

I recurved my ignition with a MSD-6AL-2.

My problem was that the actual curve on the distributor I had available did not suit the engine, it advanced to early. My solution was to first install a MSD-6AL-2 ignition, advance the distributor to much, and then retarded the timing with the MSD unit. With the help of a timing light and an old PC with a RS 232 serial port I was able to get the curve back to spec.