[JMG9350]

This is my first post, I'm not new to Foxbody Mustangs but I am new to tuning and modifying the EEC-IV system. I'm also experienced in automotive and equipment repairs so most terminology and diagnostics are not foreign.

I'm running QH and BE, and Clint has answered several questions through emails for me already. Here are my questions:


Is there any benefit to adjusting the timing curve on a stock engine?

Everyone talks about the "10 minute tune-up" and then mechanically advance the distributor to 12-14° essentially tricking the computer to advance more on the top end.

So, leaving the base timing at 10° BTDC but changing the timing curve in the computer to get 29-31° at high rpm like advancing the base time would potentially be beneficial.

Am I wrong on this or is it a sound theory?

[cgrey8]

When you twist the dizzy from 10 to 14, you adjust all running conditions by that same 4 degree advance adjustment.

The benefit of making this adjustment in the tune is that you can keep some conditions at stock values, while making other areas of the tune more aggressive. The tune offers far more granularity than a simple dizzy-twist. For example, you can limit the advance to only WOT conditions. Or you could do far more useful stuff like adding advance to specific conditions as long as the ECT (and/or ACT) temps aren't too high. Since the stock tune was intended for 87 octane, there are some gains to be had if you plan to pump a higher octane into the tank, even if the engine is bone-stock. But there are still some running conditions that don't benefit from the higher octane, and thus the stock advance values are still best (e.g. cold startup).

So yeah the tricks of yesteryear that were popular were only popular when people didn't have access to make the changes in the tune. Since you can, a lot of those tricks don't apply, or don't fully apply.

Another example of this kind of thing is having to buy "matched" MAFs when upgrading the injectors. When you have access to the tune, they no longer have to be "matched." With access to the tune, you just enter the actual parameters of your upgraded MAF and injectors (e.g. MAF curve, injector slope/bp/offset pars). The only thing that's important about the components, themselves, is that the components are capable of satisfying the worst-case demand of the engine AND that you know what the parameters are.

[JMG9350]

Would there be any benefit to advance the WOT timing a bit further at the top end? Let's say add 1° at 2600 RPM, 2° at 3500 RPM, and 3° at 5000 RPM (to get 29° total) and leave all the timing at lower RPM alone. I would also leave all the other spark tables alone.

[cgrey8]

If you are going to run higher octane, then yes. And it's not just WOT areas that might benefit. Some of the cruising RPM/Loads might get better fuel economy with slightly higher numbers. Note I said "might" not "will."

But the point is with access to the tune, you can experiment. One of the 1st things I started experimenting with was EGR. Since I maintained the EGR on my engine when I did the swap, I was curious as to just how beneficial it is to cruising fuel economy. It had some benefit, but not a lot. It was still worth the time to tinker with it though.

[tvrfan]

Just something to add... In the 'old days', ignition tuning options were pretty much down to -
A) filing down/welding dizzy stop to get more/less advance at high rpm, or getting center assembly from different model.
B) changing dizzy springs to change advance curve
C) changing/disabling vacuum advance (and retard in some cases, e.g. superchargers)
D) changing dizzy position to give static change for entire ign curve.

I did this kind of stuff in UK, where a lot of models had same dizzy made by Lucas, and bits were highly interchangeable - I guess similar in US, but maybe not as much ??

Of course these old methods all still had drawbacks - new springs gave a different overall curve, which was still unable to compensate properly for all conditions. In effect they had only rpm and [some] throttle input (via manifold pressure) to work with.

Fantastic thing about computer ignition control is that it's a multi-dimension 'calculation' which can use lots of things - e.g. throttle position, air flow (or manifold pressure), rpm, atmo pressure, block temp, air temp, and also rate of change of - throttle, flow, rpm, and a stack of other stuff too. Plus there is no restriction on what shape the 'curve' is, it doesn't have to be smooth, and can go forward/backward anywhere, which an old mechanical dizzy can never, ever do.

Similar story for fuel, and fuel ratio can be changed *instantly* per individual cylinder per firing stroke..... by comparison a carb is very, very crude indeed and works only on airflow through it.