We all know that spark timing will effect performance and economy, but is there a noticeable correlation to timing and the amount of air the motor injests? If I were to retard my timing -10* would I see a diffrerence?

Tuning for mileage or power is easy enough in areas of the table I typically drive in, but hitting the far ends isn't always practical putting around town. Eventually what I'd like to do is use a combination of inputs like egt's, recorded knock occurrences, estimated mpg and torq and other things to get a working spark estimate to make building spark tables easier.

 

Timing is most correlated with cylinder fill density (and internal EGR), and engine speed - those both affect the burn rate (actual cause for timing requirements). It's not possible to make a good correlation just to air flow, when using degree based 'timing'.

 

It would be nice to find a definitive way to nail down timing without a dynamometer and everything the oe's have. Got any suggestions for me?

 

It's not easy without an engine dyno to get dead nuts on.

Maybe in a few years, I'll make an aftermarket capable ion-sensing peak pressure detection monitor that will sync with a crank wheel for the position, and output a signal to an ECU, with a knock flag signal too.

 

I bet they would sell like hot cakes. I'd buy one of the price were right.

 

It would only work on a coil per cylinder basis though... Never would work for a distributor.

 

Timing does, to a small extent, impact the VE of the engine, and hence the airflow, but its small, and doesnt really give an indication of whether the engine has the right ammount of timing. The timing could optimize power and VE, but cause detonation.

I have it easy. Low 9.1:1 compression motor with fast burn heads. Too little timing, and the engine doesnt make good power, too much timing and the pressure in the cylinder rises too quickly on the compression stroke, causing the engine to buzz. Teh difference between the two is only a few degrees or so, which gives a fairly small window for the timing to be in. If you push it it'll go into detonation, but not before it starts to run rough.

 

Yea, I'm only at 9.35 so tuning is pretty easy. Everyone I talked to kept pushing me to bump it into the 11-12 cr region while it's n/a but why would I when I can make the power I want without a tweaky engine? I can run 85 octane and still get 30 mpg on the highway if I want to. Technology is great.

Ranting... anyway RednGold I'm running DIS do you think your 'ion-sensing peak pressure detection monitor' would work for me? I'm writing some of my own code now so I think I could do the work on my end to make the computer ignore the waste spark.

 

To return to the original topic, which areas are you having trouble hitting in the timing tables? I assume that your using the LV8, and the low RPM, high LV8 values are hard (or impossible) to hit with the 7000-R4? I wouldnt really sweat them too much as you cant really get there anyway, except maybe during a stall condition when the engine recovers. LV8 is sort of like cylinder airmass in that, IIRC, its more of an indication of the airmass load of each cylinder rather than like MAP. While its easy getting to 100 kPa at 400-600 RPM with a stick. I probably couldnt get to the high LV8 values as the actual airmass in each cylinder is still relatively small due to the low VE there. With this type of system, there will always be areas that you cant access.

The later PCMs use cylinder airmass, and this is one of the reasons I dont like it. With MAP, the entire table is accessable for tuning, and is much more intuative. With cylinder airmass, there are large sections of the table that you will never have access to due to the fact that its impossible for the engine to get to them.

 

Actually I rewrote 6E for a 3bar tta map, along withsome other stuff to make it more FI friendly. The auto does make hitting the far ends of the table a little annoying, especially when the track is closed for winter. Although it's not turbo'd yet, it will make things more complex once it's done.