Timing thread

[Dom]

I've been trying to understand the timing tables. This is what I got so far and if you have any input of your own, that would help greatly.

Since my main concern was WOT, I just took my WOT MAF airflow readings which are in lb/min and converted them to grams/cylinder so I can see exactly which colums on the table I'm using.

They were mostly between 19-23. And during the 1/4 I'm also between 4200 and 6000RPM the whole time. So there is the values I need to convert to get my ranges of timing values I'm using.

19lb/min and 4200RPM = .69g/cyl
19lb/min and 6000RPM = .48g/cyl

23lb/min and 4200RPM = .83g/cyl
23lb/min and 6000RPM = .58g/cyl

So table that is used on my 1/4 mile run is from 4200 to 6000 and from .48 to .83.

This is just something I thought of doing so I don't have to mess with the whole table and it makes it easier to fix values if I get any KR. I'll know exactly which cell caused it.

On top of this table there is this IAT correction table. According to it we're pretty much in the 0 cells most of the time. Between 32 and 122. I don't think we need to mess with it.

Same for ECT.

Any other tables that can affect timing?

For the track I'm thinking of bringing in the laptop and copying my high octane table to low octane table just so I can control the timing. I'll of course monitor KR after every run.


Any thoughts on optimal timings for 3.8s? Should I go progressively higher as RPM increase?

[guardsman01]

I wouldn't replace your low octane table, I'm keeping mine stock as a back-up, so the PCM can still fall back to that if I over do it with the timing.

Wwhat you're talking about with increasing the timing at higher airflow rates makes sense.....

The only issue right now is that we can only control WOT (PE) fuel, so if you aren't in PE where you advanced the timing, you're still stuck with the increased timing, but aren't getting the extra fuel.....So, I'd watch that carefully.

So far, I've been able to increase the timing by 2 degrees at higher RPM/Airflow rates without any problem.

But, I still have the stock timing at low RPM.

One thing I found is that where the stock timing is negative (-10, etc.), it won't save as anything else below zero, so it defaults to 0 if you try to put any negative value besides the stock one.

With the timing in those areas at zero, I was getting tip-in knock, so I put them back to stock.

I'm going to e-mail Keith and let him know about it (they may already be working the issue).

Let us know how it goes. John

[Dom]

I am in PE as soon as I hit 50% throttle. That's what the base table is for. Why do you think adding fuel helps?

I had gotten better results leaning out the car and adding timing till I had no more gains. That's back in the days of MAFT+.

I was going to do the same at the next track test and tune.

First I'll add timing till I see no more gains. Then I'll lean it out and add timing the same way. Repeat till I see no more gains.

Just the way I did things before.

Do you think the process is wrong? Let me know of a better way I'll try both. I'm all about experimenting at the track.

[guardsman01]

Personally, I'd rather go richer, then adjust the timing to use that extra fuel, than the other way around.

The way you're doing it, IMO, you risk leaning the car out too much, and damaging something (burning a hole in a piston or worse).

Being too rich, you just waste gas, being too lean, you start overheating things, and burning stuff up.

I don't know how familiar you are with electronics, but the peak power output of the amp is found by saturating it. As you increase drive, the output power will increase, until it reaches the saturation point, where the power will start to drop off.

You should be able to do a similar thing with the fuel and timing, except that your saturation point will be a result of both your fuel and timing (two input variables instead of one).

Make your PE AFR richer, then add timing until the power starts to drop off, or you run into knock. Using a wideband O2 would make it easier, because then you could watch your AFR that way.

In any case, it's going to take a lot of time to dial it in right. You'll have to set one AFR, try different amounts of timing, then increase or decrease the AFR, try different amounts of timing with that, and so on, until you get the best overall performance.

The thing, though, is that you need to watch your timing very carefully so that you don't end up with a lot of timing in an area where you aren't in PE.

With the Grams/Cyl value, I've been watching mine, and I don't know if it's my scanner, or my car, but it stays right around 65gms/cyl (the dynamic grams/cyl on the table display on the scanner) most of the time (cruising, WOT, etc.). It will occasionally dip to 48, but most of the time, if I'm above idle, it's at 65. So, I'd be really leery of depending on that.

If you could get some dyno time with a wideband O2, I'd say that'd be the best bet to start out, because then you can get a lot better picture of where the car actually is in terms of AFR and the power output at different RPMs, and you could do a couple of changes, and see what kind of effect they have.

The dyno is more controlled conditions, so it would give a decent baseline to work from, and give you a better idea of how the engine and computer react to inputs.

Then, you could do your street and track tuning from there.

John