Just double checking. I'm tuning my SAFC-II right now, and i just want to make sure that if i dont tune it right on, or if i do, but timing isnt correct, the Stock ECU will pull timing before detonation to save the engine correct? The stock ECU will never allow a knock?

 

This is a kind of backwards assertion

The way it works is the car knocks and then the ecu pulls the timing

Ideally with proper tuning knock is minimized if not eliminated

Each knock event results in mechanical and thermal stress on the engine's parts

 

Okay, but with the SAFC-II, it doesnt control timing, but if i keep my wideband reading around 10.5:1 on 92 octane, with just the bolt-ons that i have, it wont throw timing off really will it?

 

No, your timing will be the same as stock, and you won't make much power, because 10.5 is nasty rich. You should try for 11.3-11.5 while watching your timing to ensure that it still climbs to 19-20* by 7k rpm. Unfortunately, with the S-AFC, you will see a big dip in timing to nearly 0 when you hit peak torque. This is unavoidable without a tuning device that can manually control timing unless you get upgraded injectors. This is not a very good solution, though.

 

You're right that 10.5 is very rich and you can lean it out to low 11's on pump in MOST cases without any harm done.

However, you are incorrect about the S-AFC's affect on ignition timing. While you can only adjust fueling directly with the S-AFC, by changing what the ECU sees for airflow, you place the ecu in different cells in it's maps which prescribe different than stock ignition timing.

For instance, if you have negative correction in the S-AFC the ECU thinks you're flowing less air, hence less load, and it advances ignition timing. I'll explain. Cars often run 38-48 degrees of timing while cruising (light airflow/load) and lets say 10-25 under high airflow/load. In each instant the ECU chooses an ignition timing value based on the current airflow reading (among other things). Any time you adjust airflow readings you adjust the result ignition timing indirectly.

Negative correction will result in less perceived airflow/load and more ignition advance than the car would have run stock. When combined with leaning the car out, this can be dangerous.

The ECU pulls back ignition timing for a period of time AFTER it senses knock, not before, so damage has already been done at this point. While it may be small, continued knocking once in a while can lead to engine failure. Make sure you know what you're changing and the result it will cause before you make changes.

-Mike

 

I'm not sure which part was incorrect. You didn't correct anything I said. With an S-AFC, you have to either leave the settings at 0 or add fuel in the peak torque range, because the factory tune is very lean (over 12.0:1). If you add fuel, it causes a less aggressive timing map to be used, which can cause dips to 0*. This is common knowledge to begin with, but I have witnessed it myself on every log I've ever made while tuning my S-AFC on pump gas. I eventually got a flash so that I could get the mid-range AFRs down to 11.5 without adding fuel on my S-AFC while also setting the timing to 8* at peak torque. This provided MUCH more low-end grunt and smoother mid-range, because my timing never goes below 8, stays flatter, and then increases perfectly on the top end. Before, with just the S-AFC, i was able to get good top-end power, but my peak torque was 20-30ft-lbs low, thus my 294whp/269wtq rating...

 

Also, beware that stock map will switch to limp mode when the engine or air gets too hot. timing difference can be as large as 4 degrees! It is better to leave the mid range (3k~5k) alone. You can't do much with S-AFC unless you have big injectors. walbro fuel pump will help to raise bit more timing.

 

Any % correction positive or negative that you make with the S-AFC changes the result ignition timing for the reason I explained above. It will not "be the same as stock."

-Mike

 

OKay, but with an exhaust, hi-flow cat, downpipe, intake filter, and Manual boost controler, if professionally tuned, they can give you the correct setting to use. Then you basiaclly never change it correct? Unless you get some bad gas and the EGT is higher than 900, if in that case, just illiminate some boost and that will solve the high EGT and prevent knock...correct?

 

If the tune is good to begin with, has the proper margin of safety built in, you don't change parts, adjust the unit or boost levels etc., and you keep up with maintenance you should be in good shape. That said, some systems can account for certain parts changes, and some can't. For instance, speed density based systems can't account for changes in airflow at the same pressure level unless they're running o2 feedback or do it indirectly through EGT trimming etc.

Remeber that maintenance intervals on certain things shorten when you mod a car. As an example, spark plugs gap out quicker when you bump up the boost. Ask your tuner what changes you should make from the manufacturer's recommended maintenance schedule based on your mods, usage, and state of tune.

Some tuners offer check-ups for free or at a reduced cost once in a while. Even if you don't change any parts on the car this isn't a bad idea for peace of mind if nothing else.

On an unrelated note. Bad gas and high EGTs don't necessarily go together.

-Mike

edit: I just noticed something in your post. You mentioned an MBC. The amount of boost a car makes with an MBC is affected by temperature change. Keep an eye on your boost level as the seasons change and make sure it doesn't go too high as it gets colder. On the stock setup the ECU adjusts for this as it tries to hit it's boost target, but the MBC will not. You need to make the adjustment manually.

 

Well Mike, lets say that i dont want peak power...i just want the car to be super reliable, daily driver, with the mods that i have, put down about 275 to the wheels...i can tune to 10.5:1, and that will reasure i never knock right?

 

Since your car almost makes 275whp stock, then you shouldn't even waste your time with the S-AFC. There's no reason to tune to 10.5:1, because that's not tuning at all. I'm not sure why you're so worried about the car running properly and are preferring to stay rich. If you don't want to change your tune and want it to be better than stock, but still completely safe, then just get a flash. It will give more power than the S-AFC along with other nice features and won't require an extra device that you keep track of. The S-AFC is for self-tuning, not for having a shop tune it.

 

Hmm, you missed the point. I wasn't inferring that timing maps weren't going to change. I was referring to the basic timing curve that you see when stock will be the same as when tuned if tuned properly. When I was stock, I ran off the charts rich down to AFRs in the 9s, but my timing advanced nicely to a peak of 19-20*. I then tuned it with an S-AFC, got the AFRs into the mid-11s, and _still_ had a very nice timing curve that peaked at 19-20* at 7k just like before. It wasn't like this right away, but after adjusting the settings and getting the tune right, I made good, linear power that had a great timing curve. The only downside was the loss of timing in the mid-range where I hit peak torque, because the addition of fuel to make a safer AFR was causing the ECU to use a less aggressive timing map at that point in the powerband.

 

You'll find that good tuners never like to say never...unless they're saying never wail on the car cold, never boost to 40 psi on pump gas, etc.

Running 10.5:1 is super conservative, but knock can be caused when a spark plug fouls out, when you get a vacuum leak, a bad tank of gas, etc. so it's not a gaurantee.

If you want to be conservative, tune to low 11's AFR on pump gas at full boost and tune the boost level so your EGTs are where you want them. If the car stumbles under acceleration, or your boost or EGTs get too high, look for mechanical issues first, and make tuning adjustments if necessary.

-mike

 

Ok so you're saying the shape of the curve won't change. That would be the case if your correction on the s-afc is the same at all RPM points. The curve will simply move up or down intact.

This contradicts your statement on timing curve not changing. You now have a mid-range dip in your timing curve that deviates from stock.

You seem to understand how this works and I don't mean to argue with you. I'm trying to help here. I don't want anyone to be confused about how this works, including yourself. If I'm not explaining myself clearly let me know and I'll give it another shot.

-Mike