AFCII+660cc inj= too much timing advance?

[project_tsi]

try lowering presure to 35 and then doing a log. If knocking, add more fuel in. Ecu should not advance timing so much if u do that. If it still advances that much, then look for a boost leak. There might be one. when was the last time u did a leak test?

I last did a leak test last week, when I installed my FMIC and piping. I came up with none. is it possible that my base timing ~3-~5 is off? If it were off the mark, would that couse it to be high like it is?

 

[Staytuned]

so do you always drive with your boost up there? I would imagine you run around 17-19psi to get that airflow. I dont' like boosting that high all the time, so tuning down to 12psi would be a problem you think? Or low boost and high timing work fine?

I run 22 psi all day every day. I have over 6000 kms at this boost level and literally 50 or more logs. Low boost and high timing would only be a problem if it caused knock. I just see no reason to turn down my boost.

 

[Forces32psi]

so i have kind of a retarded question.. i have a 90 tsi /w a 255hp, rewire, 850 fic ball and disk inj, tmo and keydiver stage 3 eproms, and the hks 550 chip in my vpc and the eproms were burnt for the 850 compensation, w/ a afc2. i have a spoolin up afpr. which way do i turn the screw on it to add or take away fuel?? and what should i set the presure at ?? my guage is on the fuel filter. and when people say "base" fuel presure is that set w/ the car idling? and dont you have to disconnect a vacume line or 2 while doing this?? thanx steven

 

[Newlogics]

so i have kind of a retarded question.. i have a 90 tsi /w a 255hp, rewire, 850 fic ball and disk inj, tmo and keydiver stage 3 eproms, and the hks 550 chip in my vpc and the eproms were burnt for the 850 compensation, w/ a afc2. i have a spoolin up afpr. which way do i turn the screw on it to add or take away fuel?? and what should i set the presure at ?? my guage is on the fuel filter. and when people say "base" fuel presure is that set w/ the car idling? and dont you have to disconnect a vacume line or 2 while doing this?? thanx steven

Turning the screw in will raise the fuel pressure on most AFPRs. You have to disconnect vacuum line off the regulator and then set the base pressure.

 

[desolateboosted]

People people, turning down the base fuel pressure will defeat the purpose of running larger injectors. That is just band-aiding the problem. You are making the injector act as a smaller one. Get something that can tune the timing curve (dsmlink), a burned eprom chip or standalone.

 

[GPTourer]

I have Denso 660s, Super AFCII, Aeromotive AFPR set at like 41.5, and a rewired Extreme Motorsports high press FP which I guess is equivalent to a Walbro HP 255 and a stock ecu.

Because of my 34mm flapper I only see about 16psi at redline and my timing is ~14 on 93 octane. Right now. I'm thinking this is about right, but once I upgrade my turbo we'll see how my timing looks.

 

[Forces32psi]

Turning the screw in will raise the fuel pressure on most AFPRs. You have to disconnect vacuum line off the regulator and then set the base pressure.

so i can unhook the vacume line from afpr and then just turn the screw and watch my fuel presure guage at idle on my fuel filter?? is there any particular psi its "suppose" to be set at?? and if so what?? and if not then what should i set it at?? thanx

 

[project_tsi]

so i can unhook the vacume line from afpr and then just turn the screw and watch my fuel presure guage at idle on my fuel filter?? is there any particular psi its "suppose" to be set at?? and if so what?? and if not then what should i set it at?? thanx

IF you spent 5 minutes, and read this entire thread, you would easily find that base pres. for a 1G is 38psi, and 43psi for a 2G

 

[Forces32psi]

IF you spent 5 minutes, and read this entire thread, you would easily find that base pres. for a 1G is 38psi, and 43psi for a 2G

i SPENT 5 min reading this entire thread, and i know what the base presure is.. IF you would spend 5 seconds and read my posts w/ my current mods then you would know why i asked the question in my last post... and if you forgot im asking IF i should try and set the base presure OR set the presure at something else because of my fuel pump, injectors etc. BASE presure is 38 psi w/ 450cc inj, and a stock fuel pump and fpr. i have a 255hp, 850's and a spoolin up afpr.

 

[Newlogics]

i SPENT 5 min reading this entire thread, and i know what the base presure is.. IF you would spend 5 seconds and read my posts w/ my current mods then you would know why i asked the question in my last post... and if you forgot im asking IF i should try and set the base presure OR set the presure at something else because of my fuel pump, injectors etc. BASE presure is 38 psi w/ 450cc inj, and a stock fuel pump and fpr. i have a 255hp, 850's and a spoolin up afpr.

I just read your profile, and it looks like you have one serious setup. No pun intented, but how where you able to choose all those components without extensive tuning knowledge? (much less put 'em together and make them work)

 

[Forces32psi]

I just read your profile, and it looks like you have one serious setup. No pun intented, but how where you able to choose all those components without extensive tuning knowledge? (much less put 'em together and make them work)

anyone can put parts together nowadays.. ive had 4 dsm's but never anything that had the mods or make NEAR the power that i have put into this car. i bought this car w/ that spoolin up afpr regulator on it and i have just never messed w/ it, ive tried to find directions for it online but cant really seem to find anything (maybe thats just my own ignorance). and ive been around cars all my life and im 30 now and when you read as much as i have (when you can find the info) you just learn it all i guess??. the afpr is about the only part i havent played w/ yet. i have yet to run the car all out balls to the wall or to its max yet, so thats probably another reason i havent tinkerd w/ it .. and now that you mention my profile, that was the old setup, i just updated it. so would i be ok setting the fpr at 38 psi, at idle w/ the guage on the fuel filter, w/ the vacume hose off??? and thanx for the help Newlogics............ steven

 

[Kevin Jewer]

The key to getting normal timing with an AFC type device and large injectors is moving a lot of air. Believe it or not, the more air you flow the better off you are. As you raise boost and airflow timing will naturally come down until you reach the highest load map in the ECU. Unfortunately many people interperet this drop in timing as knock and stop short of thier setup's full potential. I'll try to pass on some info on how this works.

With a 2g ECU the highest load map is used when you get over 2.1 g/rev airflow. Timing will reach 10 degrees by 5k rpm, and will peak at 16-17 degrees at 7000 rpm. Intake temps above 84 degrees F or below 34 degrees will cost you one degree of timing. Coolant temps over 206 degrees will cost you 1 degree, and over 226 or so will cost you 2 degrees. Armed with this information, you can see why getting onto this high load map would be advantageous. Anywhere below 2.1 g/rev there is no way to know what target timing is without using DSMlink. But at anything over 2.1 it remains the same and you know what the ECU is shooting for. Anything less is obviously due to knock.

The 2.1 g/rev figure is taken at the ECU, or what you see in the logger. The AFC will cut down this value according to the correction you have entered in the AFC for injector compensation and then target AFR. So more negative the number, the more air you need to flow to get over 2.1 g/rev, and the higher target timing is going to be. The timing that you get in this way is the number one source of knock, and is the problem 90% of the time when people say "I get tons of knock even at such low boost!" It gets worse at lower boost, since airflow is less.

To see where you are at with airflow, use the logger and do a little math. 1Gs guys are screwed without DSMlink, I am not aware of any logger that can display airflow besides DSMlink, but this hardly matters since knock is available. But any 2g logger should be able to display airflow as part of the OBD2 setup, the pocket logger shows it in lbs/minute, which is my favorite unit. But to get to the units that the ECU uses you have to convert that lb value to grams, then divide by rpm (grams per rev). You can see that if airflow remains constant, airflow/rev is still going to drop with rpm. Luckily airflow is usually rising to redline helping to keep airflow/rev relatively level. The problem obviously is that as airflow/rev drops with increased rpm, timing will be going up accordingly. Typically at higher RPM you can get away with a little more advance since piston speed is higher and cylinder pressure is lower (drop in VE). But it's not always desireable.

Some examples. If you are logging 25 lbs/min at 6k rpm, you are getting 1.89 g/rev. Timing will be over the 16-17 degree figure by some amount since you are below 2.1 g/rev. More timing equals higher tendancy to knock. But, if airflow was 30 lbs/min at 6k rpm, airflow/rev would be 2.27 g/rev, and timing would be predictable, allowing you to spot knock easily.

The problem with large injectors and an AFC is that airflow at the ECU will be lower than what it actually is at the motor. Lets assume you are running 650s and are going another 10% leaner to get closer to ~11:1 target AFR. Thats a -41% correction. You would actually need 50 lbs/min through the sensor in order to read 30 lbs/min at the ECU. (30 divided by 1- .41) You can see where this is going. With 550s, you would only need ~42 lbs/min to get 30 at the ECU. The larger the injector, the more timing you are going to get, because of the lower airflow.

This helps to explain why people with large setups can still run very fast on an afc and large injectors, while the regular guy with a 16g struggles with knock.

The key to making a setup like this work is to know what target timing is, which then allows you to see how much timing has been pulled due to knock. And that is hard to do at less than 2.1 g/rev since we don't have access to what timing is on each load level below 2.1. I have the maps, but not the corresponding airflow values.

This all applies to 2g ECUs of course. The figures given here will not be correct for a 1g ECU. Target timing is a little higher, and I don't know what airflow value corresponds to the highest load map.

If nothing else, this post should provide some insight to the true value of having a system like DSMlink instead. It really is worth every penny, I won't run a car without it. But with some knowledge of how the ECU works and what effect your tuning devices have on that ECU, you can do some more "educated" tuning that simply watching for timing to drop. This really is a vast topic, and this post barely scratches the surface, but I hope people find it helpful.

 

[kazzam]

wow, you explained it really well! Good job!
So tunning with an afc and 650 injectors for 14-16lb will be a headache. Tuning for over 20 psi is actualy simpler.
Getting 550 and tunning for low psi is easier then tuning with 650s for the same psi because of the signal modification that afc sends to the ecu. 2.1g/rev is the target airflow reading for the ecu to see so timing could be predictable.

in that case, since i don't plan on boosting anything over 18-19psi on 93 oct. Would 550cc injectors be enough for that with a 50 trim and hks 272 cams and all other supporting mods? WOuld that put me over 2.1g/rev?
Thank you.

PS: that write up is magical

 

[Newlogics]

People people, turning down the base fuel pressure will defeat the purpose of running larger injectors. That is just band-aiding the problem. You are making the injector act as a smaller one. Get something that can tune the timing curve (dsmlink), a burned eprom chip or standalone.

Running larger injectors at lower pressure isn't always a bad thing. In a lot of cases that we deal with here, people get big injectors with future upgrades in mind, but untill they have the setup to take full advantage of large injectors, those injectors need to be run at less then full capacity, and using fuel pressure is a great way to do it, as it allows you to somewhat retain decent timing map.

 

[Kevin Jewer]

in that case, since i don't plan on boosting anything over 18-19psi on 93 oct. Would 550cc injectors be enough for that with a 50 trim and hks 272 cams and all other supporting mods? WOuld that put me over 2.1g/rev?
Thank you.

550s at 43 psi, target AFR of 11:1, and pump gas (assuming a Specific Gravity of .76) will support 40 lbs/min airflow. A well setup 2 liter (50 trim and cams would qualify, assuming the basics like intake and exhaust) will move 40 lbs/min at 20 psi, so you would be just below that. A little close though. Assuming you are moving that 40 lbs/min and you have a correction factor of -28%, you'll peak at 28.8 lbs/min at the ECU. That would allow you to remain above 2.1 g/rev up to ~7600 rpm. Depending on the shape of the airflow curve it would be safe to assume that you would be over 2.1 for most of the time, or damn near it.

The only problem I have with tuning like this is that I like to size the fuel system acording to the maximum airflow the turbo is capable of. 650s fall just shy of a 50 trims capacity assuming the same variables as above at 47.8 lbs/min. The reason I like to do this is to provide some protection against the event that you lose control of boost. The ECU will maintain your target AFR no matter how high AFR goes, so there is a good measure of safety in this regard. If the fuel system is too small however, AFR will go leaner in proportion to the increase in airflow, and the results usually aren't good. BUT, that being said, assuming you are going to keep an eye on airflow and keep it below the injectors limitations, it would make it easier to maintain decent timing advance values.

As for using larger injectors and turning down FP, lets look at some numbers, as I've never looked into this before. 650s at 31 psi base pressure will act like 552s. The question becomes will the injectors still atomize fuel well at that pressure (I honestly have no idea, nor the means to find out), and what will you need to do with your global adjustments to compensate and allow trims to remain functional in closed loop. You would simply use correction values on the low table (Assuming AFC, you would use base or similar with a MAFt) for the adjusted injector size I guess. In this case I'm getting 18.5% for a 2g ECU, which makes sense. So thankfully base pressure has a pretty good sized effect on injector flow, so you can drag it down without having to go too far on pressure. I'm still a big fan of leaving base pressure at what the ECU expects, but when tuning with piggy back devices I guess you have to make some sacrifices, and they should be worth it.

 

[kazzam]

while i have an ecu expert at hand, i want to ask you how does the ecu calculate fuel cut.
You say that the ecu will run off the last timing map which is anything over 2.1g/rev of airflow. Does the ecu cut the fuel when it sees over that or is that determined by injector duty? Reason why i am asking is because i still have a stock injectors and no piggyback. How high of boost will make my ecu run at that last timing map? I am sure there is no way to tell exactly, but if you can, please throw some numbers around and enlighten us.
thank you for your help

One more thing, can you post a log of a run that runs at this highest fuel map so we could all see and compare our timing with yours. We could even put it into axcel and get a nice graph.
This would prabably be helpful to a lot of people on here. Again, i appreciate your help. thank a bunch!!

 

[Kevin Jewer]

I am no expert by any means! I still have a lot to learn.

Fuel cut is something I neglected to mention because I haven't dealt with it in so long... It is deterimined based on airflow, not IDC. I don't know if its airflow per time or airflow per rev or Hz alone, and I don't know what that value is. That would be important to know, since many poeple are running larger injectors and AFCs to also push off fuel cut. The more I think about it, the more I hate tuning with piggy backs I'll see if I can get that number...

On my website there are some logs of mine you can review if you have DSMlink installed (it can be downloaded by anyone). The logs on my 2g for sale page would probably have stock timing curves. Otherwise I will try to put something together when I get some time (at work now). But basically it reaches 10 degrees at 5k rpm and 17 degrees at 7000 or so.

To know if you are on that high load map you need to convert your airflow per minute (assuming 2g here, 1g loggers don't display airflow AFAIK) to grams, then divide by RPM to get airflow per rev in grams. If its over 2.1 at that rpm, you're on that last load map. Its very common for airflow to drop off over 6k rpm or so, so expect to fall off that map as rpm goes up if you are barely on it. One could easily come up with a spreadsheet to do this math for you and plot the curve, especially if you have a sweet logger that can output to excel.