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  #21  
Unread 08-18-2007, 08:48 AM
lemming's Avatar
lemming lemming is offline
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Join Date: Nov 2005
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Unless somebody comes along who has actually worked with that software, you're going to have to explain a little better--blocks?

What kind of control system is the XFI, anyway? Speed density? Alpha-N*?


*Alpha-N is the crudest form of EFI engine management. Usually only used for race cars, it can be implemented without any air meter at all--it just uses throttle position and RPM to estimate fueling needs. Ford's factory engine control system has an alpha-N fallback table which it uses to assist with transitional fueling, although it's also designed to keep the car running if the MAF gets unplugged of has an electrical problem. You wouldn't want a full alpha-N control system in a street driven car.
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[2003 4.2L V6 Mustang] [1999 Subaru Impreza WTF]
On our way back from the beach, we were trying to decide where to eat dinner. At that moment, we were passed by a Rendezvous with the Ohio license plate "ASK GOD." So we did, and we ended up at some shitty Texas roadhouse-style place. Next time, I pick.--AchTTung

Last edited by lemming : 08-18-2007 at 08:51 AM.
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  #22  
Unread 08-18-2007, 11:47 AM
pontisteve pontisteve is offline
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The FAST systems are speed density. Instead of an airflow meter that actually measures air, they use a MAP sensor that measures manifold vacuum or boost. The computer uses this figure to calculate airflow, and then uses that airflow number to calculate fuel flow. The blocks he's probably referring to are the "transfer function" from the map sensor (in KPA's) to airflow numbers. In other words, how much boost is equal to how much air?

To tune them, I believe you get a load bearing dyno, and put the car at all different loads and throttle positions. Then once a particular position is running consistently, you move the number until the a/f ratio you commanded is right. The good news is that they can tune on the fly, so it's just a question of hitting the up or down arrow keys until the wideband spits out the right number. (Boy do I wish I had that luxury!). This is why it's a favorite among racers. Tuning is easy. There's a separate table for commanding different a/f ratios.

The blocks he's unsure of sound to me like odd blocks where the motor rarely runs. Maybe spots where it's really high rpm, but really light throttle. Who cruises at 7,000 at part throttle? So these blocks become less likely to be ever used. Some never get used. You can view these maps in 3D and hopefully blend the odd blocks into the blocks around it. In other words, smooth the mountain on the 3D map. Make it blend. Get the car on a load bearing dyno if possible. If not, drive the car on deserted roads at lots of different throttle positions and rpms, and adjust the map as necessary on the fly. The nice thing about using a load bearing dyno instead is that you can keep the motor from revving up, so you can tune a heavy throttle position at lower rpms without the motor trying to climb in rpms. Without a dyno, you can only try starting in like 3rd gear at a very low rpm, and a particular throttle position and then hold that TP until the motor is kind of revved out. Datalog that setting, and adjust accordingly. Then do the same thing with a slightly different TP, and again and again until you have many different scenarios of load vs tp vs rpm logged.

I think a load bearing dyno makes short work out of this setup. It would probably be worth it to pay somebody to do it. Maybe get all the rest of the tune exactly how you want it, and then bring it to a pro to tune that KPA table. I believe you'll also find it much easier to tune that if you set most of your commanded a/f ratios to the same number. For example, all WOT type stuff at 11.5:1, and all light throttle stuff at 14.64:1. Then you're not having to go back and see what a/f ratio you commanded. You'll know it's either one or the other.

Last edited by pontisteve : 08-18-2007 at 11:52 AM.
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  #23  
Unread 08-18-2007, 11:58 AM
lemming's Avatar
lemming lemming is offline
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Quote:
The FAST systems are speed density. Instead of an airflow meter that actually measures air, they use a MAP sensor that measures manifold vacuum or boost.
That's what I figured, and your suggestions make sense.

Quote:
Who cruises at 7,000 at part throttle?
Me, sort of, although it's more like 5,000-6,000. I actually need to at least have "safe" fueling at lift and light throttle Of course, we're talking about EEC-V, so it's not hard to get "good enough" in that case--once the MAF transfer function is correct, I can just tweak the base fuel table. I've also written quick and dirty utilities that let me build a reasonable failed MAF table (which is used for transitional fueling on some applications) based on datalogs without investing any real effort. Just drive around for a while and try to hit a lot of different RPMs, let the program crunch the logs, and paste the results into Advantage
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[2003 4.2L V6 Mustang] [1999 Subaru Impreza WTF]
On our way back from the beach, we were trying to decide where to eat dinner. At that moment, we were passed by a Rendezvous with the Ohio license plate "ASK GOD." So we did, and we ended up at some shitty Texas roadhouse-style place. Next time, I pick.--AchTTung
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  #24  
Unread 08-18-2007, 12:25 PM
vwdave vwdave is offline
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Quote:
Originally Posted by pontisteve View Post
Stuff.
Well, you explained the system and some of the tuning stategy well, but not directly relating to my question.

Basically, how do I know my corrections on my boost screen are correct? Basically at 7psi its adding 30% fuel (for example.) How do I know that 30% is too rich on spoolup and too lean on WOT and so on and so forth?

FAST has a ton of base maps you can download and being that my car is nothing really special, I should be within 15% in all areas. What do you think with my combination?

SBC 360" (350 0.040") Around 9.1:1 compression
AFR 195's 67cc
Comp Custom HR. 224/230 .570" with 112 LSA, 4/7 swap
XFI Full sequential with 4/7 swap
42# greentops
Holley Stealth Ram
52mm TB
45psi FP.

I know the injectors are slighly too big (30's would probably be perfect) compression is a little too low for the cam, but, its what I have around. The heads were purchased for a 383, then built for boost on a 350, so yeah, its kinda weird. Still should make over 300whp without a problem before the S400 goes in.

Thoughts?
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  #25  
Unread 08-18-2007, 12:52 PM
NitrouStang96 NitrouStang96 is offline
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Quote:
Originally Posted by lemming
I've also written quick and dirty utilities that let me build a reasonable failed MAF table (which is used for transitional fueling on some applications) based on datalogs without investing any real effort. Just drive around for a while and try to hit a lot of different RPMs, let the program crunch the logs, and paste the results into Advantage
Hook me up.
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  #26  
Unread 08-18-2007, 07:04 PM
lemming's Avatar
lemming lemming is offline
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Join Date: Nov 2005
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Do you have an actual use for these utilities? There is no way in Hell I would hand them out as-is; I would need to do several hours worth of minor tweaking and some documentation work. It's not that I'm against doing this; however, I don't want it to be a wasted effort.

So far, I've written separate quick little calculators to do the following operations:

1. Given TP and RPM axes, along with a datalog, estimate failed MAF values. Some cars use the FMAF logic for predictive fueling; this varies from year to year. You still have to use a little common sense since this will obviously only give you values for RPM/throttle combinations you've actually used, but it's good enough.

2. Given two rectangular tables and X/Y scales for each, add or subtract them. This is handy when building spark maps for IMRCs and whatnot. Basically, when IMRCs activate, various spark adders are computed from little half-scale spark tables and applied to the normal spark values, so this calculator makes it easier to play with that stuff without getting a headache. I've even tried to model the typical Ford interpolation pattern (interpolate between nearest four neighboring cells unless at a table edge, clip to two nearest cells if at or past table edge).

3. Given a datalog, pick one column, and average all other columns in relation to it. I wrote this so, once I got the MAF transfer function in the right neighborhood, I could just datalog the car after I'd driven it for a while, and find what the "typical" long term corrections were for each distinct MAF A/D count value. I could then just open the output in Excel and plot it, find what the typical corrections were for various ranges, and apply them to my transfer function.

This is what happens when a CS geek is too lazy to solve problems the normal way...
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[2003 4.2L V6 Mustang] [1999 Subaru Impreza WTF]
On our way back from the beach, we were trying to decide where to eat dinner. At that moment, we were passed by a Rendezvous with the Ohio license plate "ASK GOD." So we did, and we ended up at some shitty Texas roadhouse-style place. Next time, I pick.--AchTTung

Last edited by lemming : 08-18-2007 at 07:10 PM.
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  #27  
Unread 08-19-2007, 11:20 PM
pontisteve pontisteve is offline
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Lemming, your programs sound cool. I haven't built my load w/failed maf table yet. I figured it would take me a long time, one by one... and I have better things to do, lol. I have heard they use that table for predictive logic, which I guess translates into accelerator pump logic. But that honor also is bestowed upon intake manifold volume, so I guess I don't know. It would be nice if there were charts out there that told us this kind of thing. And which years, pcms, etc. I nice breakdown of the whole pcm's logic would be neat.


VWDave, what kind of blower setup do you have? You didn't mention. In my opinion, a SBC with AFR heads and a roller cam ought to break the 400 rwhp barrier in N/A trim, without much trouble. A little less if the cam specs are wimpy. But with boost, you ought to make a lot more power than that. A 360" blown motor with AFR heads, roller cam, and 10 psi of boost ought to put that thing in the 500 rwhp range I would think. Just look at factory cars with a blower, such as the GTO or Trans Am. They're about 350" motors with a hyd. roller cam, and they can make big power without getting radical.

Without boost, your 42# injectors are bigger than necessary, but so what. As long as the car is tuned for them, they aren't going to hurt you. Lightning trucks come with 42's stock, so obviously the driveability of them isn't bad. But with boost, the 42 might be light if you get up into that 475 rwhp+ range.
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  #28  
Unread 08-20-2007, 07:12 AM
lemming's Avatar
lemming lemming is offline
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Join Date: Nov 2005
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Heck, I'm using 42 lb/hr injectors.

Quote:
It would be nice if there were charts out there that told us this kind of thing.
Indeed; it seems like the usage of those parameters varies from model to model and year to year. To make matters even more confusing, there are also transient fueling parameters (which most people with the PRP, including myself, can't see which determine how the EEC models fuel going in and out of the "puddle".
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[2003 4.2L V6 Mustang] [1999 Subaru Impreza WTF]
On our way back from the beach, we were trying to decide where to eat dinner. At that moment, we were passed by a Rendezvous with the Ohio license plate "ASK GOD." So we did, and we ended up at some shitty Texas roadhouse-style place. Next time, I pick.--AchTTung
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  #29  
Unread 08-20-2007, 04:28 PM
vwdave vwdave is offline
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Quote:
Originally Posted by pontisteve View Post
VWDave, what kind of blower setup do you have? You didn't mention. In my opinion, a SBC with AFR heads and a roller cam ought to break the 400 rwhp barrier in N/A trim, without much trouble. A little less if the cam specs are wimpy. But with boost, you ought to make a lot more power than that. A 360" blown motor with AFR heads, roller cam, and 10 psi of boost ought to put that thing in the 500 rwhp range I would think. Just look at factory cars with a blower, such as the GTO or Trans Am. They're about 350" motors with a hyd. roller cam, and they can make big power without getting radical.

Without boost, your 42# injectors are bigger than necessary, but so what. As long as the car is tuned for them, they aren't going to hurt you. Lightning trucks come with 42's stock, so obviously the driveability of them isn't bad. But with boost, the 42 might be light if you get up into that 475 rwhp+ range.

None at the second as I have a stock shortblock. I plan on using a BW S400 turbo in the future. We have made 440whp on 42's with a rising rate regulator on a 1.8t. It was running leaner than ideal, but it did it. I figure at his ~40psi base pressure and 36psi of rise under boost he was at 75-80psi. He went to 580's after that.

I would love to have 400whp, but I am pretty sure it wont do that. I am running a built 700r4 and after the engine gets running, going to do a 9" swap. Thats alot of power loss through those two. I would honestly be happy with 330-350whp like that.

Based on what I know about XFI, the blocks determine fuel needs by VE right? You can change injectors, change the injector constant and be relatively close in fuel trims?
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  #30  
Unread 08-22-2007, 09:55 PM
Rogue9 Rogue9 is offline
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Join Date: Aug 2007
Location: Peoria IL
Lemming,
I have experience in EFI spark/fuel tuning in race applications, but as you mentioned, we only run TPS input for load. I see that while a lot of the concepts are similar, production EFI is a bit of a different ballgame.

Mostly I was wondering, what is the failed MAF table used for? Is this when the MAF sensor cannot keep up with changes to airflow so the ECU reverts to this table?
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