SAFC & Economy

[Hotwire]

Here's one for the ECU/Tuning Guru's

When installing an SAFC it allows the AFM signal to be modified to either lean out or enrich the mix, giving better AFR's and ultimately smoother better power. This is generally done via a power run where the ECU would ignore the O2 sensor and revert to base fuel maps.

BUT my question is this: How would this effect economy for normal driving? If the car is utilising the 02 sensor during normal running, would it still be just as bad as prior to installing an SAFC?

Just trying to sort out what would be the best option for better power AND better economy

Cheers
Lee

 

[naughtika]

hhmm my isn't tuned yet.. i'll let you know once i've tuned mine..

but my guess is.. if you lean out your fuel mixture then your fuel economy should increase.. and i'd say if you replace your 02 sensor too, that'll even make your car run better and more fuel efficient..

 

[bradc]

an afc should indeed give you a bit better fuel economy.

 

[Guest]

hmmm economy and power in the same sentence!! im looking at getting a safc bud dont realy care bout the fuel, just dont what the engine to knock..

 

[Hotwire]

Brad: Thats what I have heard, that it helps improve economy (as long as you keep your foot at a reasonable height). But my question is how? If at 100% throttle, the ECU is looking to a base fuel map, it can be adjusted. BUT if running at 1/4-1/2 throttle, and it is looking to the output of the O2 sensor, how can this make much difference? OR am I looking at how the car runs at 1/4-1/2 throttle incorrectly?

 

[SiliconAngel]

Ideal fuel mixture for maximum power should also be the peak of the efficiency curve. Either too little or too much fuel vs airflow will both reduce your performance, so the sweet spot overlaps both power and max efficiency. Hell, an AFC will help improve your efficiency even without any other mods (although an upgraded or piggyback ECU will help), as the VR4 (and indeed just about every manufacturer ECU) stock fuel map is slightly rich 'just in case', to avoid engine damage.

So for a given level of power and time, running a car with an AFC will give you better fuel economy than the same car in the same conditions running stock fuel maps.

 

[bradc]

what he said ^

The problem with VR-4's is that the turbos are tiny and are always making boost, so the ecu puts in more fuel. It is transient driving of normal acceleration that uses a lot of fuel in a VR-4, you might as well floor it and get up to speed quickly, you'll probably use less fuel!

A VR-4 is always referring to it's fuel maps because of this, hence a properly tuned S-AFC can make a big difference

 

[Guest]

Keep in mind the ECU has no idea what fuel or conditions the car will be used in. So its made to run quite rich. The AFC can be made to lean it out a little ... If u get a wideband O2 sensor u can use that with the SAFC to get more acurate results.

 

[Hotwire]

what he said ^

The problem with VR-4's is that the turbos are tiny and are always making boost, so the ecu puts in more fuel. It is transient driving of normal acceleration that uses a lot of fuel in a VR-4, you might as well floor it and get up to speed quickly, you'll probably use less fuel!

A VR-4 is always referring to it's fuel maps because of this, hence a properly tuned S-AFC can make a big difference

Thats what I was wondering, thanks for clearing that up.
When my Leggie lands, I think an SAFC will be one of the first items to be addressed then

 

[jungle]

I've ordered the latest one from the states, should be here in a few weeks...although I'm STILL waiting my bloody compliance plate

The SAFC i've ordered has 16 load and rpm sites so it will modify the standard map throughout the rev range and load range. The one Kritian has can modify 12 sites on both axis, both will have the same effect, mine has slightly more resolution, although i don't think this will be much of advantage

IK expect to make at least 1-2km/L with this fitted and a big improvement during full load as most of the Leggy's from the Dyno day AFR's went into the 10's, high 11's to low 12's is more like it...remember though, you cant change the ignition values

It works by modifying the air fuel ratio of the base map.

When tuned, the AFR's for the entire map can be modified if need by. I'll be concentrating on the light load area as this is an area i expect to make good gains.

 

[naughtika]

got a question about the S-AFC and ECU..

on hot days, I notice that the "KNOCK" senses alot more than usual..

what is this knock wire?! I assume it's one of those camshaft, crank angle sensor or some sort..

can anybody explain?

 

[Dr_Josh001]

got a question about the S-AFC and ECU..

on hot days, I notice that the "KNOCK" senses alot more than usual..

what is this knock wire?! I assume it's one of those camshaft, crank angle sensor or some sort..

can anybody explain?

I'm not sure how far knock sensors have come since the day of the old 4G62T cordia engine, but in laymans terms its a crystal that senses shock when the engine is detonating prior to combustion; this comes from running a lean mix of fuel.

If your engine knock sensor is registering, especially on a hot day, then you need to look at how lean your fuel fix is. This is bad news Christian, you need to get your SAFC tuned and make sure you're not killing your engine!!

 

[Guest]

This is probably a stupid question, but Im gonna ask it anyway. With the SAFC, could it be tuned to get rid of the fuel/boost cut, or is it necessary to get a piggyback/standalone ecu or fuel cut defender?

 

[bradc]

Not really, you want a proper ECU to do it

 

[Rasi]

Christian,
It will depend on how much it changes, but I wouldn't worry too much about it if only slightly higher. It seems that the sensor will pick up other engine noise (possibly normal combustion noise) and on hot days it seems to pick up slightly more than on cold days. The amount of knock you see on your SAFC will also depend on when to set the knock setting on it. If you set the setting just after you started the car (ie when cold) then that will be the base reading of the SAFC. This is what I did origonally in my skyline and the SAU forum had this discussion a number of times. I then set it up after driving for a while on a hot day and now I hardly ever see any knock except for when it actually is knocking. If you haven't noticed the knock will increase slightly when idleing and reduce back down once you have taken off again.
When I would be concerned is when a large difference is noted from normal driving to when I put the foot down. My knock reading would be around 12 - 20 when normal and spike to 75 or higher when it registered knocking.
Hope that helps. Do a search on the SAU forum as there is a lot of good information on there that can be related to any performace car.
Mike

 

[Murph]

Ideal fuel mixture for maximum power should also be the peak of the efficiency curve.

Peak power AFR <> peak efficiency AFR!

Peak efficiency is found at the stoichiometric AFR of 14.7:1. At this AFR your engine should be making a complete burn of the air fuel mixture. However, for maximum power you need to drop a little lower to around 12:1.

IK expect to make at least 1-2km/L with this fitted and a big improvement during full load as most of the Leggy's from the Dyno day AFR's went into the 10's, high 11's to low 12's is more like it...remember though, you cant change the ignition values

Speaking of ignition timing, remember that it WILL change. The SAFC works by modifying the AFM voltage to trick the ecu into running on a different part of its maps. However, it will also start pulling timing figures from that corresponding part of the maps. Not ideal really.

 

[naughtika]

thanks guys..

when i first start the car on hot days.. it quickly registers knock at around 10-15 then at one time it went up to like 50.. so i was like "wtf!?" what i usually do is turn the engine off for about 5 minutes and it goes away..

 

[Hipsi]

the 2 most important gauges for me are boost and wideband afr. That's all I'll be fitting to my leggy when I eventually get one. Stoich gauges that work off ur standard o2 signal are 'ok' but will never be as accurate as a wideband.

 

[VR4Rocket]

I notice knock as well but it just usually hovers round 35 to 40 but can drop down a few while accelerating

 

[Guest]

the 2 most important gauges for me are boost and wideband afr. That's all I'll be fitting to my leggy when I eventually get one. Stoich gauges that work off ur standard o2 signal are 'ok' but will never be as accurate as a wideband.

i agree, thats what i had in the foz but i had just a stoich gauge was saving for the wide band..