Fuel injection? Open or Closed loop?

[Darrel Goheen]

Originally Posted by Ed Wright

The manifold air temp sensor helps consistency a lot. All weekend at Houston recently, it varied exactly one hundredth. First three passes over two days at No Problem Raceway last week, it only varied four thousandths, then it broke a lifter. Did not repeat that close without the manifold air temp.

Interesting. My LS1 did not have a MAT on it. I put one on it but have since learned it isn't controlling anything anyway. You have your MAT modifying fuel at different temps?

[Ed Wright]

Originally Posted by Darrel Goheen

Interesting. My LS1 did not have a MAT on it. I put one on it but have since learned it isn't controlling anything anyway. You have your MAT modifying fuel at different temps?

I don't know about others, but the FAST uses it to control air/fuel vs intake air temp. The Intake Air Temp Air/Fuel correction table has a straight line across it, at zero correction. You alter the correction at a given temp by moving that up or down for more or less fuel.

[Darrel Goheen]

The Holley system can do the same thing but both of mine are set flat line with no correction. I didn't know anyone used that in race applications.

[Ed Wright]

Originally Posted by Darrel Goheen

The Holley system can do the same thing but both of mine are set flat line with no correction. I didn't know anyone used that in race applications.

I have worked with the Holley system on a couple of COPO cars. Not real crazy about it. Maybe if I had more time with it.
I don't know how anybody could expect the guys building the system to have any idea how a given engine would respond to air temp changes. Too many variables. Just because that is a straight line does not mean it isn't using the data. You would have to, I would assume, change that baseline for your application. I could be full of crap (wife says I am) but have altered that line in colder and warmer than normal (70 to 80 deg F, I consider normal) air temps. I just figured everybody altered that. Wife is likely correct, I'm just full of crap.

[cmracing]

How much air temp decline do you see on a typical pass?

[Ed Wright]

Originally Posted by cmracing

How much air temp decline do you see on a typical pass?

Depends. Usually more in cool weather. In my case, FAST XFI (with the straight line across the Manifold Air Temp correction table/"map"), "compensated" a little too much. (Added just a little too much fuel in lower temps, etc) It would take somebody much sharper than myself to simply dyno tune one on a given day to get that part dialed in right. I guess some dyno rooms could have the inlet air temps adjusted that much?
I have to do it the hard way.

[Robin Lawrence]

I saw this post last year and always meant to respond. I see it's back from the dead!

I prefer closed loop. While I am not very consistent the system has been. I suggest to most racers to use a CTS and IAT modifiers if their engine combination is temperature sensitive. In a street application it can help drivability at various air temps. In the race car not so much.

Our system reacts very quickly to input from the 02 sensors. Probably faster than most of our competitors. Once you have a good base tune the closed loop will chase the target within 1 to 2 percent. Like someone previously stated you can limit the parameters of the amount of correction either up or down in air fuel ratio.

The Holley also has a learn table. It's exists on top of the base fuel table. The learn table retains the correction that the ECU uses to attain the target A/F ratio. This table can be transferred to the base or deleted. It can be left alone as many street cars use this as their "self learning" or "self tuning" function. The latter being very overused in the EFI Market. The learn function is similar to long term learning in early to mid 2000 year cars. It's a great feature to get a map within a few percent of the target. I use it on the dyno and then turn it off after I have a good base map. The system reacts faster when in Closed Loop with the Learn feature turned off.

I have seen many tuners have very radical air temp correction tables. Unless you are running a supercharger where the temps change dramatically during the run I would not spend a ton of time on that.

Robin

[cmracing]

Originally Posted by Ed Wright

Depends. Usually more in cool weather. In my case, FAST XFI (with the straight line across the Manifold Air Temp correction table/"map"), "compensated" a little too much. (Added just a little too much fuel in lower temps, etc) It would take somebody much sharper than myself to simply dyno tune one on a given day to get that part dialed in right. I guess some dyno rooms could have the inlet air temps adjusted that much?
I have to do it the hard way.

Same here. About 23/24* drop in cool weather, 18/20* in hot/humid weather. But, this is in a Bracket Car with a cowl hoodscoop and an air pan sealed to the hood.

I do very little compensation for air temp, in fact, in the range it is in for racing it does nothing. When its really cold (below 50*) I add 2% just to help it. We don't race in that cold of weather though.

Same thing for coolant temp. Below 80* I add fuel to help with warmup, but above 80*, no change.

It is interesting Robin mentioned not using the Learn function once the engine is tuned. I still use it, but it is severely limited in what I let it do. I may as well turn it off and just let the Closed Loop take care of things but still limit it's range like present, +-2%.

[pbp1]

This is a great post so I thought I would bring it back to the top and add some information that is missing here about Air Temperature and its impact on fuel needs.

There is no need to guess or add "Corrections" for air temperature!

Air Temperature does have a proven, direct, and significant impact on Air Density.

The Ideal Gas Law was formulated way back in 1834. It defines how pressure and temperature changes affect the density of a given volume of air.

Since we measure the fueling of an engine in Air / Fuel ratio (? parts of air to one part of fuel), if the Air becomes cooler, or more dense, or heavier, then the only way to maintain the same Air/Fuel Ratio is to add more fuel.

In a TRUE Speed Density EFI system, the Air Temperature reading plays a part in the equation that is calculating fuel needs behind the scenes.

There is a fuel correction vs Air Temp table in the FAST software just like most any EFI software, but just because you have this table zeroed out, that doesn't mean that the Air Temp is not impacting fueling (This statement is only true if you are running in Speed Density).
That table is there for those who run in Alpha-N mode and wish to build in some manual correction for changes in air temperature. I always run in Speed Density mode and leave this table zeroed out.

This is not some black magic that FAST or any other EFI company invented. It is basic physics and it works as long as the system is set up correctly and you have all the correct basic information in your tune (Cubic Inch, Injector size, Fuel type used, etc.)

An incident happened a few years ago that prompted me to do an experiment to validate how the Air Temperature is used to maintain a constant Air Fuel Ratio while Air Temp is changing.

I have two customers with very similar LT1 SS combinations. Both run my system, Both run Speed Density in Open Loop, Both have tunes that have been extensively calibrated so their actual Air/Fuel ratios run right on target with no O2 correction in all conditions at different tracks without changing their tunes. Both are very FAST, consistent, and dependable.

One of the racers decided to try Icing down his manifold to squeeze a little more ET out of his car. He staged the car and when he let go of the transbrake, it was so lean that it coughed and died. Let it warm back up and all was well. I asked where his Air Temp sensor was located and he said it was out near the entry of the throttle body. That would ordinarily be a fine location for it as that is sampling the air entering the throttle body. The issue here was that the ECU was being lied to. The Air Temp sensor was telling the ECU that 100 degree air was entering the engine when the air going into the intake ports was actually much colder than that. He had increased the density or weight of the air without adding any fuel. More parts of air for the same one part of fuel = a leaner Air/Fuel ratio!

So here is the test we conducted. Took the other car, put the Air Temp Sensor in the intake manifold, Iced it down, made a run, and it picked up big time! We got the car back and looked at a datalog of a previous run with no ice, compared to the run with ice. Here is what we found that was different on the run with ice:
The Air temp was obviously a lot cooler.
The Pulsewidth and #s per hour of fuel delivered was a lot higher.
The Air/Fuel ratio was EXACTLY THE SAME!!!
This is with the O2 correction turned off, so what happened was the Ideal Gas Law was once again proven to be true and the True Speed Density strategy was proven to maintain a constant Air/Fuel ratio as the density (Temperature) of the air changed.

Don't believe any of this, I've got a couple of witnesses who can testify.

Hope this comes across as helpful and informative as I intended it to be.

[Ed Wright]

Mine is Speed Density as well, Open Loop. Leaving the line across the Manifold Air Temp table straight @ zero, my air/fuel ratio was going too rich in cold air, too lean in hot air. I now have it repeating in all air temps I have encountered so far. Car is much deadlier in bracket mode than the driver.
The tweaks I made were pretty small.
I'm probably doing something wrong. LOL