Thoughts on FI and Overlap

[stangslayer]

just thinking....... on a fuel injected engine, if you were to build for max effort, using a very high duration camshaft( for high rpm operation) how would one manipulate the computer. if you think about it, at low rpm there is such overlap that there is some unburned charge that escapes into the exhaust. the oxygen sensor would read lean and tell the computer to add more fuel. this would max out the fuel trim and set the ses light. at the same time the computer would allow way to much fuel out the injectors and cause a rich condition. the engine would actually run rich but still be reading lean.

how would one offset this problem. is there anything that can be done besides going to an aftermarket computer that could be programmed for a specific application

[RallyBob]

Originally Posted by stangslayer just thinking....... on a fuel injected engine, if you were to build for max effort, using a verry high duration camshaft( for high rpm opperation) how would one manipulate the computer. if you think about it, at low rpm there is such overlap that there is some unburned charge that exscapes into the exhaust. the oxygen sensor would read lean and tell the computer to add more fuel. this would max out the fuel trim and set the ses light. at the same time the computer would allow way to much fuel out the injectors and cause a rich condition. the engine would actually run rich but still be reading lean. how would one offset this problem. is there anything that can be done besides going to an aftermarket computer that could be programmed for a specific application

On the Opels it's a moot point. On the US cars that got EFI (1975), it's antique analog L-Jetronic. No O2 sensor is used, and it can't be adapted. And it has an air flow meter (literally a hinged flap), which will oscillate back and forth once duration and overlap go beyond a certain point. The moving flap tells the 'computer' ( I use that term loosely here!) to run lean, then rich, then lean, then rich as the flap moves back and forth. Modern engines tend to use multiple inputs, like rpm, a true mass air flow meter, O2 sensor, temp sensor, TPS, and even MAP sensor in some cases. Our old systems don't have this capability.

The ticket is to use a programmable ECU, and if you really want a hot cam, forgo the O2 sensor (you don't want a stoich mixture anyway on a hot engine, it needs to run richer than 14.7:1!), and map via TPS values, and rpm.

Bob

[Hiro]

Originally Posted by stangslayer just thinking....... on a fuel injected engine, if you were to build for max effort, using a verry high duration camshaft( for high rpm opperation) how would one manipulate the computer. if you think about it, at low rpm there is such overlap that there is some unburned charge that exscapes into the exhaust. the oxygen sensor would read lean and tell the computer to add more fuel. this would max out the fuel trim and set the ses light. at the same time the computer would allow way to much fuel out the injectors and cause a rich condition. the engine would actually run rich but still be reading lean. how would one offset this problem. is there anything that can be done besides going to an aftermarket computer that could be programmed for a specific application

my way with high duration cams is using Megasquirt without WBEGO regulation & never under 4500-5000rpm,
admitedly not OK for a street usage but this works.
Hiro

[wrench459]

Originally Posted by stangslayer ..how would one offset this problem. is there anything that can be done besides going to an aftermarket computer that could be programmed for a specific application

It mostly depends on when the intake valve opens.
You can have a long duration (>300) cam that opens the valve late and possibly get away with it.
...maybe...

[davegt27]

how would one manipulate the computer

It could probably be done with enough effort
I know I tried using another AFM one from a 260z but I took the stock 1.9 AFM circuit card from the Opel and put it in the 260Z AFM

Then I tried to manipulate the spring tension
This was all done at the drag strip
The attempt failed
When I adjusted the motor to have a smooth idle it was a dog
I then adj the spring so loose that black smoke cam out the tail pipe
And the car sounded like it had a big cam (the AFM was bouncing back and forth like Rally Bob said)

The car would not rev past 5k on the 1/4 mile

So to answer your question it can be done but you need to make the system adj

Adding an AFR meter would be a must
The stock 1.9 AFM is tiny so that would need to be changed out
And ADJ FPR would need to be added
Then you would need to have a way to adj when the fuel gets injected (or pulse of fuel gets injected into the motor)

On the low end you could maybe hook an ignition timing device in with the ecu to allow you the control that is needed

Maybe adapt a SAFC or SAFC II (the older version is better)
A'PEXi U.S.A. - Products: Electronics

Another option is an AIC or additional injector controller

So all kinds of things can be done

Going with a stand alone ECU might be the easiest

I have a MR2 that failed emissions so I wanted to see if I could get it to pass emissions with out a CAT

Well I spent more money then it would of cost had I just went and bought a new CAT

But I did learn something and it did pass on the third attempt

Davegt27