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Goldy
16-01-2006, 22:40
Just been thinking again..... (uh oh I hear you say)

A while back I ran an mr2 turbo AFM on my car as it was much larger capacity and I thought there may be gains to be made, however the result was that the car ran lean mc lean..... now todays brainwave was....

if I was to run turbo injectors (make my car run rich as they are larger) and then use a turbo afm would this effectivly give me some extra fueling capacity or am I out of my tree again?

Come on .... answers and piss takes on a post card :tease:

djdna2000
17-01-2006, 00:23
It wouldn't work the way you expect. For any given amount of airflow the engine is sucking in, there is a corresponding 'correct' amount of fuel for it. Turbo injectors are 430 cc (or 540 for gen 3), whereas NA are 320 IIRC?

Let's consider an example - a particular load point in the ECU map, corresponding to a particular manifold pressure (obviously vacuum in the NA case). Now say the NA AFM and ECU tell the NA injector to fire at say 50% duty cycle, 160 cc/min for this amount of air.

If you add gen 2 turbo injectors, the NA AFM/ECU is still telling them to fire at 50%, but now 50% is 215 cc/min so you are getting too much fuel.

If you had stock injectors with a turbo AFM, the turbo AFM thinks that it's injectors are 34% bigger so it thinks it should be using a 37% duty cycle, hence the engine runs very lean cos 37% of 320 is 118 cc/min.

If you had turbo AFM, turbo injectors and the NA ECU I imagine you would be back where you started except not as good cos the ECU is mapped for using NA AFM and injectors.

In order to use any extra fuel, you need more airflow. Now you do this by either increasing RPM, nitrous or turbo/supercharging - none of which your NA ECU has maps for anyway, hence not possible. And all the above is assuming that the NA ECU can talk correctly to the turbo AFM (not such a hefty assumption though, given Toyota's propensity for common technology between engines).

Sorry that's a bit long winded, got carried away.

Driftin_AW
17-01-2006, 01:04
Actually just to be different, I think it might work.
The AFM door is attached to a fairly basic potentiometer, so the further open it is, the less resistance it has. When fully closed it would output around 0v, when fully open it would output about 5v.

If you have half the airflow capacity of the NA AFM flowing, then let's say you get 2.5v output, and the ecu supplies fuel accordingly. Let's say it provides a 50% injector duty cycle

When you put a larger AFM in, the same amount of airflow is going to equate to a smaller AFM opening, let's just pull a number out of the air and say it's outputting 2v. Because the ECU thinks there is less air going in than there actually is, it provides less fuel, assuming a linear relationship it would be 40% injector duty cycle.

If you then put in injectors that were 25% larger, that 40% duty cycle would give you the same amount of fuel.



Having said that, you would have to get injectors that were perfectly suited to the increase in size of the AFM, so if the cross sectional area of the turbo AFM is 50% more than the NA one, you need 50% larger injectors.

You also have to make the assumption that there is a linear relationship between airflow and AFM opening, which I believe is not the case.

A lot of people have success doing similar, like on 7MGTE supras, it's a fairly common mod to upgrade the AFM to a larger Lexus one, and install 550cc injectors (stock is 440). Those are Karman Vortex AFM's, not flapper doors like ours, so it might be different.

I've also seen people with MAP sensored NA engines, which only have a 1 bar map sensor (from -1bar to 0) swap the map sensor for a 2 bar (-1 bar to +1 bar), then go for injectors double the size, when doing turbo conversions. IMO a bit dodgy, but it appears to work.

djdna2000
17-01-2006, 10:52
But Malcolm, the point is that although the larger AFM and injectors provide more theoretical fuel capacity, this capacity will never be used because there is no way of getting the extra air into the engine to burn the fuel. The examples you have used above are of turbo cars or NA to turbo conversions.

The bit of the turbo ECU map where it is in vacuum is probably similarly fuelled to the whole of the NA map (since that is all in vacuum), just with lower resolution as it has load sites for the positive boost area too.

Driftin_AW
17-01-2006, 10:59
But isn't Goldy doing a supercharger install on his car, hence necessitating more fuel?

djdna2000
17-01-2006, 11:34
I read from the above that he just wanted to increase fuelling to his NA as it stands, which is what he tried when he stuck the turbo AFM on - perhaps I am wrong though. If it was for installing a supercharger then it would most likely work, though again it wouldn't be perfect.

Driftin_AW
17-01-2006, 12:08
plus you wouldn't want to increase fueling if you were keeping it NA, would kill performance and be of little use

Goldy
17-01-2006, 15:08
For what its worth, I know already that the turbo afm will work with the afm however as its a larger size the airflow at a given voltage is larger that on my n/a afm. I think i would need to calculate the airflow increase vs fueling increase and see if they are the same.

I was thinking that if the afm lets in say 50% more air at a given measured voltage and the injectors put in 50% more fuel at a given injector duty cycle then it'll work ok? The mapping could be adjusted slightly with the SAFC

djdna2000
17-01-2006, 15:20
Is this for the supercharger or just on the NA?

superchargedsam
17-01-2006, 15:27
I was wondereing this as well as cant see a mjor advatgae in an NA of overfueling and adding that much more air or am I missing something ! If this is for the SC then I can fully appreciate it !

Goldy
17-01-2006, 15:52
I thought it might be an easy way of adding some extra fueling capacity for when the supercharger is fitted without having to get a stand alone / piggy back ecu / undergo mapping

In my head it works, but theres just something niggling that I can't put my finger on, on why this wont work out right. I'm just waiting for someone to point it out :neutral:

djdna2000
17-01-2006, 16:37
It will probably work, just not very well. If you have a SAFC then it will help matters, but you'd still be better off with a proper controllable ECU, or at least a turbo ECU to go with the AFM and injectors.

Goldy
17-01-2006, 19:32
Hrms.... its all expensive... i've thought about it a bit.... just sortof had a mini brainwave last night and was wondering if it would work.

I'll be leaving as is I think.