ITB tuning

Hi Guys,

I am setting up my Elite 1500 for a Jenvey ITBs kit and i'd like to share some thoughts with you, hoping for some always valuable feedback too. :)

The points are relatively generic, but I know that some details are always interesting. So, the engine is a 1.3ltr N/A 11.2:1 rally car engine, currently making around 115bhp on the OEM intake with 140 cc/min injectors. The Jenvey kit is a 4x45mm SF type kit, designed for this engine, running on 4x250cc/min injectors and has no vacuum pickup.

I have 2 main concerns. Tuning model and fuel pressure.

Given that there is no vacuum pickup, besides the anyway special characteristics of such intakes, I believe that VE model tuning is not relevant in this case, so the only option is AlphaN with TPS load input. Right? This means that the fuel map has to be pulse width based.

Now, having no MAP reference leaves me with another open question. Fuel pressure...

The fuel system is fitted with an adjustable regulator directly on the rail, no vacuum hose connected, and a return line. The fuel pressure is adjusted at 3 bars.

The Elite software allows for 2 options, MAP referenced fuel pressure and Constant. The MAP referenced is not useful in this case, since there is no such reference and referencing to atmosphere is no the right way to do it, in my understanding. On the other hand, the Constant option needs again a MAP input to calculate the pressure drop across the injectors, which would make perfect sense for a charged engine, but not so much for an N/A ITB application.

Adding a fuel pressure sensor in not changing the above picture. Since this cannot be used as input in those settings. It should help with injectors characteristics thought, wouldn't it?

Would it be acceptable to use the MAP reference option, even though there is no real MAP input? Will this only affect the low load areas where the engine will be making some vacuum, or will it also affected higher loads?

In addition, are any injector flow data at different pressures relevant in this case? The pressure drop across them should not be affected that much, right?

Generally, i see the need for accurate injector dead times, but are any other injector data useful, if the fuel map is anyway pulse width based?

My target is to be able to use the ECU O2 control and ideally also consider barometric changes somehow.

Thanks for your time and hints!

You can specify TPS as the load (Alpha) for the VE based fuel map

The Fuel system you describe is of the Constant type. It's not that difficult to add a MAP port to each individual manifold (make it very small, like < 1mm). Connect the individual manifolds together with a small accumulator and attach your MAP sensor to this. You can get a reasonable MAP signal doing this, certainly sufficient to calculate the injector differential pressure using a fuel pressure sensor (which you would want for diagnostics anyway).

Yes, you are right, but I forgot to mention that I do not intend to modify the manifold.

I agree that the fuel system is a Constant type, but the Haltech software only accepts a constant type if a MAP sensor is connected. This is my point..

So, in my understanding, I am practically left with either:

- setting it up as MAP referenced, (in this case, having a MAP input is not necessary in the Haltech software)

- leaving the MAP sensor open to air and using it as Barometric input

- Tune on pulse width, obviously on TPS

and bake whatever deviations in the tune,

OR:

-Setting it up as Constant

-Leaving the MAP sensor open to air, assigned

-Using this pseudo-MAP as Barometric input for baro-corrections

-Tuning again on pulse width, obviously on TPS

-and again bake any deviations in the tune.

To be honest, i don't see what's better from the above, i am just trying to choose the least "wrong".

What i am missing is an indication of how much the vacuum is changing- and therefore affecting the fuel delivery- on such intakes. I have the feeling that once the throttle is slightly open, there is effectively no vacuum to measurably affect the injectors.

I am also slightly concerned about the rail pressure being affected by the increased demand on higher RPM/Loads.

In any case, I do intend though to connect a fuel pressure sensor for diagnostics as you mention as well as my last point.