ITB Strategy for NA motor

Hi, I have an ITB manifold to install on my LS7 V8 engine which is currently runs a stock manifold tuned with a Syvecs ECU using conventional map sensor as primary load.

From the information on here, I understand that for a naturally aspirated engine simple TPS as load for both fuel and ignition, with finer resolution at low throttle openings is the appropriate strategy.

The manifold does have a built in plenum to provide a MAP sensor output, but as it's not a turbo engine, I'm wondering if there is still any benefit to using the map output as a load correction and how best to use, or don't bother?

Also wondering if the current map/rpm values for injection and timing can be used as a guide to populate a tps/rpm base map that will at least get it started, or if they are unrelatable?

Steve,

Great questions.

Since the ITB setup you're describing has a manifold, the MAP reading should be somewhat usable.

In that scenario I generally convert the VE or fuel on time table to be throttle based, but compensate fueling in linear fashion based on the MAP reading, and use a baro comp or exhaust pressure comp on top of that.

If I remember correctly, Syvecs calls linear MAP compensation of fueling the Simple Manifold Pressure Multiplier.

In a main VE or fuel table you can copy values at 0 RPM, atmospheric pressure and move them to 0 RPM 0 TPS for starting, move values from idle areas to idle RPM, 0 TPS to get things going, then work carefully from there.

In terms of load, you may find MAP still represents engine load reasonably well, but during load bearing testing you may find the relationship between cylinder filling, torque no longer follows MAP the way it used to, in which case you can keep MAP as your load axis but readjust timing values, or switch to TPS based with separate baro compensation to account for air density changes. There are other options as well of course, especially if you are monitoring exhaust pressure, but I've offered the most basic, common ones.

Steve mentionned that TPS would be based for both fueling and ignition timing. I usually retain MAP as the load axis for ignition timing when tuning Alpha-N (because I'm mostly tuning turbo engines), I'm guessing that using MAP as the load axis for ignition on a NA engine with ITB would lack resolution? Or would it still be accurate enough?

When talking about switching a single throttle SD tuned car over to ITBs, you can expect to need to adjust it in many cases, especially if it's been tuned aggressively, because the change in MAP reference will generally impact the readings at least in some conditions, perhaps more at light loads, but I think MAP can still be used as a load axis for ignition timing IF the MAP reference accurately represents load still. That will depend on a number of factors.

Here are some examples of situations where I feel MAP may not be the ideal load reference:

If the ITB setup causes a super dirty MAP signal and the ECU doesn't allow you to smooth it, that alone might make your mind up for you to use TPS instead. You certainly don't want ignition timing jumping all over the place because of a dirty MAP signal.

As another example, if the heads/cam package is so wild that there isn't much margin between idle MAP and WOT MAP, whether it's single throttle or ITB, that's another situation where TPS would better represent engine load than MAP.

I think as long as you think of choosing your ignition timing load axis based on which piece of data best represents the load on the engine, you'll be in good shape.

Thank you for the advice Mike!

You're welcome!

Thanks a lot for your advice Mike.

The manifold is a Harrop Hurricane, and I just had a reply from Harrop who said the MAP signal can be used as the main load reference. They said "You will need to max out the 'effective throttle area' table otherwise it is normal process tuning."

Not sure how that translates in the Syvecs, but perhaps its worth fitting it initially without changing the load configuration and see how it runs and how good the MAP signal is, before deciding to change to Alpha-N? What would be the best way to assess the quality of the MAP signal and make a decision if we did that?

Steve

I am running a similar setup on a Big Block Ford.The manifold has a plenum in the valley area to which I've added a MAP sensor. My ECU (Performance Electronics) is configured in Alpha-N and then it allows MAP compensation. I find this really smooths out the TPS load control and gives you the best of both worlds.

As I understand it, the issue with TPS load control, you can be in different modes of load at the same TPS and RPM setting. The addition of the MAP compensation determines what's going on with the load and adjusts accordingly.

It really helps driveability to increase your table resolution at lower loads and rpm values. The amount of air flow between 1% and 5% is dramatic yet the amount of air flow between 80% and 90% is negligible.

Also, converting your Speed Density (MAP Load) to an Alpha-N (TPS Load) is quite a bit different. The trends will be similar but the values won't be close.

I do defer to the experts on this however I'm doing it and for the most part, pretty successfully.

Paul

Thanks Paul, what you suggest is the direction I am heading. Are you using Alpha-N as primary load for both fuel and ignition, or only fuel?

Harrop seem to think their manifold will run fine with MAP as the primary load for fuelling, but I'm skeptical.

I wouldn't be surprised if its possible if they've plenum'd a signal from all 8 (or even a single bank of 4) cylinders. I've played around with it on rotaries - 2 rotors no bueno even plenum'd with manifold presssure troughs, 3 rotors are a different story and pretty smooth.

In your case I think it'd depend on cam overlap and how many of the ITB runners they've merged.

Steve

I use TPS as the load signal on both fueling and ignition. I was told it works better if you're tables are consistent thru all of them.