[Jaap Struyk]

Hello, I was wondering how to deal with values beyond firmware's capability like MAP pressure > 511

In the code I notised that for MAP there was a change from 255 to 512 by a divider value so one could modify that with another divider but that would loose accuracy even more, I suppose that's because values are stored in byte, would it require a huge code change to int?

[pazi88]

It's not huge job to do, but in which kind of engine you need more than 4bar of boost? I know that with diesels it's not uncommon to run higher than 4 bar of boost, but speeduino isn't meant for diesel engines anyway.

[PSIG]

3-bar of boost on a 400kPa absolute-pressure sensor; 1 bar up to atmo, and 3 of boost. Offhand, in-addition to changing the multiplier in Speeduino, there are other options. One is to use a higher-pressure sensor, such as the MPX5700AP (700kPa PCB mount), PX3-006B (600kPa remote mount) or other similarly linear output unit and custom calibration. This forces a substantial loss of resolution (especially off-boost with only about 0.5V signal range from 0-101lPa), but could be useful in certain applications.

Depending on the application; Speeduino can also run RPM-only fueling, where MAP signal is limited but the RPM continues to increase on the table in a fashion similar to WOT A-N fueling. Again, this may be suitable only for certain applications that are consistent or predictable in their MAP changes above their sensor limit. There are other options.

[Jaap Struyk]

Hello guys, thanks for your response!

It's for use in tractor pulling and boost pressure for methanol can go up to 10bar (and diesel even higher), currently I am building a tiny engine and aren't going further then 4 bar boost (staying within Speeduino limits) with a MPX5700AP

WhatsApp Image 2021-01-06 at 17.01.55.jpeg (136.58 KiB) Viewed 3926 times

For further use in the future however I was looking for a way to go beyond that limit, using a 5V pressure sensor and "mis"calibrating (10bar real life calibrated as 5) is one of the options but that's not the proper way.
Loss of resolution isn't a big deal since these engines don't need a nice acceleration curve, most of them wil only have boost above 4Krpm so it's revving up until the boost kicks in then release the clutch...

[65ShelbyClone]

I, too, would like to have access to the full 700kPa of an MPX5700. I'm new to Speeduino with a background in MegaSquirt and was a little surprised to discover that the sensor is officially supported, but not fully supported, if you know what I mean.

Barring a change to the variable type, how badly would accuracy be degraded by changing the multiplier?

I had a play around with the source files and got it partly working on a 3x multiplier, but doing it right seems to be beyond my meager amateur programming experience.