View Single Post
      03-31-2020, 07:29 PM   #1
Moderator
Moderator
32
Rep
436
Posts

Drives:
Join Date: Feb 2007

iTrader: (0)

Modifying the rev limits per gear on the MSS5x DME

Credit goes to p0lar for this writeup.

Since the topic was recently discussed in another thread, and mentioned (more than once) how difficult it is to find information in the megathread, here's a quick howto on modifying the rev limits per gear on the MSS5x DME.

The first thing to understand is where to find the configuration values for these variables within your DME. To do this, you MUST know what version your DME is. Please see this thread about how to make that determination.

Name:  Screen Shot 2020-03-31 at 4.21.57 PM.png
Views: 116
Size:  223.3 KB

A typical map would look as follows:

Quote:
08 00 00 00 00 01 00 02 00 03 00 04 00 05 00 06
00 07 1F 40 1F 40 1F 40 1F 40 1F 40 1F 40 1F 40
1F 40
To simplify the meaning of this, let's look at it in a more organized fashion:

Quote:
08 00
00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07
1F 40 1F 40 1F 40 1F 40 1F 40 1F 40 1F 40 1F 40
The first '08 00' denotes the size of the table, meaning it has 8 "x" components and 0 "y" components. Don't worry about this bit, it won't change and is used internally by the DME.

The second '00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07' string denotes the gear in question and the third '1F 40 1F 40 1F 40 1F 40 1F 40 1F 40 1F 40 1F 40' string represents the speed (RPM) in hexadecimal representative to the gear above. To convert this to a more reasonable format:

Name:  Screen Shot 2020-03-31 at 4.24.06 PM.png
Views: 442
Size:  58.8 KB

So, to modify a particular gear's engine speed limit in RPM, simply convert the desired RPM to hexadecimal and substitute in the string above. Here's an example to convert from the OEM 8000 RPM rev limit to 8100 RPM:

Quote:
8100 RPM = 0x1FA4 = 1F A4

So, if you wanted to raise the rev limit to 8100 RPM in every gear, including neutral, you would recreate the original string as such:

Quote:
08 00 00 00 00 01 00 02 00 03 00 04 00 05 00 06
00 07 1F A4 1F A4 1F A4 1F A4 1F A4 1F A4 1F A4
1F A4
Let's say you wanted neutral to be rev limited at 4500 RPM, 1st gear limited to 8200 RPM, and 2nd -> 5th gears limited to 8300 RPM, 6th gear limited to 8100 RPM, and reverse limited to 5000 RPM for a more complex example (all disclaimers apply). First, calculate the necessary hex RPM values from your desired decimal RPM values:

Quote:
4500 RPM = 0x1194 = 11 94
5000 RPM = 0x1388 = 13 88
8100 RPM = 0x1FA4 = 1F A4
8200 RPM = 0x2008 = 20 08
8300 RPM = 0x206C = 20 6C
So let's line it up and recreate the desired string:

Quote:
08 00
00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07
11 94 20 08 20 6C 20 6C 20 6C 20 6C 1F A4 13 88
The following is a table provided for those who don't want to calculate the hex values for the most common rev limits from 7900 to 9000 RPM (you're on your own if you spin your engine at 9k RPM!):

Name:  Screen Shot 2020-03-31 at 4.27.59 PM.png
Views: 433
Size:  134.1 KB