Pages: [1]
Author Topic: On using KFLDHBN instead of LDRXN to set WOT req boost pressure  (Read 1036 times)
nyet
Administrator
Hero Member
*****

Karma: +416/-47
Offline Offline

Posts: 9226


WWW

The conventional wisdom is to use LDRXN to limit req boost. But it comes with a lot of (sometimes unexpected) side effects; the load -> boost path can be confusing and difficult to understand, in particular, its sensitivity to IAT and VVT angle.

Wouldn't it make more sense to simply use KFLDHBN instead and raise LDRXN out of the way? It can be tuned directly off of a compressor map. It is not sensitive to IAT (other than the obvious effect by axis), or VVT angle. It compensates for altitude naturally. It is a 2 axis map which allows for more flexibility (not to mention possibly easier map switching via dynamic axis change, etc.).

It seems to me the only reason LDRXN is exclusively used to limit boost in tuned ECUs is because aftermarket tuners discovered that map early on via reverse engineering, before FRs became readily available, and it has to be raised anyway.

Comments?
« Last Edit: August 31, 2018, 10:47:12 AM by nyet » Logged

ME7.1 tuning guide (READ FIRST)
ECUx Plot
ME7Sum checksum checker/corrrector for ME7.x

Please do not ask me for tunes. I'm here to help people make their own.

Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience.
nyet
Administrator
Hero Member
*****

Karma: +416/-47
Offline Offline

Posts: 9226


WWW
« Reply #1 on: August 31, 2018, 09:28:09 AM »

My rationale:

For stock cars, limiting the load makes the most sense; there is plenty of compressor map headroom to compensate for all altitudes and iats such that the driver experience is identical (i.e. more boost for higher temps and altitudes) during WOT.

But once you are tuned, the limiting factor becomes the turbo itself (other than timing limitations for shit gas).... and LDRXN stops making sense as a limit.
Logged

ME7.1 tuning guide (READ FIRST)
ECUx Plot
ME7Sum checksum checker/corrrector for ME7.x

Please do not ask me for tunes. I'm here to help people make their own.

Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience.
woj
Sr. Member
****

Karma: +20/-1
Offline Offline

Posts: 400


« Reply #2 on: August 31, 2018, 10:54:48 AM »

Certainly a comment Wink I am actually surprised this is brought up only now. This method is actually one of the first things that came to my mind when I was trying to understand ME workings with ME7.9.10 as my case study. There I raised LDRXN counterpart (there it is done by a torque limiter, not load, called MDMAXNMOT, but it is almost immediately recalculated to load) so that the max load would first hit KFLDBHN instead of the torque limiter to get the maximum factory safe power (under the assumption that whoever came up with LDBHN knew what he/she was doing). No ill effects whatsoever. On my ECU MDMAXNMOT is waaay above what the engine / turbo can do in very low revs, the actual boost meets requested only after 2000 (take into account that this is a tiny turbo setup). So I do not see any reason why MDMAXNMOT cannot be maxed out and boost controlled by LDBHN. And another map that limits load according to IATs, because on this ECU LDBHN is actually 1d and only RPM dependent.

Short version: this is what I actually did and it worked fine Wink
Logged
Palle
Hero Member
*****

Karma: +16/-13
Offline Offline

Posts: 548


« Reply #3 on: August 31, 2018, 01:30:49 PM »

Seen this also, but never tested. Using HBN instead we could get boost level vs temp. Less boost at higher gears =  lower egts maybe even more timing in higher gears = faster pull.
This deff needs to be tested.
Logged
Rick
Hero Member
*****

Karma: +62/-3
Offline Offline

Posts: 702


« Reply #4 on: September 01, 2018, 03:55:14 AM »

You should use both, that's what they are there for, it's pretty simple!
Logged
woj
Sr. Member
****

Karma: +20/-1
Offline Offline

Posts: 400


« Reply #5 on: September 01, 2018, 03:11:51 PM »

You should use both, that's what they are there for, it's pretty simple!

Depends what you are after. If you want an all-round drive that maintains, particular conditions permitting, output characteristics at different conditions / climate / altitude, then you go by torque / load making sure that you stay below turbo limits (what I understand factory tunes are). If, however, you want to show off your dyno plots / WOT power to your mates when maxing out your turbo then you may as well make the ECU hit LDBHN in the attempt to hit 100% torque. No?
Logged
Pages: [1]
  Print  
 
Jump to:  

Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Page created in 0.016 seconds with 17 queries. (Pretty URLs adds 0s, 0q)