Soft Limit. Why??? - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 01-09-2011, 11:50 AM   #1
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jan 2007
Location: Los Angeles, CA
Posts: 8,782
Total Cats: 119
Default Soft Limit. Why???

What's the point of a soft RPM limit? According to my Hydra manual, it cuts fuel. I haven't done a lot of it, but I've seen knock on my knocklite right where the soft limit comes in, which makes sense to me because I'd think that trimming fuel at 18psi would cause some detonation.

So, what's the point of this setting? Do I have anything to lose by setting it to the same RPM as the hard limit?
Faeflora is offline   Reply With Quote
Old 01-10-2011, 08:17 AM   #2
Elite Member
iTrader: (1)
 
Join Date: Jun 2006
Location: Warrington/Birmingham
Posts: 2,658
Total Cats: 39
Default

Soft limits are usually a spark retard, pulling straight fuel is kinda harsh.

The point is to slow the addition of rpms as you near the redline, makes actually hitting redline a lot less harsh (on you and the car).
richyvrlimited is offline   Reply With Quote
Old 01-10-2011, 11:29 AM   #3
Senior Member
iTrader: (4)
 
Join Date: Jan 2008
Location: Falls Church, VA
Posts: 1,367
Total Cats: 16
Default

I have my soft limit set to retard spark to 10* at 7000 rpm, with the hard cut pulling fuel at 7200. At 100 kPa under WOT (not turboed yet) I'm usually running 28* advance, so you definitely notice when you hit the limit and it retards to 10*, but it's not so hard as to upset the balance of the car too badly if I happen to be accelerating out of a corner when it happens. Also because the car is not yet turboed, that 200 rpm difference between soft & hard cut gives me enough time to react and get the shift done.

In practice I don't make a habit of hitting either soft or hard cut. The stock tach reads a little high and I usually shift when that reads 7000 or just a hair above, which is only about 6800 rpm in Megasquirt's reality. I'm only doing HPDEs so far, I just don't need to wring the last 100-200 rpm out of it while hitting the limiter before every shift.
ScottFW is offline   Reply With Quote
Old 01-10-2011, 12:13 PM   #4
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,367
Total Cats: 1,331
Default

I don't use the soft-cut limiter. Retarding timing like that up top just spikes the EGTs. If I rev to 7400, I want the car to make as much power as possible at 7350rpm.
Savington is offline   Reply With Quote
Old 01-10-2011, 12:19 PM   #5
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,196
Total Cats: 2,583
Default

I think soft cut might be beneficial if you want to set up flat-foot-shifting.
Though most new ecu's have that as a seperate feature.
18psi is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Raleigh: Fiberglass headlight scope, 1.6L ECU, AFM, Hardtop latches, more bigmackloud Miata parts for sale/trade 13 09-22-2017 01:34 PM
Leaky Wilwoods mx592 Suspension, Brakes, Drivetrain 1 10-01-2015 01:45 AM
Upgrade my MSM coilovers springs or KW ? elior77 Suspension, Brakes, Drivetrain 14 09-17-2015 10:20 PM
Jeep soft top help aidandj Insert BS here 1 09-15-2015 09:09 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 09:27 PM.