Soft Rev Limit & Boost - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 04-30-2012, 01:43 PM   #1
Newb
Thread Starter
 
Join Date: Feb 2012
Posts: 3
Total Cats: 0
Default Soft Rev Limit & Boost

According to the 2.6 Hydra users manual, the soft rev limit "begins to cut fuel events to reduce torque output and produce a “soft” limiting effect on engine speed."

Since it is a rev limiter it is typically going to be doing this at high rpm and high load (max boost).

I would think pulling fuel under those conditions, especially on a boosted car, would be a very bad idea. Am I missing something here? Should I set my hard rev limit lower than the soft and let it just cut ignition to begin with?
disney7 is offline   Reply With Quote
Old 04-30-2012, 08:27 PM   #2
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,669
Total Cats: 1,560
Default

Quote:
Originally Posted by disney7 View Post
According to the 2.6 Hydra users manual, the soft rev limit "begins to cut fuel events to reduce torque output and produce a “soft” limiting effect on engine speed."

Since it is a rev limiter it is typically going to be doing this at high rpm and high load (max boost).

I would think pulling fuel under those conditions, especially on a boosted car, would be a very bad idea. Am I missing something here? Should I set my hard rev limit lower than the soft and let it just cut ignition to begin with?
I wondered this also but never got around to asking. Also wondered the same for the fuel cut on overboost protection.
sixshooter is offline   Reply With Quote
Old 04-30-2012, 10:41 PM   #3
Elite Member
iTrader: (2)
 
Join Date: Jan 2007
Location: Los Angeles, CA
Posts: 8,782
Total Cats: 119
Default

It will cut fuel sprayed per combustion stroke

Now auck me
Faeflora is offline   Reply With Quote
Old 08-15-2012, 12:16 AM   #4
Newb
iTrader: (1)
 
Join Date: May 2008
Location: Pickering, Ontario
Posts: 32
Total Cats: 1
Default

My understanding is, as you thought, that cutting fuel on a boosted engine is a bad thing. So using the ignition cut out is much safer.
dynodragon is offline   Reply With Quote
Old 08-16-2012, 02:31 PM   #5
Elite Member
iTrader: (3)
 
concealer404's Avatar
 
Join Date: Aug 2011
Posts: 8,465
Total Cats: 782
Default

It probably cuts it completely... many stock turbo cars have a fuel cut overboost protection on them. It was fine.
concealer404 is offline   Reply With Quote
Old 08-17-2012, 10:39 PM   #6
Newb
iTrader: (1)
 
Join Date: May 2008
Location: Pickering, Ontario
Posts: 32
Total Cats: 1
Default

Quote:
Originally Posted by concealer404 View Post
It probably cuts it completely... many stock turbo cars have a fuel cut overboost protection on them. It was fine.
Yes, and fine for the safe boost that OEM's use. Pushing 15+ psi on an engine not originally built for a turbo is a different scenario. If you have the capability of choosing fuel cut or ignition cut, why not choose the latter and eliminate the lean mixture risk?
dynodragon is offline   Reply With Quote
Old 08-18-2012, 01:34 AM   #7
Elite Member
iTrader: (2)
 
Join Date: Jan 2007
Location: Los Angeles, CA
Posts: 8,782
Total Cats: 119
Default

Quote:
Originally Posted by dynodragon View Post
Yes, and fine for the safe boost that OEM's use. Pushing 15+ psi on an engine not originally built for a turbo is a different scenario. If you have the capability of choosing fuel cut or ignition cut, why not choose the latter and eliminate the lean mixture risk?
Not how fuel cut works. Typically revlimit cuts a percentage of ingnution or fuel events. If there is no fuel in cylinder, you are not lean. There is just air. Nothing to burn.
Faeflora is offline   Reply With Quote
Old 08-18-2012, 10:49 AM   #8
Elite Member
iTrader: (3)
 
concealer404's Avatar
 
Join Date: Aug 2011
Posts: 8,465
Total Cats: 782
Default

Quote:
Originally Posted by dynodragon View Post
Yes, and fine for the safe boost that OEM's use. Pushing 15+ psi on an engine not originally built for a turbo is a different scenario. If you have the capability of choosing fuel cut or ignition cut, why not choose the latter and eliminate the lean mixture risk?
Not how it works.

Quote:
Originally Posted by Faeflora View Post
Not how fuel cut works. Typically revlimit cuts a percentage of ingnution or fuel events. If there is no fuel in cylinder, you are not lean. There is just air. Nothing to burn.
How it works.


That said, if i had the choice, i'd go with ignition as well. Mostly because i'm a ricer and think it sounds cool.
concealer404 is offline   Reply With Quote
Old 08-18-2012, 02:30 PM   #9
Elite Member
iTrader: (2)
 
Join Date: Jan 2007
Location: Los Angeles, CA
Posts: 8,782
Total Cats: 119
Default

Quote:
Originally Posted by disney7 View Post
According to the 2.6 Hydra users manual, the soft rev limit "begins to cut fuel events to reduce torque output and produce a “soft” limiting effect on engine speed."

Since it is a rev limiter it is typically going to be doing this at high rpm and high load (max boost).

I would think pulling fuel under those conditions, especially on a boosted car, would be a very bad idea. Am I missing something here? Should I set my hard rev limit lower than the soft and let it just cut ignition to begin with?

The purpose of soft and hard limit is for driveability.


Quote:
Originally Posted by concealer404 View Post
Not how it works.



How it works.


That said, if i had the choice, i'd go with ignition as well. Mostly because i'm a ricer and think it sounds cool.

Yah. It is cool. Actually it is frikken awesome. One of te joys of turbo car
Faeflora is offline   Reply With Quote
Old 08-18-2012, 02:52 PM   #10
Junior Member
 
Join Date: Jan 2011
Location: sacramento ,ca
Posts: 402
Total Cats: 46
Default

Quote:
Originally Posted by concealer404 View Post
That said, if i had the choice, i'd go with ignition as well. Mostly because i'm a ricer and think it sounds cool.
x2
fastivab6tg25mr is offline   Reply With Quote
Old 08-19-2012, 06:10 PM   #11
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,669
Total Cats: 1,560
Default

It washes down the cylinders, increases the chances of fouling the plugs, sends your turbine housing temps through the roof, and will add quite a bit of spool to your turbo when you might be trying to limit boost (if you are using it for boost cut and not rev-limiter).
sixshooter is offline   Reply With Quote
Old 09-03-2012, 10:16 PM   #12
Newb
iTrader: (1)
 
Join Date: May 2008
Location: Pickering, Ontario
Posts: 32
Total Cats: 1
Default

Quote:
Originally Posted by Faeflora View Post
Not how fuel cut works. Typically revlimit cuts a percentage of ingnution or fuel events. If there is no fuel in cylinder, you are not lean. There is just air. Nothing to burn.
Right. Thanks. I looked up my Hydra manual and it describes cutting 40% of the injector cycles...
dynodragon is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 58 Yesterday 10:04 PM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
Going back to stock. Need some 1.6 parts. Trent WTB 2 10-01-2015 01:15 PM
Leaky Wilwoods mx592 Suspension, Brakes, Drivetrain 1 10-01-2015 01:45 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 02:27 AM.