Jump to content
Sign in to follow this  
Chipset

sr20det rpm limiter

Recommended Posts

I wanna ask about the rpm limiter before i fine tune mine .   ( Car = Silvia s14a - sr20det )

 

What i noticed  after tuning my car with my new link ecu is that the limiter ( the default one not with the advanced options enabled ) is much softer that the stock my car had .

 

In sound terms  the stock rpm limiter  sounds like a very loud TAK TAK TAK ( like a weapon is firing )   and the default  Link one is more like a  smooth  FROOP FROOP FROOP if you get what i mean.

 

After searching about how the stock limiter which i think its safe  ( it has to be as its the stock one )  i found this :

 

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 There are actually 2 rev limiters in the stock ECU (3 counting the stationary rev limiter, which is converted to a launch control rev limiter in TunerCode). One is a hard fuel cut rev limiter that cuts all 4 injectors at the limit with a stock hysteresis of 500rpm. The other is a soft cut rev limiter that cuts 1 injector at 150rpm below the limit, 2 injectors at 100rpm below, 3 at 50rpm below, then all four at the limit. The resolution for the limits and hysteresis is 12.5rpm.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 

I don't know if this is exactly the way the stock ecu handles the limiter  , but im curious about how is it possible to make my rpm limiter to work as the stock one and if there is something that i must afraid of ( i was spending too much time on stock rpm limiter due to drifting and never had any problem )    .

 

Some rumors  speak about broken rockers  cause of hard limiter  during launch control or even the normal rpm limiter.

 

 

ps : Im using the default fuel cut rpm limiter without any adjustment of the advanced options yet.

 

 

Thank you

Share this post


Link to post
Share on other sites

I wanna add that it seems tha the stock ecu first cuts ignition and after that the fuel cut take over , but in link ecu the type of rpm limiter that is " ignition + fuel cut "  described in the help file as A ROTARY ONLY  and i feel confused , please can someone explain about this .

 

Thank you

 

Share this post


Link to post
Share on other sites

As per the quote from the Tunercode vendor in your post, the stock ECU is a fuel-only limiter.  This isn't an issue on standard engines, but once you start turning the wick up it can cause detonation when on the limiter.  Set your limiter to IGN cut.

Consider that a harsh limiter like the factory one introduces some pretty severe accel / decel forces onto the engine, including the valve train.  This could in certain situations cause the engine to throw a rocker.  If you keep the limiter smooth, then you avoid this scenario and the car should become easier to control when you're sideways and hitting the limiter, as you're giving the engine/drivetrain/suspension/tyres a more gradual reduction (and reintroduction) of power.

Share this post


Link to post
Share on other sites

Thank you Kieran I can understand the part for the hard limiter accel /decel but as for the fuel cut limiter and detonation i think that detonation occur when ( let say that our ignition advance is right ) burning very lean mixtures , so the question here is how exactly does the link limiter is working when you have it set it up as Fuel cut ? Does the soft limiter allow the engine for some time to burn lean mixture ? Or is it only changing the rate for completely shutdown the injectors ? The only thing that is sure is that when you shut your injectors and you have only pure air going in there is no chance of detonation. As for the Ignition limiter i still don't know if it is so good especially in drifting that you spent time on limiter cause of the extreme temperatures that gonna build on your turbo , manifold from the unburned fuel that ignite and the excess fuel that may wash you cylinders and find his way to the oil pan . I'm hoping for an answer from someone in Link that know how exactly is the fuel cut limiter working , that may help me - us decide Im also wanna know about the Fuel + Ignition limiter mode that is described as ROTARY ONLY there has to be a reason Thank you

Share this post


Link to post
Share on other sites

Here is how the current rev limiter works. There is a cut within the control range (smooth cutting), then there is a hard cut following that. The control range cut is all based around a percentage cut. The percentage can be considered a percentage of power reduction. The control range is below the RPM limit set in the table. In the advanced settings you can adjust the percentage cut at the start and end of the control range. The percentage cut at any point within the control range is interpolated from the start and end cut. The percentage is the number of missed firing events over a fixed number of firing events. Say for example the fixed number of firing events is 32 and the percentage cut is calculated to be 25% at a specific RPM. This means that over the 32 events, 8 of them will be missed, this spread out across the 32 events means that every 4th event will be missed. Hence reducing the power output from the motor by 25%. This same principle works for any given percentage. The hard cut is obviously all cylinders completely cut until the RPM falls below the hard cut activation. Adjusting the start and end cuts controls how aggressive the limit comes on. You will notice that there is a TPLow and TP100%, this if for correcting the start cut based engine load. (You don't need such an aggressive cut at lighter loads). This system of cutting allows you to have a limit that holds a perfectly stable RPM. Having a perfectly stable RPM limit allows for much more repeatable launches when using launch control. The choice between fuel and ignition cut is based on the application, there are pros and cons to both. Launch control typically calls for ignition cutting as it allows fuel to burn in the exhaust, banging and helping the turbo to spool up. With ignition cutting the chance of detonation is very small. The downside to ignition cutting is the banging in the exhaust can force the exhaust valves open, this can take load of shims (they may fall out) or it could allow a hydraulic lifter to pump up meaning the exhaust valve won't close fully. Heavy duty valve springs protects against this problem. The final problem with ignition cut is that it destroys catalytic converters, hence stopping factory from ever cutting the ignition. Fuel cutting eliminates the banging exhaust and keeps the exhaust valves happy, but can punish the bottom end instead. Detonation is common when fuel cutting (explained by Kieran's last post). Even factory cars detonate on the fuel limiter. Even though detonation is not ideal, engines can withstand it, as long as its not too extreme. When Nissan designed its factory rev limiter they probably weren't thinking that people would drive down the road wide open throttle on the rev limiter, although in saying that the cars were sold with a warranty. Rev limiting is never going to be good for the engine, but if its necessary do it and you engine will probably be fine. I know from experience that stock sr20 heads don't like ignition cuts as the hydraulic lifters pump up and hold the valves open, causing the motor to run on less that 4 cylinders for a few seconds. There is rev limit ignition trim which is ideal for fuel cut as it reduces the chance of detonation. If you want your fuel cut to be more aggressive like the stock, turn advanced mode on, change the control range from 200 down to 100, and you will start to see results. The next thing to do is increase the start cut values. Hope this points you in the right direction.

Share this post


Link to post
Share on other sites

Yes you are correct, the smoother the cut when cutting fuel, the higher the chance for detonation. I suggest having an aggressive fuel cut. The 'rotary only' cut is a special cutting method designed for twin rotor engines. It cuts the first rotor then the second rotor with both fuel and ignition. If this mode is selected on a piston engine, no cutting will be performed.

Share this post


Link to post
Share on other sites

One last question about the limiter is : Whats the difference between having the end cut = 100% and having the hard limit enebled ? Hard limit suppose to be 100% fuel , ignition , or both cut ( source link manual ) Thank you

Share this post


Link to post
Share on other sites

The difference is nothing. The advantage of this is you can set your end ignition cut as 100% and put your hard cut method as fuel with the hard limit activation set to 0. This cuts both fuel and ignition so you won't get a big fuel dump into the exhaust. (Reduces the huge explosions.)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×