93BlackFD

is it possible to run the j&s with the powerFC?

will it control timing properly? how does it interface with the car?

Engberg

I thought, and could be wrong, that the Power FC has the features of the J&S Safegaurd already.

AMRAAM4

I'm far from an expert, but I too thought the PFC would cover this. Not so much by fixing the detonation issue as it occurs, but by providing the optimal setup via the right program for your mods/system so that you will not have any issues.

jramosrx7

They can work together, but you have to make sure their settings are coordinated. I forget what the issue is, but it involves the retardation caused by the J&S.

Recommend you search/post to the PowerFC forum and/or consult with the tuner from whom you are getting the PowerFC.

airborne

AMRAAM4 was right and also, and don't quote me on this but i had it explained that unless you have the stock ecu the j&s has the potential to do more harm than good. since the leading and trailing are run seperately you would require multiple j&s' to work properly. example: you put the j&s to retard the timing on the leading plugs, it reads noise from something like the power steering or some damn thing as a big knock, and retards the leading past the trailing. that would be bad. if you still want a j&s i have one for sale

Nathan Kwok

You need to make sure you run adequate timing split when using the PFC. Some tuners narrow the timing split (I think stock is something like 20 degrees) or eliminate it entirely, and if its too close, when the J&S retards the leading (it can't control the trailing), it could retard it so much that it fires AFTER the trailing, a big no-no. Obviously if you just leave the timing split alone then you're fine. PFC can't function like a J&S although it does give a readout of the stock sensor, which is nice.

Nathan Kwok

You need to make sure you run adequate timing split when using the PFC. Some tuners narrow the timing split (I think stock is something like 20 degrees) or eliminate it entirely, and if its too close, when the J&S retards the leading (it can't control the trailing), it could retard it so much that it fires AFTER the trailing, a big no-no. Obviously if you just leave the timing split alone then you're fine. PFC can't function like a J&S although it does give a readout of the stock sensor, which is nice.

es

I think the factory split is more like 15°, but the apexi default map has all kinds of "no-no's" in it. It looks like they generated it through knock sensor feedback & just used whatever came out of the test engine.

The problem with J&S's+PFC is that although your retarding the leading to reduce combustion pressure you're also reducing the split which has the inverse effect on combustion pressures. End result? Very little reduction in pressure making anything the J&S is capable of obsolete!

You're better off with correct EGT & WBO2 tuning, or reconfiguring the ignition to fire the leading & trailing together via the leading ignitor port (and running much less advance). For me it was easier to just produce a sensible ignition map...

Trout2

iTrader: (5)

J&S retards leading timing by up to 10 degrees. To use with the Power FC you need at least a 10 degree split between when the leading and trailing ignitions fire. It is dangerous for the trailing ignition to fire before the leading. There are spots in the base PFC maps where the split than 10 degrees. Doing a search for "J&S" and "timing split" will reveal more detailed information.

The J&S is another tool that can have benefits if used properly. Like many upgrades, if used or installed improperly it can do more harm than good.

Jack

AMRAAM4

Can someone point me in the direction of a good explanation of :
--timing
--leading
--trailing
--retarding
--timing split

es

http://personal.riverusers.com/~yawpower/jultech.html

http://www.rotaryengineillustrated.com/RE101.html

Howstuffworks.com

AMRAAM4

Thanks

remydrm

just by the definition, if the leading plug hasnt knocked, how can the trailing plug even have an opportunity to knock

remydrm

is there anyone that is in favor of knock sensors on a rotary? and what are the pros?

Nathan Kwok

Remy,
When you say "knock", you are probably thinking of pre-ignition, whereas rotaries suffer more commonly from detonation. They are not mutually exclusive, but pre-ignition is ignition before the spark, whereas detonation is the creation of a secondary flame front (think of a spontaneous secondary combustion occuring somewhere else in the chamber). The creation of this secondary flame front is what kills the engine, and it can occur at any point during combustion, including before the leading spark, after the leading spark, and after the trailing spark (although I don't think this ever happens in reality). The idea behind a knock sensor is to retard timing to reduce combustion pressures, which is one of the causes of detonation. The idea is the knock sensor will hear the occurance of the secondary flame front when it very tiny, retard igition timing the next time around, and therefore eliminate it. Detonation by its nature gets worse and worse every combustion cycle if nothing is done to stop it, so stopping it early can save a lot of damage. On a piston engine car the usual protection is your ears, you hear "knocking" and let off the gas. Rotaries do not have this luxury because by the time your hear the problem its already too late. The J&S can hear the knocking long before you could hear it, but the fact that it can only control leading timing does partially counteract its effect. I knew about this before buying it but I'd still rather have a device that retards only the leading ignition rather than nothing at all.

Nathan Kwok

Remy,
When you say "knock", you are probably thinking of pre-ignition, whereas rotaries suffer more commonly from detonation. They are not mutually exclusive, but pre-ignition is ignition before the spark, whereas detonation is the creation of a secondary flame front (think of a spontaneous secondary combustion occuring somewhere else in the chamber). The creation of this secondary flame front is what kills the engine, and it can occur at any point during combustion, including before the leading spark, after the leading spark, and after the trailing spark (although I don't think this ever happens in reality). The idea behind a knock sensor is to retard timing to reduce combustion pressures, which is one of the causes of detonation. The idea is the knock sensor will hear the occurance of the secondary flame front when it very tiny, retard igition timing the next time around, and therefore eliminate it. Detonation by its nature gets worse and worse every combustion cycle if nothing is done to stop it, so stopping it early can save a lot of damage. On a piston engine car the usual protection is your ears, you hear "knocking" and let off the gas. Rotaries do not have this luxury because by the time your hear the problem its already too late. The J&S can hear the knocking long before you could hear it, but the fact that it can only control leading timing does partially counteract its effect. I knew about this before buying it but I'd still rather have a device that retards only the leading ignition rather than nothing at all.

remydrm

what using the J&s with a Power FC?

Has anyone had good results with this setup ?