Knock control and J&S Safeguard
 

Does anyone have the J&S Safeguard?

I was looking into it but found out that the J&SS only controls the common coil to the leading sparks but not the two trailing coils. I am puzzled. When the J&SS detects knocking it can only retard ignition to the leading sparks. I guess you could get into a situation where the trailing sparks are actually fired ahead of the leading.

Would this be still effective in minimizing detonation?

I do have one but it is not in use at this time .Do you have a Power fc , if so then adjust the split so the J& S does not put the trailing before the leading if it hears knock .If you are using a stock ECU then you can just hope that the factory split is enough to keep the leading timming ahead of the trailing .With good tuning you should not need the J&S but I am not a tuner so I did have one in use untill the car was tuned by BDC.

someone made a knock unit that pulls BOTH leading and trailling, but its designed for haltech.
may be adapted to some other ECUs if they can be setup in a similar fashion.

and just like garco said, you have to make sure you run more split at all times than the J&S can pull in total or else your motor goes KABOOM

Yes, I understand with the Haltech, the TEC, and may be other programmable ECU you can adjust timing (and retard on knocking) individually on each spark. Not so with the PFC. The PFC only provides knock monitoring, looks like a step back from the stock ECU closed-loop control. I just wanted to hear from users since it appears the J&SS was en-vogue time ago (at least by reading the Robinette and Cirian collections).

The last time I spoke to John from J&S in February of 2005 he said he was working on a version for rotaries that would pull both leading and trailing ignition timing. Needless to say, I still don't think that product is yet available, which is disappointing since I would probably be one of the first in line to pick one up.

Many j&s units--the purple boxes--allow you to choose the maximum retard (i.e., 10 or 20 deg.) on a dip switch. If you use 10deg setting for max retard, you should be able to avoid negative splits in most situations, unless you're running low or no split. Some of the units can also be reprogrammed for 5 & 10 deg maximums.

The reality is that you only need to retard the leading spark to control detonation with any normal amount of timing and split. That being said, it will probably start some detonation right in this thread....

Yes, that's what J&SS told me as well. That they could send the unit programmed for 5-10 deg retard, and that I should keep the split L/T split above that.

I have one of the purple J&S boxes. I believe the stock split is 15 degrees and the max split on the J&S is 10 degrees the way I have it setup, but its been awhile so don't quote me on that. In any case, its hard to really say how well the unit works. Its definitely very sensitive, and the concept of what it does is valid, but demonstrating that it "works" is kind of like proving a negative. My engine hasn't blown up on me, but I don't know if I can credit the J&S. It's never pulled more than 2 degrees while I was looking at it, and usually it stays inactive. If you have it setup properly, it definitely can't hurt, and at the very least it provides yet another layer of protection as a sensor.

My one complaint about the design of the gauge is that the knock/retard light is difficult to use at night, since only one light comes on no matter how much timing is pulled and you can't see which one it is. A better design would be for more lights to illuminate as more timing is pulled. Some kind of audible alert would be nice too.

i run a late model J&S w my methanol injection...

the late models can retard IGL 10 degrees at the set of a switch.

it is important to have the model that inputs boost to an internal MAP sensor since you can set the unit to activate only in the boost areas of the map. the reason being that most run close to zero split in vacuum. you don't want to retard the leading 10 degrees w zero split.

my unit has a very nice series of red lights that do show the amount of retard...

i have yet to encounter retard as i haven't seen any knock yet but do expect the unit to help my motor out if i encounter alot of knock. i think it is an excellent product.

howard coleman

knock sensor j/s
 

i have the purple box j/s knocksensor with the harness for rx7 $250 plus shipping

Thanks Howard.

But why did the J&S designers decide not to retard the IGT? I have started investigating the J&SS to complement the Power FC, which does not have any knock control at all (only monitor). I have posted a similar question in the PFC section. One of the answers I receved was that retarding the trailing spark is not that relevant/ effective in avoiding detonation. However, I am still puzzled because I believe the stock ECU retards both IGL and IGT if it senses knock.

Back to your posting, this strategy of making the JS&S operational to certain MAP boost areas, wouldn't this impose limitations on the desired split? For instance, small or diminishing split angle with RPM to close to zero may not be possible.

I have also corresponded with John Pizzuto at J&S, who suggested to look into possibly connecting leading and traiing signals together, and fire them at he same time. He indicated that Carlos Lopez Racing (CLR) was doing this in '92, when they first started building units for the rotary. Could you please comment on that? - or, maybe I should start a new thread in the Rotary Performance section?

Most likely, these issues have ben discussed at length in the past. I apologize if I am asking old questions but I am a new active participant to this forum. I have searched back threads but did not find any comprehensive discussions.

Basically, I am just looking for layers of protection before starting modifying my healthy car.

Thank you again Howard and all of you who have been answering.

Sandro

man I wish there is something out there that would totally cut IGN all together in case of a large enough knock. One of my secondary injector wires BROKE OFF and i blew my shit up in a 3rd gear pull. I was so damn lucky I was just around the corner from my house.

I have had a J&S system for about 5 years. My conclusion is they provide a small margin of safety in pulling back timing but a huge margin in providing a warning. Over the years the unit has come in handy detecting when I get gas that is not up to par and cold mornings when the engine is not completely warmed up.

My opinion is they are worth the 2-300 used, they sell for now.

Sandro,

i am tuning up w pump and methanol and after reviewing all the safeguard options re a system failure decided the J&S was the best option. please see my thread in the new Auxiliary Injection section entitled, "80% pump, 20% methanol."

since the J&S can be set for 10 degrees max retard and since you don't want the lead firing after the trail i settled on 11 degrees split in boost. obviously other run less split but i would point out that there is a differing opinion as to the benefits of less split w some significant players running 10 plus degrees.

like many decisions, you weigh the plus and minus.... do i want to blow my motor if my alcohol doesn't come on or do i want to run a few degrees more split. it seemed like an easy decision.

if you look at my hp/tq results on page 11 post #164 of my thread i think you will find the decision even easier:)

a word of caution... i would not use any J&S unit that did not have a boost line input and internal MAP sensor. we generally run zero split in vacuum and if you were to get knock in vacuum and the unit retarded the IGL you'd be in the soup. my unit is set to kick in around 5 psi.

howard coleman

Thank you Howard, very useful information.

Sandro

Howard:

The "Start" knob only sets the boost retard start point.

Software enables knock retard when the vacuum drops below 10 inches.