Are they worth it???? Also where is the best place to buy it for service and price???

thanks Guys

 

Depending on what you already have on your car, the money could probably be better spent else where.

 

I've got one waiting to be installed. Mahjik--do you think I should hold off?

I've got a huge SP, DP, MP, CB, IT, IC, 1300's, FP, PFC, Stock twins.

worth it?

-BN

 

Single turbo setup
Power FC
All the Fuel Mods
yada yada yada

 

From what I understand, the J&S system (at least the older one) only worked on the leading, not the trailing and detonation can be trailing as well.

I guess if you can add the sensor to both, then it would be a worth while upgrade for both of you guys.

 

Here's a good thread with more info:

https://www.rx7club.com/forum/showth...hreadid=167767

 

could you explain that a *bit* more? I'm new to the timing thing. I'll be right in that neighborhood replacing the plugs & wires tomorrow, so I was thinking about installing that monstrosity too.

-BN

 

Hehe, we replied at the same time. Check that link, there is a good explaination of the J&S system there.

 

I think it's a big hoax, I have friends who have J&S and they dont' do anything but trip out and retard the timing. I had a friend who used to have one and when he had his car dyno tuned, the j&s unit was tripping out on the dyno and it was hard to tune because the damn thing kept retarding the timing. At the end, they gave up and tore the thing out and the car ran fine afterwards.

 

I hear that is what most people do, they install one, get to a dyno and it acts up and they can't control it, and rip it out and take the risk of detonation.

 

I had one then ended up getting rid of it.

It has two main draw backs.

(1) You have to adjust the sensitivity which controls how
fast it reacts to knock or noise. Too little and you will not have any protection, too much and you loose power or even can cause pre-ignition or detonation.

(2) It only retards the leading plug timing. This prevents you from running a close timing split. If the J&S retards the leading enough, it can cause a negative split situation and that can also blow your engine.

I was running 10 degree timing split under boost, and with low knock levels on a datalogit, the J&S was retarding. The retardation itself caused more noise until it was causing negative split. This made it retard more until we heard light pinging. When I turned the sensitivity down, then it would not come on at all.
The datalogit log showed it all. Turned the J&S off and relooged a run with no knock problems. That is when I got rid of the J&S POS!

If they would make one that controlled both leading and trailing, then it would be OK. For our engines, it would require three normal units using the same knock sensor and running the exact amount of senitivity. Hard to do and too expensive.

 

Anyone out there like the J&S? I never hear anyone say much good about it.

I'm getting a car that has one and will need to decide if I should keep it or not. Car is fairly stock. Only DP.

 

Just curious...why three units and not two?

 

#1: Leading ignition
#2: Trailing 1
#3: Trailing 2

The leading plugs for both rotors fire at the same time in a "wasted spark" configuration. That means you can use one J&S unit, since there is only one coil shared by both rotors. The trailing plugs do not fire together, so you would need one for each.

I wonder if J&S makes a multi-coil system in one box, kind of like the DIS-2 and DIS-4 ignition amps from MSD? Perhaps you could use a 1-channel and a 2-channel box together, or use one 4-channel box and just not use one of the channels.

-Max

 

Thanks maxcooper, good explanation.

J&S makes a four-channel unit, if it would work better than the single channel for an RX-7, why don't they sell it that way?

I'll email John Pizzuto and ask him.

 

You are definetly supposed to bypass the J&S when dyno tuning your car.
It is crazy to even try to dyno tune with a J&S connected.
However, it is a nice visual knock monitor if you re-connect it after dyno tuning.
After tuning, you may even want to take advantage of bieng on the dyno to re-adjust the J&S sensitivity so it does not retard needlessly.

The retard range needs to be set correctly, depending on your split. Setting the retard range too high will allow a potential neg split to occour. If you have a 10 deg split a 20 deg retard range will definetly cause a problem. The 10 deg range setting will certianly be more appropriate in that case, as would a slightly higher split.

The sensitivity should be set low enough so that it will only retard if there really is detonation.
If your car is not detonating then you should not see any retard on the J&S, if it is set right.
Be aware, it does false a lot when the engine is cold.
Set it so that once your engine is fully warmed up, you never see >2 deg (1 led) of retard.

Keeping the sensitivity low is the key for those of you who don't want to loose power needlessly.
If you have a dyno tuned ECU then you will be safe with lower J&S sensitivity than someone who does not have dyno tuning.
Also, know that the J&S needs re-adjusting with every power adding mod.

I also agree that the $600 it cost is better spent towards a new ECU and a dyno tune.
To date I have not seen much benifit from it other than confirming that I get lower knock readings when mixing in some 100 octane gas at the track.
I have no plans to get rid of it though.
I don't know if it can save an engine but it can alert you to a potential problem situation.