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RB Trigger spacing

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Hi everyone!

I am planning to make my own trigger system for the RB25DET with 2 hall sensors, a 12-1 wheel at crank, and 1 tooth on the cam.

I dug deep into the topic and found a lot of different recommendations. But also questions. I draw a timeline map of where I want to place my triggers based on the things I read, but I'm still not sure about the placement of the cam home signal.

I am using an ECU Master EMU black, and the maximum angle it allows between the trigger tooth and TDC is 120°. Which is enough, i planned 60°.

I've heard I have to put everything into the compression stroke before 1st igniton event. Since I'm using a 12-1 tooth wheel, every tooth is 30°, so the triggers are a bit close to each other. The first question comes here. Since the ignition events are happening 120° from each other, do I have to place all the triggers within 120° before 1st ignition event, or does it not matter? if the home event happens lets say on the 4th. ignition event, will it confuse it? My understanding of it is that it should know via crank where it is in the cycle, but on the other side, i couldn't really find a way to tell the ECU that hey, the home signal should be here. I don't want to troubleshoot for hours just because i placed the triggers to early or too late compared to each other.

The next thing is, that I heard that the home should not be close to the missing teeth, and it has to be before that. Also I should align it, so it will occur between 2 crank tooth. Well, if everything has to be between 180, then barely, but I have space for it. i will also set it to watch rising to be as far as possible from the mising teeth (tho 15 degrees of play should be enough).

I am pretty sure something is not right with the way I planning it, and all my confusion is coming from the home signal placement. Another thing, I planning it like this so i don't have to type in lagre amount of ignition offsets. i want it to do it nice and clean. I could also space them out better if i would make a 24-1 crank wheel, but im not 100% sure if that is still low enough res for the hall sensor at high rpm. (7200 max).

Here's the plan! what did i do wrong? (bit of extra confusion, ecu master counts the teeths from 0)

Attached Files

What sensor are you using? If it can only cope with a 12-1 at 7500 rpm, it does not sound like it is the correct sensor. I would look for a OEM crank trigger from a vehicle that runs either a 36-2 or 60-2 trigger so that you know that you have the correct type of sensor. Also note that Hall effect sensors that are designed for use as a wheel speed sensor quite often do not like being used with missing tooth triggers and their internal error correcting can generate a false signal to fill in the gap created by the missed tooth.

The ECU Master should support a 36-2 trigger wheel, this will give you more accurate timing compared to the 12-1 trigger. You would need to check the sensor specifications for the minimum tooth dimensions.

Personally, if you are going to this level, I would not use the OEM CAS location for the crank trigger, I would move it to the crank (allows for a bigger trigger wheel as well, so you can fit more teeth in) as this is what you are actually wanting to calculate the position of. I have seen data from testing the CAS, where there was a 36-2 trigger on the crank, and a 12-1 in the CAS housing, and the 12-1 had a variance in position relative to the crank of ~+/-7 degrees at higher engine speeds.

Yes, sorry if it wasn't clear. I am planning to separate the cam-crank trigger. one on the crank (12-1) like the PRP one, and a 1 tooth "gear" on the cam for home. I kind of realized that a bit higher res wheel would be better on the crank, like a 24-1. (or maybe a 36-2 as you recommended)

I would like to stay with the hall sensor, because for my logic thats easier to set up. I haven't decided which hall sensor i am going to use, the whole setup will be a custom one, and now im at the planning stage to decide what will i use. Although there are things i don't understand clearly, which would affect my tooth count etc.

I've heard that the home signal on the cam shouldn't align with the missing tooth on the cranck, and that it should be before the crank sensor would hit the missing tooth, and also i should put it as far away from that as possible. well, so far so good, but.. i've also heard that the home signaling should happen on the compression event (before #1 ignition event), which, if true, would not leave me much space to play with, if the available space for it is between the missing tooth and start of compression. Another thing, which is my own speculation... is the home signaling should happen between #6 ignition event and the next #1 ignition event? because then the time frame/spacing for it is really tight.

Also, since the emu black only allows 120 degrees of ignition timing adjustment, i really have to plan it good so it wont happen 360degrees later in the exhaust stroke.

So my question is, do i really have to place the home event that accurately, or it doesnt matter when it happens, it just has to happen somewhere before the missing tooth of the #1 igniton event?

Hello Peter!

I'm not sure why you say that the EMU Black only allow for 120deg or adjustment. You can offset the ignition outputs to achieve virtually any angle as you need.

You are right, the home and crank signal shouldn't be aligned as it will get the ECU confused on the number of teeth present after the home signal, especially if there is some timing belt stretch. Home signal should be happening between two crank teeth as much as possible.

I'm just curious, are there any reasons why you don't want to use an off the shelf kit like the PRP one you mentioned? I've installed many of them on EMU Black with great results.

Ohh, thank you, it's good to know, i didn't know that you can offset it somewhere, i am going to look after it then.

I am not planning to use an off the shelf one because i have acces to a laser cutter, cnc machines etc. So imo it would be a smart move choose the cheaper option if i can, since i can achieve the same result.

I understand the part that it could get confused if they are on the same place, what i dont know is how far should i place the home tooth from the missing one, and if there is a max "distance" or there isn't. Will the ecu get confused if i put the home let's say between 5th. and 6th. ignition event? so do i definitely have to place it between 6th. and 1st.? or it does it not matter? Will it finish the igniton cycle, no matter when will it get the home?

There is no "safe distance" that you need to put your home from missing tooth. As long as the home doesn't occur during a missing tooth.

The way the ECU will interpret the trigger with a single home signal and missing tooth :

1. Wait for the home signal.

2. Once found, wait until the primary trigger sees missing tooth/teeth.

Then there is 2 options :

3a. If your trigger is set as missing tooth, the first tooth after the missing will be number tooth #0.

3b. If your trigger isn't set a missing tooth, the first tooth after the home signal will be tooth #0.

I would suggest if you haven't done so to check the manual at this link, from page 95.


Hope it helps,


Thank you very much. It's fully clear now, i am going to check the manual too.

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