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Old 06-23-2009, 12:58 PM   #1
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Default Cam signal idea for full sequential

I asked this question a month or so back on miata.net forum and although I got some helpful answers I didn't get a direct answer to whether my suggestion would work so I am asking here. Here's the plan:

I'd like to loose my modified Mk1 cam sensor which is supplying the required cam signal for sequential injection, as it takes up room at the back of the engine and looks messy.

My plan is to remove 4 of the 5 stainless steel studs holding one of my Flyin` Miata adjustable cam gears and replace them with titanium or aluminium studs. Setting a mag sensor in front of the cam gear aligned with the studs should then provide me with one cam signal per engine rotation.

So what do you all think? What are others running full sequential doing?
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Old 06-23-2009, 01:16 PM   #2
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we are running cars with built in CAS

you could get one of the future Boundary Engineering adjustable cam gears that has cam sensor tabs on it.
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Old 06-23-2009, 01:47 PM   #3
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we are running cars with built in CAS

you could get one of the future Boundary Engineering adjustable cam gears that has cam sensor tabs on it.
Sigh, walked right into that one. Wouldn't you like the extra space and cleaner look though?

Anyhow I checked boundary engineerings site just before posting this and couldn't see any reference to the sensor tabs?
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Old 06-23-2009, 02:13 PM   #4
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This is interesting...

Truthfully, I've never really thought about the behavior of a hall-effect sensor in the presence of non-ferrous trigger materials. But come to think of it, aren't the stock NB cam gears made of something other than steel? The NA gears certainly seem to be.

Actually, I think that the same principle as an eddy-current brake would apply here, since the hall effect sensors we typically use have an integral permanent magnet. Eddy brakes use non-ferromagnetic rotors or rails, and they work just fine.

So I question whether replacing a steel stud with a titanium or aluminum one would have any effect upon the sensor's ability to detect it.

(Also, I don't see anything about the Boundary cam gear that shows a sensor tab.)
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Old 06-23-2009, 02:42 PM   #5
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I'm using an Electromotive GM magnetic sensor. Given how the hall effect works I wonder what the difference is between a magnetic sensor and a hall effect sensor (separate options within the tuning software so there must be some difference - perhaps voltage output?).
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Old 06-23-2009, 03:01 PM   #6
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steve, check the boundary engineering section or search for posts by TravisR about the cam gear. it's too new for the site I guess.

https://www.miataturbo.net/forum/t33797-4/#post416806
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Old 06-23-2009, 03:44 PM   #7
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Originally Posted by slowmx5 View Post
I'm using an Electromotive GM magnetic sensor. Given how the hall effect works I wonder what the difference is between a magnetic sensor and a hall effect sensor (separate options within the tuning software so there must be some difference - perhaps voltage output?).
Is it a variable reluctance sensor perhaps? Or perhaps something stupidly simple like a reed switch?

How many wires coming out of it, and is there a shield?
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Old 06-23-2009, 03:54 PM   #8
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Is it a variable reluctance sensor perhaps? Or perhaps something stupidly simple like a reed switch?

How many wires coming out of it, and is there a shield?
Shield plus 2 wires, GND and signal. Here is the EM sensor sensor page. The magnetic sensor I am planning on using is 255-72218 (the same as the sensor used in the 60-2 tooth trigger wheel setup).
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Old 06-23-2009, 03:56 PM   #9
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electromotive calls it a "magnetic sensor". the trigger wheels are steel. the sensor has two wires and a shield.
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Old 06-23-2009, 03:58 PM   #10
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looks like they say any bosch motronic sensor will work... and have a list of sensors. seems easy enough to figure out.
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Old 06-23-2009, 04:03 PM   #11
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electromotive calls it a "magnetic sensor". the trigger wheels are steel. the sensor has two wires and a shield.
That's a VR sensor. Basically a coil of wire behind a small magnet, same as I'm using with my 36-1 wheel (mine's an OEM Ford piece). It outputs an analog waveform.
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Old 06-23-2009, 05:12 PM   #12
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That's a VR sensor. Basically a coil of wire behind a small magnet, same as I'm using with my 36-1 wheel (mine's an OEM Ford piece). It outputs an analog waveform.
Yes, puts out something very close to a square wave (hand held oscilloscope). So do we think this would work? I'd just need to mount the sensor just in front of the cam gear.
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Old 06-23-2009, 06:57 PM   #13
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The original CAS uses a hall effect switch and it is going to give a digital square wave pattern with a 0-5 volt range.

A magnetic sensor similar to ABS and 36-1 tooth crank wheels output an analog ac signal.

So long as the new sensor outputs a pattern that is recognized by the PCM it should be ok.

BTW, I just took my Tekscope out of moth *****, let me know if you need any waveforms.

Last edited by mrtonyg; 06-23-2009 at 10:17 PM.
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Old 06-23-2009, 08:45 PM   #14
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You can build a digital circuit that takes the miata's cam and crank sensors, and outputs a TEC friendly cam sync signal.
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Old 06-24-2009, 12:18 AM   #15
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You can build a digital circuit that takes the miata's cam and crank sensors, and outputs a TEC friendly cam sync signal.
not if you dont have them... i'm guessing he's got an early car without crank+cas and wants to get rid of the dual duty cas
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Old 06-24-2009, 09:15 AM   #16
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A wacky idea that I came up with a while back while thinking of how to add CMP back to my car w/o a CAS:

What if you mounted a hall-effect sensor on the top of the VC such that it read one of the lobes of a cam?
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Old 06-24-2009, 11:25 AM   #17
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wouldn't your waveform be a little soggy? you wouldn't have the rapid change in flux like you do with a square-cornered tab I'd think.
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Old 06-24-2009, 01:33 PM   #18
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not if you dont have them... i'm guessing he's got an early car without crank+cas and wants to get rid of the dual duty cas
Yes, I don't have them. The engine is a bit of a Frankenstien, '96 short block with FM 2L stroker whilst the top end is a fully worked '99 with VICs.

I guess what I need is confirmation that mounting a sensor in front of a cam gear with 4 titanium and 1 stainless steel stud will give me 1 signal per engine cycle. The TECgt only uses this signal to provide a rising voltage between 180 and 6 deg BTDC compression for No. 1 cylinder - it's just a sync pulse, so no real need for accuracy (60-2 tooth crank trigger provides this).

This method would be a little cleaner (no requirement for pull-up resistors, less to go wrong etc) than the OEM CAS mod on there currently and give more space at the rear of the engine.
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Old 06-24-2009, 02:33 PM   #19
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you have a 99 head... do you no longer have the front of the cam cover?
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Old 06-24-2009, 02:38 PM   #20
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Could you just use a taller bolt in that one hole? Or put some sort of funky washer?

Also, you could use a run of the mill hall switch and glue a magnet to any number of your existing bolts. I sort of like that. Should be really straight forward.
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