For anything related to the 'official' Speeduino boards (Eg v0.3, v0.4 etc)
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By 4art4
#64594
I am trying to set up my '91 v8 Mustang to a drop bear, using sequential fuel and spark. My plan is to first convert the distributor to a cam and crank sensor. Getting a single pulse from the existing hall effect sensor is as easy as cutting off 7 teeth. Getting a proper crank signal is a bit more of a pain. As I understand it, I need a multiple of 8 teeth for my 8 cylinders, and times 3 to get enough detail, 24 teeth. but the number of teeth needs to divide 360 evenly. However, because my signal wheel moves at cam speed, it needs twice as many teeth: 48.

Do I have this right? Is there an advantage to more teeth? Maybe I should go for 80 or 144? Is there a maximum number of teeth, if I can make 720 teeth work?
User avatar
By PSIG
#64597
While the number of teeth can improve resolution (to a point), the most common cam-speed tooth counts are 8, 12, 24 and 36. All of those (and others) divide 360 evenly. Add a cycle sensor with single pulse per 720°.

An alternative is to run one of those with one missing tooth for sequential without a second sensor (Missing Tooth Cam Speed decoder).

Yet another option is to use the Ford or aftermarket crank wheel (available separately) or a compatible damper unit, such as the Explorer GT-40 damper with 36-1 wheel. You'll have to check for length and such, as the Explorer front dress was a bit shorter than Mustang, so it may need a thin spacer? Not meaning to add to confusion, but... options. :lol:
User avatar
By 4art4
#64601
I really appreciate your feedback. This is my first go at a project like this, so I am being a bit timid and really want to nail down the concepts before buying/building things to just junk them. Also, the engine runs great right now, but the ECU is a prototyping rig with a battery that will quit on me and dump the map. (This happened once already, I have regrets.) The engine was built by a guy who really knows what he is doing (not me), but it was something he liked to experiment on a bit.


PSIG wrote: Sat Aug 26, 2023 5:20 am An alternative is to run one of those with one missing tooth for sequential without a second sensor (Missing Tooth Cam Speed decoder).
That would be one less sensor... I think this is the right choice, but I feel weird about building a speeduino-only device (rather than something that any mechanic and/or ECU would understand). But I guess I am in uncharted waters anyway. I could build my sensor a 48-1 at cam speed. Do ya think that is a good idea?


Yet another option is to use the Ford or aftermarket crank wheel (available separately) or a compatible damper unit, such as the Explorer GT-40 damper with 36-1 wheel. You'll have to check for length and such, as the Explorer front dress was a bit shorter than Mustang, so it may need a thin spacer? Not meaning to add to confusion, but... options. :lol:
3 reasons I was avoiding that: My engine bay is a bit cramped as the car is actually an NA Miata with an engine swap. The crank assembly is dynamically balanced, and I would rather not change it. The aftermarket trigger wheels I found were 4 pulse for some reason (I am sure it is a good reason, just not relevant to my goals).
User avatar
By PSIG
#64603
4art4 wrote: Sat Aug 26, 2023 4:11 pm That would be one less sensor... I think this is the right choice, but I feel weird about building a speeduino-only device (rather than something that any mechanic and/or ECU would understand). But I guess I am in uncharted waters anyway. I could build my sensor a 48-1 at cam speed. Do ya think that is a good idea?
It would confuse mechanics, but many (most?) aftermarket ECMs can read cam-speed wheels. Many Miatas (including turbo'd) are running well on stock 4-tooth wheels, to give a perspective on tooth count. While the real-world data is empirical, there has been no outpouring of demand or required benefit of higher-count wheels. Also, the tooth count is the available resolution, for any number of cylinders. You're starting with 8. ;) Is better... better? Sure, but by how much and is that necessary for your application? Well...

It is all perspective and judgment, and you have little to go on at this point. Understood. Perhaps you can save some time by trying what you have, simply adding a cycle sensor, and using the 8T that's in there. Test it! That's double the teeth of a Miata. Are the results good enough in your judgment?

Finally, consider the loss in accuracy by using the distributor, versus the crank for signals. You may be too tightly focused on teeth, when the basic system is less accurate through the timing and gear-drive slop. You have error to contend with before you start. ;) Not saying crank is the direction to go, but to keep all of your thoughts in-perspective and in-context.

Some of this perspective and context may be answered by why you are intending full-sequential? What are the goals and what do you hope to gain with that, and does that affect what triggering system you choose? This falls back to the beginning, with project goals and priorities, and whether your choices comply with them.

4art4 wrote: Sat Aug 26, 2023 4:11 pm 3 reasons I was avoiding that [crank wheel]: My engine bay is a bit cramped as the car is actually an NA Miata with an engine swap. The crank assembly is dynamically balanced, and I would rather not change it. The aftermarket trigger wheels I found were 4 pulse for some reason (I am sure it is a good reason, just not relevant to my goals).
Wheels are typically neutral-balance, so they do not affect current balance. There are 101 ways (at least) to mount a crank trigger wheel; on the pulley, mod the pulley, on the damper, the shaft, mod the flywheel, and so on. Likewise, there are many ways to source a 720° cycle signal, from the timing gear, the FP eccentric, a rocker arm, stub distributor, distributor shaft, and more, that may be simpler or easier than other choices, and allow other modes such as distributorless. Maybe that's now, or maybe that's later. Common stamped wheel example from Vems:
Ford_36-1_stock_wheel_adapt.jpg
Ford_36-1_stock_wheel_adapt.jpg (12.64 KiB) Viewed 11925 times
One comment that may be useful, is that anything you do, you will have done it differently when you're done. Do not regard, nor strive, to make the first iteration the final perfect version. It won't happen, you always learn more to apply, and it is a living project to develop - not create and ignore. Start simple and quick to get experience and perspective with this system. Enjoy the journey and the freedom of options and directions you could go. If you're not having fun, you're doing it wrong. 8-)

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