How many teeth?

[mxrob]

Hello all,

FI newbie who has and user install journals till my head is having "drop-outs". I'm trying not to ask the redundant questions but I'm suffering from information overload. So, I have: 650cc single cylinder motorcycle, uS with latest code loaded and communicating with Megatune. MAP, IAT, CLT, TPS all operating and calibrated on the bench. Fuel system worked out.

My impass: I need a multi-toothed wheel for more accurate timing control at low engine speeds(so I have read). The engine redlines at about 7800rpm. I'm planning on using the stock VR sensor on a 36-1 crank wheel that I will fabricate.... but I see posts where this does not work out.... one user ended up going with a 12-1 wheel because uS "can't handle the data" ??? MS manual says it can.... but a link to Lowell Technologies from MS says "For timing applications where the tooth size can be kept close to that of the sensor pole piece diameter, the V/R sensor is an excellent choice. It is not suitable, however, for applications requiring complex or multiple-width target profiles." So would even spacings between the target and gaps (as stated on MS) be more important than the target to VR sensor pickup width? Certainly my 36-1 wheel will have wider teeth than the sensor pole on the VR. If I make the targets the same size as the pole width, and gaps between them, there will be a very large number of teeth. I'm confused here......

[Paul_H]

Have a look at this website, it may be of some help.

http://www.aitekinstruments.com/pdf/cat08_sensors.pdf

[Matt Cramer]

That note about large teeth and multiple-width target profiles refers to things like the Dodge Neon crank trigger and other oddities that use the width of the tooth to communicate information and have teeth of different widths. For a 36-1 wheel, you're fine.

[mxrob]

Have a look at this website, it may be of some help.

http://www.aitekinstruments.com/pdf/cat08_sensors.pdf

Thank you. Any data is good at this point.

[mxrob]

That note about large teeth and multiple-width target profiles refers to things like the Dodge Neon crank trigger and other oddities that use the width of the tooth to communicate information and have teeth of different widths. For a 36-1 wheel, you're fine.

Thank you! I just wanted to make sure I was on the right track for my application. I do have one other question. I've read some installs where the poster said the missing tooth needs to be positioned in a certain location for the best results... based on what I've read (so far) it looks as though it really doesn't matter where the missing tooth is located. Is there actually a placement position that is ideal for the missing tooth?

[grippo]

The Delay_Tooth input allows you to move the timing so the first tach pulse starts anywhere you want. So you can configure in the software inputs. However if you end up with Delay_Teeth = say 30 teeth, then you will add that many teeth (basically an extra rev) to the starting process. In many cases this isn't noticeable, in others it is.

The only other reason to be concerned about a specific position is if you want to use a cranking trigger - that is - while rpm less than cranking rpm (a user input) it fires on a tach tooth without looking at table advance or trigger offset. So you can get the tach tooth within 10 deg using Delay Teeth but then you would have to position it closer by its physical placement. But with a 36 tooth wheel you really don't need to use a cranking trigger.