Need to brake your Q`s up in several parts.
The HALL sensor doesnt like to be used with a high teethcount wheel at high rpm. Some dont recomend to go over 36 teeth as it can loose track (a VR sensor doesnt have this issue)
I opted for 24 to be on the sure side and it is really enough resolution for this application. 15 degree resolution that is. Think of the AEM disk that have 24 teeth, but as it is mounted on the cam it is in reality a 12 teeth CRANK wheel. And thats 30 degrees pr tooth. That works good to.
A friend of mine got a Ford Cosworth and that car got a stock pully with 4 teeth and its running very accurate. Thats 90(!) degrees folks.Now the -1 part of a triggerwheel.
When i was about to order my damper i decided to order it as a plain 24 triggerwheel (not -1) with the thought that if i wanted i could always hack of a tooth if i wanted to. And i actually did, so i now run a 24-1 wheel.
Let me explain first how the ECU thinks when running a plain 24 wheel with a cam sync signal.
The cam sync signal occures a while before piston 1 comes up for its spark event. It cam yels to the ECU. Hey! here comes nr 1, start counting crank teeth NOW! And the ECU starts counting crank teeth until it sees fit to fire the spark. Then it moves on to the other cylinders until it gets the heads up from the cam again and starts all over.
The cam pulse should come somwhere in between two of the crank teeth. Now say i am running a 36 wheel on the crank thats 10 degrees between teeth. As the CAS is still ran by the cam with its stiff springs and belt harmonics and all that crap It will still flicker back and forth as explained earlier.
If the cam signal is timed to come in the middle of two teeth it will have 5 degrees to flop about in each direction. If it should flop about more than those 5 degrees at the time of the cam sync signal there is a chance it is on the wrong side of a tooth and tells the ecu to start to count at the wrong place. Now timing would be 10 degrees of. In my case it would lessen the chance of this happening as it is has 7.5 degrees in each direction before it ticks over, but IF it should do so my timing would be 15 degrees wrong. Although this probably isnt likely to happen i still decided to take meassurements to eliminate this potential probelm all together.
This is where the -1 wheels come into play. and why i hacked off the one tooth.
Here is what the ECU thinks with theese wheels.
The cam goes, HEY here comes nr 1 dude! The ECU goes, Understood! then WAITS for the -1 to pass before it starts to count teeth until it sees fit to throw a spark. As the -1 is on the crank and doesnt wobble around the potential problem described above is not there anymore. So all is good. So can you just run a -1 (or -2 or +1 for that matter) and ditch the camsync alltogether?
Yes you can run the engine on such a triggerwheel alone.
The ecu goes, There is the -1! 1-2-3-4-4.5. FIR----wait... what sparkplug do i fire? is it nr 1 or is it nr 3? Heck i dont know. I wish i had the cam signal to let me know if it is number 1 or 3 that is coming up for its spark. Think i better fire them both to be sure.. FIRE 1 AND 3!
Thats called running a wasted spark setup. Its the same with the injectors obviously.
So yes you CAN run it on a crank wheel alone. But you will not be able to run the engine in sequential mode. Only batch fire/wasted spark. And you would need to be running a -+1/2 wheel. A plain wheel with no missing teeth would not work as the ECU would have NO idea of where the crank is at. Thats my "short" answer.. ;)
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14:27:02 10/22/14
