rlm328

So far no problem, It revs and runs smoothly. I could probably go to more magnets, but as Tom said the Motec has a ton of computing power so it is deriving where the cam should be. Once you get over a certain RPM the injectors are just dumping fuel into the intake. So the duty cycle is like 65% at 4500 rpm and it just goes up from there, then it is just spark.

I personally think you can have too many reference readings and it can lose count especially the older ecu's, one of the reasons the sync is there so it can start counting again. Where my motor has trouble is at load speeds but that is primarily a mass issue as I have an aluminum fly wheel and a knifed crank which limits how much inertia mass I have. And on top of that I have a 4 puck clutch, so it can get interesting in the pits

odonnell

My concern would be spark timing angle rather than fuel. Especially in those low speed situations where the next engine speed update is still waiting up to 90 crank degrees plus has an inherent error from the belt stretching slightly (assuming that the timing table was tuned during steady states, no quick RPM changes). The Motec is really capable of course but it will only be as accurate as the signal it gets. Sorry if I come off as being critical, I'm in the process of building my 951's setup and I'm just interested in the pros and cons of different schemes. I agree that too many teeth are an issue, I went to a 36-1 on my red car because the ECU doesn't work well with the raw signal from the stock speed sensor... needs outside help for dividing the signal into smaller groups every sync. Not to mention the integer/division issue inherent to the number of teeth per sync vs the number of cylinders firing per cycle. Luckily a lot of the newer stuff is compatible because of the demand from Audi guys and improvements in processing speed versus cost/availability.

rlm328

You are here in Houston and when I get my car back together (hopefully I get my turbo this week) we can get together and you can see for your self. It so far hasn't had any problems, I was pulling over 425 rwhp at 16 psi, with the new turbo I am expecting 450, I don't believe in high boost to achieve HP but where it builds for track use. I will sacrifice HP at the high end for a faster onset of boost. But where the HP ends up is a we will need to see for now.

One of the reasons I went with the set up I did is I did not want a my sensor sticking out on a bracket. A lot of the sensors key off of a toothed wheel that go in front or behind the engine pulleys, and the sensor is on a low mount bracket. I have seen these systems knocked out of alignment due to an off. My system is keyed off the cam gear and all my sensors are hard mounted to the cam gear cover which moves them from a low mount to a high mount position hopefully removing it from taking a hit during an off. I could easily double the magnets I have mounted in the cam gear but I have not seen the need to. The Motec is an amazing ecu that has a lot of capabilities I will never use, it also has the flexibility to adjust to different sensor configurations. The ecu requires a minimum of 1 reference signals per revolution and I am using 4. There is one sensor out there that combines the ref and the sync signal into one. Be interested to see how that one is set up.

Tom M'Guinn

I agree the bigger challenge is the timing. Fuel is largely based on air/oxygen flow, but firing the spark plugs at just the right moment requires knowing exactly where the motor is. If the RPMs remain constant, you could in theory calculate the exact position of the motor with just one reference point, since every revolution of the motor takes the same amount of time and you can just calculate 10/360ths of that time to get 10 degrees etc. The challenge is when the speed of the motor is changing rapidly because you then need to estimate the speed of the motor based on the most recently available data. If the motor is speeding up at rate X, then you could estimate the current speed based on that rate and calculate your timing accordingly. That requires both processing power and well-engineered software, and will always be an estimate rather than verified data like you'd get with 132 teeth or a 60-2 flywheel, etc. On a race car that runs mostly in a narrow RPM range with predictable RPM changes, it's probably easier to get away with virtual timing like that, and I have no doubt MoTec does a good enough job that it works as a practical matter for most cars. I'm absolutely sure there is way way more to it than I understand, but I got a crash course when I grappled with making an ignition timing monitor (linked below). All the same challenges seem to apply, and even with 132 teeth and 2.72 degree actual resolution, calculating the virtual ticks in between the 2.72 degree teeth can make one's head implode.... In my case I was trying to calculate where the motor was when the spark fired, whereas the ECU is trying to calculate where the motor is in order to know when to fire the spark -- but it's essentially the same challenge...

https://rennlist.com/forums/944-turb...ing-gauge.html

neunfünfeins

I'll wager that the 'S' in 'S100' stands for 'Schottky' (as in diode)

Were we to dissect that chip I think we'd find that it could be replicated in a straightforward manner with off the shelf components.

Tom M'Guinn

Recreating it functionally with off the shelf parts doesn't seem like it would be that difficult. Filter out the negative cycles and anything over a certain voltage, and feed the filtered signal to a schmitt trigger to turn it into a square pulse. When the last S100 dies, maybe I'll give it a try

neunfünfeins

I meant to say Schmitt not Schottky... got my 'Scheisse' mixed up.
You have the right idea. Another way would be overdrive it into a receiver chip that would square up the edges and clip the peaks.
Have done that to turn sine into ECL clock before.

Tom M'Guinn

It's on my someday list. If nothing else, it might be helpful for guys who want to use the stock sensors with a stand-alone, perhaps with some active processing that produces a 60-2 pulse since 132 teeth isn't the norm.

odonnell

Most higher end standalones support the 132+1 pattern, FYI. A lot of Audi builds have similar setups and the vendors have added support for this style of pickup.

NCLA951

Tom M'Guinn