datalogging to decipher stock timing map

[zjasonz]

I am wondering if data logging can be used as a tool to read a factory ignition map if the megasquirt is run in parallel with the stock ecu. I intend to run a stock 2001 pathfinder vq35de in a datsun 280z. In the future I would like a single turbo upgrade. I want to be able to run either computer without much fuss so as I make changes I can always go back to the stock tune and drive the car. I searched but didn't find anything specific. More simply, is there a way to datalog actual ignition timing events and accurately map them vs rpm and load without controlling them? Any advice or links to relevant info would be greatly appreciated.

[LT401Vette]

You could use parallel logging with a megasquirt to generate some tables to a degree, like say an AFR target table, but spark timing really can't be done as the MS would have no way of knowing the spark timing or seeing when it occurred to log it.

[coyoteboy]

This would actually be quite an interesting project. Develop a logging box with a timing wheel pickup, spark output pickup and MAP pickup that basically just logs existing spark tables. It's the one side of my tuning that I find rather tough to achieve on road alone and there's dozens of timing maps out there on the net that with the slightest throttle knock away like mad so it's not even worth touching them. But if you could log the OEM...

[zjasonz]

Thanks for the responses. So I guess I first need to figure out how to pickup the spark output signal, maybe a tachometer? Then figure out how to input this signal to MS. Then graph this signal versus load and rpm. I'll keep digging.

Thanks

[trakkies]

You'd need an MS with two tach inputs. One from the crank, and one from the ignition output. Whilst this could be done and special software written I'd guess, I doubt there's the demand.

It would be easier to get the base advance curve by fitting a protractor and pointer to the crank pulley and using a timing light, logging the advance at set RPM points. That would be close enough as a starting point for a MS map.

Most crank pulleys have a vibration damper which is wide enough to take a scale. Measure the diameter and work out the circumference.
Using a CAD etc prog, draw a rectangle the length of the circumference and the width of the damper. Divide it into 360 degrees in 10 degree steps. Fill in the 0-40 or so part in single degrees, and print out to the real size. Make up a pointer from some wire and attach to a convenient bolt. Set the engine at TDC and glue the scale to the crank pulley with zero at the pointer. It would be easier to read if you print the strip with a black background and white scale.

[zjasonz]

That sounds like a great way to get the base advance curve very close to optimal. What is left are the tricky parts of the map that a dyno tune can reveal. I am curious about the possibility of accurately seeing actual timing. If the factory timing map could be duplicated before tuning fuel, I think the best tune might be quicker and easier to achieve especially with a qualified tuner. I suppose this is more complicated than I thought. Thanks for the good ideas. After playing with the MS on 2 different engines, I've come to appreciate the work that goes into the tuning on any vehicle. I really don't see myself pulling this off, just thinking out loud; however, from a DIY perspective this would be a great advantage, especially as a safe starting point to tune a modest single turbo upgrade. Off to read some more!

[trakkies]

Just a thought - have you done a search to see if the basic engine timing map isn't published somewhere? However, if it's an old engine, the ideal map today with an MS is likely rather different due to different petrol formulation.

[zjasonz]

Not an exhaustive one but I have searched for timing map databases. Since each motor is different I see that a database would only benfit people running bone stock motors which is not the goal of anyone using MS. I am starting to think that ultimately it doesn't matter and I should follow the same path as others. My two experiences tuning were with a worn out VG30ET with 325000 miles and a poorly built sbc 350. This time I'll be starting with something that already runs well. I plan to focus on wiring it in parallel and taking baby steps this time. If I develop a good map I'll share it on this board but that will probably be a long time from now. Until then I don't think I have anything useful to post and am starting to ramble.

[firefoxx04]

your obdII.. just run the stock ecu and see what the ign timing is via a logger tool

i know my buddies 95 eclipse had obdII (mitsu started in 95) and remember reading ignition timing when we were cruising. you could video tape it with a freind in the car and then later on look at the data and see what degree happened at what rpm.. do various videos.. one full throttle, one while cruising at certain speeds, and a few while part throttle.