Looking for help on ignition advance curve

[Guest]

Hi all,

although not with racing intent, I think this subforum will be the best to ask this... I have just started work on a diy project to convert the ignition of my GSX400E engine to a programamble unit with vacuum advance. I am looking for ways to determine a basic timing curve, of course I will need to fine tune it when it's up and running. I have found some 'rules-of-thumb' for car engines which might translate to bike engines as well, but for instance the standard unit curve / setting would be nice to know.

Any input is welcome,
Cheers,

Hugo

BTW, this is my first post here, I will take some time later to introduce myself and share pics of my fully customized bike project in progress.

[Brendan W]

Hi HugoW and welcome. Interesting project.
This http://members.dslextreme.com/users/bikecliff/ has a service manual for the GSX400 which should have details for static and full advance angles.
Am I correct in assuming you are looking to advance at part load. What device are you planning to use and where is it going to be put ?

The advance information should be in the specifications section. For comparison my 850 is 17 degrees below 1500 rpm and 37 degrees above 2350 rpm. When you consider it the bike is operating fully advanced most of the time.

[HugoW]

Hi Brandon,

thanks for the quick reply and info. The curve as you describe is the full load curve, required at WOT. As soon as you run part load, less than WOT, the ignition timing can be advanced further. This saves fuel and makes it all run smoother.

The link you gave gives me a screen full of programming language, I fear there is something wrong with that site.

I am quite handy with Arduino, and I have recently stumbled across a variant called Teensy (version 3.2) which is the same in use as an Arduino, but a lot faster in processing. For what I have in mind it seems to be fast enough. It will all be one big experiment, but for a change one with the possibility of success. The position of the final ECU will be under the tank probably, as my modified Moto Guzzi tank leaves a lot of space there. Or it might go under or into the home made saddle. In case you are curious, this is my topic on a Dutch forum: click

Cheers,

Hugo

[Brendan W]

I just got in no problem.
Google sometimes throws up robot problems. Try Firefox or another.
Specs
20 degrees below 1650 rpm
35 degrees above 3500 rpm points ignition
40 degrees above 3500 rpm fully transistorised ignition

[HugoW]

Thanks for the numbers, great. I'll have a look on another PC tonight using Firefox. Getting a service manual never hurts.

Cheers,

Hugo

[Brendan W]

Interesting thread and great work on the seat and always nice to see smiling faces on a bike
I take it you will be taking an analog signal from a vacuum transducer as input to the advance 'map'.
Keep us posted. I have a raspberry Pi 3 sitting here looking for something to do.

[GregT]

On a 4V cylinder this small bore, my opinion is that it won't make an appreciable difference to the way it runs or economy...
But you should be wary of introducing any more heat into normal operation - which could well happen with more midrange advance - as these engines are well known for developing cracks in the heads between the plug holes and the exhaust valve seats.

[HugoW]

Thanks, that's useful information. I've already planned a temperature sensor on the cylinder head because this might be the first step to EFI. My first step is to simply copy the stock curve to the new system, when I get that running I will note the cylinder head temps. After adding advance, I could add a function either warning me and / or reduce the added advance. I was looking for a maximum head temperature anyway, any advice?

@Brendan W; Thanks! From what I can find the raspberry is slower than the standard Arduino, which is already fairly slow in processing. To only copy the stock curve it might work since it is only devided into 3 sections, but my system is set-up in steps of 150 rpm. I will keep you posted here, or set a link to the Arduino forum where I wil do / get help on the development.

Cheers,

Hugo

[GregT]

Advice ? Yes, lift the head before you start modifying and check if it's already cracked...I'll give you 60/40 odds on it's being cracked already.

No idea what would be a safe head temp, it appears to be a design fault which makes them prone to cracking.

[HugoW]

Hmmm, OK, I'll check. I have two complete engines, I hope one is OK! So basically, doing any real tuning will raise the motor temperature, and without controlled (liquid) cooling these engines cann't handle that? Bummer. I casted alloys before but redesigning the heat to be liquid cooled was not on the to-do list... I am not sure continuing the project makes sense, then.

[EDIT] Or would oil cooling add something substantial to the heat dissipation? I am not looking for heaps of power, BTW, just like to develop the electronics. [/EDIT]

Hugo