Commando ignition and AFR

First of all, thank you for approving me to the forum! I'm a proud owner of 3 brit bikes, -71 Triumph NRE 750, N15CS -66 and 920cc Commando with 270°crank.

Since I'm a Finn, I'll go straight to the topic... ;-D I've spend a lot of time trying to find correct timing advance and fuel mixtures with these bikes. Most of the time with Boyer ignition and Amal/Mikuni VM's. I've always felt that I can't find no satisfactory compromise in those areas when it comes to tuning these engines up. Now that I've once again found myself mixed with EFI:ying (that's not a word) an old air cooled engine, it crossed my mind: why not try to ask more experienced people to what they think. So, the question is in general: if you could choose the ignition advance what you get when you twist the throttle and what kind of AFR you are aiming to when doing so, what could it be in numbers? I know that this is extremely complex topic and there is no simple answer to this, but... I'll attach the tables I've created to start with my 920cc 270°crank Commando EFI engine. This is not a racing engine mechanically, but a bit tuned up. I don't want this to be a EFI topic but a general question of ideal ignition advance and fuel mixture in couple of different load situations, TPS vs. RPM. Appreciate any comments on this. And I hope that this is not too much off place where to ask this question. Hope the images show. If not I'll post them some how.

You are asking the list to comment on what a preferred AFR/ignition advance non steady state is, good luck with that. Not meaning to be snarky here but it's a load of question there.

I would reframe this and suggest you get the bike on a dyno and see what the motor wants and whether it meets your requirements without holing a piston. You need to temper this with all reasonable conditions load, speed and ambient conditions you expect to encounter.

Another thing to look at is some example (comparable) dyno pulls with AFR trace to see what the results are ...for that specific motor.

Dances with Shrapnel said:

You are asking the list to comment on what a preferred AFR/ignition advance non steady state is, good luck with that. Not meaning to be snarky here but it's a load of question there.

I would reframe this and suggest you get the bike on a dyno and see what the motor wants and whether it meets your requirements without holing a piston. You need to temper this with all reasonable conditions load, speed and ambient conditions you expect to encounter.

Another thing to look at is some example (comparable) dyno pulls with AFR trace to see what the results are ...for that specific motor.

Click to expand...

Yes, I hear you. But I was aiming to a more generic point of view. Like is it ok to have max ignition advance from 2500rpm like regular Boyer, and more like is there a point making e.g. ignition curve like Trispark, dipping the advance a bit when you twist a throttle from zero throttle. Or what kind of AFR you should aim when cruising with constant speed, let's say 3500rpm. AFR14.7 for modern engines would do just fine, but I think that e.g. AFR13.5 could be much better for let's say for Commando engine. But yes, I know that this topic might be too wide to be handled here or anywhere else... But there is just too much snow up here to do any road testing ;-D so I'm desperate to have at least some conversation about this ;-D

If you narrowed it down to the planet earth and who could answer your question in any experience, the pin would land right on Jim Comstock's house.

How are you going to do that (curve) with a Boyer and no TPS or GPS ?

Time Warp said:

If you narrowed it down to the planet earth and who could answer your question in any experience, the pin would land right on Jim Comstock's house.

How are you going to do that (curve) with a Boyer and no TPS or GPS ?

Click to expand...

Exactly my point. You can't do it with Boyer. But I'm doing this with MicroSquirt "computer". So my question is if you could do it with Boyer what would these curves look like?

Like a Boyer curve but with a microsquirt you would have a 3d curve not a single line. Get it on a dyno and tune to match your requirements.

kommando said:

Like a Boyer curve but with a microsquirt you would have a 3d curve not a single line. Get it on a dyno and tune to match your requirements.

Click to expand...

Spot on. Except I do not have that luxury here in Finland. I need to determine by myself what to aim. I have observed what kind of behaviour you can expect from Boyer,Lucas etc. and I feel that this is not even close to optimal. Even if we are not talking about unsteady conditions, just RPM. I'm not expecting anyone to give me 3d table for this, but maybe some ideas.

I've started to understand that this really is too wide a topic to be handled like this...

Take a look at Fast Eddie's thread on spark plugs today where ignition advance is discussed after dyno investigations.

HoveToo: thanks. That is very interesting!

This is the 2016 version of the main ignition mapping for a 961 Commando with aftermarket pipes. Not an old style Commando, but it might at least give you some insight into a similar engine.



I didn't post the fuel injection map because it is in ms of injector time, not AFR, so wouldn't help you.

Ken

lcrken: thank you for sharing the ign table! This most certainly gives a bunch of ideas where to head! I haven't come across anything this close to what I've been looking for. Of course older Commando engine is not that sophisticated than 961... but I think that the general ideas can be picked from this table! I think we can clearly see here that EFI with properly shaped combustion chambers does not need very high advance at WOT? Gasoline sprayed particle size is maybe smaller and burning event becomes faster when cylinder head is well designed. And alcohol in modern gasoline makes the mixture burn faster. This is good stuff.

And yes, fuel table with injector times would not be any use here. I want to continue trying to find info about target AFR though. I found a thread from Triumph forum about target AFRs for Hinckley Triumph. One gentleman seemed to know what he was talking about: he told he had been using AFRs from 13(idle/cruising) to 12.5 at WOT. So 12.5 - 13 throughout the whole table. To me that actually started to make sense just to avoid any extra heat due to leaner mixtures. Fuel economy is not what I'm after but best usability and optimized performance.

There is a brief discussion of ignition and AFR tables here, on the Daytona Sensors site.

http://www.daytona-sensors.com/engine-tuning-and-recommended-guidelines.html

lcrken: excellent summary there! There are actually good points to consider getting a knock sensor to my system. Need to study how it can be done with Microsquirt...

Have ran couple of tuning runs now and boy does this bike fly ;-D Info from lcrken found very useful, thank you again sir! I can confirm that 270 crank gives horrible vibration under 4k rpm, but above that no vibration at all. It feels like 4cyl jap bike. So for racing this construction could work. Engine revs so beautifully that I could probably explode it easily. I have restricted rpms to 7000 now. Thats more than enough! I might go back to 360 crank next winter because I'm not racing this bike and it could be pretty sweet with properly tuned EFI and some nice cam. I'm running now 1-1 exhaust but I have 2-1 ready to be tested at some point. Recognize this Winning pipe?

I have something seriously wrong with my gearbox... Gears 1 and 5 work ok, but the rest keep jumping out of gear. Camplate related I reckon. It remains to be seen how parts are available for this 5-gear box. I do not know which setup is inside the gearbox since I did not build it...

Here is my spark map. Note that it is modified by cylinder head temp also so the timing advance will be reduced a few degrees at higher temps.

comnoz: looking good! You've done impressive work on your bikes that I've seen in your posts. I think I'll improve my ign map with the data from your map. Since I started with the modern Norton map.

Here's my current map. I don't have head-temp adjustment yet. Even now it feels great.

Can I ask you, how do you get proper MAP? I have MAP sensor(GM-1) installed with hoses from both inlets but I get values from 80 to 100... should I use smaller diameter hoses or what? It would be great to have ITB mode in use.

I use timed map sampling. It only reads the sensor for a few milliseconds just before the intake valve closes. I am using custom firmware that gives me a table to set the sample time according to RPM.

Ok, I hear you. Need to study that. I’m using ms2extra code, so that’s available.

You might get there with ms2extra. I don't think it has the ability to change sample time according to rpm so you may have trouble getting around pulses in the intake tract from an active exhaust system. If your cam has wide lobe centers you will have a better chance of making it work.

All right, thank you for the info! So much to learn.... I’m not even using timed injection yet. But I do have full sync from cam sensor to continue with.