Alpha-N on a Microsquirt and 2stroke engine

[johnbannell]

Hi,

A bit off the wall this one, I am trying to fit fuel injection on a 2-stroke twin of 400cc (1958 vintage). I have a set up with a Microsquirt ( running 2.88 code), 36mm throttle body with TPS and MAP and a single 3bar injector (220cc) (Honda VFR800 pump delivering 7gph @ 3bar and at 2.7Amps for those that are interested!). I also have an Innovate LC1 in the eshaust down pipe and this works well provided that the engine isn't four stroking. (I am hoping to use Autotune once I get the thing a bit nearer!) Curently I am using the Microsquirt for fuelling only since I already have an electronic ignition fitted. I am using a custom dual opto-isolator driver assembly to trigger the Microsquirt from both coils and this works pretty flawlessly to drive the Option inputs on the Microsquirt. I can get the engine to run, tick over and rev reasonably well at a range of AFR and speeds down to about 1000rpm where it becomes unstable due to the low inertia of the engine. Starting, well not there yet, since a 2 stroke really needs a lot of fuel to start from cold and I could do with a big priming pulse which I don't have.

Difficulty is that with a piston port 2-stroke with 156 degree duration inlet timing I get very poor MAP response - try 800mb at tickover and 900mb at WOT. Ergo - no reasonable mixture control for load (and yes, the MAP does work and there are no leaks in the tube!). (the engine is now tuned to modern spec 10:1 cr, 168 deg exhaust, 112 deg transfer but still has a siamesed inlet, though mixture ballance between the cylinders seems to be pretty good) - reason? the MAP averages the inlet pressure signal and the blow-back rules the short duration and poor (in comparison to a 4 stroke) suck!

I am trying to change over to Alpha-N which would appear to be ideal for this installation. I have reset fuelling to 'pure Alpha-N', and used the configurator to re-set the fuelling algorithm as well. I can find an Alpha-N VE table in the Megatune menus, but it is only 6x6, NOT 12x12. Also, if I open the MAP VE table, it still appears to be controlling the injection timing! I can happily swing the mixture with the VE table! To all intents the Microsquirt seems to be still running MAP not the Alpha-N I want. The Manuals seems to be a bit thin in this area!

Q1, what have I done wrong?
Q2, shouldn't I have a 12x12 Alpha-N VE table for 'pure Alpha-N' (and no MAP VE table, or one that doesn't appear to work!)?
Q3, is the Microsquirt actually running Alpha-N now despite all of the indicators?
Q4, with Alpa-N do I need to decouple the MAP sensor from the TB so that it is a baro only? (the manual seems ot indicate that only prestart readings are used for correction)
Q5, Anyone got any experience of this sort of application?
Q6, Has anyone done a 'sampled' MAP on an engine - I was thining of an ADC, triggered by the spark pulse driving a DAC into the uS MAP input, since the MPX4250 has 1ms resolution and should see the pressure variation in the inlet - but I still have to put a scope across it!) Pitty there isn't a converion timing control available within the code!)


Hellp!? and any suggestions?

Many Thanks,

John.

[newtyres1]

John,

Searching the msefi.com site for alpha-n will help you a lot, as you may not realize that uS code and MS2 code are the same. Basically you need to go into the "Other Tables" / "Alpha-n MAP" table and set this up to translate TPS% into MAP, so set 0,20,40,60,80,100 in the TPS% column and 0, 2000, 4000, 6000, 8000, 10000 in the RPM bins. Where TPS = 20% set 20 in the table for all RPM's, for TPS = 40% set 40, and 60 for 60 and so on.

So uS sees you are using Alpha-n, then it looks up the "Alpha-n MAP" table to convert TPS to a 'MAP' value, then that value is used in the normal VE table i.e. TPS is converted to 'MAP'. Hope that makes sense, Lance explained it a lot better just a few days ago.

To see if it works, connect a laptop to the bike, and in the tuning screen, see if the "bouncing ball" moves up and down the fuel map as you open and close the throttle. If it doesn't move, then no good. You might want to set up a throttlegauge or tpsadcgauge to monitor the throttle in MT. Right-click on a gauge you don't need and set it as the new gauge.

I would disable baro correction or disconnect the baro sensor until you get the bike reasonably tuned and need something else to play with.

BTW best wishes and welcome, all your questions are good ones, alpha-n isn't used much but I think it will help you a lot with your particular motor. I have used alpha-n and it worked very well for me, and easy to tune. It's easy to hold a constant throttle, but difficult to hold a constant MAP, when tuning.

Ian.

[johnbannell]

Ian,

Many Thanks, a great pity that pure Aplha-N on the Microsquirt is only a 6x6 table, it could make it a bit difficult to get right on 2-strokes with pulse tuned inlets and exhausts where the torque curves can be highly non-linear! (and YUP I have both a megaphone inlet and tuned exhaust! - one of the reasons I decided to try fuel injection - I just couldn't get the parts to get a Bing carb right. I needed new atomiser collars as opposed to jets, and they are a bit difficult)

I followed your suggestions, but set the bins in a progression, small at the bottom end and larger at the loud end. I also pulled off the MAP hose! Fortunately I knew roughly where the mixture should have been to tick-over, so I could sort and scale the table appropriately with the 0% bin giving the necessary fuel when calculated out with the required fuel pulse width.

I couldn't start it! Played about and cleaned the plugs and got it to fire and run, though very rich. I played around with the Alpha-N tuning table and nothing changed at all!! I scratched my head a bit and then went back to the MAP table - I got instant changes. Went back and checked the set up (again) and I was, as far as I can tell, properly set up for pure Alpha-N. I then found a bit which was 'Alpha-N blend', which I shouldn't have needed on pure Alpha should I!!!!!!! With the engine ticking over at about 2500 I changed the MAP blend speed to 10000rpm and the engine instantly leaned and the revs went up to 5300!!!!!!!!!!!!!!!!!!!!!!!!!!!!! The Alpha-N VE now gives me control of the mixture as well and stops the MAP doing anything! I am not quite sure if this is what should happen, or if there is a whoopsey somewhere. Seems odd that the blend control still needs to be set when you are running pure Alpha-N!

Reason it would't start, because it was trying to do Speed/Density it was getting WOT fuel at tickover throttle and had flooded the engine - even 2-strokes won't start on 3:1 AFR

Will keep you posted on progress once I get the thing out of the garage again over the next couple of days. By the way, and I hate to say this, but it doesn't have 2 wheels - it has 4!!! It is a 1959 Goggomobil Coupe (I can hear you saying 'A WHAT!). The engine is reconned by legend to be the source of Yam twins. I am hoping that I should get about 36 to 38bph at 5200rpm from it, as opposed to the original 16-17! (but then it only weighs about 350kg)

John.

[newtyres1]

John,

Ooops, I forgot to mention to turn the alpha-n blend up.
The 6 x 6 Alpha-n MAP table is simply there to convert TPS to MAP, and you then use the normal VE table to tune. The normal VE table still says MAP for the LHS column, but it is a "MAP" value derived from your TPS by using the Alpha-n MAP table. I have been setting up this 6 x 6 table so that at any RPM, TPS = MAP, then in the normal VE table you can space the "MAP" and RPM bins to suit the motor, and do all the tuning. The 6 x 6 table is just set and forget. The tuning is all done on the standard VE table.

Sounds like you have a very interesting project. I used to read Roy Bacon's books on tuning 2-strokes in the 70's. You may easily end up with one of the best-tuned sweetest-running Goggomobil's ever...

Ian.

[johnbannell]

Ian,



Thank you so much, I am now starting to understand how to get Alpha-N to work. I have re-set the Alpha-N TPS table as you suggest, And think that I am now on the curve of getting the Cranking and Warm up ramps into place, Tickover was sorted out yesterday. Pity that the uS and MS2 manuals dont mention the Blend control in pure Alpha-N.

I must admit that the VE table starts to look very odd, with tickover at about 12%. Standard calculations gave req fuel as 6.8ms with my injector, and I ended up with very small VEs at tickover - hence no control. I have re-set to 5ms with re-scale, and this at least gives me a bit more resolution. Typical tickover pulse width is about 1.99ms total on a 0.995ms opening injector once the engine has warmed. The cold start this morning was from 6 deg C. and it allowed me to play with the enrichments as the engine warmed through. It looks as if my 4stroke 220cc injector is about right (1 to 6ms of actual fuel) for my 200cc per cylinder volume. (I am using one of the four standard Keihin injectors that came with the VFR 800 Injector bank (£15 on e-bay!) - one choke of which I am using as my TBI)

Took it for a drive, and mamaged to get about 100yds this afternoon, before I ram out of petrol!! First I got about 2 yds, then about 5 yds, then 10 , then 20 and then 40 (then no fuel!). But even in those 100yds, I had made a lot of progress with the VE table! It rises very steeply from the no-load line, even at 1000rpm. Fuel? well, I thought about it and realised that I had had it ticking over in total for 3 or 4 hours! and I only had 2 gals in the tank to start with! When I drained the tank I only had less than half a gallon left (my fuel gauge went awol during the dip tube mods - now fixed!)

Again,

Many Many Thanks for the help.

[newtyres1]

But even in those 100yds, I had made a lot of progress with the VE table! It rises very steeply from the no-load line, even at 1000rpm.

Just some thoughts from tuning my bike, with alpha-n, do not space the TPS ("MAP") bins evenly. Big changes in airflow occur at very small throttle openings, and smaller changes of airflow occur at larger throttle openings, so put lots of bins just off throttle and in the cruise area. From half throttle to full throttle, you may only need 3 rows max to cover that, so use the other 9 from just below idle up to half throttle. A lot of factory m/cycle alpha-n setups have the spacings in a sort of exponential form, i.e. very small spacings from idle that gradually get bigger and bigger. For example, if you are using TPS% (TPS 0 to 100 representing idle to WOT), maybe space your TPS bins ("MAP" in the VE table) something like this -

0, 2, 4, 7, 10, 15, 22, 30, 40, 55, 75, 100. This is just an example. Settings with very similar spacings have worked well for me, and gives fuel control in the areas I need it. This works well for modern m/cycle engines, in your application it may be very similar or maybe not. It may sound radical at first, but I can assure you it is not : )

Ian.

[johnbannell]

Ian,

Sorry, it has been a long time since I replied and gave you an up-date. However, during that time I have been VERY busy, I replaced all of the ignition and put on modern Honda coils (4ms dwell with a 0.9mm plug gap), changed onto a phonic wheel on the fan of the dynastart, blew up the engine comprehensively when one of the needle roller little ends collapsed and destroyed the crankcase, one of the special high compression heads, and ruined one of the tuned barrells! Re-engineered the inlet manifold and replaced almost every single part of the engine to try and find the shunt that had originally driven me to fit Microsquirt.

Up-shot - I have finally found the problem - a Universal Joint in the drive train was 'bottoming' and causing the whole engine to rock about like mad. Now permanently fixed by judicious use of an angle grinder!

Now? well the engine is running very sweetly, but on standard barrels while I get the damaged one sorted out. I did find a significant difference in the VE maps between the tuned and standard barrels, I am still bottoming this out, and am far too rich above 5500rpm. (this appears to be the limitation with Mega Log Vierer, if you cant quite get to the revs where the setting is excessively rich, it only reduces the richness bit at a time so it takes several runs to re-map at the top end of the rev range) Of course as the mixture richens aboue about 12.5:1 the engine goes soft and power drops off very quickly.

Haven't been brave enough to try out autotune, so have stayed with a run log and correction with Mega Log Viewer for the corrections - this still allows me a hands on control of the mixture changes.

Starting, - couple of pumps on the throttle whilst cranking and the engine bursts into life like any two stroke. WUE ameans that no extra throttle is required and the engine quickle settles down to a nice 1000rpm tickover, where is seems to be very happy. Although with standard barrels and high compression, the engine is very smooth at the bottom end and pulls strongly from about 1500rpm, which is quite remarkable for a 2stroke. Engine is very sweet to about 4000rpm, where there is some vibration between 4000 and 5000 rpm, am not yet sure if this a 'rock' resonance of the engine due to poor ballance of the engine itself with the very big pistons of the 400, or perhaps a bit too far advanced, am still looking into it. Engine starts to sing again at 5000, but the top end has been limited to about 5500 rpm due to excessive richness (12:1) as the breathing drops off (an aweful lot it is quite surprising). Torque is very good, and the local (German) parts supplier, Uwe Staufenberg, was really gobsmacked by the car when I had it across for the International Glas Club meeting a couple of weeks ago. It really is quite a lot quicker than a standard car, but limited in top speed by revs.

Although I am not there yet, and I still need to get the nice tuned bits re-instated and the engine tuned out further, the results are quite remarkable, and remember this mod does show that pre-mix oil and fuel will work with modern fuel injection parts. The Bosch LC4 is also still working, I keep starting up the car and thinking - it will be bust this time won't it, and it continues to work. It has probably survived about 15 hours so far, some of it VERY rich!

Do I recommend it? - most definitely, takes a bit of work to get on top of the technology, but then there are so many bells and whistles to play with.

Will file some detailed information once I have bottomed out the tuning, but again, many thanks for your help.

John.

[hybrid]

Hi all.
For those of you who have tuned your two stroke using alpha-n, what did you do for cold starts?
At the moment, I'm having to spray some fuel into the TB throats to get the bike to fire initially from cold.
After doing that a couple of times, the bike will generally keep running from there and it will be fine.

Two strokes generally need a fairly rich mixture initially to fire from cold, so how did you achieve this in your tuning?
Its currently around 10 degrees celcius here in the mornings.

What were your WUE and Cranking Enrichment settings? Bare in mind that I'm kick starting also, not electric starting.

[johnbannell]

Hi,

Well to try and answer that question. Firstly, yup you need a very rich mixture to first fire a 2-stroke, I have heard the figure of 6:1! Basically because you need to wet out the crankcases.

Currently my engine starts as follows: -

key in ignition,
turn engine over - electric at about 600 rpm
pump (tickle) throttle whilst cranking
after about 1.5 seconds the engine is running

This is very like normal starting for a 2stroke with a dynastart adn a choke, only I don't haev to pull out the choke and the throttle tickling is a bit more vigorous!

Once the engine has first fired, it will start again on the 1st or 2nd compression - i.e. instantly with no throttle. I use the transient enrichment as a method of getting the extra fuel into the engine to start. The engine has to cool right back for several hours before I need to use the starting proceedure again.

What I did was to bang up the cold start enrichment as much as possible - at 0C we are talking about 190%! - I think that the max you can get is about 220% from memory. Bang up the cranking pulsewidth to at least double if not 3 times the normal tickover pulsewidth. I have problems with the cranking enrichment because my cranking speed is high, and if I am not careful the cranking pulsewith affects the tickover - I have no tickover control, and tickover is about 1000 rpm.

This is really a bit of a 'black art' area - and of course you only get one shot at it every day, since as soon as the engine has started, it will fire again immediately with no throttle. Somewhere I think that there is an 'injector prime' facility that is used to blead the fuel system of air, but I haven't found the control for it. In theory you could use this to inject a wetting dollop of fuel to get the engine going when cold, but this might make you too rich when starting from hot.

As soon as the engine is running use the cold start wizard (WUE) and then adjust each bin as the engine warms through to correct the mixture as the engine warms up. This is really good, and once the engine is runing, even from cold, there is no blue smoke at tickover, and I am using pre-mix at 35:1. (and the injector and pump seem to be very happy wih it)

Sorry I can't be of more help, I had some problems with this area with a lot of tinkering until I found ot how to start the engine reliably - I can see that with kickstart only, you are going to have some problems.

Hope that this helps, Best of luck

John

[hybrid]

Hi John,
thanks for the reply.
I did find the priming pulse. When I remember where I found it I will let you know!
I did try setting that higher but it didn't seem to make much difference, and was also told not to play around too much with that because its really only meant for purging air.

I will try going higher with the WUE settings.. maybe to 190% like you did and see how that goes.
My concern with that is that we don't really need to be too rich once the engine has fired.

This would suggest that its cranking PW we need to play with. BUT! When the engine is warm, we don't need this big cranking pulsewidth any more, so it could prove to be a problem. I guess its just going to be a matter of lots of tinkering.
There is probably not going to be one magic setting that will help us all.