DIY Fuel injection thread.

[downtrail]

Easiest way to tune a motor to avoid going in circles chasing problems is to get your main ve table tuned. That is 100% as good as you can get each cell you can physically get into. This is with no trims in place ie clt at temp iat at temp etc.

Then leave the main table the rest is trimmings and it can take a while to get it all right. Post start and warm up are good to do next. Theres a thousand diffrent conditions out there so compromises that will need to be made every now and then. When a motor is warming up or just after its started they like to be a little rich. If not youll get hunting even is afr is 14.7 go for somewhere between 13.8 - 14.2 its impossible to give you a figure sometimes you just need to feel the motor and give it what it wants. Some motors ive done like to be in around 12.5 just after starting when warm. helps with situations like you describe. Lean hot starting.

Best of luck the main table is easy to do. Just remember once its tuned its tuned it may need tweeks here and there for timing changes etc but mostly youll leave it. its all the other little things. Acc enrichement can also be a pain with megasquirt but nothings impossible.

How would inlet temp get that high when caning along? It reads so much cooler when driving.. like low 20s due to the cold air feed. It certainly never sees anything as high as the temps when parked up idling on a hot day.

I think the after/post start enrichment only works for a few seconds? Me still learning.

Happy to note that after having re-advanced the ignition table back to where it was ages ago we filled up in blenheim and had managed 32 mpg It certainly pulls a lot nicer in the mid range and smoother too. Man its fun when kept past the 4000 rpm on hill climbs

[yoeddynz]

Yeah I have got my main VE table pretty damn sorted and it was idling sweet but like Spencer said its not often I have seen such hot days and that with it being parked up on hot gravel put it in a place its not been before. If I had just gone for a quick drive it would have been OK but this time I wanted to do a three point turn and it had just gone so lean. Now that I had added a bit of fuel in the idle area to see me through that episode it idles at around 13. Once I stop after a run and park up it will lean out to 14 or but still at least idle. So what Id like to do is have it sitting around 14 whether its a hot day or cold. I think that hot fuel going back into the surge aint helping and I'll sort that out easy.  But id also like to see the ECU add fuel when really hot. First off though I'll sort out the fuel return. I dont think my engine is at a level of power where it needs a fancy cooler though.

[kpr]

have you tried disabling the iat correction  when it does this, to see if thats the actual problem?   iat shouldn't be able to do that much correction. and can pretty much run without one in alot of cases

 

if im reading that correction graph right. seems very aggressive. 10% removed for 30deg increase in temp?

[yoeddynz]

Good idea! I'll try that out.

 

This morning I started it up at around 10am. Started sweet, warmed up on warmup enrichment curve sweet with revs slowly drpping as it warmed. Settled onto VE table in the idle area which I have now set a little richer so around 13. Drove to Motueka. Sweet. Hot in town. Parked up. Went to market and caught up with all my smelly, ragged clothed, barefoot, mung bean eating hippy friends. Had a dairy free icecream and bought two Avacados.

 

Back to car and started it. Sure enough it was a touch lean but not too bad as I had made that area richer. If I was to stay parked there and idle it would stay lean because no air flow. But once driving it cools down.

 

Otherwise a thoroughly enjoyable morning out.

 

That's my story. I hope you enjoyed it. For those that might like it I will endeavor to draw an awesome graph depicting it all tonight.

[kpr]

Dave;  I have a graph for you.

 

100% load row of fuel map.   

grey line  original acetal trumpets.    75mm ish.

blue line  115mm ali trumpets (cut tuning short as vibration problem, peak at 4800 probably isnt 100% correct)

pink line  125mm acetal trumpets. since ali trumpets failed, i made these ones slightly longer hoping it would pull the hole out at 6400rpm.  but made it worse along with pretty much everywhere else.

ignore anything before 3500rpm as hasn't been corrected. 

same deal as below without the fuel scale cut off https://garage4ag.files.wordpress.com/2015/12/trumpet5.jpg

 

 

 

 

so this was pretty much the main reason why my trap speed was lower at the drags.   while it had more power between 6800 and  7700.  it was either short shift it and drop it   into  the hole at 6000rpm.  or rev the shit out of it  to try avoid dropping it the the dead spot.  the latter seemed to work best.   thinking around 95mm trumpets should be the sweet spot.

[kpr]

So your fuel is still climbing at at rev limiter?!   would usually mean you haven't reached peak torque yet, let alone  peak power.  seems strange.

keen to have a gezz at your tune and some of you logs. 

 

 

 

 

 

[Roman]

Yeah keeps gaining fuel but I'm already pushing my luck with 8300rpm haha so not keen to test any higher.
I'll PM you in a bit and send you some stuff.

 

So, on the topic of peaks and troughs, have found something really interesting.

 

If you do a manual calculation of Helmholtz frequencies, as in, calculate the length of time it takes a sound wave to go from the back of the valve, reflect at end of the runner and then get to the valve again.

 

You end up with an RPM that the first reflected wave hits. Then the wave travels back up and reaches the valve a 2nd time, (weaker pulse) then 3rd, then 4th. (weaker pulse each time)

 

What's interesting about this though is that If you change the runner length, or the speed of sound, the ratio of time between the 1st, 2nd, 3rd, 4th etc peaks stays exactly the same.

 

 

Soooo this is useful, because if you look at the rpm distance between the peaks on your graph, you can tell which harmonic wave it is that's causing the peaks and troughs. And then you can extrapolate out to find the others.

 

So in my instance, a peak at 4000rpm and a peak at 5500rpm. 4000/5500 = 0.72 so it must be the 3rd wave reflection happening at this RPM?

 

So if I play with my calculator, to see if I can find what runner length it believes is necessary to get a 3rd wave reflection occuring from 4000rpm to 5500rpm

 

59.8cm effective length from valve to runner end gives a peak that's only 1300rpm wide, not 1500. No matter what I do, changing runner length or speed of sound I cant get a 1500rpm wide peak to peak starting at 4000rpm.

 

(note how the standard intake manifold has a 2nd harmonic peaking at 8100rpm, good times had by all)

So then I thought... Maybe its because you dont want the wave to return 720 degrees later (as the valve is already shut!) but something earlier like 650 degrees. But this just makes the same difference as changing the runner length, so wouldnt widen the peaks.
 

So then the next thought... Not only are there "good" reflected waves, but there are also ones where the reflected pulse pulls the fuel back out of the motor instead. Happening at twice the frequency.

 

So if I make an RPM plot of where both the peaks and troughs theoretically occur, and then subtract the peak strength from the trough strength to get an "effective" wave strength. The effective peak to peak becomes slightly longer or shorter because of some instances where waves cancel each other out. The lines on this graph below should probably be sine waves instead of pointy, but I dropped out of 6th form maths so dont know how to make a sine wave in excel

The blue line is the "good" pulse. Red line is the "bad" pulse and the green line is the "effective" pulse, AKA what I'd perhaps expect to see affecting the fuel map

 

My graph is shitty and I've made some heinous assumptions about wave strength etc.

 

But you get the idea. Check out that peak and trough that both happen at about 8100rpm. Maybe this is why intake manifolds are tuned for 3rd harmonic instead of 2nd, the 2nd cancels itself out.

[Roman]

Dave;  I have a graph for you.

 

100% load row of fuel map.   

grey line  original acetal trumpets.    75mm ish.

blue line  115mm ali trumpets (cut tuning short as vibration problem, peak at 4800 probably isnt 100% correct)

pink line  125mm acetal trumpets. since ali trumpets failed, i made these ones slightly longer hoping it would pull the hole out at 6400rpm.  but made it worse along with pretty much everywhere else.

ignore anything before 3500rpm as hasn't been corrected. 

same deal as below without the fuel scale cut off https://garage4ag.files.wordpress.com/2015/12/trumpet5.jpg

 

 

 

 

so this was pretty much the main reason why my trap speed was lower at the drags.   while it had more power between 6800 and  7700.  it was either short shift it and drop it   into  the hole at 6000rpm.  or rev the shit out of it  to try avoid dropping it the the dead spot.  the latter seemed to work best.   thinking around 95mm trumpets should be the sweet spot.

Applying my shoddy maths to the above on the 75mm graph.

You've got a peak at 3200rpm and a peak at ~4700rpm, so ratio of 0.68

 

So looking at my numbers means:

 

Must be the 2nd and 3rd harmonics making these peaks

 

So doing some wizard magic in my thingy, your other harmonic pulses happening at:

 

Next one coming up to 9500rpm

 

Also notice where it says that theoretically one of the "troughs" is at 6300rpm which is what it shows on your fuel map too.

If you went 10mm longer it goes like this

 

20mm longer (to 95mm) like this

 

 

50mm longer (to current) like this (Chucking air back out at 6500rpm....)

 

 

95mm sounds good by the maths too, because it pushes that trough below 5500rpm

[kpr]

Interesting,  ^ this is why i took the  test on car approach  haha

 

those peaks in the lower rpm are probably not so great to reference it off.  think its something else weird going on.  once it comes on cam past 4500 starts to settle down.  my total runner length shouldn't be long enough to catch the 1st or 2nd wave.

manifold + itb length is 140mm.  port length. roughly 70-80mm?   plus the 125mm trumpets  -  335mm

 

crappy calculator i found  says  first wave is  around 26000rpm

[Roman]

My calcs show that if the pressure waves are going at speed of sound, my runner length must be 600mm, which definitely isnt the case.

 

I'd say it's maybe 350mm total length or something like that. But the shape of fuel graph still looks as though its happening I think.

 

So my thoughts... The pressure waves dont actually travel at the speed of sound, maybe half that speed.

[Celica RA45]

you need to be in the 390mm range from back of valve to the lip of the ram tube,for the beams 

[Celica RA45]

then extractors can play a part as well ,4into 1 versus 4,2into 1 also what size pipe dia etc 

[Celica RA45]

also 1 last thing yamaha stands for to fucken big  inlet ports 

why there is a drop around 4000 ,not enough air speed 

[Yowzer]

If you're driving at 4k you're driving it wrong.

[Celica RA45]

talking of std motor not race motor 

[Yowzer]

I know.

[Yowzer]

In slightly other news I was reading about resonance and inertial ram tuning on the older V10 F1 engines, and how at higher rpm the ram effect had much more impact on power than resonance tuning. It went into some very in depth technical analysis that was a bit beyond me a 2am, but interesting non the less

[Celica RA45]

but i get down to 4500 rpm ,coming out of mg corner and honda corner at 65% throttle 

[Roman]

FFS my new wideband shit itself today.

It lasted a month!

Time to throw this shit heap innovate controller in the bin.

[cute wee gem]

Bad luck man! I've had an lc1 for years and it just keeps on going, it gets used every day at the moment.

 

Can you send it back?