Elusive fuel
 

An area of the fuel flow through the system that needs some discussion, or, at least I do, is precisely what happens between the torque peak rpm and the redline.

Suppose an engine makes 200 ft-lbs at 5000 rpm, and drops to 170 at 5750
Since torque sort of represents the number of oxygen molecules ingested per putt, I think it fair to say a drop in torque of 15% would yield a 15% excess of fuel if a pulse duration remained constant.

If one tunes the pulses to shorten up 15% by the time 5750 rpm is reached, the afr should remain constant. Or so it seems.

If one doesn't do that, what happens to the afr? It must grow rich....? If any pulse increase is left.

If one has reached 100% duty cycle at 5000 revs and full boost, would it not automatically lean itself out. Yes, maybe. And by about 15%. Maybe not leaner, but surely less fuel per putt. Wouldn't that be what we wanted anyway?

Is this a delicate thing? Or a useful thing? It seems to me it is a useful thing. Why not?

For the reasons of pursuing top end power, I've always used a larger air correction jet to lean out the top rpm. same o same o.

was ist los hier?

corky

I see you've started trolling. Can't say I'm not impressed :giggle:


I'll bite:

I've a great example for you, I just tuned this car last night:
https://www.miataturbo.net/attachmen...ine=1419182524

Here's the log showing what you need to see:
https://www.miataturbo.net/attachmen...ine=1419182524

IDC still goes up, even though boost, and storque, drops like a rock up top. It doesn't go up really fast after peak torque, I'll give you that, but the turbo and setup on this car was completely tapped out, so it's not even close to what you're suggesting "will work" on our miata's, which don't taper boost up top like this due to engine being way too big for the turbocharger.

The setups I've tuned where a turbo was more properly sized for the engine, the IDC goes up way faster past peak torque.

IDC follows the HP curve pretty close. Since HP is TQ x RPM that makes sense.

HP includes the time component (or lack of) of TQ so basing fueling needs off that is wise.

And basing needs off torque is unwise ;)

Hp=idc

Torque=pulsewidth.

Ta-da

wait

wut?

idc=pulsewidth

No: idc = pulsewidth / potential pulsewidth

potential pulsewidth meaning the maximum time available for a pulse at a given RPM.

idc = 100% any time the injector is open all of the time, which is the maximum fuel possible, which is the maximum power that injector can support. Joe P reminded us of that.

I see where you're going with that.
But like idc, pulsewidth doesn't go down or even stay the same past torque peak like Corky is attempting to suggest.
Should I re-screenshot the above log for demonstration? I think we all understand, well, except corky.

Idc != pulsewidth

?
9ms at 2k rpm and 9ms at 4k. do not have the same idc.
idc does not = pw

And Vlad.

Screenshot that log with pulsewidth too.

Screen shot says it well. DC follows HP, as does air flow. DC and air don't completely follow each other, I presume because, as boost builds, you fatten up the fuel (lower AFR); but then I'm assuming the voltage output of the MAF is linear with flow. Torque falls as HP is fairly flat.

I can't tell from the graph if PW went down with torque (after about 4500 RPM), but my guess is that it did. Would appreciate it if you would re-check that.

Dann says it succinctly.

Don't forget fuel flow and pressure affected by FPR and opposing boost pressure in the inlet manifold.

Based on your log, the PW should be around 16ms at redline, and 19.5ms at 5000 rpm.

Well crap. I think I see what you guys are all talking about now.

I'll see if I logged PW and post up if so.


......someone clarify: why wouldn't pw go up same as IDC? Maybe I'm not comprehending pulsewidthds (which to me means "how long the injector stays open"). What am I missing here? if you're using more fuel up top, are you not lengthening the pw? isn't that how you get to 100% IDC anyway?

I'm used to dealing with properly scaled/dialed in injectors and relying on idc to see where I'm at rather than pw, so bear with me.

Cylinder fill is torque, rate of airflow over time is power.

that doesn't help much.

but I think I get it. idc goes up cause you're spinning faster, pw may or may not go up because you might not need more fuel per spin (or "putt" as corky posted), you just need it more frequently.

how does this change corky's original application in regards to maxed out injectors though? wouldn't torque need to plummet past peak torque to keep pw the same and not run out of fuel so fast? plummet even faster than the 21-15 example I posted

At 7000 rev/min (1/7000 min/rev -> 60/7000 sec/rev) each revolution takes 0.085 seconds, or 8.5ms. The injector squirts every other revolution. That means you have 8.5x2=17ms to complete the squirt. This means that at 7000 rpm a PW of 17ms is 100% duty cycle, because the PW equals the time of two revolutions, hence it's constantly open.

At 4000 rpm, two revolutions take 30ms. If an engine makes the same torque at 4000 rpm as it does at 7000 rpm, it will take the same PW. If that PW is 17ms, then 17/30*100=56% duty cycle.

Pulse width can go down while duty cycle goes up because the rate of pulses goes up over time( i.e. revolutions -per minute-).

I am sure you can get your head around the rest.

Jesus Adam don't conduse him!