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!

Vlad, if you are referring to the other thread, it doesn't change anything about the question of stock injectors being too small to support the HP claimed.

Dann, as we don't know the fuel system, we are using the simplifying assumption of a 1:1 manifold referenced regulator.

He confirmed what I already said with math. There was really no need for that condescending "edit".
How about we don't start a pissing match in every thread and try to discuss the topic at hand? So far your only contribution is vague/arrogant posts.

Corky is obviously attempting to justify the "other" thread with this troll thread, and I don't think its working. But I'm open for being convinced otherwise.

Why would torque, or pulsewidths, drop fuel requirements up top, when you're still flowing more air and need more fuel? Pressure =/= flow.

Maybe I should re-read his post upside-down and I'll undestand everything (;))

Look at Mass Air Flow. Raw meter voltage is very non linear, so a small increase in voltage at the high end is more air than it seems. Add fuel as required to maintain the desired air/fuel ratio.

Due to the decrease in volumetric efficiency as rpm increases, you get less air per cylinder cycle but more cylinder cycles per segment of time. However, looking at the plots, the volumetric efficiency does not drop off fast enough to fulfill Corky's Xmas wishes.

I think, in Corky's case we are seeing the benefits of 60psi fuel pressure and a very conservatively flow rate specification specification for the OEM injector. I have no problem maintaining 11.5/1 on OEM injectors at 7psi and ~190whp.

Computer control of internal combustion engines is easy compared to world class petrochemical plants. Our cars just lack sufficient instrumentation and computer horsepower.

+100
Thank you.
This is, pretty much exactly where I was going.
Especially the bolded part.

it's always shocking when i agree with dann.

You are correct that fuel flow is proportional to IDC which is proportional to HP. It doesn't make sense in the OP to compare fuel flow to torque.

ingesting the air faster?

ignore me. i had a brain fart.

i was literally thinking displacement.

at 4000RPM the 1.8L @10psi is drawing in roughly 190CFM of air, at 7000RPM it's at roughly 333CFM. about 75% more VAF.

I'm being as condescending to your stupid posts as you were to corkies.

And I answered exactly what was asked extremely succinctly in my first post in the thread.

My posts disagreeing with corky are stupid? Please explain oh great one, perhaps you and corky should get together and finally release the OMEGA-OMEGA kit that makes 350whp on stock 1.6 injectors with reverse boost creep and an upside-down fake dyno plot.

You dont understand VE.

You don't understand how IDC does not correlate to pulse width.

You don't understand that pulse width at a given duty cycle changes with rpm.

And you feel justified in mocking corkys understanding in these topics..

This thread is literally me answering the OP in 4 words, and 2 pages of people explaining it to you.

wat?
go ahead, I'm dying to hear this one.

seems like I confused the two (idc/pw) and you jumped in with the quickness to piss all over me cause you're still bitter. you stated nothing but arrogant vague bs and attempted to sound smart.

So now for the final question: do you agree with Corky's logic or no? If yes, explain, if no then we have our confirmation that you're still a bitter little b and posted for no other reason than to point out my confusion at the begining.


... ta daaa?

You are an idiot. Screenshotted.

I'm going to sit back and watch another 2 pages of people explaining my 4 word answer to you.

okay chief

:laugh:

Exexx, we are not debating 190 HP, but 240 HP. Sure, there's headroom in the stock injectors, but 100%?

The higher fuel pressure gains sqrt(53/43) or 11% more fuel at 7psi over manifold referenced system.

My last post on this thread. Com'on guys, be civil.

you know what's easier than all this bench racing?

taking a car with 265cc injectors to a dyno, pushing it to 240rwhp and see if you can still maintain >12:1AFR at redline.


oh wait... :P

Shits gettin too real
https://www.miataturbo.net/attachmen...ine=1419266453

You know, I was impressed by that.
I was also impressed that it was backed up on a different dyno.
I think the stock fuel system on our cars is underrated, perhaps the fuel pump is able to keep up even with the injectors never closing?

No shit, 1L/ minute!?

Corkys post is a little cryptic, but in general, yeah, he's right.

My math says that at 12.5:1 Afr, on a 60psi non referenced system 240 crank is possible at 10psi.

Go to bed Vlad youre drunk.

Good grief wft is going on in this thread. I've now realized that either the automotive world has hacked up normal engineering terms to where they make no sense, or that everyone is just generally confused...

So PWM: Classically PWM is a means to control average current to something with a purely digital system. In a valve you set a fixed frequency that is much higher than the valve can physically operate and control the duty cycle of that digital signal to control the average current to the valve. This average current control allows analog control of valve position with a digital system.

WTF is going on in the car world? I see people talking about PWM being a digital signal and that the injectors actually go binary and completely turn off/on with the PWM signal? I think the MS3 is set to 60us PMW freq? I don't see a $100 mechanical valve operating at 60us...

It's like I'm at work looking at a marketing hack job of my project.

apparently. i dunno, i still wouldn't use stock injectors on that system if i was running 10psi. at 6psi, as shipped, sure. But that thing is too efficent of a setup apparently.

So you agree with corky, that tapering torque increases the fuel system overhead and nets you more power?



:laugh: k

here's how to test that: increase timing until boom! note the AFRs.

I mean if he's gonna claim that the stock fuel system can go beyond the injector duty cycle limits because the pump is strong, and that you can keep going with injectors never closing until you run out of fuel pressure, I think I would have to agree with that. At least based on what they've provem already with the AO kit.

Most of us would agree that is very dangerous, but appears possible.

I agree that torque=pulse width.

You still don't understand thats pulsewidth at a given duty cycle changes with rpm.
That baffles me.

pulsewidth at given rpm changes the duty cycle

potato pohtahtoe

can you unwad your panties so we can move on and discuss the actual interesting topic of this thread is drifting to, which is the oem miata fuel system "real" limit?

Calculate it.

I did.

240 crank, at 12.5:1afr, 10psi, 60psi flat pressure in the rail.

omg, are you on 28kb connection or something? did you not see the last few posts? We know its possible, because it was already done. And backed up.

and it's not 60psi flat on an nb returnless system. but that doesn't matter, because BEGi already proved that its still possible, even with a tapering rail pressure.

ill give you some tapering rail pressure.

omfg, this thread is painful to read.

Someone with a Dynojet plot of their car and a datalog of a WOT pull please post the following four traces on the same plot:

1. horsepower (SAE corrected)
2. torque (SAE corrected)
3. ECU-commanded pulsewidth
4. ECU-calculated injector duty cycle

BTW, before that chart is posted, here's what I think it will show:

-injector pulsewidth correlates to torque, but not as closely as Corky thinks
-injector duty cycle correlates to power, but not as closely as anyone thinks
-both of these are true because BSFC (fuel mass required to make X horsepower for X hours) goes up as engine speed increases

Here's a cool chart to show why this is true:

Attachment 234561

[/thread]

Yep. Along with the fuel system variables etc

I am very curious to see pulse width at peak torque and there after.

Also Sav, forgive my stupidity but I've never seen a graph like that. Can you explain what I'm looking at here? Are the camel back lines the torque curves at different load percentages? And what is the pink line? Also not sure why looks like horspower lines are going down while rpms are going up.
Or just point me at some reading materials so I can read up on this.

I didn't have a PW log of the above tune (different car).

Here's one I dug up from years ago of my gt3076 miata on e85

https://www.miataturbo.net/attachmen...ine=1419300506


You were saying?

Is it safe to say that peak torque is at 4600ish? Looks like pw is still going up until MAF begins to fall. So if 100% dc is hit at peak torque that would be bad news. AFR would have to fall at that point.

here's an even better one with MAP falling toward redline

pw still goes up

https://www.miataturbo.net/attachmen...ine=1419302789

if someone has better examples post up.

last one cause now I'm getting bored
https://www.miataturbo.net/attachmen...ine=1419305841

pw maximum at peak is 15.1, and minimum at the end is 14.4

Lots of little things contribute to the consistent rise in PW/IDC that everyone sees in reality. Things like the lack of mixture homogeneity that comes as the injectors are forced to open while the intake valve is open (ideally the entire fuel pulse would be delivered to a closed valve). Increasing BSFC is a big contributor, though - if BSFC goes up by 10%, fuel requirements go up by the exact same amount for the same power/torque being produced.

"Camel lines" are torque curves, yep. The colored areas are BSFC. Google "brake specific fuel consumption"

Horsepower lines are going down because torque goes down as you move down the Y axis. If you multiply RPM and torque anywhere on that chart, you get a horsepower number, and those are shown graphically on the chart by curving lines.

I'm not 100% certain on the pink line, but I believe it is a peak efficiency line from idle to redline.