Engine falls flat after ~6,800, can't figure this out! - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-22-2015, 09:07 PM   #41
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It's possible, as when I shut the water injection off the car clearly makes more power. It's off now though (pumps off, outputs off, pressure is low), and power is still down and falling off despite airflow going up, Duty cycle going up, etc.
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Old 05-22-2015, 09:15 PM   #42
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That's what I mean man, pulsewidth is actual time the injector is open, see how it stays flat? The other is duty cycle, the window of time available for the injector to open is 100% duty cycle, decreases with RPMs because there's less time to actually squirt fuel in there if you keep a constant pulsewidth.

Your pulsewidth stays relatively flat, the fueling is not increasing with RPMS.

If I had to take a SWAG I'd say less fuel, it may be way too wet if torque is falling off.
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Old 05-22-2015, 09:19 PM   #43
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Quote:
Originally Posted by deezums View Post
That's what I mean man, pulsewidth is actual time the injector is open, see how it stays flat? The other is duty cycle, the window of time available for the injector to open is 100% duty cycle, decreases with RPMs because there's less time to actually squirt fuel in there if you keep a constant pulsewidth.

Your pulsewidth stays relatively flat, the fueling is not increasing with RPMS.
The pulsewidths staying flat means that every cycle of the engine, it's sucking in the same amount of air/fuel since the AFRs are flat. And since I keep reving the engine faster, there are more "cycles" so this means the duty cycle is climbing too. This means the engine is breathing, not choking.

If the pulse widths were flat, but my AFRs were tanking rich, then yeah, the motor can't breath. The fueling is definitely increasing as duty cycle is going up up up with RPM.

Right?
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Old 05-22-2015, 09:26 PM   #44
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No, I would think it means the engine is struggling to breathe as torque falls off. If I'm not mistaken you should be using more fuel with more RPMs as power is torque x rpm, it should not be linear.

Does the peak in pulsewidth line up with anything signifigant in virtual dyno?
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Old 05-22-2015, 09:38 PM   #45
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From here: Tuning Your MegaSquirt

Quote:
Pulse width is the measure in milliseconds (1/1000 of a second) of how long the injector is opened for each pulse, regardless of how many times it is opened in a cycle. Duty cycle gives the percentage of time the injector is open irrespective of individual pulse duration.
Regarding your question, the pulsewidth reaches a peak of 9.8ms, and it ranges from 9.63ms @ 5,800 to 9.72ms at 7,071. Thus is basically flat for that range, and so are AFRs.
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Old 05-22-2015, 09:40 PM   #46
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And yes absolutely you use more fuel with more power, that's why the duty cycle is climbing on all my logs. I'm certain this thing is breathing since AFRs are flat, while duty cycle is climbing.

It's just about got to be that it needs more timing. Will experiment and see what happens. Fingers crossed I don't break any more pistons, this shortblock was much more $$$$ than the last one....
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Old 05-23-2015, 01:10 AM   #47
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Stop this guessing ****.

Your fuel table is jacked. Your power is going down above 6500, therefore your fuel should go down, instead it's going up, but AFRs are flat?

Completely disable any and all WI system. Go dyno tune. Nail your fuel table. Then dial in ignition. Fuel will probably change, dial it in as you change ignition. Assuming it's a competent dyno, ignore your wideband and tune solely off the dyno's WB. Once your ignition and fuel maps are NAILED, try adding WI bit by bit. If it doesn't let you increase timing and therefore increase power, throw the system in the trash.

You can NOT tune your ignition, fuel, and WI all at once on the street. It just won't happen, and you'll be tripping over yourself all day long.
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Old 05-23-2015, 01:22 AM   #48
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EDIT: wrong user, you say lots of clever ****

Last edited by nitrodann; 05-23-2015 at 02:45 AM.
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Old 05-23-2015, 01:41 AM   #49
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Quote:
Originally Posted by curly View Post
Stop this guessing ****.

Your fuel table is jacked. Your power is going down above 6500, therefore your fuel should go down, instead it's going up, but AFRs are flat?

Completely disable any and all WI system. Go dyno tune. Nail your fuel table. Then dial in ignition. Fuel will probably change, dial it in as you change ignition. Assuming it's a competent dyno, ignore your wideband and tune solely off the dyno's WB. Once your ignition and fuel maps are NAILED, try adding WI bit by bit. If it doesn't let you increase timing and therefore increase power, throw the system in the trash.

You can NOT tune your ignition, fuel, and WI all at once on the street. It just won't happen, and you'll be tripping over yourself all day long.
What's wrong with the fuel table? AFRs are pretty close to target. Target is 11.0:1, AFR's are 11.2-10.9, mostly 11.1-11.0 That's really close, not jacked! Logs I've posted show the AFRs are very flat under load. New log below shows same thing. Not sure why you think this is "jacked"? What's wrong? Fuel within 0.2 AFR of target is ok by my standards, unless you think the target is wrong?

WI is disabled, it's been off, I said that when I posted the first VD graph. It's still off, and yes I AGREE one thing at a time.




Ok...

So I did some tuning with the timing this evening. I was previously running 10 degrees advance. I tried adding 2 degrees, then 2 more, then 1 more. It seems to be helping. I left the fuel on autotune during the pulls so it would keep it close to 11.0, this feature seems to work very well.

Results:


Datalog of last pull with 5 degrees:



The last pull with 5 degrees shows to be down on power vs 4 degrees up to ~6,400, but I checked the log and the belt was slipping a bit and boost was higher on the 4 degrees pull vs the 5 degrees pull at those RPMs. At higher RPMs where boost is the same, 5 degrees made more power.

I pulled the plugs after every pull, they look clean, no signs of detonation.

I am now at 65.7% duty cycle, burning 772cc/min of fuel at 11.0:1 AFRs. Peak power is going up and to the right, but it's still not where it should be!
Attached Thumbnails
Engine falls flat after ~6,800, can't figure this out!-vd%2520added%2520timing_zpsv9iwilx9.jpg   Engine falls flat after ~6,800, can't figure this out!-datalog%25205%2520degrees%2520added%25203rd%2520gear_zpsbpp3ugdn.png  
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Old 05-23-2015, 01:44 AM   #50
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Quote:
Originally Posted by curly View Post
....Your power is going down above 6500, therefore your fuel should go down, instead it's going up, but AFRs are flat?....
This is the big question mark to me. If everything was "normal", this wouldn't happen. The fact that fuel is going up and AFRs are flat confirms it's still breathing well, but VD shows it's not making more power. Something fishy is going on.

Why is the big question I can not answer right now.
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Old 05-23-2015, 02:09 AM   #51
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Afrs are about a half point rich, and like I said VE should go down in order to keep afrs stable. And what's the 130kpa high rpm stuff? Entire row should have the same basic curve, just at smaller numbers at lower kpas.
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Old 05-23-2015, 02:45 AM   #52
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Quote:
Originally Posted by curly View Post
Afrs are about a half point rich, and like I said VE should go down in order to keep afrs stable. And what's the 130kpa high rpm stuff? Entire row should have the same basic curve, just at smaller numbers at lower kpas.
Thanks for the feedback sir!

Yeah 11.0:1 is probably too rich. I'm keeping it on the rich side for now for safety. I've never tuned a SC car and I blew a motor 3 weeks ago.... I'm learning!

I do see the cells at 130kpa need to be fixed. I haven't noticed that spot, I'll have to fix that. I haven't smoothed the table in a while to be honest.
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Old 05-23-2015, 04:09 AM   #53
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I see nothing wrong with 11.1afr on pump on a super hot supercharger.
What is baffling me is you burning enough fuel for 300whp and putting out like 230.
Unless you're doing the pulls up a crazy mountain this shouldn't happen.

Also when you ingest more air and more fuel, you should make more power. Your car seems to be defying logic in that regard
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Old 05-23-2015, 04:28 AM   #54
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Originally Posted by 18psi View Post
I see nothing wrong with 11.1afr on pump on a super hot supercharger.
What is baffling me is you burning enough fuel for 300whp and putting out like 230.
Unless you're doing the pulls up a crazy mountain this shouldn't happen.

Also when you ingest more air and more fuel, you should make more power. Your car seems to be defying logic in that regard
Thank you! Yes this is baffling me to. I agree physics says more air + more fuel = more power. Yes the blower uses power but damn not this much!

Unless I have VD setup wrong the numbers are way off from what they should be. The pulls are done on either flat-ish or slightly uphill. I didn't do any downhill for obvious reasons. I have yet to find a good flat stretch to tune on.

It's burning enough fuel to make MORE than 300whp.

772cc/min per cylinder is 297.6 lb/hr of fuel being burned. With a terrible 0.65 BSFC that should mean I'd make 297.6/.65 = 457 at the flywheel, with 20% drivetrain loss that would be 366whp. Obviously nowhere near that according to VD.

And yes the higher I rev it, the more it seems to breath and burn fuel. So it's not a restriction I don't believe, I think it's a tuning issue of some sort. I'll whip out the timing light tomorrow and see if I can find anything fishy with it.
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Old 05-23-2015, 04:35 AM   #55
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you set the final drive correctly in VD?
(although looking at the vids your speedo seems to be very similar to my msm which is also in the low 200's whp)
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Old 05-23-2015, 04:40 AM   #56
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I have it set as a 4.10. I'm pretty sure it's a 4.10, though it might be a 3.909. I guess I could spin and count the diff tomorrow to verify that so I know for sure. I have a clutch type LSD so it makes this test easy. Also have car weight at 2400, it might weigh more I've have never weighed it. I doubt it's much more than 2400 though if it is heavier.
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Old 05-23-2015, 08:59 AM   #57
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The car weight needs to include you. And unless you are a pygmy....it's heavier than 2400 with you in it.
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Old 05-23-2015, 07:31 PM   #58
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For discussion sake, let's say there's no mechanical problem with your engine like spark blowout of something, or an exhaust leak.

How high were you expecting it to make torque on stock cams??? Any way you slice it, the stock intake cam closes the valves at like 60 degrees ABDC (at least on the 1.8 with vvt head). Porting a head doesn't change that. Without a later intake valve closing or more air from the boosting device, there's only so much you can expect. There's also the backpressure issue, but thats less of a concern on a blower than a turbo.

My diagnosis, assuming no mechanical problem, is stock cam not breathing well enough. It's the nature of a stock intake cam. The intake valve closing timing is the biggest contributor to torque band on a naturally aspirated or supercharged engine. That's why Honda was using late closing lobes 25 years ago and just about every new engine can at least phase the intake cam.
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Old 05-23-2015, 07:56 PM   #59
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Quote:
Originally Posted by TNTUBA View Post
The car weight needs to include you. And unless you are a pygmy....it's heavier than 2400 with you in it.
Yeah I've got the car weight set at 2,400, plus me at 210 for 2610 total.

I don't know exactly what the car weighs, but it's a 99 with full interior, ac, p/s, sc, big ic, two ecus, two wiring harnesses, full tank fuel, 5gal water tank, upgraded radiator/fans, SC setup weighs 43 pounds for the blower/brackets/tensioner. I think exhaust is probably similar to stock weight. I'm also driving around with tools and a jump box, probably 30 lbs for that stuff. And laptop.

Quote:
Originally Posted by arghx7 View Post
For discussion sake, let's say there's no mechanical problem with your engine like spark blowout of something, or an exhaust leak.

How high were you expecting it to make torque on stock cams??? Any way you slice it, the stock intake cam closes the valves at like 60 degrees ABDC (at least on the 1.8 with vvt head). Porting a head doesn't change that. Without a later intake valve closing or more air from the boosting device, there's only so much you can expect. There's also the backpressure issue, but thats less of a concern on a blower than a turbo.

My diagnosis, assuming no mechanical problem, is stock cam not breathing well enough. It's the nature of a stock intake cam. The intake valve closing timing is the biggest contributor to torque band on a naturally aspirated or supercharged engine. That's why Honda was using late closing lobes 25 years ago and just about every new engine can at least phase the intake cam.
Thank you for the feedback sir! I do appreciate yours and everyone's help. I want to get this fixed.

Ok let me answer your questions and ask you a couple too.

I was expecting this motor, if it were Naturally Aspirated, to probably make 150whp more or less. It's a VVT motor, flat top intake, 01 header modded with 3" collector, 3" exhaust, and pretty decent headwork but as you say, stock cams. I think it should make peak torque about 500 RPM to the right of where a bone stock VVT motor makes it, and not fall off quite as hard. Maybe more, but it's only about 9.5:1 compression with stock cams on pump gas.

I think expecting 150whp with this motor being N/A is reasonable. And if it is, with 20 PSI boost, it really should be making more than 230whp.

With the SC, boost builds with RPMs, so torque should be flatter up top as boost keeps building. Most MP62 miatas, the torque is flatter at higher RPMs vs when they were NA due to the SC pushing in more air/more boost, kinda masking the lack of VE of the engine to some extent.

Ok now a question for you or anybody else who can answer it: What is the stock VVT cam specs for the intake valve closing ABDC? 99' heads close the valves at 49* ABDC stock. On my old 99' head I put the intake cam retarded such that the intake valves closed in the low 60's and that made a nice difference in top end power as expected.

I've considered timing the VVT cam a tooth retarded and playing with the VVT so I can get get the intake valves closing later at higher RPM. That may be worthwhile though I can't find anyone who has posted about doing it, I suspect it's been done though.

New post in a minute!
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Old 05-23-2015, 08:09 PM   #60
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Quote:
Originally Posted by arghx7 View Post
For discussion sake, let's say there's no mechanical problem with your engine like spark blowout of something, or an exhaust leak.

How high were you expecting it to make torque on stock cams??? Any way you slice it, the stock intake cam closes the valves at like 60 degrees ABDC (at least on the 1.8 with vvt head). Porting a head doesn't change that. Without a later intake valve closing or more air from the boosting device, there's only so much you can expect. There's also the backpressure issue, but thats less of a concern on a blower than a turbo.

My diagnosis, assuming no mechanical problem, is stock cam not breathing well enough. It's the nature of a stock intake cam. The intake valve closing timing is the biggest contributor to torque band on a naturally aspirated or supercharged engine. That's why Honda was using late closing lobes 25 years ago and just about every new engine can at least phase the intake cam.
No offense but the head/cam(s) should not be anywhere near maxed out. Maybe things are drastically different on a blower, but there's plenty of guys on here with stock heads/cams making over 400whp/350wtq to disprove that theory
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