What Is Difference Between Normal & Total Inj. Duty Cycle - Miata Turbo Forum - Boost cars, acquire cats.

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Old 01-10-2012, 08:11 PM   #1
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Default What Is Difference Between Normal & Total Inj. Duty Cycle

I think I may have maxed my Toyota 315cc injectors at ~7.5psi in a 1994 1.8L with EManage Blue.

Question is on datalogging the "Normal inj. Duty cycle" is fine as maxed out at ~80%

but the "Total inj. Duty cycle" is maxed out at 100+%


Whats the difference between Normal and Total?



Should I up the fuel pressure?
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Old 01-11-2012, 12:40 AM   #2
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I'm pretty sure you're maxing them out. As in total 100% = bad. You'll want to take it easy until you get a FPR. I ran 95psi on my Supra injectors for a few thousand miles no prob. Then I switched to MS and 550s.

Could you post a screencap/datalog with both parameters showing? My first setup was EMB but it's been so long I don't recall everything about it.

Edit: It sorta came back to me. I think normal duty cycle is more or less what the stock ECU is putting out. Total shows what the duty cycle is with your additions to it from the INJ map.

Last edited by messiahx; 01-11-2012 at 01:07 AM.
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Old 01-11-2012, 09:46 AM   #3
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I'm still sipping on my morning coffee so I hope this makes sense to you.

Typically we aim to inject all the fuel before the intake valves open. There's only a small window to do this when you factor in the 720 cycle. On the miata, IIRC, the intake open 5 BTDC all the way until 51 ABDC, so a total of 236...

So if you consider how long the intake cycle takes, then the window to inject fuel has become even shorter, because you must wait to inject again once the intake valves close, and really only have 484 to get all your fuel in front of the valve.

So let's say you're injecting 80% duty. That may mean you're sparying fuel the entire time after the intake cycle end, and possibly during it, to ensure you have all the fuel you require once the intake opens again.

If you step up to bigger injectors this isn't a problem since more fuel can be supplied in less time, so the "normal" and total duty times will reduce.
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Old 01-11-2012, 10:08 AM   #4
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In other words, yes you're maxing them out. Most people/tuners prefer never to go over 80% duty cycle on any injectors because at that point they're open nearly the whole time and/or can go static. I never took that seriously til one day tuning a wrx and 3 out of 4 injectors atually did that. Just started gushing fuel into the motor and the car wouldn't even stay running or restart after initially dying.
Megasquirt and some reall injectors (460+) is what you should be considering at this point, or just stay within the limits of the current setup. You could bump the pressure like previously stated, but that's only going to get you so much more fuel. Like 1-2 psi worth? not sure if worth it.
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Old 01-11-2012, 10:57 AM   #5
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I've actually did math with my injectors running 80% DC, and in order to get all the fuel I need at higher RPMs in front of the intake valve before it opens so 10 BTDC, I need to never stop injecting.
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Old 01-12-2012, 12:17 AM   #6
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Quote:
Originally Posted by 18psi View Post
In other words, yes you're maxing them out. Most people/tuners prefer never to go over 80% duty cycle on any injectors because at that point they're open nearly the whole time and/or can go static. I never took that seriously til one day tuning a wrx and 3 out of 4 injectors atually did that. Just started gushing fuel into the motor and the car wouldn't even stay running or restart after initially dying.
Megasquirt and some reall injectors (460+) is what you should be considering at this point, or just stay within the limits of the current setup. You could bump the pressure like previously stated, but that's only going to get you so much more fuel. Like 1-2 psi worth? not sure if worth it.
If he runs a ridiculous 95psi rail pressure like I did, he'll be able to pretty much get everything out of that turbo. Pretty much makes them into 460s. At ~14psi on my 2554 I was getting 75% DC IIRC. Same setup as him pretty much. If he doesn't want to take the leap into MS just yet and can find a cheap used begi RRFPR it would certainly be a viable setup.
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Old 01-12-2012, 06:52 PM   #7
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Some great info here, thanks.

messiahx: "I think normal duty cycle is more or less what the stock ECU is putting out. Total shows what the duty cycle is with your additions to it from the INJ map."
I think that makes perfect sense now.

Braineack: "only have 484 to get all your fuel in front of the valve"
Really interesting way to think about it, but I like it as it helped me visualize the problem.


messiahx I think raising the fuel pressure as you did will probably be the way I will try for now. However the cost of a rising rate FPR seems really costly from BEGi or Vortech at about $180 !

Precision Turbo injectors could be about $230 for 390cc's. By my calculations the standard injectors were 265cc x 150% = 397.5cc so the EMB can handle 390's. This might give me enough fuel at low enough total duty? How do I calculate that I'm wondering?


Unfortunately I don't have $230 at the moment. So can I not just buy a cheaper adjustable FPR, increase the EMB injector change to suit with upping the pressure till the total duty is ~80% max?

Or will the engine not like this, so is a rising rate FPR a must?
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Old 01-12-2012, 06:55 PM   #8
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buy a cheap vortech knock off.

with the red 240cc stock injectors and a 12:1 ratio FMU I've seen the EMB (with Bruce's [olderguy] autotune) put out perfectly flat 12.0:1 AFRs and <80%DC pushing around 240rwhp.
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Old 01-12-2012, 07:20 PM   #9
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Braineack "buy a cheap vortech knock off"

Sounds interesting. Any suggestions on make? or where from? would be appreciated thanks
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Old 01-12-2012, 07:28 PM   #10
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fleabay
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Old 01-13-2012, 11:49 PM   #11
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Old 01-14-2012, 10:43 AM   #12
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hell i might have a vortech FMU in my closet. i cant remember if i sold it or not.
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Old 01-14-2012, 09:53 PM   #13
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On my 99 with emb, greentops, and 60psi stock regulator pressure I was running 11psi and seeing about 95% dc. My car seemed to like 12-12.2 afrs so that's what I tuned for.

fwiw, I just disassembled my motor last month and it looked great. No detonation marks and the rods and pistons looked brand new.
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Old 01-24-2012, 07:07 PM   #14
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Well doing some calculations raising the fuel rail from the stock 43.5psi to 68psi will let the 315cc's flow as 393.84cc's at a safe 80% duty = good enough for potential 200bhp and the EMB can handle it. (Much safer than the standard 265cc's at 96psi).

Therefore as its unlikely to make 200bhp, a FPR that can increase the rail by 24.5psi ideally with a gauge and fitting kit, should do.

The two unknowns at the moment are:
Finding out how high a pressure the 315cc's can run at safely?

Finding what max psi the OEM fuel pump can cope with safely?
I have read the pump tends to max at 85psi on here but is it the same for a 1.8L Eunos roadster?
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Old 01-25-2012, 08:37 PM   #15
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Depends. My OE pump lasted at high pressure for a little while. Now I have a walbro. Your injectors will be fine. "Lock up" seems to be exaggerated. I ran 95psi on my Supra injectors without issue.
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Old 01-28-2012, 09:45 AM   #16
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Thank you for the reassurance messiahx, I thought "lock up" would be unlikely at ~68psi I might have to run up to.

Hope to test max psi the pump can run before I drive car.
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Old 01-31-2012, 09:27 PM   #17
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How accurate do you think the emb is when dealing with duty cycle?
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