98 fi car d1sc 408cu 125duty cycle?
12-29-2009, 10:09 AM
#1
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98 fi car d1sc 408cu 125duty cycle? dual walbros..detacated #8 to rails with boost ref reg.. 60lb deka..set at 60psi.. fuel ve numbers at 175-180kpa are 125-130 hp tuners.. still runs 12.0 a/f.. am i out of inj? not sure on hp of car either.. any ideas why so high on duty cycles?
12-29-2009, 10:24 AM
#2
I Don't think your injector flow rate table is scaled right in the tune. You shouldn't have 125-130% in you boost VE table, should only be around 100%. I'm running the same injectors with a return style fuel system and, and my boost VE table is in the 98% range at 175-180kPa Deka's at 60psi are in the 70lbs/hr range (their rated 60lbs/hr @ 43psi of fuel pressure). You DC is high because it doesn't have the correct injector size to do the calculations with. DC is just a calculated number.
12-29-2009, 12:19 PM
#4
You're probably are running out of injector. If your fuel pressure is only 60 psi at WOT then your 60lbers will only support around 625 rwhp. You'll have to bump up that fuel pressure to get any more out of them.
Both of my FI tunes had VE over 100 and my IFR settings were right on. When the engine gets into boost, the volumetric efficiency (VE) of the engine will be greater than 100%. If the motor was NA and had >100 cells then something would be wrong.
BTW: IFR and VE table are used to calculate IPW. Then IPW and RPM are used to calculate IDC. So the higher you spin your motor the less time the injector has to squirt fuel. This site explains it well:
http://www.stealth316.com/2-calc-idc.htm
My new engine made 620 rwhp at 58 psi and hit 98% IDC at 6700 rpm with the same 60lb injectors you have. IPW was 17.685ms. Sucks because they are brand new and I thought they would be enough. I guess that's why you see so many low mile injectors for sale.
Both of my FI tunes had VE over 100 and my IFR settings were right on. When the engine gets into boost, the volumetric efficiency (VE) of the engine will be greater than 100%. If the motor was NA and had >100 cells then something would be wrong.
BTW: IFR and VE table are used to calculate IPW. Then IPW and RPM are used to calculate IDC. So the higher you spin your motor the less time the injector has to squirt fuel. This site explains it well:
http://www.stealth316.com/2-calc-idc.htm
My new engine made 620 rwhp at 58 psi and hit 98% IDC at 6700 rpm with the same 60lb injectors you have. IPW was 17.685ms. Sucks because they are brand new and I thought they would be enough. I guess that's why you see so many low mile injectors for sale.
Last edited by white01ss; 12-31-2009 at 10:17 AM.
12-31-2009, 10:48 AM
#6
At 6000 RPMs it takes 10 ms for the crankshaft to go one revolution. It takes two crank revs to complete a 4-stroke cycle. So thats (60s/6000 rpm) * 2 revs = 20 ms. So @ 6000 RPM the PCM has only 20 ms to fuel that cycle.
So 125% means the PCM is attempting to hang that injector open for 25 ms to give the proper amount of fuel for that cycle, but it's physically impossible to do so because the next cycle is already starting after 20 ms. When this happens the injector is said to go static because it is never actually closed and that is a dangerous place to be because the PCM isn't in full control of the injector any longer.
The reason injector makers and automakers try to stay under 80% duty cycle is to stay in control of the injector. More importantly, to give the injector time to fully close before the next open event.
Bottom line, changing your IFR and VE tables isn't going to affect duty cycle at all if they result in the same pulse width. Play with those numbers some more and you'll see what I'm talking about. In the mean time, I would lower the rev limiter so it doesn't go over 95% duty cycle.
12-31-2009, 11:09 PM
#7
125% duty is 125% duty cycle. In my previous post I was talking about how duty cycle is calculated. Do you know what duty cycle means? Going over 100% is a very bad thing.
At 6000 RPMs it takes 10 ms for the crankshaft to go one revolution. It takes two crank revs to complete a 4-stroke cycle. So that's (60s/6000 rpm) * 2 revs = 20 ms. So @ 6000 RPM the PCM has only 20 ms to fuel that cycle.
So 125% means the PCM is attempting to hang that injector open for 25 ms to give the proper amount of fuel for that cycle, but it's physically impossible to do so because the next cycle is already starting after 20 ms. When this happens the injector is said to go static because it is never actually closed and that is a dangerous place to be because the PCM isn't in full control of the injector any longer.
The reason injector makers and automakers try to stay under 80% duty cycle is to stay in control of the injector. More importantly, to give the injector time to fully close before the next open event.
Bottom line, changing your IFR and VE tables isn't going to affect duty cycle at all if they result in the same pulse width. Play with those numbers some more and you'll see what I'm talking about. In the mean time, I would lower the rev limiter so it doesn't go over 95% duty cycle.
At 6000 RPMs it takes 10 ms for the crankshaft to go one revolution. It takes two crank revs to complete a 4-stroke cycle. So that's (60s/6000 rpm) * 2 revs = 20 ms. So @ 6000 RPM the PCM has only 20 ms to fuel that cycle.
So 125% means the PCM is attempting to hang that injector open for 25 ms to give the proper amount of fuel for that cycle, but it's physically impossible to do so because the next cycle is already starting after 20 ms. When this happens the injector is said to go static because it is never actually closed and that is a dangerous place to be because the PCM isn't in full control of the injector any longer.
The reason injector makers and automakers try to stay under 80% duty cycle is to stay in control of the injector. More importantly, to give the injector time to fully close before the next open event.
Bottom line, changing your IFR and VE tables isn't going to affect duty cycle at all if they result in the same pulse width. Play with those numbers some more and you'll see what I'm talking about. In the mean time, I would lower the rev limiter so it doesn't go over 95% duty cycle.
Now that he has the correct value in the IFR table and he gets his VE tables back in line, his IDC will be in line and will show he has plenty of injector left. I believe he said the car was making around 580-600 rwhp, with Deka 60's on a boost referenced, return fuel system and they should handle it easily.