89% duty cycle on a bolt on car
06-06-2011, 09:09 AM
#1
89% duty cycle on a bolt on car I always knew 2000's had small injectors but is 89% duty cycle on a bolt on car a little high? I keep seeing threads with people camming and still being okay. I have lid, throttle body, ls6 intake, headers, exhaust and only revving to 6200rpm
could it be in the tune? just running crazy rich at high rpm's?
could it be in the tune? just running crazy rich at high rpm's?
06-06-2011, 11:42 AM
#2
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well, has it been tuned? do you know your WOT AFR value?
The industry accepted standard for maximum duty cycle is 85%, take it as that and do what you want with it.
I suggest going under 85% duty cycle. When getting new injectors, you can nearly use a scaling factor from old to new injectors and guesstimate your new duty cycle with whatever size injector you want to put in its place.
The industry accepted standard for maximum duty cycle is 85%, take it as that and do what you want with it.
I suggest going under 85% duty cycle. When getting new injectors, you can nearly use a scaling factor from old to new injectors and guesstimate your new duty cycle with whatever size injector you want to put in its place.
06-06-2011, 01:06 PM
#3
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I'd have to go back and look at my old logs, but off the top of my head that doesn't sound too far off. When I installed the cam my duty cycle went up over 100%, so I quickly swapped out for a set of 42s. Duty Cycle now peaks a tick below 70%. My WOT AFR runs 12.7-12.8 on the wideband in the collector.
06-06-2011, 03:45 PM
#5
I had it dyno tuned 2 years ago with a wideband both part and full throttle, I never saw what the final numbers actually were a/f wise
I just got hptuners and started datalogging and that's what I found, I just see all these people running crazy power on stock injectors and never thought about touching mine until I saw these numbers. Thanks for the offer but I can get 28# injectors for $30-40 and if I did upgrade I'd probably go to 36# if not 42# just to be safe
I just got hptuners and started datalogging and that's what I found, I just see all these people running crazy power on stock injectors and never thought about touching mine until I saw these numbers. Thanks for the offer but I can get 28# injectors for $30-40 and if I did upgrade I'd probably go to 36# if not 42# just to be safe
06-06-2011, 04:35 PM
#6
Agree you can find stock injectors for that price but they are going to have crazy miles (despite what the seller says) and who knows how long they will last before you get a clog or have one fail. Mine look brand new and that's because they nearly are.
Based on your current mods, you don't need even 36# much less bigger, but they would be a good idea if you plan to mod further. In other words, they would give you "room to grow".
Based on your current mods, you don't need even 36# much less bigger, but they would be a good idea if you plan to mod further. In other words, they would give you "room to grow".
06-06-2011, 08:45 PM
#7
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from 26 to 28.8 its honestly not worth it. not trying to kill a sale, but here is my reasoning
28.8/26 = 10% different, so roughly 10% less duty cycle. Awesome if you don't plan on doing anything else and you need to go from 85 to 75% duty cycle.
but won't do much in the way of future mods.
28.8/26 = 10% different, so roughly 10% less duty cycle. Awesome if you don't plan on doing anything else and you need to go from 85 to 75% duty cycle.
but won't do much in the way of future mods.
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06-06-2011, 11:12 PM
#9
well thanks guys, I'm going to datalog my friends' car (also a 2000, tuned by the same shop) and see where his injectors are at. then I'm either going to buy or borrow a wideband and figure out this tune. it was a half a4 half m6 tune with pieces of my original tune thrown in randomly with the 6 speed flash I had done when I swapped
I plan on upgrading injectors at some point, it's a daily driver for a few years yet but I set up the new trans for something bigger in the future. I have a TDP stage 2 clutch, some little upgrades to the t56, and a tick master. I also have some heads ready to be ported at some point in the future and some other goodies laying around for when the day comes to build it.
I plan on upgrading injectors at some point, it's a daily driver for a few years yet but I set up the new trans for something bigger in the future. I have a TDP stage 2 clutch, some little upgrades to the t56, and a tick master. I also have some heads ready to be ported at some point in the future and some other goodies laying around for when the day comes to build it.
06-07-2011, 08:53 PM
#12
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I just looked on my laptop at my old dyno run logs. 94% duty cycle peak just before fuel cutoff at 6200 with most of the standard bolt ons - headers w/ cats, exhaust, ls6 intake, lid, ported tb, etc. AFR was 12.7 measured in the collecter on a NGK AFX w/ NKT sensor. I believe that run netted 355rwhp, so the stock 26lb injectors don't support much.
06-08-2011, 12:25 PM
#13
thanks! I always see people saying 450 is about the limit on the stock 28's but that always sounded pretty high to me. I figured a very small cam would be the limit for 26's but not bolt ons. I'll definitely upgrade them before any other modding. I'm just surprised the shop that tuned the car wouldn't mention it to me.
06-08-2011, 12:29 PM
#14
My '99 Z28 is at 350 RWHP (full bolt ons) and I upgraded it to 28.8 injectors. I cannot remember the exact duty cycle, but we were checking it and it was fine. Not much extra room, but fine at that power level.
I would not expect 28.8's to support 450 wheel, not even close.
I would not expect 28.8's to support 450 wheel, not even close.
If.. 
06-08-2011, 08:05 PM
#16
That sounds about right to me, I generally see duty cycles in the 80's for bolt on cars with stock injectors. I don't know how guys claim over 400rwhp on stock injectors but I've never heard of them saying what their duty cycle is either. They're probably also running on some happy dynos.
