Injector Duty Cycle

[oldskool]

Hi, I posted earlier in Tuner Studio forum, not sure which forum to post. I'm reviewing logs with Megalog viewer, my Duty cycle 1 at 5,000 rpm is 114.9, Duty cycle 2 is 109.6. PW is 27.217, PW2 25.98, AFR 10.4. I'm concerned if my 38lb injectors are enough. Is Duty Cycle in Tuner Studio same as injector duty cycle? I'm sending MSL & MSQ. I have a few more files I can upload with same tune & component combination in different roadtests. Thanks.



67 Firebird 400 .060" over.
Comp Cams custom ground solid roller
Twin T04E turbos
75mm LS1 TB on Edelbrock elbow
Tomahawk intake
HEI7
38# injectors
40psi fuel at idle
46 = WOT

[pit_celica]

Yes, Duty Cycle in in the log is the injector duty cycle. It is correctly calculated as you are opening the injector for about 25ms at 5000 RPM. At 5000 RPM, a complete cycle (720°) is 24ms. So, your injector is open all the time and this lead to a 100% duty cycle.

Using a BSFC of 0.5 and a max duty cycle of 100%, your 38 lb/hr injectors should be delivering about 600 crank HP in fuel. Do you think you are developping that kind of power? If so, than your injectors are too small. If not, then you're not using all this fuel efficiently, or maybe your fuel pressure regulator isn't raising the fuel pressure in a 1:1 ratio when in boost. Is your fuel pressure regulator referenced to manifold vaccuum/boost?

Sam

[oldskool]

Sam, thanks for the reply, I should have a boost reference regulator, I'll make sure. I upped by base fuel pressure from 40psi to 55 psi to see if it made a significant change. Didn't seem to, looking at my logs, there nothing consistant of when duty cycle is maxed out, it has it's peaks. Today I took to track to test, added 2nd wideband to "bank 2 bank" system with each wideband controlling it's own bank. I'l can post some logs. I have a set of RC 72lb injectors, going to bench test them & install if they're OK, same time lower my fuel pressure back. I was reluctant to try them thinking they're too big, several people I spoke with today said their cars worked well with 72's.

67 Firebird 400 .060" over.
Comp Cams custom ground solid roller
Twin T04E turbos
75mm LS1 TB on Edelbrock elbow
Tomahawk intake
HEI7
38# injectors
40psi fuel at idle
46 = WOT

[9secz]

SI have a set of RC 72lb injectors, going to bench test them & install if they're OK, same time lower my fuel pressure back. I was reluctant to try them thinking they're too big, several people I spoke with today said their cars worked well with 72's.

I ran 96 lb/hr low impedance injectors in a 385 cu in Chevy small block on the street for 4 years with no driveability issues.

Jeff

[oldskool]

SI have a set of RC 72lb injectors, going to bench test them & install if they're OK, same time lower my fuel pressure back. I was reluctant to try them thinking they're too big, several people I spoke with today said their cars worked well with 72's.

I ran 96 lb/hr low impedance injectors in a 385 cu in Chevy small block on the street for 4 years with no driveability issues.

Jeff

Thanks for reply. I've since installed RC 750cc injectors, set required fuel in Tuner Studio, duty cycle is 41% at 4,100 rpm then rises to 77% at 5,900 rpm (10.0 AFR, trying to get to 11.5). I'm now using VE Analyzer through Megalog viewer to set VE table, it's setting lower numbers where AFR is running rich, just need some more drive time.

It's been a few weeks since I changed injectors, I've had a "hard start when warm" (probably don't notice as much cold as it needs to be richer) like it's flooded, hold throttle wide open to start w/black smoke upon startup. Thinking maybe possible fuel bleeding off through injectors, I pulled from intake, tied to fuel rails with injectors unplugged from harness. No leak energizing fuel pump, plug in, injectors squirt turning key on.

Is this a settings issue with larger injectors? I'm running Bank 2 Bank with default setting on injector "dead time". What controls how much initial fuel gets squirted with turning "key on" ?? Thanks in advance.

67 Firebird 400 .060" over.
Comp Cams custom ground solid roller
Twin T04E turbos
75mm LS1 TB on Edelbrock elbow
Tomahawk intake
HEI7
750cc injectors - were 399cc
40psi fuel at idle
46 = WOT