Mercruiser Marine intake injectors

[onegonewild]

i have purchased a used Mercruiser MPFI intake for my 383 Vortec and am wondering which injectors i should use with it. I plan on 500 horsepower and according to the injector calculator: Brake Specific Fuel Consumption is roughly 0.50

So 0.50 x 500hp= 250 lb/hr of fuel used
8 cylinders 250/8=31.25lb/hr

Duty cycle should be at the highest of 0.8 so 250/.8=39lbs/hr injecotrs

Does 39 lbs/hr injectors seem applicable for this engine? its not like i'm going to be running at WOT all the time so i think i would be ok with the factory Mercruiser injectors of 29lb/hr. What do you guys think?

[stroker97k1500]

I am also running the marine intake with the factory injectors with my 383. I haven't come close to running out of fuel at all yet or even maxing out the duty cycle on the injectors I think it gets to about 60% at WOT, But I will go and double check this to make sure. I have a pretty mild cam though. zz4 350 cam with RHS heads, 10.5:1 CR N.A.
Robby

[hquick]

I'm running the marine intake with 42lb injectors on my SC'd 350 and only see about 30% max duty cycle.
I'm happy having the 42's though...plenty of room for growing.

[Aloicious]

I'm running the marine intake with 42lb injectors on my SC'd 350 and only see about 30% max duty cycle.
I'm happy having the 42's though...plenty of room for growing.

you're only seeing 30% max duty cycle? I wonder if the injectors being too big might be causing some of your transient fueling issues? what are your minimum pulse widths/duty cycle? just a thought sorry to hijack the tread

back on topic though, I'm running a MPFI intake on my vortec 350, its not the marine though, I'm also using a adjustable FPR, some specs in the sig.

I'm currently running some bosch 890 24# injectors at 45 psi on a vacuum referenced return system. I also had the injectors flow tested and bench tested for offsets and what not by yaw power, I typically see around 72% max duty cycle at WOT pulls, and around 3% min duty cycle.

I don't think I'm anywhere around 500hp, and its not a 383 (yet). your math sounds about right to me, I would think some 39# injectors would do pretty well for you, are you planning the engine to be n/a, or forced induction, etc?

[COMP]

any updates ?

[hquick]

From me...no.
I'm still having fuel issues but not sure if its pump related.
Doesn't hold pressure after I turn the key off and can have perfect AFR in the morning and way lean in the arvo.

[COMP]

From me...no.
I'm still having fuel issues but not sure if its pump related.
Doesn't hold pressure after I turn the key off and can have perfect AFR in the morning and way lean in the arvo.

injecters bleeding off ??

[stroker97k1500]

I am also running the marine intake with the factory injectors with my 383. I haven't come close to running out of fuel at all yet or even maxing out the duty cycle on the injectors I think it gets to about 60% at WOT, But I will go and double check this to make sure. I have a pretty mild cam though. zz4 350 cam with RHS heads, 10.5:1 CR N.A.
Robby

I went back and checked again to see what the actual duty cycle of the stock marine 24# injectors were at WOT and I saw up to 73 %....

Howard are the temperature differences in the morning and evening making the iat sensor read hot air going in and leaning it out perhaps?
Robby

[hquick]

I've considered those possibilities. The temp's aren't different enough to cause a 3 point lean out Robby. I was just watching my fuel pressure guage and I saw it change from sitting around 60psi to sitting around 40-45psi.
I don't think the injectors are an issue....they were brand new when installed.
I think I'll drop my tank and check the harness at the pump as these vehicles are known for having issues there.

[stroker97k1500]

I hope you will figure it out soon. I have faith you can figure it out! Good luck man.
Take care,
Robby

[hquick]

Thanks Robby,
I'll conquer it..afterall...it's only a machine...a smart one, but still...a machine. Lol!
My 14bolt diff should be leaving Canada in 2 days. On the pallet...among other things is a new dizzy gear (been waiting since before last Xmas for this). I reckon mine's stuffed and is a big cause of other issues.
So...we'll see. It's running ...ok, for the moment.