93flatbed

Today in a discussion I was having with a group of performance minded friends an interesting topic was brought up, and I'd like to propose the question to a larger group of folks, as our small group was split on the answer.

Let's say an engine with 360 cubic inches was being used. We are at sea level, we had 28~ pounds of boost feeding the engine. Do you/we select an injector that is capable of fueling 360 CI or 1080 CI? Let's pretend that the head flows perfect (we WISH being cummins owners...), Yes heat builds boost, boost flows bla across bla. Let's pretend everything is perfect for our hypothetical engine, for sakes of discussion. What injector do we need to fuel our 360CI engine? Support your decision with ideas behind your selection.

patdaly

You need the Injector capable of flowing enough fuel to support the max Hp. that the engine in question can produce given the air flow it is capable of.

There are entirely too many variables from port design, to air temperatures given a turbo design, to fuel energy densities to reduce it to a straight cubic inch formula.

I don't play too much in the performance Diesel area, but do in the Gasoline side.

I can produce roughly 1350 Hp with my 489 inch blown injected BBC with 83 Lb Injectors and I have friends who are producing roughly the same Hp. with 5.3 L ( 327 CI ) engines that need 210 Lb injectors.....

For the purposes of your question though, which Injection Pump will we be using, for that makes but another very interesting variable in the ointment.

93flatbed

Well we are in the first generation area, so of course a VE. Let's say our hypothetical engine has 400 CC'S worth of VE at 3,000 RPM.

patdaly

Fair enough, I admit I am not well versed in the Diesel area, so I will be learning along with Y'all.....

93flatbed

Since this isn't getting any traction let's change the question a bit. Our same scenario but rather than injector selection let's determine how much cubic inches our engine is. Is it hypothetically still just 360CI or 780CI or 1,080CI? What I'm getting at, is shoving two extra atmospheres into our 360CI make it bigger? Not that it changes the physical dimensions of the engine but we are shoving way more air in our "air pump" than what it can "drink" on its own..

j.fonder

400cc!!! Must be a 14mm...

Anyhow, yes, fuel for your theoretical ~1050 ci.

[(28psi+14.7) / 14.7] x 5.9L = ~1050 ci.

More air allows for more fuel. Hence the reason for forced induction...

93flatbed

400 cc's pish posh little pump stuff.

Thanks for throwing an end wrench in my math, we were talking hypothecal...

I like your answer, I fell on that side of the fence. I do however look over the fence at times, grass may be greener over there....???

KATOOM

Exactly.

And this sounds like a fun group too. I enjoy people who like such discussion.

As for an answer, even though the discussion is taking place in a "prefect world" there are too many variables involved for a black and white group answer. Like what type of engine, type of fuel, altitude, ambient temperature, is this engine making usable power or just WOT, etc... But for the sheer sake of physics the stoichiometric AFR depends on fuel type.

1972RedNeck

Over on 4BT Swaps there are quite a few threads about calculating horsepower from available air and fuel.

This is just an example.

Calculating 300hp using cc/ 1000 shots and turbo sizing

93flatbed

Okay if we'd like to go down that road we can. Let's middle the road and assume we are around 70VE for our hypothetical engine. So are we at 252,504,756 CI?

I'll throw my own junk pile out there so we can attempt to figure this out. I have a 63/76 compound system, water to air inner stage, air to air on the final run. I should be running around 55-65 lbs of boost if I can get the big guy spinning. My head is well worked over, but still stock valves so I will not pick much up there... If you do the math with no boost our horribly designed engines have around a 65%VE, not much we can do about that besides call Zach for a warhead, or one of the many other head design guys out there. BUT this is a first gen and we are all cheap so most of us have a stock head with heavy spings and maybe a 3" elbow...

I digress, let's try to figure out with my projected CI using what I'm hoping I'll be at. We are still assuming (yeah I know assume makes an ... out of...and me) 70% VE with my projected 4-4.4 added atmospheres I'm trying to shove in a bottle neck is my engine still just a 360CI or do I have a monster 1584(or using our 70% rule) an 1108 CI between my frame rails..??

We are on a diesel site so we are using diesel fuel. So I'll even throw this out, are my 5LPM injectors going to lean me out or over fuel my engine? We are back to the crux of the original question, how much fuel do I need for a a given CI of an engine, and how do we decide?

Or is this all a waste of time and I should order a 3200 spring an M&H pin and stop thinking about it..??

I'm really not sure if there are any right or wrong ideas, so don't be scared of typing what's on your mind. This is how ideas form and things get figured out, group discussion. I may have part right and billybob has the other part and jimbob has the last piece of the puzzle...

GO.

1972RedNeck

WAY under-fueled. I think somewhere between the 70 and 80 LPM range would work well for your setup.

93flatbed

Awe sorry, forgot some measure your injectors using air. If mine were flowed using air (never understood why a company would flow air threw an injector that moves fuel) I'd be in the 80+ range..

j.fonder

agreed. but since i know the stock injectors are ~40LPM air, we'll use air for this theoretical comparison.

if we use 18psi as our baseline boost number, because thats what most stock trucks will give you. heres what we come up with

[(18psi+14.7) / 14.7] x 5.9L = ~800 c.i.

so we can say that stock 40 LPM injectors will fuel the stock 800 c.i.

now for your massive air pump

[(55psi+14.7) / 14.7] x 5.9L = ~1707 ci.

thats 2.13x the cubes

so 40 LPM x 2.13 = 85.2

so i could theoretically say that as long as fuel supply is there, meaning you don't suck your A1000 lift pump and Giles IP dry, 85 LPM injectors would fuel your 1707 CI.

as previously stated, this is by no means a scientific way of determining injector size. just a fun, theoretical convo.

j.fonder

I forgot to factor in the 5% increase in VE gained by head porting.

So 85.2 LPM x .95 = 80.94 LPM would be required for your theoretical air pumping monster

ofelas

I don't understand the math. Subscribed.
1/ Why a blanket 5% for head porting?
2/ So wouldn't variable displacement on a forced induction engine throw fixed injection event out the window ?