fuel injectors calculations vs experience
 

Working on my single turbo selection and i started with my fuel system first. For once i did things in order.

Here are some constants (approximates)

1 Gallon = 3785 CC
6.25 lbs/gallon of gas (variable on density)
14.27 CF/lb of air
14.7 stoich AFR (in mass)
weight and mass have same ratio(while gravity is constant)
7.5RWHP for every 1lb/min of air

Stock fuel system:
2X550cc/min and 2x850cc/min
2800 cc/min MAX flow --> convert to gal
0.74 gal/min MAX flow--> convert to weight
4.62 lb/min of gas MAX flow --> multiply times stoich AFR to get air weight/mass
68 lb/min of air --> times rough RWHP calc
510 RWHP MAX flow

I was bothered that this hypothetical situation yielded so much power when ive hit 90% injector duty at 12 AFR and probably peaked at 300hp... then it hit me

2800cc/min --> 90% max
2520cc/min --> convert to gal
0.67 gal/min 90% flow --> convert to weight
4.16 lb/min 90% flow --> multiply times 12 AFR instead of stoich
49 lb/min air --> times rough RWHP calc
375 RWHP

Much better. Now i did that just to understand the upgraded system that im installing. staying 550s in the primaries and upgrading to 1680s in the rear.

2X550cc/min and 2X1680cc/min --> addition and multiplication duh
4460 cc/min max flow --> 85% max for safety reasons
3791 cc/min --> convert to gal
1 gal/min -->convert to weight
6.25 lb/min --> multiply times 12 AFR, yes ill do Water Injection
75 lb/min air flow at 85% inj duty --> rough RWHP calc
562 RWHP

Im sure there are write ups before me, but how do your real world experiences compare with 550s and 1680s? im pretty familiar with 550s and 850s and their limits.

You are only looking at a component of a system.

Fuel pumps can be limiting factors and there is fuel pressure variable.

I personally went 850/1600. I went 550cc/1600 but perfered the transition of 850cc.

I found with 550 primaries i had high duties before transition then very low after - a large disparity.

could you feel a hesitation as they transitioned or was it just duty cycle numbers?

here's my take on it...

4460 CC/Min = 1.1782 GPM
93 octane 6.35 lbs per gallon... 7.4815 lbs/min
10.5 AFR ( i think you need to have enough gasoline delivery to run rich if necessary.)
7.4815 X 10.5 = 78.55 lbs/min air
max duty cycle 85%... so 78.55 X .85 = 66.77 max air
66.77 X 966 CFM/1.92 = 503 rw rotary hp.

as you can see we are fairly close given my more conservative assumptions.

this shows me that your 550/1680 setup will be fine w a GT3582r since it flows 62 lbs.

it will not work w a 76 mm turbos such as a GT500, TO4Z or PT67 as they deliver 73 pounds.

howard

Good point on the run rich first and tune down from there. 850cc primaries idle and hesitation is a thing of the past right? Sounds like that's improved dramatically. The kit I'm buying has a wastegate spring at 15psi and I'm not blowing my engine until after deals gap event. I'm doing AI from the start though. :-)

the Power FC has a locked minimum Ms ontime number... you can input a lower ontime but it will not register... causing 850 primaries to idle a touch richer than 550s the limited options for a fix generally create worse related issues.

there are no hesitation problems.

good for you on the AI and it is nice to see someone doing the "math" w re to fuel.

good luck,

howard

I use a haltech.

I could but that's not to say it couldn't have been tuned out with more time/effort.

I just perfer lower duties before transition. I was in the 7-8ms range with 550cc.

You can see i'm about 4.5ms now.

It idles better with the 850cc (I attribute that to cleaned injectors).

It was free for me to upgrade (modified primary rail).