I know the topic has probably been covered before, but the 'search' didn't give me the answer I was looking for. I just need to know how big injectors do i need for my engine. 8 injectors, expected power around 480hp at the crank.
Thank you for your help.
injector calculation
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Q45tech
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- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Simple each pound/hour of fuel [gasoline] can make 0.5 HP.35lb/hr [370cc] can make 70 HP x 8= 560 for safety [not to overheat injector by giving it some off time [0.8 or 80% duty cycle is the max safe time] 560 x 0.8= 448 HP .........480 HPwould be 86% duty cycle..........a no no!
A cheap easy way is to raise the fuel pressure above the 43.4 psi spec 480/448=1.0714 or 8% more flow.............50 psi would be perfect 50/43.4=1.1507 take square root=1.0733 more fuel flow.
Now if supercharged a differet HP per flow correction factor is used: 0.55 vs 0.5 so you would be 10% leaner than the normal for supercharged again you could raise the fuel pressure more to a max of 60 psi.......to accomplish a safe flow.
Or just go for larger than 370cc [35lb/hr] injectors but the larger the injector the more problematic it is to reduce the opening time enough to idle.........Nissan does this with a reduction in fuel pressure at idle and cruise to 34 psi. 34/43.4=12% reduction in flow at the same opening time............once you get down to 1.2 miliseconds the flow is further reduced by the pintle ramp up [opening time] so it may be half what you calculate.
On the 370cc injector the linear range is 2.5 to 13.5 milliseconds at standard pressures. The Q uses a max of 11.5 milliseconds and a minimum of 1.2 millisecs.........the 400HP JWT Nitrous kit for the Q just increases injector time by 25% from 11.2 to 14.0 as the rpms move thru the torque peak rpm but it is back in the linear range by 6,000 rpm.
A cheap easy way is to raise the fuel pressure above the 43.4 psi spec 480/448=1.0714 or 8% more flow.............50 psi would be perfect 50/43.4=1.1507 take square root=1.0733 more fuel flow.
Now if supercharged a differet HP per flow correction factor is used: 0.55 vs 0.5 so you would be 10% leaner than the normal for supercharged again you could raise the fuel pressure more to a max of 60 psi.......to accomplish a safe flow.
Or just go for larger than 370cc [35lb/hr] injectors but the larger the injector the more problematic it is to reduce the opening time enough to idle.........Nissan does this with a reduction in fuel pressure at idle and cruise to 34 psi. 34/43.4=12% reduction in flow at the same opening time............once you get down to 1.2 miliseconds the flow is further reduced by the pintle ramp up [opening time] so it may be half what you calculate.
On the 370cc injector the linear range is 2.5 to 13.5 milliseconds at standard pressures. The Q uses a max of 11.5 milliseconds and a minimum of 1.2 millisecs.........the 400HP JWT Nitrous kit for the Q just increases injector time by 25% from 11.2 to 14.0 as the rpms move thru the torque peak rpm but it is back in the linear range by 6,000 rpm.