anachranerd

10-22-2008, 09:47 PM

Ok all, I need your input here.

I am trying to make some calculations on injector duty cycle here.

For starters, I made an excel sheet. one row i have rpm. then i take that rpm, divide it by 2, then divide it by 60 seconds. I take that result x, and calculate its inverse (1/x) to obtain how many seconds per cycle(intake+compression+combust+exhaust).

So for example, at 800 rpms's, 1 complete cycle takes .15 seconds..( 1/((800/2)/60)).

Then, I divide that cycle time by 4 to get the time of the intake stroke.

.15/4 == .0375 seconds.

So if I fire my injector the entire intake stroke, it will be on for .0375 seconds.

I did a test/cleaning of my injectors. I took the rail out, attached the injectors, an inline fuel pump and filter, and ran each for 15 seconds. Each output ~70 cc's.

So 70cc's for 15 seconds, that is 4.6 cc's per second. 4.6 per second, by .0375 seconds, gives me .175 cc's of fuel in that stroke. So let's say I have the perfect mix, and have 14.7 cc's of air for every cc of fuel. I have

.175 cc of fuel + (.175 *14.7)air == 2.74 cc's of combustible mixture.

I have a 1998 cc engine( lets use 2000 for simplicity). So at each cylinder i have 500 cc's. Now I dont know the CR of my own engine(surprising as ive been playing with it for two years :smokin: ). But let's say it is 10:1. At full compression I have 50 cc's of space, but only 2.74 cc's of material. this doesnt make sense to me.

What am I missing?

I am trying to make some calculations on injector duty cycle here.

For starters, I made an excel sheet. one row i have rpm. then i take that rpm, divide it by 2, then divide it by 60 seconds. I take that result x, and calculate its inverse (1/x) to obtain how many seconds per cycle(intake+compression+combust+exhaust).

So for example, at 800 rpms's, 1 complete cycle takes .15 seconds..( 1/((800/2)/60)).

Then, I divide that cycle time by 4 to get the time of the intake stroke.

.15/4 == .0375 seconds.

So if I fire my injector the entire intake stroke, it will be on for .0375 seconds.

I did a test/cleaning of my injectors. I took the rail out, attached the injectors, an inline fuel pump and filter, and ran each for 15 seconds. Each output ~70 cc's.

So 70cc's for 15 seconds, that is 4.6 cc's per second. 4.6 per second, by .0375 seconds, gives me .175 cc's of fuel in that stroke. So let's say I have the perfect mix, and have 14.7 cc's of air for every cc of fuel. I have

.175 cc of fuel + (.175 *14.7)air == 2.74 cc's of combustible mixture.

I have a 1998 cc engine( lets use 2000 for simplicity). So at each cylinder i have 500 cc's. Now I dont know the CR of my own engine(surprising as ive been playing with it for two years :smokin: ). But let's say it is 10:1. At full compression I have 50 cc's of space, but only 2.74 cc's of material. this doesnt make sense to me.

What am I missing?