Ok guys i am trying to understand this thing (bhp per injector)

we have 1.5 bar of boost
we have 4.0 bar fuel press on idle

4.0 bar on greens = 493 cc/min

so on WOT (Wide Open Throttle) you have(need) 4.0 + 1.5 = 5.5 bar fuel press


5.5 bar of fuel press on greens = 390 cc/min (2.5 bar) + 427 cc/min(3.0 bar) (given by matts figures)

= 817 cc/min

now convert cc/min to lbs/hr

817 / 10.5 = 77.80 lbs/hr

now i want to calculate the bhp per injector

inj. size (lbs/hr) * 0.8 (80% ducty cycle) / 0.6 (.60 lbs (turbo charged)) = bhp per injector

77.80 * .8 / .6 = 103.73 per injector

all 4 injectors 103.73 * 4 = 414.92 bhp

now is this correct? (i think not but where did i fooked up?)

and is there a way how you can calculate which plug gap u need?


thanks!

 

Fuel pressure...

 

could u correct the point where i went wrong ? (just that part not the whole lot)

 

Beat me too it


You will always only have 4.0 bar fuel pressure. I'll tell ya seeing as Stu won't

 

you mean the fuel press you set on idle wont get any higher then that?

 

Are the cossie fuel press reg's not riseing rate?

PJay

 

my question exactly

 

4 bar ABSOLUTE pressure

pluggap depends on boost, plugs, coil etc.

oh, and haircolor
Come and pick up that radiator and give me back my cd's...

 

1st thing i thought wen i saw that u replied was OHOH

u got the rad then ?

will soon come up your way then we can have a nice chat

btw any figures so i could calculate the plug gap?

 

oh and how does it works if you havent set it up on absolute pressure ?

does above apply then ?

 

Well you should set it up at absolute pressure i.e. sans vacuum...
You don't calculate the plug gap as far as I know: you just ask a tuner and go by that! At a guess I'd say 0.6 will do nicely!

 

The fuel pressure at the injector tip 5.5 bar but you have 1.5 bar in the inlet manifold. So you have an actual 4.0 bar.

HTH

 

thanks hooligan and guinnless for explaining that so it should always be setup on ABSOLUTE press (not that i was doing otherwise i do what ive been told to do just want to understand it )


thanks!

 

Glad to help

 

Wahay stevie..

I reckon that answer puts you in the most knowledgable 3% of users on here...

I know for a FACT that most tuners in the uk dont know that M8, hence i thought id wait around and see who said what

Oh well.. You blew that plan to fook

 

just did a calculation on 4 bar absolute but the max i can get out of it is 250.4 bhp

still don't get it

 

Thanks Stu

 

Yes as Stu rightly pointed out its amazing that many folk dont realise why we use a rising rate fuel pressure regulator!

Put simply any liguid or gas will always flow from a region of high pressure to a region of lower pressure until the pressure is equalised.

If we set our fuel pressure to 4bar at atmosperic pressure then we have an effective 3 bar fuel pressure above atmospheric. For every 1 bar boost we add, we must increase the fuel pressure by the same amount in order to keep the 3 bar differential pressure.

Failure to do this will result in a diminishing injector flow rate as we increase boost!

 

84 views... at least 70 of em resulted in a loud "Ehhh? " i reckon..

 

so acutally my story in my start post works just isnt for setting up as absolute pressure

 

think so but i would like to understand

 

It's actually pretty logical I'd say...

 

hooligan then why doesnt my calculation works?

i used 4 bar fp and the best i can get out of it on all 4 injectors ie 250.4 bhp

 

Another wickid passionford post

 

aye now understand, i must

 

please someone explain in plain proper english cause i am foreign i am getting headaches

why does my calculation on 4 bar dont work ?

 

Puts hand up

Is good info tho

Ben

 

ok i got this stuff in my calculation you do a x 0.8 (80% duty cycle) then the end result = 250.4 bhp on all four injectors

100% duty cycle = 313 bhp

guess that's it then ?

 

Try it with a BSFC of 0.75 mate

 

:blonde: dime bar

i read this try to understand and then my mind shuts down and tells me to play minesweeper

 

thanks stu

but i think ill see if hooligan can explain it to me in dutch

cause with a BSFC of 0.75 i would need to flow 620 cc/min to get a 315 bhp (is that correct?)

 

well thats me lost

 

"Ehhh? " i reckon..

 

The point being, a small adjustment of the BSFC figure results in a large eror in injector choice..

How do you know the BSFC of the YB?

 

Don't bother understanding Rene: pay Stu or Tony to understand and use your time to better effect i.e. learn how to fuckin drive properly to save me having to wait on you after every corner on the ring next year!

 

it is the measured fuel flow in pounds per hour divided by the horsepower.

 

just need to get mine setup still running just about 1 bar ill try not to blow up me engine this time

where can i get a decent FP gauge hooligan like marijns's one? cause i am fed of telling that not having any time to setup me car

 

Drop by and I'll do it for you...

By: How do you know the BSFC of the YB? STU means SPECIFIC for the YB-engine I think...

 

cool happen to have a welder by any chance ? i've got a lambda sensor wich still needs to be fitted

thought that what i replied was a std rule ?

 

Yes but I imagine it differs per engine you plank!

Got a welder, need a downpipe and the boss for the sender to fit it...