Injector choice?

[Alexiskayak_7]

How you know what size of injector to choose? I'm talking generaly not only for g40s
I found on the net some calculators but the are not accurate...

 

[hayesey]

easiest way is to go off other people's experience.  To actually calculate it accurately you need to know your bhp aim and work out how much fuel per bhp the engine will consume.  You shouldn't need anything more than 310cc in a g40 unless your aim is over 230bhp. If your aim is somewhere between 160-180bhp then use 250cc, if you are just wanting 160 max then standard ones are fine.

[Vizor]

with oscilloscope watch the duty cycle..!
i'm with ihi rhb5 (0,8bar) and stock g40 injectors, stock fpr, stock camshaft and duty cycle is between 87-90% (remapped!)

[Yoof]

Vizor- I'd replace them with a larger injector or increase the fuel pressure. I'd consider anything greater than 85% to be static.

There's several simple formula on the internet to work out injector sizing.

Just need to know your bhp target, how many injectors, and brake specific fuel consumption (BSFC) i.e the amount of fuel required per horsepower.

[hayesey]

yeah its the BSFC that I was getting at being difficult to calculate.  I *think* it'll be about 0.45 for a g40, but obviously it'll vary to some extent. 

You don't want to be pushing injectors beyond 80% duty really.

On the other hand, you can't just use the biggest injectors you can find in your local scrapyard as you'll get poor atomisation and fuel drop-out at lower load levels if you are using injectors that are too big.  This will at best give poor mpg and poor part throttle driving and at worst not pass an mot or even cause bore wash in extreme cases. 

To complicate things even further, even two Bosch 310cc injectors might not be the same.  Some have a single large pintle and some have quad small pintles.  The max flow rate is the same but the behaviour on part load is different.  You'll get better atomisation with quad pintles and slightly better mpg. 

[Vizor]

Vizor- I'd replace them with a larger injector or increase the fuel pressure. I'd consider anything greater than 85% to be static.

I had another thought. ~ 240 cc injectors and FPR should be enough. We just do not see sense to raise their flow. In these data I am with 10.8 afr at the end of exhaust (However, there is more oxygen).

[hayesey]

~240cc injectors and standard 3bar FPR should be ok with 0.8bar boost, although it obviously depends on the spec of the rest of the engine.  Increasing fuel pressure is certainly a common way of increasing fuel flow though, I've seen an eaton conversaion on a g40 engine where the "remap" consisted of nothing but increasing fuel pressure until an acceptable AFR was seen.  It ran like shite though but the conversion was full of bodges like that so the running issues could have been a number of things.

[djtez]

Should you change the FPR when running G60 greens?
What pressure does the standard G40 FPR run at ?

[hayesey]

it runs at 3bar and you just leave it at that all the time.  No need to change it.

[Alexiskayak_7]

Yoof, i can't understand that BSFC value...
For example:


Aiming 180hp, with 4 injectors and 0,6 bsfc (turbocharged) it says that i have to use 350cc... and we with g40s are ok with 300cc injectors for that power...

[djtez]

it runs at 3bar and you just leave it at that all the time.  No need to change it.

cheers bud.. just making sure

[hayesey]

Alexis, most of the examples I've come across like that are probably designed with old yank v8 engines in mind, a 1272cc g40 engine is somewhat more efficient than those.  You simply can't apply such simple rules for BSFC for any engine in existence.  I seem to get reasonable values out of the calculators using a BSFC of about 0.45 which suggests that BSFC for a g40 engine lies somewhere around there.  You'd need to have the engine on a dyno to actually observe BSFC or you could probably calculate it by working out the CFM of the engine but the maths makes my head hurt even thinking about it.