Calculating Injector Sizes

[Error404]

I know most people use B.S.F.C. as the factor in injector sizing based on the following:

(B.S.F.C. x Target HP) / (No. of Injectors x Max Duty Cycle ) = Injector Fuel delivery in lb/hr

For example:
Target HP = 500
B.S.F.C. = 0.65 (suggested rate for FI engines)
Injectors = 5
Max Duty Cycle = 0.80

So: (0.65 x 500) / (5 x 0.80) = 81.25 lb/hr

Converting to metric = (56.25/60) x 453 = 613g/min
Fuel density = roughly 685kg/m³
So 613g/min / (684/1000 = 895cc/min

I know the BSFC is very approximate ratio and different for different engines, but that sound like a lot to me.

[tomwood_uk]

I know most people use B.S.F.C. as the factor in injector sizing based on the following:

(B.S.F.C. x Target HP) / (No. of Injectors x Max Duty Cycle ) = Injector Fuel delivery in lb/hr

For example:
Target HP = 500
B.S.F.C. = 0.65 (suggested rate for FI engines)
Injectors = 5
Max Duty Cycle = 0.80

So: (0.65 x 500) / (5 x 0.80) = 81.25 lb/hr

Converting to metric = (56.25/60) x 453 = 613g/min
Fuel density = roughly 685kg/m³
So 613g/min / (684/1000 = 895cc/min

I know the BSFC is very approximate ratio and different for different engines, but that sound like a lot to me.

If I can offer some advice Alex, speak to whichever mapper you're planning on using.

[Error404]

I'm planning on using myself

[tomwood_uk]

I'm planning on using myself

Aah good on you! Motronic?

[newsh]

You need about 750cc/min at 4 Bar the 85% max duty fo 600HP

Can you check your maths against this? http://fuelinjectorclinic.com/flow-calculator

[prj]

I recently mapped a 2.2T with a somewhat higher hp.

750cc injectors at 85%. However, about 15% of fuel was coming from the WMI with huge jets that was installed on it. And the fuel pressure was rock solid.

So I would say without WMI, 750cc is 100% at 650hp (stock FPR).

[prj]

P.S.
The higher power you make the lower the BSFC will be.

To make 360 hp, 360cc injectors are enough.
But for 650 you need 750cc and so on.

750cc injectors are also the biggest you can fully utilize with a single 044 pump, after that you need a surge tank and dual/triple-pump system. Or you need to find something that produces more flow than a 044 (Walbro 400 comes to mind).

For 500hp and a 4 bar FPR the bare minimum is 550cc. But they will be maxed. For more headroom think 600cc and bigger.

[Error404]

Thanks guys, that's what I thought I was expecting to use something like a 650cc unit, giving around 750cc at 4bar and leaving plenty of headroom at 80% duty. So for "moderate power" around 500ish the BSFC is somewhat lower for our engines, we can assume more like 0.5 BSFC?

[prj]

With the EV14 there is really no such thing as a too big injector until you get to big sizes (2000cc or so).

So anything between 600cc to 1200cc is just fine for your application, choose whatever you can get your hands on for the least money

[Rocco]

In Spain some people says that RS2 injectors being 360cc 3bar can make more than 400bhp easily on ABY FPR and 98 octanes.

Personally I think is hard to believe, even more having the original 25 years old ABY fuel pump...

[quattro-nick]

i have 520 hp with siemens deka 630cc,4bar fp and 044 bosch pump
i believe i have around 80 % duty cycle in vems

[Error404]

With the EV14 there is really no such thing as a too big injector until you get to big sizes (2000cc or so).

So anything between 600cc to 1200cc is just fine for your application, choose whatever you can get your hands on for the least money

Great info thanks

In that case I might go large and leave headroom for E85 if we ever get it over here in the future

[speeding-g60]

^^^^ good plan :-)

[macspring]

Good thread.

Thanks lads.

What's the significance of the EV injectors compared to other injectors, I am assuming this question makes sense, and there is a difference.

[driftin jo]

We had E85 once before, up until about a year ago morrisons petrol stations sold it, not all of them, but it was available until they abandoned it, through lack of demand apparently