Anyone good with Injectors, want a non-BMW person to look at figures

Matt Simis

I posted this to a BMW forum already, but they can sometimes be a bit stuck in their ways


Stock Fuel Injector on 850 and 850CSi
Bosch: 0280150715
BMW: 13641734776

From http://www.need4speed.at/download/files/Bosch_Einspritzduesen_Datenblaetter.pdf I get these stats for the injector:

Bosch Says wrote:

lbs/hr 14.2 / cc/min 149.2
PSI 43.5 / 3BAR

So using any online calc you can work out IDC or Fuel Injector Sizing:
http://autolounge.net/calculators/fuelflow.html

In an M70 engine: 300bhp, 12cylinders, 80% Duty Cycle (recommended max for any Bosch Injector) at 43.5PSI with a generous .47 BSFC (anyone know what this is exactly for these engines?), fuel rail 43.5 PSI (as we use 3.0BAR FPRs) means the M70 requires:

M70 300bhp = 14.68 lb/hr or 154.21 cc/min Injectors x12
So thats close enough to the injector rating, they might creep into 81% IDC but its fine.

The same injector and 3bar FPR is used on the S70 where things are not adding up at all!?
S70 372bhp = 18.21 lb/hr or 191cc/min Injectors x12
Stock is undersized by 28% or Injectors need to run at a whopping 105% IDC (80% is the max..) when at WOT!?

My CSi is dyno'd at 391BHP meaning it should be equipped with 200cc/min Injectors or its running at something off the chart IDC wise and most likely very lean at WOT.

Why is it designed in stock form to do this? This also seems to imply that any tuning or mods will hit a wall immediately on a CSi, it doesnt have the fueling stock to support even its factory BHP correctly..

kona

Matt Simis wrote: »

I posted this to a BMW forum already, but they can sometimes be a bit stuck in their ways


Stock Fuel Injector on 850 and 850CSi
Bosch: 0280150715
BMW: 13641734776

From http://www.need4speed.at/download/files/Bosch_Einspritzduesen_Datenblaetter.pdf I get these stats for the injector:

So using any online calc you can work out IDC or Fuel Injector Sizing:
http://autolounge.net/calculators/fuelflow.html

In an M70 engine: 300bhp, 12cylinders, 80% Duty Cycle (recommended max for any Bosch Injector) at 43.5PSI with a generous .47 BSFC (anyone know what this is exactly for these engines?), fuel rail 43.5 PSI (as we use 3.0BAR FPRs) means the M70 requires:

M70 300bhp = 14.68 lb/hr or 154.21 cc/min Injectors x12
So thats close enough to the injector rating, they might creep into 81% IDC but its fine.

The same injector and 3bar FPR is used on the S70 where things are not adding up at all!?
S70 372bhp = 18.21 lb/hr or 191cc/min Injectors x12
Stock is undersized by 28% or Injectors need to run at a whopping 105% IDC (80% is the max..) when at WOT!?

My CSi is dyno'd at 391BHP meaning it should be equipped with 200cc/min Injectors or its running at something off the chart IDC wise and most likely very lean at WOT.

Why is it designed in stock form to do this? This also seems to imply that any tuning or mods will hit a wall immediately on a CSi, it doesnt have the fueling stock to support even its factory BHP correctly..

Its got to do with fuel pressure, the standard pressure in EFI systems is 3 bar, however if you up this you essentially manage to force more fuel through the injector, hence increasing the flow rate for your injectors.

The only way you can tell if your running lean would be fitting a wideband lambda ( AEM do them for around $120).

Part of my theses is on EFI and as regards to your question about BSFC here is a exert from one of my reports, it will help you to work out the BSFC for your car (since Im too lazy to do it for ya )

Why do you want to fit bigger injectors? Unless your upping the Volumetric flow rate there isnt really a need.

Looking at the figures above I have a question:

Where is the calculator getting is BSFC figures? mine work out nowhere near .X its more like .0X .

Edit: ah I see it its Fuel Used in kilo / Horsepower little cruder than my calculations.

Those online calculators will get you in the ballpark IMO, but to get it done properly takes a bit more effort, and you have to take into account the type of injector, the design of the head, the cams overlap, possible charge robbing etc

Also, Bosch Im sure quote in SI units, alot of online figures are derived from yankee figures which are imperial, so you have to be very careful.
******************************************************
The Next Part of the report deals with the fuel system, in order to specify what fuel injectors and fuel pump the engine will need, I need to work out the fuel flow rate at the peak power.

Petrol has a Gravity of 0.71 and a weight of 5.92 Pounds per Gallon, it releases 19,000 British Thermal Units, (BTU) of energy per pound.
The British Thermal Unit is defined as the heat energu required to raise the temperature of one pound of water by one degree Fahrenheit. 1 BTU = 778 Ft/lbs of work.

Brake Specific Fuel Consumption is a measure of fuel efficiency within a shaft reciprocating engine. It is the rate of fuel consumption divided by the power produced. It may also be thought of as power-specific fuel consumption, for this reason. BSFC allows the fuel efficiency of different reciprocating engines to be directly compared. This is an excellent figure to use, as it allows comparison with a range of different engines.

B.S.F.C = r / P
Where P = tω (t= Engine Torque in N/M and ω is Engine speed in Radians/sec)
and r = Fuel consumption in grams per second.

Usually BSFC is quoted in grams per Kilowatt Hour (Kwh), so this is given by:
BSFC X 3.6x10^6 = 72.42 Kwh


***************************************************

Matt Simis

kona wrote: »

Its got to do with fuel pressure, the standard pressure in EFI systems is 3 bar, however if you up this you essentially manage to force more fuel through the injector, hence increasing the flow rate for your injectors.

The only way you can tell if your running lean would be fitting a wideband lambda ( AEM do them for around $120).

***************************************************

Yes, but BMW didnt change the Fuel Pump, Fuel Pressure Regulator or the Fuel Injectors between the 850i to the 850CSi. The injectors are flat out at 80% IDC on the 300bhp car, which no improvements to flow this puts them at over 100% on a 372bhp engine and thats using an unrealistically low BSFC. Speaking of which thanks for the overview, it explained it better than I have seen before, though I have no idea on fuel consumption in grams per second in this car (or any other)!

A Wideband O2 would solve many of my concerns indeed, but I still cannot understand their logic here.

kona

Do you know roughly the MPG for your engine and the higher powered engine?. The other engine may be more efficient, hence use less fuel. I have no idea what the design of the engines are Im presuming they are a V12 Quad cam? Id imagine the difference is in the desgin and efficiency of the engines, is there any links to the engine specs such as Cam Duration, timing, Compression Ratio, etc? Ill mess around with some figures and get back to ya.
Are you worried your engine is running lean at the top end? Its very unlikely that the engine will run lean at WOT with those injectors. However it is entirely possible if you are getting a extra 91 BHP, that the top end is leaning out. What mods do ya have? Where in the engine rev range is max torque and power produced?

Matt Simis

BHP chart here:


Both the M70 and S70 are SOHC engines (ye olde world stuff), this summary covers off most of the differences between the two:

How is the S70 engine different from the M70 V12 upon which it is based?
When creating the 850CSi's S70 V12 motor, BMW Motorsport began with the standard 24-valve SOHC M70 engine and instituted the following changes:
-Increased bore (from 85mm to 86mm) and stroke (from 79mm to 80mm) for a new total displacement of 5,576cc (from 4,988cc)
-Lighter pistons
-Increased compression (from 8.8:1 to 9.8:1)
-More aggressive valve timing for increased high-rpm power
-Larger diameter exhaust pipes
-Variable rpm limit (6,400 in 1st+2nd, 6,200 in 3rd, 6,100 in 4th. 6,000 in 5th+6th)
-Adjustable throttle sensitivity via dual mode (Sport or Komfort) console-mounted switch
-Engine oil cooler (European-spec models only)

These modifications resulted in an increase in maximum power from 300 hp (DIN) or 296 hp (SAE) at 5,200 rpm to 380 hp (DIN) or 372 hp (SAE) at 5,300 rpm. In addition, maximum torque was increased from 332 lb/ft at 4,100 rpm to 402 lb/ft at 4,000 rpm

Ive replaced the original Rotors and Distributor leads and caps (yes this is that old of a design, no Coil on Pack!), new plugs, 1 new MAF (of 2) but the main performance mods really are Magnaflow backboxes and complete decat, straight pipes.


The 850CSi is quite rare so people generally dont change much from stock, but I have seem people suspect it was fuel restricted in forums posts over the years. Ive ordered some new design 19lb (200cc) injectors anyhow.