RB20det fuel economy.

[love_boost]

please dont flame, i know i shouldnt be worried about fuel economy but i am lol, my hours got cut so...

i was wondering what gear i should be drivng around in the city, i always seem to get horrible fuel economy, around 275kms to 1/4 tank left in my car but i drive so nicely, rarely if every touch boost. so i always thought the lower the rpm the less fuel used, but then a buddy told me that i should drive in 3rd becuase the motor dosent have to work as hard?

please dont laugh lol i know i shouldnt be worrying about this but yes i do now.

[J-Ran]

get a wideband sensor and you will be able to see at what throttle positions and rev ranges you will get the best economy at. it will allow you to see how much fuel your car is dumping in.

[dm1133]

I doubt the wideband would help much with fuel economy, since it's giving a ratio value, and not an absolute value. For example, when I'm slightly giving gas and decelerating it is showing rich, however, when I'm accelerating, but not boosting, it's showing close to stoic. The wideband is an important thing to have, fuel economy or not, but best way to get good fuel economy in the skyline is to stay below 95, our cars are definitely not aero-dynamic, mine gets a much better fuel economy in the city rather than on the highway.

[billboa]

I doubt the wideband would help much with fuel economy, since it's giving a ratio value, and not an absolute value. For example, when I'm slightly giving gas and decelerating it is showing rich, however, when I'm accelerating, but not boosting, it's showing close to stoic. The wideband is an important thing to have, fuel economy or not, but best way to get good fuel economy in the skyline is to stay below 95, our cars are definitely not aero-dynamic, mine gets a much better fuel economy in the city rather than on the highway.

Rhat dosen't seem right at all, u might wanna get that checked out. Cars generally get way better fuel mileage on the highway.

[mcfly]

with advancements in ecu's these days you could use a standalone to calculate instant fuel economy.

You would need to take pulse width of the injectors and vehicle speed then set up the variables to calculate miles per gallon, or km/l of fuel. If you were to log it you would just compare it against load+rpm and you could find the cars sweet spots.


then again if you have a standalone you really shouldn't be humming and hawing over a few mpg.

[J-Ran]

I doubt the wideband would help much with fuel economy, since it's giving a ratio value, and not an absolute value. For example, when I'm slightly giving gas and decelerating it is showing rich, however, when I'm accelerating, but not boosting, it's showing close to stoic. The wideband is an important thing to have, fuel economy or not, but best way to get good fuel economy in the skyline is to stay below 95, our cars are definitely not aero-dynamic, mine gets a much better fuel economy in the city rather than on the highway.

im not saying the wideband is a fuel economy gauge by any means, but it helped me to understand that even though my rpms might be lower in 4th gear, im still dumping a ton of fuel in to keep it at 50 compared to higher rpm but near/over stoic in 3rd... just for example

[Skym]

275km to 1/4 tank is really good fuel economy for a RB20DET. Should be getting around 400+km to a tank with functioning 02 sensor, good ECU tune and normal driving. Lower rpm's (just above 1000rpm max to kick in fuelcut which helps with fuel economy) is better. Also stock ECU does inject less fuel at lower rpm's.

I would think a higher gear keeps rpm's lower hence less fuel is injected but also puts more load on engine which engine would hit the higher load / richer parts of fuel map. Car pulls best in 1:1 gear inside gearbox, which I think is 3rd gear.

Stock ECU uses a fuelcut at lower rpm's (around 1000rpm) to save fuel. It's something I noticed that aftermarket ECU's don't have, as they are built for performance not fuel economy. Stock ECU is a good allround ECU for performance, fuel economy, etc.

If engine has a bad stock 02 sensor, fuel economy gets worse. Installing a higher flowing fuelpump that runs engine rich can clog 02 sensor and make fuel economy even worse. Adjustable FPR to drop fuelrail pressure or even better a ECU retune should help to solve the rich problem. Replacing o2 sensor should fix the fuel economy problem.

[love_boost]

so when i put my GTR pump in it will probably be worse mileage?

[Skym]

Runs richer thus uses more fuel.

From what I understand higher 195lph GTR fuelpump forces more fuel through stock injectors at the same duty cycle (Duty cycle is the percentage from 0-100% that injector is open). That's why stock 259cc RB20DET injectors can support more hp, as the stock R32 RB20DET 135lph fuelpump is meant to supply fuel to 370cc injectors (same 135lph fuelpump that feeds 370cc injectors on R33, R34 RB25DET) not 259cc injectors.

Adjustable FPR on return end of fuelrail (to fueltank) drops fuelrail pressure and returns more fuel to fueltank thus less fuel goes through injectors at same duty cycle and engine doesn't run rich.

[91rsrskyline]

I dont know guys, i think rb20det's get pretty damn good gas mileage, mine is mostly stock, (i think) with presumably a stock tune, it gets a little over 500 to a tank with a mix of city and highway, with getting into the pedal pretty hard once in a while. The car has great power too, pretty hard to believe it has only around 220 hp.

[Skym]

Also depends on what boost level your running, as more boost = more fuel.

The earlier spooling factory turbo (fullboost at around 2500rpm) makes a stock RB20DET feel fast. It took me by surprise the first time I drove my Skyline, as it picked up quickly.

[sexonwheels]

How will a high flowing fuel pump put more threw the stock injectors when the stock ecu will only put enough fuel to match the amount of air? I presumed high flowing to just mean it will keep up with more supporting mods and\or bigger turbo.

...And does the LPH rating mean it will constantly push 195 LPH or is that just the peak amount it will push out?

[Skym]

lph = liters per hour.

Higher fuel rail pressure can force more fuel through stock injectors. Bigger lph fuelpump than what suits stock injector size + adjustable FPR (when adjusted, can return less fuel to fueltank, which turns up the fuel rail pressure) is what is called a band aid fix. This band aid fix is used when upgrading injectors is too expensive or injectors are too small. Upgrading injectors, fuelpump is the proper way.

Some who have just upgraded the fuel pump have found out that engine runs richer at higher rpm's with bigger turbo, bigger intercooler, etc + higher lph fuelpump (depends on lph of fuel pump, turbo size, boost level, etc, but I think they were using BOSCH fuel pumps that were higher than 195lph). I noticed their solution was too reduce the amount of fuel being injected at higher rpm's on fuelmap to get rid of rich A/F ratio.

I noticed some who have just a intercooler, intake, exhaust, have found out engine runs richer with stock 195lph GTR fuel pump.

From what I understand on R32 the fuel pump is controlled by a controller that's connected to ECU. This controller varies the voltage to fuel pump which varies the fuel pressure. If you bypass this controller (some do this on higher hp RB engines), can have fuel pump running at 100%, but shortens the lifespan of fuel pump.

On a pinout diagram for stock ECU plug, I think it's called "Fuel Pump Terminal Voltage Control Output (FPCM)". I think there are 2 wires for this controller.

Also can buy what is called a rising rate FPR that raises fuel rail pressure as revs rise and supposedly gets rid of sudden lean spots under hard acceleration -

http://www.cartech.net/fmu2020.htm

Stock single feed fuel system goes in this order -

Fuel pump - Fuel hoses - Fuel damper - Fuel rail (injectors are connected to fuel rail) - Fuel Pressure Regulator - Fuel hoses - Fuel tank.

From what I understand fuel damper helps to get rid of or smooth out the pulsations inside fuel rail -

http://www.freepatentsonline.com/6032651.html

[love_boost]

i would think the stock FRp would regulate the fuel.
im also upgrading to a RB25 turbo soon and FMIC.

[mcfly]

i would think the stock FRp would regulate the fuel.
im also upgrading to a RB25 turbo soon and FMIC.

it will, the stock fpr will do fine with a walbro pushing it.