This doesn't happen very often from me but I applaud Shiv for this recent thread on e90. Thanks for the data, great contribution indeed and if only most posts were like this (i.e. zero hype) :( Thought I'd copy it over here to share...10mins for fuel to mix, very interesting stuff, what do you guys think?
I recall seeing a fuel system diagram on the 1M with some extra lines to/from the tank and I'm not sure if its possibly a return-type fuel setup, doubt it though.
I recall seeing a fuel system diagram on the 1M with some extra lines to/from the tank and I'm not sure if its possibly a return-type fuel setup, doubt it though.
Quote:
Originally Posted by shiv@vishnu
Hi guys,
Now that I'm back from Asia, I've been doing some more testing on the Vishnu/FFTEC Flexfuel system. This time I wanted to document how long it actually takes for fuel to mix in the tank and to find its way to the fuel injectors. I've often heard other tuners suggest that its okay to add e85 at the pump and then to immediately start running their car on the "e85 map". This clearly shows a lack of understanding of how our fuel system works.
Since the N54 fuel system is return-less and doesn't benefit from a stream of fuel circulating from the fuel rail back into the tank, it's clear to those who understand that more time is needed for newly added fuel to be available at the fuel injector. Here's the proof.
Our FlexFuel/Fuel composition sensor isn't mounted underhood near the driver-side shock tower. There is still roughly 2' of 5/16" fuel line between the HPFP inlet and the FlexFuel sensor. A whole lot better than mounting it in the fuel tank which would mean that there would be much longer column of unmixed fuel between sensor and the HPFP.
Below is a log of Ethanol % (raw un-smoothened signal from FlexFuel sensor) and RPM. We started off with approx 1 gallon of 91oct pump gas (10.2% ethanol content according to sensor) and then added 5 gallons of E85 at the time marked below. It took approx 30 seconds to add all 5 gallons. The engine was running during the fill up time to speed along mixing (probably illegal at most gas stations![Click here to enlarge]()
). At approx the 320 second mark, I started to drive the car on the road at speeds of 10-50mph.
![Click here to enlarge]()
The result:
Once the 5g of e85 were added, it took nearly 7 MINUTES for the fuel to start mixing at the FlexFuel sensor. And then it took another 2.5 minutes tofully mix even with the help of driving the car! What this means to everyone who doesn't have a FlexFuel sensor: You should wait at least 10 minutes to switch over to your e85 map after adding fresh E85 to your tank of pump gas. Most of that time is required for the engine to consume the column of old gas that is between the LPFP outlet and the HPFP inlet. Hope that helps!
Cheers,
shiv
Now that I'm back from Asia, I've been doing some more testing on the Vishnu/FFTEC Flexfuel system. This time I wanted to document how long it actually takes for fuel to mix in the tank and to find its way to the fuel injectors. I've often heard other tuners suggest that its okay to add e85 at the pump and then to immediately start running their car on the "e85 map". This clearly shows a lack of understanding of how our fuel system works.
Since the N54 fuel system is return-less and doesn't benefit from a stream of fuel circulating from the fuel rail back into the tank, it's clear to those who understand that more time is needed for newly added fuel to be available at the fuel injector. Here's the proof.
Our FlexFuel/Fuel composition sensor isn't mounted underhood near the driver-side shock tower. There is still roughly 2' of 5/16" fuel line between the HPFP inlet and the FlexFuel sensor. A whole lot better than mounting it in the fuel tank which would mean that there would be much longer column of unmixed fuel between sensor and the HPFP.
Below is a log of Ethanol % (raw un-smoothened signal from FlexFuel sensor) and RPM. We started off with approx 1 gallon of 91oct pump gas (10.2% ethanol content according to sensor) and then added 5 gallons of E85 at the time marked below. It took approx 30 seconds to add all 5 gallons. The engine was running during the fill up time to speed along mixing (probably illegal at most gas stations
). At approx the 320 second mark, I started to drive the car on the road at speeds of 10-50mph.
The result:
Once the 5g of e85 were added, it took nearly 7 MINUTES for the fuel to start mixing at the FlexFuel sensor. And then it took another 2.5 minutes tofully mix even with the help of driving the car! What this means to everyone who doesn't have a FlexFuel sensor: You should wait at least 10 minutes to switch over to your e85 map after adding fresh E85 to your tank of pump gas. Most of that time is required for the engine to consume the column of old gas that is between the LPFP outlet and the HPFP inlet. Hope that helps!
Cheers,
shiv