Question for you Lemmi Pro's
12-18-2007, 08:55 AM
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Question for you Lemmi Pro's
Say you have a program written for the stock fueling setup and K03's. Then you go to K04's keeping the same amount of boost but raising the fuel pressure to 5bar. You've now increased the fuel pressure 25% so you'll need to pull some fueling. I'm assuming the relationship is not gonna be linear between how much fuel pressure I added and how much fuel I have to pull in lemmi to get close to the original tune. I've pulled around 5% primary and I'm still at about -18 for my ltft's.
The reason for the 5 bar reg. is that the stock injectors were over 100% duty cycle. By raising the fuel pressure and cutting fuel back in lemmi, I'm figuring i'll drop the fuel injector on time because it's injecting more fuel per second at 5 bar than at 4.
Your insight will be much appreciated.
The reason for the 5 bar reg. is that the stock injectors were over 100% duty cycle. By raising the fuel pressure and cutting fuel back in lemmi, I'm figuring i'll drop the fuel injector on time because it's injecting more fuel per second at 5 bar than at 4.
Your insight will be much appreciated.
12-18-2007, 09:51 AM
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The trick here is balancing idle and part throttle fuel trims with...
your wide open throttle (WOT) fuel delivery.
You are correct in your assumption that going from a 4bar to a 5bar will net you more fuel because more is squeezed through the injector with each pulse.
To keep you from going to rich at idle and part throttle you'll need to pull enough fuel with Lemmi to stay stoichiometric (14.7 AFR). However, pull too much and you will be lean when WOT.
Do you have a wideband O2? If so, and if you can maintain 14.7 AFR at idle and part throttle, then you are fine. I can tell you that if you are using the stock injectors then you are fine with 5bar. They're not big enough to push enough fuel through at idle/part to go rich.
If you are going to stay at Stage 3-, be careful with boost levels. Even with 5bar you will be maxing injectors with K04s around 15 psi up top for <12 AFR.
You are correct in your assumption that going from a 4bar to a 5bar will net you more fuel because more is squeezed through the injector with each pulse.
To keep you from going to rich at idle and part throttle you'll need to pull enough fuel with Lemmi to stay stoichiometric (14.7 AFR). However, pull too much and you will be lean when WOT.
Do you have a wideband O2? If so, and if you can maintain 14.7 AFR at idle and part throttle, then you are fine. I can tell you that if you are using the stock injectors then you are fine with 5bar. They're not big enough to push enough fuel through at idle/part to go rich.
If you are going to stay at Stage 3-, be careful with boost levels. Even with 5bar you will be maxing injectors with K04s around 15 psi up top for <12 AFR.
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12-18-2007, 10:51 AM
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FWIW When I switched to a 5bar on my 3- set-up I pulled 8%
IIRC my LTFT's were around -3%. Every car is going to be a little different tho (I was running APR). Best bet is to make small changes and log to make sure your running at a safe AFR.
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