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As some of you guys know we have been working pretty hard on a high compression set-up thats a workable solution using pump gas. About 2.5 years ago on V Board we had a pretty interesting discussion but the main concerns was that timing was an issue to be address and that the QR would destroy itself in the process.

Fast forward 2 years 3 months and we now have the first QR25 with QR20 Pistons swapped into it. In order to move the car around E85 was used as a fuel source to control knock. After an unexpected accident with the vehicle the project was delayed until we could find a new home for the high comp motor.

We stand here now and offer up some pretty interesting informaton/research that has been done and what I believe is a daily driven 12.3.1 compression motor finally.

**** THIS IS MY OPINION ON HOW THE ENGINE OPERATES AND THE ECU REACTIONS TO IT *******

Cracking the ECU is no simple task. It requires a close attention to detail as well as how certain codes can manipulate engine performance. A few months ago I had said that I believed the engine had a "low octane mod" as well as a "high octane mode". I now further believe that my research was pointing me in the right direction.

We have been running a 12.3.1 compression engine and closely monitoring the timing values on the motor. some have said that yanking the base timing back is the solution to how turbo applications can be tunned safely, or that doing the same on a high compression engine would yield positive results. I do not believe this to be true at all.

The Nissan ECU's have something called Calculated Load Values. It's a mathmatical equation that is derived from certain variables in the engines sensors. The ECU uses this in lue of a cylinder pressure sensor, something not present in the QR25. From my research the CLV (calculated load value) is formed from the following: throttle position, intake air temp, MAF Voltage, Gram's Per second through the MAF, Intake Cam Position, and AFR.

I found that on pump gas we would knock at low RPMS and part throttle. The itneresting thing we discovered is that the knocking didn't actually start until 28% CLV from the ECU. Given this starting point we believe that cylinder fill rates above the 27% CLV are enough to the cause knock on pump gas. We took note that anything under the 28% mark didn't seem abnormal or did we have any issues with knock. we just don't think there is enough air going into the motor to create the knock below this point.

Now, you may be scratching your head, and some of you will need to read that a few times to undertstand it as well

Given the 27% mark we started recording different variables like the IAT, throttle position, grams per second, and voltage from the MAF. We tried to hit this number in a series of different driving styles like bumper to bumper, highway driving, around town driving, and just about any scenerio someone would encounter on the street.

What we found the most was that the grams per second really dictated the volts on the MAF. Usually around 18-20 grams per second we would see a 2.3-2.4 voltage on the maf. It didn't matter on the CLV, or any other variable. While the CLV may be as low as 22% or as high as 25% these variables would remain unchanged if held stable.

Now this all sounds like a big WTF and I know it's kind of confusing, but here's the skinny:

We started running this high compression engine looking for a street engine setup. The complication is that pump gas is just not a solution by itself. We started working with a meth kit and started injecting before the throttle plate. Every once in a while, the motor would quench or we would spike on our afr's. With good speculation that the 150 psi from the injection pump was overspraying the power of the vacum. We then moved the nozzle to behind the throttle plate and resolved all the quenching issues.

Looking at the knock points and comparing them to our Grams per second with Maf Voltage, we have been able to determine the injection of this kit to start ar 2.4 volts. The nice thing here is that 2.4 volts is 20 Grams Per second and is enough vacumm to draw in the water/meth injection with no quenching, no knocking, or any other problems. It's also lower then the starting knock point on the CLV. The good thing about this is that with the meth running, we started seeing lower CLV numbers in the mid range and full throttle applications. By comparison (and back to what I was initially saying about yanking timing back) we see more aggressive timing patterns through the maps with the lower CLV numbers vs ones with the high CLV %'s.

It is my opinion that this setup is a viable option for those interested in 12.3.1 compression over a turbo application. I also believe that turbo applications benefit from this since most people are running on factory ECU's and the CLV's would be lower generating more agressing timing
 
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