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First Alpha-N 4D Tune

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Hey Andre & fellas.

Im working through my first 4D Alpha-N Tune... Ive attached my current fuel map... you can see that between 20% TPS and 30% TPS the VE values jump a large amount also between 30-40%

Should I be adding in some 25% and 35% columns? or are you fine to let the ecu interpolate by itself? Im sure it would be "ok" left as is. But since the ecu has the capability it would only result in a better tune by doing so with the only negative the small amount of extra time to do so.

Also in regards to the 4D side of things, you can see its going over 100% VE is that normal? (ive only actually tuned to 7500rpm the rest was just extrapolated) does it mean my injector sizing is off maybe?

Attached Files

It appears the VE values are increasing around 10% for each jump of 10% in the TPS columns so additional columns shouldn't be necessary. Essentially if you're seeing a smooth trend in your VE table then you can get away with wider break points in your axis. Tighter break points are more important if you're seeing an erratic change in VE across a specific range that wouldn't be correctly modelled by a linear interpolation.

Values of over 100% are pretty typical so I wouldn't be concerned and I certainly wouldn't take those VE values and assume they are actually realistic. This all depends on the background fuel model and how well the ECU characterises the injectors (among a range of other aspects that can affect the VE values). What I would be a little concerned at is the VE continuing to increase at high rpm and WOT. Generally the VE table will follow the engines torque curve relatively closely, and hence I'd expect to see the VE rise, peak, and then drop off at higher rpm. The trend you have would make me look at the fuel system to make sure it can keep up - Is the fuel pressure dropping off?

Thanks Andre,

On a stock turbo'd 26 when would you expect torque to drop off?

As mentioned I had only actually tuned to around 7500 then just added more fuel manually from there so at least its rich if it does get there (my limiter is set to 7500)

Its a walbro 255, with 875cc Injectors. have not checked it recently but when I was on the dyno last time pressure was keeping up.

I intend to get a fuel pressure and oil pressure sensor and Aux harness soon tho so will double check.

Ok so just to revisit this... I looked at one of my older dyno runs from when I was using the nistune and Torque drops off at around 5500rpm.

reviewing my logs Ive noticed that even with the boost control turned off the car makes 9psi but in the higher rpm's the boost creeps up to about 12-13psi would this be whats causing the increased VE numbers at the top of the graph? Would putting some numbers into the MAP correction for those boost levels help

For a stock RB26 I'd expect to see peak torque reached around 4500 rpm. The fact that your boost is increasing through the run 'shouldn't' affect the VE numbers dramatically though as this is taken care of by the back ground MAP compensation table. This is why once the TPS based VE table is tuned, you can raise the boost and the AFR will track your target correctly.

Ill have to check fuel pressure, have done multiple logs and its happy with the VE as it is.. its a 255LPH pump but maybe there is a restriction somewhere. This is where having a fuel pressure input to the ecu would be really handy!

Are you running the standard Nissan fuel pump speed control? If so run a fresh relay controlled power supply and earth to the chassis