Boost Control.

[Sassimac]

Hi there...

Contrary to popular theory, I am wanting to limit the boost pressure generated to no more than 16-17psi maximum. The turbo on the CX7 is not a high pressure fellow. Considering this, and knowing VersaTune uses load targetting as opposed to boost targetting, what is the best way to do this?

Also, can you confirm the "MapTargets (Boost Targetting Mode)" table is absolutely NOT used?

Thanks.

[Steve @ VersaTune]

100% certain it is not used.

Target a load that delivers a lower boost. Load is a better measure of engine strain than boost. 16 psi at 2000 is very different that 16 psi at 6000. 16 psi with a K04 is very different than 16 psi with a GT35R.
Just look at what load value you are hitting and tune for that. That's the whole point of load tuning.

[Sassimac]

Thanks for the Info Steve. I'll reset the "MapTargets (Boost Targetting Mode)" table to standard.

Please confirm the what the axis on the "Requested Load Multipler Accel/Deccel Adjustment" tables mean. Current RPM and Previous RPM...??

Is it:
- Previous RPM = RPM at time of shift,
- Current RPM = RPM after shift?

Thanks..!!!

[Steve @ VersaTune]

It's not clear when exactly the previous RPM is taken from. It is some time previous to the current rpm though.

[Sassimac]

Thanks..!!

[Sassimac]

Looking at a log I took with a load target of 1.98, it is pretty apparent to me that trying to target a load that high would involve a boost pressure of over 17.5PSI. In fact, almost any load over 1.80 in my log is a boost pressure over 17PSI. Anytime I managed to hit a 1.9+ load, the boost pressure was 18+PSI. I still feel this is way way too high for a CX7.

I do suspect that in order to maintain lower boost targets, I will actually not be able to raise the load targets much beyond stock. However, I will be able to bring a higher load in earlier, and keep the load up at higher RPM's.

So, the next file I just loaded onto the car has revised targets of a maximum of 1.80 load, down from 1.98. The ramp to that target in the APP Requested Load table also lowered. Having exported the log to a spreadsheet, I was able to dial in the WGDC table as well. So I am trying to bring down the boost pressure in a number of ways.

I do have one question. Is it possible to target a higher load without raising the boost pressure beyond 16-17PSI..???

[skiptownmcat]

Load = boost + barometric pressure, no getting around that.

[Sassimac]

Load = boost + barometric pressure, no getting around that.

I suspect, this is the case. Sadly, with a smaller turbo, I believe higher loads (and boost) would be mechanically stressful to the turbo.

It will be interesting to see what the logs show for the new file. Hopefully with the lower load target (1.80), I'll see a stable lower boost pressures. The next issue after getting the pressure right will be elliminating spikes.

[Steve @ VersaTune]

Load = boost + barometric pressure, no getting around that.

Load = the effective volumetric efficiency of the engine. This is calculated by taking MAF g/s and dividing by the g/s the engine would flow at that rpmat 100% VE.

There is absolute load and calculated load. Calculated load has a compensation for ambient barometer which is why tuning at altitude is a little different than at sea level.

[Steve @ VersaTune]

Load = boost + barometric pressure, no getting around that.

I suspect, this is the case. Sadly, with a smaller turbo, I believe higher loads (and boost) would be mechanically stressful to the turbo.

It will be interesting to see what the logs show for the new file. Hopefully with the lower load target (1.80), I'll see a stable lower boost pressures. The next issue after getting the pressure right will be elliminating spikes.

The only things that will really hurt a turbo are compressor surge, overspeeding, and overheating - typically from over lean mix and high egts.

Surge won't happen with the K04 unless the BPV fails. Overspeeding is when you run it beyond the choke line. You will see MAF g/s flatline at high rpm and load. That is the compressor hitting the choke line. It's like putting your hand over the inlet on a vacuum and the motor races. Overheating is self-explanatory.

High load is hard on the engine and driveline. Rods, head gaskets, clutch, etc.