Power tuning

[RickyB]

A while ago I promised to discuss the power tuning process. While power tuning is a spectator's sport, it is the tip of the iceberg in the calibration process. Most of what you would see if you walked into the shop while I am tuning is boring. The car is loaded on the dyno simulating a slow drive down a country lane or a 60mph run up a 4% grade. It's not very interesting to watch, but because the car will likely be driven in such situations, it is important to get the calibration right for these activities. This drivability tuning process takes a full day. The power tuning takes several hours. Cold starts, throttle enrichments, temperature trims, idle adjustments and the many other little things that go into a calibration take several weeks spread out in short time increments several times a day. Because of this, our calibrations are done only for a very specific setups. If any changes are made to the fuel system, intake, turbos, intercooler, pipes, engine or exhaust the calibration is no longer a perfect match.

In some cases, we are asked to perform a baseline before anything else. This is a good idea. The dyno is just a tuning tool. It lets me know if I'm making more torque or less torque. It can provide a horsepower number but that may not be a perfect match to the big horsepower meter in the sky. Regardless, if the dyno tells me the car has significantly more area under the torque curve than when it came in, the car feels a lot quicker on the street.

Here is a standard baseline from an M400:



There is a dropout in the middle because the RPM pickup lost the signal, but the general shape of the torque curve and the area under it is clear. For those not familiar with dyno charts, torque is alway higher than horsepower below 5252 RPMs as we can deduce from the horsepower equation: hp = torque X RPM / 5252. The bottom chart shows the intake manifold pressure in pounds (1 bar = 14.7 psi).

The car was then fitted with a full 3" exhaust system and the drivability tuning started and upon completion the power tuning started. The ECU determines how much fuel and ignition advance to run by looking at the speed of the engine and the load on the engine. Load is determined by the density (pressure and temperature) of the air in the intake manifold. Strong vacuum is low load, zero vacuum is medium load, boost is high load. Load between strong vacuum to around 4 psi is all covered in drivability tuning. Power tuning starts at the lowest boost level that the turbo actuators can deliver and proceeds in 3-4psi increments to cover the entire range of part-throttle boost pressures that may be used during hard cornering. The first power pull with the new exhaust was done at low boost:



In the bottom chart I graphed the air-fuel ratio (AFR) alongside boost. With the boost set to minimum, the car made only 8 psi. The red dotted line indicates an AFR of 12:1. This is my target for boost and high RPMs. I start with a conservative (rich) fuel map when doing power tuning, and here we can see that the AFR dropped below the red line to indicate that there was more fuel than absolutely required to keep the engine safe. I take the AFR readings from the graph, apply some simple mathematical equations, and make the proper alterations to the fuel to hit the target.



Now the AFR is right about perfect, and the motor makes a little more power at a little less boost. One aspect of power tuning I won't show is ignition advance. Timing advance has a bigger impact on torque than fuel but it is also a game of cat and mouse requiring the motor to be adjusted right to the edge of detonation with a stethoscope and then backed off a certain amount to insure safe operation under all conditions. Suffice it to say, I can make more power at this boost level but it won't be "safe" because it may cause the motor to ping during hot track sessions. I'm limited by what the motor will accept and what my experience tells me is a safe margin.

It's time to crank the boost up 3-4 psi.



Now we are running around 12 psi and the new exhaust system flows so much better on the top end that my conservative estimates were not conservative enough. The AFR was a little bit leaner than I like, but not seriously unsafe or I would have stopped the pull. I make the required fuel adjustments and do another pull to verify.



We lost a tiny bit of power but gained a nice safety margin. Now we crank the boost to the next level.



Boost control is not perfect so it went a tiny bit higher that I wanted at first but then settled right down to the desired range. The AFR is safe and can be cleaned up sligtly to wrap up the final calibration for this setup.

Then, the customer decided to upgrade the intercooler and intercooler pipes. For this modification, the calibration needs changes that I can almost predict. To verify my predictions the car went back on the dyno.



This pull is with the boost turned completely down to verify the changes under low boost. My prediction was not too far off, but the AFR chart gives me what I need to make the exact final settings to the calibration at this boost level. Now it is time to see the improvements the intercooler and pipes give under full boost.



Not too shabby: about 30 peak horsepower at the same boost level over the exhaust alone. Again, the AFR is a little on the rich side, but the graph gives me the information I need to put into the final calibration.

A final comparison of the baseline against the last power pull gives a good impression of what the exhaust, intercooler and tuning changes provide:

[jmg944t]

Ricky,
Would you consider these results typical?

[RickyB]

Originally Posted by jmg944t

Would you consider these results typical?

It's within the expected range for this set of modifications and 91 octane California fuel. Some motors will make a little bit less, some a little bit more. The AER is a built motor so slight differences in compression and clearances are to be expected.

[caccobra]

Thanks for posting this, Ricky. It certainly highlights the fact that the Noble ECU's factory mapping needs to be addressed whenever intercooler flow and/or exhaust system flow are upgraded. It also highlights where a couple of tweaks on the stock map might also be considered by anyone with a stock exhaust and intake setup.

Do you have a stock graph on an M400 that isn't broken up because of sensor failure? It would be helpful to see the complete graph for comparison purposes. My guess is that M400 graph is pretty representative of the stock map that is in SJ's magazine loaner.

Can you imagine how much more impressed the magazine writers could have been with a properly tweeked ECU map? I hope they will finally get to experience that with the Rossion. It will be using a completely different ECU and (reportedly) improved mapping. It will be very interesting to see the plot on the Rossion compared to the factory Noble map.

[Zezinho]

Actually, the differences may be even more dramatic than what Ricky is showing. I know several M400's were showing baselines in the 315/320 whp range...can be dyno differences but is quite a lot.

[Hoover]

We've experienced stock M12's make the same or more horsepower than M400's with the stock configuration.

[RickyB]

Originally Posted by caccobra

Do you have a stock graph on an M400 that isn't broken up because of sensor failure? It would be helpful to see the complete graph for comparison purposes. My guess is that M400 graph is pretty representative of the stock map that is in SJ's magazine loaner.

Can you imagine how much more impressed the magazine writers could have been with a properly tweeked ECU map? I hope they will finally get to experience that with the Rossion. It will be using a completely different ECU and (reportedly) improved mapping. It will be very interesting to see the plot on the Rossion compared to the factory Noble map.

I have lots of base M400 and M12 charts, but I wanted to stick to the same car. The stock cars have quite a lot of variability. We've seen from around 280rwp to 365rwhp right off the street. Some of these car obviously have a problem like fouled plugs or boost leaks. When everything is right, stock M400s register around 340-350 on our dyno. The torque curves are all similar. Torque comes on, peaks at around 5K and then drops quickly towards redline.

Some of the early M12 maps look like works in progress. The later M400 maps are pretty good. The cars are very sensitive to boost and VE (volumetric efficiency) changes. I do not recommend making any such changes on a stock M12 or M400 without a programming change or at the very least a dyno evaluation of the resulting configuration to insure that fuel and timing advance are still safe.

I think that what our shop can do for Nobles from a power/performance perspective is a matter of personal preference on the part of the owner. One man's faster car is another man's unbalanced nightmare. If you like the looks of our parts but don't want an extra bunch of power, I'm more than happy to leave the boost down and keep the car right around the same power level it came with.

[S.J.Morgan]

Originally Posted by Zezinho

Actually, the differences may be even more dramatic than what Ricky is showing. I know several M400's were showing baselines in the 315/320 whp range...can be dyno differences but is quite a lot.

The differences may be due to setup problems in the installation, and adjustments to the turbo system. Everything from vacuum/boost lines and wiring to rigging of the turbochargers. A thorough check and calibration of the entire system is necessary to get the best performance from the power unit.

The rest was a nice presentation by Ricky B, especially hiding the bit about the timing. That is the hardest part to get right, and causes most of the pinging and drivability related problems that occur with modified maps. This part of tuning is the "Don't try this at home, kids" part of the process.

Too bad that the base line run was not complete, nor was the AFR shown. Running the stock map with the modified exhaust would have shown both the efficiency of the exhaust, as well as the effect on AFR. The only information shown is that of a modified map with a modified hardware package.

One might assume that the basic M400 map is a bit on the rich side for safety. If this is so, a properly designed muffler can be substituted, which brings the AFR into line, producing some additional power.

Later M400s, such as the test car (which had a perfect, recommended setup), have a less restricted muffler and no other changes to the map. 1/4 mile trap speeds show that these cars do indeed produce the full advertised HP, and may be quicker than earlier M400s. This is not to say that a change in the map could not extract more power. However, the long term performance of the test car has been exemplary, and extraordinarily well documented.

Now, after running that all day drivability dyno session, run about two weeks of solid road work to verify and make adjustments. This development would interface the shop dyno with the ass dyno. Eventually, the development driving can be shortened as modifications and systems are standardized.

[RickyB]

Most of the stock Nobles we have measured AFR for run a bit on the rich side (11.0-10.5 AFR) at WOT. That is quite standard for turbocharged production cars. Factory tuners know that customers are going to modify the cars and as flow improves, AFR will lean out.

There are two issues preventing us from just putting our exhaust systems on a stock Noble and running them. The first is that the mufflers are really not the problem. You can replace and even simply remove the muffler and still be quite safe although there will be some effects on the overall drivability. The y-pipe is the real restriction. Removing this part makes such a dramatic change that the factory map ends up going into the 13 AFR range near redline at WOT. Run this way for any length of time and you will soon be looking for a new motor.

The other issue is that the factory map is set up to 1.14 bar. If you go above this boost level, the AFR will start to lean out regardless of how much extra capacity the fuel system has. Because of the improved flow characteristics of the new exhaust, the ECU's stock boost solenoid pulsewidth map settings allow boost to rise into this danger zone.

Some try to work around the stock calibration with an adjustable fuel pressure regulator. Going this route gives you two knobs. One is the ramp of the fuel pressure vs. manifold pressure. The other is the base pressure setting itself. Both of these affect the entire calibration across all RPM and load points. Thus, you can make the motor safe at WOT but alter drivability, fuel consumption and emissions in ways that that are beyond the adaptive capabilities of the ECU to correct.

[Zezinho]

Originally Posted by RickyB

Most of the stock Nobles we have measured AFR for run a bit on the rich side (11.0-10.5 AFR) at WOT. That is quite standard for turbocharged production cars. Factory tuners know that customers are going to modify the cars and as flow improves, AFR will lean out.

There are two issues preventing us from just putting our exhaust systems on a stock Noble and running them. The first is that the mufflers are really not the problem. You can replace and even simply remove the muffler and still be quite safe although there will be some effects on the overall drivability. The y-pipe is the real restriction. Removing this part makes such a dramatic change that the factory map ends up going into the 13 AFR range near redline at WOT. Run this way for any length of time and you will soon be looking for a new motor.

The other issue is that the factory map is set up to 1.14 bar. If you go above this boost level, the AFR will start to lean out regardless of how much extra capacity the fuel system has. Because of the improved flow characteristics of the new exhaust, the ECU's stock boost solenoid pulsewidth map settings allow boost to rise into this danger zone.

Some try to work around the stock calibration with an adjustable fuel pressure regulator. Going this route gives you two knobs. One is the ramp of the fuel pressure vs. manifold pressure. The other is the base pressure setting itself. Both of these affect the entire calibration across all RPM and load points. Thus, you can make the motor safe at WOT but alter drivability, fuel consumption and emissions in ways that that are beyond the adaptive capabilities of the ECU to correct.

EXACTLY what happened with my car. Opened up the exhaust to 3" (basically straightpipe now) and jumped up about 60 rwhp (as you say, restrictive y-pipe)...but also had to immediately re-regulate the AFR bc jumped up to near 14...now running safely in the low 12's/high 11's but hadn't expected that jump up when we straightpiped it....