May 282012
 

There were exactly 69 miles on the ODO of our BRZ, and it was only two days old, then it was bolted to the dyno. This may be extreme to some but this is what we always do. The last time a new Subaru came out, we had it on the dyno with-in hours of owning it.

The dyno we use for all our testing is our Dynapack AWD dyno. This is a type that you remove the wheels from the car and bolt on adapters which then fit into pods which do all the magic. Some people say they read high, some people say they estimate flywheel HP, but in the end, it doesn’t matter. What matters is, what does it read stock, and what does it read after the modifications.

You can see from the below graph how consistent the runs were. Only one of them was different than the rest and even then it was only a few HP off. Looking at these numbers, 168 Whele HP isn’t too far off from what i expected to see. If Subaru rates the engine at 200 HP this makes for a drivetrain loss of about 15%. Not terrible at all. What is interesting is that Subaru says 170ft-lbs of torque and normally we see wheel torque numbers very close to this, but in this case, we do not. We also are not running 93+ octane, like a lot of US, but rather 92 octane. That could have something to do with it.

So how does this compare to another dyno? Locally we have Cobb Tuning(Surgline) and they had a chance to dyno a BRZ recently as well. Their dyno is a Mustang Dyno, which typically read low compared to some. We have found our dyno’s both read very similar. You can see from the two graphs, that both cars made very similar HP. (168 vs. 164)

From both our graphs you can see the large dip in torque. This has been up for some debate for a while. Its a 25ft-lbs loss right in the middle of things. There has been speculation that its from cam timing, or fueling or something else. There is still some mystery to this, but I think its done on purpose. Since most people drive in the 1000-4000 range during normal driving this creates a powerband that drives people to shift early and save fuel.  Then you have those times where you are shifting at redline, and in these situations you are always about 5000RPM or higher. This falls right into that second hump in TQ and power. Can we tune this out? I say yes, but only time will tell.

So how does the BRZ run? The data logging parameters are very limited and at best not very accurate with our Innovate Datalogger. What we can see is Air fuel ratio from the dyno. The leaner air fuel ratio was expected, but not the super rich condition from 6500 on up. The 02 sensor is behind two cats and from what we have leaned over the years is that this causes the AFR (air fuel ratio) to leaner than it really is by 1 full point. Meaning if you see 12.0 AFR, its actaully 11.0.

The above graphs are in Lambda which is 14.7 multiplied by the Lambda number. So (.85) Lambda is about 12.5 AFR, but because its behind the cats, its actually 11.5. Which is a very rich AFR for a non turbo car. Especially an efficient direct injection engine like this.  What is a safe AFR?  There are some basic rules to follow. Under full throttle an engine can run very lean but not for very long as the heat can melt things. “Safe” could be a wide range of AFR. Safe for this engine could be that 10.0-11.5 range. We won’t really know until we can start tuning the BRZ. Then we will find out how lean we can run before knock occurs.

What AFR makes the most power? 12.5 AFR is a good range to shoot for. 13.2AFR is a known best TQ AFR, but this is where things could run closer to the edge. Again, we really won’t know until we can tune these.

Here is a screen shot of a Logworks run. I logged tons of things and there were a few that makes sense, but a bunch that don’t. STFT is always changing under full throttle, but we found evidence that its not active as different MAF housing throw off the AFR. If STFT was actually working, it would compensate.

Here are some other comparisons of some other cars. First one is a 2.5RS. When you look at these two cars side by side, you will see that the BRZ will blow the doors off a 2.5RS. You then add the weight factor to it and you really have a much faster car with the BRZ.

Here is another 2.5RS, but this time its modified with cams, pistons, and tuning. Even then its still no match.

Lastly is a comparison of a MINI Cooper S and BRZ. The MINI’s dyno very high for some reason. But you can see a car that has similar overall Wheel HP to the BRZ, but the MINI has way more torque. Boost is the answer here.

 

This is just a snippet of what is to come with this car. Be on the look out for even more dyno results!

 Posted by on May 28, 2012 About Your Car, BRZ / FR-S, Dyno Test & Tune Tagged with: , , , ,

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