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After our first dyno testing we did on all our exhaust pieces and intake parts, we created a ton of buzz in the BRZ/FR-S world. Being the first to do this, sparked many other vendors to do the same. We may not have been posting up tons of dyno graphs recently, but we have been spending most of our time learning about this new engine. Since we can now tune the ECU, we are able to see many things going on. Some of them explain the constantly varying HP results, and some of them don't. With our added knowledge about the ECU, knowing how our 3 cars act on the dyno, and knowing what kind of HP all our parts make, it really makes me wonder about some of the dyno numbers I have seen lately....
In previous tests we did the dyno proving all spread out over a couple of days. This makes our overall HP numbers not quite as accurate, but since parts were swapped out on the same day (minutes apart), the part to part accuracy still holds. We wanted to really see what kind of HP we would make doing all our parts, back to back to back along with adding our headers to the mix.
Before getting too far into the results there are a few things to discuss. First is the variance we see from run to run. We start by letting the car warm up to 90C. We do 7 runs and after the 5th run, we see the HP level off and stop gaining. After we get to the 9th run (60sec intervals) we see power drop. Even if we let the car idle for 2 minutes, it hits a wall where HP falls and doesn't go any further. This varience is about 8WHP. See the below graph. Keep in mind this is the difference in HP gains shown by exhaust, and other parts on the car. This is a HUGE variable to how the car runs, run to run.
So what causes this? I had see this before while tuning the ECU, where our HP gains would go away. While doing our initial testing of our individual parts for HP, we saw signs of this, but nothing huge as we stopped the car after about 3 runs then changed parts.
There are a few factors, one of which is coolant temp. If runs are done at 80C or less, you loose HP from the ECU pulling back cam timing and ignition timing. This is 20 HP or more easily. At 85C coolant Temp you make a little more, and 90-92C is where the coolant temps like to sit when the car makes the most power. I never saw more than 94C during runs, which is very good. This is a factor, but not THE factor that plays into this.
After spending about 10 runs looking over what is going on the only thing that stood out was the oil temp. We would see 110C easy, which by Subaru standards is hot! STI's rarely see this because of the oil warmer (its really a cooler....) that is installed. The BRZ has nothing to cool the oil down except it running past the engine block and sitting in the oil pan. Its obvious to us that the BRZ needs is a real oil cooler using a thermo-stat to still allow for proper warm up of the engine. Parts are already sitting waiting to be installed to prove this part works and solves the inconsistency with HP problem. Much more on this later.
So with all that above taken into account, you can see how testing done days, hours or minutes apart can "make-or-break-or-fake" an aftermarket parts dyno result. What we have done is learned what oil temps the car made the best power at and used those results to give you consistent results. More on the oil temp and the solutions for this soon.
First up is the biggest more important test, the catback exhaust. Our inital dyno results showed a gain of about 7 WHP. During this initial test we proved how the removing the muffler made about 3 Wheel HP and then how our midpipe and high flow muffler made 7. This proves that contrary to other competitors, the midpipe DOES make HP. During our re-testing of the catback, we found almost the same HP! Besides the cool added sounds, take note of the change to the dip in torque. It gets narrower by about 250 RPM.
Next up is our catless Front pipe. Just like in previous tests, this was done back to back in about 10 minutes. As you can see there isa decent amount of HP gained at the upper RPM's. The 5-6 WHP from 7000 to redline is a noticeable change to power along with some additional cool exhaust sounds. Like before, in previous tests, we say about the same HP gains. One more important thing to notice is the TQ dip got even narrower!
Then comes the over pipe. This part didn't show much in the way of HP gained the first time around. I expected to see the same thing this time as we were more controlled and had a better grasp of what was going on. Same thing this time, as it showed pretty much no change. My guess is that its not the restriction in the exhaust. Anyone who sees this part is going to want to replace it, so there isn't going to be arguing if this part makes HP in the long run.
And finally the fun parts, headers!