2006 SI Dyno (Stock#'s)
The K-series Strikes Again
The 2006 Civic Si's K20Z3 engine is one more member of the highly exalted K-series lineup. Combining elements from a variety of other K-series engines (K20A2 style head, Euro-R RBC intake manifold, K20A3 style balance shaft, K20Z1 style camshafts, etc.), it exhibits a smooth, refined demeanor along with a typical Honda high rpm rush of power, and a typical Honda VTEC dip as well.
While nothing leads us to believe that the K20Z3 won't be just as capable in the aftermarket as other K-series engines, it does face the hurdle of a completely new ECU and drivebywire, so modifications may be a little more difficult (we'll be the first to tell you in our project car chronicles).
In the case of our particular example, the gains may be even tougher still. Take a look at the dyno results.
The lowest curve, 197.9 hub hp, was recorded in completely stock trim after a few runs. We think this is more representative of what our car will do. The next run, 204 hub hp, was recorded with a little cool down. Note that the biggest difference occurs from 7500 rpm on up. The final run of 209 hp was recorded with the airbox cover off (note the bottom end losses). While the car gets much noisier and loses the refined growl of the stock intake system, the 5+ hp gain indicates that an intake system will probably be able to pick up some noticeable power (do not drive with the cover off, with the hood closed, you'll kill power by ingesting hot air from the engine bay).
Now take a look at the AF ratios. Note how smooth they are. Also note that they are relatively close to the optimal range of 12.5-13:1. Finally, note that on most runs, with the exception of our stock 204 hp run, that the AFR goes very rich after 7000-7500 rpm.
We think there are a couple factors at play here. First of all, either Honda has underrated the new K20Z3, or we have a ringer. On the same dyno, a stock 05 RSX (rated at 210 hp on the old system) will put down around 185 hub hp. The best one we ever did (another preproduction car) put down 190 hub hp. Given how strict the new ratings systems are, we suspect we have a ringer, but we'll wait to see what other gains we get, and what production cars do. If you live in SoCal, we'll do free dynos for the first 3 production Si's that come in (310-518-4966).
The fact that the AF ratio goes rich at high rpm on virtually all runs tells us that the K20Z3 is either very temp sensitive, very knock sensitive, or both. The very flat AF curve is also unusual for a factory car (Honda or otherwise), which is one reason why we suspect a little tweaking.
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