Long forgotten information about the K20a3 is that it makes more power than both the F20C and the K20a2 below 6000rpms, so not great for peak power, but pretty damn good for mid range.
From back in 2003.....
While I was looking through Comptech's website to look for new products, I found some dyno charts of the 02' Civic Si (K20A3), 02 RSX-S (K20A2), and the S2000 (F20C). Since I was bored, I decided to plot the charts together and do some simple analyses. The numbers come directly from Comptech's published numbers for the cars in stock form.
In this first graph, I plot the horsepower for all 3 engines. The blue line is the K20A3 (02 Si), the red line is the K20A2 (RSX-S), and the yellow line is the F20C (S2000). What struck me was the fact that the K20A3's horsepower is higher than the K20A2 and the F20C until about 6000RPMs.
We can get a better idea of the horsepower difference by looking at the following graph. I plot the Delta (i.e. the difference between the engine horsepower). The blue line is the horsepower difference between the K20A3 and the K20A2 (i.e. K20A3 - K20A2). The red line is the difference between the K20A3 and the F20C and the yellow line is the difference between the F20C and the K20A2. A positive number indicates that the reference engine is producing more power at a given RPM. For instance, the blue line shows that the K20A3 produces more power than the K20A2 up until 6000RPMs. Similarly, the K20A3 produces more power than the F20C up until about 5800RPMs. Notice that the S2000 produces more power than the RSX-S except for a few spots.
The torque graphs show a similar trend.
So at about 6000RPMs, there is a definite change between the power characteristics of the K20A3 as compared to the K20A2 and F20C. I've heard that the Civic Si has a restrictive intake and exhaust. Another obvious problem is the fact that the Civic Si only has 6800RPMs versus the 8000RPM and 9000RPM limits of the RSX-S and S2000 respectively.
What happens when we add some modifications? I used Comptech's data for a 02 Civic Si with their intake, header and exhaust combo to compare it to the stock S2000 and RSX-S. See the next 4 graphs.
To be fair, the dyno numbers are not from an independent source so we need to take them with a grain of salt. However, we see that the RPM point at which the K20A3 is overtaken by the other two engines gets pushed out by one to two hundred RPMs.
The only thing we are missing is the improved redline. According to Hondata's website, a totally stock Civic Si with 91 octane gas and their flash upgrade produced about 10HP at the peak.
http://www.hondata.com/k20a3civicsirelease.html
What we really need to see is a dyno numbers for the Si, RSX-S and S2000 from an independent dyno. Furthermore, we need to see a dyno from the Si with the hondata flash tuned for an intake, header and exhaust.
My question: Is it possible to maintain the good low RPM characteristics of the K20A3 while simultaneously improving the high RPM characteristics? A Hondata flash seems like it would help, but a change in cams may be in order. It doesn't look like Toda makes cams for the K20A3, so it looks like we're out of luck.
Why do I ask? Simple. You can get a Civic Si for well under MSRP. My friend picked one up for $17K out the door. Compared tto a RSX-S at $24K, you have about $7K to work with (assuming that you like the look of the Si ;-)). Anyway, if Toda made their engine kit for the K20A3 (or if you could use the K20A kit) and sold it for $2400, you'd still have $4.6K to work with. Is it possible to make a Civic Si perform as well as a similarly modded RSX-S?
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