A frequent question that gets asked is “What downpipe makes power on my 9th gen?” I have gotten in the habit of simply directing people to Full Race Motorsport’s website as we use their catless downpipe & exhaust on our supercharged vehicle, and I know the setup makes power.
Now here’s empirical evidence that it does.
Philippe was down at the shop and had us install the Full Race catless downpipe before I tuned his 2012 Civic Si. The vehicle came in with the following modifications on it already:
- Invidia Q300 Exhaust
- HPS Intake Hose
- K&N Drop in Filter
Now from previous baselines of completely stock 2012 Si’s, I know they do about 160-164whp on our shop Dynapack. Before we installed the downpipe we baselined the car as it arrived. Sure enough, it did about 162whp with the power curve I’m used to seeing on a stock 2012 Si. This leads me to make the following conclusions:
- The HPS intake hose and K&N drop in filter do absolutely nothing. Pretty pointless modifications and honestly a rip off (spend your money elsewhere).
- The Invidia Q300 is a nice sounding exhaust, as always, but does not make any power, at least not without a tune. Maybe this will change with a tune?
We installed the catless downpipe, and put the car back on the Dynapack and ran a couple more baseline pulls on the stock tune. The results are as follows — solid line is with the downpipe installed, dashed is before the downpipe.
We netted as much as +10whp and +10wtq from simply installing the downpipe. That’s a sizable gain for a simple modification.
Now let’s throw a good tune on the car… and the results are as follows. Solid line is fully tuned, dashed line is our baseline with the downpipe installed. The tune netted as much as +12wtq in spots and as much as +18whp on the top end.
What’s this look like over the original baseline before the downpipe was installed? Here you go. Netting almost +30whp in spots with a downpipe and tune on the top end. Sizable gains, the part worked well and the tune brought it all together.
How does the exhaust factor into the power curve? Until I do a fair comparison of an exhaust swap on the car I can’t say with absolute certainty. However, we do know what other parts do make power already — A CAI nets 4-5whp, which would put this car around ~190whp, which is about 3-4hp shy of what the average 2012 Si maxes out with using bolt ons on this Dynapack dyno. So to make an educated deduction — an exhaust may net 3-4hp and maybe some mid range torque due to the ability to adjust the variable valve timing on the motor. It also seems that a 3″ exhaust would be the way to net any power at all, and anything smaller may not net any gains. With the integrated exhaust manifold design on the 9th gen cylinder head, the gains we’re used to seeing with a 3″ exhaust on previous K series engines don’t really hold true on the K24Z7.
Safe to say — if you want PROVEN performance, a good catless downpipe (Full Race works well as I’ve shown) and a good tune will get you 95% of what you’re going to get N/A with bolt ons. A cold air intake will net some power as well — and the exhaust is a wash at this point it seems.