Getting the Most From 91 Octane Pump Gas with a Honda K Motor, Part Two

For the cylinder head itself, we turned to Drag Cartel for their Pro Series head.  The Pro Series is basically all of the Supertech parts we just described, put in a K20A2 casting that has been modified by Drag Cartel.  The intake valve seats are changed out for larger ones and the intake and exhaust ports are hogged out with a 5-axis CNC machine to Drag Cartels prescribed port shape. Then the head is flipped and the port bowls and entrances are CNC machined to improve flow.  Finally, the combustion chamber is unshrouded around the valves and contoured to Drag Cartel’s specifications.

After the ports and combustion chambers have been machined, the valve seats are radius cut for the best flow and blended into the port and combustion chamber.  Finally, the head is given a finely finished deck compatible with MLS gaskets. The head is assembled using the Supertech components and its ready to ship.

In the old days, getting a head done, ported and the machine work finished has always been the choke point in engine building.  Usually, head guys are cranky or even crazy due to the many hours of tedious handwork that it used to take to produce a racing cylinder head.  It would sometimes take months or even years to get your head done! Now companies like Drag Cartel have fully prepped heads built with the highest degree of precision sitting on the shelf just waiting for you to buy them!

The CNC intake ports of the Drag Cartel Pro Series head are awesome.  With 5-axis CNC machines, every single head performs to its intended best due to there absolute repeatability.  This was not possible with the hand ported heads of just a few years ago.

Drag Cartels CNC ported exhaust ports are awesome as well.  We are so stoked that Drag Cartel has these assembled and ready to go without the drama and handholding often needed to get the cranky and crazy head guy just to finish your stuff!

A close look at the fine CNC cuts of the Drag Cartel ports.


  1. I don’t understand why that collector necks down before the V-band, the “reverse cone”. I don’t get how it would not induce a back pulse, granted turbulent flow physics is not my domain.

    At what point in a build would you consider going to individual lambda versus the one? Would there be any gain without ITBs?

    1. Okay well I went studying a bit on reverse cones and it seems they do generate a backpulse but in a certain RPM range that backpulse turns into a negative pressure backpulse (because of the megaphone shape) that helps suck in fresh air during valve overlap. The bad side seems to be that it has a negative impact on low RPM torque and leaves a torque dead zone during the transition into that negative pressure backpulse. That dead zone seems to be minimised by 4-2-1 headers since the second pulse mitigates the first one during that transition period… This just confirms that turbulent air is not my domain, I’ll let wizards deal with it.

        1. That would make sense, the pulse sucks air in during valve overlap when your piston is near TDC where it’s not doing anything, so that pulse is virtually lengthening your intake duration.

          The article I read was about reverse cone exhausts on MotoGP bikes with high RPM NA 4 where they are used to broaden the usable RPM range.

          Good thing ASP only doesn’t do BP headers, I need to spend on a new winter car instead.

    2. I don’t like complications and additional stuff on cars. Maybe for dyno headers, I might do that on a well-funded engine development program. Once you start paying for stuff out of your own pocket, you idea on how you ought to do things changes.

  2. Wow, that’s it eh? I guess with the cam timing and (maybe) small combustion chamber volume of these engines you do not need to run a significant amount of advance? I have a lot yet to learn on K tuning.

  3. I have a good price on a 2012 SI, but it looks like the Z block is way less popular than the A for tuning, is it just a production quantity thing or is there some downside to the Zs that I don’t know about, I could just drop on a 20A head and keep my stock 11:1 bottom end?
    Is anything specially bad on the FG that would need to be addressed for autocross? Like the EP steering/suspension geometry problems?

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