SOHC Header on DOHC D-Series Engines

Finding an aftermarket header that fits Dual Overhead Cam D16/ZC engines can be a real challenge. Nowadays, D16A1/DOHC ZC header selection is extremely limited and the few options left are either Japanese imported used parts or the handful of 86-89 Integra applications still being made. While the basic port shape and bolt pattern is the same as SOHC D15/D16s (for which many headers exist), the ports are slightly shifted on DOHCs and there are other minor interference problems. Attempting to bolt a header designed for a SOHC on a DOHC motor may result in exhaust leaks, diminished performance, and overall improper fit.

All is not lost, however. The modifications needed to make a SOHC header fit are minor and straightforward, and being able to use one opens up a whole new world of options.

Making the Mods

The modifications needed are some minor opening up of the ports and some simple grinding at one corner of the header flange. By and large, most aftermarket headers you run into will need both of these modifications. Since aftermarket designs vary so greatly, you may get lucky and end up with a part that requires only one or even neither of these mods to fit. The only way to make sure is to test fit the header of your choice and check for proper fitment.

To see how much (or if) the ports need to be opened up, use your old DOHC metal exhaust manifold gasket as a template. Line it up against the new header flange (using the bolt holes as a reference) and mark any areas that may impede exhaust flow. Use a felt-tip pen for marking or, alternatively, a can of spray paint with the gasket used as a stencil. Once you know how much to grind, go ahead and do so with a Dremel or similar rotary tool equipped with a grinding stone.

The next obstacle is a small chunk of the engine block that sticks out behind the flange mating surface, preventing the header from bolting down flat. This will cause a nasty-sounding exhaust leak. Although it may be tempting to grind the block down, I highly recommend grinding the header flange instead. This is a simple mod that can be performed with the same rotary tool as before, or an angle grinder if you prefer. The pictures below show exactly where to make this mod.

Miscellaneous Info

• The above info only helps in getting the header bolted up to the engine properly. The downpipe bolting up to the exhaust is another story. Headers and exhaust manifolds are pretty much interchangeable on 88-00 SOHC Civics/CRXs/Del sols (except those with cat/manifold combos), so as long as your header was designed for and is being installed on one of these, you should be okay.
• Early cars such as 86-89 Integras and DOHC-swapped 84-87 Civics/CRXs suffer from having too many different downpipe designs. Count on taking your car to an exhaust shop for modifications if you own one of these.
• If you're planning on going turbo, you may have the same kinds of problems with your turbo manifold as described above. As far as cast iron manifolds go, I know for a fact that 92-95 Civic GReddy manifolds bolt on fine but will still need port matching. Edelbrock's cast D-Series turbo manifold will need both port matching and flange grinding. Others such as Rev Hard, DRAG, Apex'i, no-name cast iron, and tubular manifolds I have no experience with, so you'll have to test fit to make sure.