Port Matching Heads to an EH Intake
Nick Chrimes, BaySHO Performance
When an intake manifold gets extruded honed or ported, the heads need to be port matched to the enlarged holes in the intake, otherwise a ledge will exist between the intake and heads, disturbing air flow.
Here's a method of making templates to accomplish the job, and tips on doing the porting:
Get a sheet of fairly thin malleable plastic from Tap Plastics or some such. This stuff can be rolled into a tube and cut with scissors or a Stanley knife.
Cut two 3" x 14" strips from the sheet for the two templates.
Place template blank over head dowels and wack each dowel with a hammer to indent the plastic:
Cut holes dead central to the indents. The perfect size is that of a 3-hole paper punch, except that it won't give you enough room to reach the indents. Tool shown is a single hole paper punch. Check availability at your local office supply store:
Now you have holes in your template, time to put it on the Intake for port matching. MTX flywheel dowels are exactly the right size for holding the template in place while the holes are being cut. A slight push fit that requires a light tap with a hammer to seat them firmly in place.
*** VERY IMPORTANT NOTE ***
If you have the intake apart and are working with just a bare snake, be aware that they can be warped. Not a problem with an assembled intake as the snakes are held in the right position. If you create the three holes and the template blank fits fine on the head, but the holes don't line up when offered up to the snake, it is definitely warped. Offer the snake up to the head to see what has to be done to make it fit over the dowels. In my case one of the pipes had to be bent outwards by hand a good 1/8". It's really best to reassemble the intake before making the templates, and bolting it back on to the engine to make sure everything lines up perfectly. Otherwise your template will be off.
Cut the holes using a Stanley knife and scissors:
Finished set of templates. These heads had already been ported, but the porting was so shallow that there was still a sudden change of direction at the bottom of the chamfer (a distinct ridge there), and the heads hadn't been matched to the intake too well.
Mark an 'L' and 'R' on the the templates.
Total time to make the templates around 2 hours:
Closeup of a couple of the ports showing how far off the original porting was:
Detail of another car that shows how deep the porting should be. Note that there's no ridge at the bottom of the chamfer:
Porting of this kind is done using a grinder, and can be done at a machine shop specializing in cylinder heads.
However, it's fairly easy to do the porting yourself. Expect to spend 4-6 hours, though. On the left in the picture below is a grinding tool. The one shown is actually for steel: a bit for aluminum would have fins that are more widely separated without the crosshatching. The steel bit goes a lot faster. Can be got from here:
The middle bit is a Dremel abrasive wheel, used to smooth out the walls after the basic grinding is done.
The right bit is a Dremel grinding stone, used to port match the gaskets:
The head needs protecting during the porting process to stop swarf (metal shavings) getting to the internals. Stretchy garbage bag with red draw strings and a slit cut in it, sealed with duct tape:
Next up is to mark the heads. If you haven't reassembled the intake and find that the snakes are warped, best to make sure that the piece of template between the two ports is dead central on the ridge separating the ports on the head. Paint mechanic's blue round the ports, place your template over them, and use a scribe to mark a line in the blue. Easier than keeping the template on the head while you grind:
Do the grinding with the steel bit in a variable speed drill set to a fairly low speed setting, then smooth it out using the abrasive wheel in a Dremel.
The manifold gaskets also need porting. It helps if they are bolted down. Oil pan baffle bolts or exhaust manifold heat shield bolts work fine. Use the Dremel grinding stone.
- Important note: now the gaskets have been matched to the heads, make sure you don't mix them up next time you take the intake off.
Last step is to get rid of the swarf. Paper towel wrapped around a bristle brush with lots of lacquer thinner. Don't forget the underside: clean around the valve seats with lacquer thinner and Q Tips with the valves open. Don't forget the valve stems. Ideally use compressed air to blow out any remaining material.
You need to do a thorough job here, especially if you are going to adjust the valve clearances after. You don't want a bit of swarf holding the valve open while checking the clearance, otherwise you will finish up with too small a gap: