HOW TO: Portmatch heads

Step-by-step DIY guide.

T he traditional method for increasing the horsepower potential of your engine is to open up the ports allowing more air in; making it flow much better and in turn, atomise the fuel more efficiently; all to gain a strong burn and more of it. You can spend a fortune with a head specialist that’s invested acres of time not just in experience but research, coupled with flowbench development and — in the example of our chosen engine developer, Joe Allenby-Byrne of Throbnozzle Engineering — computer simulation, too. All to get the ultimate flow for your application and a monster amount of horsepower and torque. Alas, you can destroy a large chunk of that investment simply by bolting on your own bits of hardware… We all know that, part of the package is the induction side, and it’s easy to look at everything as separate components — you fit your sidedraughts, you’ve already got that trick, free-flowing exhaust and in theory, they should all work together. But the thing they have to do is match — if they don’t then you could be going backwards, but in truth you’ve probably got a restriction you don’t need, simply because your ports don’t match up in size and perhaps, orientation.

The best idea is to give everything to your engine builder to match for you, although you can do it yourself. Say, for example, you’ve bought a trick engine but you’re using your own carbs and exhaust — you’ll need to match everything together so it works as a package and you get the power you’re entitled to. With this in mind, Joe showed us how he port matches the manifolds — both intake and exhaust — along with a few tricks and dodges on the way. All of the examples here then are aimed around a Throbnozzle Pre-Crossflow, but they equally apply to any engine.

“YOU NEED TO MATCH EVERYTHING SO IT WORKS AS A PACKAGE”