Racecar drivers are always chasing a tenth of a second. Generally, racers don’t care where the tenth comes from. They just want to be a tenth of a second faster than before. Maybe it is a tenth of a second from a wider tire. Maybe it is a tenth of a second from making the car lighter. Maybe it is a tenth of a second from an engine upgrade. Regardless of how the time is saved what racers really love about saving a tenth of a second is when they can do it and not spend much money. Drivers love that!

Here is a cheap, NASA legal — at least in H4 — and easy way to find a tenth of a second: port match your intake manifold.

Step one for intake manifold port matching: take the intake manifold off the car and clean it up. This process can’t be done while the intake is on the car.

Port matching can be completed on literally any vehicle, however how we port matched this intake manifold off of a Honda B18A1 engine was in accordance with NASA Honda Challenge rules. The rules state you can port match the intake and the head, however, you can only go as deep as one inch into the intake or the manifold. This is an important detail to understand because if you use a tool to port too deep, then your parts may not pass post-race inspection and you may be handing your trophies to somebody else. Nobody wants that.

First use a Sharpie to mark up the face of the intake manifold. Then place the gasket, or phenolic spacer, on the intake manifold, then finish by using a scoring tool to line where you want your port matching to stop.

The concept of port matching an intake manifold to a head is to ensure the flow of air to the cylinder is as big, smooth, and efficient as possible for maximum power. By ensuring the mating surfaces of the intake manifold and head have holes that match perfectly will help air flow through the engine. This can be achieved by removing material off of one side (the head or the intake) or both to promote air flow efficiency.

Here is one way of looking at it. If you are trying to pour a five gallon bucket of water into a soda straw you are going to spill water everywhere. But, if your five gallon bucket and the soda straw had the same diameter hole as one connected with the other, then you would have some smooth flow of water from the bucket into the straw. Port matching is ensuring the intake — pouring air into the head — has smooth flow.

The black Sharpie is used to allow the scoring tool to make a visible mark after tracing the gasket to know where to stop porting. The material inside the scored mark should be removed.

Since you can’t see what these two holes look like once an intake manifold is bolted to a head, it is important to use a gasket, or phenolic spacer, to verify the diameter and “line up” of the two tubes for air. We used a phenolic spacer (a thick plastic gasket that limits engine heat transfer to the intake manifold) to determine how our head and intake matched up. The phenolic gasket showed us that there was a fair amount of material that could be removed from our Honda B18 intake manifold to help it match with the head better.

Using a Dremel and a one inch sandpaper bit with an aggressive grit made quick work of the aluminum intake manifold. We used a 1-inch deep sandpaper bit to ensure we didn’t go beyond the NASA rules for port matching depth.

I purchased a porting kit through Summit, which came with a ton of different size sandpaper bits in different grits that could go on a Dremel or an air tool. The 1-inch deep sandpaper bits were best for our use since we always knew that if the entire bit was inside the intake manifold, but right at the edge of the face, then we were exactly at one inch depth per NASA rules.

Here you can see the 1-inch deep sand paper bit being used right at the face edge of the intake manifold to get the perfect one inch deep port matching for this Honda Challenge intake manifold.

This is not an expensive upgrade to chase that tenth of a second. The only cost is a few sand paper bits for a Dremel attachment. But in racing, there is always a price. Nothing is free. In the case of port matching, that cost is time. This is a slow, time-consuming process. If you don’t have any patience, this is not the project for you. Set aside a nice long afternoon for grinding away aluminum. You will be doing this for hours.

Using the phenolic spacer to check our work we could still see black Sharpie marks on the intake manifold face meaning we needed to keep on grinding. “Just keep grinding. Just keep grinding.”

There is a bit of artwork to porting an intake. If you port too much, you could destroy an intake manifold and you will be jumping in the truck to head to Pick-A-Part for a new one. The trick is to take your time. Grind, check your work, grind, check your work, grind. If you grind too much, you could make things worse for smooth air flow once the phenolic spacer is put into place. The whole point of this project was to make the engine more powerful, not less. Pro Tip: Slow down.

Using higher-grit sandpaper can smooth out the port matched section of your intake manifold. This one had three different grits used, smoother each time, before we called it good.

If the head port diameter matches the gasket and the gasket matches the newly port matched intake manifold then you are ready to put everything back together for nice smooth efficient air flow. If your head does not match the gasket (or phenolic spacer) then you will need to do this exact same process with the head. “Just keep grinding. Just keep grinding.”

Assembly is the reverse of disassembly. Once we had our newly ported intake matched with our head and phenolic spacer, it was time to bolt it back onto the engine.

Because we changed the amount of air flow that would be reaching the combustion chamber, we took our car to Performance In-Frame Tuning in Napa, Calif., and had the wizard, AJ Gracy, tune the car so the air-fuel-ratio was perfect for engine safety and performance. The dyno is the ultimate tool to know if all that grinding was worthwhile, or a complete waste of time.

Step one for intake manifold port matching: take the intake manifold off the car and clean it up. This process can’t be done while the intake is on the car.

Port matching is free horsepower, and in NASA road racing where the competition is tight, I certainly see it is a “must do” if your class rules allow for it. So, what are you waiting for? Get to grinding!

Rob Krider is a NASA Honda Challenge 4 National Champion and the author of the novel, Cadet Blues.

Images courtesy of Rob Krider and Rob Krider


  1. I’d do the same thing if I were in your shoes, but wouldn’t expect much if any of a gain. Did you net anything appreciable?

  2. How are you going to port the intake but not the head? That’s useless. Ever tried to fit a baseball in a golf sized hole?

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