What is Porting Polishing
 

I understand what polishing the cylinder head is all about; but I can't seem to get a straight answer from various internet searches as to what porting actually is or whether it would benefit me in terms of fuel economy.

Would porting the cylinder head undermined fuel economy for my Civic VX?

It enables your heads to flow more air....which means more fuel. Port matching is meant to smooth the flow of air as it transitions from the intake to the cylinder heads. It too leads to better airflow and more fuel. Larger displacement can increase your engines low end power enabling you to pull higher gearing (new Prius)...but thats a whole other ball of wax.

In terms of fuel economy, don't worry about it, if you intend to use it on a gasoline engine.
Now if you were going to swap a smaller engine into your existing vehicle then you might want to think about using P&P for maximizing power.

Driving around using as little throttle as possible, porting and polishing is not going to have much effect on fuel economy.

After I saw some photos of a VX manifold and gasket, it looked like some port matching would help with potentially cracking manifolds. There were apparently, based on the markings from the gasket on the manifold gasket surface area, areas where the cast iron manifold would interfere with exhaust flow, particularly on the inside of the two center exhaust ports. Much higher temperatures in the center of the manifold, combined with the proximity of the center ports to the catalyst COULD be instrumental in the manifold cracking which seems to be almost universal at some point in time.

http://ecomodder.com/forum/showthrea...ory-32194.html

regards
mech

Very general terms--

The intake port is the hole in the head leading from the intake pipe to the intake valve. Likewise, the exhaust port is the hole in the head leading from the exhaust valve to the exhaust pipe.

"Porting" means using cutting and grinding tools (and, rarely, building up the material with welding) to change the shapes of these holes. Traditionally, this is done to open them up and allow more air to pass through them, allowing the generation of more power at high throttle settings and high RPMs. Note that air flow through a tube can be kind of odd, so just opening up the ports can result in less power if done indiscriminately and without good knowledge.

There may be a few instances where a good port job helps engine efficiency at the power levels that we typically care about, but that would be a very significant exception, and the original parts would have to be quite sub-optimal for it to help noticeably.

-soD

What is Porting Polishing? An art or science? People like Jocko Johnson built businesses like Jocko's Porting Service if they knew what they were doing. It's a balancing act between flow and velocity.

Consider Extrude Honing. It can offer improvement over and above an already ported and polished intake/head/exhaust.

Larger ports are of no value when shifting at 2000-3000RPM. When you floor it, the large ports come in to play. Porting will simply move your torque/HP peaks to a higher RPM...exactly what you don't need.

As for an Extrude Hone...just adding up the prices on the website it would cost $1755. for an intake, head, and exhaust manifold port. Your car could travel 70,000+ miles for the cost of the hone. The process would enlarge ports that Honda intentionally made small in their efficient design.

What good is a 10" pipe if you only need water hose volume? Instead of water forcefully exiting a hose you would have water falling out of the oversized pipe.

There is a good book that explains called "performance with economy". Came out in the early 80's for hotrodders that wanted to be able to afford to drive their car.

The short version is, on carbed or throttle body injected gas engines you don't want to polish your intake at all, because the gas is actually small drops when it gets to the cylinder instead of a mist, so the turbulence from the rough intake helps to decrease drop size, increasing torque and fuel economy.

Super simplified explanation of porting is taking a cylinder-ish shape and changing the ends to be more cone like. This allows more flow of air. Sounds good but with a gas engine or a non turbo diesel there is an effect called scavenging, where the exhaust in the exhaust system is traveling fast enough it helps suck the burnt gasses out of the cylinder on the exhaust stroke. This can help by putting less back pressure on the piston and/or ridding the cylinder more completely of burnt gasses so fresh fuel and air can enter more easily. Porting can increase air flow to the point that it reduces this scavenging effect.

I welded up a set of headers for a geo metro optimizing for this scavenging effect, one of the real engineers one here helped me calculate size and length. The runners were TINY! As in, they don't sell exhaust tubing that small. Torque and fe both increased. This custom header was essentially the opposite of porting.

The book I mentioned has nice dyno charts showing these effects.

I would have liked to have seen those headers. I'm guessing they were long tube if you were trying to maximize scavenging.

That's for "wet" manifolds; carb'd or throttle bodied with fuel and air flowing through. Most anything newer is port injected and the manifold runs "dry". Don't know what prevailing theory is on intake smoothness but I'd think the smoother the better.