Many people have no idea what one is so let me explain.
Ok, as previously discussed in an earlier post airflow is probably the most important thing to consider when trying to increase the power of your engine, if you can get more in and match it with more fuel you are going to get more power, simple.
How do you know if your modifications to the airways have done any good without checking the output of the engine? You don't unless you have a flowbench to give you a good idea of what is going on. You see, sometimes you can make things worse or spend a lot of time on something which gives little or no improvement.
Don't buy a reworked head from someone who cannot prove what they have done.
(Very!) basically a flowbench has a few electric fans inside it which draw a vacuum through the test hole, they can be reversed to blow and can also be controlled to give a certain airflow at which you take your readings at, the basic Superflow 110/120 is what many people have, it is rated at testing up to 100bhp per cylinder and maxes out at 185cfm (cubic feet per minute)
Ours is a bit bigger, it runs 6 motors and will pull your arm in if you get too close! It pulls over 28" and 250cfm quite easily. 28" is called test depression, it is read from a manometer which is T'd off from one of the chambers within the bench. The more vac and CFM you can pull the closer and more accurate to a real life situation you will get. Air is much heavier than you would think and (just like a car going round a bend) the faster it goes, the less chance it has of actually getting round smoothly so the more air your bench flows, the more accurate and closer to real life your results will be.
Whilst it has to be said that your own flowbench is better used with your own before & after figures it's sometimes good to compare with others, so the ability to be able to check at 10 or 28" is useful as not everyone uses the same test depression.
The Superflow has liquid filled manometers to take the readings which you manually log, we have digital ones on ours which are displayed on the laptop screen and can be logged into the laptop if needed. This makes the job much easier and quicker and photographing your good work a bit easier too as you will see.
With a fair bit of work we can get an integrale 16v bare inlet port up to 170cfm, it isn't just the high cfm numbers which you are chasing, you need good air speed throughout the port, no good if the air speed is too slow or too high even. We read airspeed in FPS (feet per second) with a probe which we can push into any part of the port to check for high, low or dead areas where nothing much is happening and shape the port to suit.
There isn't much point in beyond 170cfm BPF either if you are still using the OE sized valve or untouched inlet manifold as it will pull those figures back down once it is fitted.
Below is a graph of results from a head I did last week compared to standard. It shows the flow of the port with the valves fitted and at different lifts in increments of 1mm. Stock head versus modified which has a 3 angle valve seat too. It also shows a comparison at BPF (bare port flow) no valves fitted.
As you can see, it flows more air from the start, but really comes into its own at the higher lifts from about 7mm onwards.
What is interesting to note is that with the standard ports the CFM with the valve in at full lift matches the BPF. With the modified port and valve in test it never matches the BPF (well it might do if you lifted it higher), this indicates that we could fit slightly larger valves and maybe make some small gains.
Why do you need a gasflowed or ported head on your engine?
Many people modify their cars without doing much to the head, I don't know why this is, maybe because they don't understand how important it is or because it's not a bolt on shiny part which you can admire and show people....
About 75% of the power in your engine is made in the cylinder head so it makes sense to start here. Many modifications which you do to an engine have a downside to them, the cylinder head is not one of them. When you fit a properly modified head you gain in power, driveability and economy - it's a win-win situation.
As outlined in the engine related articles it is important to start an engine modification project by getting the basic core of the engine right before going any further. Any clod can bolt on a huge turbo and ram the air in to get a bigger power figure, not of much use if the car is horrible to drive though.......
.
