- Is hand porting better than CNC porting or vice versa?
Both have advantages and disadvantages. A good CNC port really needs to come from a proven hand port in the first place. Sometimes if the head casting has major core shift, it is easier to work with that using hand porting rather than CNC. The largest benefit of CNC porting is of course perfect consistency and repeatability.
- Is a rough surface finish better?
In some instances it is but others it isn’t. Chambers and exhaust ports can benefit from smooth surface finish, where some intake ports can benefit from a rougher finish that gives a different boundary layer condition. We use the dimple finish (or golf ball finish some call it) in certain parts of intake ports to promote fuel atomisation on a carburettor engine, and other parts of the intake might be polished.
- My engine is turbocharged, I just add boost to make more power, do I need things like cams, bigger valves and porting work?
When you optimise port flow and valve area, you are making the engine more efficient, therefore requiring less boost to achieve the desired result or making a lot more power on the same boost level. More exhaust port efficiency and flow will spin a turbo sooner and harder so larger turbos or reduced lag are achieved. On a 600 hp 4G63 engine, we gain 100+ HP from modifying the head (on the same boost as prior and provided the turbo has enough capacity in it)
- Why do cam makers ask for cylinder head flow figures when they design a custom cam?
In naturally aspirated engines, the intake port flow capability is directly relevant to how much power you can make. So it is important to choose a camshaft that complements the head. If your port doesn’t flow enough to make the desired power, no cam will fix that, and your cam guy should tell you to fix the head first. Exhaust flow will dictate exhaust cam lobe choice. If you have great exhaust flow in the blow down period, you can open the valve later and make more torque. If you have a blower or turbo motor, the exhaust lobe is going to be dictated by horsepower, exhaust flow and rpm.
- What is the best intake to exhaust flow ratio?
There is an old myth of needing 75% exhaust to intake flow. This is not accurate at all. The exhaust port and system has the job of evacuating the cylinder efficiently to the desired rpm so as not to create a pumping loss situation. If you have an inefficient exhaust port, you will need more “time” to do the job, hence a larger duration and lift. If you have a port that flows great at low lift and you can “blow the cylinder down” easily, then you have the opportunity to open the valve later and for less time, resulting in more mid-rpm range torque. We design intake flow and velocity requirement to match the application and we treat the exhaust side separately. Sometimes we will intentionally over exhaust to change the driving characteristic of the vehicle.
- Is a bigger always better?
Maybe bigger is better if you are entering a fishing contest, but certainly not when it comes to head modification. Engine design, including port size is all about correct combinations and good engine maths. Too big can certainly kill engine performance. Head porting is an art and is best performed by experienced tradesmen.
- I have big brand name heads cams manifold, pistons and rods. Why am I getting beaten at the track?
Simply because you have mismatched parts combinations within the engine. We see this a lot – intake runner tuned lengths might suit 8,000 rpm, with an exhaust header that suits 6500 and a cam choice that is the biggest available. All resulting in a complete lemon on the race track. We offer a basic and affordable design service that will give you the runner lengths and sizes you need as well as the cam choice to meet your goals. Understanding what is needed prior to sourcing the parts can save you money and get you a better result.