BMW 2002-cylinder heads are not the worst cylinder heads ever made to try and improve but they are definitely in the running. The 2002 port runners are short and the short sides go right up to the back of the valve seat inserts and there is little to no short side radius. You can mess around with the port runners for months and never get them to flow much better. I have tried numerous times in the past with limited success. So, when Raffi, the owner of The Pit Stop, a high-end exotic car garage in Brisbane, Ca. told me to be creative and make it the best 2002-cylinder head ever, I may I confess, have possibly become sexually aroused. A good customer was giving me the rare chance, to do something well beyond the norm and ordinary. Something Great! Something Bigly!! Something Covfefe!!!
Since the gains to be gotten from the 2002 head are finite when it comes to just porting we had to think out of the box. To go beyond porting, we would have to think about thermodynamics and combustion. Internal Combustion engines work on basic Thermodynamic and a few other scientific principles. The prime thermodynamic principals include Volume, Pressure and Temperature. Each of these can refer to a number of states and actions in our engine. Volume can be noted as a measurement reference as to a cylinder’s Swept Volume. IC engines breathe on a “Per Volume” basis. There is also the Volume of the crankcase which also has its effects on operation, but we will pass that by for now. Without Pressure there would be no compression of the in-cylinder Air/Fuel charge, and there would be no external pressure on the Air/Fuel charge to assist it entering into the engine.
Atmospheric or Barometric pressure is how much the weight of the ocean of air that we live under is pressing upon us. This pressure is relative to our elevation in the Troposphere. Barometric pressure also changes with weather conditions. Barometric pressure is higher at sea level than it is on the top of a mountain. Or the higher one goes up into the Troposphere the less are the effects felt by the weight of our ocean of air. Temperature affects the amount of Oxygen in the air that we and our IC engines need to breathe and survive. Cooler temperatures will generally, but not always, provide more oxygen molecules per a given volume of air. Oxygen content is also affected by the amount of water in the air. But again, we do not want to make this story overly complex at this time.So, what does all of this mean? It means that our wonderful Internal Combustion engines are, at an elemental level, thermodynamically driven.
I spent some time thinking about what I had done to 2002 heads in the past and knew that I could just about port this thing with a sand paper roll and make it as good as it was ever going to get. Or I could put the cylinder head on Mister Flow Bench and do some testing and thinking. I began testing both CFM and velocity numbers in the port runners. I wanted to find out if this thing had any secrets. I needed to think positively! Try a new approach to thinking about this problem child and try something new.
Not every cylinder head’s air flow problems are located in the port runners. For some heads, you can grind in the runners until you start to see shapes in the port runner walls that look just like Jesus on a tortilla. That might get you an audience with the Pope, a room in a padded cell, but it will not likely proffer any helpful relatable airflow information. So, I started looking beyond the port runner and to the combustion chambers. I put some clay in the chamber and put the head back on Mr. Flow Bench. The intake air flow picked up! I did some more sculpting. The cylinder head was now traveling back and forth from my porting/work bench to Mr. Flow Bench. I had started to wear a game trail into the concrete floor. But the intake port runner air flow had continued to pick up. It picked up enough that the clay started peeling off the chamber walls. There was now too much air flow for the clay to adhere. Excellent!!!
I mixed up some epoxy and started filling in the combustion chamber areas where the clay had previously been. The next day after the epoxy had hardened, I started to do some conservative shaping. The flow slowly started to return to the numbers that I had seen in the day before, so I shaped the chamber some more. The head’s air flow kept getting better. I was now wearing a deeper path in the concrete floor between Mr. Flow Bench and my work table.
I continued this routine over the next few days until I had a definitive shape. What I have described here took many, many hours spread out over days of testing and shaping. This is very slow, detailed, and tedious work. It is not a box of Lego’s or a Christmas jigsaw puzzle prize from your favorite Aunt. Airflow Trolls do not suddenly jump up out of Mr. Flow Bench and tell you what you should do. You have to listen; watch the numbers and look for clues. Use your flow tools in the port runners, watch for turbulence and dead spots, etc. You have to think and figure it out with this and other such cases by trial and error. Cylinder heads do not come with improvement instructions with regards to port flow CFM and especially not port velocity.
I wanted the intake flow to spiral around and down the cylinder bore. Not as per stock which had the charge blowing out the intake valve and straight across and out the exhaust port during overlap. I did a little backyard wet flow test to confirm that I was moving in the right direction. I was. After I had tested my modifications backwards and forwards for a few days. I made a silicone mold of the port and then had my friend Robbie, The Welder, weld up the four combustion chambers.