PRO-1 RACING’S VIEWS ON: Porting a Cylinder Head



YOU NEED A GAME PLAN:


Before you start porting you need a plan of attack. First, all modern-day cylinder heads are in a very fine state of tune from the factory. Here are some things to consider before porting a head. You should ask the person who plans on porting your head these very simple questions.


  1. 1.Do you have a good record on head porting?

  2. 2.What type of equipment do you have?

3. Do you replace the valve seats in-house?


If they cut or grind the seats: stay away!

If they have a formed tool machine: stay away!

If they have a CNC NEWEN head machine: this is your machinist!


Ask how they size the valve guides:

    -They should ream and then hone the guides to size.


Ask if they know the proper valve protrusion on your head:

    -If they cannot answer, get your head out of there real quick!


Do they have a flow-bench? If so, ask to be given an overview on its operation.

Do they have a swirl-meter and a tumble meter?*

    *NOTE: these are not really needed.


Do they know how to cc a combustion chamber, intake and exhaust ports?

This is important an question to ask for two reasons:

  1. 1.A combustion chamber must be cc’d to deterime its compression ratio.

  2. 2.The cc volumes deterimine the port volume, which is needed to know the port velocity- to-air cfm readings.


Take a look at their ported head and be sure to examine these things:

  1. 1.Look at valve seats or valve job.

  2. 2.Check the valve guides. Are they ground off in the port? Stay away from that type of work. A valve guide is needed to assist in valve sealing.

  3. 3.Ask for a “before” and “after” flow sheet.

  4. 4.Ask for a “before” and “port volume” port sheet.

  5. 5.Get a “before” and “after” combustion chamber sheet.


What to look for in flow data:

    -Are the numbers realistic? Try and compare.

    -If the port volumes are over 6 cc, there is a lot of port velocity lost in the port.

    -Verify the compression ratio.   



PRO-1 RACING HEAD PORTING PROCEDURES:


Before we get into porting procedures, I want to address the problems I see and hear about on METRIC PORTED CYLINDER HEADS. Not many people are happy with the results they get from other companies, and the biggest complaint is “what happen to all my low end?”. Next they are told they need more compression or a different camshaft. It begins to get more expensive to ride these state-of-the-art 4-Stroke engines.


All engines are designed by engineers that use math equations to design the parts and pieces. A cylinder head is the most important part of the puzzle, along with the camshaft, piston, cylinder assembly and crankshaft. These parts must work in unison to obtain optimum horsepower and torque.


CYLINDER HEAD:

Most modern day cylinder heads have a multi-valve set up. Most heads use one or two camshafts to open the valves. NOTE: Cam lifts in most applications do not exceed a .450 lift. It is interesting to note that these heads flow as much air as 2in. per valve at .600 lift. The point here is that the valve opening envelope is very important. This area is .100 below and .100 above the valve seat, since we have only .400 of valve lift. NOTE: Average valve lift is .200 of the valve open time average. The design of the valve seat profiles is very important to the air-flow and port velocity of a port. All the air that goes in and out of a cylinder head must go through a valve/valve seat.