When I first started building engines it was rather common for guys to drop heads off at the local machine shop and have the heads rebuilt and a valve job done, this consisted in most case in getting a 3 angle valve seat cut and a two angle cut on the valves and checking the guides and seals for wear and replacing them if it was required.īut after a few years of reading and doing some research I found I got much better results driving over a 120 miles to a PERFORMANCE machine shop that charged about twice as much for a valve job, but they cut three angles on the valves and 5 angles on the seats and cleaned and blended the bowl area under the valves, it was not unusual to see a car run one or two tenths faster in the 1/4 mile once that was done, compared to the stock, as cast factory heads, on a muscle car.Ĭcing the heads is always a good idea as is smoothing the combustion chamber and removing casting irregularities, I know from multiple experiences, that a throat and bowl clean up, mild combustion chamber contour smoothing, and a well done multi angle valve job, and upgrading to the correct valves and valve springs can very easily allow well over 1000 higher rpm and 30 plus extra horse power on a BBC. so if you look closely you see a tendency to cut the seat on a port in 15 degree steps or less. as a general rule air flowing over a change in angle across a surface tends to become noticeable.Īs a general rule air flowing over a change in angle across a surface tends to become noticeable more turbulent, if the change in angle exceeds about 15 degrees, and that tends to reduce flow. Valve seat angles and air flowvalve seat angles and the actual angles cut on the valve edges them selfs and how you have the area under the valve in the port bowl area cut and blended has a marked effect on your engines air flow. Include diagrams and written instructions where needed YES THIS WILL ALWAYS COST YOU MORE THAN A TYPICAL HIT OR MISS ONE ANGLE VALVE JOB< IT IT WILL GENERALLY RESULT IN A MUCH HIGHER QUALITY WORK AND MORE ATTENTION TO THE DETAILS You need to be specific, saying I want a 3 angle or 5 angle valve job, what the angles are, what you want in valve mads, if they are too add new valve seats if required, test and replace all the valve springs, set the installed valve spring height at lets say 1.78" and a valve spring seat pressure falls in the expected range of of 180-193 lbs install new valve seals, verify the valve guide clearance back cut angle on the valve etc. You can't for example say, "DO A VALVE JOB" Lower quality work, missed machine work being done, or a total failure of the machinist do do what you intended. When you drop off heads to be machined, its MANDATORY you are very clear and specific about what you want done,Īnd establish both the expected total cost and parts finished date or,ĭelivery time frame with the machine shop before work is started.įailure to do both almost always results in mis-understandings, Valve seat angles and the actual angles cut on the valve edges them selfs and how you have the area under the valve in the port bowl area cut and blended has a marked effect on your engines air flow.
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