Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Montreal Head & valve shaping
Since the Montreal engine going into the "coupe" is being developed for improved low end torque and drivability and generally only a moderate increase in output, I decided to get the headwork done as I had a buyer for my SuperFlow flow bench and I wanted to measure some of the results before it was picked up.
The intake and exhaust cams I built for the motor are typical RJR designs with less overlap but more open valve duration. Lift (at valve) increases of 1.25mm on intake and 1.32mm exhaust.
Since the motor is a low milage piece and not being preped for "High Output", I decided to concentrate on the bowl, seats and valve shapes to get maximum flow from the typically congested Alfa seat/valve area.
The guides were like new and I decided to work around them, which was not a problem as the ports are adequate in size for the combustion chamber volumn. Cleaning up and reshaping the bowls, and throats into the ports was simple once the valve seats were opened.
The seats were typical Alfa parallel sleeve sections that are the same OD as the valves. They had enough seating area that significant opening could be done and adequate seating width be left to seat the reshaped valves at the outer margin and pick up 2mm intake diameter and 3mm exhaust diameter at the seat.
The seats were cut away with a 75 degree cutter then a 45 degree stone was used only to break the edge left at the 30 degree seats. No 45 degree cut was made as the seats were opened maximum for flow to the seat area, and the valve seat area left as small as reasonable for a street motor.
( For those of you that think "3 angle" valve cuts are best you are way behind. You do NOT attempt to manage flow at such small radiuses and high speeds with "shapes"! Larger valves applied to such seats only add additional interference to fluid flow (air). )
The valves (stock) were re-shaped on the back side & margins to a shape I have used for years. Seats (30 degree) were left at the outer 1mm of the valves cutting away the "lip" between the flare & seat area. Margins rounded from seat to face on intake & exhaust.
The flow at .200 lift (50% of total valve lift) improved over 20% above the stock seat/valve flow rate. I did not have time to measure higher lifts but the significant measurement was more than I expected, and was likely a result of smaller valves/seats than normally played with.
I added O2 sensor bungs to the headers for fuel mixture calibration, and had them Ceramic coated with a satin finish locally.
Pics below of before & after.
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Last edited by Alfar7; 05-11-2010 at 06:29 PM.