Just asking... I hear a lot about this. Thanks

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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, MSD 6AL, Aluminum Driveshaft, TB Coolant Bypass, Ported Plenum, Modified MAF, Syclone Fuel Pump, JET Airfoil

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

http://www.geocities.com/transam85tpi/

 

Lets say you have a 305 (3.736 bore) and a 350 chevy head with 2.02&1.60 valves that are literally touching. This leaves a whopping .116" of space, lets say .058" each side. Thats not much, about 1/16" is close enough to imagine how little that is. It doesnt exactly work like this, but the valve opens (or so you think) and the air rushes into the cylinder... and sees a 1/16" gap to flow through. Doesnt flow too well like that. Of course there is more space on the other sides, and some other things going on, but simply put the valve is so close to the cylinder, it blocks off a usable airflow path, and they call that 'shrouding'

 

cool... thanks madmax

 

Illustrations here:

Shrouded valve: 1.94" valve retrofitted into a 305 head



unshrouded valve: modified chamber, blended into the head gasket line.



For more pictures see: http://www.isthq.com/~dan/ported.html


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Daniel Burk
http://www.isthq.com/~dan/fcar.html
'84 Trans Am WS6/L69
KB SFC, Moser axles, Torsen Diff. PST suspension, Braided stainless brake lines, Koni struts, 11-inch rear disks,Spohn Adj. torque arm,
Ported 305 heads w/1.94"intake valves, Comp Cams XE262H, Griffen alum. radiator,
Turbine Technologies 2500 stall converter, underdrive pulleys, Crane Hi-6 & more.
1.05g skidpad verified.
New best E/T! 14.039 at 100.82 MPH in 41 degree air at Stanton, Michigan.