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It's the width of the seat that determines which is better for street or strip. Obviously for the street and valve sealing longevity you want the widest seat possible, so a three angle is considered the best. However, with a 5 angle job, the air transistions more smoothly around the valve head and that makes a bit more horsepower, but the valve sealing over the long haul isn't as good.
A wider seat transfers heat from the valve head to the head better. GM uses a single cut, the head is 45 degrees and the valve is 46 degrees, a three angle valve job will add horsepower over this arrangement and will give acceptable life, but the GM single cut will last longer. Honda uses a three angle on all of its engines, and gets maybe 250,000 miles out of a valve job. With a high quality valve, such as a Feria 6000 series, or Manley Pro-Flow, it doesn't seem to make any difference how many angles are cut.
I'd go with a three angle for the street and using stock valves.
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Year: 1994
Make: Pontiac
Model: Formula
Engine: Modified LT1
Transmission: 6spd
Modifications:
6spd manual transmission, with 3.42 diff. Fully ported and polished heads, big valves, Titanium retainers, AFR Hydra Rev Kit, Crane 1.6 roller rockers, Extrude Honed exhaust manifolds, K&N filter, air foil, OBDII PCM, teflon coated air intake, flow bench corrected intake and exhaust passages, ported and polished intake manifold, everything port matched. Custom, high output, dual diode bridge alternator. Borla Exhaust system. LT4 clutch and hydraulic clutch release unit. Custom driveshaft. KYB AGX shocks. X-Brace. Cross drilled brake rotors. One of only two verified 1LE Firebirds made in 1994. Engine has 6,600 rpm shift limit. Green with gray leather interior and all factory options.
That's the good news, bad news is that I no longer own the car.
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3 angle valve job vs. 5 angle valve job
Sep 23 2008, 08:53 PM
