| Cylinder head exhaust valves [message #282903] |
Thu, 23 July 2015 01:02  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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455 olds heads used 45 degree exhaust seats on most engines till 1972 . Then 1973 up they are 30 degree seats. I always thought 45degree were a better seat. Any thoughts on this ? Does it matter? Pros or cons? The intake seats remained at 45 degrees.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Cylinder head exhaust valves [message #282914 is a reply to message #282903] |
Thu, 23 July 2015 08:01  |
Chris Tyler
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Location: Odessa FL
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as I recall early Pontiacs had the lower angle as well.
There was the idea that the lower angle increased flow at lower lift, although unquestionably 45 is better at higher.
Not sure how durability is effected either way, But a wider margin is needed on the exhausts
Durability with low lead gas may have played a role.
76 Glenbrook
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| Re: Cylinder head exhaust valves [message #282941 is a reply to message #282903] |
Thu, 23 July 2015 11:27 |
bwevers
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Location: San Jose
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I thought only the intakes were 30 degrees.
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: Cylinder head exhaust valves [message #282943 is a reply to message #282903] |
Thu, 23 July 2015 11:35 |
bwevers
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Found this explanation on 442.com/oldsfaq/ofhed.htm
"Generally speaking, there were two intake valve sizes: standard run of the mill engines used 2.000" valves [which also served as the small blocks' "big valve"], and performance engines used the larger 2.072" intakes. A small, but not negligible, 3.6% difference. Generally speaking, for heads up to and including G, the large valves have a 30 degree face, and the 2.000" valves have a 45 degree face. Almost all heads used 1.625" exhaust valves with a 45 degree face. Notable exception would be the 1972 Ga heads. Aftermarket performance exhaust valves are commonly larger than stock: 1.710" diameter. "
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: Cylinder head exhaust valves [message #282991 is a reply to message #282943] |
Thu, 23 July 2015 23:33 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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bwevers wrote on Thu, 23 July 2015 09:35Found this explanation on 442.com/oldsfaq/ofhed.htm
"Generally speaking, there were two intake valve sizes: standard run of the mill engines used 2.000" valves [which also served as the small blocks' "big valve"], and performance engines used the larger 2.072" intakes. A small, but not negligible, 3.6% difference. Generally speaking, for heads up to and including G, the large valves have a 30 degree face, and the 2.000" valves have a 45 degree face. Almost all heads used 1.625" exhaust valves with a 45 degree face. Notable exception would be the 1972 Ga heads. Aftermarket performance exhaust valves are commonly larger than stock: 1.710" diameter. "
My motors manual shows most all small valve big block heads from 1973 on we're 45 intake and 30 exhaust including the motor home shop manual. A friend that used to do cylinder heads(still has a head flow machine in his shop) insists the 30 degree exhaust valves in my "J " head is the reason a guide wiped out on the end cylinder at 14000 miles due to poor sealing that caused excessive heat at the guide He feels 45 degree seats seal a lot better. I don't see it but what do I know. He was an automotive engineer.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Cylinder head exhaust valves [message #283042 is a reply to message #282903] |
Fri, 24 July 2015 12:58 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
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Roy here's a link to Joe Mondello's rebuilding guide:
http://www.mondellotwister.com/articles/RebuildYourFirstEngine.pdf
On page three he makes a comment:
"Oldsmobile heads usually have 45º valve seat angles with a few exceptions that are 30º.
Most 455 4 barrel heads have 30º degree intake seats, 1972 and 1973 G heads have a 30º
degree exhaust seat and a few small block heads (1972 and later) have 30ºdegree exhaust seats."
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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