327 Double Hump Head Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

wlee · 08-01-2002, 12:53 PM

I recently acquired a pair of 327 double hump heads and have a casting # question. One of the heads is cast #3782461 and the other is #3890462. I’ve done a little research to try & find the differences between the two castings, and have found conflicting information. Thought maybe some of you experts could shed some light on my situation.

According to http://www.mortec.com/ the 461 is a 62cc chamber, and the 462 is a 64cc chamber – my SBC rebuild book says they are both 64cc . . . anyone know which is correct? Can these heads be used together without conflict?? Thanks!!

bigjimzlll · 08-01-2002, 03:29 PM

i believe the 461 is 62 cc...but thats only close...if you cc"d it yourself it could be more or less...the 462 might have been milled to match. The best this is to cc them your self and find out. Im not sure, but i thimk the 461 has bigger intake runners

Blazer1970 · 08-01-2002, 03:29 PM

3782461 is the original double hump head, they would have come with 1.94/1.5 valves. 3890462 could have come with the 2.02/1.6 "big" valves or not, depending on application. 3890462 was the head (with the big valves) that was used on the 302. These heads should be very close, but the castings are not identical, there should be some difference in the combustion chambers. My book lists 3890462 as having 66cc chambers?

wlee · 08-01-2002, 03:32 PM

Thanks for the reply . . . How do I "cc" the heads myself? The heads have been milled to remove warpage, but I doubt there was anything done in the way of milling to match the two heads to each other.

wlee · 08-02-2002, 12:54 PM

Here's a scan of my rebuild book that shows both head styles - is the indent in the 462 the additional 2cc's?

08-01-2002, 12:53 PM	#1
wlee Just an Old Mr Goodwrench Join Date: Feb 2002 Location: Green Ridge, MO USA Posts: 259	327 Double Hump Head Question I recently acquired a pair of 327 double hump heads and have a casting # question. One of the heads is cast #3782461 and the other is #3890462. I’ve done a little research to try & find the differences between the two castings, and have found conflicting information. Thought maybe some of you experts could shed some light on my situation. According to http://www.mortec.com/ the 461 is a 62cc chamber, and the 462 is a 64cc chamber – my SBC rebuild book says they are both 64cc . . . anyone know which is correct? Can these heads be used together without conflict?? Thanks!! __________________ 1969 CST 20 Longhorn 1970 CST 20 Fleetside 1991 Jaguar Sovereign 1992 Mazda Miata

08-01-2002, 03:29 PM	#2
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	i believe the 461 is 62 cc...but thats only close...if you cc"d it yourself it could be more or less...the 462 might have been milled to match. The best this is to cc them your self and find out. Im not sure, but i thimk the 461 has bigger intake runners __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

08-01-2002, 03:32 PM	#4
wlee Just an Old Mr Goodwrench Join Date: Feb 2002 Location: Green Ridge, MO USA Posts: 259	Thanks for the reply . . . How do I "cc" the heads myself? The heads have been milled to remove warpage, but I doubt there was anything done in the way of milling to match the two heads to each other. __________________ 1969 CST 20 Longhorn 1970 CST 20 Fleetside 1991 Jaguar Sovereign 1992 Mazda Miata

08-02-2002, 12:54 PM	#5
wlee Just an Old Mr Goodwrench Join Date: Feb 2002 Location: Green Ridge, MO USA Posts: 259	Here's a scan of my rebuild book that shows both head styles - is the indent in the 462 the additional 2cc's? Attached Images __________________ 1969 CST 20 Longhorn 1970 CST 20 Fleetside 1991 Jaguar Sovereign 1992 Mazda Miata

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08-01-2002, 03:29 PM	#3
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	3782461 is the original double hump head, they would have come with 1.94/1.5 valves. 3890462 could have come with the 2.02/1.6 "big" valves or not, depending on application. 3890462 was the head (with the big valves) that was used on the 302. These heads should be very close, but the castings are not identical, there should be some difference in the combustion chambers. My book lists 3890462 as having 66cc chambers? __________________ Tim



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