Original '70 454 high horsepower?


New Member
May 31, 2014
Murfreesboro, Tennessee
I have a 454 I got for a trade recently and am going to drop this into my 77 camaro, but I'm still trying to figure out what it is.?
-Block number is 3963512
-Vin number is T1008CGU
-Partial Vin is 10R1153
Here is where I'm very confused, drive head is a 336781 head dated "D 7 76" but the passenger head is a 353049 head dated "F 21 78". Both heads stamped "pass" for passenger car.
This block is all kinds of Frankenstein to me and I haven't taken heads off yet to see pistons. Ideally I'd like to drop this into my car with maybe just a cam swap and possible springs and rockers but now that this thing has different heads i don't know what to do.? Someone please chime in thank you and God bless!!


Veteran Member
Lifetime Gold Member
Oct 8, 2009
Emerald Isle , NC
I think the port sizes are different . I would find another 33681 if your going to reuse one. I doubt they are expensive . Have a machine shop rebuild the heads , start from new so you know what you have. This is .... if you can 't afford some modern heads .

Gary S

Lifetime Gold Member
Apr 14, 1999
Bismarck, North Dakota
CGU is Passenger car 454/390hp engine for 1970. It should be a 2 bolt main block.
That engine should have originally had 3964290 heads with 101cc chamber.
A 336781 head has a 113cc chamber.
A 353049 head also has a 113cc chamber.

Those two heads should work OK together, but will obviously give lower compression than the original 1970 heads.


New Member
Oct 19, 2012
Redmond, WA
I find it interesting, but not surprising, that it's the same casting code as the 1969 427/390 motors. I guess the bore stays the same and it's just the stroke that changes...