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Hello there! I am new! My name is Cristian and I am from Orange County, CA!


I bought my 71 nova about 5 years. When I bought it, the seller told me the motor was a Pontiac 400 small block out of a GTO. I knew very little about muscle cars back then and I thought I was buying it for a good deal.

Now im 23 years old and wanting to rebuild the motor yet IDK what I exactly have. I was looking around the block and I saw on the passenger block above headers had some numbers. I also looked under the distributor cap. After doing my research I understood that the 6x heads were never in a GTO to begin with because they started in 77-79. I uploaded two images. Where else should I look on the motor?


The numbers by the passenger side above headers were C306 Then over the last spark plug it was D then N. Also vertically as you can see it is GM3 and horizontally 6X.

Under the distributor cap as you can tell by the picture the numbers are A038.

I googled these numbers and have no luck. Can anyone steer me in the right direction on finding out what I exactly have? Thank you. I really want to build this motor to 300 ponies or more!
 

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The heads are '76. C306 - March 30th, '76
Block is a '68 or '78 - A038 January 3rd '68 or '78. Block casting number would help determine the year...

D and N is the shift - Days/Nights
 

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Sweet thanks for the info.

On the driver side of the block I saw 6x and also A068.... Vertically it said G M 7. After the A068 to the right it said D and N.

On each head the stamped ID is 8.
 

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So I have a 1968 block with one side 76 head and the other 78?

A068 was driver side head.

C306 was passenger side head.

Weird....
 

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I would double check the last digit on those heads. 8s can look like 6s and 6s can look like 8s.....
 

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It would appear that your engine block may be a 1968 based on the first three digits "979". 1968 used 9790..., 9791..., 9792..., 9793... So it may be an early production block for 1968. The 6X heads are later 1970's heads, the "8" stamping is the one preferred.

PS - Pontiac does not make a "small block" like other manufacturers. And, you should already have good horsepower depending on cam selection, but you want to aim for torque when building a Pontiac.
 

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Oh I didnt know that about Pontiacs.

I have a lot of torque already, I think I will rebuild it to put out more horsepower.
 

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I am getting a good deal on a super built 700R4 to replace my turbo 400. I got the 3.73 posi already, so I want to rebuild the motor for horsepower.
 

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One of my biggest pet peaves in the automotive world is people who assign "big" and "small" to Pontiac engines.

BTW, when my daughter was little she thought Chevys were pronounced 'shabbies'. Why would I correct that? ;)
 

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I am getting a good deal on a super built 700R4 to replace my turbo 400. I got the 3.73 posi already, so I want to rebuild the motor for horsepower.
OK, sounds good. The overdrive 4 speed auto and 3.73 gears should be a good combo and cruise comfortable in OD. I know that one of the Pontiac magazines did a conversion as I recall, with this trans. They did a step by step conversion in a two month coverage. It was not a drop in, so figure on some fabrication.

Rather than build for HP, you might want to consider building your engine based on its RPM operating range. Too much cam and it will be a little sluggish on the bottom end (although your trans and gear combo should minimize this) and possibly to high for your given range of RPM's with your engine -if its a stock bottom end. Forged rods and pistons change this, but then the air flow of the stock heads become the limiting factor. You can upgrade here to increase breathing and RPM. The bottom line again here is that its not a high revving small block like a Chevy -where you build for hrosepower in the upper RPM's. The Pontiac is a torque monster and you build for torque within a given RPM range -the HP follows.
 
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