C-3 big block Intake manifold casting #'s???

[Jacob A.]

Hello,

I am doing a body on restoration of a 69 Big Block/A.C. Roadster. The engine I pulled today is a 1972 Corvette 454 cast # 3999289, cast May 29, 71. The intake manifold on this engine was G.M. part # 3963569. When I bought the car, no air cleaner was included. I was told by the "billy bob, bubba" seller, one wouldn't fit under the stock big block hood. I am questioning if that was actually the truth. Reason being is that the same seller told me it was a 1878 truck engine in the car, but that wasn't exactly true based on the #'s I found on the block.

Does anyone know if this part #, G.M. intake manifold # 3963569 will fit with any regular 454 or 427 and Holley 4 barrel to fit with an aircleaner under my regular factory big block hood?

Thanks,
Jacob
40987

[Joe L.]

Re: C-3 big block Intake manifold casting #'s???

Jacob-----

Used with a STOCK TYPE air cleaner, the GM casting #3963569 manifold WILL fit under a stock 68-72 big block hood. In fact, it is the ONLY rectangular port, Holley carb (i.e. square bore) manifold that will fit under the 68-72 big block hood. This includes both original GM manifolds and aftermarket manifolds. As further testament to this fact, consider that the 1971 Corvette with LS-6 used this exact manifold and also used a standard big block hood (i.e non L-88 type).

Keep in mind, though, that the GM #3963569 is a RECTANGULAR PORT manifold and it is designed to work with RECTANGULAR PORT HEADS.

[Jacob A.]

Re: C-3 big block Intake manifold casting #'s???

Hi Joe,

Thanks for shedding some light on this for me.

So if the intake is square port, then the heads should be too.... The heads in question bolted up to this 3999289 block are 3964290 they are dated G-9-9 and J-27-9. What's the story on the heads? My Black Book claims that they are for a 1970 LS-5 Corvette with a Big Block 390 horse engine. Did a 1970 454 Corvette have square port heads and intake etc...?

My cars b-day is Dec 29-69 too bad the head casting # is wrong, as the dates are good!

thanks again,
Jacob Angel
NCRS 40987

[Joe L.]

Re: C-3 big block Intake manifold casting #'s???

Jacob-----

The GM casting #3964290 heads are oval port heads. When used with the 3963569 manifold there will be a serious port mismatch. Just what the effect of this would be on performance or functionality I do not know.

The 3964290 heads were used for 1970 Corvette with LS-5 as well as other 1970 Chevrolet model big block, oval port applications. No 1970 Corvette with big block originally used rectangular port heads. Some big blocks used for 1970 Chevelles and Camaros did, though. These applications also used the 3963569 manifold.

[Jacob A.]

Re: C-3 big block Intake manifold casting #'s???

Joe,

This would probably explain why it ran like *&#@! I guess I will pull the heads and intake off and sell them separately. It did seem as if the sides of the heads, the holes where the headers bolted up were rectangular holes? I am a little new to engine pulling/diagnosing etc.... Is that always the case,.... oval port holes for headers/exhaust manifolds with oval port intake manifold too, and square port holes for headers/exhaust manifolds with Square port intake?

Thanks a bunch!
Jacob

[Joe L.]

Re: C-3 big block Intake manifold casting #'s???

Jacob-----

Some say that mismatched port configurations between manifold and heads will work ok for big blocks. I've never verified it, though.

If you have the GM #3964290 heads, those are DEFINITELY oval port heads. Keep in mind that the term "oval" as used in this context is not, strictly speaking, an oval shape; it's more like a rectangle with highly radiused corners.

[Mark #28455]

290 heads are OK

Just get a 1970-72 low rise stock oval port intake (284 casting?) in the junkyard for about $25 to $50, add a Q-jet or Holley spreadbore carb with a stock air cleaner and you're good to go.
Mark

[Jacob A.]

Re: 290 heads are OK

I actually have a killer 1978 High Performance 454 with Solid Cam and Mechanical LIfters that I could pull out of a Mid-Year, and put the low rise square port manifold on it and then I could stuff that engine in the 69. However, I was hoping to put the correct block in it. The motor I just pulled out was a 72 Corvette 454.

I have the correct 512 block, but the date is J-10-8 and my car is 12-29-69

Thanks,
Jacob

Here is a pic of the car I am in the middle of surgery with. She was built 2nd to last day of 69 production.