I'm thinking about getting a new intake manifold but I'm not sure If I have rectangular ports or oval ports. I have a 1970 396, any help would be appreciated.

Your best bet would be to pull a valve cover and get the casting number, it's 6 or 7 digits, cast into the iron between the valves.

The most common, 396 - 325 HP used oval port heads, but you really want to verify the #'s before spending $$$. A lot could have been changed over the years.

I'm pretty sure they are still the stock heads but that's good advice!

You don't even have to check the casting numbers. If the head is marked under the valve cover HiPerf it will have the rectangular ports; if they're marked Pass then it will have the more desireable round ports.

It would probably be under the passenger side valve cover right? or would it be under both?

You don't even have to check the casting numbers. If the head is marked under the valve cover HiPerf it will have the rectangular ports; if they're marked Pass then it will have the more desireable round ports.

LD, I know very litle about BB's. All I have ever owned is SB's. Please explain why the oval ports are more desireable. Because of the smaller chambers?

LD, I know very litle about BB's. All I have ever owned is SB's. Please explain why the oval ports are more desireable. Because of the smaller chambers?

I'm a SB guy too, but if I remember correctly, the rect. port heads have intake runners that are too large for most big blocks used in that era, and as a result give up some power.

The oval-port heads make better torque at low and medium revs for normal street operation due to increased air velocity; the rectangular port heads give up some low- to medium torque for more high-rpm power. Factory hydraulic-lifter engines used oval-port heads, and solid-lifter engines used rectangular-port heads.

:beers:

Reason I'm asking is, I was looking into one of those dual plane edelbrock RPM Air Gap intake manifolds but I wasn't sure what type of ports were on the heads. I've only had the car about 1 month. Everything is pretty much stock except the 750 edelbrock carb and the guy said it had a mild cam in it.

Since both heads should have the same identical casting numbers (don't freak if they're not because the heads may have been changed in the past during a rebuild) a look under either side should suffice.

Oval port heads work best on engines below 500 cubic inches because as noted the rectangular port heads were a race only wide open throttle NASCAR design to win on Sunday and sell on Monday. If you have rectangular ports don't be depressed, they will work on any big block engine. You are just giving up street manners and derivability in exchange for the ability to rev it like a small block (just don't expect a whole lot of performance below 4,200 RPM).

Since there are few rectangular port heads installed on engines that have been rebuilt; I would expect yours will have a set of oval port heads as well. The desirable casting numbers to have would be a set of '049, '236, '781, or the '820 heads. These are all 255 cc oval intake runners, 127cc exhaust ports with 2.06"/1.72" valves in open chamber heads (113cc to 119cc combustion chambers). What you may have are more modern "Peanut port" (225 cc) intakes with larger (127 cc) combustion chambers off of a '76 up 454 light truck engine. These heads are good for building torque with a roller hydraulic cam but the heads fall flat on their faces above 5000 RPM (454 TBI truck engines ship with an electric rev limiter of 4,800 RPM in the distributor).


Larger Dave

Thanks for all the advice, I appreciate it! I think I'm going to take one of the valve covers off tomorrow.