Intake Ports are always rectangles- why?

Just wondering about this. I'm sure there's a reason for it but I don't know why, sad to say. Everything is basically a tall rectangle at the port entry. An LS-1 being the most extreme example I can think of. Even oval-port BBC heads are still basically rectangles with the corners rounded off.

High flow exhaust ports are usually D-shaped. What's up with the intake port being a rectangle?

Obviously, I'm talking about 2-valve production wedge heads not 4 valve stuff, hemis, etc.

Pushrod clearance is probably the main reason for rectangular intake ports. As you mentioned, DOHC engines often have intake ports shaped to fit the valve area of the heads.

Round ports are sometimes used, and there have been cases of pushrods (in thinwall tubes) going thru the middle of the port. "Tunnel port" Ford heads in the 60s are an example. Pontiac RA V had tunnel ports also, I think.

Also, given the space involved, the maximum area port is a rectangle that fills that space. Sharp corners are not good for flow and difficult to shape with cutters, so rounded corners work. Round gets the least area in a given space, but they have the least wall area also.

Top Fuel engines are a good example of BIG rectangular ports. I'd really like to see some finished Pro Stock ports, but there's not a lot of chances to do that. Even the intakes are disguised with tape, panels, etc. when the cars are in public.

Some of LS1 port shape is for injector targeting. I'd like to see the port shape for F1 engines and Audi's direct injection LeMans engines of a few years ago.

If a port has to turn (most do to some extent), perhaps the port shape should mimic what the air wants to do and where it wants to go. The port shape "suggests" to the air where to go, but the air decides for itself. Much port modification is biased this way.


My $.02

mostly for pushrod clearance while still maintaining required cross-sectionaL area

OldSStroker..just about covered all the reasons

sometimes theres one more reason
and its to "slow mixture velocity fps" if you have to


and oval ports pickup speed in corners
oval ports are used when you already have the
correct cross-sectional area

http://www.maxracesoftware.com/BBC_14_Deg_Olds_Int_Guide.jpg

Thanks, guys. Makes sense to me.

F1 engines? I get that intake port is like a rifle bore towards the back of the intake valve(s).

Agreed, that corners are not good for mixture velocity. That's basically what started my thinking about this. I imagined a port that was a "D" but upright so that the flat part of the D was against the pushrod. Probably not worth the effort, but I wake up at night screaming when I think about stuff like this too long.

Originally posted by MaxRaceSoftware
mostly for pushrod clearance while still maintaining required cross-sectionaL area

OldSStroker..just about covered all the reasons

sometimes theres one more reason
and its to "slow mixture velocity fps" if you have to


and oval ports pickup speed in corners
oval ports are used when you already have the
correct cross-sectional area

http://www.maxracesoftware.com/BBC_14_Deg_Olds_Int_Guide.jpg Wow. How much is a set of those heads?

Wow. How much is a set of those heads?
===========================

the head in that picture will cost you an "ARM"

the other matching head will cost you a "LEG"

so an Arm and a Leg for a pair :)

just joking :), its probably not as much as you think ??


nosfed .... thats a 60 grit finish , but near valve seat insert, its still same 60 grit, but worn cartridge roll with different pressure and hand/grinder movement...makes that area look different