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Oval or rectangle port?

canadianchevy33

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canadianchevy33 Enthusiast

canadianchevy33

Posted
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Like the topic says which of the two are better for performance? Im wanting to get rid of my peanut ports and switch to a carbed setup. Also whats a reasonable price to pay for oval or rectangle port heads?

cardoc Enthusiast

cardoc

Posted
Posted

I've built several carbed big block engines, and the late sixties oval port, closed chamber heads would be my choice for a street motor. You get a boost in compression and the velocity of flow the oval ports is better until very high rpm.

 

Unfortunately, they are getting hard to find and expensive so an open chamber, big oval port would be my second choice.

 

Both will require a trip to the machine shop for truing, guide checking, valve spring selection, and seal installation. They didn't call them "rat motors" for no reason!

Whopper809 Enthusiast

Whopper809

Posted
Posted
The rectangular ones are bigger and have more flow than the oval ports. More flow equals more power...

 

 

 

rectangular heads do not make very good streetable power due to flow characteristics they work best only at high RPM's great for the saturday night hotrod but not great for a truck that does work duty or towing duties.

miket Enthusiast

miket

Posted
Posted

Oval port heads are better for street applications---they provide better low end torque which is normally where street driven motors spend most of their time. You can do some port work to them to make them flow well to just begin to kiss the flow capabilities of the rectangualr port heads but still have great torque and driveability.

 

Rectangular port heads make power higher in the RPM range which affects the rest of the vehicle and whatever it's main purpose may be. Rectangualr ports make more power but they are not suited for street applications.

 

To add credibility;

 

I have a tweaked ZZ502 with the GM Aluminum Oval ports....with a little bit of work (and a cam change) it dynoed at 663 hp (6100) and 630 lb/ft torque(4200)...on pump gas.

 

My .030 over 427 with Reher Morrsion BB2X heads running 110 octane achieves it's (well over 660hp) power above 6k. This is fine because the car has the right stall and gears to accomodate that.

 

With a ton of work----those same GM oval ports made over 750hp on a 502 on pump gas----but it wasn't lower in the rpm range and it had a pretty nasty cam.

jstwkd Enthusiast

jstwkd

Posted
Posted

what size cam are you using,whats your comp ratio,what rpms do you plan on spinning,what type of truck will this go in 2x4 or 4x4,whats your gear ratio,are you going to use a high stall converter or stock..? these questions need answering before you can pick a cylinder head....to decide best performance...need to know application...I agree oval for street low end torque ... rectangle for higher rpms...depends on what you are trying to do..

I also have a tweaked 502 with ovals running over 700hp on pump gas...but this is in a jet boat..which desires torque and hp..spinning it to 6500 rpms

bigdogs Senior Enthusiast

bigdogs

Posted
Posted

I guess I should have prefaced it by saying a rectangular port head (rat port head) will make more power but may not be the best choice especially for a truck (altho knew some that used them in punched out 454s) jstwkd was right in that you have to consider a lot of things before deciding on what is the best choice of heads.

canadianchevy33 Enthusiast

canadianchevy33

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Ok the compression ratio is stock for a 89 454 Im not sure on the chamber size so I cant say what it would be when moving to a oval or rectangle port. The cam specs are in the area of [email protected] and 510 lift with stock ratio rockers. The transmission is an M20 4 speed with a creeper first gear. Truck is an 89 dually. Rear end gears are 4.10's. Its also running on propane if that matters. Rpm wouldnt be past 5500.

miket Enthusiast

miket

Posted
Posted
Ok the compression ratio is stock for a 89 454 Im not sure on the chamber size so I cant say what it would be when moving to a oval or rectangle port. The cam specs are in the area of [email protected] and 510 lift with stock ratio rockers. The transmission is an M20 4 speed with a creeper first gear. Truck is an 89 dually. Rear end gears are 4.10's. Its also running on propane if that matters. Rpm wouldnt be past 5500.

 

 

 

 

 

Oval ports would be ideal.

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