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Old 09-27-2003, 09:45 PM
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Oval vs. Square Port Heads?

Hi Gang.
I am hoping to get some info from you big block gurus. I have always been into the small blocks but now have decided it is time for a big block Chevy.
Here is what I am wanting to know. I believe the square port heads are the good or maybe I should say better heads for hi performance application. Am I right thinking this? Also, I imagine if you are using square or rectangular port heads you must use the right intake. So no oval port intake unless using oval port heads.
Any info would be appreciated. I am hoping to build a late 60,s style 427 or maybe a 454. Thanks a lot!!

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Old 09-27-2003, 10:01 PM
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well from all the build ups I've seen the oval ports can equal the square port at high rmp and beat them at low rpm maybe if you are gonna be reving 6500 plus then the square ports might have a small advantage I'm sure many will disagree with me here though as it seems to be a very controversial topic
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Old 09-28-2003, 07:15 AM
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You are correct on the oval intake will only fit oval heads, tho you can use the rectangle port intake on the oval port heads. As to the h-power difference, there are many different castings and flow rates in the oval port heads, some ( with a bit of work) flow almost as good as stock rectangle ports, on the average hydraulic cammed street runner the oval port heads are plenty.
The rectangle port heads are for more serious h-power, they start to breathe when the ovals are running out, about 5500 rpm and up, these were available since the late sixties in iron and aluminum, on the higher h-power solid lifter motors.
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Old 09-28-2003, 07:55 AM
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The rule of thumb is the ovel port is for low end power, and square port is for top end power.

Troy
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Old 09-28-2003, 05:24 PM
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I have a 427 Vette running with Rectangular ports and will be putting in Ovals this winter, becuase I am runnig a comp 268H that stops at 5500RPM. Here are somes things to consider.
1) Rectangulars start flowing at 3500RPM in a 427 this would be lower in biggers ci engines for example I want to go with AFR CNC ported 315 cc rectangulars for my 496 running high compression 12.8:1 with a high duration 315 cam with .750" lift.
2) Ovals are better for the street and strip of small BBC 396 - 427. I know the infamous 435HP and L-88 are rectangulars but we are talking 12:1 + with high duration cams where they do not come alive till 3500-4000RPM and pull hard up to 7500RPM. It is a great ride but not practical.
3) You want the most flow out of the smallest cc. the Ovals flow great in the low end and have a tremendous amount of air velocity that will produce a ton of bottom end torque. They flow quite well upto 5500 - 6500 (Depending on your cam)
I am re-camming and will try a set of old GM 290 Large oval closed chamber heads with big valves 2.19" and 1.88" I will try the 270H or 274H keeping it pretty close to stock. I want to keep the stock exhaust and stall. If you are running large headers and big stall 280 - 292 duration will make some nice power. Anything over the 300 duration start considering the rectangulars and build a very stout bottom end to turn 7500-8000RPM.
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Old 09-28-2003, 05:32 PM
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Bottom line " Oval Ports for the Street" No need to yap more.
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Old 07-22-2004, 03:17 PM
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which would u recommend for a blown 496?
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Old 07-22-2004, 03:43 PM
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I remember walking into a performance shop down in arlington one day when I went to get some copper exhaust gaskets. The guy was build some massive ford BB and he had it together minus the intake. Those oval runners in that head where so big I could almost get my hand in there(that just doesnt sound right ).
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Old 07-22-2004, 04:23 PM
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Rectangular ports particualrly the 320cc and larger type are good for just about any engine over 505 inches regardless of rpm range.I run them on a 440 inch bigblock,but I run in the 5000 to 7500rpm range with a 5000 stall convertor,and I think I am right at the brink of where 300cc rectangular ports out run even the best oval ports.The bad part of the factory oval port isnt the size,but the positiong of the port.The oval port sits on what would be the floor of the rectangular port.If you moved the oval up until the roof of it hit roof of the rectangular port you would get even more flow and velocity out of the port and it would run much better.As a point of interest current NHRa prostock heads have only a slightly larger port cross section then some of the new aftermarket oval ports and they flow more then any factory layout head,much more.
Truck oval ports are kind of uselfess for all but the lowest rpm of pulling type engines.Factory large ovals are good for most stret and bracket 468 and smaller buildups while a set of roval ports like the GMPP heads will run well on more bracket race type 509 and smaller engines.I tried an oval port intake on my rectangular port 440 and it killed the top end with only a slight gain in the 60 foot times.I have run rectangular intakes on oval heads with great improvemnts on small displacement bigblocks so you figure it out.
BTW,my Ebay name is actually Bigblockguru,so you tell me what my favorite engine is.
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Old 07-22-2004, 05:07 PM
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Mean_1, You should start a new thread as this one was answered and dead in september of last year.

Troy
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