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  #1  
Old Mar 28th, 06, 10:05 PM
oddities oddities is offline
 
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Question Big Block Chevy Square Port Or Oval Port

I Would Like To Know Out There On Some Ones Experience From Going From A Oval Port Head To A Square Port Head Lets Say You Were Running A Gear Ratio 3:73 Or 4:11 Big Block Car-what Horsepower Gains Did You Have And Also Was The Car Quit A Bit Less Street Friendly?? Also The Advantages You Found Going From A Ported Oval Port Cast Head To A Aluminum Square Port Head This Is All For Running A 496ci Or Less Cubic Inch Thanks
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Old Mar 28th, 06, 10:12 PM
furball8994 furball8994 is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

Plane and simply the rec. port heads flow a lot more air. More air = more power. You could see 20 to 30% more hp with everything else the same
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  #3  
Old Mar 28th, 06, 10:14 PM
N20 GO N20 GO is offline
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Smile Re: Big Block Chevy Square Port Or Oval Port

Quote:
Originally Posted by oddities
I Would Like To Know Out There On Some Ones Experience From Going From A Oval Port Head To A Square Port Head Lets Say You Were Running A Gear Ratio 3:73 Or 4:11 Big Block Car-what Horsepower Gains Did You Have And Also Was The Car Quit A Bit Less Street Friendly?? Also The Advantages You Found Going From A Ported Oval Port Cast Head To A Aluminum Square Port Head This Is All For Running A 496ci Or Less Cubic Inch Thanks
How many r.p.m's do you turn the engine?How do you use the car?
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  #4  
Old Mar 28th, 06, 10:28 PM
427L88 427L88 is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

"I Would Like To Know Out There On Some Ones Experience From Going From A Oval Port Head To A Square Port Head "

Yeah, me too. Just the facts, jack.
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  #5  
Old Mar 28th, 06, 10:50 PM
2BlueLS6's 2BlueLS6's is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

Quote:
Originally Posted by furball8994
Plane and simply the rec. port heads flow a lot more air. More air = more power. You could see 20 to 30% more hp with everything else the same
That's REALLY NOT a true statement. You asked for firsthand information, so here's mine. First a little background background: I have over 20 big block chevy cars, most with SHP options (high horse, high compression, solid lifter, rect ports). In addition to the 2 LS6 cars these include a factory L88 Corvette, several 427/435's in both alum and cast iron heads, and a Camaro with an LS7 crate motor (12:1 454, open chamber ZL1/second design L88 camshaft) There's also a 70 LS5 Corvette (oval port 10.25:1, hyd camshaft) and an L78 Nova (body now gone) 396/375 with rect. port.

What I HAVE NOT done is compare anything in the above list to the same engine with oval ports, BUT............ the LS5 Corvette with it's oval port heads is a torque monster, and Chevy actually published higher ratings on it torque wise 500 Ft/lbs than the other SHP big block Corvettes. From a roll in first gear it smokes the other cars in the barn, probably for several hundred feet or more. Also, I bought a 71 LS 5 (lower compression from the 70) several years back that somebody had stuck a set of rect. port heads on, and upgraded the camshaft. It had Hooker sidepipe headers on it. The guy had some time slips in the pocket on the dash where the car had run several times at the drag strip. I think they were like 13.60's if I remember, and fairly consistent over a period of multiple dates. I was gonna sell the car and wanted the open chamber rect. port heads for one of my hot roddy projects at the time, so I though it'd be a good thing to swap a set of oval ports. Long story short, made the swap, previous owner ended up with the car back about 6 mos. later and called and wanted to know what we'd done to it. He said it picked up a tenth and a half to two on a good day.

In another case, I've got a boat with 540 Big Block Chevy/Mercruiser. It's 9.5:1 with a BIG Crane camshaft. Boats of this type generally operate in relatively flat RPM ranges for extended distances and are pitched (geared) to max at 5K to 5500 for that reason. In a pinch once I replaced the open chamber square port heads with a set of open chamber oval ports. (remember now 540 inches and geared to need max torque in the mid 5's, where you'd think the rect. ports would be in the fat part of their band) The boat lost 1 MPH on top, but gained tremendous bottom and midrange, and I ended up leaving them on it until I built another motor several years later with more compression. The engine guy who builds a lot of Super Stock motors has said repeatedly that for anything under 600 horsepower and 550 inches that he can make more power with the oval ports than rectangular.

The reality is, properly designed ports increase velocity, and THAT is where horsepower is, and bigger isn't better in all cases, especially on smaller engines. I doubt seriously that there's an L78 (396/375) around that wouldn't benefit from a change to a good set of oval ports. Even many of Chevy's crate motors of medium displacement use the smaller ports, such as the ZZ502 crate motor, which has CONSIDERABLY smaller ports in the alum. heads than the old rect. port design. The Boss 302 Mustang and Boss 429 Mustang were both pigs off the showroom floor, mostly because of the huge intake ports mismatched to the other components.
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  #6  
Old Mar 28th, 06, 10:51 PM
Doug F. Doug F. is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

On a 502 with a 255/264 solid roller, changing the heads from 2.19 Holley oval ports (270 or so runners) to 2.25 310 Canfields gained about 30 HP with no change in peak torque basically. Peak HP changed from 620 to 650. HP dropped of after 6500 with the ovals a lot quicker.

If the ovals had 2.25's and bowls opened I'd expect the difference to be less yet.

Single plane intakes to match the port.

That is a fact .
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  #7  
Old Mar 28th, 06, 11:16 PM
Bob West Bob West is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

Quote:
Originally Posted by furball8994
Plane and simply the rec. port heads flow a lot more air. More air = more power. You could see 20 to 30% more hp with everything else the same
I don't think so, you're saying my 505 that makes around 600hp is going to jump to 720-780hp with just a swap to rectal port heads?, I think thats a stretch. I could see it with more cam,more compression, and an aftermarket head like AFR or Brodix or Dart might get the job done. Just bolting them on my motor, 20-30% isnt going to happen. You have to be able to use that air, at 6500+ rpms. I shift at 6k, oval ports get the job done, and we'll soon find out what the shiny oval ports will do.
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  #8  
Old Mar 28th, 06, 11:47 PM
540Hotrod 540Hotrod is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

I did some testing on a 427 in a 3600 lb race weight '68 SS/RS Camaro. It ran 11.70's@118 at the time with pocket ported "semi-open" chamber heads, 2.06/1.72 valves, a solid flat tappet, 9.8 compression. It used 4.10 gears and both an automatic and a four speed.

I later installed some closed chamber rectangular ports with a little pocket work. Same cam, ended up at about 10.2 compression, tried several intakes. Basically made a pig out of it. It was a lot of fun with the 4 speed, but you had to shift in the 7400 rpm range to make it really run. I ended up installing 4.56 gears and when it was all done it ran 11.60's! The ovals could shift at 6200-6400 and never have an issue.

Later over the years it tried open chamber ovals as well as rectangulars. Same shortblock. Ovals were always better.

Later same shortblock was installed in my '67 Vette. I used a real nice set of Merlin ovals (ported) a Comp 288 Street roller and it ran 11.20's@123 in pure street trim with 3.36's and a 5 speed.

My general take on it is that 396's and 427 are almost always better off with ovals unless you REALLY want to spin it. With rectangular ports I knew I had better not get caught on the street in the wrong gear...cause the sucker was a slug until you passed 5500 rpm!

Once you hit 454's, I think ovals are generally better.but if you have a cam that will rev and you like to really get it, rectangulars might be good along with compression.

A 496/502 is getting into smaller rectangular port area. But a nicely ported set of ovals will pull hard to 6500 rpm or so.

I think 540's need to be in the rectangular ports. There is no lack of TQ and the trick is to feed them as RPM goes past 5500-6000 rpm. It takes some volume to do that.

Then there are the 572/598/632 guys,...definitely need some heads.....I think GM is a little small on their crate motor.

Heads are where the power is. I'd spend money on good heads before I'd buy a crazy cam setup. A set of medium sized AFR 335's, Dart 335's or Brodix M2's would do great on a 496.

I saw a buddy make 660 Hp with a set of very lightly ported Merlin iron ovals on a pump gas 496 and a solid flat tappet. Sweet little truck engine!

Gearing will be important. 3.73's will likely be plenty N/A with a 496..but you could sneak out to 4.10's with a tall tire if you can rev into the 6500 range.


JIM
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  #9  
Old Mar 29th, 06, 12:06 AM
nola454 nola454 is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

My engine builder (1000+ HP motors for offshore racing) told me to stick with the oval for the street. They will make gobs of torque and HP on the bottom and middle and still hold steady on the top.
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  #10  
Old Mar 29th, 06, 1:17 AM
rednecks70 rednecks70 is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

Here we go again .
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  #11  
Old Mar 29th, 06, 8:14 AM
joespanova joespanova is offline
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Talking Re: Big Block Chevy Square Port Or Oval Port

Ovals , definately Ovals................I put em' on everything from 396's to 800 inches and every single one of those combos made more torque and peak power with the Ovals! They are simply put, unbelievable!
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  #12  
Old Mar 29th, 06, 8:27 AM
BillsCamino BillsCamino is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

Quote:
Originally Posted by joespanova
Ovals , definately Ovals................I put em' on everything from 396's to 800 inches and every single one of those combos made more torque and peak power with the Ovals! They are simply put, unbelievable!
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  #13  
Old Mar 29th, 06, 8:50 AM
67RS502 67RS502 is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

For an 800cube motor I hope youre talkin oval Big Cheifs
Around 500 cubes is the break for oval / rect. heads and 6500rpm,
when the airspeed becomes to high.
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  #14  
Old Mar 29th, 06, 9:12 AM
N20 GO N20 GO is offline
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Smile Re: Big Block Chevy Square Port Or Oval Port

Quote:
Originally Posted by joespanova
Ovals , definately Ovals................I put em' on everything from 396's to 800 inches and every single one of those combos made more torque and peak power with the Ovals! They are simply put, unbelievable!
I promised to be good.Oval port heads on a 800 cu. engine??I think the post was referring to stock type heads.
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  #15  
Old Mar 29th, 06, 10:06 AM
427L88 427L88 is offline
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Default Re: Big Block Chevy Square Port Or Oval Port

Just relevant facts gents! Opinions are like, well you know, we all have one...
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