Square vs. oval heads
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Joined: May 2002
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From: Savannah GA
Square vs. oval heads
I posted this on two other forums and so far nobody has the answers.
I have been told by a race engine builder that you can get more horsepower out of oval port heads versus Square or rectangle port heads. He proclaims that Leindenfelter proved this in one of his books on building race engines. Is this true? If this is so, why are all old corvettes with high horsepower ratings have square port heads? What needs to be done to oval port heads to outperform square port heads?
I have been told by a race engine builder that you can get more horsepower out of oval port heads versus Square or rectangle port heads. He proclaims that Leindenfelter proved this in one of his books on building race engines. Is this true? If this is so, why are all old corvettes with high horsepower ratings have square port heads? What needs to be done to oval port heads to outperform square port heads?
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All depends on what you're doing. If you intend to stay under 6500 on a 427, maybe 6000 or so on a 454-496 then the ovals are great if properly prepared. Remember, Lingenfelter made just oover 600 HP with a 496 using heads that he did a lot of porting with. There were old comparisons of out of the box aluminum ovals just barely beating his in house ported ones. But again, that's apples and oranges. By the time his wizards port them, they aren't regualar heads anymore.
It all depends on combo. If you intend to operate in the 4000-6000 rpm range most of the time fine, but above that the rectangular ports shine. The old big blocks were designed to make power in the mid-high 6000 range with mild cams that could live a long time. AND not fall off in power as you went above 7000 rpm. That's where big heads help...the extend power band out further. You make basically same amount of TQ, you just do it at higher rpm and by definition that equates to more HP due to the math involved.
In racing ...."He who makes the most "explosions" (plugs firing) between the starting line and the finish line will typically win". That's why racing engines are made to peak HP at high rpm and geared accordingly.
There is also a point of no return. I've driven a ZZ502 and was unimpressed. The power curve falls off so quickly after 5000 rpm it's ridiculous. To the point of being useless without 3.55 gears or less.
Jim
It all depends on combo. If you intend to operate in the 4000-6000 rpm range most of the time fine, but above that the rectangular ports shine. The old big blocks were designed to make power in the mid-high 6000 range with mild cams that could live a long time. AND not fall off in power as you went above 7000 rpm. That's where big heads help...the extend power band out further. You make basically same amount of TQ, you just do it at higher rpm and by definition that equates to more HP due to the math involved.
In racing ...."He who makes the most "explosions" (plugs firing) between the starting line and the finish line will typically win". That's why racing engines are made to peak HP at high rpm and geared accordingly.
There is also a point of no return. I've driven a ZZ502 and was unimpressed. The power curve falls off so quickly after 5000 rpm it's ridiculous. To the point of being useless without 3.55 gears or less.
Jim
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Joined: Oct 2004
Posts: 510
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From: Pipe Creek TX
Originally Posted by 427Hotrod
All depends on what you're doing. If you intend to stay under 6500 on a 427, maybe 6000 or so on a 454-496 then the ovals are great if properly prepared. Remember, Lingenfelter made just oover 600 HP with a 496 using heads that he did a lot of porting with. There were old comparisons of out of the box aluminum ovals just barely beating his in house ported ones. But again, that's apples and oranges. By the time his wizards port them, they aren't regualar heads anymore.
It all depends on combo. If you intend to operate in the 4000-6000 rpm range most of the time fine, but above that the rectangular ports shine. The old big blocks were designed to make power in the mid-high 6000 range with mild cams that could live a long time. AND not fall off in power as you went above 7000 rpm. That's where big heads help...the extend power band out further. You make basically same amount of TQ, you just do it at higher rpm and by definition that equates to more HP due to the math involved.
In racing ...."He who makes the most "explosions" (plugs firing) between the starting line and the finish line will typically win". That's why racing engines are made to peak HP at high rpm and geared accordingly.
There is also a point of no return. I've driven a ZZ502 and was unimpressed. The power curve falls off so quickly after 5000 rpm it's ridiculous. To the point of being useless without 3.55 gears or less.
Jim
It all depends on combo. If you intend to operate in the 4000-6000 rpm range most of the time fine, but above that the rectangular ports shine. The old big blocks were designed to make power in the mid-high 6000 range with mild cams that could live a long time. AND not fall off in power as you went above 7000 rpm. That's where big heads help...the extend power band out further. You make basically same amount of TQ, you just do it at higher rpm and by definition that equates to more HP due to the math involved.
In racing ...."He who makes the most "explosions" (plugs firing) between the starting line and the finish line will typically win". That's why racing engines are made to peak HP at high rpm and geared accordingly.
There is also a point of no return. I've driven a ZZ502 and was unimpressed. The power curve falls off so quickly after 5000 rpm it's ridiculous. To the point of being useless without 3.55 gears or less.
Jim
