Oval or Square Port Heads on a 427 L72, what's better for the street.
10-09-2003, 02:22 PM
#1
Instructor
Thread Starter
Oval or Square Port Heads on a 427 L72, what's better for the street.
I had a choice when I had my engine rebuild done, Oval or Square port's for my 66' 427. I went with the oval ports, they work fine but I wonder what the other types of heads would do. If I decide to change what should I change too?
Raj
Raj
10-09-2003, 02:59 PM
#2
Advanced
Member Since: Sep 2003
Location: Toronto Ontario
Posts: 84
Likes: 0
Received 0 Likes
on
0 Posts
Re: Oval or Square Port Heads on a 427 L72, what's better for the street. (Sixgun)
For the street oval port is fine up to 6000 rpm however if you want to scream a big block chevy, square port is the way to burn more air and fuel. I have a friend of mine who races a 69 vet in Super Stock and he screams his motor thru the traps reving 8300 rpm ( not for every one ) and the cars goes 140 mph at 9:60 ets. It all depends on how you want to play.
10-09-2003, 05:58 PM
#3
Drifting
Re: Oval or Square Port Heads on a 427 L72, what's better for the street. (Sixgun)
I have square ports on my 66' 427/425 coupe, but thats the way it came. Oval ports are better for the street, more low speed low end torque. Square ports work best at high speed wide open applications. :D
10-09-2003, 06:32 PM
#4
Safety Car
Re: Oval or Square Port Heads on a 427 L72, what's better for the street. (Sixgun)
it's hard to get 2 guys to agree on whats "best" lol
what do you use the care for? it really depends on your complete setup....... gears, cam, etc. and in what RPM range you're trying to maximize performance (all the component should be designed for "best performance" the same RPM range).
all rects (and ovals) are not equal. some of the new aftermarket rect heads, flow better and have smaller intake runner volume than our old GM heads, so the vel is higher (that's a good thing, and you'll get improved low RPM power for low performance street use... if thats important to you).
So, you have a L-72? and have your rect port intake on a set of oval heads now ? thats far from optimum, just imagine the low disruption thats created
what do you use the care for? it really depends on your complete setup....... gears, cam, etc. and in what RPM range you're trying to maximize performance (all the component should be designed for "best performance" the same RPM range).
all rects (and ovals) are not equal. some of the new aftermarket rect heads, flow better and have smaller intake runner volume than our old GM heads, so the vel is higher (that's a good thing, and you'll get improved low RPM power for low performance street use... if thats important to you).
So, you have a L-72? and have your rect port intake on a set of oval heads now ? thats far from optimum, just imagine the low disruption thats created
10-09-2003, 08:34 PM
#5
Race Director
Member Since: May 2000
Location: Redondo Beach USA
Posts: 12,487
Received 1,973 Likes
on
1,188 Posts
Re: Oval or Square Port Heads on a 427 L72, what's better for the street. (66427-450)
If you want SHP type of performance and engine character you go with an L-72 including the OE mechanical lifter cam and rectangular port heads. If you want stump pulling low end torque you go with a L-36 - medium performance hydraulic cam and oval port heads.
Rebuilding a L-72 with what I assume is the OE or equivalent cam and oval port heads makes absolutely no sense to me.
The cam kills some low end torque, but the heads plug up the top end where the cam really shines.
Chevrolet engineers matched the cam an heads on both engines to get a suitable torque curves for each performance category. Mixing oval port heads and a SHP cam is a kluge!
Duke
Rebuilding a L-72 with what I assume is the OE or equivalent cam and oval port heads makes absolutely no sense to me.
The cam kills some low end torque, but the heads plug up the top end where the cam really shines.
Chevrolet engineers matched the cam an heads on both engines to get a suitable torque curves for each performance category. Mixing oval port heads and a SHP cam is a kluge!
Duke
10-10-2003, 12:03 PM
#6
Race Director
Member Since: Jan 2000
Location: Corsicana, Tx
Posts: 12,603
Received 1,874 Likes
on
912 Posts
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Re: Oval or Square Port Heads on a 427 L72, what's better for the street. (Sixgun)
Just as they said...depends on what you want to do.
The basic L-72 package is a really sweet deal overall. The rectangular port heads on it are overkill for it's size, but the combination of a good flowing dual plane intake, relatively short rods, decent compression and a cam with wide LSA add up to a solid ride. It likes RPM to really be happy...like 6000+ rpm!
But I can tell you from first hand experience running my 427 for 20+ years in many different combos, the oval port heads are easily capable of supplying the air that most 427's can use. I ran open and closed chambers versions of ovals and rectangulars, different valve sizes, who knows how many different cams, several intakes and different headers, different compression,different gears, transmissions etc dialing it in. Without a doubt, the ovals were the best overall on it. All the heads were similarly prepared. There were times the rectangulars were slightly faster at the track (maybe one tenth!) but they required 4.56 gears and 7500 rpm shifts to do it. On the street from a roll the ovals were hands down killer. I loved spanking friends with rectangulars on the street. They always believed I was hiding more cubes the way it would pull them in the midrange. I could shift at 6400 rpm in every gear and it pulled hard. The rectangulars literally felt like you flipped a switch at 5000-5500 rpm and they just came alive. With a "crashbox" 4 speed and 4.56's they were a blast. Not really any faster than the ovals and 4.10's...but a lot of fun!
Now remember, this includes choosing a cam that compliments them etc. They really respond to cams in the low .600 lift range and they love good flowing single plane intakes. The new Edelbrock RPM air gap dual planes probably would work even better these days.
The ovals actually do run real well with the L-72 cam. I've seen many 11 second passes with it and it is very driveable. The aftermarket ones allow for more power, but the basic L-72 works pretty decent.
Once the cubes get larger or the rpm gets higher, the GM sized rectangulars get better. Not sure how much real work went into developing the package past the original version. There's not a whole lot of difference in the hard parts of a 396/425 L78, a 427/425 L72 or a 454/450 LS6. Bigger exhaust valves, little different cam and that's about it. GM used what was on the shelf despite the 58 cube increase. It worked well though, proving the parts are good, The street manners of the engine just got better as the cubes got bigger.
If you are going to look aftermarket, I'd seriously look at the smaller AFR 305 cc rectangulars or most definitely at the new Brodix oval ports. The numbers they are showing are fantastic for an under 280 cc port. and the exhaust ports are in the stock location. The Edelbrock/GM aluminum stuff isn't even in the same league as these new heads.
JIM
The basic L-72 package is a really sweet deal overall. The rectangular port heads on it are overkill for it's size, but the combination of a good flowing dual plane intake, relatively short rods, decent compression and a cam with wide LSA add up to a solid ride. It likes RPM to really be happy...like 6000+ rpm!
But I can tell you from first hand experience running my 427 for 20+ years in many different combos, the oval port heads are easily capable of supplying the air that most 427's can use. I ran open and closed chambers versions of ovals and rectangulars, different valve sizes, who knows how many different cams, several intakes and different headers, different compression,different gears, transmissions etc dialing it in. Without a doubt, the ovals were the best overall on it. All the heads were similarly prepared. There were times the rectangulars were slightly faster at the track (maybe one tenth!) but they required 4.56 gears and 7500 rpm shifts to do it. On the street from a roll the ovals were hands down killer. I loved spanking friends with rectangulars on the street. They always believed I was hiding more cubes the way it would pull them in the midrange. I could shift at 6400 rpm in every gear and it pulled hard. The rectangulars literally felt like you flipped a switch at 5000-5500 rpm and they just came alive. With a "crashbox" 4 speed and 4.56's they were a blast. Not really any faster than the ovals and 4.10's...but a lot of fun!
Now remember, this includes choosing a cam that compliments them etc. They really respond to cams in the low .600 lift range and they love good flowing single plane intakes. The new Edelbrock RPM air gap dual planes probably would work even better these days.
The ovals actually do run real well with the L-72 cam. I've seen many 11 second passes with it and it is very driveable. The aftermarket ones allow for more power, but the basic L-72 works pretty decent.
Once the cubes get larger or the rpm gets higher, the GM sized rectangulars get better. Not sure how much real work went into developing the package past the original version. There's not a whole lot of difference in the hard parts of a 396/425 L78, a 427/425 L72 or a 454/450 LS6. Bigger exhaust valves, little different cam and that's about it. GM used what was on the shelf despite the 58 cube increase. It worked well though, proving the parts are good, The street manners of the engine just got better as the cubes got bigger.
If you are going to look aftermarket, I'd seriously look at the smaller AFR 305 cc rectangulars or most definitely at the new Brodix oval ports. The numbers they are showing are fantastic for an under 280 cc port. and the exhaust ports are in the stock location. The Edelbrock/GM aluminum stuff isn't even in the same league as these new heads.
JIM
