oval vs rectangle port bb heads
Thread Starter
Le Mans Master
Joined: Oct 2000
Posts: 6,209
Likes: 33
From: Texas-out west
oval vs rectangle port bb heads
OK, which do you guys think would be best and why for a hot street motor, close ratio 4 speed, 3.70 gears, something along 250 duration @.050 and 570 lift, solid lifter cam. Will have headers and tripower or holley 800 carb. looking at chev alum or edelbrock :cool: :cheers:
Burning Brakes
Joined: Aug 2001
Posts: 1,002
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From: Bay City MI.
Re: oval vs rectangle port bb heads (LT1driver)
I built my BB last winter and we used a set of Merlin rectangular port iron heads. They have 310 cc runners with 119cc intake combustion chambers. I think they are a little bit of over kill , but my motor runs like a race engine! I love it, and other than some bracket fit problems, because of the raised port design, they are awesome. My combo is also a Muncie M-20 trans with a 3.70 rear gear. The cam I am running is a Crane powermax 296-2, hydraulic. I believe the merlins are about the same price as the others. Good luck!!
Pro
Joined: Aug 2002
Posts: 502
Likes: 1
From: Georgia
Re: oval vs rectangle port bb heads (LT1driver)
You didn't say how many inches, but I think that's a primary consideration in intake port design. A local race engine shop who builds super stock engines exclusively talked me into a set of oval port heads on a 540 in my boat. Later, thinking I'd made a mistake I changed to rectangle port and couldn't read it on the speedo, but lost some on the bottom. A boat engine is a good way to guage component changes because they're operated at full throttle with a given load and it's easy to see small differences in max RPM and speed. The engine in question has the Crane solid lifter camshaft thats slightly bigger lift wise than the ZL1/LS7/2nd design L88, but has tighter lobe separation. I wouldn't even consider the rectangle ports on a small engine, although the 375's of course came with em. I also think you'd prefer the single Holley to the tri power if max performance is your priority. Even though the tri power is advertised at 1050 CFM, because of poor runner design, the velocity's just not there to run with today's intake/carb set ups.
Le Mans Master
Joined: Oct 2000
Posts: 6,563
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Re: oval vs rectangle port bb heads (LT1driver)
Got a ZZ/502 crate with 110cc oval port aluminum heads and 2x4 carburetion in the '79; also got an HO 454 crate with 118cc rectangular port iron heads in the '67, along with tri power..
Solidlifters is right on the money here. THe oval ports make power immediately; the rectangular ports pull strongest on the upper end.
On the other hand, I know that the big single 4 bbl. is the 'best'- but I really like multiple carb setups. I had a 780 Holley and 850 annular Demon on the 502; the Holley stunk, and the Demon was the fastest on the upper end; but the dual quads give TREMENDOUS low and middle end punch on the street, and are more streetable at lower speeds than the Demon or Holley!
The tri power runs real good, but doesn't give the big kick in the **** that the Demon or dual Edelbrocks do, because of the vacuum secondaries. It really starts to pull on the upper end, though. Incidentally, 1967 tri- power manifolds have longer runners than the '68 or '69 'trip' manifolds. It's got to do with the hood clearance. My 2c.
:yesnod: :chevy :chevy :yesnod:
Solidlifters is right on the money here. THe oval ports make power immediately; the rectangular ports pull strongest on the upper end.
On the other hand, I know that the big single 4 bbl. is the 'best'- but I really like multiple carb setups. I had a 780 Holley and 850 annular Demon on the 502; the Holley stunk, and the Demon was the fastest on the upper end; but the dual quads give TREMENDOUS low and middle end punch on the street, and are more streetable at lower speeds than the Demon or Holley!
The tri power runs real good, but doesn't give the big kick in the **** that the Demon or dual Edelbrocks do, because of the vacuum secondaries. It really starts to pull on the upper end, though. Incidentally, 1967 tri- power manifolds have longer runners than the '68 or '69 'trip' manifolds. It's got to do with the hood clearance. My 2c.
:yesnod: :chevy :chevy :yesnod:
Melting Slicks
Joined: Jun 2001
Posts: 2,340
Likes: 2
From: Moro IL
Re: oval vs rectangle port bb heads (LT1driver)
I think the general rule of thumb is the large Ovals for street and the square ports for race. Of course a lot depends on how streetable you want it. And some of the aftermarket oval ports I'm sure can flow with some of the stock square ports, but in general if you want an engine with good low end torque and spends most of it's time cruising around town stay with Ovals. In my situation I don't really see any need for me to go to Square ports at the power levels I'm trying to achieve eventually (400-450 net hp) plus the fact I love the low end grunt to blast me out of a low speed corner. In fact the plan as of right now is to clean up my 049 heads and install larger valves since this should make them adequate to make the numbers I want with some other mods in the future.
:cheers:
Pat Kunz
:cheers:
Pat Kunz
Thread Starter
Le Mans Master
Joined: Oct 2000
Posts: 6,209
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From: Texas-out west
Re: oval vs rectangle port bb heads (73 LS-4)
Mass Vette, want to sell your tri power?
I want tri power because I like the look and they run acceptable to me.
motor will be 427 since I already have short block :D
I don't plan to spin motor much over 6500 and only on street light blast against ??? :cheers:
I want tri power because I like the look and they run acceptable to me.
motor will be 427 since I already have short block :D
I don't plan to spin motor much over 6500 and only on street light blast against ??? :cheers:
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
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Re: oval vs rectangle port bb heads (LT1driver)
For your description with a 427, you definitely want ovals. You can do pretty nice with GM iron ones if ported heavily. I also ran Merlin Irons, but they were oval. They were fantastic. If you are looking at Aluminum ovals, don't rule out the Dart or Brodix versions. There is also a -1 Brodix that is a small rectangular port that will work great. I think any of them are stronger than the GM/Edelbrocks.
Rectangular port heads on a 427 will start to come alive around 5500 rpm and pull hard past 7500. On a 4 speed car with 3.70's you won't get much of a chance to use them well. Oval ports that pull hard to 6400-6500 will work better for you.
Solid lift flat tappet cams as you describe up to the low .600 range will work great.
You'll likely run stronger with a 750-850 DP Holley, but the tripowers are beautiful. They can be made to run especially well on an oval port set up.
JIM
Rectangular port heads on a 427 will start to come alive around 5500 rpm and pull hard past 7500. On a 4 speed car with 3.70's you won't get much of a chance to use them well. Oval ports that pull hard to 6400-6500 will work better for you.
Solid lift flat tappet cams as you describe up to the low .600 range will work great.
You'll likely run stronger with a 750-850 DP Holley, but the tripowers are beautiful. They can be made to run especially well on an oval port set up.
JIM
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Safety Car
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From: NorCal
Re: oval vs rectangle port bb heads (LT1driver)
I agree with all of the advice so far, but have a unique problem. My oval port 3x2 intake was long gone when I got the car, but I scored a '69 rec port set-up that is on there now and works well with the stock engine, even with the gross mis-match on the ports (square to oval)! Sooo, I want to go with aluminum heads, mainly for weight and better performance, yet after my BOSS 302, I know about top end only power and want to keep my power band as low as possible. Is there a square port setup that works reasonably well on a (admittedly overpowered) street car? Any experiences?
Hans
Hans
