Rectangular/Oval port debate.
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,674
Likes: 197
From: Loveland, CO
Rectangular/Oval port debate.
I am planning a winter upgrade of my '69 L-71 to a roller cam and alum. heads. This month's Car Craft, and other studies, show the increasing efficiency of oval port BB heads. Here is my problem, I want to retain my tri-power manifold (after all, that is the reason I have the car, and nothing has the pazazz of a tripower).
I have been looking at the Edelbrock rec. port heads and a roller in the 233-245 duration range. Other head makers (AFR, etc.) have smaller oval port heads that make more power in the usable ranges. Will putting a stock tripower on an oval head kill the performance benefits of the heads (or, is that even a fit possiblity)? Or, do I just live with the performance deficit of the large rec. ports on street usage of my tripower?
Anybody out there have similar conflicts?
Ralph.
I have been looking at the Edelbrock rec. port heads and a roller in the 233-245 duration range. Other head makers (AFR, etc.) have smaller oval port heads that make more power in the usable ranges. Will putting a stock tripower on an oval head kill the performance benefits of the heads (or, is that even a fit possiblity)? Or, do I just live with the performance deficit of the large rec. ports on street usage of my tripower?
Anybody out there have similar conflicts?
Ralph.
Race Director
Joined: Jan 2000
Posts: 13,011
Likes: 2,249
From: Corsicana, Tx
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
Those AFR's will kick butt over the Edelbrocks. They are really nice heads.
Since you're willing to swap heads...you aren't too worried about dead stock appearance or #'s I assume.
While not perfect...the rectangular port intake will bolt up to the AFR heads. There will be some mismatch...but it's been done for years and actually works well. If you want to spend the time you could epoxy or weld up the intake exits and port to match heads perfectly...but probably not worth the effort.
For sure even with the mismatch..you will have tons more power than you had before.
Are you going hyd roller or solid roller?
JIM
Since you're willing to swap heads...you aren't too worried about dead stock appearance or #'s I assume.
While not perfect...the rectangular port intake will bolt up to the AFR heads. There will be some mismatch...but it's been done for years and actually works well. If you want to spend the time you could epoxy or weld up the intake exits and port to match heads perfectly...but probably not worth the effort.
For sure even with the mismatch..you will have tons more power than you had before.
Are you going hyd roller or solid roller?
JIM
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,674
Likes: 197
From: Loveland, CO
Going hydraulic roller. Correct again, not to much into stock appearing/,numbers oriented, but do have all original parts. Will be street engine, and don't want reliability issues of solid roller. If you would use head/intake mismatch, which gaskets would you use?
This all seems really stange to me. My neighbor, Lars, will go into his rocket scientist orbit if he sees this.
Ralph
This all seems really stange to me. My neighbor, Lars, will go into his rocket scientist orbit if he sees this.
Ralph
Race Director
Joined: Jan 2000
Posts: 13,011
Likes: 2,249
From: Corsicana, Tx
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
You use the rectangular port gaskets.
This was very common years ago before there were any decent intakes for oval port heads. Throwing a rectangular port one on there really allowed ovals to work well and pull some RPM.
Those heads aren't exactly perfectly oval either.
Again..it's a long way from perfect....but I once saw some flwo bench testing and when you looked at it the airflow was through the center of the port and upper portion primarily....so pulling through a larger runner didn't quite have to effect of the mixture *slamming into* the ledge that's created that you would think. It was actually much better than the other way around with an oval port flowing into a rectangular port where you had the huge area increase and the resultant drop in velocity and turbulence as it opened up so quickly.
Lars will need a beer or two to get used to the idea......
But he's been around a long time...probably did it once or twice himself!
Doing a little welding on the intake wouldn't hurt it..you can always open it back up later if you wanted to.
JIM
This was very common years ago before there were any decent intakes for oval port heads. Throwing a rectangular port one on there really allowed ovals to work well and pull some RPM.
Those heads aren't exactly perfectly oval either.
Again..it's a long way from perfect....but I once saw some flwo bench testing and when you looked at it the airflow was through the center of the port and upper portion primarily....so pulling through a larger runner didn't quite have to effect of the mixture *slamming into* the ledge that's created that you would think. It was actually much better than the other way around with an oval port flowing into a rectangular port where you had the huge area increase and the resultant drop in velocity and turbulence as it opened up so quickly.
Lars will need a beer or two to get used to the idea......
But he's been around a long time...probably did it once or twice himself!
Doing a little welding on the intake wouldn't hurt it..you can always open it back up later if you wanted to.
JIM
Advanced
Joined: Jun 2011
Posts: 93
Likes: 4
From: KS
Interesting article from Car Craft and really fun to watch them make very respectable numbers from that 454 on the cheap. One question came to mind while reading part 2 of the article...
Say you leave things as they are in their second build but swap out the ovals for a set of rectangle port heads (and port matching intake of some sort), would it make more power (and/or) torque with the rectangle port heads?
Say you leave things as they are in their second build but swap out the ovals for a set of rectangle port heads (and port matching intake of some sort), would it make more power (and/or) torque with the rectangle port heads?
Last edited by Sam and Jess; Sep 1, 2012 at 11:44 AM.
Drifting
Joined: Oct 2005
Posts: 1,527
Likes: 148
From: East London/SW Essex UK
Interesting fact that some of the latest BIG bbc race heads are of an oval port configuration. Have Brodix Race Rite ovals on my 489 - very efficient. Dyno'd with 465 ft/lb Torque @ 2500 rpm and 565 ft/lbs @ 3850 rpm.
Forgot to mention that even with a 950 cfm dp economy is fractionally better than stock L36 427!
Forgot to mention that even with a 950 cfm dp economy is fractionally better than stock L36 427!
Last edited by roscobbc; Sep 1, 2012 at 08:39 PM.
Instructor
Joined: Apr 2007
Posts: 142
Likes: 6
From: Indianapolis, Indiana
Ralph,
If you are wanting a head that will provide good low/mid speed drivability and work with your tri-power rect port manifold, you might look into the Brodix Race Rite rect port. It's one of the smallest rect port heads on the market at 294cc. The exhaust port is in the sock location so header install wont be a problem. This head flows around 350cfm with the CNC chamber out of the box, and at only 294cc, velocity is good which translates to good torque. It should work well with your combo.
http://www.brodix.com/heads/raceritebb.php
If you are wanting a head that will provide good low/mid speed drivability and work with your tri-power rect port manifold, you might look into the Brodix Race Rite rect port. It's one of the smallest rect port heads on the market at 294cc. The exhaust port is in the sock location so header install wont be a problem. This head flows around 350cfm with the CNC chamber out of the box, and at only 294cc, velocity is good which translates to good torque. It should work well with your combo.
http://www.brodix.com/heads/raceritebb.php
Last edited by 71454Chevelle; Sep 1, 2012 at 07:28 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
The welding (to add necessary material) would have been done in the same area, but IMOE there's nothing wrong with a proper epoxy job. If you're not up to the task, any good performance machine shop worth their salt will be able to do it for you, and it shouldn't cost an arm or a leg.
Last edited by TheSkunkWorks; Sep 1, 2012 at 11:11 PM.
Racer
Joined: Oct 2010
Posts: 259
Likes: 3
From: Plano TX
Heads
Is the commentary here, as it relates to the OP's question, suggesting that rectangular port heads are "obsolete"? I would think with a tri power set up and reasonably "stout" cam, rectangular port heads would perform very well. But...having said that, I haven't read the Car Craft magazine article so I don't know what's been done in their testing.
Surfing, I found this table of head flow for different heads:
http://www.airflowresearch.com/westech_figures.php
So if we were considering rec heads for more moderate applications, are we saying that the smaller flow numbers on a few of the heads listed (steel or aluminum aside) would tend to be better performers than the high flowing heads, so as to keep velocities up? I have a head ache.
Surfing, I found this table of head flow for different heads:
http://www.airflowresearch.com/westech_figures.php
So if we were considering rec heads for more moderate applications, are we saying that the smaller flow numbers on a few of the heads listed (steel or aluminum aside) would tend to be better performers than the high flowing heads, so as to keep velocities up? I have a head ache.
Racer
Joined: Feb 2007
Posts: 259
Likes: 5
From: Valrico Florida
Ralph,
If you are wanting a head that will provide good low/mid speed drivability and work with your tri-power rect port manifold, you might look into the Brodix Race Rite rect port. It's one of the smallest rect port heads on the market at 294cc. The exhaust port is in the sock location so header install wont be a problem. This head flows around 350cfm with the CNC chamber out of the box, and at only 294cc, velocity is good which translates to good torque. It should work well with your combo.
http://www.brodix.com/heads/raceritebb.php
If you are wanting a head that will provide good low/mid speed drivability and work with your tri-power rect port manifold, you might look into the Brodix Race Rite rect port. It's one of the smallest rect port heads on the market at 294cc. The exhaust port is in the sock location so header install wont be a problem. This head flows around 350cfm with the CNC chamber out of the box, and at only 294cc, velocity is good which translates to good torque. It should work well with your combo.
http://www.brodix.com/heads/raceritebb.php
581/573 lift
242/250 @.050 duration w/112 separation
This combo makes very good power for me and have great reliability ( 5000 miles and not a single issue ) Advise the use of a stud girdle. check mine once and everything was spot on.
Drifting
Joined: Oct 2005
Posts: 1,527
Likes: 148
From: East London/SW Essex UK
http://www.carcraft.com/techarticles...s/viewall.html
This was published about the time I purchased my heads - I wanted to use off the shelf headers so didn't consider the raised port heads.
This was published about the time I purchased my heads - I wanted to use off the shelf headers so didn't consider the raised port heads.
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,674
Likes: 197
From: Loveland, CO
If someone knows how to reference the Nov. 2012 Car Craft article, it would be helpful here. I am too old for that advanced technology, and don't have access to a teenager. Anyway, the AFR 265 heads they tested really kicked butt on the stock heads, especially on the exhaust side.
That being said, I see most of the better flowing heads have raised exhaust ports. How much port rise can you get by with using stock manifolds? I understand all the benefits of headers, but just don't want to use them for my application.
Great information. Ralph
That being said, I see most of the better flowing heads have raised exhaust ports. How much port rise can you get by with using stock manifolds? I understand all the benefits of headers, but just don't want to use them for my application.
Great information. Ralph
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,352
From: Santa Ana CA
I get Car Craft, read the story, looked at the heads, and decided that they are not really oval port heads at all, and actually more like rectangular port heads, but radiused to reduce the dead areas where the corners of the rectangle come together.
To compare these to true GM oval port heads is not a fair comparison.
To compare these to true GM oval port heads is not a fair comparison.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Is the commentary here, as it relates to the OP's question, suggesting that rectangular port heads are "obsolete"? I would think with a tri power set up and reasonably "stout" cam, rectangular port heads would perform very well. But...having said that, I haven't read the Car Craft magazine article so I don't know what's been done in their testing.
Surfing, I found this table of head flow for different heads:
http://www.airflowresearch.com/westech_figures.php
So if we were considering rec heads for more moderate applications, are we saying that the smaller flow numbers on a few of the heads listed (steel or aluminum aside) would tend to be better performers than the high flowing heads, so as to keep velocities up? I have a head ache.
Surfing, I found this table of head flow for different heads:
http://www.airflowresearch.com/westech_figures.php
So if we were considering rec heads for more moderate applications, are we saying that the smaller flow numbers on a few of the heads listed (steel or aluminum aside) would tend to be better performers than the high flowing heads, so as to keep velocities up? I have a head ache.
Le Mans Master
Joined: Oct 2007
Posts: 5,996
Likes: 1,727
From: Richmond Kentucky
2025 Corvette of the Year Winner- Modified
2024 C2 of the Year Winner - Modified
2022 Corvette of the Year Finalist -- Modified
2021 C2 of the Year Winner - Modified
2021 C1 of the Year Winner - Modified
2020 Corvette of the Year (stock)
C2 of Year Winner (stock) 2019
2017 C1 of the Year Finalist
I am planning a winter upgrade of my '69 L-71 to a roller cam and alum. heads. This month's Car Craft, and other studies, show the increasing efficiency of oval port BB heads. Here is my problem, I want to retain my tri-power manifold (after all, that is the reason I have the car, and nothing has the pazazz of a tripower).
I have been looking at the Edelbrock rec. port heads and a roller in the 233-245 duration range. Other head makers (AFR, etc.) have smaller oval port heads that make more power in the usable ranges. Will putting a stock tripower on an oval head kill the performance benefits of the heads (or, is that even a fit possiblity)? Or, do I just live with the performance deficit of the large rec. ports on street usage of my tripower?
Anybody out there have similar conflicts?
Ralph.
I have been looking at the Edelbrock rec. port heads and a roller in the 233-245 duration range. Other head makers (AFR, etc.) have smaller oval port heads that make more power in the usable ranges. Will putting a stock tripower on an oval head kill the performance benefits of the heads (or, is that even a fit possiblity)? Or, do I just live with the performance deficit of the large rec. ports on street usage of my tripower?
Anybody out there have similar conflicts?
Ralph.
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,674
Likes: 197
From: Loveland, CO
Dr L-88. I guess that would be an option, but I guess I didn't know oval tripowers existed. However, I suspect, finding and pricing an acceptable oval tripower (not sure if they are available new) might be prohibitive. I'm almost certain new smaller rec. port heads would be cheaper (than buying both oval heads and intake manifold). Am I way off base?
Thanks, Ralph.
Thanks, Ralph.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Tri-Power intakes (oval or rect) have certainly been getting very pricy for the past couple of years or so.
Modern, small'ish rect port heads would be an improvement over older factory castings. Are you open to considering a modern solid flat tappet cam to go with them, keeping the rect port trips? FWIW, I've done a number of high-perf 427's over the years, including with 3x2's, and would certainly be interested in designing/building one for you. PM if interested.
.
Modern, small'ish rect port heads would be an improvement over older factory castings. Are you open to considering a modern solid flat tappet cam to go with them, keeping the rect port trips? FWIW, I've done a number of high-perf 427's over the years, including with 3x2's, and would certainly be interested in designing/building one for you. PM if interested.
.
Last edited by TheSkunkWorks; Sep 2, 2012 at 06:45 PM.
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,674
Likes: 197
From: Loveland, CO
I think I am leaning toward the small Brodix Race Rites at the moment. I would like to think about the AFR 305's, if I could get my stock exhaust manifolds to fit without too much forcing (due to the raised exhaust ports).
Thanks, Ralph.
Thanks, Ralph.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
Even though the AFRs will flow a bit more than the Brodix heads, its not too big a deal once your intake enters the picture.
The Race Rites will easily flow as much as your intake will.