Rectangular/Oval port debate.
Race Director
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From: Corsicana, Tx
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I think the rectangle port Race Rites would be a great choice for what your doing.
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.
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.
I don't think the AFR raised ports are an issue. Tons of Vette folks are using them. My Brodix heads are raised .600" and it actually helped the old 2-1/8" Hooker headers fit better than they did with stock heads. I can tell you I've recently put a set of Corvette Central's shory headers on them (for the turbo installation) that are replacements for cast iron manifolds and they clear everything fine.
JIM
Instructor
Joined: Apr 2007
Posts: 142
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From: Indianapolis, Indiana
When I was looking at heads for my 496 build, I was leaning toward the AFR305's. Everything I had heard, the 3/8" raised exhaust ports would not be a problem with header fitament but after looking at my setup I had a header tube that run very close to the clutch z-bar. I didn't want to take the chance of having to purchase high dollar custom headers so I went with the Brodix heads.
The Race Rites exhaust port is not as effecient as the AFR port but this can easily be rectified by a custom cam with several degrees additional exhaust duration. For a cam that will allow you to get all the HP out of your system you might want to contact Chris Straub. He will grind you a cam that will be perfectly matched to your combination. Guys over on Team Chevelle have been using him with very good results.
http://www.straubtechnologies.com/
The Race Rites exhaust port is not as effecient as the AFR port but this can easily be rectified by a custom cam with several degrees additional exhaust duration. For a cam that will allow you to get all the HP out of your system you might want to contact Chris Straub. He will grind you a cam that will be perfectly matched to your combination. Guys over on Team Chevelle have been using him with very good results.
http://www.straubtechnologies.com/
Last edited by 71454Chevelle; Sep 3, 2012 at 09:03 AM.
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
When I was looking at heads for my 496 build, I was leaning toward the AFR305's. Everything I had heard, the 3/8" raised exhaust ports would not be a problem with header fitament but after looking at my setup I had a header tube that run very close to the clutch z-bar. I didn't want to take the chance of having to purchase high dollar custom headers so I went with the Brodix heads.
The Race Rites exhaust port is not as effecient as the AFR port but this can easily be rectified by a custom cam with several degrees additional exhaust duration. For a cam that will allow you to get all the HP out of your system you might want to contact Chris Straub. He will grind you a cam that will be perfectly matched to your combination. Guys over on Team Chevelle have been using him with very good results.
http://www.straubtechnologies.com/
The Race Rites exhaust port is not as effecient as the AFR port but this can easily be rectified by a custom cam with several degrees additional exhaust duration. For a cam that will allow you to get all the HP out of your system you might want to contact Chris Straub. He will grind you a cam that will be perfectly matched to your combination. Guys over on Team Chevelle have been using him with very good results.
http://www.straubtechnologies.com/
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,691
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From: Loveland, CO
Roscobb, how do you like that cam? With the increased exhaust timing suggestion, I see Howard cams has a couple around what I'm thinking: two at 233/247, with 112 and 114 lobe separation, one at 233/245 and 112 separation, all at lifts of .600 to .634. What do you think?
Ralph
Ralph
Instructor
Joined: Apr 2007
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From: Indianapolis, Indiana
Roscobb, how do you like that cam? With the increased exhaust timing suggestion, I see Howard cams has a couple around what I'm thinking: two at 233/247, with 112 and 114 lobe separation, one at 233/245 and 112 separation, all at lifts of .600 to .634. What do you think?
Ralph
Ralph
http://www.straubtechnologies.com/
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
Roscobb, how do you like that cam? With the increased exhaust timing suggestion, I see Howard cams has a couple around what I'm thinking: two at 233/247, with 112 and 114 lobe separation, one at 233/245 and 112 separation, all at lifts of .600 to .634. What do you think?
Ralph
Ralph
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,691
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From: Loveland, CO
I have about decided on the Brodix race rite 294 rec.port heads. With the exhaust ports in the stock location, the exhaust obviously flows less than a raised port. The AFR 265's (but oval port) have about .80 ratio of exhaust to intake flow., the Race Rites, about .63. It has been indicated here that this can be rectified by just adding a little more exhaust duration.
Roscobbc, I have been looking at the Howard Cam kits also. I see your exhaust duration is only 4 degrees more than your intake. With heads like the Broxix Race Rites, shouldn't the spread be more? I wonder what spread the "experts" would be looking at? If I want to use a cam in the 236 intake duration range, what would be my exhaust duration? I think I would also go a little more lift than you have. I am at Denver altitude, but not sure if that makes a lift difference. I want a hydraulic roller cam with better performance than the Comp Cams 224/224, 110, solid flat tappet I have now.
Thanks, Ralph
Roscobbc, I have been looking at the Howard Cam kits also. I see your exhaust duration is only 4 degrees more than your intake. With heads like the Broxix Race Rites, shouldn't the spread be more? I wonder what spread the "experts" would be looking at? If I want to use a cam in the 236 intake duration range, what would be my exhaust duration? I think I would also go a little more lift than you have. I am at Denver altitude, but not sure if that makes a lift difference. I want a hydraulic roller cam with better performance than the Comp Cams 224/224, 110, solid flat tappet I have now.
Thanks, Ralph
Last edited by rponfick; Sep 6, 2012 at 05:16 PM.
Drifting
Joined: Oct 2005
Posts: 1,528
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From: East London/SW Essex UK
n.
Roscobbc, I have been looking at the Howard Cam kits also. I see your exhaust duration is only 4 degrees more than your intake. With heads like the Broxix Race Rites, shouldn't the spread be more? I wonder what spread the "experts" would be looking at? If I want to use a cam in the 236 intake duration range, what would be my exhaust duration? I think I would also go a little more lift than you have.
Roscobbc, I have been looking at the Howard Cam kits also. I see your exhaust duration is only 4 degrees more than your intake. With heads like the Broxix Race Rites, shouldn't the spread be more? I wonder what spread the "experts" would be looking at? If I want to use a cam in the 236 intake duration range, what would be my exhaust duration? I think I would also go a little more lift than you have.
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Racer
Joined: Jul 2004
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Duration is time, how long is the valve open. If a port flows well then it doesn't need as much time to let air in or exhaust out. CID and rpm affect this time.
Heads with hi I/E ratio (intake to exhaust flow ratio) need mild splits because the exhaust port is effiecient. 75% is the control number and at this % an engine would use a single pattern cam at .050". Your other tappet referrence points, adv., .100, .200, .300 will have some split.
A BBC with at 427 CID can make the same power with Brodix or AFR heads, but with totally different cam profiles. The brodix head engine running to 6500 rpm will have a 12 to 14 degree split at .050". The AFR headed engine about 2 degrees.
Heads with hi I/E ratio (intake to exhaust flow ratio) need mild splits because the exhaust port is effiecient. 75% is the control number and at this % an engine would use a single pattern cam at .050". Your other tappet referrence points, adv., .100, .200, .300 will have some split.
A BBC with at 427 CID can make the same power with Brodix or AFR heads, but with totally different cam profiles. The brodix head engine running to 6500 rpm will have a 12 to 14 degree split at .050". The AFR headed engine about 2 degrees.
Heel & Toe
Joined: May 2006
Posts: 15
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From: Novato CA
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
What you want to do is perfectly fine. People do it all the time, I wouldn't fill or epoxy anything on your intake manifold.
Enjoy the additional HP...
Le Mans Master
Joined: Apr 2007
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From: Graceland in a Not Correctly Restored Stingray
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,691
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From: Loveland, CO
Talked to Chris Straub and he is coming up with a proposal for my needs. Is suggesting the Race Rite 294 rec port heads with his hydraulic roller at 620/590 lift, 222/236 duration at .050, 109 lobe seperation. As you can see, he recommends a 14 degree difference in intake to exhaust duration to allow for the lesser flow capacity in the Race Rite exhaust ports.
I'm assuming there will be enough vacuum with these specs. to run the Vette vacuum systems.
Ralph.
I'm assuming there will be enough vacuum with these specs. to run the Vette vacuum systems.
Ralph.
Racer
Joined: Jul 2004
Posts: 254
Likes: 1
Racer
Joined: Jul 2004
Posts: 254
Likes: 1
Talked to Chris Straub and he is coming up with a proposal for my needs. Is suggesting the Race Rite 294 rec port heads with his hydraulic roller at 620/590 lift, 222/236 duration at .050, 109 lobe seperation. As you can see, he recommends a 14 degree difference in intake to exhaust duration to allow for the lesser flow capacity in the Race Rite exhaust ports.
I'm assuming there will be enough vacuum with these specs. to run the Vette vacuum systems.
Ralph.
I'm assuming there will be enough vacuum with these specs. to run the Vette vacuum systems.
Ralph.
I answered your email.
Drifting
Joined: Oct 2005
Posts: 1,528
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From: East London/SW Essex UK
Are we saying here that despite comment that rect inlet to oval heads is OK (and despite mismatch can perhaps show some airflow benefit) the 'hot' trick is epoxy filling and subsequent port matching - or is this only theorical ?
Le Mans Master
Joined: Apr 2007
Posts: 7,353
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From: Graceland in a Not Correctly Restored Stingray
Just because a combination of intakes and heads with bad runner/port matches will work doesn't do anything to disprove that properly matched ones work better. And, epoxy has long been a fairly well proven method of building up sufficient material for proper matching when the intake runner happens to be larger than the head port. IMCO, there's nothing theoretical about either point.
Racer
Joined: Jul 2004
Posts: 254
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The miss alignment of ports if done correctly can enhance power but the average street guy with basically stock suspension can't hook what he has now.
The OP is going to a small rec. port head. The camshaft is small but will make power to his intended rpm range and make for a nice combination in the end.
The OP is going to a small rec. port head. The camshaft is small but will make power to his intended rpm range and make for a nice combination in the end.
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
The miss alignment of ports if done correctly can enhance power but the average street guy with basically stock suspension can't hook what he has now.
The OP is going to a small rec. port head. The camshaft is small but will make power to his intended rpm range and make for a nice combination in the end.
The OP is going to a small rec. port head. The camshaft is small but will make power to his intended rpm range and make for a nice combination in the end.
Race Director
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
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You're usually better off with as perfect a match as you can get...and with a good smooth transistion into the head. I was giving a *quick and dirty* method of putting them together that will work,,,but likely not as good as a perfect match. Will you notice it in a motor like this? Not likely.
Epoxy is commonly used all the time and will last pretty good if you get it installed properly. AFR heads often need a little *match work* to mate an intake to them perfectly due to their port shape and placement..but it all works well.
JIM
Epoxy is commonly used all the time and will last pretty good if you get it installed properly. AFR heads often need a little *match work* to mate an intake to them perfectly due to their port shape and placement..but it all works well.
JIM