Rectangle intake with oval heads - Team Camaro Tech
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post #1 of 14 (permalink) Old Jan 4th, 06, 09:20 PM Thread Starter
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Question Rectangle intake with oval heads

I have an old edelbrock intake "c427" that appears to be a recatngle port intake. I really I love the vintage look of it and the casting numbers that tell you it is a 427 although my block is a 454. The heads I am going to be running are 049's which are a large oval port. Will this work or will it be like trying to put a square peg in a round hole?
Thanks!!!
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post #2 of 14 (permalink) Old Jan 4th, 06, 09:52 PM
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Re: Rectangle intake with oval heads

Just make sure you use square port gaskets. The oval gaskets wont get it to seal.

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post #3 of 14 (permalink) Old Jan 4th, 06, 10:38 PM
 
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Re: Rectangle intake with oval heads

Yes it will work but it wont be optimum. You can however use the rectangle intake gasket as a template and somewhat port match the heads. Be cautious not to try and port the head way down into the runner you just roll the leading the edges to help it out some. I have a friend who ran a setup like this on his car for years with no problems.
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post #4 of 14 (permalink) Old Jan 5th, 06, 07:14 AM Thread Starter
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Re: Rectangle intake with oval heads

I have read there might be a velocity problem if I do this. What does that mean? I would really hate to screw up a nice set of 049's by tapering the ports. Will there be any performance drop? I am looking for around 475 HP out of the 454. I have an Edelbrock 2162 cam and lifter set.
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post #5 of 14 (permalink) Old Jan 5th, 06, 08:28 AM
 
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Re: Rectangle intake with oval heads

All I can say it it will work. Like I said earlier its is not going to be optimum but it does work and I don't think you will ever know when driving it. The friend of mine had no problem with fuel distribution. He made roughly a estimated 700hp based on his cars ET ([email protected] mph 1/8mile) at the strip. But it was a race only car. One thing to consider is that if you do any port work its pretty much for life. Thats about all I know about it maybe someone else will have some input.
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post #6 of 14 (permalink) Old Jan 5th, 06, 05:31 PM
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Re: Rectangle intake with oval heads

I'd call or email Edelbrock directly. I'm sure they get this question once in a while and they probably have some dyno tests available to see if there's any drop in power. Who knows, you might actually gain power, as sometimes a disturbed air flow atomizes fuel better.

-

Dave F. in Rhode Island
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post #7 of 14 (permalink) Old Jan 5th, 06, 06:06 PM
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Re: Rectangle intake with oval heads

Search around for an Edelbrock C396 intake. It looks the same, but is an oval port manifold.
I see them on ebay from time to time and at swap meets.

68 Camaro, 555 big block, Doug Nash 5-speed, 3.54 gear.
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post #8 of 14 (permalink) Old Jan 5th, 06, 06:16 PM
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Re: Rectangle intake with oval heads

Yes, it will work, I've tried it.

As someone mentioned, you might even gain some bottom end power.

I'd say go for it.

Don ~ TC Member #15 ~
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post #9 of 14 (permalink) Old Jan 5th, 06, 07:06 PM
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Re: Rectangle intake with oval heads

As mentioned the motor will run. I addressed this issue the other day with a 8-71 blower manifold a guy wanted to install for looks. Performance wasn't as important as display as it was built to cruise car shows.

The velocity people are talking about is the velocity of the air in the runners. When the 427 Mark IV went into production, it was based upon the designs of the Mark II big block that was built in 1963 to compete in NASCAR. NASCAR is all about WOT. They do not normally spend much time rowing through gears from stop light to stop light.

Because of this the engineers were looking to optimize laminar flow for peak horse power. That is why the intake was taller than similar Rochester 4G carbs, with straighter shorter length ports. Now I do not know how much time you spend holding the accelerator pedal on the floor, but in Florida such behavior will probably come to the attention of the local constabulary.

For that reason and probably to keep those party poopers in California happy (the originators of the smog police) Chevrolet also introduced the "large port" round heads you have. Racers learned over time that the 350 horse 396 actually ran better than the 375 HiPer version on the street. Especially when given a high lift cam similar to the 375 horse cam.

It is generally now accepted that anything less than 500 cubic inches is best served with oval port heads because the smaller diameter of the ports really sends a strong vacuum signal to the carb to suck in more air. With 500 cubes the break point, Chevy ships their premium street engine ZZ502 (502 hp) with oval ports, but the lower rated 502HO (450 hp) with the larger rectangular ports on cast iron HiPer heads.

You can demonstrate this with soda straws. If you get a bunch of straws of varying diameters you will quickly see that on the jumbo red Slurpee straws from the Seven/11 can suck up a lot of water but you can hardly pull a vacuum with air. Conversely the little red swizzle stick from the coffee counter wont hardly let water pass but you can pull a "hard" vacuum with it. The red and yellow striped white MacDonald's straws are perfect for sucking up both air or water. This is a Three Bears demonstration of the physics principle of fluids based upon formula developed by Bernoulli.

Motors run on air not liquid gasoline. The amount of air that can be ingested by the engine determines your peak horse power. But it is the torque curve that allows you to live with the internal combustion engine on the street, and it is a compromise of peak air flow and cylinder filling with the correct ratio of air and gas. Bigger is not always better.

But in your case it is way cool at car shows so if that is what you want go for it. Just watch for vacuum leaks because of the port mismatch, and be prepared for a slight loss in power and throttle response.

Larger Dave (of I remember when fame)
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post #10 of 14 (permalink) Old Jan 5th, 06, 08:34 PM Thread Starter
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Re: Rectangle intake with oval heads

Wow, thank you all for your time and thought on this subject especially "Larger Dave". I want it to look good but I hate the thought of doing something that can potentially hurt horse power. I'll call Edelbrock tomorrow and see what they have to say. I would love to see some dyno results on this combo. Heck, maybee I'll just have to get the c396 and the c427x and do the dyno in the 049's if no one else has. It won't be any time soon though. Let me know if you have a c396 or comparable HP aluminum oval intake for sale.
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post #11 of 14 (permalink) Old Jan 6th, 06, 06:39 AM
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Re: Rectangle intake with oval heads

Check out Ebay item number 8027229613

68 Camaro, 555 big block, Doug Nash 5-speed, 3.54 gear.
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post #12 of 14 (permalink) Old Jan 6th, 06, 05:51 PM Thread Starter
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Re: Rectangle intake with oval heads

Well I called Edelbrock today and they were not much help. I could tell the guy was fairly young and the intake part numbers were way before his time. He put me on hold for a while as he referenced some old catalogs. The only thing he could tell me was the c396 and c427x were both 2000 6000rpm and of course that the c396 was the oval the the c427x was the rectangle port which we all knew. He also told me the always discourage mismatching ovals to rectangles. Well, so much for the cool c427x part number, I think I will have to go with the c396 or some other intake. If someone ever has dyno
results for the c427x with oval I would love to see it.
Thanks everyone.
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post #13 of 14 (permalink) Old Mar 6th, 06, 07:30 AM Thread Starter
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Re: Rectangle intake with oval heads

Well I got the c396 and the 049 heads. I test fit them last night and ran into problems. I posted my issue with pictures here:
https://www.camaros.net/forums/showth...highlight=c396
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post #14 of 14 (permalink) Old Mar 9th, 06, 09:26 PM
 
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Re: Rectangle intake with oval heads

Quote:
Originally Posted by Larger Dave
As mentioned the motor will run. I addressed this issue the other day with a 8-71 blower manifold a guy wanted to install for looks. Performance wasn't as important as display as it was built to cruise car shows.

The velocity people are talking about is the velocity of the air in the runners. When the 427 Mark IV went into production, it was based upon the designs of the Mark II big block that was built in 1963 to compete in NASCAR. NASCAR is all about WOT. They do not normally spend much time rowing through gears from stop light to stop light.

Because of this the engineers were looking to optimize laminar flow for peak horse power. That is why the intake was taller than similar Rochester 4G carbs, with straighter shorter length ports. Now I do not know how much time you spend holding the accelerator pedal on the floor, but in Florida such behavior will probably come to the attention of the local constabulary.

For that reason and probably to keep those party poopers in California happy (the originators of the smog police) Chevrolet also introduced the "large port" round heads you have. Racers learned over time that the 350 horse 396 actually ran better than the 375 HiPer version on the street. Especially when given a high lift cam similar to the 375 horse cam.

It is generally now accepted that anything less than 500 cubic inches is best served with oval port heads because the smaller diameter of the ports really sends a strong vacuum signal to the carb to suck in more air. With 500 cubes the break point, Chevy ships their premium street engine ZZ502 (502 hp) with oval ports, but the lower rated 502HO (450 hp) with the larger rectangular ports on cast iron HiPer heads.

You can demonstrate this with soda straws. If you get a bunch of straws of varying diameters you will quickly see that on the jumbo red Slurpee straws from the Seven/11 can suck up a lot of water but you can hardly pull a vacuum with air. Conversely the little red swizzle stick from the coffee counter wont hardly let water pass but you can pull a "hard" vacuum with it. The red and yellow striped white MacDonald's straws are perfect for sucking up both air or water. This is a Three Bears demonstration of the physics principle of fluids based upon formula developed by Bernoulli.

Motors run on air not liquid gasoline. The amount of air that can be ingested by the engine determines your peak horse power. But it is the torque curve that allows you to live with the internal combustion engine on the street, and it is a compromise of peak air flow and cylinder filling with the correct ratio of air and gas. Bigger is not always better.

But in your case it is way cool at car shows so if that is what you want go for it. Just watch for vacuum leaks because of the port mismatch, and be prepared for a slight loss in power and throttle response.

Larger Dave (of I remember when fame)
...... well put dave...that was beauitiful.......iv been drinking so excuss meon my spelling
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