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opinions needed. Best factory cast BBC intake.
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seventy468
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PostPosted: Sat Mar 27, 2010 12:01 pm    Post subject: opinions needed. Best factory cast BBC intake. Reply with quote

Whats your opinion? I have done some dealing with aftermarket intakes, but when it comes to a factory cast iron intake... of all the years/makes/models which is best? Does the tall deck offer anything over the factory height engine?
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SkinnRodd
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PostPosted: Sat Mar 27, 2010 1:09 pm    Post subject: Reply with quote

What kind of heads would it be for and what kind of induction, cubic inches? I'm no pro but I might be able to refer you to some reading material. These guys on here have experience though, which is priceless if you want to win. I'm just getting started, but I know the answer to your question depends on the application. What are you running?
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seventy468
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PostPosted: Sat Mar 27, 2010 1:44 pm    Post subject: Reply with quote

naturally aspirated 505..(would like to do 520 but am limited to a factory intake and exh manifolds soo not sure where to much cubic inch is doing more harm than good on a factory cast int. & exh manifolds. Also trying to choose a good comp ratio. I am running ported 990 heads.
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seventy468
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PostPosted: Sat Mar 27, 2010 3:15 pm    Post subject: Reply with quote

just to clarify the block is originally a td 427
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SMOKEmUP
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PostPosted: Sat Mar 27, 2010 5:17 pm    Post subject: Reply with quote

Big Dave is a good resource for BBC questions.
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Big Dave
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PostPosted: Sun Mar 28, 2010 12:07 am    Post subject: Reply with quote

Rectangular HiPerf heads I would use a 1968 L-88 Holley manifold off the Corvette casting number 3885069, or the 3886093 off of the 1967 L-88 (only difference is the machine work on the plenum separator and the open plenum was only used on the Corvette with other vehicles having either a a three hole manifold or a two hole version). After 1969 they dropped the mounting flange for the Holley manifolds down nearly two inches to clear the new C3 hood lines.

If you have to have a cast iron Holley manifold acording to the rules you are going to be running oval port heads as all of the rectangular port manifolds were cast by Winters in aluminum. The cast iron 3866948 manifold was used on the 350 horse 396 and the 390 horse 427.

If you have to run cast iron exhaust manifolds then you are really hurting. Though there was a set of cast iron exhaust manifolds cast for the ZL-1 Mark-II BBC in 1963 that approximates the flow rate of headers. (they are museum pieces now worth their weight in gold but I have seen two sets).

The square exhaust port is the restriction in the BBC's ability to breathe. The Corvette had the best manifold (3856301 LH and 3856302 RH), but it also didn't rely on mid engine mounts so it could dump straight down on the the early 'vettes and the motor has always been set back since there is no rear seat to worry about. If you can find a set of manifolds they probably will not fit the A-body or F-body, X-body or the H-body (which is hard enough to stick a BBC into anyway). All of the rest of the cast iron BBC manifolds are a simple log manifold with the exception of motor home stainless steel tubular exhaust manifolds which are a set of factory made block huggers.

Big Dave
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seventy468
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PostPosted: Sun Mar 28, 2010 3:28 pm    Post subject: Reply with quote

thinking about changing plans. I can build my td 427 for an altered class and not have to worry about cast int. exh. manifolds, and use my 468 out of my chevelle for the street stock class. I found a good set of the 781 heads race ready and can acquire one of those cast intakes pretty easy as well. Would 13:1 be feasible for the cast iron class? Or if someone could explain to me at what point of to high of a comp. ratio would no longer benefit me with factory cast class I would greatly appreciate it. The internals of the engine will be more than capable of holding that kind of pressure. This class also requires a full exh system... or atleast mufflers and turn downs.
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Big Dave
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PostPosted: Sun Mar 28, 2010 5:10 pm    Post subject: Reply with quote

Being a modified hemispherical engine (the modification is in having both valves on the same side of the head and not the shape of the combustion chamber) it likes lots of compression and will reward you with more horsepower up to about a 15.0:1 compression ratio (at which point you need to burn something besides gasoline). Because the chamber has no appreciable quench area it is not going to be as efficient a chamber as found on the small block. Where the big block does beat the small block is on engine size (big blocks are built today a twice the size of a small block). But because of the valves being on the same side of the head they are limited in size (compared to a true hemi), and with size limited valves feeding increasing displacement we begin to think of the BBC as a nail head Buick on steroids.

You are talking about using '741 heads which have 256cc intakes feeding 2.06" intake valves. You can easily fit a 2.25"intake valve in place of it allowing you to open up the throat cross sectional area to a maximum of 1.845 inches in diameter (with complimentary pocket porting to smooth the transition). You can also install a 1.88" tuliped exhaust valve to assist the notoriously poor exhaust port that the BBC has with only 114cc of port area pointing down after making an abrupt U-bend after leaving the cylinder. The stock 1.72" valve weighs as much as the tuliped valve and is a poor heat sink. Because of your head choice you are restricted to about 500 cubic inches in displacement so a 496 will work in your tall deck 427 block.

With new heads you can punch out that TD block to build a 632 cubic inch motor, but they would require larger raised ports and reduced valve angles to make any serious power with that kind of displacement.

Big Dave
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seventy468
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PostPosted: Sun Mar 28, 2010 5:55 pm    Post subject: Reply with quote

Originally I wanted to do my td 427 with a set of ported 990's that I have, however the class is a factory cast iron intake class, and as you stated before the only factory cast intakes that were square port were aluminum... I wouldn't have a problem continuing the TD427 build but then I have to find a intake and spacers, and hope that is legal. Or I could use the TD and build it for the altered class (514 +/- 2% cubic inch rule) and use my 990 heads with whatever intake/exh system I want and use my 468 in the street stock class with a set of 336781 oval port heads (Heads are 1973 781 casting oval port,
bronze guide liners, 2.190 intake valves, 1.880 exhaust valves, stainless steel pro flow, springs for solid roller, 10 degree retainers,
heads have been ported and polished, 3-5 angle valve job. ) the holley cast iron intake that you referred to earlier, some exh manifolds and I would be competitive... maybe. Them ford boys and their cobra jet stuff are hard to beat when it comes to factory cast iron. My compression ratio question was aimed at the 468 with factory cast iron intake and manifolds. The internals will be sufficient enough to withstand the 15:1 CR but how would 15:1 work with the factory cast iron stuff heat/efficiency wise? I apologize if I am not speaking clearly, please be patient, I am learning.
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Big Dave
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PostPosted: Mon Mar 29, 2010 8:55 pm    Post subject: Reply with quote

Combustion chamber heat works more to your advantage with cast iron than with aluminum heads. Just like copper and aluminum are are used in wiring because of their low resistance to electricity, they also transmit heat equally efficiently. Iron holds that heat in the chamber longer because it doesn't transmit energy as efficiently through the walls of the casting (cylinders or heads).

Big Dave
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af2
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PostPosted: Mon Mar 29, 2010 10:50 pm    Post subject: Reply with quote

seventy468 wrote:
Originally I wanted to do my td 427 with a set of ported 990's that I have, however the class is a factory cast iron intake class, and as you stated before the only factory cast intakes that were square port were aluminum... I wouldn't have a problem continuing the TD427 build but then I have to find a intake and spacers, and hope that is legal. Or I could use the TD and build it for the altered class (514 +/- 2% cubic inch rule) and use my 990 heads with whatever intake/exh system I want and use my 468 in the street stock class with a set of 336781 oval port heads (Heads are 1973 781 casting oval port,
bronze guide liners, 2.190 intake valves, 1.880 exhaust valves, stainless steel pro flow, springs for solid roller, 10 degree retainers,
heads have been ported and polished, 3-5 angle valve job. ) the holley cast iron intake that you referred to earlier, some exh manifolds and I would be competitive... maybe. Them ford boys and their cobra jet stuff are hard to beat when it comes to factory cast iron. My compression ratio question was aimed at the 468 with factory cast iron intake and manifolds. The internals will be sufficient enough to withstand the 15:1 CR but how would 15:1 work with the factory cast iron stuff heat/efficiency wise? I apologize if I am not speaking clearly, please be patient, I am learning.



With a cam correct combo spinning 9000 you could have a chance! Most people only want to spin the engine 6500 and that will limit you on HP. You will never catch a Ford.
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seventy468
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PostPosted: Tue Mar 30, 2010 12:08 am    Post subject: Reply with quote

haha I agree! Well a buddy of mine says he can turn a oval port intake into a square port one with his mill... so maybe I can still get away with these nice 990's and use my td 427. Now I need to find a tall deck intake to see if he can do what he says he can, or if I can get a hold of one of the above mentioned intakes I will make it work with tall deck intake spacers. anyone have a nice cast intake laying around they'd part with cheap?
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clay
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PostPosted: Tue Mar 30, 2010 10:37 am    Post subject: Reply with quote

Quote:
Well a buddy of mine says he can turn a oval port intake into a square port one with his mill...

That's sort of what I was thinking. Even if you couldn't get the intake port quite as large as the head port, it shouldn't be a problem - maybe even have some antireversion benefit. Dave - how about marine applications? I seem to remember from our dirt track days that the Chevrolet's were running a marine 4bbl. intake. Probably nothing different about it and it could have been all rumor though - you know how racers are..........Clay

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Knarley Darley
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PostPosted: Tue Mar 30, 2010 5:49 pm    Post subject: Reply with quote

Good call Clay. I had a 21' daycruiser back in the day with a 454 square ports and a cast iron manifold with a 4150 holley carb flange. I have no idea where to get one but they did make them.
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seventy468
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PostPosted: Tue Mar 30, 2010 6:11 pm    Post subject: Reply with quote

That would be amazing to find one of those! I am going to do a little digging, thanks for that info!
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