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Old 11-01-2008, 08:10 PM
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double hump heads

have a set of 461 double hump heads all set to go for a 400 sb just wanted to know if they would be good for making 400hp. heres what i got block 406 with stock crank rods and flat top pistons cam Hydraulic Flat Tappet Advertised Duration 268/280 Lift .477/.480 heads have 2.02in 1.60ex screw in studs and guide plates with 64cc hoping for 9.5 to 1 c/r let me hear what you got to say Thanks

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Old 11-01-2008, 11:31 PM
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Flat top pistons and 64cc head on a 406ci SBC give you 10.96:1 compression.
Too much compression for pump gas.

You want a 72 to 76cc chamber cylinder head for that motor. Sell the 461's and get some World Products Sportsman II iron heads with 72cc combustion chambers.
You'll have a pump gas friendly cr and will make the hp you want to make with the 268 cam.
The 461's do not have bolt holes for the alternator bracket and do not have hardened exhaust seats for unleaded gas.
Sell them to someone restoring a 60's era 327.

A water injection system is a workable alternative to allow running near 11:1 cr on pump gas without pinging.
http://www.alcoholinjectionsystems.com/
http://www.snowperformance.net/
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Old 11-01-2008, 11:42 PM
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double hump heads

I agree with F-bird, besides, the newer inexpensive aftermarket iron heads have larger intake runners that will flow better with your cam selection.
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Old 11-02-2008, 12:04 AM
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what if i went with a stock like piston with a small dish and also the heads have been ported for a better flow with a bigger cam
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Old 11-02-2008, 12:10 AM
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You would want to use a 18cc to 22cc dished piston. EG: KB147 or KB168
This swap would require rebalanceing the crank.

Swapping the cylinders heads is the easier way. Especially if your short block is already done. The Sportsmans will make more power reguardless and are a much better head in every aspect.
Someone that needs the 461's will pay you well for them making the swap/upgrade cost minimal. You'll be much much further ahead.
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Old 11-02-2008, 12:14 AM
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ok ebay here i come thanks guys
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Old 11-02-2008, 12:27 AM
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double hump heads

You'll still have the inconvenience of no external bolt holes. A good runner for that cam would be 200 cc. Most early humps had 187cc runners with the major restriction located in the short turn area. These newer heads are cast better than the old heads can be ported.

Regarding the hard seat issue: If you use your heads, do not use the exhaust rotators and make sure your springs are correct and installed correctly. Re curving the distributor and making sure that your fuel system is jetted correctly will be adequate for a normal use street car - without hard seats.
However, if you plan on towing or extended severe duty, then hard seats are definitely needed - which increases the price comparative to the aftermarket ones.

Remember, your heads are probably more than 40 years old. That's a lot of stress cycles. The newer ones also have thicker decks to resist cracking.
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Old 11-02-2008, 09:45 PM
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461's will need the steam holes drilled for the 400 also.

Heads, not a fan of the sportsman II's, Dart Iron Eagle Platinums better imho.

For the record- the largest intake runner of any small block chevy production camel hump heads were 172cc 461X castings, most 462's, 461's, and 291's were 160cc-167cc. The largest SBC prodcution head runner is the LT4 195cc. Vortecs measure in at 170cc also.

To get 400hp out of a set of uported double humps on a 406 would take a lot of cam, even out of a 406.
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Old 11-02-2008, 10:04 PM
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what do you guys think about these heads Aluminum Strike Force 64cc heads you can look them up at performanceauto.us its a shop in town where i live
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Old 11-03-2008, 02:31 AM
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Quote:
Originally Posted by GenYnNC
For the record- the largest intake runner of any small block chevy production camel hump heads were 172cc 461X castings, most 462's, 461's, and 291's were 160cc-167cc. The largest SBC prodcution head runner is the LT4 195cc. Vortecs measure in at 170cc also.
And what I always find so interesting about these comparisons (kudos, genYnNc) is that the Vortecs with 2cc smaller runners outflow the 461s by almost 20%. That is HUGE. Add in the supremely efficient chambers and its a no-brainer.
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Old 11-03-2008, 09:36 AM
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don't use those heads. If you do, You are going to need 110 octain gas for a 11.6:1 compression motor
http://www.csgnetwork.com/compcalc.html

Last edited by lg1969; 11-03-2008 at 09:43 AM.
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