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Old 01-04-2012, 09:40 AM
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First bbc 427, 3904390 heads questions

Hi, im building my first big block chevy. Its a 454 .030 over block, 2 bolt. 396 crank turned .010/.010. Domed pistons (dont know size), shortblock was assembled buy the guy im getting it from. He said it would make 10:1-11:1 compression with i assume standard 110cc-120cc heads. I picked up a good set of 3904390 heads. They are i believe 66-67 chevelle 396 390hp heads. Oval port closed chamber 98cc. I plan to port them. Any body have any experience with these heads and what can help them breathe better? They need to be rebuilt but i can get most of the work done for free. I want to run a roller cam, not sure on size but prolly a comp xtreme roller. Any body have any suggestions for me to get this thing into the 450-500hp range and be able to turn near 6000rpm safely? Cam, head porting, valve size, intake, compression, exhaust manifold suggestions would be appreciated. Its going in a 82 shortbed 2wd chevy. Thanks guys!

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Old 01-04-2012, 09:50 AM
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Heads & motor

Cut my teeth on these-Im old school - so bear with me = Id port & clean the heads up- use 454 valves-yet - look closely @ the pistons- must be for closed chamber heads -!!- very diff chambers . Back in the day these were factory engines - usually had 10-11 - 1 comp ratios too. as for the 6000 rpm range - it will do that even wit a hydraulic cam & some nice valve springs - dont nessaraly nheed that expense of a roller cam. That motor should make the HP your after easily too.Id guess the 396 crank is due to having that? Easy to get a used marine setup with all the good parts cheap id guess? if needed.You dont mention what type intake carb ect you will be using? With that motor -likely need to use the higher octane pump gas also. Should be ba nice easyly done motor too-hap-y Roddin
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Old 01-04-2012, 11:47 AM
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The 396-427 crank will make it a 427+.030 with the correct pistons. You will have to use closed chamber piston. If you use a factory 427 closed chamber forged piston it will hit on the head around the exhaust side of the piston. As these pistons were designed for the rect port heads that were more open in that area.

You will be able to rev the thing 6000 rpm with all factory parts. Just a re-bolt and resize job on the rods. If you can get the labor $$$ low. The heads will respond to a 2.19/1.88 combo. If the bowls and shrouding on the intake wall are correctly delt with.

It is wise to run a roller cam on these. Modern oils and the seat pressure/ramp rates make for short lived hot rod flat tappets..
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Old 01-04-2012, 11:55 AM
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dang that sucks, well maybe i can sell the pistons on craigslist. Any experience with an ls5 head? i can get a set for free in rebuildable condition and keep the pistons maybe. I couldnt agree more on the roller cam, plus itll give me more turnover time if its hard to start on break in and it will be peace of mind. Thanks for the info so far guys!
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Old 01-04-2012, 03:39 PM
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How do i find a closed chamber piston on summit racing for example. Because their is no sub category that says "closed chamber piston". Are they defined by their compression distance or dome volume or both? If so, what would they be to fit a 454 .030 over block. thanks guys
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Old 01-04-2012, 05:26 PM
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Not many affordable new closed chamber piston sets available for 427. KB-176+.030 can be ordered. Closed chamber Keith Black hypers. Also has open chamber piston listed..

Fed-Mogul/Sealed Power/Speed Pro list a couple different pistons. But, many are no longer available since production was moved to India/Pakistan a few years ago. Maybe some in an obscure warehouse somewhere.
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Old 01-04-2012, 06:14 PM
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Well if i cant get pistons for under $750 i'll just find different heads cause they need a rebuild anyways, i just figured they were decent and i got them for free but oh well. Is it a clearance issue with the smaller combustion chamber or a compression issue? Are ls5 heads decent cause i can get some for free probably
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Old 01-04-2012, 08:02 PM
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awesome those keith blacks run only $360, not bad at all. Will i have to get my rotating assembly balanced again???
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Old 01-05-2012, 04:04 AM
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"Storm Warning"

You can get lots of inspiration on this Joe Sherman Racing built street 396 that uses the 390 head castings.

http://alteredwheelbasenova.com/
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Old 01-05-2012, 03:53 PM
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just read the whole build, very inspiring. Im not sure if those are 390 casting heads though because they are open chamber...
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Old 01-05-2012, 05:12 PM
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Okay, after much debating i have decided to ditch the 390 heads as i would have to spend 400 bucks on pistons, 250 on rebalance and still have to rebuild the heads and this is after i spent 6 hours porting one head.... BUT!!! i can get a set of 781 heads bare for free. I have heard these are some of the best oval port heads gm ever made. Are they all the same or are some different? are the exhaust ports rough on these and could use bowl blending and typical porting?
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Old 01-05-2012, 06:00 PM
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while you at it, get a 454 or 496 crank.

more cid = more power
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Old 01-05-2012, 07:56 PM
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that would be great, and if i had built the engine then i would have no doubt went with a 4" stroke but i didnt.... and this setup is ready to go all balanced, just needs heads, cam and intake. If i got a long stroke (496), would i have to get different length rods? id think so. Im pretty sure i could use the same rods depending on journal size if i were to go with the 4" stroke crank... correct me if im wrong. Thanks for the input, im considering it even though money is tight!
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Old 01-05-2012, 08:17 PM
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If you use the 781 heads. On a 427. Only aftermkt domed KB type open chamber pistons will work and they will have to be checked for dome clearance. (not TRW/FedMog/Sealed Power/Speed Pro/Manley/2308).

The 2308 style piston is the factory style L-88, 12-1 compression design. Hits in various places and is a hollow dome piston with not much meat on the top to cut on..

781 heads respond well to larger (and longer) valves..2.19+.100 long and 1.88+.050 long..

Yes, most 496 cranks require +.250 long rods unless you are using a tall deck..
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Old 01-05-2012, 08:26 PM
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why do only kb open chamber domed pistons work? Idk what it has yet unfortunately.... Thanks for the info, i was unaware big blocks had to be so strategically put together. way different ball game then the small blocks where almost any part will work on any size engine.
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