Boring 396 to 427,and compression question - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-30-2006, 12:26 PM
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Boring 396 to 427,and compression question

Hello.I have a 1969 396 block that has been previously bored to 60 over.It came with some Grumpy World Heads.Now the cam snapped heartbroke etc.I would like to rebuild as a 427.According to my hotrodding chevy engines book there should be enough there to bore.I have a new crankshaft 427 weight.I also have some 68 closed chamber oval port heads.And some flat top 454 pistons that I would like to use.If I put these together, will the flat tops be A) useable with the closed chamber heads,B)Bring the compression down to a pump gas useable engine?Also if you have a cam suggestion I would appreciate it. Thanx Monte

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Old 01-30-2006, 12:35 PM
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Most 396 blocks will go to 427 but not all. A safer way would be to use a 454 block with your 396 crank, same bore as 427. As far as the flat top pistons. Even the low performance 396 and 427 had a small dome so you might be too low with flat tops.
Bob
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Old 01-30-2006, 12:52 PM
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block

Find a 4.250" bore block and sell your 396...The only way you could bore that block to 4.250 would be to sonic check it first, Untill you add up all the time and money fussing with the 396 you would be ahead just to start with the 4.250" bore block....
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Old 01-30-2006, 01:40 PM
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and 454 pistons will not work in a 427
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Old 01-30-2006, 01:49 PM
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Tricky to bore a 396 out that big.

Either bore the 396 to +0.070 to make a 413 or sell all your old parts on e-bay and get a 454 short block.

No, 454 pistons will not work with a 427 or 396 crank, wrong wrist pin height.
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Old 01-31-2006, 08:13 AM
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A big Thankyou.

Wow you guys are great.I like the idea of boring to over 70 for now.And I appreciate the advice about the sonic testing.I live near Cleveland Ohio,could anyone point me in the direction of a good machine shop for the boring?Also I have some Merlin Heads I need to have looked at.Thanx again
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Old 01-31-2006, 08:20 AM
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Relationships 396 to 402.

Ok,here is my next question.The 396 I have is a 69.As we know they became 402's.Now if I buy pistons that are 402's over 60,is that the same as a 396 over 90?And if it is would this still be better to use than my original 427 idea?Thanx
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Old 01-31-2006, 10:10 AM
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That is right. A +0.060 402 is a +0.090 396 which makes a 415 cid. Not too bad.

I would forget the 427 and just bore the 396 to 0.090" and use 396 pistons. And it would be best to use the stock 396 heads. The 396 heads have smaller combustion chambers than the World Product heads. The World Product heads were designed for 454 cid and larger. It would be hard to build compression with the world product heads.

It is possible to install larger valves in the 396 heads and do a little bowl work to increase performance. I have a set of 396 heads with larger valves (2.19/1.88) with a mild bowl job that flowed 260 cfm at 0.500" on the intake and 199 cfm at 0.500" on the exhaust. These heads had 110 cc chambers and small 240 cc intake ports.

But, I still think you would be happier with a 454. Buy a complete 454 (with 781 or 049 heads) in need of a rebuild. Then rebuild it to stock specs but install a piston with a little more compression and a cam with a little more duration. It is just easier to make more hp and torque with a 454 than with a 396 or a 427. Plus 454 pistons are cheaper.

Or maybe sell all your 396 and 427 stuff and buy a 454 short block and bolt on the world products heads. Those are the oval port street head, right?
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Old 01-31-2006, 10:50 AM
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Wow you are a big help.And I can tell you love those 454's.When I bought the Monte it had a built 396 over 60, high dome pistons, TeamG intake, Holley 0-4780-5,World rect. port heads.a never used nitrous system,built for the quarter mile.MSD 6 AL,the works.Tragedy struck when the cam snapped.Then I bought a 68, 396 over 30 running engine,but upon inspection on rebuild the block looked pretty rough inside.It came with some 68 heads#3917215,closed chamber used on the 396 and 427's.in great shape.Now what I would like to do is build a more streetable BB to put back in the Monte.I have so many 396,427 parts I'd like to keep it internally balanced.According to what I've read(and I know that doesn't equal experience).I should be able to get 375 hp with these heads.The Big Block Chevy Engine book said in 65 they had a 396 375/425 Hp.The Head data looks the same.And Thanks again for your time and knowledge. Monte
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Old 01-31-2006, 11:24 AM
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check out this 396 build-up.

http://www.chevyhiperformance.com/te...48_0309_build/
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Old 01-31-2006, 11:58 AM
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I just kept getting more and more excited as I kept on reading.When it said the engine dynoed at 384 that fit right in with what I had hoped for.I have a simular exhaust on the car allready.Thanx you are helping me to breath life into a truly deserving car........
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Old 02-01-2006, 06:34 PM
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How much less power would that motor make without the pocket port job and larger valves? That would be very close to my combination.
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Old 02-02-2006, 07:09 AM
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Well, a stock Goodwrench 350 picks up about 15 to 20hp with a some mild bowl work. It is hard to say on 396 since it is a BBC and a completely different engine with much better heads to begin with. But I would guess at least 10 hp down without the pocket port job and bigger valves. It would depend on the heads you are currently using.
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Old 02-02-2006, 09:09 AM
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There is a block that was bored to both 396 and 427 back in the 60s. I think if my memory is correct the last four numbers of the cast number are 5961. I don't think that a cast number block would be costructed with two cylinder wall thicknesses. Regardless I would sonic test the cylinder walls to be sure the walls haven't thined from the water jacket side as the result of rust. Usually around the top or bottom level of the freeze plug holes.
I sonic test every block before I bore it. Odd but most people won't pay for the sonic test and risk a water break through. The test is cheap insurance against thin wall.
If just one or so walls have a thin spot you have the option of a sleeve in that hole.
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