427 Engine rebuild - Impala Tech
Engine General Engine Discussion.

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post #1 of 13 (permalink) Old 11-30-2019, 09:51 AM Thread Starter
 
 
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427 Engine rebuild

I'm looking for some advice. I will be pulling my numbers matching 1968 SS 427 motor out to be rebuilt. I want to know if I should upgrade from a flat tappet cam to a roller rocker set up. Also do I have to have the block decked, because I need to keep the engine pad numbers.
Any and all advice is much appreciated.
Thanks Tom B.
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post #2 of 13 (permalink) Old 11-30-2019, 10:22 AM
 
 
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One thing the rebuilder did on a straight 6 I had rebuilt is install hardened valve seats to help wear with unleaded gas. The block was decked because it had some pitting as well. I had a very good rebuilder and a very worn engine so I left it up to him on what needed doing. Good luck
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post #3 of 13 (permalink) Old 11-30-2019, 10:24 AM Thread Starter
 
 
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Good idea about the hardened seats. Thanks
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post #4 of 13 (permalink) Old 11-30-2019, 10:38 AM
 
 
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This is my rebuilt inline 6 for my nova
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post #5 of 13 (permalink) Old 11-30-2019, 10:49 AM
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Pull your numbers matching engine and put it in a bag. You can store it on an engine stand or under a bench. Then buy a 454 out of a light pickup and rebuild that as a 496 or bigger motor.

Big blocks are not very efficient on today's pump gas. To get anything out of them you have to increase the displacement. A Mark IV BBC can be easily stroked with a 4 inch stroke crank (so a 454 stroked a quarter inch to get to 496 cubes by boring it 0.060" over) and a more modern Gen V or Gen VI block can be stroked to 4 inch to obtain a 518 cube motor. You will need a new oil pan either way as only a light truck has had a 454 under the hood since 1974. And the truck pan will not fit a car chassis (this goes for all of GMPP's 454 or 502 crate engines as they all ship with pick-up truck pans).

You can recycle your entire top end or buy replacement aluminum heads. You want a roller cam because modern reduced ZDDP motor oil will fail; wiping the cam, if you try to use it with a flat tappet cam. If you want the cheaper flat tappet then you will be paying a lot more for ZDDP rich motor oil which usually runs $8 bucks a quart. So if you run the engine much over time you would actually save money installing a roller cam in the first place.

You can stamp the rebuilt block with your old numbers if you like them: though numbers won't make it any faster or more reliable. Your rebuilt truck engine will look just like your old 427 with the proper decals.

Big Dave
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post #6 of 13 (permalink) Old 12-01-2019, 10:53 AM Thread Starter
 
 
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Thanks Dave' but it took me many years to find a real SS427 and numbers matching engine so I really want to put the original mill back in.
Any suggestions along that line would be very appreciated.
Thanks
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post #7 of 13 (permalink) Old 12-01-2019, 12:24 PM
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If it is the original engine it will all fit, without looking for aftermarket parts. The engine you have now requires premium leaded gas and makes it's power by reving. Think of it as a 350 horse 327 engine only super sized. At 6,800 RPM it will make 480 horse on 100 octane fuel (it was derated not by changing any parts for the insurance company, but by testing the engine power at a much lower RPM).

So your 427 engine is just the way the engineers designed it back in 1963 for NASCAR racing, including it's domed high compression pistons. It will also have the closed bath tub shaped small combustion chamber heads that shroud the valves. In 1967 that head had the walls of the combustion chamber laid back to open the chamber up for free breathing. This dropped not only the static compression, but also the power it makes if you do not use a hemi-spherical dome cut in half piston to fill the void (why the Rat was called a Semi Hemi).

With flat tops it will make more than a 396 with open chamber heads, but not as much as it would with 11.0:1 pistons and 100 octane fuel. The big block was designed to be a high compression deep breathing high reving race car engine. That design and tooling was paid for by also using it as a truck engine, but that truck engine had different heads, pistons, block, and cam to make it a slow reving torque beast that is an additional inch wider and two inches taller than a passenger BBC. (the only common parts between the truck and passenger engine was the water pump and valve covers.

The open chamber 454 replaced the 427 in the production line up in 1971 (introduced in 1970 exclusive to the Corvette and the Chevelle SS). In 1972 the compression dropped in an effort to save the engine for use in cars, but the power drop off was so great that people opted for the 350 small block instead of the smog motor version of the big block. It was last installed in a car in 1973 (carried over to the Corvette as an option through 1974 when it was dropped there also). But like I said the small block had more power and better mileage which was important in 1973 because of the OPEC crude oil embargo. This made gas hard to find in 1973, and by 1976 that gas was unleaded with 87 being the highest octane you could buy.

By 1974 you could buy a 454 SS Chevelle or Corvette for twenty to thirty percent of the resale value of a 427 or 454 version of the same car (Hemi 'cudas and 440 GTX-Road runners were being crushed because no one wanted them at any price). That is why the seventies trough the late nieties were called smog era cars and if you wanted a powerful fast ride you bought a BMW or a Porsche, or a Jap hot rod like the Datsun Z.

It wasn't until GM introduced the redesigned second generation small block that power returned. GM did this redesign of the small block not because people were crying for more powerful engines; but to reduce emissions as mandated by ever tightening standards. Making more horsepower was a side benefit that people quickly noticed. Especially when older muscle cars still on the road had their doors blown off by a 4600 pound four door Impala SS.

The LS-x engines know as generation three small blocks replaced the gen two SBC two years after they were introduced; so you may never have even heard of them. From 1974 and up the only vehicle with a BBC installed under the hood was a light truck, because they were exempt from the emission laws of the era (it had to be a three quarter ton or a one ton truck to be exempt).

Big Dave

Last edited by Big Dave; 12-01-2019 at 12:39 PM. Reason: spleling
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post #8 of 13 (permalink) Old 12-01-2019, 02:26 PM
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Talk to your local machine shop. Tell them exactly what you want. No machining of numbers. The block may or not need over boring.



Why does it need a rebuild? Smoke? Compression test results?

Two doors, four doors, wagons, and ragtops.
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post #9 of 13 (permalink) Old 12-01-2019, 05:25 PM Thread Starter
 
 
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In general it is just tired. doesn't ping with 93 octane, I'm sure the heads are worn to enable it to run on 93 octane. Been together for 50 plus years.
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post #10 of 13 (permalink) Old 12-05-2019, 05:20 PM
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I'm a fan of changing to the roller cam setup, I've had it done on 2 engines now.

Regarding the decking of the block, I think you have to 'go through the motion' so that you can clean up anything too uneven but somehow ensuring 100% that the machine shop guy knows not to go so far as to wipe out those precious front pad digits.

Good luck man!

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #11 of 13 (permalink) Old 12-06-2019, 09:28 AM Thread Starter
 
 
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68 Big block 427 engine rebuild

Thanks for the info and support.
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post #12 of 13 (permalink) Old 12-06-2019, 12:31 PM
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Decking without removing the numbers can be done it is just going to cost you a lot more. I have never seen any one pop a hood at a car show and say oh look an IE application code! Only you will know that it is all original unless you make a big sign that states it is numbers matching. Even then only you an very few others at the show will care. All the show goers are interested in are those wide valve covers and what you have done to it to make an all original faster.

In 1966 the 427 was a brand new engine. The 427 in a Biscayne two door sedan was considered to be a sleeper; because no one knew anything about the combination. That, and expectations of performance were low compared to a Chrysler with a Hemi or a Ford with a 427 side oiler which where tearing up the track in that time period.

In 1966 the best performing car (that year's stock and super stock winner) was a 350 horse 327 in a Chevy II SS. (because it offered the greatest horsepower to weight of any vehicle this side of a motorcycle). In 1967 it was the 375 horse Camaro in stock and a 427 Camaro in Super Stock once again it was power to weight.

In 1968 the Impala and Caprice were running neck and neck in size and weight with a Cadillac that had a 472 cubic inch V8 powering it. Ford introduced the 427 SHOC engine that made Fords competitive again in racing and in stock and super stock they had the 428-429 powered Mustangs From 1970 through 1975 it was all Chrysler thanks to the 426 Hemi being offered in lighter car bodies.

Newton said it best with his second law of motion with F=ma. Nothing has changed since then, and it is all about power to weight which is why in the sixties it was all about larger engines being introduced every year. The 472 Caddy became a 500 cube engine, the BBC 396 became a 454, and though Chrysler lost the Hemi head to emissions, it still had their 440 as the big dawg.

You can not easily change your car's weight, but you can easily turn a 427 into a 496 and still have all the original numbers and decals on the air cleaner cover. Because the Mark IV block has the mains fed by an oil gallery it is limited in the length of the stroke, so the 4.25" stroke is the max for a Mark IV block. A Gen V block can contain a 4.5 inch stroke because the oil gallery was moved above the cam tunnel.

Using a new Gen V 454 block, that doesn't leak oil thanks to a one piece rear main oil seal, you change the displacement by lengthening the 4.25 inch bore block by adding to the stroke length.

427 had a 3.76" stroke
454 had a 4.00" stroke
496 has a 4.25" stroke
511 has a 4.38" stroke and a
525 has a 4.50" stroke

The 4.500 bore ZZ 502 Gen VI block adds even more cubes, and still looks like your 427. They all look alike from the outside. Retain stock mufflers and dual exhaust pipes you can speak softly and still carry a big stick to beat the competition with. The only 427 that I would run would be a stroked SBC 400 block thanks to today's gasoline.

Back when 104 octane rated Sunoco 260 was pump gas I ran an L-88 427 in my 1968 Camaro RS SS thanks to a Yenko built block in my Baldwin Motion III conversion. It put my Edelbrock tunnel ram equipped, Vertex mag fired, solid roller Crane cam Camaro into the low ten teens with 14 inch wide Firestone slicks to launch it. Power to weight!

Big Dave
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post #13 of 13 (permalink) Old 12-06-2019, 08:39 PM
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