Big Blocks [Archive] - Nova Tech

: Big Blocks


whyman
Feb 4th, 11, 06:36 PM
Hi could someone tell me why the 396,427,454 castings are all different but the 396,402,427 share the same crank. & parts can be interchanged. ie- 396crank into a 454 = 427. Also can a 396 be bored to 454.Thanks.

brian oneil
Feb 4th, 11, 07:22 PM
Read through this post

http://www.camaros.net/forums/showthread.php?t=131618

Big Dave
Feb 4th, 11, 08:33 PM
Hi could someone tell me why the 396,427,454 castings are all different but the 396,402,427 share the same crank. & parts can be interchanged. ie- 396crank into a 454 = 427. Also can a 396 be bored to 454.Thanks.

A 402 is a 0.030" inch over bored 396. It shares the same stroke as a 427. The 427 and the 454 share the same bore size but have different length strokes. For this reason a 396's 3.760" length stroke crank installed in a 454 truck block gets you an out of balance 427. (I mention the out of balance part because the 396 crank has only three 0.750 inch thick counter weights for it's smaller, lighter pistons; compared to the four 0.875" inch thick counter weights found on a 427 crank which had larger heavier pistons).

There are four Chevrolet big block's cast with the standard 9.8 inch deck height. The 4.094" bore 396 and it's 0.030" inch overbored 402 cousin make up one casting. There is the obvious 4.250" bore 427 and 454. A special service block that was never installed in a production car though used in several hundred COPO Corvetes and Camaros for seven liter USSCA and CanAm and TransAm racing having a 4.440 inch bore 430 cubic inch short 3.500 inch stroke engine. Finally there is the other service block used by GMPP to build the ZZ502 that has a 4.470" bore.

To answer your question can a 396 inch block be bored out to make a 427 the answer is a very conditional yes! But only for one unique casting that is as scarce today as hen's teeth today. When the 396 went into production the board of directors had not decided whether the engine would be built as a new and improved 409 with a 4.313 inch bore and a 3.50 inch stroke or the one that got the final release two months before it went into production. Because of this the very first seven months production run of 396 blocks have extreemly thick cylinder walls that can be bored out safely to 4.440 inches (which will swallow a 427's puny bore) to make your own CanAm racer, or something much larger with a 454 crank in it.

Just bear in mind that only block casting number 3855962 cast before 10/65 (Feb-Sep) can accept this size of overbore. This block also requires a special cam shaft should you find one.

Big Dave

62 NovaWagon
Feb 5th, 11, 11:04 AM
A 402 is a 0.030" inch over bored 396. It shares the same stroke as a 427. The 427 and the 454 share the same bore size but have different length strokes. For this reason a 396's 3.760" length stroke crank installed in a 454 truck block gets you an out of balance 427. (I mention the out of balance part because the 396 crank has only three 0.750 inch thick counter weights for it's smaller, lighter pistons; compared to the four 0.875" inch thick counter weights found on a 427 crank which had larger heavier pistons).

There are four Chevrolet big block's cast with the standard 9.8 inch deck height. The 4.094" bore 396 and it's 0.030" inch overbored 402 cousin make up one casting. There is the obvious 4.250" bore 427 and 454. A special service block that was never installed in a production car though used in several hundred COPO Corvetes and Camaros for seven liter USSCA and CanAm and TransAm racing having a 4.440 inch bore 430 cubic inch short 3.500 inch stroke engine. Finally there is the other service block used by GMPP to build the ZZ502 that has a 4.470" bore.

To answer your question can a 396 inch block be bored out to make a 427 the answer is a very conditional yes! But only for one unique casting that is as scarce today as hen's teeth today. When the 396 went into production the board of directors had not decided whether the engine would be built as a new and improved 409 with a 4.313 inch bore and a 3.50 inch stroke or the one that got the final release two months before it went into production. Because of this the very first seven months production run of 396 blocks have extreemly thick cylinder walls that can be bored out safely to 4.440 inches (which will swallow a 427's puny bore) to make your own CanAm racer, or something much larger with a 454 crank in it.

Just bear in mind that only block casting number 3855962 cast before 10/65 (Feb-Sep) can accept this size of overbore. This block also requires a special cam shaft should you find one.

Big Dave

What he said!..

jackb
Feb 5th, 11, 11:22 AM
is a 402 a completely different block from a 396.
i read that is . so really dont know the difference.
i know it is the same as a 396 bored 30 over in size
but woundered if you bore a 402 how big can you go.

62 NovaWagon
Feb 5th, 11, 11:31 AM
It is the same block, only difference is since it came out in 70 it does not use a grooved rear cam journal!..

Big Dave
Feb 5th, 11, 12:03 PM
All thin wall casting Chevrolet motors (the last thick wall block cast was the venerable 235 stove bolt six) can go no more than 0.060 inch over on the bore. (you can bore any stock production block out more if you do not mind the cost of lining the block with eight new machined cast iron sleeves, though it is much cheaper to buy a larger bore aftermarket block.).

Some motors such as the SBC 400 shouldn't be bored more than 0.030 inch over because it will cause cooling issues if bored out too far. Further, not all blocks are candidates for the boring bar until you have first verified that the block is properly cast (no core shift) by first sonic checking the block cylinder wall thickness to verify they are of uniform thickness.

The 402 was designed to meet a great need as seen by the marketing department. This was because no manufacture offered a motor smaller than 400 cubic inches other than Chevrolet at the time it was introduced. (this is the same marketing department that retained the 396 name for the 402 engine when sold in a SS 396 Chevelle or SS Camaro because of the rep the motor had garnered with earlier owners). In fact the 402 is actually a 401 and is called a 402 because American Motors already had a 401 and no one wanted to associate the 402 big block with a Rambler (or heaven forbid a Gremlin); once again a marketing decision.

Other than the heads the only difference between the SBC 400 and the BBC 402 is 0.016 inch difference in the crank length throw (the 396, 402 and 427 all have a 3.766 inch stroke, compared to the 3.750 inch small block' arm). The pistons will actually interchange if they are flat tops and you do not mind cutting valve relief's for your valves.

The 400 SBC will make more power than a 402 and the car will be faster because he SBC has better heads (smaller ports generally, but a much better combustion chamber design), and it is also 280 pounds lighter which is nearly a 0.3 second advantage before you ever leave the starting line. Where a big block out shines a small block is in that it is capable of a larger displacement. So even though you can easily build a one horse per cube small block it usually can not go larger than 406 cubes. A big block starts at 402 cubes and builds up to 632 cubes with a stock block (granted it requires a tall deck truck block, but it is a production piece, not an aftermarket part that looks like any other block) and can also make one horse per cube. It doesn't take a rocket scientist to figure out that a 632 will blow away any 406 small block using a stock production block.

Big Dave

whyman
Feb 5th, 11, 07:55 PM
Thanks for the information.What im trying to figure out is whether the 402 i have is of standard bore & stroke. Fuel consumption is 12mpg us per mile, highway crousing at 60mph at 2800 rpm. The cam is not stock, but i would imagine its not performing at that speed. I run a vacuum advance dissy & a 770 vac holley, which is opperating on primaries at that speed. Anythoughts on this.

Big Dave
Feb 5th, 11, 08:52 PM
Thanks for the information.What im trying to figure out is whether the 402 i have is of standard bore & stroke. Fuel consumption is 12mpg us per mile, highway crousing at 60mph at 2800 rpm. The cam is not stock, but i would imagine its not performing at that speed. I run a vacuum advance dissy & a 770 vac holley, which is opperating on primaries at that speed. Anythoughts on this.

Sounds good to me. I have owned big blocks that have gotten as little as a half mile to the gallon of gas.

Big Dave

Philip
Feb 5th, 11, 09:33 PM
Thanks for the information.What im trying to figure out is whether the 402 i have is of standard bore & stroke. Anythoughts on this.

it would need to be taken apart and inspected to know for sure.

whyman
Feb 6th, 11, 04:25 AM
Thanks. I didnt want to pull it down just for that reason, so i will keep on driving.