428 motor

[miata347]

what are 428 a blocks selling for

[jtschug]

Depends on:

1) Condition of the block (bore, deck, wall thickness, repairs, cracks, etc)
2) Type of 428 - (passenger car, cobrajet, SCJ, Industrial, etc.)
3) Date code - some are more valuable than others. A lot were cast in 1974 just before they shut down the plant
4) Credibility - is this a greasy block just stripped, a rusty block from the junkyard, or a cleaned and inspected block from a reputable seller?

[sseebart]

I just purchased an FE block. Generally, a refurbished block, bored .030 over and tested will run somewhere in the $1100 - $1400. Add a little extra if you want a block with a specific date code.

Just to clarify, while there are numerous FE variations out there 352 - 390 - 428, the differences in displacement are determined by the rotating assembly, not the block itself.

And, one last point--when I was looking around for a used block, I found plenty of scams and false leads on craigslist and eBay. I went with a reputable dealer that others in the Thunderbird community know and trust. If you go another route, be ready to perform a thorough inspection of the block before handing over any cash.

~Steve

[redstangbob]

the differences in displacement are determined by the rotating assembly, not the block itself.

Not so, a block cast as a 428 has cylinders that are thick enough for the 428 bore. Some guys have safely taken a 390 out to a 428 bore and changed the crank to gain the needed stroke, but some have tried and run the cutter into air if the block had thin cylinder castings and core shift. true 428 blocks can be identified in a few ways, Google is your friend. good luck, Bob C

[jtschug]

The most common FE blocks are 390, 427, and 428. The blocks are different.

390 standard bore is 4.05" 428 standard bore is 4.13" 427 standard bore is 4.23". Max recommended overbore for 390 and 428 is 0.040", 427 is 0.020", so you can not bore a 390 block into a 428 block, the cylinder walls will be too thin. With a sonic check it is possible to confirm if a block can be overbored beyond 0.040", so you will see 0.060" overbores out there.