boring out a block

[Pirate]

Ford does not have the confidence in a "factory" production 351W that you do if you are placing it above a Boss 302 block. A Boss 351 block however is nearly worthless.

The funny part with the Boss 302 block is that it was also the basis for the 1968 302 tunnel port motors (Trans-Am Series)....and they blew up right and left. Shelby talked about having '7-engine weekends', where they replaced up to seven engines during one race weekend; they didn't have time to swap out 8....but the same short block (different pistons, obviously) was used in the '69 and '70 Boss 302 cars....and worked pretty well for the most part.

Concerning whether or not the Boss 302 is as strong or stronger than a regular production 351W block, it really depends on which 351W block we're talking about; I like the early (72-74 preferred, 69-71 has the 9.480 deck) blocks, but I've ran across two Boss 302 blocks that broke down the middle just like modern 302 blocks, both in N/A applications (both engines just a tick over 400 hp, one block was in a friend's machine shop up until a few years ago)....they're not a bad block, I'd just prefer something that wasn't....abused with high-rpm running, as that's about the only place those engines made power. In addition, it's fairly easy to find a roller-cam 351W block, where it's almost impossible to find a usable Boss unit....

Concerning the Boss 351....gawd, what a joke of a block. 4-bolt mains? My ass. That outer sets of main bolts are merely locating pins. The oiling system? What a train wreck. And don't even get me started on core shift in the cylinders, or how inconsistent the cylinder wall thickness is from bore to bore....the rods and cranks sure are tough, however....

[Mercracer]

The funny part with the Boss 302 block is that it was also the basis for the 1968 302 tunnel port motors (Trans-Am Series)....and they blew up right and left. Shelby talked about having '7-engine weekends', where they replaced up to seven engines during one race weekend; they didn't have time to swap out 8....but the same short block (different pistons, obviously) was used in the '69 and '70 Boss 302 cars....and worked pretty well for the most part.

A 351W factory block would cry like a little school girl if you tried to use it unmodified under the same application that Boss 302 engines lived in the Trans Am series back then.

Concerning whether or not the Boss 302 is as strong or stronger than a regular production 351W block, it really depends on which 351W block we're talking about; I like the early (72-74 preferred, 69-71 has the 9.480 deck) blocks, but I've ran across two Boss 302 blocks that broke down the middle just like modern 302 blocks, both in N/A applications (both engines just a tick over 400 hp, one block was in a friend's machine shop up until a few years ago)....they're not a bad block, I'd just prefer something that wasn't....abused with high-rpm running, as that's about the only place those engines made power. In addition, it's fairly easy to find a roller-cam 351W block, where it's almost impossible to find a usable Boss unit....

Ford rated the roller cam 351W block at 600hp when they were selling them through FRPP. Most engine builders would not even think of using the factory rods for a serious build. I have seen Boss 302 engines used in NMRA cars making well over 800HP with either boost or nitrous. It does not suprise me that you can find examples of hard used 20+ year old Boss 302 blocks which have failed. As you mentioned, they were used in a high RPM application where the RPMs are maintained which is much harder than 10 or less seconds at a time unless there is detonation. I will bet that many more 351W blocks of whatever vintage you choose failed with more regularity at a lower power level at lower RPMs.

[Pirate]

A 351W factory block would cry like a little school girl if you tried to use it unmodified under the same application that Boss 302 engines lived in the Trans Am series back then.



Ford rated the roller cam 351W block at 600hp when they were selling them through FRPP. Most engine builders would not even think of using the factory rods for a serious build. I have seen Boss 302 engines used in NMRA cars making well over 800HP with either boost or nitrous. It does not suprise me that you can find examples of hard used 20+ year old Boss 302 blocks which have failed. As you mentioned, they were used in a high RPM application where the RPMs are maintained which is much harder than 10 or less seconds at a time unless there is detonation. I will bet that many more 351W blocks of whatever vintage you choose failed with more regularity at a lower power level at lower RPMs.

Concerning the lifespan of the Boss 302 vs. a 351W block: Apples and....Grandma Smith apples. One can handle high-rpm (smaller main journals)....and the 351W, unless you do oiling system mods....smokes the main bearings because they're 460-sized.

Concerning Boss engines being used in NMRA competition, and making 800hp....I've also seen some making that kind of power, but it's highly recommended that one upgrade to a better block if you want it to live very long at that level....however, that being said, that's merely the block, not the stock block, rods, crank, etc. And we still get into actually finding one intact....

Whatever perceived/actual strengths both blocks have....there are very few Boss blocks remaining in circulation, and they command a premium....

[Mercracer]

Whatever perceived/actual strengths both blocks have....there are very few Boss blocks remaining in circulation, and they command a premium....

If someone is looking at a Boss 302 block, they have the $1000 to spend on one and are getting it because they are trying to save a few hundred instead of going with a $1800-$2000 B302 or R302 block.

It is absolutely silly to worry about a Boss block for a 400HP CV.

[Pirate]

It is absolutely silly to worry about a Boss block for a 400HP CV.

....yes, because nobody is going to buy one for use in a CV.


Case closed.

[1987cp]

Depends on the goals for the build, of course ... :p

[sick88tbird]

My 351W cost me like $180....with 60k miles. New top end and cam and it runs like a champ.....that's a much more budget approach than trying to build a boss 302. The whole thing about mexican blocks being stronger...it's a myth...a myth that started years ago when people thought the strength of a block came solely from it's weight.

[1987cp]

Nice that you got lucky with a junkyard shortblock. When I did the same with a 5.0L, it cost me more money and needed a rebuild.

Don't think anyone said a Boss was even remotely budget-friendly except in comparison to some high-priced aftermarket blocks ......

[sick88tbird]

Nice that you got lucky with a junkyard shortblock. When I did the same with a 5.0L, it cost me more money and needed a rebuild.

Don't think anyone said a Boss was even remotely budget-friendly except in comparison to some high-priced aftermarket blocks ......

I wouldn't have just dropped a j-yard shortblock in...I got if from a guy I worked with, he junked cars on the side and scrapped an E250 that was wrecked but it still ran and drove....only 60k miles...still had the factory motorcraft plugs with the blue dot on top. Plus he was a really trust-worthy guy...lol.