Author Topic: Ford's Big Bore Boss 302 block  (Read 3331 times)

mlplunkett

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Ford's Big Bore Boss 302 block
« on: August 30, 2021, 11:27:26 AM »
I'm planning the engine build for my 65 GT350R tribute and want to use modern internals (a 302 roller block) while maintaining as much of the original external appearance of the Hipo 289 as practical. I'm thinking about stepping up to the large-bore Boss 302 block from Ford Performance. It would give me the strength of 4-bolt mains and additional interior webbing, roller lifters, extra displacement from the 4.2" bore (in addition to what I would get from 331 stroker components) and with aluminum heads (my only external giveaway) and 10:1 compression I think I'll have upwards of 450 HP. Is anyone aware of anything about these blocks that would prevent me from using all the other Shelby external parts (intake, carb, valve covers, distributor, competition oil pan, etc.) to make this modern block look like a 289?

https://shop.watsonracing.com/BOSS-302-CYLINDER-BLOCK-BIG-BORE-M-6010-A460BB-p/wr-6010-b302bb.htm
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gt350hr

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Re: Ford's Big Bore Boss 302 block
« Reply #1 on: August 30, 2021, 11:45:29 AM »
  Maximum safe bore on those blocks is 4.155 not 4.200. They do not accept a "standard" camshaft because of the "common size" cam bearing machining. 1/2" head bolts ( 351W) head bolts are required as well. The block is significantly heavier than an early 289 block. "I" would ( and have) use a '65-69 block and add Cobra Automotive "HiPo" caps. My 520hp 331 has done this for 20 years without issue. However it is your money.
   Randy
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98SVT - was 06GT

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Re: Ford's Big Bore Boss 302 block
« Reply #2 on: August 30, 2021, 12:32:44 PM »
Trust Randy - put that $2,100 somewhere else in the motor. The best rotating parts you can find is the secret to long life at high RPMs. If you're stuck on four main bolts find a good used Boss 302 block. Of course the screw in freeze plugs will be a give away.
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gt350hr

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Re: Ford's Big Bore Boss 302 block
« Reply #3 on: August 30, 2021, 12:49:59 PM »
   "My way " is NOT  "the only way" for sure but it works. The "big bore" is not a great advantage on an "inline" valve head. It is a big deal on a canted valve ( Boss 302) head. Been there , done that. As my friend pbf777 reminded me there IS a "conversion" cam bearing set from Durabond that allows the "standard" cams to be used. "I" would still spend less and use a stroker crank/rods , just me.
   Randy
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pbf777

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Re: Ford's Big Bore Boss 302 block
« Reply #4 on: August 30, 2021, 04:08:46 PM »
Is anyone aware of anything about these blocks that would prevent me from using all the other Shelby external parts (intake, carb, valve covers, distributor, competition oil pan, etc.) to make this modern block look like a 289?


      To the best of my memory, the only components not compatible between the O.E.M. production blocks would be the head retention fasteners (the BOSS 302 blocks utilizes fasteners with are about 1/2" longer), a few other fasteners, the cam bearings, and perhaps a little "fitting" of the oil pan.

      Now I'm not sure how much like an O.E.M. 289 block you expect to try and make any of the current production aftermarket blocks to be, but the castings are quite different in external appearances.

      If I were wanting an improved block over the production unit, but that replicated the originals' appearance, the one to find is the older Ford Motorsport M-6010-A4 unit (though these were not intended for the .125+ over-bore); but these are not easily found as they are searched for by many others with the same intent.     ;)

     Scott.
 
« Last Edit: August 30, 2021, 04:12:55 PM by pbf777 »

gt350hr

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Re: Ford's Big Bore Boss 302 block
« Reply #5 on: August 30, 2021, 04:43:28 PM »
     My A4 block was safe to 4.100 in a road race type use or 4.125 in a drag race application. I used a 3.5 stroke , Moldex crank for 351ci. The new RDI aluminum block is 4.125 for 374ci. 60 lbs less weight and 23 more inches.
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mlplunkett

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Re: Ford's Big Bore Boss 302 block
« Reply #6 on: August 30, 2021, 08:16:28 PM »
Thanks guys. That's exactly the kind of input I was looking for. I'll give this some more thought but it sounds like the new block isn't worth the extra $. I wasn't really hung up on the overbore but since they charge the same for the big bore as they do the standard bore I figured it was just free displacement which is free HP. I'll look for a good 302 roller block and go with a stroker and a good set of aluminum heads. I've been told that the Scat and Eagle stroker packages are about the same from a quality standpoint. Any arguments on that front? Seems like I've seen more good press on the Trick Flo heads than others but didn't find a recent comparison test.
« Last Edit: August 30, 2021, 08:27:39 PM by mlplunkett »
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gt350hr

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Re: Ford's Big Bore Boss 302 block
« Reply #7 on: August 31, 2021, 10:37:23 AM »
 Late model hyd roller blocks have a 450 hp "safe limit". Don't waste money on a girdle ( main or valley) as they are worthless. Keep the RPMs down ( 6-6,500) as the blocks also crack because of harmonics. Usually the second main web begins to split . If not abused , it will work fine.
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pbf777

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Re: Ford's Big Bore Boss 302 block
« Reply #8 on: August 31, 2021, 01:47:13 PM »
I think I'll have upwards of 450 HP.

Late model hyd roller blocks ................Keep the RPMs down............... If not abused , it will work fine.


      Randy has provided very sage advice, and I agree, but would like to add an emphasis on the "if not abused" part of the statement, as although in instances these blocks have been pushed to this level, and even beyond it for many, but understand for some others, the results,........well.........not so good.      :-\

      Do understand that these O.E.M. blocks were not truly engineered to tolerate such loads, and although as we have practiced in the performance world since its' inception, we push the envelope until realizing failures, that at an unacceptable rate, and then will draw a new line in the sand as to where 'WE' think the components are suitable; but understand that this line is not as definitive as one may often think, and failures, though they should not be necessarily unexpected, are surely unappreciated.     ;)

      Please realize that my perspective is one of a person who is not a real mechanical engineer, and probably suffers from trying to over-build anything I come into contact with; as if the sum of the metal in the structure can be made greater or there is room for one more bolt or just a larger one, then why not mentality.  But ya-know, the guys in battle, in the tank with the most steel armor between them and the munitions being thrust in their direction, usually feel more comfortable and generally will experience better results in survivability   ::)

      Scott.

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Re: Ford's Big Bore Boss 302 block
« Reply #9 on: August 31, 2021, 02:05:57 PM »
Please realize that my perspective is one of a person who is not a real mechanical engineer, and probably suffers from trying to over-build anything I come into contact with;

This is sage advice. It's cheaper to over build the first time than have it break and need to do it all over again.
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gt350hr

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Re: Ford's Big Bore Boss 302 block
« Reply #10 on: August 31, 2021, 05:05:26 PM »
    The 5.0 roller block was designed as a "weight savings" block. Bolt holes that used to be "blind" are now "open" ( head bolts , main cap bolts etc.) The main webs were thinned to where they look anorexic. None of this is condusive to reliability with high horsepower. keep that in mind when using them.
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mlplunkett

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Re: Ford's Big Bore Boss 302 block
« Reply #11 on: September 01, 2021, 02:37:26 PM »
So the early 289 blocks are stronger than a 302 roller block? Any issues with converting the early blocks to roller lifters?
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gt350hr

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Re: Ford's Big Bore Boss 302 block
« Reply #12 on: September 01, 2021, 03:37:15 PM »
   Use "retro fit" tie bar lifters and it's a breeze.
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pbf777

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Re: Ford's Big Bore Boss 302 block
« Reply #13 on: September 01, 2021, 03:48:42 PM »
So the early 289 blocks are stronger than a 302 roller block?

     YES!    ;)

   Use "retro fit" tie bar lifters and it's a breeze.

     YES!     :)

     But just costs more!     :o

     Scott.

mlplunkett

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Re: Ford's Big Bore Boss 302 block
« Reply #14 on: September 02, 2021, 03:52:43 PM »
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