500rwhp the real limit?

Discussion in 'Fox 5.0 Mustang Tech' started by dubbsix, Jan 6, 2007.


  1. millhouse

    millhouse Founding Member

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    What really splits blocks is the lack of material in crucial areas. The cracks typically start at the main journals and work their way up through the lifter valley. Detonation is not the cause of the block weakness. That's not to say that it wont contribute to failure...it's not the cause. What really splits the block is the exceding of the torque limits put on the mains and webbing.

    I've said it before, stock internals will outlast the stock block...be them forged or hyperutectic.

    As far as n/a outlasting f/i goes...I don't see it happeing at similar h/p levels. To reach the h/p levels you get with forced induction requires extremely high compression and extreme rpms. Your streesing the living hell out of the block doing so...and it's not going to be any more safe than a f/i or nitrious setup.
  2. Speeds8erM-1

    Speeds8erM-1 Founding Member

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    Well, if you run lean a piston can go first but the block wont be far behind, the stock cranks CAN fail before the stock block but 8 times out of 10 the block is what can go first. Power rating wise, not tune issue, the block is the weakest link.

    "it's all in the tune" is bs and true at the same time, NO MATTER HOW TUNED the stock block will NEVER be RELIABLE (key word there!!!!!) at 600 rwhp and will never last at 700-800-900 rwhp.

    The ones that last the longest are generally track cars that see WOT passes 3 times a week or less. If you BEAT the **** out of the car at 550+ rwhp it's not gonna last long, 500 might last longer. The real factor is ACTUAL rwhp, aka what the car actually makes, the motor doesnt know anything about an SAE correction factor, cold night, more HP = boom if pushing it.
  3. NKau

    NKau Founding Member

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    You can blow up a lot of stock $100-$150 junkyard shortblocks with excessive forced induction for the price of an aftermarket block/internals :D
  4. seijirou

    seijirou Founding Member

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    That's not counting the cost of each build, and paying yourself for the labor if you build it yourself. Realisitically, 2 rebuilt stock motors will go over the cost of building 1 good aftermarket block.
  5. seijirou

    seijirou Founding Member

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    :nice:
  6. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    :nice: Exactly, what a waste a Money the 302 Sportsman is, the 351 Sportsman however is a nice piece and holds decent power.
  7. seijirou

    seijirou Founding Member

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    How weak is the factory 351 casting? Are we talking basically the same limits of the 302?
  8. millhouse

    millhouse Founding Member

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    From what I can remember they are usual thought safe up to 750-800 rwhp.
  9. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    The latemodel roller 351 blocks unfortunalty are not much stronger then the 302, they still split at the #2 main and lifter valley. The older castings can hold 800 or so, sometimes more with a 4 bolt main conversion to keep the crank from walking. Those blocks are 69-70 9.48" deck, 71-74 9.502" deck. After 74 the blocks changed slightly and have less nickel in them as well, although I've made 500HP from them with a power adder in a street car with no issues.

    The 351W has it's own set of issues, 3" mains, oiling issues to the front lifters, etc...all which can be helped by doing some proper maching, plumbing, etc..
  10. seijirou

    seijirou Founding Member

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    I've got an 88 block with 206K I've been thinking about using. I've heard of people using special bearing spacers or something and turning down the crank to use cleveland main bearings. But I've always wondered why... is it only the frictional losses?... What is it about 3" mains that aren't liked? And if you have the time, what machining is needed? I always thought it was the clevelands that had oiling problems, this is the first I've heard about a Windsor. I guess while I'm at it, if I wanted to use a 3.85 crank, does it require any clearancing?
  11. millhouse

    millhouse Founding Member

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    After a quick search over on TM it seems the general consensus is ~ 700 h/p on a late model 351…although there have been some that have gotten away with more. There is not nearly as much info on strength like the 302.

    On a side note I stumbled across a great reference thread I forgot about. http://www.turbomustangs.com/smf/index.php?topic=23254.0 :nice:
  12. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    It is really about bearing speed/surface area, yes they do have the bearing spacers to go to a Clevland main but I here mixed results about them. I personally have never used a set.... They need to be align honed as far as I know to make sure it is all straight before you mock up and use them. The oiling issue is there but most guys do not know how to correct it, or just do not pay enough attention to it, most builders do not bother with it more most street combo's. I can fill you in if needed... I pay very close attention to my bearing clearances on a 3" main, they are crucial.

    With the 3.85" stroke it usually requies some clearancing, depends on the exact rod and bolt combo.
  13. seijirou

    seijirou Founding Member

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    Well I'll tell you what I have in mind, and feel free to let me know any suggestions you may have. I'm always a sponge for all the information that I can get. My goal at this time is an EFI turbo clevor for street use, and some club road race duty. The turbos will be on the smaller side, i'm not looking for peak output and heaven high rpms, 400-450 rwhp is probably more than enough. The aim is some grunt in the mid and high to push through longer 3.08 gears.

    With that power I'm hearing the stock 351 rods are up to the task, and the block should be aswell. Any oiling problems would concern me though naturally, it may not be alot of power, but I don't anticipate a lazy life for this motor. The pistons would have to be aftermarket most probably for the canted valves, I don't know 100% that a modified/cleveland piston would work properly yet. I don't know why I wouldn't use ARP fasteners unless someone can really convince me that it'd be a waste of money. If there's anything else that would benifit you to know, please ask!
    Any insight that you care to share would be vastly appreciated! :flag:
  14. NKau

    NKau Founding Member

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    Build? What does it cost to re-ring and put new bearings in a stock bore 5.0? Why pay myself for labor; it's a hobby :p I realize that unless you really enjoy working on your car a lot or do not value reliability, this isn't a wise way to go. Just from a car-crafter/cheap, stupid fun viewpoint, you could really blow up an awful lot of junkyard 5.0 engines before approaching the price of a 'built' motor. If I ever seriously venture into into the forced induction arena, this would be my approach, due mainly to poverty. Not sure why you don't see more people do this (other than the work and reliability issues).
  15. 09secondGT

    09secondGT Member

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    my car made 535 rwhp and 510 tq. with stock block, stock balanced crank, rods, pistons and i had a main girdle and run 10.86@127, took out the motor for an a4 block 342 before it split!!!!!!
  16. 93GTStang

    93GTStang Founding Member

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    Trying to guess about the HP rating of a stock block is like guessing if a T-5 will blow it, it's not If it is when. I have had friends run 10's with ORIGINAL T-5 trannies and never break, and I broke 2 on the street with a 12 second car. Like stated, anything over 450rwhp is going to be pushing it. A turbo car probably more since it has less parasitic loss.

    A guy at the track I run at had a 347 based on a Sportsman block and it held for awhile with a T-Trim running 9.87@142 with a built AOD. But eventually it broke.

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