306 vs 347 stroker

Discussion in 'Fox 5.0 Mustang Tech' started by coreyhayman, Jun 8, 2005.


  1. coreyhayman

    coreyhayman New Member

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    right now iv got a 306 in my car thats in need of a rebuild....is it worth it to go with a 347 stroker or just leave the motor as a 306?.......is it much of a difference in power from a 347 vs a 306?........my mods currently are 306, holley 65-dp carb, torker intake, ported 351w heads, crane roller rockers,x-cam,pulleys, long tubre headers, n.o.s 200 shot nitrous kit, scat crank
     
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  2. diponyou50

    diponyou50 Member

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    i have no exp but form what ive read 347s have tons more torque,and if you can afford it i would deffinately get the stroker
     
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  3. srothfuss

    srothfuss Last night I stabbed the same guy 7 times in a row

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    Typically Displacement = HP. But it also means stroking out your block to it's maximum limits so you really have longevity problems. A 347 isn't bad, but it's just not something that you want to put in a daily driver. Your best bet is a 311 or 331 to get some more durability out of the motor.

    I can't give you an exact figure on the HP gains. Maybe someone else though...?
     
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  4. accidentprone86

    accidentprone86 New Member

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    I think your block will need more machiening to allow for the shorter rods and angels. "tell me if i am talking out of my ass"
    That in mind it is already bored so i would do it if money isnt a HUGH concern.

    And why would changing the stroke of the motor decrese durability? Isnt it just moving the piston further down to allow more cubic inches, i.e. air and fuel?
     
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  5. ms93gt

    ms93gt New Member

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    It's nothing to do with the stroke it's the fact that the block is being bored so much it weakens it.
     
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  6. accidentprone86

    accidentprone86 New Member

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    Is .030 over so much? 306 331 and 347 all have the same bore.
    a 342 and 327 is a block with stock 4 inch bore with a 347 and 331 storker kit in it.
     
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  7. 90mustangGT

    90mustangGT I felt sorry for girls because Founding Member

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    To prep the block for a 347 only cost a little more because you usually need to notch the bottom of the cylinders, which can be done at home. Having the stock crank machined, stock rods magnafluzed, cleaned, and pressed into the new pistons, then buying new pistons, the cost difference isn't that much more than just buying a new crank and rods. The only thing is you'll probally need a different flywheel and balancer because most strokers are 27oz while 302-306 is usually 50oz. The power to price ratio is definatly worth it. Strokers (esp 347) usually make lots more torque and more HP to boot. With decent flowing induction and exaust, and the right cam, 400hp and 350tq is not a tall order.

    I have a 306 sitting in the garage right now, forged pistons, nicley machined. I got good deal on it but I am hesitant because of my dream/goal and I am thinking of selling it to put the money towards a 347.
     
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  8. accidentprone86

    accidentprone86 New Member

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    so would stroking the rotating assembly to make 347 ci make the engien less reliable? I think i have herd that somewhere before.
    Also since the piston is pulled further down in the stroke, dose it go as far back up "tdc" as it would stock? if so what makes up for the difference if the shorter rods is what pulls the piston down further.

    Hope i am helping you as well as me with my questions, so i am not jacking your thread.
     
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  9. 89CopCoupe

    89CopCoupe Banned

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    Longevity:

    The piston in a 347 travels faster (at the same rpm) than a 302 due to the longer stroke ...

    Simple physics : 1000rpm .. distance traveled by piston = 3.0" (302) vs 3.4"(347) per revolution

    ... the 347 must travel a greater distance in the same amount of time ... therefore it moves faster in the cylinder.

    Plus a 347's rotating assembly has sharper angles and greater force in typical direction changes due to both size engines being confined within the same size box or block.
    ... 347s side load the piston into the cylinder with greater force therefore creating greater friction and greater friction creates greater wear.

    331 has the same physical issues, only not as great :nice:
     
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  10. Allforspeed

    Allforspeed New Member

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    from what i understand, a lot of the durability issues on a 347 come from where the rings on the piston and the wrist pin go together, they end up with poor oil control quite often also, the more you stroke a motor, the less meat on the piston there is on top, fordmuscle.com has a real good article on this, a lot of engine builders think that the worse the rod ratio gets the worse the motor ultimately performs at the limits, smokey yunik (sp?) was a real leader in this theory, thats why 331's are so common, more displacement, better rod ratio due to shorter stroke and a stronger piston, i dont think i would do a 347, i have heard some horror stories of them only lasting 10k miles or less:( the better rod ratio of the 331 should make similar power but with more reliability, with a blower either displacement will make more than enough power to crack a stock block though so the choice is yours, i would just go 306 with a blower or nitrous, if i wanted more displacement i would just build a 351W that are much, much stronger and not real expensive anyway. any path is a good one and they will all be tons of fun, i have never built a 347 though, so this is just my opinion, anyone else?
     
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  11. Grn92LX

    Grn92LX Fidanza Man! Founding Member

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    Physics vs the real world ;)

    If you believe what you just typed that absolutely rules out EVER buying a 4.6L stang with its longer 3.60" stroke. Afterall, piston speed wears the engine out faster, right?

    Rick 91GT on here is building my 347 as we speak. For sh its and giggles I asked his thoughts on the stuff I read on the net. He said "its all bullsh it if its built right". Another builder I talked to on another site has a 363" (same 3.40 stroke as a 347) with 185k miles.

    Some people need to get their ass out of books and magazines and see whats going on in the REAL world ;)

    Fwiw, my 347 has the SAME rod ratio as a 331. Not that rod ratio means a fu cking thing but with the 5.315" pistons my 347 has its the same rod ratio as a 331.
     
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  12. 89CopCoupe

    89CopCoupe Banned

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    What is the deck height on a 4.6?
    What are the journal diameters?
    Why can a 302 be built to spin and sustain more rpms than a 347 in the "real world"

    Don't try to @$$ clown me ... it is a physical reality that a 347 has dimensional drawbacks ... ask some people with "real world" experience.

    Not that your 347 won't be sweet and last plenty of miles for you, but post up the 185K when you get there. ;)

    347 with 5.315 rod = 1.563RR
    331 with 5.315 rod = 1.635RR
    347 with 5.400 rod = 1.588RR
    331 with 5.400 rod = 1.662RR :scratch: With these "sames", the space shuttle would never make it off the ground :nice:
     
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  13. 90mustangGT

    90mustangGT I felt sorry for girls because Founding Member

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    Some people build 347's that only last 5K miles, well I have scene the same thing with 306's. Blame it on rod ratio, blame it on the break in procedure, even the oil your using, when it comes down to it it's in the build. A 306 probally will have longer life than a 347 considering build and quality parts being equal, but I promise the difference won't be known to someone who races thier car because they will probally blow it out, not wear it out.
     
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  14. Grn92LX

    Grn92LX Fidanza Man! Founding Member

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    I did ask people in the real world. Remember, i'm doing a 347 as we speak. My builder posts on these sites, maybe he'll chime in. If its done right, theres nothing to worry about :nice:
     
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  15. Daggar

    Daggar New Member

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    You seem to be confusing our 'old school' stroker problems with the improvements that have been made in the last 10 years. Things like offset wrist pin locations and things of that nature. It's true that stokers at one time had some serious issues and were not great 'streeters' but things have changed. A builder worth his salt can design and build a reliable 331 or 347 stroker these days. Reliability would only be an issue if you tried milking every ounce of HP out one those blocks and ended up exceeding the limitations of the block and mains itself. That portion of the subject is an entirely different matter.
     
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  16. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    Exactly :nice:

    The 331 is better IMO because of the better piston/rod ratio it gives...that is why I would choose it over a 347 for a daily driver.

    Grn92lx - There is many more factors in the 4.6L than the 5.0L...not a equal comparison and it doesn't hold much water with me or others for that matter when you know the differences...it isn't all just about the piston travel...

    This real world junk gets on my nerves... :rlaugh: It doesn't prove anything in typing...

    I believe physics over someone's impressions or "real world"...because we have seen how unreliable that can be :)
     
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  17. Grn92LX

    Grn92LX Fidanza Man! Founding Member

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    I'll take what my builder says over a text book :)

    Regardless, my 347 has a 331 rod ratio so best of both worlds for those who care about rod ratios :) Copcoupes math is off fwiw. He must have not realized the piston pin is 60* offset ;)
     
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  18. 89CopCoupe

    89CopCoupe Banned

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    I agree ... I realise improvements that have been made ... however most stroker kits sold (people have) are not fully addressed in every regard at this new school time.

    The point is not that a 347 is a pos ... it is that a 302 (under typical circumstances) will outlast it. Yes, a 302 can blow up faster than a stroker, but based on percentages, this would not be the case. I personally would rather have a 347 myself for the obvious reasons :nice:

    Offset wrist pin mounting, putting a shorter rod in, buying a block with a taller deck are design "improvements" that became evident by necessity.

    We are all speed freaks and I concur in the realm of most of our use of these vehicles, it amounts to a hill of beans ...
    but I think we are all in a pursuit of 'best' ...
    a reason why racers run longer rods in a 302 ...
    why we sit here and read any of this tech ...
    we want the best for our money.

    I didn't earn my masters in engineering for fun ...
    I was giving the new guys a bit of info that might be helpful to them ...

    I don't mind someone calling bs, only when and if they can point out exactly what technical data (typical realities) were bs ...

    That's all.
     
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  19. 89CopCoupe

    89CopCoupe Banned

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    So your 347 with a 60* offset has the same rod ratio as a 331 with or without a 60* offset?

    BTW: What is the formula for calculating RR with your offset?

    So why have a 60* offset wristpin if a 347 doesn't experience physical ailments .... in theory of course :nice:

    Edit: I should make an animated rotating assembly with my Solid Works Stress program ... but have too many projects right now ... aw who gives a **** if they believe me ... I wouldn't want to be friends with anybody who'd believe me anywayz :D
     
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  20. 89CopCoupe

    89CopCoupe Banned

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    :rlaugh:
     
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