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Old 07-31-2011, 02:59 PM   #1
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331 vs 347

I'm thinking about building a stroked motor for my next car and these are the big two I see for foxes I would like to know pros cons to both motors and which one is best thanks
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Old 07-31-2011, 04:44 PM   #2
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Re: 331 vs 347

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I'm thinking about building a stroked motor for my next car and these are the big two I see for foxes I would like to know pros cons to both motors and which one is best thanks
The 347 has more cubes, but suffers from longevity issues due to the overbore needed and the fact that the oil ring intersects the piston pin. This cubic inch size stretches the stock 5.0 block to its limits.

The 331 has fewer cubes but tends to last longer because it does not suffer the issues that the 347 has. It would be my choice were I building a stroker from a stock 5.0 block.

Your best bet if you are after more cubes would be to go with a 351W. It has a much stronger bottom end than the 302 and can be bored and stroked to a much larger cubic inch size and still be reliable.
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Old 07-31-2011, 05:09 PM   #3
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I would build a 331 over a 347, it has a wider power band and will rev a little higher into the rpms, on a non race car I would choose a 347 over a 351. It weighs less and there is no guess work needed for swapping motors since actually all you are doing is swapping the bottem half of your stock motors, now on a carbed- race inspired motor on a stripped out car, then a 351+. But that's just mo
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Old 07-31-2011, 06:40 PM   #4
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Re: 331 vs 347

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The 347 has more cubes, but suffers from longevity issues due to the overbore needed and the fact that the oil ring intersects the piston pin. This cubic inch size stretches the stock 5.0 block to its limits.

The 331 has fewer cubes but tends to last longer because it does not suffer the issues that the 347 has. It would be my choice were I building a stroker from a stock 5.0 block.

Your best bet if you are after more cubes would be to go with a 351W. It has a much stronger bottom end than the 302 and can be bored and stroked to a much larger cubic inch size and still be reliable.

im not tryn to one up u or anything.....

but the first part where you refer to "stretching cubic inches" isnt really correct. to make a 347 overbore is only .030 u can even use a standard piston makinig it a 342. the main deal that hurts the 347 is the pressure exherted on the sidewall of the cylinder from the longer rods used to make the xtra stroke. the piston pushes on one side of the cylinder xtra hard creating an "elleptical shaped cylinder".

that sidewall pressure is also wut messes up the rings and the pistons themselves.

however, you can get a piston with an "off-set wrist" which decreases the side wall pressure and extends the life of the motor considerably.


original post.....

347 makes tons of torque, usualy better for heavier cars.
331 doesnt make as much torque, but as previuosly mentioned...it typicaly has a longer life span.

347 is good if you opt for the high end pistons and rings... not the wideley sold base kits.

again, as mentioned above.. just stroke a 351
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Old 07-31-2011, 07:38 PM   #5
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Re: 331 vs 347

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im not tryn to one up u or anything.....

but the first part where you refer to "stretching cubic inches" isnt really correct. to make a 347 overbore is only .030 u can even use a standard piston makinig it a 342. the main deal that hurts the 347 is the pressure exherted on the sidewall of the cylinder from the longer rods used to make the xtra stroke. the piston pushes on one side of the cylinder xtra hard creating an "elleptical shaped cylinder".
that sidewall pressure is also wut messes up the rings and the pistons themselves.
however, you can get a piston with an "off-set wrist" which decreases the side wall pressure and extends the life of the motor considerably.
I am not worried about you "one upping" me. I'll be the first to admit that I don't know everything and sometimes I make mistakes.

However, I did not refer to "stretching cubic inches".

What I said was, "This cubic inch size stretches the stock 5.0 block to its limits."

Which it does because:
1. Ford does not recommend overboring past .030, so it is at the sensible limit.
2. The excessive sidewall pressure from the longer stroke puts more pressure on already thin cylinder walls.

My point was that for most intents and purposes the 347 is the limit for a stock 302 block and for the majority of the end users.

That being said there are always cases where they can and have been pushed past that limit.

I once bored one out to .060 oversize, because that's what it took to clean up the cylinders and I couldn't afford another block at the time. I did however, check the block for core shift and had it sonic tested first.
That engine ended up lasting another 100K+ miles.
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Old 07-31-2011, 11:11 PM   #6
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Well I have done a 351 swap before so it isn't that big a deal and foxes don't weigh a lot and I'm trying to make a decently fast daily driver without doing another 351
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Old 07-31-2011, 11:41 PM   #7
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A lot of people that build 331s put boost to them and make decent power. 347s you see people with Spray on them. I built a 347, always wanted one. I put all forged internals in it and put a pro charger on it. I never had a problem with it. I have just over 8000 km on it. And I drive the **** out of it.
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Old 08-01-2011, 08:16 AM   #8
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Re: 331 vs 347

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Old 08-01-2011, 10:31 AM   #9
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So all this really depends on the budget then I guess is what I'm hearing. If I have enough for custom pistons with offset wrists and do forged a 347 will be just fine but if I don't do all that a 331 will last longer without all that. Am I in the right ballpark with that concept
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Old 08-01-2011, 11:03 AM   #10
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Re: 331 vs 347

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So all this really depends on the budget then I guess is what I'm hearing. If I have enough for custom pistons with offset wrists and do forged a 347 will be just fine but if I don't do all that a 331 will last longer without all that. Am I in the right ballpark with that concept
i dont know for sure how long a 347 with a basic kit would last. for a street driven car it may not be a big deal at all. if u have a smaller budget u may wanna stick with 331, or just do a blower... the cost is about the same.
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Old 08-01-2011, 01:12 PM   #11
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Re: 331 vs 347

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i dont know for sure how long a 347 with a basic kit would last. for a street driven car it may not be a big deal at all. if u have a smaller budget u may wanna stick with 331, or just do a blower... the cost is about the same.
+1 I agree.
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