347 vs 331 Stroker? - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 9 (permalink) Old 11-20-2002, 02:24 PM Thread Starter
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347 vs 331 Stroker?

I was working on a 331 stroker but a lot of poeple keep saying go all the way to 347. I was going to build 347 but i was scared away from building one because of all the talk about the piston pin potruding into the oil ring and the life of the motor was shorten and so on. How does everyone here feel about this matter? If you were to build a street 347 how would you build it?
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post #2 of 9 (permalink) Old 11-20-2002, 02:39 PM
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347 vs 331 Stroker?

I too have wrangled with this, and after careful consideration I realize I'll do fine going out to 347. Although a 347 using oil is a consideration, I think it is something which may have been overstated and now looms larger than it should. My car is a street car, not a dragstrip racer, BTW. CHP uses a piston now that moves the wristpin out of the ring and that takes care of the oil consumption problem. The other consideration is the 347 has to use an even shorter skirt piston than the 331 does, and this may contribute to "rocking" of the piston in the cylinder at high rpms. Again, I don't think it's a major problem, and there are plenty of guys out there beating the hell out of their 347s and not having any trouble. Check into the FM archives on their 331 buildup. The first part talks about this issue. I say, go for the 347.
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post #3 of 9 (permalink) Old 11-20-2002, 02:41 PM
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347 vs 331 Stroker?

I think 347s are great motors, but I don't really like the idea of having an oil burner on the street. The 331 is just a little more streetable and reliable in my opinion, although you won't be disappointed with either one thats for sure!
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post #4 of 9 (permalink) Old 11-20-2002, 03:01 PM
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347 vs 331 Stroker?

The general "word of mouth", as I hear it...the 331 will rpm easier, but the 347 has more torque. Its more than the difference of 29 ci. vs. 45 ci. the stroke, crank shaft strength, and the rod angle/bore length ratio. But at the simplest level, the 347 has a bit more torque, due to its longer stroke. The 331 tends to live longer and run to higher rpm due to its shorter stroke and piston travel. As far as a street engine, especially if you intend to Blow or spray it sometime in the future...it's a wash. 'course, bigger is better, that's why you go for the stroker anyway, isn't it? Usually the cost is pretty much the same.

The pistons that have the full oil ring land are "usually" heavier, again affecting the RPM ability of the engine. I think even FMS has a 347, street kit on the books now, I'm not real sure, but I think they even have a short block? That's to say that longevity and oil burning, in the "short con rod" version of the 347 is not a problem.

[ This Message was edited by: Beoweolf on 11/21/02 3:08am ]
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post #5 of 9 (permalink) Old 11-20-2002, 08:50 PM
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347 vs 331 Stroker?

I was concerned about many of the same things that you are regarding the 347 stroker including reliability/longevity. The short skirt and reputation of oil burning 347's was enough for me to do some research on my own. At the time, even the 331 stroker piston design had the piston pin in the oil ring area so both the 331 and 347 suffered from the same shortfall (I believe there is a 331 kit now that has the piston pin below the oil ring).

Anyhow, I selected a 289 rod and a 331 crank as a starting point and then went in search of a piston that would give me the right compression height and compression ratio. The 289 rod / 331 crank combo gives the same rod/stroke ratio as a 347. Well...I found just what the doctor ordered...the KB322 piston. Compression height was within .015 of what I needed (just milled the block a little to compensate) and the valve reliefs gave me 9.9:1 compression. On top of that, the skirt is relatively long and the piston weight is almost identical to a 302 lightweight piston. The KB322 is a 351W stroker piston for a 372 or 383, but 351W pistons can be used in 302 blocks just perfectly. I'm going to be firing up the engine this weekend...can't wait!

Tracy Blackford: Anaheim Hills, Ca
65 Mustang, 331 custom built with 289 H beam rods and 383W piston, 282S cam, self-ported '70 351w heads, T5z, 9" w/3.50s. 430 HP@6500
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post #6 of 9 (permalink) Old 11-20-2002, 10:22 PM
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347 vs 331 Stroker?

Sounds like you really hit on something. That sounds great. Does having the same rod ratio as the 347 mean it produces the same amount of torque as the 347? Or is that what allows you to run higher compression?
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post #7 of 9 (permalink) Old 11-20-2002, 10:26 PM
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347 vs 331 Stroker?

neither one. A better rod/stroke ratio just take some of the side loading off of the piston and bore. This side loading can rob a couple horsepower up high (like above 6000 rpm, and then it's very slight). Not worth considering on a street motor, unless it's a SERIOUS (read: 7000 rpm/500 HP) one.
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post #8 of 9 (permalink) Old 11-21-2002, 01:10 AM
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347 vs 331 Stroker?

There must be something to this side loading theory. Most all stock 289/302 blocks that I have tore down in the past have had cracked pistons at the side skirt area. This is with stock cast pistons though. Better pistons with reinforced skirts don't crack as easily. I chose to build a 331, 5.4" rod, using forged pistons with the oil ring away from the pin, for this reason.

I'm waiting for Tracy to run his short rod motor before I decide to try it.

1966 Mustang Cpe, 302 stroked to 331 c.i., 5.4 H-beams, Probe forged slugs, ported TFS alum. heads, ported Stealth 8020 intake, 230/236 - .580/.600 solid roller,Holley 750 HP, Hedmans, BFG DR

"Too much for the street, not enough for Pro Stock"

[ This Message was edited by: bluestreek on 11/21/02 1:17pm ]
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post #9 of 9 (permalink) Old 11-21-2002, 10:51 AM
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347 vs 331 Stroker?

Just my opinion, but if you are going to stroke, why don't you consider stroking a 351W? They will fit in ANY mustang (even '65-'66) and there are a ton of options. 383W, 408W, 427W. And the added weight to added power ratio isn't that bad. The added power makes up for it.

If you really want to stroke a 302, i'd go 331 max for street car reliability.


1966 Mustang Fastback
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