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Discussion Starter #1
Yeah I know its been asked a million times but humor me.I have the chance to go either way and I need some help comparing the two.What I really want to see is some N/A horsepower numbers.I know that the 347 is capable of some impressive numbers but what about the 302.So if you dont mind brag a little.
Thanks
Scott
 

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make no mistake, a WELL tuned 302/306 can make 350 at the wheels no problem and be reasonably streetable... my 306 made 355rwhp and was a daily driver in chicago traffic... but my definition of streetable is prolly different than most... mine was set to rev out to 7000rpm and had plenty of head/cam/intake to do it... surely a 347 or a blower would have stepped this pig up quite a bit...
 

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A motor is just an air pump. The more air it pumps, the more horsepower it makes. You can pump more air by revving the engine higher, by increasing it's displacement, or by forced induction of some type.

Your question of 302 versus 347 boils down to revs versus displacement. A 302 is fully capable of generating high levels of naturally aspirated horsepower; you just need to rev it about 15-20% or so higher than the 347 to get the same peak power. Because of the 0.4 inch shorter stroke of the 302, piston speeds remain reasonable compared to a 347 turning 15% slower. Somewhere around 4000 feet/minute, piston speed reaches the limits of reliability; somewhere less, of course in a street engine where you want longevity. Piston speed limits considered, and given equal induction/exhaust and other breathing components, both the 302 and the 347 can produce about the same amount of peak power.

Where the 302 reaches a practical limit is usually in the valve train. In order to rev to the regions necessary to make peak power competitive with a similarly decked-out 347, the valve train components are highly stressed, and will either be short-lived or very expensive and maintenance-intensive. Not the most practical route for a street-strip/hobby type car. This is one reason, IMHO, why the 347 makes more sense as a performance street/strip choice. The same power can be produced at a lower stress level. Of course, it you're willing to tolerate the same stress level in the valve train and build the bottom end hell-for-strong, the 347 can obviously pump more air...and therefore make more peak power.

The place where I see the 347 has the most advantage, though, is torque production throughout the low and mid-range. With its 0.4 inch longer crank arm, any given amount of cylinder pressure is going to produce more lb/ft. of torque due to this leverage advantage of the rod working the crank throw. Although the 347 enjoys only a 45 cubic inch displacement increase over the 302, it's not unusual to see as much as 60-75 lb./ft. additional twist throughout the mid-range compared to a similar 302. As this rpm range is where a street/strip car actually spends most of its running hours, the bigger displacement motor will provide the most driver satisfaction. Building a 302 strong enough to equal the peak HP of the average 347 will cost at least as much as the 347 (or more) due to the stress levels involved. IMHO, this makes the 347 not only the winner in overall performance, but also in value. It's why I'm builiding a 347 for my street/hobby/playtoy car right now.

Steve A.
 

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I have a 306 combo and am very happy with it. It made 346rwhp and 334rwtq. I have out run a couple of 347's on the street. I would go with a 306 anyday.
 

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Ever consider a 331? I've heard that 347s sometimes have crankshaft issues and that a 331 is more reliable for a street/strip car. It should make about the same power too.
 

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I have heard of ring issues and oil burning but not crank issues. I would build a 331 before a 347 bc of more longliveity and better rod to stroke ratio. Or just build bad as* 306 and drive it forever and smoke em all!!
 

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blk91coupe said:
I have heard of ring issues and oil burning but not crank issues. I would build a 331 before a 347 bc of more longliveity and better rod to stroke ratio. Or just build bad as* 306 and drive it forever and smoke em all!!
Not me. Screw rod to stroke ratio.

347...more cubes...more airflow.

Build it right and it'll last.

Greg
 

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I am just going by what people tell me and their dyno #'s and track times. Very few have impressed me and most of them were solid roller or carb setup. Want DISPLACEMENT go WINDSOR!!! Want 0 maintenance go 306 or 331. Just my .02.
 

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Discussion Starter #14
I thoght the pistons now have a lot better oil control.I have heard of no problems with the crank please elaborate.And what will it take to build a bad as* 306?
 

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I'm amazed at how many people have heard all these issues but can't prove them. I have zero "crankshaft problems", no oil using issues with my kit and the rod ratio is livable at 1.563:1. Everybody likes to talk about sidewall loading and rod ratio, but most have no clue what it even is. I have to agree with mustanggreg, you must have good machine work and build it right for any engine to last.
 

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DSS pro lite pistons 10.2-1 comp., stock resized rods with ARP bolt shot peened, new stock crank, HV oil pump, and main girdle down low.Lightly ported track heats( 263cfm/200cfm) that are gasket matched to holley systemax. Tfs stage 2, 1.6 FMS rollers, 24lb, 70mm TB, 75 mass air, cold air kit, under drives, Eletric fan and Griffan rad., MSD ig. and coil, no AC or smog, FPR set at 42psi, Full length headers and timing at 34 total. 346rwhp at 5900rpms and 336rwtq at 4600rpms. Not 350 but close. I need to get a Pro-m 77 and an Anderson NA powerpipe and I think I will be over that. Very hard to tame on street.
 

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Depends a lot on your budget and what your intentions are. As Billy stated, "Theres no substitute for more displacement!" If your pockets won't allow room for a 347, then do what you can with a 302. If your 302 is tired with tolerances out of specs(as mine turned out to be)then simply refreshing the ole block is just not gonna do. And from what I see, doing a 306 is not too much less expensive than going 347. Some have even stated a 306 being nothing more than a "cleaned up 302". But, if ya run across a nice 306 and it fits you budget and intentions, grab it and go! Hell, they can go fast too!
All in all, it boils down to what your individual taste, what you wanna spend and your intentions of the car. Have it built by a reputable machine shop(whatever it is) and be ready to live with the outcome. I like the 347 route! I'm not buying all the "problematic issues" which have been floating around since the dawning of the stroker setup!
 
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