347 vs. 351



If you’re considering extra cubes, then chances are you’re wrestling with a fairly common dilemma: Do you build a 347 out of your 5.0 or step all the way up to a 351? Perhaps the following info will help you decide.

351W: Advantages

• Strength: The 351W block is stronger than the production 5.0 by a long shot. Thicker walls and 3-inch main, and 2.311-inch rod journals (versus 2.248/2.123 for the 5.0) are contributing factors.

• Taller Deck: The 351W features a deck height of 9.503 inches versus the 5.0’s 8.206 inches. This means a longer rod can be used for even more cubes—up to 435 with a production two-bolt block, and 454 cubes with a four-bolt FRPP block, according to George Klass at Coast High Performance.

• Rod-to-Stroke Ratio: In stock configuration, the 351 has a better rod-to-stroke ratio than a 347 (1.70:1 for the 351W versus 1.58:1 for the 347) by virtue of its longer rods (5.956 versus 5.400 for the typical 347 rod). The 347 also features ½-inch head bolts instead of the 302 block’s 7/16-inch bolts.


351W: Disadvantages

• Size: The 351W is 2.250 inches wider than a 302, necessitating a number of changes (at additional cost) to make the swap possible. Hood clearance can become an issue, and there will be less room to service the plugs.

• Heavy Weight: As discussed in the Keep the Muscle, Lose the Fat sidebar, the 351W is beefier and is typically more than 100 pounds heavier than a 302-based engine.

347: Advantages

• 302-based: The 347 is created when a 302 block is bored 0.030 and fitted with a 3.400 stroke crank and custom rods/pistons. This means a 347 has the extra cubes you desire, yet it can still use the same headers, manifolds, brackets, and so on as a stock 302.

• Light Weight: The 302-based engine is more than 100 pounds lighter than the 351 in stock form, and it can be made downright feathery with a few aluminum components.

347: Disadvantages (and perceived disadvantages)

• Limited Growth: While 347 ci is certainly a respectable number, it’s the practical displacement limit for a two-bolt-main production block.

• Limited Strength: A two-bolt-main production block is typically capable of withstanding up to 600 hp, and that’s with a girdle, studded mains, and so on. Even a mildly built 347 with a supercharger can bust that figure. An R302 block will solve the problem, but there goes your budget.


• Poor Rod-to-Stroke Ratio (perceived): There has been a lot of talk about the 347’s rod-to-stroke (R/S) ratio. Simply stated, the R/S ratio is the length of the connecting rod (center-to-center) versus stroke of the engine. A higher ratio means the piston stays at top dead center longer, promoting better combustion and, theoretically, more power. Compared to the 351W’s 1.70:1 R/S ratio, the typical 347’s R/S ratio of 1.58:1 doesn’t look good, but it’s actually better than a lot of other noted performance engines, including the 454 big-block Chevy (1.53:1) and 400 small-block Chevy (1.48:1). Even the legendary 428 CJ was only marginally better than a 347 at 1.63:1. Unless you’re building an engine to compete with Billy Glidden, R/S ratio really doesn’t add up to much in an otherwise well-built engine.

• Oil Burner (perceived): Piston design is critical to the success of any 347 kit, according to George Klass at CHP. Trying to improve upon the 347’s R/S ratio only moves the pin further up into the piston. If the pin is moved up into the oil ring land, the top of the pin will be located above the oil ring, allowing more oil to get past the oil rings and into the combus- tion chamber. This is how the 347 got a reputation as an oil burner. However, George says, many kits—including CHP’s—place the pin below the oil ring, so oil consumption is not a problem.

Cost Factor

The next thing you’d probably like to know is, which would be cheaper, a 347 or a 351W? As discussed, the 351W requires numerous extra parts to accomplish the swap, while the 347 doesn’t. However, depending on what 347 kit you purchase, the initial short-block may be more expensive than a 351W. Since we can’t know what combo you have planned, the best idea is to add up the cost of a 351W, factor in the extra parts, and then compare that to the cost of the 347, keeping in mind both engines can use the same heads. Our guess is that the 347 will probably be less, but depending on how serious you plan to get, a 351W swap could be equal to, or less than, the cost of a truly serious 347.

 

ahhh yes the age old debate rages on.....but nothin sounds like a 347 hittin 7800....music to my ears....

 

The 351 Windsor, built from 1969 to 1996, adds 0.5" to the stroke of the 302. It is of considerably stouter construction. Engine weight is 510 lbs. The 351W was designed as a long-stroke replacement for the 302 in passenger car use. It later served as a truck and marine engine through 1996.
To avoid very short connecting rods and excessive piston side loads, the 351W uses a taller block than the 289/302, 9.480" (1969/70) and 9.503" (1971/96). The crankshaft uses very large 3.00" main journals, shared with the 400M. 2.311" rod journals are shared with the 351C. The same 28 oz.-in. external balance is used as found on the 289/302 and 351C.
Before 1976, the heads feature larger valves than the 289/302 and provide a simple bolt-on horsepower upgrade. 351W exhaust manifolds, similar in design to those used on the 289 Hi Perf, also flow more freely than standard 289/302 manifolds.

Another way to tell the 351W apart from the 289/302 in most cases is the number of intake manifold to cylinder head bolts. The 289/302 has 12, the early 351W (pre 1976) has 16.

Some aftermarket manifolds do not have provisions for the 4 extra bolt holes.

 

Make this fair why dont u do 302 Vs 351 and then 347 Vs 408

351 is stronger motor and if u are building a motor to beat on the 351 will always be better.

 

hmm... why dont u make the write up than?

 

Many Late Model guys ignore the 351Cleveland option, probably due to these motors being discontinued before they were born, but they were designed as ChevyKillers, and can easily do just that. In fact back when famous NHRA driver/builder Bob Glidden started competing in a 351C engined Pinto, they handicapped his car because it was so much faster than anything else out there it was ruining the class structure of NHRA racing at the time !

One of the reasons Ford discontinued the 351C engine line-up and bastardized it into the 351M & 400M was the fuel situation at the time, and the emission issue was developing. These motors aren't as fuel efficient, but we're not in this for fuel economy are we ! Had Ford continued to develop this engine into the late 80's, like the Australins did, it probably would be the engine of choice for almost all applications.

The 351C heads are the big secret here (huge ports, big valves), and the fact that the crank journal size more easily allows you to spin this small big block engine to 8-9,000rpm done correctly .... all day long.

- 90 lbs more weight than a 351W
- Aluminum Edelbrock Heads are now availlable for it for a 100lb + weight savings
- Can be stroked to 408 etc and will blow a simlarly stroked 351W away !
- fits anywhere a 351W will fit
- parts readily available
- goes like stink
- cost no more to build (non-stroker) than 351W
- stroker kits are approx $500 more
- bolts up to small block tranny bellhousings
- in some cases uses same motormounts
- lotsa torque

You see more 67-70 Mustangs that originally had 302's now using 351Clevelands than the 351Windsor engines ... is there something the older know ?
True the 351W is more plentiful, but who isn't willing to spend a couple of extra hours searching for a 351C... it doesn't cost you anymore to look deeper & harder.
I'm an older guy (48) and I have built several of these engines myself and they continue to amaze me with the abuse they will take (example me at Mosport for the last 4 years in my 70 Mach1). I've had mechanical issues, but only 1 minor one was engine related, and we'rte talking sustained 5,500+rpm use with stock crank, rods, heads, etc.

Don't leave the Cleveland out in the cold guys, it's a viable option, and can make stump pulling torque. A 1970 351C 4V in stock form turned out 380 ft/lbs of torque.
Infact the 351C heads are so good they market a special intake manifold to adapt the 351C heads to fit a 351W called a Clevor !

Just another option to consider.
Mach1steve

 

I assume your talking 600 Flywheel HP. Stock block will hold 550 WHP is you keep the RPM under 5500. Some friends and I have split quite a few blocks. RPM is definetly a factor in the production 302 based blocks. I have seen 347 7800+ rpm motors fly apart and they were only making around 400-425 WHP.

The gidle does hold all the broken pieces together nicely.

 

hey can anyone advise on how was the right usage of my crankshaft kits, i am bothered of that thing. i was confused of where to install the crankshaft kits. thanks and good day.