just wondering so why has no one replied to this post that owns a 347? http://mmb.maverick.to/showthread.php?t=10654&page=1 maybe becuase it the same reason why i haven't it then again the next motor i'm in the works in building is a 331.. doh!
Actually I remember covering that same issue awhile back and someone was arguing the "rod to stroake ratio" theory.......hard to talk much sense into people these days! 331's and 347's will last a LONG time on the street, with no problems, if the correct parts are used..........just like anything, you get what you pay for!!
Here is a little exert taken from one of my favorite high performance Ford books, it is referenced at the bottom of the page. I think this is great support for my opinions on rod ratio...... Rod Ratio Theory- “We’re discussing the issue of rad ratio, a subject that has about as many opinions as there are engine builders. The current thinking is that longer rods are always better, but it’s not that simple. Any engine combination is a compromise, and component selection depends on what kind of use the engine is being built for. In the mix of heads, cam, headers, and displacement, there are other components that are higher on the ladder of performance importance that rod ratio. Here’s two opinions on the subject from Coast High Performance and Probe Industries. First, what is a rod ratio? The ratio results when the connecting rod length is divided by the stroke. Rod length is measured from the center of the big end to the center of the small end. A longer connecting rod, the theory goes (and tests support), allows the piston longer dwell time (in crank degrees) at TDC, so the expanding gases have a longer period (in crank degrees) to push on the piston. The higher the ratio numerically, the better it is considered. The better the ratio, the more power the engine is theoretically capable of . Unfortunately, engine reality gets a little muddy, particularly if you pursue rod length to the exclusion of all other engine facets. The chart nearby lists the rod ratios for Ford engines and CHP stroker kits. Displacement Length Stroke Rod Ratio 221 flathead stock 7.00 3.75 1.86 292 Y-block, stock 6.324 3.30 1.91 312 Y-block, stock 6.252 3.44 1.81 221 stock 5.115 2.87 1.78 289 stock 5.115 2.87 1.78 302 stock 5.090 3.00 1.69 302 CHP long rod 5.70 3.00 1.90 317 CHP stroker 5.40 3.10 1.74 347 CHP stroker 5.40 3.40 1.58 355 CHP stroker 5.50 3.48 1.58 377 CHP stroker 6.125 3.60 1.70 351W/5.8L stock 5.956 3.50 1.70 351W CHP long rod 6.125 3.50 1.75 408 CHP stroker 6.125 4.00 1.53 426 CHP stroker 6.125 4.17 1.46 435 CHP stroker 6.25 4.20 1.48 351C stock 5.78 3.50 1.65 428 FE stock 6.48 3.98 1.63 4.6L Modular 5.933 3.54 1.67 5.4L Modular 6.657 4.165 1.59 Notice that a long rod with a stock stroke, like the CHP 302 long rod, smartly increases the rod ratio. But also observe that when stroke as well as the rod length increase, ratio declines numerically. Muddiness about rod ratio influence occurs from several points. Consider the 221 Flathead and the 221 Windsor. The flathead has a terrific rod ratio compared to the Windsor. Yet the flathead was factory rated at 85 horsepower (at 3800 rpm) whereas the original 221 was rated at 145 horses (at 4400 rpm). Obviously, there are many reasons why the 221 windsor makes more power, such as more efficient breathing due to its valve-in-heads and lower frictional horsepower loss because of its short stroke. The 292 and 312 Y-Blocks have excellent rod ratios, yet they were never highly regarded as performance engines in their day. Also note that a 428 FE has a so-so ratio, but no one would accuse the 428 of being short on power and torque. Likewise, 426 or 435 Chp strokers have the worst ratios, yet they make serious horsepower. Look at the world class Modular engine rod ratio. Considering the billion or two that Ford spent developing the Modular engine, it’s a poor ratio numerically. But that doesn’t keep a 4.6L four-valve from delivering 600 horsepower with the right parts. The fact is , engines with supposedly poor rod ratios can make excellent power with the right parts combination. According to CHP, displacement is always a trump card. If you compare a long rod 302 (5.700" center-to-center length) with a 347 (5.400" center-to-center length) with displacement being the only difference, the 347 will make more power. As CHP explains, when a customer mashes the pedal on a 347, he fells the power compared to a 302 long rod engine. If CHP wanted to, they could increase their 347 rod length from 5.400" to 5.800" to improve the rod ratio from 1.58 to 1.70. But doing that would compromise piston stability in the cylinder due to the piston’s very short skirt and tight ring pack. These conditions would result from pushing the piston pin further into the piston to accommodate extra rod length. Ultimately, the question may be posed: how much more power should an engine with a good ratio make compared to one with a so-so rod ratio?? Compare a 302 with stock rods (5.090" center-to-center) with a long rod 302 (5.700" center-to-center) and the long rod will have a broader torque curve. But according to CHP, the change in rod length accounts for only about a 2 percent increase in torque. That means 98 percent of the engine’s power is the result of other components and engine dynamics. A second take on ratios is offered by Probe Industries, makers of Windsor performance pistons and engine components. Instead of focusing strictly on the issue of piston dwell, their theory relates to cylinder head airflow. The bigger the head ports are, the shorter the rod should be. One example would be a 351C with four barrel heads. They continue explaining that if you have a 327 cubic inch displacement, with a head that flows, say, an extremely good 320 cfm, they believe that a shorter rod gets air flowing through the port sooner, enhancing cylinder fill in the lower rpm range. Going up in displacement, if you have 400 cubic inches and heads that flow 200 cfm, work on a long rod. This will delay air movement in the port and flatten your torque curve. Along these lines, CHP also observes that long rod engines are especially to racing classes where induction is limited to stock heads, intake manifold or two-barrel carbs. If your engine runs in an extremely high rpm range, increase the rod length. One stellar example is the rarefied engine building atmosphere of Winston Cup racing, where every part and part relationship, including rod ratio, is a critical consideration. But don’t forget that in any given race class with a displacement limit, the engine builders build their engines as close as possible to the limit. Probe also lists additional points influencing rod ratio considerations. The include cam grind, track characteristics, car weight and traction characteristics, etc. Not that most of these are race related. Ultimately, for street use, rod ratio us way down on the list of engine things to be concerned about, particularly if you have just started building engines or racing. There are more critical areas to focus on. This would include assembling a well matched induction system, exhaust and cam to produce maximum power. With an EFI application, fuel and ignition mapping would be more productive to producing power gains. When studying engine dyno sheets for torque numbers, Volumetric Efficiency, Brake Specific Fuel Consumption numbers and exhaust gas temperatures are areas to investigate for improvement before ever worrying about rod ratio. Probe closes its comments with this observation. Talk to professional engine builders and parts manufacturers. They build, dyno and race engines constantly, so they’re always testing and comparing combinations. If they can fine tune a particularly potent rod ratio, you can bet they’ll let their customers know. Summed up, the saying “You can’t beat cubic inches” is unlikely to ever be replaced by “You can’t beat a numerically high rod ratio.”“ HP Books, Ford Windsor Small Block Performance, The Berkley Publishing Group, Isaac Martin
.....basically forget rod/stroke ratio and build it as big as you can! Makes more torque lower down with more cubic inches (great for street driving)
I would have, but I think my 347 is a "little" different than what they are wanting. and I agree with Stephen.....just not worth the time to argue with folks and you get what you pay for. I agree with Todd as well...................built it as big as you can.....enjoy it until it breaks and build it again!
Just wondering, how much horsepower will a 1977 302 block hold. Before I put the stroker kit in, it will be completely checked out & prep before anything gets bolted to it.
i run a 347 but i agree to make serious power, cubes is the way to go. i'd rather shift safely than twisting the devil out of it. kills those valve springs!!!it took bout 3 seasons to realize this. build it to last/not on the ragged edge=mo money in your pocket
the 331 kits can be had in any number of different ways. You can get just a crank, crank & rods, crank, rods, and pistons together, or you can get the crank, rods, pistons, bearings, rings, pins, clips, gaskets, all balanced and ready to assemble....or you can get a short block already built from places like Coast High Performance, etc. It's up to you. Back to rod ratio "theory"....my latest 415" windsor is actually a little different than the normal 408. Most guys use 6.200 rods or 6.250. I had to go with 6.300. The one before that used 6.250. Same engine just shorter pistons and longer rods. It doesn't run one bit better than the other one did. No more bottom end, no more top end, no more mid range..nothing. It's not even any more consistent. It does sound a little different though but so far, even after tuning a bunch, I can't get even a couple hundredths ET or any MPH. Just shows that rod ratio is highly overrated even on a 700 HP build like mine.
Yep, you get what you pay for. I have seen them as low as $900. I guess that's why I have not got one yet.
