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Discussion Starter · #1 ·
Ok, I know there are probably 1,000 thread on 347 vs 331 on here but I have not seen one that talks about why a 331 is better. I seen a few recent articles that say a 331 will make more hp than a 347 and is easier on a stock block due to less rotation mass; while a 347 will make more torque.

Has anyone else beside the two article that I read seen this? and if I am looking for a motor that will turn 7000 to 7500 will a 331 be a better choice?
 

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There's all kinds of things that could be said about it, but you have to realize your question sounds like troll bait. I'm steering clear of it, and it appears everyone else is too. If your questions are legit, try asking one specific point at a time so it's not so much like a "Ford or Chevy" comparison question. You will get better answers and less silliness, BS and pissing matches. I hope you see what I mean. Good luck!

David
 

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There are a couple of reasons that I prefer the 331. 1) The oil ring does not need to cross over the piston pin like a 347. 2) The rod angle is not as extreme with the 331 vs 347.

I can't speak to the HP on each. It would depend on the combo and the tuner.
 

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One last though after rereading your post. Make damn sure you have a rock solid valve train with those RPMs in mind.
 

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Discussion Starter · #6 ·
There's all kinds of things that could be said about it, but you have to realize your question sounds like troll bait. I'm steering clear of it, and it appears everyone else is too. If your questions are legit, try asking one specific point at a time so it's not so much like a "Ford or Chevy" comparison question. You will get better answers and less silliness, BS and pissing matches. I hope you see what I mean. Good luck!

David
David its not a pissing match and I dont see how that can be total bait. I am curious to know if anyone else has seen a 331 make more power because of the rod ratio. I will not disagree with anybody thoughts. I was planning to build a 347 but read two article that stated a 331 will make more power and will be easier on the block due to weight. Now these two articles made me think is a 331 better for me than the 347 because i plan to spin it up to 7500.

The Question is, should I stay away from a 347 because of the RPM and has anyone else seen this happen?

I ask because 2 articles are nothing i can find two articles that will say a a chicken can lay a golden egg. So you see no pissing match just a guy looking for other people opionins on the matter.
 

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Why the "need" specifically for 7500 rpm?..Most people shoot for some sort of power number not an rpm number....The 347 will make the same power at a lower rpm with all else being equal...Is that a bad thing?
 

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Well, I know somebody that built a 427 stroker for a 5.0 mustang and my 289 makes only 68 less rear wheel horsepower than that thing does. It is easy to build a dog. It is not easy to build a cheetah and I'm not even saying my 289 is anywhere close to cheetah. It is just a home garage built engine.

It is totally conceivable and possible that somebody could do a better job and build a 331 that makes more power than a 347. If the same person pays the same attention to details and builds both engines comparably we are talking about 16 cubes and that is all. If both engines have the same cube to horsepower ratio of say, 1.5 which would be healthy engines, then the 347 will make 24 more horsepower which is something but is not a lot.

There is a lot more to it than just the cubes and horsepower too. In the same vehicle, if the 331 engined car is set up better to match the engine's power curve it will post better times. If the 347 car is set up better it will post better times.

Companies that are doing these sorts of comparisons do all sorts of tricks to make the outcome come out the way they want. If you want to build a stroker either one will do fine if you build it right. How much is the 16 extra cubes worth to you is the question.
 

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has anyone tried making a 347 with a 5.15(289/b302) rod ? 1.7 + 5.15 + 1.35 = 8.2". 1.51 rod ratio , not great but better then a chebby 454. i use custom JE pistons in my 392W stroker. they have a ch of 1.35". its a great ring space package.
 

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Discussion Starter · #13 ·
Why the "need" specifically for 7500 rpm?..Most people shoot for some sort of power number not an rpm number....The 347 will make the same power at a lower rpm with all else being equal...Is that a bad thing?
The car is set up for a motor that spun 7500. So being the poor person I am I thought it would be best to try and match the RPM of the motor that came out, that way the converter and the gear ratio would be fairly close to start.
 

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how much hp do you want ? you could build a boss 302 copy that will turn 7500 rpm all day long. boss 302 rods are even cheep ! i could have bought a brand new set for $200.00. get a set of 351C 4V heads. i see b2 intakes going from 200 to 400 dollars. i recently passed on a perfect nos b2 forged crank for $350(mistake magnifee !!!). put a big solid cam in and it has the potential to make 400 hp with stock ex port configuration.
 

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has anyone tried making a 347 with a 5.15(289/b302) rod ? 1.7 + 5.15 + 1.35 = 8.2". 1.51 rod ratio , not great but better then a chebby 454. i use custom JE pistons in my 392W stroker. they have a ch of 1.35". its a great ring space package.
Almost...I built a 331 using a 5.155 289 length H beam rod. Used a 383W piston or KB322. Can't build it the same anymore 'cause KB Silvolite no longer makes the KB322...I bought one of their last sets just in case I needed to replace a piston someday. The only way they would make more is for a large quantity.

The KB322 has a 1.415 compression height as I recall and the oil ring is not intersecting the pin.

Their are a few alternative pistons that could be made to work.

This 331 has the same RS ratio as a 5.400 rod 347.

I rev it to 7000 regularly. Had it up to 7300. Nothing rad on the valve train...26986 beehives, Probe shaft rockers.

Someone was trying to tell me the opposite one day...the 347 always makes more power than the 331 per ci. Why...don't know...might be the numbers...347 is 3+4=7 and 7...two lucky 7s while 331 is 3+3+1 = 7...only one lucky 7 :rolleyes:
 

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Okay, then let my throw my 2 cents in like this so it's fact-based and fair to both strokes - rod:stroke can potentially make more power with all other things being equal. The benefit is a tiny fraction in most applications, so it's splitting hairs. Next, the difference in reciprocating weight between the two is nearly zero. Unless your comparative cranks are bleeding-edge light-weight units in the first place they can be equivalent, so no gain there. Yes, there are piston stability issues that arise with longer strokes combined with greater angle, shorter pistons and tighter ring packs at high speeds. In this case, it would not be exceeded for either, so no gain with that. The issue of oil rings intersecting the pin bore was solved a long time ago, and is not a concern with available quality parts - so that's out. And, unless you're planning a 7500 RPM engine that makes no real power, a stock block is out and aftermarket in, making many of the comparative issues irrelevant.

What you end-up with is several non-issues and a couple that might give a bit of edge. But all things are not equal between the two, and you can't split enough hairs to add up to the displacement difference they started with. To be fair, displacement has advantages that are obvious, and can allow more power at the same RPMs or the same power at lower RPMs. They can also give a flatter torque curve for better average power. The play on RPM meaning "Ruins People's Motors" isn't without merit. While again the difference is larger but still small, at the high RPMs you're looking for it can make both a power and a reliability or cost advantage, or slightly increase it's streetability and mileage (if applicable) or longevity with that advantage.

So, the differences are fairly small, and either can make a car go fast if properly built for the task, but the advantages vs disadvantages are mostly favoring the 347. If you have different goals, such as a pure RPM goal, the balance can change. I have to add here that the magazines in general are becoming rather poor at reliable info for whatever reason, and to make something to splash on the cover to get you to buy it will often play-up subjects like R:S as though it were major magic. Other times, they miss the entire point of the exercise and blab pure BS because the writer really doesn't know better. It's a shame, and has always been true to a degree you could overlook, but seems much worse in the last several years. I have not read the articles you refer to, so I cannot comment directly on them. HTH

David
 

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Discussion Starter · #17 ·
This thread is closed. I have received the information that I was looking for and would like to thank those that made a valuable contribution. I will build the 347 with a lower RPM goal. Ill just tighten the converter up, and my buddy has a set of gears that he will give to me and install in exchange for some labor. What ever power the motor doesnt make the unit will.

Thanks again
 

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A 331 can make more horsepower than a 347 just as a 347 can make more horsepower than a 408...

It is very simple... Which engine combination burns more fuel for a given amount of time will make more power, no matter what the displacement... Consume more air per given unit of time and the engine consumes more fuel. The way to make more horsepower with a smaller displacement combination is to turn more rpm so the engine consumes more air.

Unless you are building an engine for a specific class I would not worry about the rod/stroke ratio. My 3.4 stroke, 8.2 deck engine from last year had 5.4 rods and the wrist pin was not into the oil ring. These were custom pistons with thin rings. I shifted at 8200 and crossed the stripe at 8500 and the skirts had very little wear. I ran the engine extremely cold and am sure if I ran coated skirts the pistons would have been perfect.

My combination from a few years ago was a 363 in an 8.2 deck, 3.5 stroke, 5.45 rod... That combination had the pin in the oil land with 12lb rings and never had any problems keeping the chambers dry. Last years 355 used 7lb rings and did not have any problems keeping the chambers dry... Both engines were wet sump with no vac pumps.

I believe you made the right move going with the 347... If you have a good block, forged crank, rods and a good balance job don't fear turning up the rpm as far as the bottom end in concerned.
 
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