I am planning to build a 302 stroker for a 63 unibody of mine and I wanted to know if any of you have built either of these motors and what was your experiece with them. Everything I have researched has been back and forth between the two. Some say build the 331 because the 347 kits put the rod pin to high up into the piston skirt and it causes the rings to go bad fairly quickly, but others say that the 347 is the greatest thing sice sliced bread. What do ya'll think?

 

331 hands down for the aforementioned reasons. The 347 also tends to stress the block more. But, really, skip the 302 and stroke a 351...

 

There are too many 331 vs 347 myths floating around the internet. The 347 is a perfectly fine setup as the 331. 99.9% of 347 problems is the engine assemblers fault as they don't know how to set the ring clearances up correctly and the same goes for the 331 also.

Another thing people rant about is the rod stroke angle which is pretty much another myth. The 302 block will crack in half before you will every see any cylinder bore problems and a BBC has a much worse rod angle yet it can be built to big HP with no problems.

So just pick what ever kit fits your intended use as they both are the same price. The 347 is pretty much just more HP for free.

 

This is exactly what I am talking about, on this post I have two replies and one is for the 331 and the other is for the 347, anyone want to give me another opinion to break the tie please. Never having built either of these engines before its hard to know which side to choose.

 

Do you really need the maximum HP? The 347 has the potential to make more HP but there are possible problems with the pin placement compared to the ring stack. The pin height on a 347 piston is only 1.090". That puts the pin very close to the backside of the piston top for more heat and also in the ring stack. You need to pay attention to detail to keep from having ring issues. The 331 is slightly better on pin location with a pin height of 1.175. That at least gets the pin down a bit, but it's still in the ring stack.

Most 331/347 motors are race motors. They aren't designed to run a long time and are freshened fairly often compared to a street driven vehicle. I, personally, don't think of any of the 302 stroker motors as long term life motors.

To my way of thinking, the 393" 351W based stroker is the best deal out there if you really need a stroker motor. You use an off the shelf 302 piston with a 1.600 pin height and a 5.956" Windsor rod with an aftermarket crank for 393". Solid piston, good rod length but the rod angle starts to go away a bit. (The rod ratio for a 347 is around 1.588:1 while a 393 is only 1.547:1 so you lose a little there. For copmparrison, the 331 is 1.660:1 which is much better. Our race motors use a 6.2 rod in a 9.2 deck block with a 1.23 pin height and a 3.500 stroke for a 1.771:1 rod ratio which we regularly turn to 8400 RPM with Yates or Brodix heads.) The advantage is that you don't need to turn the 393 nearly as hard to see the HP as the smaller motors.

The downfall to the 393 besides the additional 80# or so, is that once you do start to turn it any substantial RPM (say over 7500) you will knock the main webs out of a 351W block. You will split a 347/331 in a stock block with repeated long term 8000 RPM runs. Drag racers tend to get away with it a lot longer than circle track guys do. Most circle track guys plan on 30 nights on a stock block before breaking the block.

Build a nice 351W, have the inches you want in a long living package.

JMO,
SPark

 

I have to agree with LM14. You'll have a little wider of an engine with a 351W but you'll also get more bang for the buck on a less stressed engine. But if you have to go 302 stroker there is a company that sells a block saver kit, lifter valley girdle, that installs in the lifter valley to stiffen the block more. I've read a few things on it in carcraft and online.

 

well, heres my two sense worth. from all the articles i have read, if the motor is to street driven, go with the 331. the reason i say this is, with the 331, the rod angle is much better for longevity reasons, the pistons dont rock in the bores as badly due to rod angles and the 331 pistons piston pin is below the oil control ring so you dont have your engine oil being burnt and being kicked out the pipes.

Now, if your for power and tones of it and dont give a crap about longevity of your motor. go with the 347.
now, as others have been saying, you might want to consider the 351W. you can get decent torque with the 351W and the 351W responds well to light aftermarket upgrades.