In reading all the tips and tricks in here, I see alot of info on stroker motors. What exactly is a stroker?

 

A stroker kit is a kit that comes with a special crankshaft and rods (and more) to lengthen the stroke of the piston. This increases the size of your engine. Generally, the longer the stroke, the more torque.


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I can add just a little for example if you have a 302 you can buy a 331 or a 347 stroker kit most will come with the crankshaft, rods, pistons, and rod and main bearings the good stroker kits will also come with a harmonic balancer or dampener some call it and a flywheel or flexplate depending on your transmission, and the really good kits come with all of that and its a ballanced assymbly to save you alot of headaches when you put it in. Just to give you an idea of exactly the difference a stock 302 has 4" bore and a 3" stroke the 347 stroker kit will come with pistons for a 302 bored 30 over to make the bore 4.03 and the stroke becomes 3.4" because of the lengthened stroke the rods are 5.4" long instead of 5.090 because of this the piston wrist pins are pushed up toward the top of the pistons and on most kits including the eagle kit the wrist pin overlaps the bottom piston ring which i hear causes oil consumption however that depends on who you talk to i have done much research on this particular kit and am still pondering if i should go with it. It would be a better choice than going with a 351 due to the fact of the lighter weight and better handling but only if it is dependable if anyone knows how dependable the 347 is please let me know THANK YOU

 

OR.......

Stroker also refers to a motor that has had the stock crank reground with a little more stroke. In fact that's what it originally meant back when you didn't buy anything in a kit. Problem is when you stroke a crank you must make the rod journal smaller. This can weaken a crank. The first 460 stroked to 514 setup had that problem before it was offered as a kit. This was because journal had a lightening/balance hole in it stock, and when you make the journal smaller and move it over you get thin on one side. Now they offer it as a kit, with a new crank that doesn't have that problem. The flip side of that is that a smaller journal is better if it doesn't compromise strength. This is because it has a slower surface speed on the bearing. Requiring less oil and generating less heat. Also slinging less weight around helps out too. Also when you go to smaller journals you need rods with smaller journals. Usually small block chevy rods, as they are available in a great variety of lengths. When you start changing that much it can get complicated in a hurry. Which is why it's available in a pre-packaged kit now.

 

Thanks all. That helps alot BUT if your lengthening the stroke, are you not going to get some slap on the heads or vallves? I was going to put my 302 crank and rods into my 289 but I was told it wouldn't fit because the stroke is longer????? I'm confused.

 

That's the complicated part.

The first way you can solve that is shortening rod length. For ex. on a 383 chevy, a 350 chevy has 3.48 stroke with 5.7 rods, which can be changed to 3.75 stroke with a 5.655(400 style crank and rods). The stock combo is 3.48/2+5.7= 7.44 or 3.75/2+5.565= 7.44 The same length. The danger here is you come close to whacking the piston with the crank when you shorten rod length. This can be solved by making pistons with shorter or notched skirts.

The other method is to maintain or in some cases extend rod length(more is good), by changing the piston pin height. Which is the distance from the top of the piston or crown to the center of the piston pin bore. However you can run into problems here too. The afore mentioned 383 with 5.7 rods is fine with custom pistons, but with 6 inch rods it moves the piston pin bore into the oil control ring groove. This can be overcome with special pistons with a 4th ring on the oil control. But you'll spend more money that way.

Other things to think about,
The longer crank may hit at the oil pan mounting surface on the block or on the bottom of piston bores. Notching required. Some extreme examples have to notch the oil pan also.

The longer crank may cause rods to whack the cam, as they travel farther. Sometimes rods can be clearanced. Or you can try aftermarket capscrew rods that don't have as much material near where they impact. Or cams ground on a smaller blank may fix it.

Lots of choices. The smallest of which can cause your engine to live or die. That's the beauty of the kits. When you call to order you can ask what you'll need to make it work and someone else has already paid the price to figure it out for you.

By the way the 289 and the 302 share a common bore. Therefore you could put the 302 crank, rods, and pistons in a 289 block. If the rods are the same you could just put in the crank and pistons. However if I remember right you may need to lightly notch the pan rail area???? Otherwise the two blocks are similar enough you shouldn't have any trouble. But your not going to gain much from this change. You'd be essentially re-inventing the 302. The only advantage I can see is if you want to rebuild and these are the parts that are available.

 

PINEGUY!!! I have been told that you can put the 302 crank rods and pistons in the 289 block and then you have a 302 the only difference in the 2 motors is the stroke but make sure you use the 302 crank, rods, and pistons. if you mix them up you will have problems but both 289 and 302 engines have a 4" bore GOOD LUCK!!

 

Regarding stroking a 289; there may be a problem with the bottom of the cylinders interfering with the crank. 302 blocks had shorter cylinders to allow the room. It might depend upon which 289 block you're using.

 

YES YES one thing i did forget whether you have a 289 or 302 i have been told you do have to take a die grinder and trim the bottom of the cylinder off for rod clearance this is very easy to do just takes a long time b/c you must be very careful not to leave any metal shavings behind you would be surprised how much of the cylinder is not used on a 289 or 302 i have recently looked at an engine that had been run for about 90,000 miles and when i looked at the cylinders you could tell that about 2 inches on the bottom toward the crank was not even touched by a piston ring so you can take out more than enough of the cylinder for clearance and not worry about running into problems just dont go too crazy

 

347's will run great at the track, the mustang kids do it all the time, but I've NEVER heard of one lasting 50,000 miles on the street. The stroke/ratio deteriorates rapidly, most of them die to excessive oil consumption because of piston slap. If you want the power, go to a 351W, it has a 3.5" stroke, and bigger main bearings for much more strength and stability. The 351W block can safely be stroked to 4" for some moster displacement! It's a bit wider, and it does weigh a bit more, but the power will more than pull it's own weight. Plus, this is one of the most durable engines Ford ever put together. I've heard many stories of 200,000 miles plus, and I've never heard of one dying for engine reasons before 180,000 miles. You can use all your 302 parts on it too! Other than a new intake, 1/2" head bolts, and longer pushrods, you're all set with your 302 heads, exhaust, and cam/valvetrain!

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ok then what about the 331 stroker for the 302 is that more dependable since it has a smaller stroke and have you seed the 347 stroker with probe pistons which have corrected the oil consumption problem they claim that it solves the dependability isue and restores the original strength and dependability anyones info is appreciated

 

[updated:LAST EDITED ON 29-Oct-02 AT 01:29 AM (EST)]sand man, I think the issue of short-lived 347's is more a matter of how the engine is built and less about the actual geometry of the engine. Many of the people who are building 347's place a high priority on power. As a result they specify forged pistons and long rods.

Forged pistons need to be fitted more loosely than cast or hypereutectic pistons, so they wobble around in the bore and the rings lose their seal, causing the oil to be washed off the cylinders and diluting the motor oil.

Another problem it the choice of the 5.4" connecting rods. Rods that length cause four problems. First it leaves little room for the rings. The rings end up at the very top of the piston where the wobbling is felt the most. This exacerbates the ring seal problem. Second, the center of the side thrust is moved into the rings where there is much less piston to bear the thrust. The ring grooves themselves end up being the place where the side thrust is felt. Third, the center of the side thrust from the connecting rod is moved above the center of the piston. Pistons are barrel shaped. The side thrust is supposed to be along the widest part of the piston to help distribute the force. The long rod puts the side thrust above the widest part of the piston. The fourth problem is the fact that the piston pin is so high in the piston, it intersects the oil ring. This compromises the oil ring's ability to do its job.

If you wanted to build a longer lasting 347 you might consider using hypereutectic pistons that fit the cylinder extremely closely and avoid the problems of side thrust and piston rocking. And you might want to use the slightly shorter 5.315" rods that lower the point of side thrust and don't intersect the oil ring.

I think a fella could build a conservative 347 that would pull hard, get good mileage, and last longer. It would be pretty close in power to a nice roller 351 EFI. But I could be wrong.

 

i have a 347 with 70,000 miles on it, kb pistons,scat crank, 5.400 rods
rooler cam and rockers weiand stealth and a 600 holley. power is great but oil consumption ic starting to inrease due to 1/16"piston rings.
dont hesitate to build one the power is great.
building a 428 winsor now