331 vs. 347 Stroker
 

Which is the best stroker kit to go with. I want to keep my engine NA in the future so which is the best choice?

if your staying n/a i would definately go 347.

How long do you want it to last? What kind of use will it see? How much are you planning on spending?

Take care,
~Chris

347 ...if your going NA get as many cubes out of it as you can. You plan on staying under the stock rev-limit?

i disagree, I did alot of research before deciding on what to do with my motor, and a 347 will make for a very poor daily driver. The rod/stroke ratio as well as thinner cylinder walls make for a less reliable engine for a daily driver. On the other hand, the 331 was has a superior rod/stroke ratio with regards to strength. Also, in 347 pistons, the oil ring intersects the wrist pin, which can cause compression problems as well as instabillity. Sacrifice the 16 cubes and go with the 331, it will last much longer.

actually the newer 347 kits have changed the configuration of the pistons and rods and have very liveable rod/ stroke ratios and chp i know has a redesigned piston that alleviates the wrist pin and oil ring intersection they have basically made the 347 just as reliable as the smaller strokers but up until recently the afforementioned problems were quite common but through research and advanced technology the aftermarket has seen fit to improve stroker kits and has greatly advanced their reliability.

Not meant as a flame
 

this is not meant as a flame but did you know most mod motors have the same exact design you just mentioned about the oil rings.

Now does that mean the mod motor is a great engine.......not yet not until they put it in a lighter car with proper gears.

As someone said there are new kits out there with the offset piston ring from CHP they stick out the most,but Lunati makes a 349 kit for a daily driver,so what does that mean now? Who knows.

I will leave you with this there is no replacement for displacement except for maybe a turbo. :)

I did a lot of research and talked to a lot of people before making the choice to build a 331. The 347 simpily didn't fit what I wanted to do with the car, which will be my daily driver and see the track a few times. This motor has to last me a long time and I won't have money to keep rebuilding it. I've head of too many cases that after 10,000 347's started burning oil. My Dad is also an engine builder and helped me make this decision. The 347 is still a great motor, like PKRWUD said, it all depends on what you want to do with your car.

argue all you want but you can't argue physics. 347 pistons have a shorter skirt which plain and simple means less stabillity. I have seen CHP's offset design, and it may work, but you certainly pay for it. The 331 is the better all around choice.

I've learned not to argue with anyone on a message forum, it's all a matter of opinion and preference (some experience helps too:D)...

I stated 347 for the reasons that have already been addressed (CHP)... however, I've had a bare R302 block that I've been wanting to turn into a 331 high-winder since '99 ($$$). I know about rod-stroke ratios... I run a long rod 306 (5.400" rods, 1.8:1)

All you can do is present your case and support it with facts... without getting ugly :D ...and let the person decide for themselves, I never woulda thought the 331 would have become the fad the 347 used to be a few years ago. I thought I was really on to something when I planned for the 331, now everyone wants to run one. I personally prefer the 331, but won't argue with the guy who says the 347 is better...

There is, in fact... no replacement for displacement! ...other than power adders ;)

Good Points Ultra
 

Very well put Ultraflo,
usually I try to stay away from post like this 331 vs 347,TFS TW vs AFR185 because I know where they end up going,right into a pissing contest about what I seen where,and who built it. :)

I think I have a happy medium here,if you want a302 based block race motor go for a 347,the extra throw of the longer rods will help to get it out of the hole,331 for reliability and a few extra revs on the top end of the track,now before someone says well a 331 can do that yes it can no doubt.

Personally speaking,I think if you get it put together properly,there is nothing to worry about with either,when you get off into junk parts and shade tree mechanics is when you run into problems. Ronnie Crawford is the father of the 347(at least he made it fashionable back in 92) and there are guys still out there with his 347's and 100k miles so it is all a crap shoot anyway.

Re: Good Points Ultra
 

Thank you sir... :)

I like, and totally agree with the point you made about assembly and machine work, along with quality components... which most people tend to overlook or even take into consideration. Properly built and tuned, either will make good, reliable HP numbers...

More cubes = more HP/TQ potential

But what if you had a bottle of compressed air, and a leaf blower? Huh Wally?

;)

Take care,
~Chris

...don't forget about the hair dryers!!! ;)

My 'bottle of compressed air' allows me to spank-up on some the N.A. BBC's I come across every time I go to the dragstrip...

Help me understand here, because this winter I'm building a stroker of some kind. Got a 392 hot on the brain at the moment. Anyway, I was under the impression that the cubes were calculated according to stroke length. If I bore a 302 .030" over, isn't the amount of cubes determined by the crank? And if you have to bore more for a 347, how much are we talking about.... .035"-.038"?? A stock 302 block should be good for at least a .050" bore.

In all reality, how many people build strokers to drive to work anyway? If a 331 were to make it 50k miles, an equally well built 347 should go for at least 45k miles shouldn't it. If you're using all the right parts, I don't see how it would make a noticable difference at all.

I believe that a 347 rod/stroke ratio is much better than most any of the big blocks were from the factory. I think it's even better than several of the brand M and brand G small block ratios. I've got a book that lists the ratios here somewhere but haven't found it yet. If I can find it in the next week or so, I'll post some of them on here for everybody's general information.

Sorry about all that babble. All I was really interested in was the necessary amount of overbore. :)

my point was that 4.000 bores will have more cylinder wall than 4.030 bores. That's all. Can't dispute facts

If you want it to last more than 50K miles get a 331

I'd have to concur with that opinion.

While it is true that there is no replacement for displacement, there are other ways of getting it. You're talking 16 cubic inches. That's less than one pound of boost. Get a small blower and a 331, and be happy for a few more years.

Remember, ALL a blower does is increase your displacement (without cutting any metal!).

Take care,
~Chris

SlowGT:

The math goes something like this for your stock 5.0 engine:

4.00 bore x 3.00 stroke x 3.141592654 (Pi) x 8 = 301.59 or 302

My 331 goes like this:

4.06 (which is a .030" overbore) x 3.25 x 3.1415 x 8 = 331.62 or 331

And the 347 kit:

4.06 x 3.40 x 3.1415 x 8 = 346.93 or 347

I personnally like the 331 kit for my application - which includes a ProCharger in the near future. Makes for a well mannered street car that can open up a can of whooop-arse by just taking the rpms up a little. :D

E

Damn. For 20 years now, I have always squared the bore, times .7853982 (easy to remember, used to be my best friends phone number), times the stroke, times 8. Thanks for the tip.

One question: What block are you starting with?

Chris - As I was ordering my 331 kit, I was screwing around with numbers trying to figure out how to calculate the volume of a cylinder when I remembered the following formula for volume (regardless of block type :D )

Formula for volume of a cylinder = Pi x Diameter x Height

Your calculation is pretty close say for a '306'

Yours = 4.030^2 x 3.00 x .7853982 x 8 = 306.133767

Mine = 4.060 x 3.00 x Pi x 8 = 306.1167882

E

Thanks for the extra info.

you gotta be careful with that formula the volume of a cylinder is not Pi x diameter x height

the correct formula is Pi x radius squared x height
for a 4" bore the radius is 2" so when you square that you get 4 again so it works out in this case but it will not work out if you had any other bore
I don't know if you figured it out or not but that is why in the "yours" formula you used 4.030 and in the "mine" formula you had to use 4.060 (4.030/2 and then squared) and this is not exact.
if you do it exactly you get the same answer to 4 decimal places

I kinda figured there hyad to be a reason I hadn't heard of that before. I wanted to know what kind of block you had because you say that your block is 30 over at 4.06", and that is only true if your block came stock at 4.030". 4.060" is 60 over.

Take care,
~Chris

not to mention that most cylinders are tapered downward. I dont know if that effects the usable cylinder volume or not, but its true.

How much taper is there in the walls?
if it only tapers by a few thousanths it would be a negligable volume to worry about
when you are talking about over 300 cubes half of a cubic inch doesn't make any difference

...please explain :confused:

Would a 351 be a better choice than either. just wondering, was a possible thought in my future

The diameter at the top of the cylinder is bigger than that of the bottom. Each cylinder in your engine block is not a perfect cylinder. They are tapered. The difference may be negligable when computing volume, but they are definitely tapered.

bore
 

4.0 bore is stock. Correct me if Im wrong, but if you're rebuilding a stocl motor, arent you going to bore the block? at least 10 over?? Generally, almost every motor Ive seen rebuilt has been at least 10 over if not 30. Also, CHP states that their 347 kit is a 100,000 mile capable engine. But everyone had their opinion;)

Conman - thanks for setting me straight with the proper formula. Like I said, I was just screwing around with my calculator trying to figure out the formula and now I see why my formula worked (2 squared = 4, which is very close to my 4.030 bore).

Chris - sorry if I confused you. Now we both have the proper formula.

This I didn't know! If it's true, then wouldn't the pistons be 'squeezed' at the bottom of the stroke - especially on a 331 or 347 where the stroke is farther down in the hole? And wouldn't this squeezing effect creat lots of extra heat, and friction causing premature wear on the piston rings/cylinder walls?

E

Why is ring gap so important if the cylinder is tapered???


Just a thought that came to mind. I've never heard of the tapered cylinder theory before.

...we're only talking a couple thousandths of an inch, but yes, he is correct about the taper... most pistons have a small amount of taper from top to bottom, again, only a couple thousandths...

Now a taper after about 50,000 mi. would be considered wear :), but again, there is a taper in the cylinders to begin with (freshly machined)

...not enough taper to 'squeeze' the piston, though ;)

When you figure a ring gap around .020 +/- a few thousandths per application, etc. then you've all kinds of room to work with the taper in the block...

.002 is something that would not be easily discernable with the 'naked' eye... a dial bore gauge comes into the equation then, which I just happen to have one and a freshly machined 400 small block (my dad's) in the garage that I'm going to play with here in a bit to see what I come up with...

...ya learn something new everyday :D

ultraflo - keep us posted on what you find out with your Dad's 400 engine. I, for one, am curious to see what you find.

E

Ok, I'll throw a bone in here.

My grasp of the 347 vs 331 issue falls into the rod vs stroke ratio.

The 347 with the 3.4 stroke and a 5.09 rod = 1.497 I figure I am off somewhat on the stock ford rod length but follow me here.

The Stock 302 3.0 stroke 5.09 rod = 1.696

3.4 stroke and 5.4 rod = 1.588

3.25 stroke and 5.09 rod = 1.566

3.25 stroke and 5.4 rod = 1.6615

A Chevy 350 3.48 stroke 5.7 rod = 1.638

327 3.25 stroke 5.7 rod = 1.754

Chevy 302/283 3.0 stroke 5.7 rod 1.90 !!!

Chevy SB 400 3.75 stroke 5.56 rod 1.483

3.75 stroke 5.7 rod = 1.52

3.75 stroke 6.0 rod = 1.60


Now you figure, what the hell is he talking about:confused:

Where the reliability issue comes to play is the side loading of the piston. Having a low rod to stroke ratio pulls the piston toward the side of the cyllinder at the bottom of the stroke. This makes for a less revving motor and can cause excess wear on the piston. On the other hand, the Chevy 302 with the big 2.02 valves and a 1.9 rod to stroke ratio will rev to the moon.

The stock Chevy 400 was thought to be a big POS for years until they started to put 5.7 or 6.0" rods in them. Note how low those rod/stroke ratios are.

I imagine the first 347 kits used the stock rods and had some problems with piston wear, with the 5.4" rods they should be ok.

The 3.25 crank and stock rods is almost as good as a 5.4 rod 347, and 3.25 crank and 5.4 rods is pretty good

One more bone for the pile :)

I set my 306 up with a 5.4 rod for a 1.8:1 rod:stroke ratio

Purrrrrs right to 7000 (more like 'screams' to 7k)

...and my lazy bones haven't made it to the garage yet (soon) to see what I can come up with for the cylinders on my old man's POS 400 small block (which he has 6.0" C&A rods and custom Ross pistons for) ;) ....it's also been converted to 4-bolt mains via the Milodon kit (three center caps anyhow)

The CHP 347 kit is the only one I'd consider if I were to run a 347... otherwise go 331. It's all about the components...

Rod:stroke ratio is a highly debated topic, but I personally adhere to and believe in it.

just do some research on the individual kits and decide which sounds most like what your looking for.

How about this ratio in my 331:

5.315 rod with 3.25 stroke = 1.635

Is this a good ratio for a soon to be blower motor?

E

quote from my builder when I posed the 331 vs. 347 question to him: "...the tolerances are right, the machine work is right, the parts are right, build the bigger motor and will be just fine for ya, Todd." I have an Eagle forged 4340 crank, forged 4340 H-beam rods, and Wiseco pistons. I trust this guy as he is not only a personal friend, but has made such accomplishments as building a 2500 horsepower 612 c.i. Merlin block-based Mopar motor (with a 10-71), a 1400 horsepower Toyota Supra T.T. motor, and a 800 horsepower 2.2 liter (that's right, 2.2L)turbo motor. He also does machine work for some heavyweight Nascar and NHRA builders.

That's exactly what mine told me, too. Then he continued to tell me about all the results of sloppy machine work and cheap stroker kits. And finished with "...there's no substitute for cubic inches". Jim Wohlford's motors came from this very same engine builder. I figure I'll put my money on his advice anytime.

Ya'll got some short standard rods in the chevies and fords. Ill have to pay attention to that when I rebuild. SB mopar standard rods are 6.123, 318/340/360.