Many guys spin their engines over 6000rpm with both standard and long stroke engines. As far as torque goes, I can tell you this.

My friend Joe's 522ci 4 inch stroke 4.560 bore setups, with a 1071 blower , made more torque everywhere thru the rpm band, than my other buddies 540s that are 4.25 stroke. They had different cylinder heads and what not, but that short stroke setup simply made excellent torque. Around 930ft lbs if I recall.

Mike tkach also recently did a 509 with a whipple and gm iron heads that exceeded 800ftlbs from 3000rpm up. I've seen plenty of guys longer stroke engines not make that power.

Bottom line, there's alot more to the story than just the stroke. Its the overall combination of parts. As stated if you can do large bore large stroke, than that's a no brainer. But if you are at a crossroads of whether to invest a few grand into a stroker crank kit for your 502 or 454 , and you only had budget for that, I'd invest the money into the top end of the engines and keep the 4 inch stroke. A properly setup high flowing 502 will beat up on a poorly setup 540, as will a 454-468 beat up on a poorly setup 489/496. Just my opinion .

I would "rpm" either one as much as the cam and valvetrain allows.

Like I said, it's been tested, and with the everything else equal, there is no significant difference.

When we took apart the supercat engine we were surprised with the 3.920 crank and a 4.540 bore. Class rules dictated 509CI and we expected a 4 inch crank and a 4.500 bore.
My buddy called up to baker who did the heads for the engines and the guy he got on the phone said they found that the optimum bore diameter for the spec heads was 4.540 so they worked backward from there to come up with the stroke.

As has already been said, it has a lot to do with unshrouding the valve and maximizing the combustion chamber.

That also hold true for a forced induction engine and a naturally aspirated counterpart. The optimal port cross section area, volume, and velocity profile for will be the same for both, all else equal.

Bob

Clearly my answer was kinda simplistic for a rather simplistic question, the basics being at sweep near 90* per cylinder, you gain a slight advantage on low end torque, much like a longer wrench turning a stuck bolt. Torque (the only thing measured by a dyno) is also, in part a result of cylinder PSI x surface, so you are correct, that can't be discounted. In real life, my experience has been the advantage of larger bore force closely offsets the advantage of stoke, so that both motors OP describes at 5500 rpm (all things being equal) will be hard to tell apart.

SB, you know I'm old school, so if I'm getting to choose a motor for a boat, I'd take long stroke in a big ol' lumbering boat every time. LOL!

I like all the insight. Very entertaining. I think there's a few takeaways from this...

1) Go with the larger bore AND the larger stroke. --> "The no-brainer"
2) Bolt on a blower for more power --> Not really part of the qusstion, and completely complicates the question, but 100% agreed
3) The consensus seems to agree, all things other things considered equal --> No measurable difference

With that in mind... let's throw in a few more variables...
--Now i'm starting to get real to life--
1) Let's consider it's a retrofit hyd roller cam at about 589, 610 lift
2) Aluminum Dart Pro 1 at 310 cc
3) 800 cfm Holly vacuum secondary
4) No room for a blower (blowers are out of the question)
5) OK exhaust (aluminum manifolds with individual runners for only 12 inches)
6) Purpose is to go 60 MPH and drink heavily when I get there in a 13,000# Baja
7) The 4.25 stroke engine is around $3500 the 4.00 stroke engine is around $4000 new (same warranty)

Oh... one more variable.... I'm not going to build them bigger in the future. :(

GO!!!!

That $$$ For shortblocks new ? And what parts are in them?

Stroke is cheaper to add later than bore. Crank and pistons instead of block and pistons. Way back in the old days they didnt neasure displacement. They measured bore area. Felt it made little to no diff how far the piston went up and down.

Diesel

You are not getting anything good for that kinda money in shortblocks.....and why run vacuum secondary? a place to fail at WOT

OP, probably ought to decide on one or both now, but not one now, one later. Stroke is crank, longer rods, pistons with shorter wristpin height, likely clearencing the block somewhere, an likely a stroker pan. (don't ask!!!) Bore is nice forged pistons, new block or bore work (and everything else you oughta do while it's open, like cam bearings, decking, etc. etc.) If you don't design it all it once, you end up buying good expensive pieces twice.
SO MUCH CHEAPER in the longrun to bite the bullet and do it all as once.

My machinist has a sign in his shop entry: "SPEED COSTS MONEY..........how fast do you wanna go???"

That is the truth!!!

a bit off the OP's plans, but just for kicks ck. out the bore and stroke combination, note the rod legth too OSO ad#60249 .. like Mild said they need to be properly set up.

http://www.offshoreonly.com/classifi...o60249-en.html

Thanks for sharing I'CE. It is interesting all the combos out there. Unfortunately no one has un biased proof on what works best, safestest, most power.

I don't like that combo personally..... Looks like they lowered the compression on a NA supercat combo with a blower stuck on top...

Ilmor did just merge with scorpian race engines...

What engines do you have now, and how fast are you going??

i have 454's and I'm running around 62 mph on a good day.That was before i lost a motor. Not that I really want to go much faster, its a tank. But if i had the same speed and really good reliability, I could be happy. Looking for a good smooth idle, easy starting, and reliability... and hopefully 65 MPH.

Are these stock 330's, 365's, custom built 454s, etc? Just trying to get a feel for what you have there, and where you need to go to meet your goals.

build 540's then!! still should be reliable they wont work as hard as a smaller CI engine to move it....

Agreed terrible combo for a tall deck. And a 4.625 bore is a worn out motor.

Why? 650hp 454's are easy aren't they?

LOL yes for Phil!!!

Hot Rod mag did a great test of these theories a few years back. They built 2 motors of same displacement. One big bore, one big stroke and they were.....The same on the dyno. Cube is a cube unless your rev very high which is not big in the boat world. Great article. Wish i could post it.

I'd beg to differ on said opinion, as the stroker engine would have a slight advantage over the big bore engine, piston speed being the advantage and if you look at an engine as what it really is (a pump) you will find that the longer stroke increases the piston speed which in turn increases the air volume of said pump... beyond that of the big bore engine... however, with that being said, if you rev the BB (big bore) engine to a point that the piston speeds match then you'd have a stroker crusher!!! as that BB engine would dominate over the stroker
says the oldest student in med school!!!

OH NO!!! WHO DUNIT!! :hitfan: someone kicked over the hornet's nest!!! :angry-smiley-044:

Well think about friction of stoker compared to not, I would use big piston less stroke due to shrouding and friction... Less up and down = less friction

Piston speed, yes, is faster with more stroke.

But.....what about rate of displacement, again, if both motors displace the same.

I thought she said piston size doesn't matter................

being that this is relative to boats lets say the big bore is happiest at 8000 rpm and the big stroke is happiest at 6000 rpm. what effect of prop and drive ratio selection would be optimal would you be giving up too much prop to spin the motor to 8?

that's a bit unrealistic as the piston speed differential in a .250 stroke differential would be considerably less than 2000 rpm

well this thread does make one think now doesn't it? lol FYI I'm a fan of the bore VS stroke, but hat to put that out there just for chits and giggles!!!

She tells you that so you will feel better about yourself.

What about mass in the equation?? Just thinking a shorter stroke has a slower piston speed, but a larger bore requires a larger piston, therefore you a reversing direction on a larger piston..larger piston= greater mass=greater inertia

So we have longer stroke=greater piston speed=greater inertia
vs. larger bore =greater mass =greater inertia

Remembering that an object in motion will remain in motion unless acted upon leads us to the point that:

To truly determine which is most efficient we must plot on a linear basis the force required to reverse piston direction. The least amount of force required should be the most efficient. Of course it must also be determined when comparing different stroke vs. bore scenarios if this difference is linear or exponential.

Who has their slide rule handy??

Hey phragle... tell GD to hurry up with the sawzall we'll get the slide rule out when building cat power!!!

I understand that i was just using that in relative terms to is building a high reving big bore short stroke wasting to much energy versus big stroke low revs torque monster. Was just curious of thoughts being i dont have much experience with this debate relative to boats

I would think that the BB engine would be in the 6000rpm area and the stroker around 5500ish...

Bore, just because it sounds better and more manly.

Most bbc heads are happier on a bigger bore so if 500 is the only difference ,go with bore ..Where are you buying a new 4.5-ish bore engine for $4000

Tech Talk #53 – Big Bore or Long Stroke: Which Is Better?
DavidTechArticlesBy David Reher, Reher-Morrison Racing Engines

“An engine produces peak torque at the rpm where it is most efficient.”

Recently I’ve had several conversations with racers who wanted to build engines with long crankshaft strokes and small cylinder bores. When I questioned them about their preference for long-stroke/small-bore engines, the common answer was that this combination makes more torque. Unfortunately that assertion doesn’t match up with my experience in building drag racing engines.

My subject is racing engines, not street motors, so I’m not concerned with torque at 2,000 rpm. In my view, if you are building an engine for maximum output at a specific displacement, such as a Comp eliminator motor, then the bores should be as big as possible and the stroke as short as possible. If you’re building an engine that’s not restricted in size, such as a heads-up Super eliminator or Quick 16 motor, then big bores are an absolute performance bargain.

I know that there are drag racers who are successful with small-bore/long-stroke engines. And I know that countless magazine articles have been written about “torque monster” motors. But before readers fire off angry e-mails to National DRAGSTER about Reher’s rantings on the back page, allow me to explain my observations on the bore vs. stroke debate.

In mechanical terms, the definition of torque is the force acting on an object that causes that object to rotate. In an internal combustion engine, the pressure produced by expanding gases acts through the pistons and connecting rods to push against the crankshaft, producing torque. The mechanical leverage is greatest at the point when the connecting rod is perpendicular to its respective crank throw; depending on the geometry of the crank, piston and rod, this typically occurs when the piston is about 80 degrees after top dead center (ATDC).

So if torque is what accelerates a race car, why don’t we use engines with 2-inch diameter cylinder bores and 6-inch long crankshaft strokes? Obviously there are other factors involved.

The first consideration is that the cylinder pressure produced by the expanding gases reaches its peak shortly after combustion begins, when the volume above the piston is still relatively small and the lever arm created by the piston, rod and crank pin is an acute angle of less than 90 degrees. Peak cylinder pressure occurs at approximately 30 degrees ATDC, and drops dramatically by the time that the rod has its maximum leverage against the crank arm. Consequently the mechanical torque advantage of a long stroke is significantly diminished by the reduced force that’s pushing against the piston when the leverage of a long crankshaft stroke is greatest.

An engine produces peak torque at the rpm where it is most efficient. Efficiency is the result of many factors, including airflow, combustion, and parasitic losses such as friction and windage. Comparing two engines with the same displacement, a long-stroke/small-bore combination is simply less efficient than a short-stroke/big-bore combination on several counts.

Big bores promote better breathing. If you compare cylinder head airflow on a small-bore test fixture and on a large-bore fixture, the bigger bore will almost invariably improve airflow due to less valve shrouding. If the goal is maximum performance, the larger bore diameter allows the installation of larger valves, which further improve power.

A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don’t travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc so the windage is reduced. In a wet-sump engine, a shorter stroke also cuts down on oil pressure problems caused by windage and oil aeration.

The big-block Chevrolet V-8 is an example of an engine that responds positively to increases in bore diameter. The GM engineers who designed the big-block knew that its splayed valves needed room to breath; that’s why the factory machined notches in the tops of the cylinder bores on high-performance blocks. When Chevy went Can-Am racing back in the ’60s, special blocks were produced with 4.440-inch bores instead of the standard 4.250-inch diameter cylinders. There’s been a steady progression in bore diameters ever since. We’re now using 4.700-inch bores in NHRA Pro Stock, and even bigger bores in unrestricted engines.

Racers are no longer limited to production castings and the relatively small cylinder bore diameters that they dictated. Today’s aftermarket blocks are manufactured with better materials and thicker cylinder walls that make big-bore engines affordable and reliable. A sportsman drag racer can enjoy the benefits of big cylinder bores at no extra cost: a set of pistons for 4.500-inch, 4.600-inch or 4.625-inch cylinders cost virtually the same. For my money, the bigger bore is a bargain. The customer not only gets more cubic inches for the same price, but also gets better performance because the larger bores improve airflow. A big-bore engine delivers more bang for the buck.

Big bores aren’t just for big-blocks. Many aftermarket Chevy small-block V-8s now have siamesed cylinder walls that will easily accommodate 4.185-inch cylinder bores. There’s simply no reason to build a 383-cubic-inch small-block with a 4-inch bore block when you can have a 406 or 412-cubic-inch small-block for about the same money.

There are much more cost-effective ways to tailor an engine’s torque curve than to use a long stroke crank and small bore block. The intake manifold, cylinder head runner volume, and camshaft timing all have a much more significant impact on the torque curve than the stroke – and are much easier and less expensive to change.

ok true all that but keep in mind this is a boating forum... its assumed that 6000rpm is tops... maybe 6500 in certain applications... not a 10,000 rpm prostock engine... apples to apples

Wow that is some garbage. Think about what you're saying.