Stroking theory question

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1970Duster

1970Duster

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Be it LA, Mag, or gen 3 Hemi can be applied to either and/or all 3. So the question is what kind of stroke (biggest) can they handle, which I already know there is a 4.250 stroke crank out there but what about a 4.5 or 4.75 hell even a 5.00 stroke in them? Is there massive interference with the block at that stroke point? Just no body has thought of/try that big or what? What do you guys/gals think about a small block with a 5" stroker crank in it. Just thinking out loud here.:burnout:

P.S. For hell of it what kind of output would it make with a 5" stroke, 10 to 1 (or 11 to 1 if you prefer) with a .650/.650 solid roller on 110 say 265/265 @50 duration (by all means pick a better cam those number were picked out of a hat)?
 
Just stuffing a huge crank in is not the answer

There's been more than books, hell there's been whole libraries written on things like stroke vs bore, rod length, piston speed, and rod to stroke ratio, along with a few other things

People like Yunick and Grumpy and uncountable numbers of Ford, GM, Mopar, and you name it, probably every serious engine builder ever born have spent lifetimes on this work.
 
I understand it not just throwing any crank in there hoping it works. I'm just curious if a 4.5, 4.75 or 5.00 stroke even feasible in any of those 3 blocks.
 
I would think if it's advantageous, would produce a good combination and hang together, LOL, someone would have already done it.

I'm not tryin' to make fun, not at all. But I see no reason to reinvent the wheel when so many good ones are already available, LOL
 
There's a line at which you meet the point of diminishing returns with anything. It's not just about the physical fit. It's also about all that weight being pushed further and further out away from the crank center line.

Also too, to "me" an under square motor is not as efficient as an over square one. This is why Pontiacs sucked balls and why for the most part they had no street cred whatsoever in the muscle car wars. I know.....here come the Pontiac lovers. But it's true. The Ram Air IV cars even got beat up on by 383 Road Runners.
 
Almost everything got beat up by a good 383 Road Runner. A friend of mine was into the 12's almost stock...
 
The block height won't allow it, the rod angle at mid stroke would hit the bottom of the cylinder and at bottom of stroke the short rod would have the piston skirt hitting the crank.

The math wont add up, the block would need to be designed to fit these dimensions.
 
66fs said:
Almost everything got beat up by a good 383 Road Runner. A friend of mine was into the 12's almost stock...
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That still doesn't stop Pontiacs from suckin. lol
 
Yeah, but they looked good on any NASCAR track!
 

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Also too, to "me" an under square motor is not as efficient as an over square one........

I don't know........I'm not saying that I'm a huge fan of under square motors...they can and do get the job done...........people seem to like the 4 inch crank into the 318, I haven't read, or heard of people crying they are no good

Sonny Leonard doesn't seem to be hindered by his 5 inch stroke mountain motors that are waaaay under square, with a 3000 hour life span between freshing's for his "street" motors, and make 1300HP NA

The most recent "Engine Masters" winner, Jon Kaase, took a mod motor ford out to 4.5 stroke I think it was, made crazy HP

Both the 170 and 225 /6 are under square; I never heard any any commentary that they were inefficient...

Like I said, under square engines can and do get the job done, they are as efficient as any thing else.
 
I think any engine taken to extremes will preform. I was speaking strictly from a mild street perspective.
 
I get a kick out of the drag way, and people. For example, I seen a stock block 440 with a solid cam, single plane intake and a 850 dp run 10.50 in a dart with 3.91's. Right next to him was a 500 cubic inch (stroker 440) with 4.56's in a duster run 11 flat. Then a 340 duster (x heads) with a "gas-leaking" dp holley turned a 10.35. lol
Cubic inches, strokers, I even seen a Indy head 440 built with no expense spared in a volare go 11's. Idk, you tell me the answers......
 
I rode some harley shovelheads with 4.75" and 5" strokes with 3 5/8" and 3 13/16" bores- they wore out faster but the torque was incredible and it was exhilerating to rev em up.

I agree that the high rev big bore short stroke motors are much faster but I like driving a 114" harley better than a faster 1000cc ninja.
 
JBurch said:
Both the 170 and 225 /6 are under square; I never heard any any commentary that they were inefficient...

.
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Not examples of anything 's far's I'm concerned. The poor ports and limited valves hardly make these a performance anything.
 
JBurch said:
The most recent "Engine Masters" winner, Jon Kaase, took a mod motor ford out to 4.5 stroke I think it was, made crazy HP

.
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If I'm thinking about the same engine, this used a 4 valve head. I guess it depends on what "is" is. Are we talking about something "we all" have here, a conceivable streetable wedge, or something so exotic that even Ferrari would have trouble selling it?
 
Coronet 500 said:
The block height won't allow it, the rod angle at mid stroke would hit the bottom of the cylinder and at bottom of stroke the short rod would have the piston skirt hitting the crank.

The math wont add up, the block would need to be designed to fit these dimensions.
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x2. Theory or not - it won't fit.
 
you want something that will make more than 10 passes down the strip also.

if you are spending big dolla, you want the engine to be survivable

the thing that made 340's shine is that with a solid lifter cam you could spin 'em pretty high. and they held together. more than one weekend of fun. no they didnt make all the hp/tq the hemi or 440's made, but they were fine for week after week street cruisin' and strip & made a name for themselves that way.

nowadays if you are talking BIG hp/tq from a small block you are pretty much talking forced induction. then again, you want a sturdy bottom end not weak

if you want to stroke to the moon for a naturally aspirated engine, people just use big blocks or gen2 hemis, if they have money they get them with wide cylinder spacing (aftermarket blocks) so they can go real big on bores too.

a lot of people just settle for a 408 small block and are happy with that. holds together well if you use the right components. cheaper by far than a gen2 and can last for years and years.
 
67Dart273 said:
Not examples of anything 's far's I'm concerned. The poor ports and limited valves hardly make these a performance anything.
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You just threw thousand's of devoted /6 fans under the bus with that...............
 
67Dart273 said:
If I'm thinking about the same engine, this used a 4 valve head. I guess it depends on what "is" is. Are we talking about something "we all" have here, a conceivable streetable wedge, or something so exotic that even Ferrari would have trouble selling it?
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Yes the head on the engine is a 4 valve; how ever the initial comment about the efficiency of under square engines didn't include head type feeding the cylinder, and 4 valve heads, in the realm of being available to us all, are everywhere.......


Kaase's mod motor, is based on production pieces; it made staggering power, coupled with a staggering price to build.

I'm not saying I'm in love with it...cuz I'm not; I used it as an example of something under square getting it done.................

Streetable, any more is an extremely vague discripter, not when you have 6 second cars driving around on the power tour, pull in to a race venue, drivers pull out their lap tops and down load their "tune", race and then just before leaving, get the lap top back out and down load the "drive"..........
 
Undersquare was more an issue (back then when conventional wedge heads and optimized valve angles and chamber designs were not well-developed) of favoring bore over stroke so that you could get the biggest possible intake valve in the motor. (all else being equal). Today motors tend to be smaller bores and longer stroke from the factory because torque and part throttle tends to be more important then peak power (as was nearly always the case back then as well). Pontiac's profit money was in loaded Bonnevilles and grand prix that weighed 4200+ pound, that took precedent over getting 10 more horses out of the GTO's 400.

Cylinder heads have come a VERY LONG WAY since then (50 or so years) so although for a given displacement an oversquare motor will tend to make more HP per cube, it's not always a practical consideration when trying to get as many cubes as possible within a given engine block. Bore spacing tends to be much more limited than crank center to deck height....more room to grow UP rather that OUT.

As for an LA, I know of a 501" 4.5" stroke motor that Ron Silva built with Cam specs nearly identical to my 517" low deck Big block.

I build my shortblocks (which tend to ALL be strokers these days) for torque and my heads for horsepower....that philosophy seems to work really well for me as the best of both worlds.

4.25" works really well in the LA with a 6.2" rod and a 1.26" compression height piston. but for maximum horsepower (hp curve, ie, shooting for between peak torque and peak HP RPM band and with the least amount of rapid fall off after peak HP RPM) I would build around the 3.79 stroke and as long a rod as I could get.
 
JBurch said:
You just threw thousand's of devoted /6 fans under the bus with that...............
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Naw. I don't think he did. I think the long stroke is what makes a 225. Think of the millions that were put in trucks.....of ALL sizes no less. Stroke makes torque. Period. Regardless of bore. It's just that in most instances, an under square motor is not as efficient, IMO. If they were, you'd see them much more prolific than what they are from a manufacturers standpoint and that's not the case.
 
Streetwize said:
Undersquare was more an issue (back then when conventional wedge heads and optimized valve angles and chamber designs were not well-developed) of favoring bore over stroke so that you could get the biggest possible intake valve in the motor. (all else being equal). Today motors tend to be smaller bores and longer stroke from the factory because torque and part throttle tends to be more important then peak power (as was nearly always the case back then as well). Pontiac's profit money was in loaded Bonnevilles and grand prix that weighed 4200+ pound, that took precedent over getting 10 more horses out of the GTO's 400.

Cylinder heads have come a VERY LONG WAY since then (50 or so years) so although for a given displacement an oversquare motor will tend to make more HP per cube, it's not always a practical consideration when trying to get as many cubes as possible within a given engine block. Bore spacing tends to be much more limited than crank center to deck height....more room to grow UP rather that OUT.

As for an LA, I know of a 501" 4.5" stroke motor that Ron Silva built with Cam specs nearly identical to my 517" low deck Big block.

I build my shortblocks (which tend to ALL be strokers these days) for torque and my heads for horsepower....that philosophy seems to work really well for me as the best of both worlds.

4.25" works really well in the LA with a 6.2" rod and a 1.26" compression height piston. but for maximum horsepower (hp curve, ie, shooting for between peak torque and peak HP RPM band and with the least amount of rapid fall off after peak HP RPM) I would build around the 3.79 stroke and as long a rod as I could get.
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Probably an accurate description^^^^^^^. But Pontiacs still SUCK. lol
 
Go to a college and take an Internal Combustion Engines I and II classes.

It's impossible to explain two semesters worth of classes in a post...


You reach a point where you get diminishing returns.


Why not sleeve it and put a 10" diameter piston in it also....

Or 22" to match the new trend in tires/wheels....
 
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