Builders: Square engine, Over Square, or Under Square for you?

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318willrun

318willrun

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  • Heads Up 1/4 mile Racing. 400 C.I. is the target +/- 3 cubes for all cars. How would you like to get there in YOUR perfect world? What would be your factors in choosing? Or would you build it the same regardless?

  • Truck Pulls, would it change your selection?
  • Family sedan and fuel mileage. ??
 
I've always preferred either square or over square. Under square is like a high torque truck motor. Pontiac is a good example. lol
 
A 4.200 bore and a 3.500 stroke but only if you can get a short deck block.

Otherwise the R/S ratio will be through the roof.

And a 9k shift point minimum.

As for a truck puller I’m not sure. I suppose it depends on if it’s a single engine deal or multiple engines. And weight.

Family sedan?? That’s what I built my engine for. Daily driver family sedan.

4.080 bore, 3.79 stroke, of course a tunnel ram for this and the big engine above. 12:1 compression.

I forgot to mention a minimum of 15:1 as long as it doesn’t compromise combustion.
 
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4 x 4 square motor would put a guy at about 402, in compliance. Basically a standard bore 360 with a 4" arm.
 
Newbomb Turk said:
And it wouldn’t even be in the same area code with a big bore engine.
Click to expand...
  • I actually like a real engine in this setting. The BB 400 mopar. 4.34 x 3.38
  • Chevy guys would say "gimme the 4.12 x 3.75 small block 400
 
318willrun said:
  • I actually like a real engine in this setting. The BB 400 mopar. 4.34 x 3.38
  • Chevy guys would say "gimme the 4.12 x 3.75 small block 400
Click to expand...


In that case (here comes the hate) I would take the Chevy.

The deck on the 400 is so tall and the stroke so short that the R/S ratio is on the high side anyway and the piston would be horribly top heavy.

You start getting to 8k plus with a piston like that and your ring seal (under load) will be compromised too much.

Even if you coated the skirts and you were running with a clearance of .0015 (or less) it still would be far too compromised to be competitive.

If you could get a 400 block with say a 9.200 deck that thing would smoke some ***.
 
There's no real performance advantage of running a square or under square engine. Obviously you can make power with them people do all the time. But smaller bore less breathing ability and less surface area for combustion force to be applied and less displacement for any given stroke, longer stroke higher piston speeds will Lessing the rpm potential but with materials we got now days is lesser of a problem, generally higher friction loss and does offer more multiplication of combustion forces but for same CID (smaller bore) there less force to be multiplied basically a wash overall, displacement matters more to torque than how you achieve that displacement.

Obviously most are gonna pick the biggest bore out of these 3.

Bore x stroke = cid , 4.07 x 3.31 = 345, 3.91 x 3.58 = 344 and 3.685 x 4 = 342 all basically the same cid the 345 has the advantages but don't mean you can't build a crazy 342 it's just the bore mainly is working against you now if you looking just for a mild build you could easily make 300 hp out of any of them.
 
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Newbomb Turk said:
The deck on the 400 is so tall and the stroke so short that the R/S ratio is on the high side anyway and the piston would be horribly top heavy.
Click to expand...
what is your idea of the perfect deck for an engine of discussion? You said your bore and stroke (4.2 x 3.5), but what would the ideal deck be?
 
Over square every time.

The quote below is from Darin Morgan;

"An oversquare motor is absolutely superior at high rpm compared to a long-stroke motor of the same displacement. Formula One and IRL motors are hyper-oversquare, meaning the bore is twice the size of the stroke. If I could do that in a Pro Stock motor, I'd do it overnight, and the power would go up accordingly.
Once piston speed hits a certain range, frictional power losses sky-rocket. By decreasing stroke and increasing bore, you're not only dragging the rings up and down the bore that much less, but you also have less windage, the crank counter-weights get smaller, rod angularity decreases, deck heights get shorter, and the induction system package looks a lot better.
With a bigger bore and a shorter stroke in a high-end engine, you don't need a tall-deck block. That lets you move the valve-train closer to the deck, shorten the pushrods, reduce the resonance frequency of the pushrods, and wind the motor higher with less valvetrain flex.
In a high-end engine, you always use the biggest bore and shortest stroke you can get. However, there are some exceptions to the rule and you have to look at the entire engine package as a complete system."


For more practical Mopar BB applications there's the 451 Manifesto.
 
318willrun said:
what is your idea of the perfect deck for an engine of discussion? You said your bore and stroke (4.2 x 3.5), but what would the ideal deck be?
Click to expand...

I’d have to do the math but I think the tallest it should be is 9.200 but it may be able to get down to 9.000.
 
Newbomb Turk said:
I’d have to do the math but I think the tallest it should be is 9.200 but it may be able to get down to 9.000.
Click to expand...
So do you believe the shorter the deck height, the better? Or, only to a point. The 302 Ford has a 8.2 deck height. What's a 318, 9.6 if I remember correctly?????
 
318willrun said:
So do you believe the shorter the deck height, the better? Or, only to a point. The 302 Ford has a 8.2 deck height. What's a 318, 9.6 if I remember correctly?????
Click to expand...

Only too a point that you don’t get the piston so short you compromise the ring pack or you get the rods so short that you side load the pistons to death.

The shorter the stroke, the shorter the deck to keep the piston and rod length reasonable.
 
I think a +.020" 383 w/a 3.5" has a 1.88 rod/stroke w/stk. rod length. Still a bunch of slug, even with some decking....
 
Newbomb Turk said:
A 4.200 bore and a 3.500 stroke but only if you can get a short deck block.

Otherwise the R/S ratio will be through the roof.

And a 9k shift point minimum.

As for a truck puller I’m not sure. I suppose it depends on if it’s a single engine deal or multiple engines. And weight.

Family sedan?? That’s what I built my engine for. Daily driver family sedan.

4.080 bore, 3.79 stroke, of course a tunnel ram for this and the big engine above. 12:1 compression.

I forgot to mention a minimum of 15:1 as long as it doesn’t compromise combustion.
Click to expand...
So a .200 over Cleveland. Got it.
 
A normally aspirated engine will always prefer a bigger bore to allow larger valves to move more air.

Higher rpm racing engine you would want way over square 4.375" or 3.91" stroke. Heads up you're going to need it still pulling at 7500 rpms without running out of head.

Depending on the level of truck pulling I would use 4.375" bore and a 4.25" stroke. I've sold several 3.91" stroke cranks to pullers that are cubic inch limited.

Family car probably never sees 4000 rpm. 4.375" bore x 4.25" stroke. Let's make that old land yacht eat rubber for a city block.

Tom
 
318willrun said:
So do you believe the shorter the deck height, the better? Or, only to a point. The 302 Ford has a 8.2 deck height. What's a 318, 9.6 if I remember correctly?????
Click to expand...

Everytime an NHRA Pro Stock engine had the deck height lowered a .100" they picked up 15 HP. Now Pro Stock deck heights are down to as low as 8.600"

It's not a secret that lower deck heights allow for more horsepower to be made.

Tom
 
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