Out of sheer curiosity, how would I get a SBC 350 to put out 350Hp without modifying the heads or the block? I'd prefer without forced induction.

 

1 HP per cubic inch isn't that much of a challenge.

Good heads (Vortec or at least 186 or similar if stock, lots of aftermarket ones are better); MODERN cam in the 220ish range on the intake and 228ish on the exhaust, as near .500" lift as the valve springs will allow; good exhaust with headers (1¾" primaries), 3" collectors, 3" cat, 3" cat-back; practically any intake & carb; my personal direction would be a Performer RPM and a Holley 650 or 750.

Then of course there's the question of USING that power. Converter, gears, LCARBs, and so on. There's ALOT more to making a car fast than just some random dyno number.

 

Then what would you recommend to get good torque? I'd like to aim for 400Ft-ibs round about.

 

Torque is a function of CID, cylinder fill, and what one might call "thermal efficiency".

CID speaks for itself. You said 350 CI, so, 350 CI it is. Doesn't make any material difference what overbore the block has had to endure to return it to useable state. So don't bother us with "355", "357", etc. It's a 350. The maintenance it has needed so that it can remain useable is TRIVIAL and IRRELEVANT.

Power comes from fuel. Nothing else. Fuel burns, which raises the temperature of the gasses it's involved in, which is ultimately what makes power. When temp is raised and volume remains constant, pressure increases. An engine works off of pressure (pounds per square inch) pushing down on a piston area (square inches) and moving it over the stroke (inches). Torque at any given RPM then, is the average pressure while the piston is being pushed down, times piston area, times stroke. Note CAREFULLY that piston area times stroke equals CID, thus, torque is INTIMATELY related to, and constrained by, CID. NOT "Pontiac", not "big block", not "castings painted orange-red instead of blue", not "came out of a Vette", NOT NOT NOT NOT NOT NOT. CID. Nothing more, nothing less. It takes air (more specifically, oxygen) to burn fuel. Air containing about 20% oxygen, and gasoline as we commonly know it, will want to be in a ratio of somewhere around 12.6 to 13:1 by mass, air-to-fuel, for optimum results at max power. Therefore, since any DUMMY (even me) can jam more fuel into anything, power ends up being controlled by how much air is available. Cylinder fill is about how much fuel/air mixture you can get into, and out of, the motor. Since fuel is EEEEEZZZZZZZZZY, managing the flow of various gasses usually dominates this aspect of engine design.

An internal combustion engine burns fuel, which generates heat energy, which it then converts into mechanical energy. Very VERY roughly, at your typical ICE's max HP conditions, about 1/3 of the energy goes out the exhaust (near 10% is wasted solely in keeping the water that's produced during combustion in vapor form, which is why in those high-efficiency home heating systems that burn gas or oil, they use a condenser to extract that heat), 1/3 goes into the cooling system, leaving 1/3 to become mechanical WORK. Anything that can be done to tilt this in favor of mechanical work pays off. Now, don't take those numbers as absolute immutable fact; they might be 35%, 33%, and 32%, for some given motor or other, or other similar numbers; butt they're always right around there. "Thermal efficiency" is DOMINATED by compression. Compression is how much the hot gas resulting from combustion is allowed to expand, which is how it makes mechanical work: a low compression engine tends to send more energy out the exhaust.

Fuel takes time to burn. It doesn't "explode" when everything is working right: it BURNS in a slow, measured, controlled, sort of way. When it burns it makes heat. (duh) Ignition timing is crank angle of rotation at which combustion is started. It's important that it's started at the optimum time such that the pressure inside the cyl reaches its peak value just as the piston passes through TDC, so that it doesn't have to compress high-pressure gasses any more than it has to, butt rather, can begin producing power as soon as the piston begins moving down.

In the real world, on pump gas (let's say 91 octane), with anything remotely like a sustainable street-driven engine, that's expected to LAST for many tens of thousands of miles, about the most torque you can expect to get out of ANY motor, is somewhere near about 1.25 time the CID. I.e, you have a 350, you're gonna be able to get, AT MOST, 430 - 440 ft-lbs of torque, if everything is PERFECT, OPTIMIZED, and JUST RIGHT. Most often, in the interest of safety and longevity, various things are compromised, such that the peak torque is lower than that; closer to 400 ft-lbs. This peak of the torque will occur at some RPM dependent on the cam, heads, etc. A truck motor might make its 430 - 440 ft-lbs of peak torque at 2200 RPM; a NASCAR racer might make it at 7200 RPM; butt in the end, if the engine is gonna run on pump gas, it's gonna be 430 - 400 ft-lbs, at best, AT THE MOTOR'S PEAK TORQUE RPM. The builder controls what that RPM will be by choice of things like the cam. If the peak torque RPM is VERY low, the compression (and as a consequence the actual peak torque value) as well as the ignition timing, might need to be reduced to prevent detonation, because the air/fuel mixture spends SO MUCH time after it gets ignited, being compressed.

HP is torque times RPM times a constant (2 pi ÷ 33000, since the definition of a HP is 33000 lbs in 1 minute, and torque is expressed in terms of a circle) which works out to torque times RPM ÷ 5252.11.

400 ft-lbs out of a 350, at the crank, is pretty ordinary. Doesn't take any "Engine Masters" kind of magic to get there. With a typical street cam giving peak torque at maybe 3000 RPM and peak HP at maybe 5000, you should end up with around 400 ft-lbs @ 3000, and around 365 HP @ 5500. Not that hard.

 

You have no idea how helpful this entire thing is going to be. I've been wondering when I'm gonna have to get into the actual science of this project. (I know it isn't very complex, but for my first time doing this, this is huge to me.) So thank you for the very useful information!

 

Exactly what do you mean by "not modifying the heads"?. Is this to say something used out of the box?
I had excellent results, and I'd say right along the lines of your build direction, with Vortec heads (unported), compression ratio in or around 10:1, a hydraulic roller cam (276/282, 224/230, 110 LSA, 106 ICL) and a tight piston to head clearance at .040". The latter might be difficult with an "unmodified block" as the typical factory puts the piston more than .025" down the bore at TDC. But there can be workarounds.
I've always understood, in this power range of engine in particular, that getting a solid cranking compression number, something approaching 200 PSI, is what gives that torque. The HP falls in line.
10:1 with a "short" cam will get you there. Peak HP RPM , will the example posted above, is below 6000 RPM. Plenty for a street deal.
Then there's the aforementioned "ancillaries". Gearing and converter make a world of difference.

EDIT: I wouldn't myself to just the Vortec heads. I'd prefer aluminium (for a variety of reasons) however it's very much "caveat emptor". When considering something aftermarket, especially a budget orientated cylinder head, (offshore in particular), there's no guarantee it's good to go right out of the box.

 

on a stock engine, nitrous the THE BEST bang for the buck.
its been proven over and over and over.

its not 1984 anymore, dont be afraid of naws...

 

Well...........not exactly. Torque is a measurement of leverage AND pressure exerted ONTO that leverage. So, for any given situation, a longer LEVER will be able to produce a higher TORQUE measurement. In the case of an engine, the LEVER is is a combined rotating motion of the crank, rods, and pistons. If the crankshaft has a longer 'stroke' then the LEVER is longer and thus the torque value will be higher. That's why a 383 'stroker' is such a great combo. Cause it makes gobs of torque. And TORQUE is what gets you going from a stop or helps you look cool doing huge smokey burnouts!! Bore size DEFINATELY plays a part in this as well. The bigger the bore, the more potential for pressure being exerted upon the LEVER.

 

Yes, EXACTLY.

You left out the most important part. Which is,

IF ALL ELSE IS EQUAL. Ceteris paribus for those of you that remember your grade school Latin.

If you take 2 engines with the SAME CID but different bore & stroke, and build them up equally (which isn't always easy to guarantee, as different ratios of rod length to stroke cause the piston speed to be different at different points and also the induction system to respond differently), they will make THE SAME torque. If on the other hand you take 2 engines with the SAME bore, and add stroke to one of them, then OF COURSE the torque goes up. It increases in DIRECT PROPORTION TO the change in CID (bore area x stroke). No magic is attached to "lever arm" in any way beyond that.

The "lever arm" part of it is thus merely one of the 2 components of CID.

You can work it out for yourself. Imagine that you have a cylinder whose bore is, say, 12 sq in area (about 3.9" diameter) and 3.5" stroke, and there's, say, 1750 psi on average in the cylinder, over the course of one engine revolution (all 4 strokes). Those #s are somewhat comparable to a 350, I just picked them to keep it eeeeezzzzy to work out. 12 sq in is exactly 1/12 of a sq ft, and 3.5" is about .343 ft. The force that the pressure exerts on the piston then is 1750 psi x 1/12 sq ft on average over the engine cycle, which is about 146 lbs. The torque in ft-lbs that this cylinder will produce is 146 lbs x .343 ft, or, right at 50 ft-lbs, from this one cylinder. Since there are 8 cylinders in a 350, then the total engine torque is about 8 times that, or about 400 ft-lbs. Now change those #s up: let's make the bore smaller so that the piston area is half of what it was (6 sq in, which is about 2.76" diameter), but the stroke is twice as long, or 7". We'll still have the exact same CID that way. Let's assume that the pressure is the same too, as it will be if it's burning the same fuel, has the same cylinder fill, and the same compression: ALL ELSE IS EQUAL. Now, this new engine will have about 73 lbs on the piston (1750 psi x 1/24 sq ft), and the torque will be that, times 7", or .686 ft; which is, guess what, 50 ft-lbs. Times 8, that's still 400 ft-lbs from this new engine, even though the stroke is DOUBLE what it was. Stroke is doubled, CID is kept the same, torque is the same.

Now of course if you leave the bore the same and double the stroke, then of course the torque will also double, BECAUSE THE CID DOUBLED. There is nothing "magical" about stroke compared to bore, when it comes to CID, other than the aforementioned effects of the ratio of rod length to stroke. CID is CID no matter how you get it.

And of course, all of this is also assuming that ALL ELSE IS EQUAL outside the cylinder as well; that is, we're comparing 2 naturally aspirated engines for example. Sure, you can take an engine with whatever CID, and get WWWWWWAAAAAAAAAYYYYY more power out of it with boost; but that violates the ALL ELSE EQUAL principle, because cylinder fill is now no longer the same.

Everything about an engine is just NUMBERS. Once you get your brain wrapped around them, it's all obvious. You no longer have to be a slave to traditional hot-rodder ignorance and legends out of the hoary mists of time repeated endlessly as "truth" without understanding any of it and "I'm no good at math" crap. Paying attention in physics class would also have helped.

 

Sofa is correct and if you want an entertaining way to see this play out Power Nation did an equalized competition between the chevy 305 and the ford 302. Same specs for the induction and exhaust, same fueling etc. They made the exact same power at the end of the day.

 

It would be amusing to see a similar comparison of a Chevy 302, 305, & 307 done that way. Same heads, cam, compression, induction, etc. Of course their uppermost RPM limits might be a little different if the chosen induction system supported them even reaching that point, for mechanical reasons not related to power output, and accounting for the differences in rod length ratio; butt it would help lay some of the old myths to rest. While none of those is inherently "bad" in and of itself, they're all "bad" in the sense that for the same money and whatever all else, you can get ALOT more even with other STOCK available combinations let alone aftermarket ones. The 302 for instance was introduced ONLY to meet the rules of one specific class of racing, the TransAm series, which at the time had a hard 5.0 liter limit, and required 500 homologues identical to the track version to be made available for sale to the general public, and NOT because it was particularly "superior" to something else. It would be more an intellectual exercise, rather than a demonstration of how "good" some one or another is.

 

GROSS, NET, or Wheel? Huge diff there....

 

THIS STOCK LONG BLOCK block L98 made over 400 net crank tq. with an intake and exhaust, only.