The Stovebolt Site Forums The Shop Area The HiPo Shop 327 torque monster

i may be a bonehead but i like to look at my 63 shop manual. you know what it says? 292cid= 280 ftlbs @ 1600 rpms, 3 7/8" bore, 4 1/8" stroke. 283cid= 275 ftlbs @ 2400rpms, 3 7/8" sroke, 3" bore. 327cid= 305 ftlbs @ 2000 rpms, 4" bore, 3 1/4 stroke.
not trying to throw out a bunch of numbers. the 292 looks to get .96 ftlbs per in2 at 1600 rpms, the the 283 gets .97 ftlbs per in2 but it has to turn 1.5 times as fast to get it! the 327 only gets .93 ftlbs per in2 and it has to turn 1.25 times faster with 35 more cubic inches!!!
well it looks to me like the ol 292 has more low end torque and well, i'll be, it has a 4 1/8 stroke. i wonder if that could have anything to do with it. maybe that and the heavier crankshaft (sorry just had to say it). so who knows what your torqe application is, but you might want to reconsider your bigger bore= more torque, per cubic inch that is. in the example above the bigger bore engine doesn't hold up so good. increasing rpms to get more torque will only work so far.

Sorry, I forgot how to calculate displacement. The correct bore size for a 302 with a 4" stroke would be about 3.46". The interesting thing to note about the 3 engine comparisons, as displacement increased, whether it was stroke or bore, torque increased also. The RPM where peak torque is produced is influenced by a lot of things, intake and exhaust designs, camshaft, compression ratio, cylinder head flow, combustion chamber shape and volume, etc... The application of the 292 was primarily a workhorse, so it is optimized to produce torque at low RPM which it does very well. The smaller V8's primary application was passenger car usage which means more horsepower, so the RPM where peak torque occurs would be higher, by design. All I know is, there have been engine comparisons done where displacement and engine design were held as a constant and the only variable was the bore to stroke ratio. And in the end after lots of dyno time the engines made the same torque and horsepower numbers whether it was a small bore big stroke, or a big bore short stroke combination. I will agree, if the engine design was optimized to take advantage of the longer stroke it would produce torque at a lower more usable engine speed. And if the engine design was optimized for the shorter stroke it's peak torque would occur at a higher rpm. The easiest way to torque though, which I think everyone agrees on, is cubic inches.

John

no and no- oh well, i guess it's just luck then. chevrolet prob just made up those #'s anyway. they may have had sir isaac newton on their design engineering staff. any engine could have been designed to do that without changing the configuration of it, i'm sure.

I just guess I'm confused. In the examples given from the GM shop manual the 283 and the 292 share the same bore, but the 292 has a 1 1/8" longer stroke. Yet when you look at the torque versus displacement the 3" stroke 283 out torques the 4 1/8" 292. Granted, it's at a higher RPM, and not by much, but it still produces more peak torque when diplacement is taken into the equation. So using the numbers provided by GM, a .060" over 283, which is a 292 would have slight, and I mean a slight torque advantage over the original 292. So in this example, what did the 1 1/8" stroke gain us?

As Panic states, it is a very complex subject and the variables are many. My opinion is, when displacement remains equal, an increase in stroke does not increase torque. I do agree the easiest way to increase an engines torque output is to increase it's displacement, and the easiest way to do this is install a longer stroke crank.

John

If you dump the clutch at an idle... you will stall the engine..right? You have to get the RPMs into the power band so that doesn't happen. You have two different engines that have different "power band" ranges. The torque curve will be flatter on the 292, and the 283 will most likely be less flat (torque range is shorter or at a higher RPM) meaning that you could dump the clutch on the 292 at a lower RPM than you could on the 283 without stalling the engine. The 292 power band starts at a lower RPM.

Stroke and displacement will "both" change the characteristics of any engine. If you install the 283, the rpms at any given operating speed will be the same. If you are not in the power band, it will take more work for the engine to get into that power band. You would have to change the ratios in the tranny or rear end to compensate.

Instead of me trying to explain more, maybe this article will shed some light better?

http://www.vettenet.org/torquehp.html

john, in the 63 shop manual example the torque is only 1/100 ftlbs per in2 less, or i thought, pretty small. that's around 3 ftlbs if the engines were the same displacement. try to read that on a old beam style torque wrench! but for the 283 having to turn 150% the speed of the 292 to get it seems to tell the whole story. thats like one driving 50mph and the other having to drive 75mph just to get to the same place.
my examples aren't as good as builders, but i just don't buy the old any engine has the same chance at being a torque monster tune. however, i am not a engineer or expert on anything, and i can't speak latin, but the romans didn't drive many chevy trucks. others have a lot more experience than i and i am not trying to educate anyone. i don't think my opinion is any better than yours.

Yep, I think this is one of those topics where we'll agree to disagree.

John

I can disagree that gravity exists too. But that doesn't keep me from floating away. It is still a factual and proven existance.

Here is a couple more trys at an explaination;

Short stroke - drag race for 1/8th mile -car can only go so fast in a short track. It can also turn around faster and make it back to the start line to run the length of the track again. It can theoretically make more runs in a minute than it can on a longer track. That is a like short stroke High RPM engine (283).

Long stroke - same drag car can go faster if given more track (1/4 mile). It will take longer for it to turn around and get back to the starting line. It theoretically can create more work in one pass down the strip. That work is like the torque of a longer stroke, but slower RPM engine (292).

The ability of the piston in an engine to go faster in its bore (the track), requires a longer stroke. The piston has to slow down and "stop" before going back to the starting point on all length strokes.

Think of pushing a wheel barrow full of dirt up an incline. Your back is against the wall and that only gives you 3 feet to get started before you get to the incline. It will take great effort to get a wheel barrow to the top of the incline if you only have two steps to get started. That is a short stroke 283.

If you have the same incline, same wheel barrow full of dirt, but the wall is further from the incline giving you 6 steps before you get to the incline, the momentum of the extra steps will help you get the wheel barrow up the incline with a little more ease. The majority of the work was exerted on the steps preceding the incline instead of "on" the incline. That is a longer stroke 292.

In both scenerios the wheel barrow will start to slow down once it is on the incline. The momentum of the extra steps (ie. longer stroke) will make less work while on the incline.

Look at the torque curves from dyno test readouts. The torque that rises rapidly and stays high longer (a flatter line) "at a slower rpm", is the type of engine you should look for to haul a heavier load like a grain truck.

Now if you want to push an empty wheel barrow (a light weight Corvette) up the same incline, two steps (short stroke) may get you up the incline jsut as fast or faster. Less work and less length to travel. A dyno torque curve for this engine may rise fast, be just as flat, but the RPMs will be higher.

If one engine is producing its peak torque at 50 mph, the other may be producing the same peak torque at 75 mph.

That's good Builder. Do you write for that show Numb3rs? That almost sounds like a Professor Epps explanation.

Make it relative to what we already understand.

Maybe you should take the best of both worlds here and build a square engine (same stroke as the bore).

It's like something going around in a circle at 1rpm. If the circle is 1 foot in diameter it is traveling at 3.14 feet per minute. If the circle is 10 feet in diameter it is traveling at 31.4 feet per minute. The bigger the circle (stroke) the faster the something (piston) travels. Did I get that right Builder?

Which one will pull 80,000 pounds up a hill better, a Corvette or a Cummins- - - - -both with 350 HP engines?

Here's the Cummins numbers:

NTC-350: 350 HP @ 2100 RPM,
1120 lb-ft torque @ 1300 RPM

I guess Cummins got it wrong, too? last I heard, those 855 cubic inch engines had LOOOOOONNNNNNGGGGG strokes!
Jerry

Jerry, did you know there is a Cummins powered Corvette out there. I think the guy is on one of the 4x4 or Diesel boards. He has swapped a Cummins (6BT?) into a Corvette. I was too shocked to retain any details of how he did it.

I doubt it will pull 80,000 up a hill, but it will probably come a lot closer than my 350 powered Corvette...

And the reason is torque. The Cummins 6BT makes a better comparison to the Chevy 350, being closer to the same size. The Cummins has a four inch (4.02) bore like the Chevy (4.00), but where the eight cylinder Chevy has a 3-1/2 (3.48) inch stroke the six cylinder Cummins has a 4-3/4 (4.72) inch stroke.

Very similar size motors. Very different strokes. And very different in purpose.

While a new Diesel pickup and a new Corvette may be very similar in price, you probably don't compare them when shopping vehicles. You're looking for the features of one or the other. The engineers designing the motors used in each know that and make choices about bore and stroke and cam profile and a million other little things trying to create what you want to buy.

Much as I like my small block Chevy motors I just can't accept anyone calling one of them a torque monster.

it must be rough having set everyone straight. i still think a little more latin will help.

I'm not sure I want another stab at a simplified response. I might complicate things more.

Maybe a wheel barrow is too complicated for some.

Keep thinking. Maybe you will get it one day.

I wonder why panic has the handle "panic"?? I edited that line for you panic. It now reads "The ability of the piston in an engine to go faster in its bore (the track), requires a longer stroke."

I choose the Cummins Jerry....and I believe in gravity.

Yes I believe in gravity, I also belive in Newtons first law, the law of inertia. The wheelbarrow example was an excellent analogy of the law of inertia, but it has nothing to do with the production of torque. Somebody else stated a heavy crankshaft increases torque, sorry same thing, gives the crankshaft greater inertia but does nothing to increase torque. If it were that easy, all I'd have to do is bolt on the biggest flywheel I could find and I'd have a torque monster. The only thing close to an apples to apples comparison was the comparison of the 292 to the 283. Both engines share the same bore size, but the 292 has a 37.5% longer stroke! Based on the calculations posted previously, when you correct for the difference in displacement, the 3" stroke 283 slightly out torques the 292 with a 4 1/8" stroke. When you don't correct for displacement the 292 wins by 5 lbft, produced from 9 more cubic inches. By the way, the 283/292 numbers were not provided by me, but by someone trying to illustrate just how much more torque the 292 produced. Now the argument was made that the 292 produced torque at a lower RPM and it was because of the longer stroke. A simple cam swap and you could reverse the results between the 2 engines. Peak torque is developed at the point where the engine fills it cylinders the best. This is largely affected by camshaft, head, intake, and exhaust design. The arguments been made a longer stroke accelerates the piston quicker therefore drawing in more air. In reality, swept volume is swept volume. If the engines have the same cubic inches they will displace the same amount of air per intake stroke given consistent cam, head, intake, and exhaust design. Some german mathametician figured all this out in the 1800's but his theories weren't proven true until the last 20 years or so when they could actually be tested with modern sensors and computers, on real engines. Sorry, forgot his name, when I remember it I will post it. So my question is, if stroke is King when it comes to torque production, why does it fail so miserably in the beloved 292 torque monster. A whopping 37.5% increase in stroke for a slight net loss in torque compared to the 283. And please no more wheelbarrow analogies, just some good sound physics this time. And I'm guessing the Cummins is turbocharged. If it can't make 1200 lbft. of torque out of 800 + cubic inches regardless of bore size or stroke length, then it's one weaksuck motor.

John

john, again i am not trying to argue with you. i have a 292 with a mild 264 grind cam and it NOT the same as a stock 283. this i can tell you for sure. while upper rpm torque and power are def increased, it still has way more guts at the lower end than a stock 283.
if you really want apples to apples bore the 283 out .060 over like you said and turn them both at 1600 and see what happens. and let me say i am not trying to drag a dead horse or annoy you.

sorry i forgot to add. i think the weight of the spinning assembly has some effect on torque curve, response, and horspower. not as large as displacement of course. why else chop the flywheel or lighten the crank in the old days. it made the whole assembly lighter and more responsive, but had a slightly neg effect on low end torque. now i am not going to produce any paper that says so. if i'm wrong that's ok, i have been wrong before.

You know,I'm not trying to argue either. Just trying to provide some current information on the production of torque from an internal combustion engine. But some of the responses recieved were long on opinion and light on fact. I do believe there is a misunderstanding between inertia and torque.

A light flywheel and crankshaft reduce the rotating mass. With less rotating mass less horsepower is required to accelerate the crank and flywheel, this frees up engine power to accelerate the vehicle. A light flywheel reduces inertia of the rotating assembly, it has no impact on torque production. With that said, an engine with a heavy flywheel will start from a dead stop easier and with less throttle applied than one with a light flywheel. Not because of an increase or change in torque, but because of the greater energy stored in the heavier flywheel, ie greater inertia.

I've been doing the car thing everday as a living a passion and a hobby for over 30 years. In college I learned long strokes make torque, exhaust flow follows the kadency theory, (basically it expands and contracts as a spring), and several other theories that have since been proven wrong. For the last 21 plus years I've worked for a major auto manufacturer in a technical position, and I have had to relearn a lot of stuff that was taught wrong 30 yrs ago. I study everyday, whether it be internal engineering memos, SAE documents, other manufacturers technical publications, or coming here or over to the HAMB. I usually just read and learn and rarely respond. When I do respond it is to correct what I feel is misinformation.
I knew the torque subject was touchy, and I probably should have just left it after my original post way back toward the beginning of this thread was dismissed. Maybe it was dismissed because in the eyes of the Stovebolt I'm still just a wrenchfetcher, or maybe I haven't posted here enough to earn any respect. Doesn't matter, I'll keep hanging around, I'll keep learning, and I'll keep posting whenever I feel my input is needed. No hard feelings, just give me some facts.

John

What??? John1 didn't like the wheel barrow analogy?? I'm crushed!!! I'm glad you didn't beat me up for the race track analogy.

So, this wheel barrow rolls into a bar and says to the bartender...

Knock, knock!
Who's there?
Wheel barrow.
Wheel barrow who?
Wheel barrow me an analogy on Torque. HAHAHAHAHA!!!
That's not funny.
Fine. I'll just wheel into a bar that doesn't take so much work to get appreciated.
You must be a short stroke, high RPM wheel barrow trying to be a low rpm, long stroke dump truck.

Oh yeah! And doesn't the change in stroke also change inertia?

john, just because you don't have a lot of posts doesn't mean you don't know what you are talking about. sounds like you have more experience than i, and i can freely admit that.
the heavier crank comment i made was just a joke because of a old conversation on another board with another poster on the thread. i wasn't holding it up as a big factor in torque production. i do believe it plays a part in low end torque. just as you describe, not in more torque being produced, but torque already present from the inertia. i am not saying this inertia prduces more torque. but has already produced it by consuming more energy to spin the assembly and accererate it to idle already. i don't think you can seperate torque from inertia totally. if you cut the engine off it would still have torque till friction slowed it down. and the six would have way more than the eight. again, not more torque production but torque already present at idle.
there are prob lots of reasons to post on here. i'm glad you did. but there are some, like the poster that posts on here and the other board, that only seem to post to tell people they are wrong or their info isn't correct. when they have more of a passion for that than chevy trucks, it's not as enjoyable for me. that's why i don't look at the hamb any more, too much opinion mixed in.

How an engine works is no more subject to opinions than any other natural law, which remain true regardless of how many people agree, or even whether they have been discovered yet.
The displacement is the total swept volume of the cylinders regardless of bore, stroke, number of cylinders, bore-stroke ratio, rod ratio, radial vs. V vs. L vs. boxer, blah.
The maximum power per cubic inch is heavily biased to an engine with the highest number of cylinders, biggest bore and shortest stroke (after Lanchester). The math:
HP ~ bore^1.65 × stroke^.5 × # of cylinders × a constant for fuel, quality of construction, etc.
Assuming 300" and the same bore/stroke ratio (to remove a variable), a V12 develops vastly more power than a 1-cylinder but only slightly more than a V8, etc.

i thought we were talking about low end torque.

While there are issues in a comparison of Diesel and gasoline fueled motors the similarities are so much closer than 'applies to typewriters' that your statement leaves me shaking my head and doubting everything else you've said.

Both convert fossil fuel to motion.
Both use fuel/air mixtures under pressure to create combustion.
Both use pistons and crankshafts.
And I could go on and on.

Apples grow on trees and provide a good source of food energy.
Typewriters are mechanical devices used to put symbols on paper.
They both have beneficial uses but further comparisons are few and far between when compared to comparisons of Diesel and gasoline.

I think these postings alone have generated a lot of inertia .....or is it torque ......no wait, it might be the bore ...or could it be the stroke?

I'm really confused now.

Anybody got a wheel barrow?

My mistake.
The end result here has about the same value as the blind men discussing the elephant.

And the usual complaint: to tell people they are wrong or their info isn't correct, and of course, we all know that only positive remarks are appropriate.

How to avoid someone telling you that you're wrong?
Learn the subject.

it doesn't matter if you are wrong or right, there's always someone to correct you.

I don't know if I can agree with that.

I wish I had some sort of snappy response, oh well, this seems like a good way to wind down this thread.

John

Knowing the subject is no guarantee someone won't tell you you're wrong.

Knowing the subject isn't even a guarantee you're right.

Claiming you know the subject better than everyone else does guarantee pretty much everyone will look for errors in your knowledge and explanation and will work hard to find ways you are wrong.

I may not fully understand these dynamics yet, but this much I have learned at the school of hard knocks.

Well said OldSub.

John

Last word.

I just spent 30 minutes reading all of this. Torque is usually felt in the the seat of the pants under acceleration.

I had a Camaro with a 383 stroker, built close to 500HP. Car was the biggest pig ever, couldn't get out of it own way. Well down to the differential shop to yank the 2:73 peg leg gears out. Installed 3:73 posi. Huge difference. Next tranny shop, installed beefier gears and a 2800 stall. Now we are talking.

Point is no one asked what gearing he had. He could have installed a variety of motors and it might not have helped at all.

True, that.
If your hot-rod parts work but move the torque curve too far north you won't get any benefit without changing the gears.

I just like the fact that I can climb into my truck and drive down the road! LOL!