custom_trucker:
What I mean is this. Torque is about getting as much quality air/fuel efficiently in and out at once. Power is about getting the most quality air/fuel in and out. Torque occurs when you get your highest volumetric efficiency, so you're taking in the most air/fuel per cycle that your motor can do and compressing it and firing it. Peak HP occurs when you are taking the most air/fuel in over the course of time. Meaning, in any 10 second period, peak HP will draw more air/fuel through your motor than you will at peak torque. What controls this is the head. Valve sizes play a part but the ports are what make the big difference. The 300 head just plain doesn't flow worth a crap. That is why it doesn't make power stock.

The reason the 300 has a 3 instead of a 4 is because its a six cylinder. Every revolution of a 4-stroke engine has half the cylinders firing. For an 8 cylinder, that would be 4. For a 6 cylinder, that would be 3.

The only real time that overlarge valves become a detriment to power is when they are so badly shrouded that they won't flow anymore or the port/valve are very mismatched. The 300 EFI heads are shrouded a bit which makes for a large-valve EFI head iffy unless you cut back that wall a bit, which lowers your compression. You also cut into your quench area a bit but i'm thinking most of these engines aren't built to take advantage of that huge quench pad.

When the VTEC closes the other valves it is because the ports do flow very well at full song. The problem is that they are on the large side for the lower rpm's. Let me put it this way. Everything in an engine is a compromise. Everything works most efficiently at one rpm. When they all line up you'll get more power (intake manifold sizing, header sizing, carb sizing, rpm, etc) (because they either increase the dynamic compression or quality of air/fuel mix). The same thing with port sizing and valve sizing. What works great at one RPM is not the best for another. With VTEC what they do is (from the motors point of view) make two heads that have drastically different flow rates. One smaller for better lowend cylinder filling (just one valve, which helps the lowend by creating a higher velocity air/fuel charge and quite possibly more swirl). Once it gets up to a higher RPM it opens the other valves to better fill them cylinders up in that range.


-=Whittey=-

 

"Torque occurs when you get your highest volumetric efficiency, so you're taking in the most air/fuel per cycle that your motor can do and compressing it and firing it. Peak HP occurs when you are taking the most air/fuel in over the course of time."

Whittey, Excellent statement (quoted above) and makes perfect sense. I am going to write that one down in my engine notebook.

I once read that the 300 I6 has a low end power advantage because of its extremely short rod to stroke ratio pulls the piston away from TDC very fast, more quickly creating a vacuum at the beginning of the intake stroke and thereby giving the intake flow a kick start.

 

Regarding the racing, I do mine at the dragstrip not on the highway. If you lined up both trucks at 70 mph on the highway and hit it the 302 truck would come out on top, but from a standing start to 80 mph the 300 will win. I don't think there's anywhere in the country you can legally exceed 75 or 80, so the 302 doesn't help much there.

As far as HP vs. torque is concerned, the total area of the pistons controls power potential and the stroke controls where the power is made. The piston area determines power potential because the bore is what ultimately limits airflow potential. Airflow=power. If you had a 302 and a 351 and both were equipped with the same parts from the heads up and the same cam and compression the peak power numbers would be nearly identical, but the 351 would make it at roughly 15% lower rpm, and the torque would be about 15% higher at any given rpm due to the increased stroke. The 302 has more power potential than the 300 because it has 33% more piston area than the 300, but it also has 33% less stroke so it makes that much less torque. Whittey statement about the strokeX#of cylinders is a little missleading. In his statement he is using that analogy to desribe torque, when in fact it actually descibes power. The 302 has 33% more power strokes in a given time period than the 300 at the same rpm, so it will make more power for a given airflow. The torque is determined by piston areax stroke. Work is forcexdistance, which would be directly proportional to bore x stroke. Power is work/time. In the 302 the work is less because for each power stroke you have 3x4=12 units of work, in the 300 you have 4x4=16 units. The 302 doesn't win out until you factor time into the equation. When this is done, the 302 will have more powerstrokes in a given time period for a specific airflow rate. Since each cylinder in a 302 has a smaller volume that each cylinder in a 300, it will rev higher at any given airflow. Let's put some numbers to this because I don't think I've been clear. Let's say we are feeding each engien enough air to run at 100% VE and the MEP in each cylinder is 100 psi. We'll throw out the geometry of the rod angles to simplify the math since it all works out to be roughly equal. The piston areas are equal, so the force pushing down on each piston is equal to 1256 lbs. That force times the stroke is proportionate to the torque produced at that rpm. For the 300 it would be 1256X.33ft=414 ft-lbs, for the 302 it would be 1256X.25=314 ft-lbs. Those are the torques you would get if each engine was running at 100%VE. Now if we put time into the equation and give each cylinder a specific airflow rate, say 40 cfm, we can find the theoretical HP that could be produced. If each 300 cylinder gets 40 cfm and each 302 cylinder gets 40 cfm the total airflow for the 300 will be 240 cfm, the 302 will be 320 cfm (the total #'s are for reference, they really won't be used in the example). In order for the 302 to move it's 40 cfm/cylinder it must spin faster because it's cylinders are smaller.
If the 300 moves 40 cfm/cylinder it will be spinning at 1375 rpm. The 302 with 40 cfm/cylinder will be at 1835. Using the torque numbers generated above we find that the 300 is making 108 hp@1375 rpm and the 302 is making 110@1875, pretty much equal. However, the torque numbers are very different, and the rpm needed to make the power is very different. For those of you keeping score at home you might remember a while back when I posted in another thread that the 300 didn't need as much carb as the 302 to generate a given power number, and this is why. Back to the topic at hand. As we can see the 300 will make the same power at a lower rpm and with less air, thus less fuel. The problem with the 300 is that it's cylinders are so big that they are nearly impossible to fill completely. This causes the 300 to run out of steam fairly early and not be able to produce good high rpm power. The 302 can easily rev beyond the 300 because it's smaller cylinders are much easier to fill at high rpm. That is why the 302 makes better top end power and the 300 makes better lowend.

 

^^ wow

 

I'll second that Wow!

Here are some tidbits I have written down on this topic.

Short rod pulls piston down faster, which helps low RPM torque. A long rod is important to high RPM (6-8K) to increase dwell time to compensate for the decreased dwell time due to engine speed.

Short rod increases fuel air velocity and therefore increases volumetric efficiency.

From Pop. Mech. Oct. 1986: Ford designed the EFI 300 intake manifold for max low end torque.

And finally from Smokey Yunik's Track Talk:

Long stroke gives more torque at lower RPM. Long stroke no good above 6500 RPM.

Piston area is very effective in relation to torque. More square inches to multiply pressure per square inch.

Longer stroke gives stronger intake signal for low and midrange RPM, so torque goes up.

 

I'm going to disagree with this. The torque is 15% higher because of the increase in displacement, not the stroke. If you took 10cid of air/fuel mix and put it in a cylinder, you will get the same power out of the 302 cylinder as you would the 351 cylinder (discounting the increased friction due to the longer stroke).

My analogy was to show that at any given RPM, the 300 and the 302 have the same overall stroke. Basically i'm saying that for each revolution of the engine a piston is moving a collective 12" down a 4" bore.

For a given cylinder airflow, yes. With equal engine airflow, the 300 and the 302 and the 144 and the 460 and the 83 will all make the same power.

Take it as an engine. 12 units of work per cylinder vs 16 units of work per cylinder. Every revolution has 4 cylinders firing in the 302, so for every revolution you have 3x4x4=48 units of work. In the 300, you have 3 cylinders firing so for every revolution you have 4x4x3=48 units of work. But I think the 'units of work' idea is flawed for this discussion.

There is a flaw in this statement. You got hte 1256 by area of piston top times 100psi MEP. 100PSI isn't that much (either imep or bmep) and those numbers only represent that particular MEP. Maybe i'm wrong because something isn't right here. Also, you're comparing one cylinder smaller than another. In your example, a single cylinder of 60cid with a 4" bore would out-torque both engines. Or that a 300 would out-torque a 4" bore, 3.5" stroke V32 (1407cid).

You're still comparing a single cylinder versus another single cylinder. And what your math proved was that total airflow is horsepower. And that bigger displacement makes more torque.

50cid is not that difficult to fill. Ford, in its infinite wisdom, decided that they should choke the living hell out of these motors. That and only that is the reason they don't make more power from the factory. The head does not flow, and as both you and I have pointed out, air flow = horsepower. The 815cid IHRA guys don't have a hard time filling their 101 7/8 cid cylinders...

One big thing you're missing is this... The stroke and bore don't make power. They transmit power. This comes from the pressure of the burning air/fuel mix. 50 cubic inches of air/fuel being burned 3 times in a period is the same amount as 37.7 cubic inches of air/fuel being burned 4 times in that same period. Both engines can produce the same amount of power, but I guarantee the 300 will last longer while doing it.


-=Whittey=-

 

How much torque will I gain if I paint the oil dipstick Blue???


Just kidding guys, I am impressed at how much you guys know about this topic. I was getting a headache from learning to much.

 

~~ The problem with the 300 is that it's cylinders are so big that they are nearly impossible to fill completely. This causes the 300 to run out of steam fairly early and not be able to produce good high rpm power. The 302 can easily rev beyond the 300 because it's smaller cylinders are much easier to fill at high rpm. That is why the 302 makes better top end power and the 300 makes better lowend.~~


Ok, so the 300 has a little trouble breathing....why not slap a turbo or supercharger (preferably a roots or pos. displacement) on it? I mean, come on....everyone knows that the 300 can't breath worth diddly at higher rpm's....so why won't someone make some form of "assisted breathing" apparatus for it? Diesel's have turbos, and if you'd like, propane injection and nitrous....look at the power and torque they produce. So it makes perfect sense to design a turbo or supercharger, or hell, even a nitrous kit for the 300. Of course, these are just my opinions, and I could be wrong....but I'll leave the rest of it up to everyone else....

 

yes, we've been brooding over the turbo topic for quite a while.

The I6 is a great engine for boost... Its got strong internals and a solid block.

 

I'm going to disagree with this. The torque is 15% higher because of the increase in displacement, not the stroke.

If the bore size is the same on two cylinders and one has a greater displacement than the other, where does the increased displacement come from? The stroke. It should be readily apparent that if you apply the same force to a lever 15% longer you will get 15% more torque.

If you took 10cid of air/fuel mix and put it in a cylinder, you will get the same power out of the 302 cylinder as you would the 351 cylinder (discounting the increased friction due to the longer stroke).

That's exactly what I said. The difference in the two is the 351 will make that power at a lower rpm and have more torque for a given rpm.

My analogy was to show that at any given RPM, the 300 and the 302 have the same overall stroke. Basically i'm saying that for each revolution of the engine a piston is moving a collective 12" down a 4" bore.

I don't dispute this, but I need to think about how to word my thoughts on it so that it makes sense to someone other than me.

For a given cylinder airflow, yes. With equal engine airflow, the 300 and the 302 and the 144 and the 460 and the 83 will all make the same power.

I used a specific cylinder airflow because the two engines have the same bore and similar valve sizes. There is no other practical way to model the system for my argument. If you use total engine airflow the amount of air available to each cylinder would be different for each cylinder and the concept of consistency in experimentation would be tossed out the window. Regardless, the 300 did more with it's air than the 302 did. If we changed the two total airflows to be equal and left everything else the same the 300 would really stomp the 302.


Take it as an engine. 12 units of work per cylinder vs 16 units of work per cylinder. Every revolution has 4 cylinders firing in the 302, so for every revolution you have 3x4x4=48 units of work. In the 300, you have 3 cylinders firing so for every revolution you have 4x4x3=48 units of work. But I think the 'units of work' idea is flawed for this discussion.

You can't calculate it that way because no two power strokes occur at the same time. They do overlap, but are not at their peaks at the same time. That is why I did the whole model as a single cylinder. At any given point in a revolution there is only one cylinder producing a full power stroke. That is what generates the torque. The number of powerstrokes per revolution determines how much power can ultimately be produced. The 'units of work' concept was used because it was a lot easier to follow that if I had gone through the math to convert it to ft-lbs. I agree it isn't exact or proper, but it is consistent and easy.

There is a flaw in this statement. You got hte 1256 by area of piston top times 100psi MEP. 100PSI isn't that much (either imep or bmep) and those numbers only represent that particular MEP. Maybe i'm wrong because something isn't right here. Also, you're comparing one cylinder smaller than another. In your example, a single cylinder of 60cid with a 4" bore would out-torque both engines. Or that a 300 would out-torque a 4" bore, 3.5" stroke V32 (1407cid).

No, it's not much mep. But 100 psi was easy to multiply and it provided numbers that everyone can relate to. If I had used 1000 psi in that example it would have been 4140 ft-lbs, and 3140 ft-lbs, both of which are pie in the sky and none of us can relate to that. As far as the 60ci and 1407ci engines you mentioned, you're right. Using the numbers in my example would result just like you said it would. The difference is that the two engines you are describing nothing at all like what we are talking about. In my example the assumption was made that the average torque would stay the same, which is not very far fetched with a multicylinder engine. This is because as one cylinder's power stroke is tapering off, the next one is just starting. When that one is at it's peak, none of the others are doing anything, and when it tapers off another one starts producing. With the 60 cube 1 cylinder engine the torque during a revolution might change from 400 ft-lbs peak to -200 ft-lbs minimum with the average for a revolution falling somewhere between. On the V32 you pretty much have to have at least 2 cylinders firing at the same time, and 4 at the same time might be more practical. The only way my example is valid is when the engines have nearly the same number of cylinders and total dislacement.

You're still comparing a single cylinder versus another single cylinder.

Like I said, that's the only practical way to do it. At least for the purposes of an internet discussion. If I was writing my thesis on this topic I would do it differently.

And what your math proved was that total airflow is horsepower. And that bigger displacement makes more torque.

And that's what we've both been saying all along isn't it?

50cid is not that difficult to fill. Ford, in its infinite wisdom, decided that they should choke the living hell out of these motors. That and only that is the reason they don't make more power from the factory. The head does not flow, and as both you and I have pointed out, air flow = horsepower. The 815cid IHRA guys don't have a hard time filling their 101 7/8 cid cylinders...

Like you said, the 300 is grossly choked. Any 50 ci cylinder that uses a 4" bore is going to be difficult to fill. You can only install valves that are so big. The largest valves I know of that have been installed in a 4" bore were the 69 Boss 302/Cleveland 4brl at 2.23/1.71 and that's in a canted valve head which has slightly more room. It isn't practical to stuff more than 2.02/1.6 valves in a 4" bore and they have a hard time getting the job done. The 815cid engines have bores just a hair bigger than 4". They also have huge cams and heads with 425cc intake ports and 2.5" intake valves. They do have some trouble getting enough air, but the size of the engine tends to cover that up.

One big thing you're missing is this... The stroke and bore don't make power. They transmit power. This comes from the pressure of the burning air/fuel mix. 50 cubic inches of air/fuel being burned 3 times in a period is the same amount as 37.7 cubic inches of air/fuel being burned 4 times in that same period.

Power, yes. Torque, not necessarily. Everyone here knows the 300 makes more torque than the 302, even though it doesn't have nearly the airflow capacity. I never said the two engines wouldn't make the same power, I actually believe I made that very claim in my argument. My point is that for a given power level the 300 will make more torque than the 302.

Both engines can produce the same amount of power, but I guarantee the 300 will last longer while doing it.

At least we agree on something.....

 

You're getting blinded by stroke man. Only 2 other Ford motors that I can think of off the top of my head have a longer stroke, the 400 and the 1.6L Kia motor. How 'bout this.....

5" bore. 2.547 stroke. 100psi MEP. 1963lbs. 416 ft lbs....
6" bore. 1.769 stroke. 100psi MEP. 2827lbs. 416 ft lbs....
3" bore. 7.076 stroke. 100psi MEP. 707lbs. 416 ft lbs....

Displacement and MEP is what gives you your torque. Stroke is just one way of getting that displacement.

I don't think there is was a 302 made that didn't make the same or slightly more torque than a 300. The 300 just has it all at a lower rpm.


-=Whittey=-

 

Great discussion here guys. Doesn't the 5.4 engine have a 4"+ stroke too?

 

Err, yup! 4.16" stroke on the 5.4 and the 6.8. Had to look that up as i'm not too familiar with the mod motors.


-=Whittey=-

 

so what do you guys think my 91 f150 xlt lariat xt-cab can run the 1/4 in? Can i beat some civics in our Florida 1/8?...modified civis that is?

 

unless you have a stick and a shortbed, i would not recomend racing too much just because of all the weight and the brick shape of the truck. stock a 300 powered auto truck will run around the 20's in a 1/4, the 1/8 though is a different story. the motor doesnt have the time to wind out all the way out of its powerband. dont know if its rice-a-roni beating, but therre ya go....