Here you go, Piston area and force.

[Mattax]

The 36% increase from @71340 is correct:
(19.63-12.56)/19.63 = 0.36

12.56/(1-.36) = 19.63

Let’s say that the tunes were matched somehow in the two different bores and everything else remained unchanged:
1,000 lbs/si * 19.63 si = 19,630 lbs force
1,000 lbs/si * 12.56 si = 12,560 lbs force
This is still a 36% increase in force on the piston:
(19,630-12,560)/19,630 = 0.36

The trick is to get the same, if not greater, explosion force out of the larger bore. This is somewhat easier to do when boring an engine for a rebuild, however the net change is far less…4.00 to 4.03 is only 1% increase (when rounding up).

If the premise is increase from the initial piston, then the reference area is 12.57 in sq.
The increase in area is 7.07 in sq.

So when phrased that way, 5" piston has 7.07" square inches more than the 4" piston.
Same as saying 56 % increase in area.
How much is a 56% increase in the area of a 4" piston?
0.56 x 12.57 in sq. = 7.04 in sq

Close enough considering I was using 22/7 for PI.

So it the percentage depends on what the comparison.
If I bought eggs for a 1.00 last week and this week I said the price went up 50%, how much did eggs cost this week?

 

[Newbomb Turk]

If the premise is increase from the initial piston, then the reference area is 12.57 in sq.
The increase in area is 7.07 in sq.

So when phrased that way, 5" piston has 7.07" square inches more than the 4" piston.
Same as saying 56 % increase in area.
How much is a 56% increase in the area of a 4" piston.
0.56 x 12.57 in sq. = 7.04 in sq

Close enough considering I was using 22/7 for PI.

So it the percentage depends on what the comparison.
If I bought eggs for a 1.00 last week and this week I said the price went up 50%, how much did eggs cost this week?

A buckfiddy.

 

[Mattax]

A buckfiddy.

eggzactly

 

[jos51700]

In my mind's eye, the bore changes we're discussing here, let's just give an example.....say going from a 4.250 bore of a 383 to a 4.342 of the 400 isn't enough of a difference to "undo" the added power of the larger bore, if that makes sense. While the pressure "may" decrease from the smaller bore to the larger, (and I'm not certain it does), it's not a large enough amount so as the larger bore of the 400 loses power. To me, that's a great example too, since the 383 and 400 share everything else in common BUT the bore size. Lets just say their compression is the same at 9.5 and the rest of their builds are also the same. The 400 wins every time and the only difference IS the bore size.

Remember, the area that is increased is also swept, so you're pulling in more air and fuel, compressing to only a fractionally larger area, etc, so all else being equal, you could see a significant increase in pressure alone

 

[RustyRatRod]

Remember, the area that is increased is also swept, so you're pulling in more air and fuel, compressing to only a fractionally larger area, etc, so all else being equal, you could see a significant increase in pressure alone

I agree. But I worded it like I did because I'm certainly no expert.......I don't believe we have any here, either. lol

 

[273]

If you look at Bmep & Imep it only cares about overall cid, not how it was created bore stroke ratio wise.

 

[fishmens67]

I'm certainly no expert.......I don't believe we have any here

Speak for yourself I already answered the question with the help of my wife.
She said a bigger piston makes more power. some stroke helps. lol

 

[dusterbing the peace]

If the premise is increase from the initial piston, then the reference area is 12.57 in sq.
The increase in area is 7.07 in sq.

So when phrased that way, 5" piston has 7.07" square inches more than the 4" piston.
Same as saying 56 % increase in area.
How much is a 56% increase in the area of a 4" piston?
0.56 x 12.57 in sq. = 7.04 in sq

Close enough considering I was using 22/7 for PI.

So it the percentage depends on what the comparison.
If I bought eggs for a 1.00 last week and this week I said the price went up 50%, how much did eggs cost this week?

You’re right, I did my math wrong. What I was actually meaning to show (and goofed up) was percentage difference:

What I showed was percentage decrease, which is the wrong direction as the thread started with small to big:

Your percentage increase, which as you noted, matters how it is phrased, is also correct:

Accordingly, the way you phrased the egg price increase would generate $1.50 as the new price.

However, if you said that eggs cost $1.50 this week and $1.00 last week, the percentage difference would be 40%.

 

[Lance Lot Link]

eggzactly

I paid a lot more than that from the Mathamachicken!

 

[Mattax]

You’re right, I did my math wrong. What I was actually meaning to show (and goofed up) was percentage difference:
View attachment 1716271021

What I showed was percentage decrease, which is the wrong direction as the thread started with small to big:
View attachment 1716271023


Your percentage increase, which as you noted, matters how it is phrased, is also correct:
View attachment 1716271022
Accordingly, the way you phrased the egg price increase would generate $1.50 as the new price.

However, if you said that eggs cost $1.50 this week and $1.00 last week, the percentage difference would be 40%.

Yes. Thank you for coming back and showing the percentage difference.
Percentage difference is the neutral observer.

 

[273]

Don't quite get the concept of percentage difference.

 

[Mattax]

Comparing the change between the average of the two.
The demoninator is the average. So for the eggs, the average of the two prices is a buck twenty five, and the difference is 50 cents. Percentage difference is .50/1.25

 

[Killer6]

Not how math works. 4 to 5 is a 56% change in area (1.25 squared)

Yeah, it's closer to 56.4%, no doubt...

 

[Killer6]

Um yeah, it kinda is.

He means 71340 had it backwards, remytherat is correct, 36% of the larger bore is 56%(+) of the smaller bore.

 

[Bewy]

I think there a few here that get it, but not the dummies '273' & Turk. I will post the info AGAIN from Harold Bettes, who does get it. [ Turk read the text, don't look at the pretty pictures ] What does Bettes get? He gets that if you increase piston area, the pressure loading over area [ using pounds per sq in as an example ] becomes less. Pressure has become confused with force.
The formula below, uses simple everyday words, is very simple.....& even the dumbest of the dumbest should be able to 'work it out'.

Totally agree that a bigger diam piston can make more hp. [ So does a longer stroke ]. What pushes the piston to turn the crank? Doesn't do it by itself.......????????????

Making it simple: the piston draws air into the cyl by creating vacuum as it goes from TDC to BDC. If you make the piston BIGGER, you are pulling more air through the same size valve opening, & that creates more vacuum..........so more air has now filled the cylinder. More hp is created because more air is drawn in to be compressed. A bigger diam piston does not guarantee more HP by virtue of it's area. Chrysler proved it!!! They made an odd ball 383 engine that was a raised block engine, not the more common low block 383. Not used by Dodge & Plym, Chrys only 1959 to 1961.
Bore/stroke RB 383: 4 1/32 by 3.75
Bore/stroke LB 383 4 1/4 by 3.38
Both engines had 10:1 CR. Both made exactly the same hp/tq: 325/425. But, but, but, but LB 383 had a bigger piston....shoulda made more hp. Huh?

Here is the formula again for HP related to piston area:
Unless you are particularly dumb, it should be obvious that the HP/to area gets less as piston area gets bigger because piston area is on the bottom line of the formula

 

[273]

I think there a few here that get it, but not the dummies '273' & Turk.

Buddy I don't call you names.

I will post the info AGAIN from Harold Bettes, who does get it. [ Turk read the text, don't look at the pretty pictures ]

You think we should change are minds just cause you say so, you think you've offered proof but you haven't nothing you have said so far is a valid argument.

Not that a majority matters but not one person has agreed with you but that gives you no pause no doubt that you might be in the wrong and just continue trashing us for not agreeing with you.

What does Bettes get? He gets that if you increase piston area, the pressure loading over area [ using pounds per sq in as an example ] becomes less. Pressure has become confused with force.

You are confusing them.

The formula below, uses simple everyday words, is very simple.....& even the dumbest of the dumbest should be able to 'work it out'.

Totally agree that a bigger diam piston can make more hp. [ So does a longer stroke ]. What pushes the piston to turn the crank? Doesn't do it by itself.......????????????

Were talking force and torque remember. A power stroke is torque, eg..1 cyl 2 stroke engine makes 50 lbs-ft it's making 50 lbs-ft per revolution, and if it happening at 5252 times per minute than it's also making 50 hp.

Making it simple: the piston draws air into the cyl by creating vacuum as it goes from TDC to BDC. If you make the piston BIGGER, you are pulling more air through the same size valve opening, & that creates more vacuum..........so more air has now filled the cylinder. More hp is created because more air is drawn in to be compressed. A bigger diam piston does not guarantee more HP by virtue of it's area. Chrysler proved it!!! They made an odd ball 383 engine that was a raised block engine, not the more common low block 383. Not used by Dodge & Plym, Chrys only 1959 to 1961.
Bore/stroke RB 383: 4 1/32 by 3.75
Bore/stroke LB 383 4 1/4 by 3.38
Both engines had 10:1 CR. Both made exactly the same hp/tq: 325/425. But, but, but, but LB 383 had a bigger piston....shoulda made more hp. Huh?

No one is saying this, for the same displacement like you mentioned 383 RB vs B, one it don't matter the hp it's the efficiency that determines the Imep, Bmep, lbs-ft per cid and if you notice none of them care how the displacement is made bore stroke ratio wise.

But back to your example the 383 B's larger piston is applying more force for a given psi but why it's not making more power but the same in your example is cause like I said in the beginning and since the 383 B also has a shorter stroke so it has less multiplication effect equaling out the torque and by extension hp. Now if you compare a 383 & 400 B engines same psi the 400 larger piston will be making more force but since now both engines have the same stroke the multiplication factor is the same so the 400 larger force becomes more torque than the 383 and if happening at the same rpm would make more hp.

You should've been able to figure this out if you really know what your talking about, you sure your right?

Here is the formula again for HP related to piston area:
Unless you are particularly dumb, it should be obvious that the HP/to area gets less as piston area gets bigger because piston area is on the bottom line of the formula

View attachment 1716271050

Again this formula has no bearing on what were talking about hp per piston surface area is similar to saying hp per cid, a given cid don't automatically make that ratio of hp same with the surface area of the piston, just a reference guide telling you how well you doing hp level wise.

Again if you think this was some kind of proof you should've known better if you know what your talking about, are you sure your right ?

 

[RustyRatRod]

Buddy I don't call you names.

You think we should change are minds just cause you say so, you think you've offered proof but you haven't nothing you have said so far is a valid argument.

Not that a majority matters but not one person has agreed with you but that gives you no pause no doubt that you might be in the wrong and just continue trashing us for not agreeing with you.

You are confusing them.

Were talking force and torque remember. A power stroke is torque, eg..1 cyl 2 stroke engine makes 50 lbs-ft it's making 50 lbs-ft per revolution, and if it happening at 5252 times per minute than it's also making 50 hp.

No one is saying this, for the same displacement like you mentioned 383 RB vs B, one it don't matter the hp it's the efficiency that determines the Imep, Bmep, lbs-ft per cid and if you notice none of them care how the displacement is made bore stroke ratio wise.

But back to your example the 383 B's larger piston is applying more force for a given psi but why it's not making more power but the same in your example is cause like I said in the beginning and since the 383 B also has a shorter stroke so it has less multiplication effect equaling out the torque and by extension hp. Now if you compare a 383 & 400 B engines same psi the 400 larger piston will be making more force but since now both engines have the same stroke the multiplication factor is the same so the 400 larger force becomes more torque than the 383 and if happening at the same rpm would make more hp.

You should've been able to figure this out if you really know what your talking about, you sure your right?

Again this formula has no bearing on what were talking about hp per piston surface area is similar to saying hp per cid, a given cid don't automatically make that ratio of hp same with the surface area of the piston, just a reference guide telling you how well you doing hp level wise.

Again if you think this was some kind of proof you should've known better if you know what your talking about, are you sure your right ?

Don't sweat it dude. We all know when someone resorts to name calling and insults, their position is very weak. I'm just blown away this argument is still ongoing. It just makes not one single bit of difference in the outcome.

 

[273]

You should've read the Indicated Power part instead.

 

[Bewy]

OK,
I apologise for using the word dummies.
This 'discussion' started because 273 claimed that more piston area gave more hp by virtue of the piston area increase. It only does this IF more air is drawn into the cyl; if no more air was drawn into the cyl, then the HP would not change, all else being equal.

THIS FORMULA SPECIFICALLY ADDRESSES EXACTLY WHAT IS BEING DISCUSSED. What do you not understand about Power per piston area???

 

[273]

Don't sweat it dude. We all know when someone resorts to name calling and insults, their position is very weak.

True, especially what were talking shouldn't get ya all riled up, I don't believe me to be wrong but if he happens to right, I'd be **** your right my bad and carry on with the new info. Like you said none of us are experts.

I'm just blown away this argument is still ongoing.

I don't mind, it just refreshes this information in my mind, I somewhat forget easily so this info is kind of recharged now

It just makes not one single bit of difference in the outcome.

True for the most part, but there is certain decisions this does effect, kind of what started this in the first place I said buddies 383/396 can have a similar powerband and torque at similar rpms as the popular 408 since there close in size, then people started coming at me

 

[Bewy]

273,
You can carry on with all the BS you want. The fact is that piston area is on the bottom line of the formula, & when the bottom line gets bigger, the answer [ power ] gets smaller.
Until you stop confusing force with pressure loading, you will never get it....

 

[273]

OK,
I apologise for using the word dummies.

Fair enough

This 'discussion' started because 273 claimed that more piston area gave more hp by virtue of the piston area increase.

Never did, your inferring that, I've larger piston gives more force to the rod and crank for a given cylinder pressure (efficiency)

It only does this IF more air is drawn into the cyl; if no more air was drawn into the cyl, then the HP would not change, all else being equal.

Again were talking force and torque, no time frame (rpm) is be discussed.

The only time I've mention hp as in where talking similar hp and torque so were comparing apples to apples.

THIS FORMULA SPECIFICALLY ADDRESSES EXACTLY WHAT IS BEING DISCUSSED. What do you not understand about Power per piston area???

Again were talking piston area and it's effect on force to the crank.

How does does say 2 vs 4 hp per square inch of piston area have anything really to do with force the piston is applying to the crank ?

 

[Bewy]

Here is refresher about force v pressure. Same force was applied to each coin, but the end-on coin penetrated further because it more force per area.
Two pistons 4" & 5" diam, 1000 lbs in the chamber. Both pistons have 1000lbs of force applied.
The 4" piston has a pressure loading of 79.6 lb/ sq in; the 5" piston has 51 lb/sq in of loading.
The 'other' theory would be creating energy...where none existed to be created.

 

[Bewy]

Here is the pic that should have gone with post #48.

 

[273]

273,
You can carry on with all the BS you want. The fact is that piston area is on the bottom line of the formula, & when the bottom line gets bigger, the answer [ power ] gets smaller.
Until you stop confusing force with pressure loading, you will never get it....

F = P x A so the force to the crank is equal to cylinder pressure x piston area.