Kingtal0n

Was searching for about 4 hours today online and I cant seem to get a direct answer to this question. Thought I might pop back in to the ol' trusty thirdgen and ask away!

Ok, the question.

Engine #1 is 3.0 Liters, has the same bottom end parts (rods/pistons/crank alloy/size/expected durability) as the other 2 engines below and is in the Straight-Line 4-banger cylinder configuration.

Engine #2 is 3.0Liters, Identical to #1 EXCEPT it is in the INLINE-6 Cylinder configuration

Engine #3 is 3.0Liters, Identical to #1 and #2 EXCEPT It is in the V8 Configuration.

Which engine will be the most efficient (fuel consumption)
Which engine will have the portential to make the most power
which engine will HANDLE the most power before coming apart.

Assume the valvetrains are all identical, and power production is not LIMITED by displacement, rather, they are all super-duper charged and can make any amount of power required for this comparison.
Fire away!

wellington

well 4 cylinders would be more reliable,less parts to break.

but the 8 would have less stress per cylinder,but it would make less power per cylinder.

the 4 would have the best fuel consumption ,less cylinders=less gas.


the six would have no advantage either way, four banger power with 8cyl milage. but the 6 might be the most reliable.
it would have less stress per cyl then a 4,but it would produce more power per cyl then a 8.

dankhound

Fuel consumption is based on airflow not engine bore layout. So assuming equal airflow in all three engines, fuel consumption will be identical for all three.
Same deal here. More air and fuel in more power out. Whether the power comes in the form of torque or horsepower depends more on the bore stroke ratios rather than engine configuration.
One thing to think about here is that a 4 cylinder engine has 4 power pulses for every two revolutions where an 8 cylinder will have 8 smaller pulses per two revolutions. Id have to say that the smaller pulses will be less likly to break a crank. However bore stroke ratio would be a large factor in calculating piston speed, which directly relates to the failure of piston and rod failure. Another factor would pison and rod weights. Assuming weights to be equal you will find that the 4 cylinder will have a higher mass per rod/piston assembly, which will cause higher forces on the crank. For longevity id have to say the more cylinders the better. Thats probably one of the reasons your high hp engines are v10's or 12's (ie ferarri, lambo, etc.)

Kingtal0n

So lets take the V8 out of the picture for a moment. You are saying that at the same displacement, the 6 cylinder would take more abuse (horsepower/torque output) because of the additional 2 cylinder absorbing load, evening out the horsepower per cylinder? But the 4 would make more overall power because of th fewest frictional losses in the cylinders?

Apeiron

The 4 will have the largest rotating mass.

This is another one of those impossible to answer questions that has no relevance at all with the real world.

dankhound

Agreed. Far too many factors missing to come up with a real world answear.

Kingtal0n

so there is NO WAY TO TELL if a given 4 or 6 cylinder, all else being equal, will be able to handle more power than one another? Realistically?

I ask because some people use this as an example:

say your making 1000HORSEPOWER.
A 4 cylinder will need to handle 250HP per Cylinder
Where a 6 Cylinder will only have to hold 166HP Per cylinder.
Where an 8 Cylinder will only need to hold 125HP per cylinder.

Then they tell me that makes the 4 cylinder the most likelly to break and come apart. They say that the 6 cylinder is 50% more effective at handling horsepower.

My initial question was based on this principle. TRUE or FALSE I guess would be a good starting point.

Apeiron

It's impossible to build 4, 6 and 8 cylinder engines with everything "equal". You can design a 4 cylinder engine to handle 1,000 HP. It will probably be heavier and use more material than one of the other two, which means it won't be "equal". It will probably also be expensive, which again isn't "equal".

Kingtal0n

Forget about equal for a moment. does what I just said make any sense at all? will spreading power output among extra cylinders mean that overall the engine *should* prove more reliable? Is an 8 cylinder TRUELY 50-100% more capable of handling power output given the same displacement?

Or, will the *abuse* remain the same, will the brake effective mean pressures in each cylinders remain (about) equal generating the same amount of stress per cylinder regardless of # of cylinders?

Apeiron

Still meaningless. Suppose I've designed my V8 with .125" rod journals and .005" cylinder wall thickness, but my L4 has 3" journals and .250" walls? I'd put my money on the L4 in that case.

Kingtal0n

YOU KNOW what I am saying! Dont complicate this anymore than it already is. Does the 1000horsepower example have ANY truth whatsoever, within reason, or is it pure bunk!

Does it make ANY SENSE, or NONSENSE.
Is it true, sort of true, or false.

there has to be a final answer here. We arnt theorizing! There are 4-cylinder 2.0L motors, and 6-cylinder 2.0L motors, both with average cylinder wall thickness and journal sizes! this isnt a question of will one handle 50 more horsepower than the other... its a question of will one handle 50% more power than the other with the same stresses imposed upon the bottom end!

Does TORQUE per cylinder go DOWN as you spread it out over more cylinders? yes I know that. But does the effective STRESSES because of the smaller CHAMBERS and CYLINDERS remain the same? Or does it allow for literally 50% more power to be extracted (from 4 to 6 cylinders)

Apeiron

We are theorizing. Unless you want to compare two specific engines, it's all monkey-spank.

Kingtal0n

Ok without filling the forum with "monkey spank"

I have a 2.0L motor. I send 1000 Ft.Lbs of torque at it, each cylinder has to handle 250Ft.lbs of torque.

Now I magically enlarge the motor to 6 cylinders without increasing displacement. Forget about which motor is more reliable.

Is it true, or false, that the stresses imposed on this new 6 cylinder are 33% less per cylinder because of the additional 2 cylinders.

84z28350

The 8 being a 3L i would assume it has a very short stroke maning its capable of pretty high rpms (formula motors for example)

the I6s i have had (ford & chev) were a strong motor but i think they lack bottom end power.

the 4 banger being a rather large displacement for a 4cyl probably wouldnt be capable of very high RPMs and just like any other 4cyl will have less torque and have a fairly narrow powerband.

Just my 2c...

Edit: yes, it should be more reliable if its making the same ammount of power, because of the reduced stress on each cylinder.

Apeiron

Which of the hundreds of sources and locations of stress are you worried about?

Kingtal0n

Im worried about the stress of TORQUE and BMEP. Just because torque output per cylinder goes DOWN does that necessarily mean that the stress imposed per cylinder goes down as well? I would think that BMEP would remain the same, since the cylinders are also getting SMALLER at the same time that there are MORE of them. Is BMEP not what determines the maximum cylinder pressure limit before, say, a headgasket pops? a simple pressure spike from an early n20 hit and you have a rediculous BMEP that does nasty things.

Bad example, but I think you get the point. Stress imposed by combustion. Stress imposed by torque. Just because torque output per cylinder is going down because there are extra cylinders, does that necessarily mean that the stress from cylinder pressure is lessened? the stress of torque is lessened?

Apeiron

BMEP itself is just a tool for comparison, since it's just a function of torque and displacement. By itself doesn't have much to do with actual cylinder pressures.

The 4 cylinder will naturally have a lower BMEP per cylinder, but I don't know if that's a meaningful quantity.

sellmanb

So, just to get this right...


You want 1000hp out of a:

4 banger
and v8.

Which one will be more reliable?

The v8.

Assuming you used the same type of materials and molding/forging processes and EVERYTHING was built the same (with obvious differences).

Basically... if you go look at rods for sale. They claim to be able to handle 600hp for V8's.

Then if you look at the forging process and the type of metal. Then go over to look at the 4 banger's version of those rods. You will notice they say they are able to handle 300hp.

Why is this? Because there's half as many cylinders to create power with, and spread the power.

You are already on the right track.

the more cylinders you can spread the torque out, the less torque is applied per cylinder, meaning the less initial wear.


I believe that answers your question?

wellington

i disagree, with less parts and less friction a 4 should last longer then an 8 at the same hp and displacement.but the 8 would rev higher.

more parts INCREASES the likelyhood of faliure.

the 8 would have a double the possiblity for faliure vs a four.

but the stress on each part would be half for the 8,but the four would have twice the strength parts to compensate for the
diffrence.

in the end i would bet on the four[im biased],but in a real world test i think they would be about equal.

Damon

The more cylinders you have the more potential you have for making power (so goes the theory). Why:

1. More cylinders means more valves. More valves means more potential for airflow through the motor. Which, obviously, means more potential for power.

2. More cylinders means smaller displacement per cylinder (assuming total engine displacement is held constant). Smaller displacement per cylinder typically means smaller parts. Smaller parts means lighter parts. Lighter parts means more potential to rev the pee outta the motor without having it fly apart. More revs means more potential to make power.

Ever wonder why the really high end exotics use 12 or even 16 cylinders for only ~5 liters of displacement? That's some of the reasons why.

As for the question about which one will handle more power..... that's a little tough to answer. There's more to making an engine stay together than pegging a max torque or HP figure and dividing by number of cylinders. I agree that question can't be easily answered.

Vader

Conversely, you can analyze a relatively large displacement 4- or 6-cylinder engine. Continental and Lycoming make large displacement engine such as this, and they are relatively heavy, using larger parts, and strain to make 3,000 RPM with any reliability. Then again, they are designed for a particular purpose. Fairbanks makes some very large (16" bore) 6-cylinder engines, and they strain to make 1,600 RPM, but produce torque like a ****. At any given displacement, the friction of the rings traveling in the bores comes out roughly equal. Fewer but larger rings traveling a longer distance in fewer cylinders creates friction similar to more smaller diameter rings traveling a shorter distance. I haven't performed the calculations, but I suspect the surface area of the ring contact over the distance is about equal in either engine. Rotating friction and balancing losses might make a difference, however. Anyone care to crunch the numbers and report in?

wellington

well the marine 3.0 l4 has a four inch bore.

we need to find out the bore of a 3.0 v8 and inline 6.


the circumfrence of the 3.0 is about 11.75 inches,so the total ring length would be about 23 inches,assuming the other two engines have the same thickness of rings we can find out how much friction each motor has from the rings.

i have no idea how to measure the surface area of the piston,thou. but if the ring circumfrence is diffrent then the total piston friction is probably about the same diffrence.


now what about the main bearing friction and the total cam friction?

then we need gas milage stats for all of the 3 engines and also have roughly the same hp and tq

dankhound

My 4 cylinder audi 20v has more valves than my sbc 16v. Yet the sbc outflows the audi. Why? Theres more to airflow than just number of valves.

Not necessarly. The weight of parts per cylinder will be lower in the v8 but the total recipicating mass will be higher in the v8. Just look at factory rev limiters. 4's almost always rev higher than v8's of comparable design and cost.

Angelis83LT

ok.. just as a little thing.. there is a 5.7 l V8 and a 5.7 V12 (standard sbc vs lambo motor) the lambo motors do seem to be more reliable and can generally do more power on equal builds.. most times anyhow.. at least that is what i gathered from comparable engines of the types for specs.

ME Leigh

The inline 6 will be the most efficient. Inline 6 engine and v-12's are inherently balanced because of the layout. The I4 and V8 will require stupid *** things such as balance shafts, balancers, dampers... The only other engine layouts that are better than I6 are flat or boxer engines and rotarys. But those each have their own flaws. The best engine layout would be a flat 12.

HP, efficiency, torque... are all functions of engine size all else being equal not a function of # of cylinders.

Angelis83LT

although the 5.7 v12 and the 5.7 v8 are the same engine size, just different bores and strokes.. ... I guess it dependinds on alot of ther stuff though like RPM range and such since they are both moving the same amount of fuel and air...which is where power comes from anyhow..

wellington

mercedes makes a 3.0 v8 that has over 550hp!!!


but the car cost about $200,00 .

PhLaXuS

I like the E55 -- 470HP out of a supercharged 5.5L V8 for I think $80 grand.

ME Leigh

Naaw, S65 AMG. AMG-built twin-turbocharged 6.0L SOHC 36-valve V-12 engine - 604 hp @ 4,800 - 5,100 rpm

And it has way over 700 TQ.

Angelis83LT

here is a question .. given the same displacement, will an engine with more cyls create more torque with the same comparable setup....

rx7speed

there are otherthings though that can reduce fuel mileage other then just saying all else equal they all flow the same air then.
which one has more friction? what is the bore x stroke difference between them? bore and storke differences can make a difference as far as gas mileage goes I would think. even if that difference might be small. also you have rotating mass differences which can vary grately on how you get the 3L for each engine.

Quote:

Same deal here. More air and fuel in more power out. Whether the power comes in the form of torque or horsepower depends more on the bore stroke ratios rather than engine configuration.

the torque and horsepower are all related to each other by math. torque at higher rpms means more horsepower torque at lower rpms means less horsepower in a nutshell.

engine configuration can have a good effect on how the torque is produced though.

Quote:

One thing to think about here is that a 4 cylinder engine has 4 power pulses for every two revolutions where an 8 cylinder will have 8 smaller pulses per two revolutions. Id have to say that the smaller pulses will be less likly to break a crank. However bore stroke ratio would be a large factor in calculating piston speed, which directly relates to the failure of piston and rod failure. Another factor would pison and rod weights. Assuming weights to be equal you will find that the 4 cylinder will have a higher mass per rod/piston assembly, which will cause higher forces on the crank. For longevity id have to say the more cylinders the better. Thats probably one of the reasons your high hp engines are v10's or 12's (ie ferarri, lambo, etc.)

bore stroke ratio doesn't determine piston speeds.
I could have a 4"bore and 4" stroke motor vs a 10" bore and 10" stroke motor. they are both 1:1 ratio but the later would have higher piston speeds

rx7speed

you might be right but then again I'm not so sure.

with the 8 cylinder you also have a lot of extra mass going to extra throws of each crank. extra mass going into extra rods. sure the pistons bigger on the 4 cylinder and the throws might be longer on the 4 cylinder also, but is the extra mass there more then the extra mass added by using 4 extra rods, 4 extra pistons, 4 extra counter weights, 4 extra crank throws. also with the 4 cylinder vs the 8 cylinder if they are both using the same rod legnth then the 8 cylinder alone would have twice the mass in just the rods alone.
but as I said you might be right I'm not entirly sure either way just stiring the pot and give way to extra thinking, explaining here.

rx7speed

amen to that

rx7speed

just as a side note I think my rotary has 3" in journals if I remember right. I just know they are huge and def larger then a soda can

rx7speed

I doubt it is that simple.
other factors come into play now also. harmonic variations I'm sure could make a little difference. and other things my mind is tryingto put to words but it doesn't

I need to think more and get some sleep

rx7speed

couldn't powerband be different though between them with the difference in time between the power pulses?

I would think with the power pulses being closer together (like a v8) it generally should widen out the power curve and allow it to happen a little lower. with the longer time between pulses the crank might have enough time to start to slow down from it's peak speed or something like htat. so in effect kinda creating a little harmonics of it's own also. but mainl it's boom speed up slow down a little then next boom bringing it up to speed. where a 8 cylinder going through the same proccess doesn't allow the crank to lose as much energy between pulses.
sure might be small but could it possibly be enough?

wellington

well to answer this we need to find the specs on three motors with about the same dispalcment and hp .this does have an answer. and it should be defnitive proof of which type and size engine is the best overall.


we need a 3.0 v8 with 200hp
a3.0 inline 6 with 200hp
a 3.0 v6 with 200hp
and a 3.0 inline 4 with 200hp

they all should have the same type of valve systems and all be NA.

then we can calculate which has the most roatating mass,the most unused roatting mass,the piston ring total surface area,gas milage and hp and tq. and a comparison between the parts materials and measurments should tell us which of them should last longer.

so,is anyone going to take a stab at this?

Irockz

iTrader: (1)

Why don't YOU do it boy wonder?

wellington

if every body finds one motor it will be alot easier.

or you could do it.

scribbles

ford in the 80 made a limited production car with a 2.something 2.2-2.3L motor.. it made something like 600hp. and was in a Verry light rally car, motor was 30,000$... the motor lasted 10 hours at WOT.. Verry fast, but way two much power for sutch a small motor... also i have seen 2.0-3.0L drag cars making 900-1000 Hp.. same thing, mabie 10 runs then dead. two much power to two small of a motor... get a viper motor.. v10, big displacement, and you have a 900-1000 hp motor with some street life. any small motor will need two mutch help to make that kind of power. will never last v4, v6 or v8.

wellington

but a viper v10 is huge compared to to a 2.0 inline 4.

were talking about the same displacement ,not giant motors doing better then tiny motors.

and if the viper was pulling 500 hp per liter it would blow up in 5 minutes.

Tibo

iTrader: (15)

Surface area is A=(pie)(radius)^2
circumference is C=2(pie)(radius)
Volume of a cylinder is V=(pie)(radius)^2(length)
I believe someone was asking for those.

You can figure out the load on a piston by
1 horsepower=550 ft(lbs/s)


Larger bore engines require more advance, smaller bore engines require less advance. Larger bores might use more gas than. Longer bores have more side stress.

ShiftyCapone

iTrader: (7)

Just go buy an IC engine text book and do some reading and math concepts that it provides. You won't need any engines at all to figure it out.

Kingtal0n

This is exactly what I was talking about.
1 horsepower=550 ft(lbs/s)

That means, that 1 horsepower in 1 cylinder exerts 550ft(lbs/second) right?

So a 4cylinder making 400horsepower would have
400/4 = 100 horsepower per cylinder
100 horsepower = 550ft(lbs/s) X 100
100 horsepower = 55,000 ft(lbs/sec)

Where a 6 cylinder would have
400 / 6 = 66.6
66.6 horsepower = 550(lbs/s) X 66.6
66.6 horsepower = 36,630 ft(lbs/sec)

If this equation is correct, it answers one of my initial questions. But there HAS to be more than that, to figuring out how much "force" a 4cylinder VS 6cylinder VS 8 Cylinder accepts to each piston @ the same horsepower figure. I mean it cant be just that easy, can it?

PhLaXuS

This is just speculation, but I'd also expect that the friction generated by the rings & bearings associated with the other cylinder's moving up/down other bores may help to increase/decrease the forces in other cylinders...

wellington

yeah,the v8 will have more ''dead wieght'' then the 4.so the forces are probably about equal.

its more personal prefrence then anything.

ill take a 4.

Tibo

iTrader: (15)

If any one wants to figure out the coefficient of friction between rings and cylinder walls, be my guest. It would change with the viscosity of oil, material of rings, temperature, condition of walls, etc.. Friction would slow it down, but not much. It does not take 550 ft(lbs/s) of force to push down a piston. You could figure out the speed of each throw of the crank with angular velocity. Without taking measurements, I don't know how you could figure out the speed of a piston. (ie. velocity, acceleration, time)

Wouldn't shorter bores have less side stress though, being able to handle more power with the same composition materials?

Apeiron

Piston speed:

d/d&theta; p( &theta; ) = s cos&theta; + ( r<SUP>2</SUP> - s<SUP>2</SUP> cos<SUP>2</SUP>&theta; )<SUP>-0.5</SUP> s<SUP>2</SUP> cos&theta; sin&theta;

&theta; = crank angle
s = stroke
r = rod length

vorgath

I didn't read more than the first two three posts .. but I've dealt more with European engines ... anyway here's the "story"


Comparing V6 for instance to an inline 6, the V6 has a lower point of gravity, and allows for a shorter design, however the inline six is a more powerful smoother running engine. Classic inline six's of Euro design would include the Jaguar E-type engine.

In Formula 1, and by F1 I mean the real F1, not our American version, they use small displacement V12's. They rev extremely high, and produce enormous amount of horsepower, however their initial torque is not very impressive.


Not sure if it was before WWII or after, but when the Le Mans series were being run, the Italian car companies Maserati and Ferrari were fighting against each other. The Ferrari's naturally had bigger naturally aspirated engines, I believe they were V12's. Maserati however used I believe 1.5 liter V8's but with dual blow-through carburetor induction together with an alcohol/gasoline mixture.
Ferrari won .. due to only one reason ... their engines were less powerful but in a 24 hour race, with old school refueling, they had the advantage as far as gas mileage goes.


In my garage I have the original production dual cam engine of all times, the Fiat Twin-Cam, an inline four, 1.8 liter. It has been calculated that if one would run the 1.5 liter version of it versus the 2L version, but reved the 1.5 maybe 2,000 rpm higher, at 11,000 rpm compared to 9,000, the smaller engine, with the smaller displacement and faster reving is more impressive.

This I take from a guy who has been working on F1 engines.


The four cylinder, 3.0 liter engine, waow, that is weird, quite large displacement for a 3.0 but anyway, would probably not be as effective as the inline 6 nor the V6 nor V8, maybe just due to the displacement, equaling too big pistons too big stroke o nthe crank for the four cylinder.


Now if you want to talk induction, my stock engine, SMOG YEAR of 1976 ... yuck (reason I'm parting out my Fiat Spider but keeping the engine and tranny) .. came with 84 horsepower .. from a 1.8 liter engine, way too small carb, a single 34 mm dual downdraft, and too much emission crap (back in those days they didn't know **** about emissions).
That engine can use two dual 40 or 44 mm Weber downdraft carbs (yes more than twice the air flow) and still run good, not too much carb for it. 120-140 horsepower is normal when modding the engine.


One guy in Australia runs a 2L Fiat engine, with a later generation 16 Valve Lancia Integrale head on it, uses his own modified fuel injection, Garrett turbocharger at 30 psi, and gets 600 horsepower.

That's 300 horsepower per liter, from a small old inline four.



I believe the best comparison would be if we would actually look at hmmmm maybe Maserati engines .. or some other ones .. I doubt Ferrari would work since I don't remember them using anything but V8''s, V6's (i nthe Dino's), V12 and flat 12 or 8.


Here in the States we rule as far as V8's go, but we were never any good with inline fours , our V6's well .. ok.. but nothing really until everything became ... may we hear it ... V O R T E C !!!


OK, enough of my rambling for now

Kingtal0n

Alright, SO i guess the real answer is power distribution is NOT a factor in comparing engine configurations. While power distribution IS affected, you cant use it as a determining factor in the power handling ability of any motor being compared because they are too different to compare, nothing can be compared as "EQUAL" In other words, its apples to oranges any way you slice it (them)