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Engine Designs


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19 replies to this topic

#1 Twitch de la Brat

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Posted 13 March 2011 - 04:51 PM

I though about putting this in the Shop Talk forum, but it's more or less, just a discussion of all types of engines, most of which aren't offered in Subarus, so Alternative vehicles it is!

Ok, we all know the H4 all too well and a lot of us know the H6 as well.
But I want to discuss the natural properties of all types of production engines, no theoretical or one-off engines please.
Like the inline engines and V engines the majority of the car world uses.
And the rotary Mazda dabbles with and the odd W engine from VW.

What are their natural properties and how do those change as you alter certain components (such as cylinder pitch on a V)?

Just feel free to discuss as you please and I'll put in what info I know as well :)

Twitch

PS: Lets stick to specs and known experiences and keep mindless conjecture to a minimum, thank you.

#2 davebugs

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Posted 13 March 2011 - 05:04 PM

I'll say this about the VW VR6's. I did an engine swap recently (then the car got totalled 200 miles later - I'm still healing).

But it supposedly has only 16% offset in the cylinders. Not because that was efficient engine design (the Germans are engineers after all) but because that's the only 6 cylinder design they could fit into existing engine compartments. So the design wasn't about mileage, power, longevity, etc but simply what would "fit". But it does have power jambed into a VW Jetta or Golf.


Myself I LOVE the horizonatlly opposed engines.

My real hobby is antique VW's with the old horizontally opposed engines. Love those replacable "jugs" that are actually the cylinders. Same idea but way different design that Subaru. The "jugs" have fins like a motorcycle for cooling to those unaware.

#3 Twitch de la Brat

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Posted 13 March 2011 - 05:31 PM

I didn't know the VR6 was only 16*, that's nuts!
And I know those things car rip like no other, very good power to weight ratio engines.

As for the aircooled flat fours, I did know the cylinders came off :)
I've been around aeronautical flat 4's, and all of their designs are built to have removable cylinders.
Only real difference is the fact they're usually 300+ CID. :cool:

Now, I know the flat four is naturally a torquey engine.
Why else would the EA81 have almost 25% more torque than HP?
But how does it stack up against an inline of the same size?
I know rev limits and head flow is a big deal here, but if we took similar head designs and same displacement engines with the same fuel delivery system, how would they fare in torque to hp numbers?

Twitch

#4 nipper

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Posted 13 March 2011 - 06:03 PM

[quote name='Twitch de la Brat']Like the inline engines and V engines the majority of the car world uses.
And the rotary Mazda dabbles with and the odd W engine from VW.

What are their natural properties and how do those change as you alter certain components (such as cylinder pitch on a V)?

[quote]


Rotary engines have a high maximum rpm, but to make HP they have to be high revving. They use oil like a high tech 2 stroke and are thirsty. They can fit in an amazingly small package. When you see one up close it is about the size of a large lawn mower engine. They run extreemly smooth as there is always one compression section being ignited at one time. Early nones were failuers and made the vega look like a quality engine. Newer ones are much better but gas milage is still poor. They are very free breathing and fast revving engines due to very low internal mass.

Straight engines can make a lot of torque for their size due to being straight. The more cylinders you add, the smoother it runs. The straight engines are cheaper to make then a V or H configuration and can produce more torque per cubic inch due to more room in the crankcase for long crank throws. They are long engines but can be mounted in any direction (some buses have them mounted flat under the floor) to package. The 5 cylinder engine was supposed to be a compromise between the fuel economy of a 4 and the power of a 6. It was hard to engineer the firing order and the balance of the engine. Straight 6's are still used by mfgs due to the torque they can produce. Staright 6's have a support bearing between every piston, where as V's do not. 6 cylinders are naturally balanced except the four is not.

Packard had a 359 inch straight 8 engine. Peirce arrow had a 385 cu inc straight 8. These engines are so smooth if it wasnt for the spinning fan belt you could net tell it was running.

". The 445.5 cubic inches gave 160 horsepower, plus a mighty 322 pounds/feet torque, which peaked at only 1,400 rpm. The latter was responsible for the V-12's terrific takeoff, especially with low axle ratios (4.41:1 and 4.69:1 were standard for open and closed bodies, respectively, with 4.06 or 5.07 optional)." Technically you could leave the car in 3rd or 4th all day and never need to shift due to the low torque peak.

There was a (incredibly large) 1931 Marmon V16 (OHV something new then) and lighter then Cadillacs V16. 491 cubic inches and 200HP over 400 ft lbs of torque (and incredible amount then).

Cadillac and lincoln had a V12 and a V16 engine in the early 30's

The V-8s came about as it was easier to package and took up less room then the straight 6 -8. The V engine could rev higher due to shorter throws of the crank journals but could spin up faster, with a trade off being torque and having to have 2 cylinders share support journals..

The slant engines were done of the reason of packaging.

Four cylnders do not run smoothly (before electronics). The invention of balance shafts (which are still used on some engines) solved that problem and made 4 v-6 cylinders a more popular choice, along with thier good fuel economy. One of the early V-6's which did not have the usual 45% angle used offset crank journals to make up for this.

W engines have cylinder mounted between the radius of the other cylinders. The advantage is using a single cylinder head for the configuration. W 6 W 8 and any other W takes up less space then its V counterpart, but are more expensize to Mfg. Most of these desgns have made possible by computers. There is a W16 in a Vayron.

H eingines allow for a very short and low pacakage, but is more expensive to produce.

This i will cut and paste as my knowledge here is weak. I am including them as they are still aound to some degree.

Early in World War I, when aircraft were first being used for military purposes, it became apparent that existing inline engines were too heavy for the amount of power needed. Aircraft designers needed an engine that was lightweight, powerful, cheap, and easy to manufacture in large quantities. The rotary engine met these goals. Rotary engines have all the cylinders in a circle around the crankcase like a radial engine (see below), but the difference is that the crankshaft is bolted to the airframe, and the propeller is bolted to the engine case. The entire engine rotates with the propeller, providing plenty of airflow for cooling regardless of the aircraft's forward speed. Some of these engines were a two-stroke design, giving them a high specific power and power-to-weight ratio. Unfortunately, the severe gyroscopic effects from the heavy rotating engine made the aircraft very difficult to fly. The engines also consumed large amounts of castor oil, spreading it all over the airframe and creating fumes which were nauseating to the pilots. Engine designers had always been aware of the many limitations of the rotary engine. When the static style engines became more reliable, gave better specific weights and fuel consumption, the days of the rotary engine were numbered.

Radial engine

Radial engine
This type of engine has one or more rows of cylinders arranged in a circle around a centrally-located crankcase. Each row must have an odd number of cylinders in order to produce smooth operation. A radial engine has only one crank throw per row and a relatively small crankcase, resulting in a favorable power to weight ratio. Because the cylinder arrangement exposes a large amount of the engine's heat radiating surfaces to the air and tends to cancel reciprocating forces, radials tend to cool evenly and run smoothly.
The lower cylinders, which are under the crankcase, may collect oil when the engine has been stopped for an extended period. If this oil is not cleared from the cylinders prior to starting the engine, serious damage due to hydrostatic lock may occur.
In military aircraft designs, the large frontal area of the engine acted as an extra layer of armor for the pilot. However, the large frontal area also resulted in an aircraft with a blunt and aerodynamically inefficient profile.

All engines listed are production engines.


Outdated but since it was Mfg STanley Steamer
http://www.stanleymo...alTechnical.htm

I think that covers it.

#5 Twitch de la Brat

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Posted 13 March 2011 - 06:43 PM

Lol, thank you nipper.
But I'm curious, how does Honda remove all of that naturally occurring torque from their I4's? :-p

I've never had the pleasure of riding in a rotary powered vehicle, but I have heard they rev incredibly smoothly.
And I have read most of that info on wikipedia, esp about the true rotary engines and the radial engine.
But I'm curious what other little things people have noticed about particular engine types.
Like how stroke and bore seem to affect the engine dynamics, compression ratios, how does adding a turbo change the numbers, that sort of thing.

Twitch

#6 nipper

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Posted 13 March 2011 - 06:51 PM

The longer the storke, the more leverage on the crank, the more torque but lower revs, the inverse is true.


my hand is sore so if no one else chimes in i will tomorrow.

#7 NorthWet

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Posted 13 March 2011 - 10:13 PM

edit: the next line was NOT meant to be in response to any previous post, but rather a general feeling about how people tend to not really understand mechanical things. (BTW, I actually started this overly-long ramble before the previous post was added... I a a slow typer.) endedit

So many misconceptions, so little time...

Cylinder configuration is all about packaging, and little or nothing to do with ability to produce power and what type of power. (even the use of "power" here is inaccurate/incorrect.) A cylinder of the same design will produce the same amount of "power" regardless of how they are stuck together with other cylinders.

The Subaru H4 is NOT a naturally torquey engine because of it's layout; in fact, it's ability to produce torque is hampered by the overall engine layout. Its short stroke is optimized away from ability to produce torque, and towards its ability to fit between frame rail. Such short strokes (compared to displacement) are usually used on very high-revving engines (which our H4s are not.).

So, you need a narrow engine, but it can be long? Use an inline design. It has to have lots of cylinders, be of moderate length but can be wide? A V-arrangement might be what you need; just; just select the V-angle tat suits the width and height available. (BTW, the our horizontally opposed engines are really just 180deg-"V"s). OK to have a wide and tall engine, but it needs to be super short? Use a radial engine. Need something to spice up your company's "who are THEY?" image? Pick a Wankel rotary. Special rules in your racing organization? Pick a "W" a "true H" (ala BRM's H-16) or something even more exotic.

Usually, the engine designers do not get to pick the engine package, as it is dictated by the "look" that the car manufacturer is trying to achieve: The engine has to fit the car. Or, almost as bad, the new engine has to be able to be built using the existing tooling.

So, now that you know the arrangement, what are the compromises? Inline engines have long crankshafts compared to V-engines of similar cylinder count and design, and can not be revved as high before the crank breaks due to harmonic and torsional vibrations. (One of the reasons that some exotic V-12s take thir power from the center of the crank rather than one end.) But inline engines can be lighter (less redundancy) and have simpler and more effective intake and exhaust systems. (Running tuned exhaust headers of the tri-Y style is virtually impossible on a standard 90-degV/dual-plane-crank V8.)

V-engines get the nod for higher-revving applications, or where the engine space is more boxy than long-and-narrow. They can be made lighter (if just OHC) and they can be made stiffer. They are less tall, typically, than an inline (except a leaned-over inline, like the Dodge slant-6, various BMW and Datsun designs.), so the lood can be lower.

Radials get the nod if you like planes with lots of power that are fault-tolerant. Or if you like dumping a couple of quarts of oil on the ground each time you try to do a cold start.

The number of cylinders and their angle relative to each other (and crank design) determine engine vibration. You get one type of vibration from the power stroke of each cylinder, and another type just from the rotating/oscillating mass of the piston/rod/crank-throw.

To get the least amount of vibration from the power pulses, you want the cylinders to have their power strokes evenly spaced. For a 2-cylinder 4-stroke (all the following will assume 4-stroke), you want the pulses 360-crank-degrees apart. With a 4-cylinder its 180deg, with a 6-cylinder its 120deg, and with am 8-cylinder its 90deg.

To get the least amount of vibration from the rotating masses, you want the masses to counteract each other, or at least not add. That means that you can get an inline twin in either primary balance or secondary balance, but not both: To get the power balanced, both pistons would have to go up and down at the same time, which makes the rotating mass vibration feel akin to riding a pogo stick. To get the rotating balance minimized (still causes an end-to-end rocking couple) the power is delivered 180deg-then-540deg apart (bu-bump, bu-bump). If you put 2-cylinders into a 180deg "V" (aka horizontally opposed) then it achieves both primary and secondary balance (with still some rocking couple).

Inline-4s are mostly in balance, but still tend to shake... can't remember exactly why right now, but seems to me that it is because an inline has to have at least 6 cylinders to be in proper secondary balance. 180deg V-4s are better off.

Options for 6-cylinder engines open up. They are well balanced in inline and V-angles that are multiples of 60deg. Quite a few 60deg V-6s, some 120deg, and some notable and familiar 180deg V6s. Detroit (and others) have built 90deg V6s, and then spent years and millions trying to tame the vibrations. (Typically done with a special crankshaft that offsets paired crankpins.)

8-cylinders start to get too long for inline design except in low-revving applications (typically industrial/diesels). V8s can be smooth and well balanced, with 90deg-multiple V-angle.

Typical V8s are smooth but near impossible to put a good exhaust system on, because complimentary exhaust pulses can occur on opposite cylinder banks due their dual-plane crankshaft design. Attempts to "fix" this used either a "basket of snakes" exhaust system, or used a single-plane crank that made the engine essentially into 2 inline-4s fighting to tear the engine apart.

Let's back up... How much displacement do you need? How many cylinders do your want to put that into? More cylinders generally means smoother, but it means heavier, bulkier, and less fuel efficient. (A lot of fuel gets used moving piston rings up and down cylinders, and the smaller that you break up the displacement the more ring surface there is.)

For most of our purposes, 4 cylinders will work, especially in a 180deg V4. Do you want the engine to produce lots of torque, lots of power (now we use power properly, as HP, KW, et all), or fuel economy? Pick one, or maybe two.

Torque is optimized with longer strokes, smaller bores, and lower speeds. Torque is a value that can be moved around, both in number and location on the engine's rev range. Torque is torque...

Power is optimized by faster engine speeds, and the shorter strokes and larger bores that allow you to get there. Power is a product of torque multiplied by engine speed, and is thus majorly dependent on engine speed. You can have an infinite amount of torque, but if the engine isn't turning even a little then it is producing 0 (zero, nil, naught) power. similarly, an engine not producing any torque but moving at infinite RPMs still produces 0 power. You have to have engine speed to produce horseposer, and you have to have the engine producing torque to produce horsepower. Torque AND RPM.

So, our little engine produces (in USA terms) more ft-lbs of torque then HPs of power. Both are made-up systems by long dead Europeans. Don't infer anything generally useful from them. Within the context of our meauring units, it is common for the torque number to be higher than the power number; it just happens that way.

More important that the unit-system or even the numbers, is where all of this happens. The figures are peak values, and everywhere else they are less. How much less, and where? In general, the higher output an engine is, the more that it has been optimized to produce its peak values at a certain RPM, usually much higher than most of us will use. The closer torque peak is to HP peak, the more highly tuned and "peaky" the engine will be. The greater the spread in RPMs between those peak values, the less "peaky" the engine will be because the torque curve is flatter, with little drop off above and blow the RPM its peak. Less peaky is FAR more fun to drive in the real world.

How do you get more power? Make the engine rev higher. How? Short stroke (minimizes piston speed which has physics implications), big bore (fits bigger/more valves), stronger drivetrain (DOHCs, multiple/smaller valves, stonger valvesprings that are often paired/tripled to control harmonics leading to spring surge)... and tuning the cam timing, the intake, and exhaust systems to shift the peak torque condition to the highest possible RPM.

Back to our beloved opposed-4. Very oversquare bore-stroke ratio would suggest that it was meant to be a high-RPM engine, but the valve gear, intake and exhaust systems say "no way". The stroke is short to allow the wide opposed-4 design to be narrow enough to fit between the frame rails of an economy vehicle. The bore has gotten big to allow for the needed displacement increases over the years. It now looks like something that it was never intended to be, and even the EJs don't make any use of the RPM potential. My 71 Datsun has a higher rev-limit.

Didn't intend to end on what sounds like a sour note, but got to eat lunch. :-\

Edited by NorthWet, 14 March 2011 - 02:04 AM.


#8 NoahDL88

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Posted 13 March 2011 - 10:22 PM

Back to our beloved opposed-4. Very oversquare bore-stroke ratio would suggest that it was meant to be a high-RPM engine, but the valve gear, intake and exhaust systems say "no way". The stroke is short to allow the wide opposed-4 design to be narrow enough to fit between the frame rails of an economy vehicle. The bore has gotten big to allow for the needed displacement increases over the years. It now looks like something that it was never intended to be, and even the EJs don't make any use of the RPM potential. My 71 Datsun has a higher rev-limit.

Didn't intend to end on what sounds like a sour note, but got to eat lunch. :-\


The bottom end of an EA series 81-82 has a piston speed tolerant of 14,000 RPM, if you could design a head and valve train to take advantage of the bottom end you'd have yourself one hot engine.

#9 nipper

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Posted 13 March 2011 - 10:36 PM

So many misconceptions, so little time...

Cylinder configuration is all about packaging, and little or nothing to do with ability to produce power and what type of power. (even the use of "power" here is inaccurate/incorrect.) A cylinder of the same design will produce the same amount of "power" regardless of how they are stuck together with other cylinders. . :-\


I suggest you do some m,ore checking. I said the crank journal throw is the determination of how much torque, limited by the mass of the crankshaft, pistons and other parts. the heavier the parts, the lower the max RPM they can handle.

The size of the oil pan and crankase determines how big the crank throws can be due to space. An inline engine has lots of room for large throws, where as V engines or H engines do not.

You are correct that the same cylinder will produce the same power no matter the number, but it is HOW that energy is transmitted that increases and decreases power. A crank throw is a simple leverage arm, and this arm determines how much torque is developed (keeping fuel mixture and cam timing all the same.

It is about packaging as far as the shape of the engine, but the crank throw is limited by that same packaging, hence reducing torque given everything else the same except for crank throws.

that is pure physics and not misinformation.

#10 Twitch de la Brat

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Posted 14 March 2011 - 01:48 AM

Sigh, also the notation that Subaru flat engines are just 180* V's is
completely inaccurate.
The traditional V engine shares a single crank with 2 cylinders.
So a traditional V8, such as a Chevy 350, has connecting rods set at 90*, forcing two cylinders to share a crank position.
A "boxer" 8 cylinder will have connecting rods set at 45* on the crank, not
90.
This allows the cylinders to have a single connecting point per piston,
stopping that fighting between cylinders.

I don't mean to come across rude or anything, but the notion Boxer engines
are just flat V's is just incorrect.

The bottom end of an EA series 81-82 has a piston speed tolerant of 14,000 RPM, if you could design a head and valve train to take advantage of the bottom end you'd have yourself one hot engine.


I do believe RAM performance has been busy making heads to go onto EA81's
that very well could handle 10,000 rpm's.
We just need to figure out how to buy a whole bunch of them for less than
10K a set :-\

Twitch

#11 NorthWet

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Posted 14 March 2011 - 01:59 AM

Sorry nipper, my casual opening comment was meant for the universe, not in any response to your previous post. If I offended, I will extend my daily self-flagellation. :grin: Truly, my comments were unrelated to yours, and frankly, I had never really considered that a long stroke requires a large crankcase to handle the crank throws, and not just a long cylinder to handle the piston's stroke; thanks for making me realize the previously unconsidered. Of course you are right that the throw of the crank is the major part of why long-strokes can produce greater torque.

On to other things... Although the piston speed might stay under generally accepted limits up to 14,000rpm (I haven't done the math, and the "generally acceptable" varies somewhat with what metallurgy is involved), bearing speed might be an issue, and rod bearing oiling might put a lower limit on things. (A "simple" change to improve oiling to the rod bearings on race-modified Datsun 240Z engines caused a large number of failures from oil starvation due to centrifugal effects at higher crank speeds.)

#12 nipper

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Posted 14 March 2011 - 11:36 PM

There is also the advantage to a straight engine where each journal has its own supporting bearing, which can make them real bears when it comes to torque.

A very high engine rpm can actually stretch the connecting rod unless the rod is made for that application.

Next lesson:

Over square vs undersquare...

Forgive me for cutting and pasting but that bi-po thing is making things hard .

Oversquare engines are extremely common, including both Chevrolet and Ford small block V8s. Most Boxer (horizontally-opposed) engines (such as those built by Volkswagen, Porsche, and Subaru) feature oversquare designs since any increase in stroke length would result in twice the increase in overall engine size.
This is particularly crucial in Subaru's front-engine layout, where the steering angle of the front wheels is limited largely by the size of the engine. Although oversquare engines have a reputation for being high-strung, low-torque machines, the Subaru EJ engine develops peak torque at speeds as low as 3200 RPM.
Extreme examples of oversquare engine designs are found in Formula One race cars, whose rules tightly limit displacement and thereby require that power be achieved through high engine speeds. Stroke ratios of 2.5:1 are typical, with engines capable of 19,000 RPM.

An engine is described as undersquare or long-stroke if its cylinders have a smaller bore (width, diameter) than its stroke (length of piston travel) - giving a ratio value of less than 1:1.
At a given engine speed, a longer stroke increases engine friction (since the piston travels a greater distance per stroke) and increases stress on the crankshaft (due to the higher peak piston speed). The smaller bore also reduces the area available for valves in the cylinder head, requiring them to be smaller or fewer in number. Because these factors favor lower engine speeds, undersquare engines are most often tuned to develop peak torque at relatively low speeds.
An undersquare engine will typically be more compact in the directions perpendicular to piston travel but larger in the direction parallel to piston travel.
An engine can be "stroked" by replacing the crankshaft with a so-called "stroker" crankshaft and modifying the connecting rod(s), piston(s) or engine block to accommodate the increased piston travel. This increases the displacement and therefore the torque of the engine, but may reduce the peak speed at which it is safe to run.

#13 Twitch de la Brat

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Posted 15 March 2011 - 12:10 AM

Although oversquare engines have a reputation for being high-strung, low-torque machines, the Subaru EJ engine develops peak torque at speeds as low as 3200 RPM.


:banana:
This just adds more evidence to the theory that boxer engines tend to be
torquey.

Twitch

#14 nipper

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Posted 15 March 2011 - 05:40 PM

Should i cover valve trains or are we good with that?

#15 Twitch de la Brat

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Posted 15 March 2011 - 05:50 PM

Should i cover valve trains or are we good with that?


If you feel like it, go for it Nip :)
If not, I'm sure someone will dig up the info.

Twitch

#16 nipper

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Posted 15 March 2011 - 06:43 PM

The lowly Flathead.

The flathead's valves are carried on one side of the cylinder of the engine. The valve area is in an area on the underside of the head in a common pocket. This allows the (poppet) valvespen and close alternativly . Each valve works without any inkages or arms in a straight line from the cam. The head is L shaped and also is called a sidevalve engine.
DUe to the valave design, "dropping" a valve was just a nussance, as no damage would occur. The velve train was extreemly simple and light which allows for better low end performance. The flat heads had a torque profile that feels just about the same as an electric vehical; Lots of pull at low RPM, runs out of grunt at higher RPMs.

The downside was that by design the engine was choked. All gases had to make 90 degr bends to enter or exit the engine. Max compression ratio was 7:1

There was a hybrid called the F head. This had the intake over exhaust configuration (one overhead valve).

From here i need to do a little cut and paste:

Another concern is that because the exhaust follows a more complicated path to leave the engine, there is increased tendency for the engine to overheat under sustained heavy use. This is especially true if the exhaust is routed between the cylinders, as in the Ford flathead. It is possible to arrange the sidevalve engine layout so exhaust will be taken away through a valve and an exhaust tract located on the opposite side of the cylinder from the intake valve, in which case the layout is referred to as a T-block or T-head. American Le France famously powered their production with T-head engines from the 1920s to the 1950s. The Cleveland Motorcycle Company produced a four-cylinder in-line motorcycle engine using the T-head configuration in the 1920s. Very early engines were T heads. This requires two passages between the block and head, within the combustion chamber, and it loses some of the simplicity.
The flathead design also greatly reduced the ability to overbore the engine for performance purposes. Since the piston, exhaust valve, and intake valve were all next to each other, the piston cylinder bore could only be slightly increased, if at all, or it would encroach upon the radii of the intake and exhaust valves, and also cause thin and weak cylinder walls

There were V-8
Another concern is that because the exhaust follows a more complicated path to leave the engine, there is increased tendency for the engine to overheat under sustained heavy use. This is especially true if the exhaust is routed between the cylinders, as in the Ford flathead. It is possible to arrange the sidevalve engine layout so exhaust will be taken away through a valve and an exhaust tract located on the opposite side of the cylinder from the intake valve, in which case the layout is referred to as a T-block or T-head. American LaFrance famously powered their production fire engines with T-head engines from the 1920s to the 1950s. The Cleveland Motorcycle Company produced a four-cylinder in-line motorcycle engine using the T-head configuration in the 1920s. Very early Stutz engines were T heads. This requires two passages between the block and head, within the combustion chamber, and it loses some of the simplicity.
The flathead design also greatly reduced the ability to overbore the engine for performance purposes. Since the piston, exhaust valve, and intake valve were all next to each other, the piston cylinder bore could only be slightly increased, if at all, or it would encroach upon the radii of the intake and exhaust valves, and also cause thin and weak cylinder walls.

There were straight4 6 8, v8, v12 flatheads. Harley still uses this design.

I just bring this up since this was the engine that powered the world for so many years it deserves to be remebered. This is where the term "breathing" started being used. These engines breathed like an asthmatic in a feather factory.

http://www.allpar.com/mopar/flat.html Yes it is a mopar site but really does a godd job of showing things.

Edited by nipper, 15 March 2011 - 06:45 PM.


#17 NorthWet

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Posted 17 March 2011 - 02:51 AM

The flathead can still be found on many/most lawnmower engines.

#18 nipper

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Posted 17 March 2011 - 01:27 PM

The flathead can still be found on many/most lawnmower engines.


yes lots of small engines and harleys due to thier low end power.

#19 Dirk

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Posted 19 May 2011 - 08:22 PM

Yikes!

Thats a lot of info to digest.

I do not have any facts or understanding of engine design but I can give you a basic engine comparison to discuss.

I have a soob 1600 dl EA71 (as you well know) and also an Alfa Romeo 33 (1.5l boxer)

These engines are more or less the same size and block design however they perform totally differently.

The EA71 feels more powerfull than the Alfa and deffinately has the low end grunt that allows me to tow consideranle loads behind it.

The Alfa does not have a tow bar but I just know that it would not be able to cope with the same loads. However it way out performs the soob as far as speed goes. The power comes on at about 4500rpm and just keeps on coming all the way to the rev limet.

The Alfa engine is a way breathier design. There is no intake manifold, just carbs mounyed direct on the heads (one barrel per cylinder). The head is for sure a better flowing design with dual intake and dual exhaust. The exhaust has 4 long headers that merge into a fairly modest looking system.

Judging from the exhaust note I suspect a more aggresive cam also.

All in all the engine seems designed to pump air/fuel in and out as fast as possible. It is also a smoother running engine that enjoys high rpm which suggests to me that it is better made and ballanced.

The EA71 does not breath nearly as fast as the Alfa. (long intake manifold, complex heads, shared intake and exhaust ports)

The EA71 does not seem to enjoy the high rpm as much despite all the hp being at the top.

It has been suggested to me that the length of intake manifold has a big influence on power band.

I don't think that a stock EA cam takes full advantage of scavenging. I think that the engine has been designed rather to use exhaust backpressure to load fuel into the cylinders.

I leave the rest for you guys to dissect.

#20 Loyale 2.7 Turbo

Loyale 2.7 Turbo

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Posted 21 September 2011 - 03:44 PM

... and the odd W engine from VW...


Not only VolksWagen...

I Remember that when I was Child, I Saw a diesel "W9" Engine in an Old Huge Truck, but I Can't remember the Details... Also I Searched on internet and only Found This W9:

http://www.atomracing.se/6M.html

Maybe someone here could Bring More info about that old one...

Kind Regards.





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