School Me: Engine Theory

This is going to be a really broad, open ended question. I know so little that I'm not even sure what questions to ask. Apologies in advance.

I understand the basics of the internal combustion engine, but I've never learned much about the subtleties of engine design. I was doing some homework planning my future engine swap (probably going to be a Chevy 250) when I started wondering about some of the other engines.

I'm not asking for engine suggestions (though if somebody in central illinois has a spare 261 or 250 give me a holler). What I'm really interested in is what the different engines do. Not which one's better, but why they were designed the way they were. Inherent advantages and flaws. That kind of thing.

What's the functional difference between a nailhead and a straight six, for example? Better still, nailhead vs. SBC vs. flathead? Or OHV vs. OHC?

I know the bare minimum. Any websites, books, or stories would be much appreciated. I've read all the engine articles in the Tech-O-Matic and they were interesting, but now I want to know WHY.

 

I'm interested in this too. Somebody please suggest some "Engine Theory for Dummies" type reading material.

 

Read some stuff like this http://auto.howstuffworks.com/engine.htm and then ask some "smaller" questions that don't require chapters to answer.

 

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What I'm really interested in is what the different engines do. Not which one's better, but why they were designed the way they were. Inherent advantages and flaws.

[/ QUOTE ] 1st thing is;stop thinking about it in terms of horsepower,or what would look cool in a hot rod.start thinking in terms of torque,fuel mileage,reliability,and the price range of the car as originally sold.

 

as it were, each design is just another attempt at refining the mousetrap. most all of them have inherent flaws (except the small block chevy !!!! HA!). but basically they all do the same thing. there is no 'functional difference' as they all suit the same purpose: create torque and horsepower for the motivation of an automobile. they are each an interpretaion of the designers ideas on how to skin the cat. its really all about configuration. if thats what you want to know about, thats a different thing all together. and then its really just about component placement.....

flathead= intake/exhaust ports, valves in block, ride on cam. cylinderhead= chunk of metal to contain combustion chamber(in cylinder). breathed poorly.

ohv (nailhead, rocket, sbc, ford, hemi, etc....) valves and combution chamber moved into cylinder head. requires use of lifters and pushrods. valve placement, combustion chamber design differ from make to make.

ohc (modern, ford 'cammer' etc...) cam placed inside cylinder head on top of valves. no more push rods(plus), more complicated drive mechanism(negative). (dohc= dual over head cam).

from there you just arrange the cylinders as necessary in groups of 4,6,8,10,12 whatever.

 

You will need to decide which is more important-Desrirebility or AVAILABILITY
The flaty and Nailhead type motors are cool and in demand but they cost a bunch more in dollars and time involved..
also the Flatty and nailheads and Hemis for example werent built for wht we know them for nowadays.
They were built to be TOURQUEY and solid as a rock to pull a HEAVY old car well and stay together a long time.
Thesmall block chevy was built and promoted as the first performance engine to exceed what was available at the time from chevy =235 6 cyls'
It was introduced as "the fast one".
and time would prove that point well.
The others wree Legends in their own time too -but later on were tweaked and built into the hotrod standards we now think of them as.....

 

Pistons go: boing boing boing

Rotaries go: MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM

 

Yorgatron says --"torque,fuel mileage,reliability,and the price range of the car as originally sold"
Choprods says--"You will need to decide which is more important-Desrirebility or AVAILABILITY"

Their different opinions illustrate the need to know what you want and need. For me torque, fuel mileage and the original price ((original price???) are not important, specially original price. George, Whatcha been smoking?" Desireability, no matter how you spell it, depends on your opinion, then you get to whats important to me----Cost--which is a function of availability. That boils down to one and only one type engine. That engine is the cheapest because more than 80 million have been made. Its horsepower, torque, and every other technical thing that matters is satisfactory. So it goes back to what you prefer.
The thing that most confounds me is why the timing of the spark is important. Sure its important at a few revolutions per minute but at 4000 rpms or 125 times per second, HOW COULD IT MATTER WHEN IT FIRES? Seems like a continuous spark oughta be just fine. Its gonna spark 125 times per second???? Incomprehensible!

 

Alteredpilot, you forgot about the 3 and 5 cyl configurations.

Frank

 

OK, OK, so not to piss off the Briggs and Stratton and the Harley owners how about the 1 and 2 cylinder jobs?

Frank

 

What about Fat Hacks Briggs and Stratton Chevy Fleetline???

 

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Alteredpilot, you forgot about the 3 and 5 cyl configurations.

Frank

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yeah, i didnt think there were too many guys waiting to plop a suzuki or audi in a model a.....could be wrong though...

 

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What about Fat Hacks Briggs and Stratton Chevy Fleetline???

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(sigh) Have you absorbed NOTHING, Hatch? I'm a devout TECUMSEH engine enthusiast! Briggs & Stratton engines are for single pattern cams!

 

I knew you upgraded from the 2.8...I just ASSUMED it was to a Briggs...

 

What the hell is your avatar photo???

The jewelry counter at a hardware store/bait shop up in Bay City???

Your Christmas tree????

Photo recon form the Voyager satellite???

Some kid's mini-bike???

 

Triumph pre-unit avatar.....Triumphs had TWO cylinders ...wow...whodda thunk?

 

The 250 Chev is a great little engine and uses 283 pistons and rods I think. It is economical and torquey. Also it will bolt to any chevy tranny so you can run a 700 R4 or whatever. Just don't get the later one with the exhaust manifold integrated into the head. The straight sixes are a little long for some engine compartments tho so take measurements before committing.
The benifits of the small block Chevy can't be denied but there seems to be more and more people who view that choice as boring and unimaginative. But who couldn't love a 283 with 3 deuces and CalCustom valve covers with a 4 speed behind it?
I am kind of a non Chevy guy but I could run a late model 6.0 if they weren't so dam ugly.
I have had several 303, 324 and 371 olds motors and really liked them but the nostalgic craze has driven up the prices on them.
I am going to dare to be different and run a 425 caddy because I found a good one for free. And that is at the essence of what rod building is to me. My whole build has changed direction a few times because of what I could get for cheap or free. Don't let that philosiphy take you to far off into weirdness though. Just because your aunt gives you her old K car doesn't mean it would be cool to have a front drive 2.6 Mitsubishi powered model A.

 

My opinion, Engines are an evolution, there is a precise amount of energy in fuel. Which differs depending on the specific gravity of the fuel. Engine manufactures are trying to capture as much of that thermal energy created by cumbustion and send it to the flywheel. Every piece of machinery in the world has a mechanical efficency.
By The Way Don't Panic if spelling and gramar sucks.
tim

 

suck.........squeeze.........bang...........blow........repeat

 

CptStickfigure
Looks to me like you're leaning toward an Inline mill. I normaly would ask WHY? but i have a lot of friends that are inline guys so I won't even go there.

I would probably lean toward a later model inline. Then I would try an decide if I was leaning toward a rrrrever or a stump puller.
I guess that the later inline isn't what is as desirable in the cool dept, but for a GM ya just can't beat the 292 for flat out grunt.
Next for dependabilities sake look at the lower end. How many mains does it have, hows it built (ie is there a lot of metal around the main saddles).
I'm real big on cross flow heads, for instance for the later GM inline mills you can get a merc-cruiser cross flow head pretty reasonable. Cross flow = better breathing.
The list goes on and on. Go to Border books or Barns and Noble and see if a company called HP books has a tunning book that covers your particular engine. It will give you all the theory that you can absorb and should be written in such away that you can understand it. It will also give you just enough info to start asking questions.
And someone here will have the words to make you understand what your asking about.
Like I started out to say I'm not a big inline fan, but I do know you can make one run, in a light vehicle they work really well.

 

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as it were, each design is just another attempt at refining the mousetrap.

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I almost put this exact phrase in my original post.

[ QUOTE ]
as it were, each design is just another attempt at refining the mousetrap. most all of them have inherent flaws (except the small block chevy !!!! HA!). but basically they all do the same thing. there is no 'functional difference' as they all suit the same purpose: create torque and horsepower for the motivation of an automobile. they are each an interpretaion of the designers ideas on how to skin the cat. its really all about configuration. if thats what you want to know about, thats a different thing all together. and then its really just about component placement.....

[/ QUOTE ]

This is really more what I was trying to ask about.
I know all the major companies were trying to build a "better" engine and thought their modifications would be an improvement.

What I'm really looking for is sort of a "history of the modern engine" sort of book that would explain why they chose those particular refinements. An engine tuning/building guide would be a close second, but those tend to focus on a single engine type.

Like I said, I know this is a huge topic. I'm just looking for a place to start.

 

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CptStickfigure
Looks to me like you're leaning toward an Inline mill. I normaly would ask WHY? but i have a lot of friends that are inline guys so I won't even go there.

[/ QUOTE ]

I'll answer anyway. Personally, I think inline engines are cool.
Then again, I also like four doors. Your mileage may vary.


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I guess that the later inline isn't what is as desirable in the cool dept, but for a GM ya just can't beat the 292 for flat out grunt.

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Not nearly as cool as the old ones, but they're common as dirt and this'll be a closed-hooded car. From what I've heard, the 292 is a brute, but gas mileage is pretty bad.

This'll be a straight up driver, so I'm looking for acceleration and gas mileage before top speed.

And Willowbilly, I think the 250 will be about 2 inches too long, so it will take a little work to get it in there. I'd take a 261 in a heartbeat, but those are hard to find around here.

[ QUOTE ]
Next for dependabilities sake look at the lower end. How many mains does it have, hows it built (ie is there a lot of metal around the main saddles).
I'm real big on cross flow heads, for instance for the later GM inline mills you can get a merc-cruiser cross flow head pretty reasonable. Cross flow = better breathing.

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Ooh. I really wanted to know more about non-inline engines, but I haven't heard much about cross flow heads. Would side draft carbs on a cross flow head be even better? Am I mixing my terms? Talking crazy talk? I don't know about much beyond stock configurations. Tell me more

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Go to Border books or Barns and Noble and see if a company called HP books has a tunning book that covers your particular engine.

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I'll check that out. I picked up California Bill's Chevrolet Inline Six-Cylinder book, but that seems more racing oriented; great if you want MAXIMUM POWER, but light on the other configurations.

Anyway, thanks for the advice.

 

[ QUOTE ]
This is going to be a really broad, open ended question. I know so little that I'm not even sure what questions to ask. Apologies in advance.

I understand the basics of the internal combustion engine, but I've never learned much about the subtleties of engine design. I was doing some homework planning my future engine swap (probably going to be a Chevy 250) when I started wondering about some of the other engines.

I'm not asking for engine suggestions (though if somebody in central illinois has a spare 261 or 250 give me a holler). What I'm really interested in is what the different engines do. Not which one's better, but why they were designed the way they were. Inherent advantages and flaws. That kind of thing.

What's the functional difference between a nailhead and a straight six, for example? Better still, nailhead vs. SBC vs. flathead? Or OHV vs. OHC?

I know the bare minimum. Any websites, books, or stories would be much appreciated. I've read all the engine articles in the Tech-O-Matic and they were interesting, but now I want to know WHY.

[/ QUOTE ]



Well my take on this question goes like this....ahem....First engine design in the early years was very limited by the quality of fuels available at that time. A Flathead Ford had compression ratio of about 6.5:1 in the early days. Further most engines were "undersquare", meaning the bore dia was a smaller number than the stroke of the crank. Development of piston engines and fuels was accelerated by the activity of WWII. High octane fuels, higher compression, ohc/ohv cyl heads, supercharging were all rapidly advanced during the war. (Remember the auto manufacturers had a large hand in this development.) Now when the war ended GM seemed to be the first manufacturer to be able to capitalize on all this good stuff. In`49 Olds and Caddy came out with their ohv V8's. They were breaktrough in that they had a large bore/ short stroke relationship, (this allows higher engine speeds and better breating) and high compression. Chrysler one upped by introducing the hemi which incorprated all of the above plus opposed valves and short direct ports for even better breathing. Ford Motor Company was in tough shape after the war and soldiered on to `53 with the Flatthead(no doubt a testament to the Flatty's overall goodness since it hung in there with all the new offerings that the others had). When Ford introduced the Y-Blocks they now had an "anvil- tough" engine with a skirted bottom end and a reinforced valley area that really made for a ridged block. This proved to be heavy, but it was a development engine designers put to good use in the late `50's early `60's in the venerable FE series Fords and the 426 Chrysler hemi of `64. Nitro hemis still use skirted cross bolted blocks to cope with the huge power loads the nitro brings to bear on the bottom end. In 1955, while trying to capture some of the youth market, Chevy intro'd their smallblock engine and it took all the the best features and combined them into a lightweight and cheaper engine design. Gone were the shaft mounted rockers of the Olds and Caddys, replaced by a light individual stud mounted rocker arm. The block was simplfied and the intake was used as the top cover. They had short direct ports were an "oversquare" design. This kinda forced all the others to design "cheaper" to manufacture V8's and many premium engines went away purely because of cost considrerations.

Interesting to note all of the characteristics that Detroit was building into their powerplants in the `50's, were pioneered by hot rodders primarily on the Flathead Ford V8. Stuff like larger bores, higher compression, higher lift longer duration cams, dual point ignition, multi carbs, redesigned ports for better breathing and of course a pushrod activated hemi V8 in the ARDUN just to name a few were all common modifications made by our hot rodding predecessors.

The thing to remember about engines is ALL engines are based on compromises of cost, performance, emissions, simplicity, seviceability, size and many other factors. Many times modern Ford engines have been knocked for the lack of interchangeability for example. What is rarely considered is Ford engineers were not willing to give up an important characteristic called the, rod length to stroke ratio. This is important because it affects the mechanical efficiency of a given engine (shorter rods increase rod angle as the crankshaft turns, and therefore impose more thrust loading on the cylinder walls, also it affects breathing as it alters the "dwell" at BDC of the piston allowing for more time for the fuel/air charge to enter the cylinder) When the stroke of a particular engine series grew to a point where the L/R ratio was seriously compromised Ford raised the decks of the block to afford the room for a proper length connecting rod. The drawback is that this by virtue of the taller but further spaced decks it then required a new intake manifold, as in the case with the 302 to 351W example.

 

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Ooh. I really wanted to know more about non-inline engines, but I haven't heard much about cross flow heads. Would side draft carbs on a cross flow head be even better? Am I mixing my terms? Talking crazy talk? I don't know about much beyond stock configurations. Tell me more



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The only real advantage I can see to side draft carbs is that its easier to mount several of them. IE the intake manifold is easier to build. Don't get me wrong I like 'em I just don't use 'em much anymore.

The real advantage to a cross flow as I understand it is that the spent gas doesn't have to make a U turn to get back out. That's probably the worlds worst way to explain it but I've got a pretty simple mind.

 

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suck.........squeeze.........bang...........blow........repeat

[/ QUOTE ]Sounds like a good time!!

 

Cross flow heads allow more desirable ports as they aren't smashed together. They also allow you to do more work on those ports.
In a nut shell the inline engines ,anyway most of them have the mains too far apart and the crank tends to flex at high RPM.
Any design or design change is always a trade off. For instance if you put a large cam in your motor it might make more Horse Power at high RPM but will have less torqe and H.P. at the low RPM. Figure where you will run the thing and then build it for that RPM.
There is nothing worse to drive than a big cam big carb 1300 rpm idleing motor with a stock convertor and a 2.94 rear end.
A motor using a torque setup with max torque at 1800 rpm will not be pleasant to drive with a 3500 convertor and 4.88 gears.
In the years messing with Drag Cars I think that most modifications, no at least half of them ,result in the cars running slower than they did before the mods.
Most tinkerers have a lot of power left in their setup ,but try for the 45 H.P. gains rather than to go after the small gains,most of which are very inexpensive.

 

I think Buick nailheads are very cool, even though I just gave my "project engine" to my fellow HAMBer, BLAKE. These aren't cheap engines to build, but they are torque monsters and get major alternative-traditional points. One of the cool things about a nailhead is that the engine is narrower than the standard OHV V8. The reason for this is that in '53 when Buick went to the V configuration from the old straight 8, they still had a very narrow engine bay in all of their cars. To fit the new V-block into the bay, Buick put the pushrods on the opposite side of the rocker arms and had the valves, now on the valley side, pointing straight down. This also helps when stuffing one into the narrow frame of a vintage rod, like Tommy Ivo did in his bucket. Check out this link for more info and a good cutaway of the nailhead valve train: http://carcraft.com/thehistoryof/65502/

On the other hand, inline sixes are inherently balanced, and sound like nothing else with a split manifold...

John

 

No discusion 2 strokes???? OK wont go there big, but I think they go; squeez bang, blow suck.
but they do it real fast so a single is twin, a triple is a 6 and a 8 is a 16 in terms of swept area efficiency.

But the sound real funy when not under load.

 

Henry Floored said "This kinda forced all the others to design "cheaper" to manufacture V8's and many premium engines went away purely because of cost considrerations."

That's kinda, sort of true... but not really.

The Small Block Chevy was "cheaper" mainly becuse of the way that it was cast. (among many other things)

For instance, the early Cadillac v8 used 22 different cores to cast the motor, while the '55 Chevrolet used only 9 major cores.

The early v8 motors up until that point were heavier. Mainly because they were thicker castings that were needed because of "core shift".

With the new green sand casting method, (developed at Pontiac for use in a Pontiac V6 engine that never saw production) core shift was reduced, so they were able to make the engine walls thinner. The green sand method of casting reduced the amount of sand needed to cast a v8 engine by 200 pounds!

Ed Cole joined Chevrolet in 1952, a huge part of his job was to develop a new engine for Chevrolet. He was instrumental in developing the '49 Caddy motor (which in '49 was revolutionary in it's own right) but it was quickly becoming a dinasaur.

Cole increased his engineering staff at Chevrolet from 800 guys to nearly 3000...

They were some of the brightest, and most talented men in the industry.

For instance... the guy who invented the stamped steel rocker arm (which was one of the SBC's innovative components) worked for Pontiac.

Pontiac wasn't willing to let him work on his design while at work at Pontiac... so he worked on the design in his basement, after hours.

Ed Cole got wind of this... brought him and his design on board, and utilized that part for the new Chevy v8.

What you have to remember is that there real people... hard working, intellegent, American engineers behind each and every part that went into the design of American Automobile engines.

No one single man did it all.

It was a constant evolution... and each engineer was picked to do his little part.

Ed Cole was a likeable guy, someone people wanted to work for, he assembled a dream team if you will, and out of that came one amazing car... and an engine that ended up surpassing everyone's expectations and went on to achieve more than any other engine ever made, or probably ever will be made.

It was that good.

But even within' GM, there was competition between the different brands. They kinda knew what was going on over at Buick... Buick knew about Chevy and Chevy about Pontiac.

I know I mentioned Pontiac a few times... but truth be told, the 1955 265 v8 had ties to other brands (mainly Cadillac) through engineers that had worked elsewhere.

Another thing you have to keep in mind is that ALL of the makes, even as early as the mid 50's, were striving for lighter, faster cars.

There were hot rodders, and guys that were into racing that were engineers at Chevrolet (and I assume other brands)... and these guys would push for things like 4 barrel carbs and dual exhaust systems.

Chevrolet was a lower priced brand... so it made sense that they would build "cheaper" motors.

Sure they were cheaper, but "cheap" in regards to the Chevy v8 had NOTHING to do with quality, horsepower per cubic inch, or horsepower to weight ratios. In those respects, it was much much better than all the rest.

Sam

 

i'm in the same boat as you----i don't know jack about engines. So, my response will probably be funny.

1) inlines generally make more bottom end torque than a comparable sized/cylindered V counterpart? But the V engines tend to have the advantage at higher rpms?

a) Notice that the vast majority of highway tractor-trailers use huge inline 6's---they need that lower end torque which is suited for heavy towing all day.

2) OHV vs. OHC:
With overhead cam, you can eliminate the lifters and pushrods? This reduces friction? It's probably better than conventional OHV setups?

3) SBC vs. all those other engines that you mentioned which i know nothing about:

The bottom of the SBC's block ends at the crankshaft centerline. (?) i'm ASSuming that the other two's blocks extended way past this centerline thus making them heavier and this is one advantage of the SBC---generally a pretty light, for a v-8, engine.

4) i'm not a naturally mechanically inclined or engine inclined person such as Smokey Yunick, Dale Armstrong etc. i'm more of a driver; i think i'm the type that being somewhat interested in cars, sort of had to learn about the mechanicals thru nessesity, not nessesarily desire. And picks things up that way. i consider myself to be sort of like Roland Leong---he's open minded to auto mechanics and has become pretty good at it, but i think, and even Roland himself will probably admit, that he's not a natural mechanic. i can pick up mechanical concepts pretty good, but i don't consider myself a natural, hard-core mechanical person such as Smokey Yunick.

i mean, if you saw the movie "the sorcerer," those guys were not truck drivers by profession---they became truck drivers thru nessesity and they were able to know how to fix cars/trucks thru probably nessisity.
If you were a guy that grew up in the 50's/60's, you probably picked up how to fix cars, just because. Even if you weren't a "car guy."

i will try to dig up some links that really helped me.

a) i would recommend reading ANYTHING/EVERYTHING by Smokey Yunick.

b) Generally, reading anything about engines, i think, will help.

P.S. If i'm wrong about any of the above, pls correct me.