What are the advantages and disadvantges to the straight-block, slant, and V-type engines? I thought V-type gave the smoothest performance, right? Do the others just look cool? Keep it simple, I’m no gearhead…
A hundred years of engine design in a few sentences . . . Yikes!
Not much difference between a straight block and a slant. The slant is essentially a straight block that is turned to one side, usually save space under the hood. Straight blocks tend to be tall, especially if they have overhead valves.
A “V” type design is two straight blocks joined together at the crankshaft. Yes, they tend to run smoother but they are more complex. Either you have one camshaft with pushrods shooting off in two different directions or you have to put in two camshafts.
A “V” design works best for 2, 4, or 8 cylinders. A 6 cylinder “V” requires some complex engineering to get the timing of the firing of the cylinders correct.
There is also the “flat” engine where the cylinders are in opposition to each other. Check out the old engine that was in the original VW bug.
Not a complete answer but a start.
It’s almost entirely a matter of packaging; shape the engine to fit the space. Compared to an inline, a V is shorter fore/aft and shorter vertically but wider horizontally. A flat is the same amount shorter fore/aft as the V, much shorter vertically, but much wider horizontally.
After that, the differences are mostly side effects, not primary engineering goals.
Now bore vs stroke ratio, cylinder count, cam shape, valve count, induction design, etc is where you really get into what makes any engine different as a powerplant.
Or modern Subarus.
Who is going to bring up rotary engines? 
Some wankel.
BTW, there are a few production cars out there with a W engine configuration. A W12 is available for the Audi A8 and VW Phaeton.
Henry Ford fooled around with “X” configuration engines. main advantage was: compact block, and short, easy-to-machine crankshaft. Technological obstacles (we are talking 1930’s technology) kept the project from success.
More cylinders = smoother. Hence an 8-cylinder will be smoother than a 4-cylinder. I question whether a V-8 is smoother than a straight 8. Straight 8’s were L-O-N-G and there was considerable incentive to shorten things.
Inherent balance = smoother. A straight 6-cylinder excels in this regard. I believe it’s smoother than a V-8. It’s definitely smoother than a V-6.
And there was there was the V-32 Dusenberg…
The Radial, from 3 cylinders to the 49 cylinder P&W R-7000
Yeah, I forgot about the other engine designs (rotary and X…or H?). Also, was there EVER a V-4? Spartydog implies there was? If there was, I wager it was just a trial that didn’t work so well.
Saab had one, why I don’t know.
The flat fours are usually (always?) “boxers” i.e. the opposing pistons go in and out at the same time like a boxer knocking his gloves together which gives good balance – but is more complex than a single row
There is also a V5, or not, more of a “Wiggly-5”
Ford and Triumph both had V4’s
SAAB started out buying Triumph V4s but deliveries were so unreliable the took to making their own.
Saab introduced the V4 to replace the 3 cylinder 2 stroke they had been using up until 1967. We had an old thread on V4s and the Saab V4 in particular:
It was actually made by Ford, who used it in Germany:
Er, it is definitely not just a matter of packaging (except for automotive “designers” who consider the powertrain to be an entirely secondary, if in fact not supernumerary requirement), and from the standpoint of a powertrain engineer there are a large number of parameters that go into the selection of engine configuration of which overall packaging space is just one. The primary choice by automotive designers is as often as not, “this is what we did last time,” hence why many manufacturers preferred the straight-4 and straight-6 despite their inherent issues, and why companies like Porsche, Volkswagon, and Subaru have built entire product lines around horizontally opposed engines. (To be fair, there are benefits to both: straight engines only require a single camshaft as opposed to two-bank cylinder engines, and HOEs have some inherent stability and torque distribution qualities as well as compactness and holistic powertrain configuration that makes them particularly desireable for certain vehicle applications.) V-configuration engines are popular because they are compact, but also because a wealth of experience exists regarding balancing, refining power output, et cetera. It took a hell of a lot for Ferarri to move away from front-mounted V-12 engines and into mid-engine V-8 and flat-12s, despite the overall performance improvement, and this was strictly due to prior experience.
There is really no answer to the question of the o.p. that will fit in any post of reasonable size. This is an incredibly complex issue that goes beyond the engine itself and into overall vehicle requirements and design. Rather than make even a superficial stab at answering this question I’m simply going to point to John Heywood’s Internal Combustion Engine Fundamentals as the predominate comprehensive text on the issue, and the Bosch Automotive Handbook is the general practical reference on automotive technology. MIT’s OpenCourseware has a upper division seminar on Internal Combustion Engines which is probably a good technical introduction to this. If there are more specific questions I’m sure many would be willing to answer them, but the question is too broad to provide a useful, overall answer.
Stranger
Look at our other thread. The Triumph engine you are referring to is a slant 4, that they used in the 99 and 900. And, yeah, they didn’t like it.
Are you talking about a radial engine configuration? If so, a radial engine with less than five cylinders is never inherently balanced, and in general you prefer odd numbers of cylinders (for larger engines arranged in banks) for smooth operation.
There is no advantage to a radial engine for automotive applications, and it would be very difficult to package this for maintenance access, compared to their presentation for prop airplane applications.
Stranger
I stand corrected.
When I lived there one of my friends had a 95 V4 and he was convinced it was a Triiumph engine in it.
If memory serves, there was a design with a Scotch Yoke rather than a crankshaft, and a 90 degree V configuration. The sinusoidal movement of the Scotch Yoke meant the piston motion could be perfectly balanced by a weighted wheel. The V could be doubled into an X quite easily using double-ended pistons. It was kind of like two Bourke engines at right angles, but a four-stroke design.
Yes, everything else being equal, the more cylinders the better because you will get cylinders firing and closer degrees in the crankshaft rotation. After that theory runs its course, practicality takes over. Manufacturing considerations, space consideration, and overall complexity can change the engineering.
A V-8 engine is elegance in its simplicity. As the old engine rebuilder told me “There’s nothing like a V-8 engine.” You can take a stock V-8 block that delivers 200 hp, modify it and turn it into a fire breathing dragon that easily delivers more than twice the hp.
Pontiac had a straight 8. As noted, it was long. As the same old mechanic told me, “The problem was that with the manufacturing limitations of the day, you could get some flex or warping of the block which would lead to engine problems.” It was obvious to the engineers that the V-8 was a better alternative. Just as powerful, smooth, smaller and could be adapted to a lot of vehicle designs. Back in the day, almost all American standard cars had a V-8 option at additional cost to the standard straight 6. The reason that was in almost all engine compartments you could drop a V-8 in the same space as a straight 6.
For whatever reason, some thing in this world are “right”. The V-8 engine fits in that category for cars that were the standard of American transportation of years gone by. That’s not to say that every car should have a V-8, it shouldn’t. But you have to marvel at the intrinsic “rightness” of the V-8 engine.