Straight-Block vs. Slant vs. "V" Engines

What are the advantages/disadvatages for each of these engine styles, and please mention how many cylinders you are thinking of. Also, why can’t a four cylinder engine come as a slant or V formation? Is it because the idle would be too rough, perhaps rough enough to stall the engine?

As an afterthought, please feel free to mention if the advantage is merely asthetics, building costs rather than performance…and please specify if performance mean more hp, max fuel economy and/or the best balance of both worlds? Last…what the heck is a “hemi”?


  • Jinx

They do.

IIRC, Saab had a V-4 engine available in their old Type 96 cars.

A hemi is an engine with hemispherical combustion chambers ( better for flame propagation, more complete combustion, more horsepower per cubic inch).

Sorry I can’t answer your other questions.

Indeed they do. In fact, my new Subaru (well, it’s a used 95 Impreza wagon, but it’s new to me) has a flat 4. At first I thought it was a V-4 and then realized that there wasn’t any slant to the cylinders (plus I read the manual specs). I figure it’s because it was actually built in Japan.

Didn’t the old VW Beetles also have an air-cooled flat-4?

Oh, I don’t know much about cars myself, but someone I trust told me that I was getting a little more gas mileage and giving up a few horsepower having the engine in that flat-4 configuration instead of straight.

I am picturing a spark plug located at the center of a hemispherical piece of metal, much like one dished-shaped end found on a cylindrical storage tank. I WAG, typically, the spark plug is otherwise centered in a piece of flat metal. In either case, it forms the absolute end of combustion chamber…beyond the bore length of the cylinder, correct?
Thanks, - Jinx

This really is a more complicated question than it sounds. I took two graduate classes on IC engines and believe me there is a lot that goes into even the basic design.

Speaking generally, “flat” engines have an advantage of low profile for body clearance, but a disadvantage of needing extra “plumbing”, being wide, and needing two cylinder heads.

Generally, a “V” configuration engine allows for a shorter block. And if the “V” is very narrow, you can still use a single cylinder head. Typically, however, they have the cost disadvantage of two heads.

Inline engines are nice, but long. They typically need only a single cylinder head, unless very long (like something you wouldn’t see in a car anyhow).

Inline 6-cylinder and V12 engines have an advantage in that harmonically speaking (in a 4-stroke engine) they are well-balanced. They have no free forces of either the first or second order. The “smooth-running 90 degree V8” however does have a free first-order moment, so it has a little bit of vibration to balance out.

Possibly the most problematic common car engine from a vibration standpoint is the 60 degree V4, which is one reason you don’t see it much. They work well in motorcycles because they give a compact power unit.

Inline engine:
Easy and cheap to build
Long and tall Particularly in 6 and 8 cylinder versions

Slant engine:
Lower hood line than an inline engine
Easy and cheap to build
Long and wide.

Shorter than inline or slant
Very smooth in 8 and 12 cylinder versions
More complex to machine
can have fuel distribution issues.

Flat or opposed
Very short motor in both height and length
very low center gravity.
PITA to work on
split case design
Very wide
Jinx you are about half right on the hemi question. A hemi head has a hemispherical combustion chamber. Other engine do not have a flat piece of metal, but rather some type of recess that the valves and sparkplug reside in. Some are kidney shaped, some are pent roofed, or what ever the designer came up with.
As far as the performance advantage of the hemi goes, don’t forget that the hemi became a legend back in the fifties. Chevy at the time had a 265 cubic inch V-8, Ford had a similar sized engine (260 IIRC)
Chrysler came out with a 331 cubic inch hemi in 1951, went to 354 CI in 1956, and 392 in 1957.
These engines were huge compared to what the other boys were selling. Needless to say they kicked ass. Like they say there is no substitute for cubic inches.

Don’t inline motors usually have lower centers of gravity which is good for steering?

Yep, they certainly did. I have one.

No, inline engines, by definition, would have a higher center of gravity than the other engine types mentioned if other factors are kept constant. By canting the cylinders, as in a 60 or 90 deg V, or horizontally opposing them a la Porsche, VW, Subaru, BMW motorcycle engines, a lower center of gravity is possible.

Honda makes a V4 engine for their VFR sport touring motorcycle. If you look at all engines (motorcycle, snowmobile, racing, and one-offs) you can find almost any configuration you can think of.

A straight six is generally considered superior to a V6 because it is naturaly (sp?) balanced, however a straight 6 will not fit in most front wheel drive cars.

Hemi engines where discussed recently -

[There aren’t very many performance or fuel economy advantages with modern engines. But here are some of the major factors:

  1. Packaging - it’s usually a question of long and narrow for a V versus short and wide for an inline. Slant engines were developed to make for a lower hoodline, and also a shorter engine by allowing the water pump to be on one side of the engine rather than the front. I know the offset water pump is used on Chrysler slant sixes and the sort of slanted four used in the K-cars, and I think BMW uses this too.

  2. Ballance. Flat sixes, inline/slant sixes, and V-8’s are naturally very well ballanced engines. 90 degree V-6’s and inline fours are a bit worse. And V-4’s are pretty much impossible to run smoothly.

  3. Cost to build - having all the cylinders in a row makes for fewer parts and cheaper machining.

  4. Center of gravity - the closer the cylinders are to horizontal, the lower the C.G. height is.

  5. Fuel distribution. Back in the bad old days of carburetors, an economical fuel distribution setup on an inline engine with six or more cylinders was a nightmare to pull off. Chrysler’s slant six did a bit better than most by making a very long intake manifold due to the slant so the runners were closer to equal lenght, but they still have distribution problems. About the only way to get decent fuel distribution with carbs on a straight six or eight (or something even larger) is to use multiple carbs. A V-type engine has its own distribution difficulties, but they are a bit smaller than a long inline engine.

Don’t forget to throw VW’s VR- & W-engines into the mix.

Isn’t there a straight 6 in the Ford Windstar? Of course, that’s a minivan.

I don’t know about the Windstar, but the Volvo S80 and XC90 both have inline six cylinder engines in a front wheel drive/ all wheel drive setups.

Well, at least you didn’t claim, as some do, that Chrysler’s success was primarily due to the hemi chambers. I’ve never seen any data to support or disqualify that claim with any authority. And I agree that there is “no substitute for cubic inches,” which more likely accounts for the hemi “legend” of that day.

As for the “other boys,” you’re partially correct. Chevrolet, for example, offered no V8 at all until the intro of the 265 small-block in 1955. But they didn’t trail for long. 1957 brought the 283/283, the first production engine with a claimed horsepower output of one per cubic inch. And the next year, Chevy introduced the 348 (Was it the “W” block or the “Y” block? I can never remember…), which was revamped for 1961 as the 409 the Beach Boys sang about.

As for Ford, I’m less familiar with the lineage, but I seem to recall a 292 ci and 312 ci V8’s being in production during the Fifties. The 260 was Ford’s dismal first foray into “small block” V8’s early in the Sixties, although it soon became the famed 289. By that time, though, Ford had released the 352 and 390 big blocks…

[end hijack]

TBone2 You are correct about the intro of the Chevy small block. After I posted I realized that I had the time line wrong.
As far as the Fords go I am in no way a Ford expert. I used my foggy memory. Using some googling I find that 292 was the engine in a 55 T-bird.

Bottom line is even the 283/283 would be way behind the 392 CI 375HP hemi with 2 4bbl carbs in a 1957 Chrysler New Yorker.

I was careful to sate that an inline six will not fit in most front wheel drive cars. I should add, for those that do not have a lot of car knowledge, that most front wheel drive cars have the engine mounted ‘sideways’ or across the car.