HEMI

This simple word inspired awe and fear from 1966-71, and still does today.  An original Hemi vehicle from Dodge or Plymouth is worth twice as much, or more, than its non-Hemi version – and might be a major star at Barrett-Jackson, a top auto auction. 

First of all, what is a Hemi?  Usually it refers to the 426 Hemi V8 used in Dodges and Plymouths from 1966 to 1971.   The Dodge models included the Charger R/T and Daytona, the Coronet R/T, and the Challenger; in Plymouth this would be the Barracuda (“Hemicuda”), the GTX & Road Runner, and the Superbird.  Plymouth did not make an equivalent of the Charger. 

Ok, fine.  Still, what does it mean?  It means hemispherical combustion chamber.  Each cylinder of the engine could be visualized like a grain silo you see at a farm: a tall cylinder with a hemispherical top to it.  The top has two circular openings, the valves. 

Four-stroke cycle.  Bear with me, this may be interesting (maybe not).  The piston goes up and down the cylinder, lubricated with oil.  Freudian, no?  Sometimes a piston is just a piston.

Intake.  The piston goes from its highest position (top dead center – TDC) to its lowest position (bottom dead center – BDC) in the cylinder.  The intake valve is open.  The piston’s downward movement sucks in the air-fuel mixture waiting outside the intake valve, which ideally fills the combustion chamber and cylinder.

Compression.  Both valves close, and the piston rushes up from BDC to TDC.  In doing so, it compresses the air-fuel mixture.  The ratio of this compression is the “compression ratio”.  The higher the compression ratio, the more power the engine can make, but it also makes the air-fuel mixture hotter and more likely to spontaneously combust without the spark plug’s assistance.  Highly volatile gas has a LOW octane rating, whereas relatively less volatile gas has a HIGHER octane rating.   This is why performance cars typically require 93 octane while economy cars can run on 87, and why running the wrong octane is a bad idea:  87 in an engine needing 93 may result in detonation, while 93 in an 87 engine is wasted.

Firing.  The spark plug fires, igniting the air-fuel mixture.  This is not an explosion, but rather a controlled burn which spreads out from the spark plug like a blooming flower.   Both valves are closed.  This is the stroke which produces the engine’s power: the piston goes back from TDC down to BDC.

Exhaust.  The exhaust valve opens, the piston goes from BDC back up to TDC, and the exhaust gases are pushed out of the combustion chamber.  Bye bye!

In a HEMI engine, the combustion chamber is hemispherically shaped, the intake valve is canted towards the intake side, the exhaust valve is canted towards the exhaust side, and the spark plug is close to the top of the combustion chamber between them.  Thus the valves are lined up parallel to the flow of air/fuel/gases through the combustion chamber.

Aren’t all engines set up this way?  Actually, no.  Most use a “wedge shape”.  The chamber shape is raised on one side and slants down to the other.  Think of those soft cloth caps working class men wore in the early twentieth century.  Nowadays pretentious people like Samuel L. Jackson wear them backwards.  Anyhow.  The valves are side-by-side, perpendicular to the flow of air-fuel/gases, with the spark plug coming in from the side rather than the top.

Looking at it from the outside, the HEMI engine has its spark plugs coming in the top of a large valve cover, whereas a wedge engine has the spark plugs coming into the side of the engine.

Power.   It’s not surprising that Hemi engines do in fact make a good deal of power.  What’s counterintuitive, though, is that the wedge design is remarkably competitive.  So much so, that the Hemi is the exception and not the rule.  Why is this?  In other words, why doesn’t everyone use a Hemi design?

            First, the Hemi head is much larger and more complex than a wedge head.  This makes it heavier and more expensive.  It makes the engine much wider and more difficult to fit in to an engine compartment.  Hemi cars needed special modifications and different suspensions and chassis stiffening.  Putting a Hemi in a car was a major undertaking.

            Second, as noted above, the wedge design works very well.   This includes all GM engines, all Ford engines (though the Boss 429 could be considered a hemi design), and the 440 V8 from Mopar.  With three two-barrel carburetors, the so-called 440 Six Pack was actually very competitive with the 426 Hemi on the street, and many enthusiasts considered it a better street engine than the Hemi. 

            In fact, the current run of GM performance engines in Camaros and Corvettes still keep the wedge design, although the LS combustion chambers are much different than the prior wedge heads.  The same holds true with Ford V8s, even in Shelby format.  While undeniably impressive, the Hemi design is not the only one which makes serious power. 

First Hemi.  From 1951-58 Mopar made the first generation Hemi engine, a 392.  This can be distinguished from the second generation by having a rear-mounted distributor the way most other engines are; the 426 has a front-mounted distributor, as all Mopar big blocks do.  The 392 was dropped, the 426 picked up later, and nowadays the 392 is esteemed only by those preferring the 50’s cars and insisting on authenticity.

Second Hemi.  The legendary 426 Hemi:  from 1966-71.  If someone refers to a classic era Hemi, they probably mean this one.  The Hemi was also used in NASCAR at this time; but the NASCAR engine only had one 4 barrel carburetor, while the street hemi had two – “dual quads”.  The street hemi also used mechanical lifters, which made it an especially noisy engine; to quote Muscle Car Review on a Hemi Road Runner, “even blindfolded you know it’s not a Lexus.” 

Street racing the 426 Hemi.  By now many of us may have seen the YouTube video which claims to show a Challenger Hellcat being blown away by a Tesla electric car at a dragstrip.  Of course, the Hellcat owner redlighted, i.e. immediately disqualified and thus no reason to blaze down the track.   Hemis are good engines, but a poor driver is always fair game for competitors with fast cars and better skills. 

            Jim Wangers, famous for promoting Pontiacs in the 1960s, gave some pointers in his book Glory Days.  What works well at the dragstrip might not translate well to the street: the 426 Hemi had a bad reputation for fouling spark plugs at idle and low speed.  Tactic?  Spool around in traffic for awhile before the race begins, so the Hemi driver’s engine is fouled.  Also, break off the race sooner rather than later, claiming victory; do not let the race go on further, as the Hemi WILL catch up with a vengeance.  This is how Royal Pontiac’s 421 4-speed GTO vanquished a Hemi Road Runner. 

NHRA.  The Hemi never died in drag racing.  Current top fuel dragsters run supercharged Hemi engines with nitromethane fuel: 8000 HP, with the supercharger draining off 850 HP by itself.  The cars go from 0-60 in half a second, cover the quarter mile at 4.4 seconds at 335 mph.  That’s fast.

Modern Hemi.  In 2003, after 32 years of dormancy, Mopar reintroduced a hemi V8 engine, in 5.7L displacement.   The new version has an aluminum block, aluminum heads, electronic fuel injection, and electronic ignition.  No more dual quads!   The modern Hemi came in Jeep Grand Cherokee, Ram pickups, the Dodge Durango, the Magnum (an oversexed station wagon) (2005-2008), the Chrysler 300M, the Charger (2006-present) and Challenger.  Like the drag racing versions, the modern version has two spark plugs per cylinder.  They’ve also introduced MDS (Multiple Displacement System), which is a cylinder deactivation system supposed to improve fuel economy without sacrificing power.

SRT8.  This is a 6.1L version of the engine in Chargers and Challengers.  The 370 HP of the 5.7L is bumped up to 425 HP.

Hellcat.  Very recent – and very powerful.  Finally the factory put a supercharger on a Hemi, and the result is 700 HP.  Be careful.

Crate Engines.   Mopar actually sells 426 Hemis (and an improved, larger version, the 528 Hemi) as crate engines.  They’re brand new and have a warranty, but they are very expensive.  Potential uses:

1.   Replacing a valuable original Hemi engine;

2.   Replacing a non-Hemi engine (e.g. 383 or 440) in a non-Hemi car, e.g. Road Runner or Charger which was originally available with a Hemi;

3.   Here’s the fun part:  putting in a small, light car like a Demon or Duster which never came with a Hemi.  Don Yenko was terrified by 427 Novas, imagine how terrified you can get with a Hemi in a Demon.

Engines 101

These are those strange things under the hood of the car – instead of a squirrel on a treadmill (though on some cars it seems that IS what’s pushing the car so damn slowly!). Very few cars have two (Citroen Deux Chevaux) or three (Geo Metro) cylinders, or as many as 16 (very old Cadillacs, with a V16, and the brand new Bugatti, with a W16). Most have 4, 6, 8, 10, or 12. (I won’t even get into rotary engines, as the Mazda RX-7 and RX-8 are the only cars with this type of engine).

Configuration. Either inline ("straight"), V (e.g. V6 or V8), or horizontally opposed ("flat"). The latter is most common with Volkwagen (flat 4 in the Beetle), Subaru, and Porsche (flat six in the 911). VW has introduced a W configuration (two V’s together) and Bugatti uses it with 16 cylinders to put out 1000 horsepower (!). The Sherman tank of WWII had a 30 cylinder engine consisting of 5 banks of inline 6s in a star formation. WWI and WWII fighter planes and bombers often had a radial engine: the cylinders arranged in a circle facing inward.

V8s. These are the kings of performance. Although Chevrolet had a V8 in 1916, the first commonly used and modified was the Ford flathead, debuting in 1932. It wasn’t until 1948 (Cadillac) and 1949 (Oldsmobile) that Ford had any real competition. And in 1955, Chevrolet released its small-block V8, which took the performance laurels away from Ford.

At Ford and Mopar (Chrysler-Dodge-Plymouth) the company made a common family of V8s, though with separate small- and big-block variants; Ford alone had 4 different series, not counting Lincoln and MEL engines which dropped out in the 60s. Until 1982 each GM division – Chevrolet, Pontiac, Oldsmobile, Buick, and Cadillac – made its own V8s, and Chevrolet, Olds and Buick produced small- and big-block variants.

The top models were the Pontiac Ram Air 400s (I, II, III, IV, and V – the RA II is pictured above) and Super Duty 455 V8s, big block Chevy LS6 454, Buick 455 Stage 1, Olds Rocket 455, Ford 428 Cobrajet, the 426 Hemi and 440 Six Pack made by Mopar, and the AMC 401.

Displacement. Take 4/3 of PI, multiply it by the bore (cylinder diameter) squared, then by the stroke (distance the piston goes up and down the cylinder) and finally by the number of cylinders, and you have the displacement, either in cubic inches (CID) or liters (metric).

Nowadays almost all engines are measured in liters, with CID being talked about only with reference to V8s. Funny, we still use quarts and gallons here in the US, but our soft drinks are sold in 2 liter bottles! Most 4 cylinder engines displace around 1.5-2.5 liters, 6 cylinders between 2.8-4.3, and V8s somewhere from 4.0 all the way up to 8.0. The 6.0L V8 in the newer GTO and Corvette, then has three times the diplacement of the average 4 cylinder engine although it only has twice as many cylinders, and the 7.0L (427 CID) V8 in the Corvette Z06 – with 500 HP on tap – has even more.

Quite simply, the larger the displacement, the more power the engine can put out. Artificial means of introducing more air to the cylinders, such as nitrous oxide injection or super- or turbo-charging, can dramatically increase power and make an otherwise smaller engine act and behave with the power of a larger engine.

Displacement and horsepower gradually increased through the 60s, peaked in the early 70s, then took a nosedive when emissions and fuel economy standards were abruptly imposed by the Federal government, like the cops shutting down a raucous party on noise complaints. After scrambling to master emissions controls, developing EFI systems, and improving ignition systems, the car makers were finally able to satisfy Big Brother that they were doing their job to protect the atmosphere and keep fuel economy decent, and then turned to improving performance again. By the early 90s the horsepower figures (and to a lesser extent, displacements) finally returned to – and then quickly exceeded – those of the 60s.

This can get a bit confusing because some displacements are repeated by different companies. Chevy and Ford both make a 302 (5.0L); Chevy, Pontiac, Buick and Olds all make a 350 (5.7L) – and all 4 are completely different and do not interchange (with the new Dodge Hemi also displacing 5.7L); the same holds true with the 4 divisions’ 400 CID V8s, adding that both Ford and Mopar also make 400 CID V8s; Chevy and Ford both make a 427; Ford and Pontiac both make a 428; and Buick, Olds and Pontiac (B-O-P) all make a 455. AMC shared displacements with Chevy (327), Mopar (360), Ford (390), and Buick (401).

The largest was Cadillac, at 500 CID, but now Chevrolet has crate engines displacing 502, 540, and now 572 cubic inches.

HP vs. Torque. Horsepower is a measure of power over time, but gives a misleading impression of a engine’s street performance. Enthusiasts know to focus on torque, the twisting action which gets a car moving from a dead stop. Just as we prefer to think of 0-60 acceleration vs. top speed, torque is likewise a more relevant measure of real-life daily street driving. In this, V8s tend to shine the brightest. Observe that most 4 cylinder engines, even those with turbo, tend to put out as much torque as HP, whereas a V8 will put out 50% more torque than its level of HP.

Fuel Injection. Until the 50s, all cars were carbureted. A carburetor uses airflow through a venturi to "suck" fuel into an airstream, mixing it through various complicated mechanical subsystems (idle, acceleration, part-throttle, main circuit, cold start up/choke, etc.) to satisfy the engine’s various fuel demands. Carburetors are sized by "barrels" – one, two, and four being the most common, and performance V8s sometimes had six (three two barrels aka "Tri-Power" or "Six Pack") or eight ("dual quads" – e.g. the 426 Hemi).

By the 80s, carburetors were being electronically controlled but also phased out. Nowadays the only gas engines with carburetors are on lawn mowers, motorcycles, and other small devices – and vintage muscle cars. The famous Rochester QuadraJet (GM), Carter AFB (Mopar), and Holley (aftermarket) 4-barrel carburetors are still sold in various forms today for enthusiasts with older cars.

In the 50s mechanical fuel injection made its debut. Patterned somewhat off diesel systems, they appeared on Mercedes, Corvettes, and a handful of other cars. It was never popular and most mechanics had no idea how to service them. Many owners switched over to carburetors out of sheer frustration.

Bendix had attempted electronic fuel injection (EFI) in the 50s, only to be hampered by vacuum tube computer technology. They sold the rights to Bosch, which was able to make EFI a practical reality in the late 60s when transistors – and later integrated circuits – vastly improved computers. VW came out with the first EFI in 1968, Mercedes followed soon after in 1972, Cadillac in 1975, and in the early 80s Detroit and Japan began switching over. By the 90s the transition was complete, even on trucks.

Saabs, Volvos, VWs, Audis and Porsches often use a strange form of EFI called CIS (continuous injection system) wherein the injectors - one for each cylinder - are always open, and engine speed is controlled by increasing the fuel pressure. As odd as it sounds, it actually works pretty well.

The earlier form of EFI on US and Japanese cars was throttle body injection (TBI), which has a device of the same size and location as a carburetor, sitting on top of the intake manifold, with an injector or two squirting fuel for all cylinders. It's not particularly fancy or effective, but it's better than a carburetor. TBI is an intermittent system with engine speed changed by increasing or decreasing the pulsewidth of the injectors - how long they stay on spraying fuel before shutting closed again; the shortest pulsewidth at idle, increasing up to wide open throttle (WOT).

The usual EFI system these days - and used on all high performance applications - is port fuel injection, with intermittent injectors, one for each cylinder. Some are sequential port (injector fires for its cylinder on the intake stroke) others are batch fire (injectors fire in pairs), though like CIS, the batch fire system works surprisingly well in practice, with no noticeable difference in performance vs. a sequential port system.

The latest wrinkle in EFI development is cylinder deactivation, whereby certain cylinders are turned off at idle and part throttle and the full engine only turned on for full throttle – saving fuel without a noticeable decrease in power. Cadillac tried that in 1982 with its 8-6-4 engine, but the technology at the time was not good enough to do justice to the concept, which only recently became practical.

OHV vs. OHC. Overhead valve means the camshaft, which opens and closes the valves, is located in the engine block and uses pushrods and rocker arms to open the valves. Overhead cam means the camshaft is located on top of the cylinder head and operates on the valves directly or through followers. The major deal with OHC is that such engines are believed to breathe better – because they usually have four, instead of two, valves per cylinder – and thus offer more top end horsepower. Certainly many of the performance snob journalists at Motor Trend and similar magazines consider OHV to be obsolete. Yet GM and Mopar have proved with their more recent OHV V8s and V10s that OHC is NOT the only way to make substantial power, and OHV is by no means obsolete.

 There’s a lot going on under the hood, but it’s all fairly simple. And there IS a difference between a 4 cylinder and a V8, as I know every time I step on the gas...and fill up at the Sunoco station.