Mopar (Chrysler Corporation/Group and FCA US) have made a huge number of V6 engines from their first in the 1980s to their current Pentastars. Including two Mitsubishi engines, buyers could choose from 2.5, 2.7, 3.0, 3.2, 3.3, 3.5, 3.6, 3.7, 3.8, 3.9, and 4.0 liter powerplants, depending on the year; there were even two different 3.0 engines (one Chrysler, one Mitsubishi) and two different 3.2 liter engines. Nobody had a choice from the whole list, but some buyers could choose between three different V6 engines... which brings up the question of why.
The first V6 used by Chrysler was supplied by Mitsubishi—a compact 3-liter engine, based on smaller Mitsubishi designs. It was essential until Chrysler, which had no truly compact straight-six or V8, could create their own—and stayed on for quite a while after, because the first Chrysler V6 was for trucks only, and the next was production-constrained for a while.
The first V6 was created in a rush, on a low budget, so the Dodge Dakota midsized pickup (itself largely created by International) could have a clear advantage over the Ford Ranger and Chevy S-10. To create it, engineers lopped two cylinders off the 5.2 liter (318 cid) V8, created new cams and such, and presto, a 3.9 liter (239 cid) engine was born.
The head engine designer, Willem Weertman, told me that, aside from speed and development cost, the V8 was a basis for the 3.9 because they could make it in the Mound Road Engine plant, where the 318 was made; the company did not have the money for a new engine line or factory. The engine bay was not large enough for the 318 itself. Chief engine tuner Pete Hagenbuch added that the vibration wasn’t so bad with an automatic, but could be felt clearly with the manual transmissions.
The 3.9 was used from the 1987 Dakota all the way to the 2003 Dakotas. From the start, it provided a bit more horsepower and a lot more torque than the four-cylinder engines, which fit the needs of pickup owners. A “Magnum” upgrade in 1992 dramatically boosted power and helped gas mileage, mainly by switching from to multiple-port fuel injection and optimizing the head design.
The 5.9 liter engine was not based on the Chrysler V8; it was a Cummins straight-six diesel. This chart includes both the Dakota, which started at the AMC 2.5 four-cylinder and topped out with the V6, and the Dodge Ram 1500 through 3500.
With its two-barrel carburetor, the 3.9 produced much more power and torque than the 225 (3.7-liter) slant six; the V6 was rated at 95 hp and 170 lb-ft from 1987 to 1991. It quickly replaced the slant six in pickups and vans, quietly ending many decades of Chrysler straight-six production. The slant six, which stuck around for nearly three decades, was the company’s last straight six.
Two other intermediate upgrades took place with the 1988 model year, when the carburetor was replaced by throttle body injection (which didn’t change power ratings but did cut maintenance and increase drivability); and when, with the 1997 models, the multiple-port system was replaced with a sequential system. The main difference was, in essence, not shooting fuel at closed valves.
* Original estimates, not adjusted, for the Dodge Dakota (RWD) with manual transmission; the Dakota itself grew larger and heavier over time.
** 3.7 liter “Next Generation” V6 was the replacement for the old 3.9.
Another change, in 1994, cut exhaust manifold and pipe sizes, dropping five horsepower but saving money and weight, and allowing engineers to drop EGR on the 1996 trucks. The 1997 upgrades were mainky focused on responsiveness, not power gains.
The 1992 Magnum upgrade was clearly a win-win, dramatically increasing horsepower and fuel economy. Moving to sequential injection raised city mileage by around one mpg, while increasing torque and cutting emissions.
The engine still ran rough, because it was V8-derived; the angle of the cylinder banks was not ideal, and the crank pins had to be split to avoid extremely unequal firing with the V8 crank pins. It was torque-biased engine, which was desirable in trucks but not so much in sedans. Something else was needed for minivans and cars, and it was on the way, but first, let’s talk about the truck engine that replaced the 3.9. (For more on the 3.9, see Allpar.)
The 3.7 liter “PowerTech” engine had been in development at AMC when Chrysler bought the company; the 4.7 V8 would replace the 4.0 liter straight-six long used by Jeeps, while the 3.7 would replace the 2.5 liter four-cylinder. The V8 and V6 were closely related—just as the old straight-six and four were closely related. The older engines had been at the top of their class when new, and indeed in middle age; but much time had elapsed, and the 3.7 and 4.7 had two more cylinders (good for marketing), were cheaper to make, and passed emissions more readily. Neither engine was meant for sedans, and they were restricted to Jeeps and pickups.
The 3.7 was first used on the Jeep Liberty (the next-generation Cherokee), but quickly moved over to the Dodge Ram and, a year later, to the Dakota. Its 210 horsepower was far above the old 3.9’s output (torque was slightly higher as well), and fuel economy was about the same, at least in the Dakota; but the engine was far smoother and quieter, and had fewer emissions. The PowerTech had a 90° V, with a cast iron block, compacted graphite bedplate, and aluminum heads; each row of cylinders was driven by its own single, chain-driven cam. A single counter-rotating, gear-driven balance shaft ran between the banks. While many new engines had four valves per cylinder, the 3.7 had just two, to provide better low-end torque at the cost of performance higher revs.
Like the 2.0 Neon engine, the 3.7 used a lightweight composite intake manifold; that provided a much smoother air path than cast setups, without machining, even with individually tuned runners for each cylinder.
A few years after launch, the 3.7 gained a number of upgrades to increase its economy and idle quality; the compression was raise to 9.7:1, and new parts included the cam, lash adjusters, and rings. It was made next to the 4.7 V8 at the Mack Avenue plant, which had been home to the 3.9 V6.
The 3.7 was a good engine overall, but eventually fell prey to the company’s desire to consolidate engine families. It was the last V6 created by Chrysler, DaimlerChrysler, or Fiat Chrysler just for trucks.
When the front-drive K-car launched, Chrysler finally had its own new four-cylinder to power it; but it had nothing for larger cars which needed more than the 86-110 horsepower 2.2 could produce. Creating a longer-stroke version (the 2.5) wasn’t enough; even the 146-horsepower turbocharged engines of 1984 and beyond were insufficient. Customers were now demanding V6 engines. A 3-liter Mitsubishi V6 filled in the gap, just as a Volkswagen and Peugeot four-cylinder had gotten Chrysler through the years when it didn't have its own four-cylinder.
The 3.3, first used in the 1990 model year, was the first truly new V-engine design for Chrysler since the B-type V8s had come out decades earlier. Though overhead cams were already seen as the norm for small cars, Chrysler leaders chose to keep pushrods for their low cost and simplicity. The end result was a little more powerful than the 3.0 liter Mitsubishi engine, with about the same efficiency. Like the company’s V8s, it had overhead valves (two per cylinder), to deliver torque early in the rpm range for minivans as well as midsized and larger cars.
But don’t count Chrysler engineers out; they had the first use of “beehive” valves in any production car, and boasted a distibutorless ignition system from day one, so nobody needed to change rotors or distributor caps. The block was cast iron, but the heads were aluminum; fuel injection was a multiple-port design. The ports were fairly large and symmetrical, with intake and exhaust alternating on the head; there were two squish areas per cylinder, taking up a third of the bore area, when the engine was first launched. Bore was 93 mm, stroke was 81 mm, teh displacement was 201.5 cubic inches, or 3301 cc. Injectors were placed in the intake manifold runners, upstream from the intake ports, at least for now.
The fuel injection system used a manifold pressure sensor rather than an airflow sensor; the computer tried to figure out the airflow from the MAP sensor. One engineer on the project told me that this was because Chrysler was cheap; another said it was because there was no good mass airflow sensor available yet. Regardless, it meant that each new application required a great deal of tuning.
The first production 3.3 liter V6 engine was made on May 1, 1989, in Trenton, Michigan; it was used on the company’s priciest cars and its larger, more expensive minivans. This new 3.3, small as it was, easily produced more horspower than the big 318 cubic inch V8, and it wasn’t anywhere near its peak (then again, neither was the 318); and it had a broad torque curve, with more than 90% of peak torque available from 1,600 through 4,400 rpm, with at least 95% on tap from 2,400 to 4,000 rpm. That made it quite satisfactory for the minivans; so did up to 15% better acceleration (in the first five seconds from a standing start) than the Mitsubishi 3.0.
* 147 hp, 183 lb-ft in passenger cars due to air path constrictions.
Engineers found an extra 12 horsepower (and 14 lb-ft of torque) for the 1994 model year by changing the intake plenum; two years later, they sacrificed some of those extra horses in favor of a wider torque curve, dropping four horsepower but gaining 9 pound-feet of torque, and bringing peak torque at lower revs. 1994 was also the first year for the compressed natural gas version of the 3.3 engine, for fleet sales.
Major changes for 2001 brought a variable intake system (with two effective tube lengths) and new heads, with higher compression and revised tuning; horsepower shot up to 180, where it would stay, while torque rose again. Finally, in 2005, the measurement process was changed across the industry to an SAE standard; some companies saw horsepower figures plummet, but the 3.3, at least, stayed right where it was.
The 3.3 was good, but as cars were getting bigger and heavier again, something more was needed. They couldn’t drop a V8 into the New Yorker or the minivans, but they could increase the stroke of the 3.3 without much expense; thus was born the 3.8 liter engine, initially used in the Chrysler Imperial, Chrysler New Yorker, and Dodge Dynasty. In its first year, the 3.8 had the same horsepower but 15% more torque—and it was felt in lower revs. That came at the expense of some high-rev power, so the 3.8 did not feel as exciting as the 3.3 in spirited driving, but did a better job of getting heavy vehicles moving from a start or up a steep hill. It would eventually end up powering, to the shock of many Jeepers, the Wrangler.
Chrysler needed much more power as time went on, and head of Engineering Francois Castaing, who had come in with the AMC purchase, wanted Chrysler to be more technologically up-to-date. He envisioned an engine with four valves per cylinder and overhead cams, with lower displacement than the 3.8 but much more power. In the meantime, tuning chief Pete Hagenbuch had engineers produce a turbocharged 3.3 liter V6 (tested by Marc Rozman to 210 horsepower). Castaing flat-out said “no,” and while we don’t know why, two reasons come instantly to mind. First, the increasingly penny-wise Lee Iacocca was unlikely to allow the 3.5 to go forward if they already had a 210-horse V6—making the same power as the 3.5 was supposed to. Second, customers had not reacted well to the old four-cylinder turbos, and might not like a V6 turbo any more.
Work on the 3.5 started in 1989, with the intention of having it ready for the LH cars which were due in just 40 months—a tall order for an engine program. The 3.5 was loosely based on the 3.3 to save time and money, but it had more modern heads and timing—an overhead cam and four valves per cylinder, by then standard on most passenger-car engines. The main benchmark was Honda/Acura’s 3.2 liter V6. Gordon Rinschler, the engineer in charge of the program, set it up with a deep-skirt cast iron block, using a forged steel crank to handle the power and 10.4:1 compression ratio. Bottom-feed fuel injectors were part of the design, to make the engine small enough to fit into the LH cars; it was the first high-volume car engine to use bottom-feed injectors. Crossbolts on two of the main bearing caps cut noise, while adding strength.
Like the 3.3, there was just one cam per head; but John Hurst designed the setup wtih dual valve rocker arm shafts so they could get four valves per cylinder. If the timing belt broke, owners need have no fear: the engine was non-interference (free wheeling), so the pistons would not hit the valves.
Spark plugs were in the center of the combustion chamber, a semi-Hemi style, with 35mm intake valves and 29mm exhaust valves;
By the time the engineers were finished, even though they had started with the pedestrian 3.3, the only part the two had in common was the oil pan; they did share bore spacing and main journal and crank pin diameters. Unlike the 3.3 and 3.8, the 3.5 required midgrade (89 octane) fuel, at least in its first incarnation; every version had sequential multiple port fuel injection and distributorless ignition (first with coil packs, then with coil-on-plug).
The first version produced an impressive-for-1993 214 horsepower and 221 pound-feet of torque, beating most other engines in the class above its own; the next iteration brought it to 250 horsepower, which is roughly where it stayed through the end of its life. Mechanical noise was lower than any other engine ever measured by Chrysler. Howard B. Padgham, powertrain engineer (with 28 years under his belt, from the 360 V8 police package to the 2.2 turbo) wrote that it was truly a “premium engine” and “bullet proof.”
Chrysler was on a huge reinvention kick during the 1990s, eager to push forward. Francois Castaing (and some of the other engineers) were never very happy with the old 3.3/3.8 line, with their pushrods and such; they wanted more power and better economy, and a smaller base engine which could fit in more cars. For the second generation LH large cars, therefore, there was not just an upgraded, 250-horsepower 3.5 for the high end 300M and LHS; the lesser 1998 LH cars were fitted with a high-tech 2.7 or 3.2 liter V6. Both of these used twin overhead cams, replacing the clever single-cam version.
Chrysler now had an almost absurd panoply of V6 engines—the new 2.7 and 3.2; the revised 3.5; the truck 3.7; the standby 3.3 and 3.8, still serving in minivans, where torque was more important than horsepower; and, still, a Mitsubishi engine. The latter was a new 2.5 liter version of the old 3.0, making roughly the same power but with better mileage. They chose among the engines based mainly on cost and marketing (the 3.5 never made minivan duty because some where afraid it would confuse customers, since it had more power than the 3.8). In addition, Mitsubishi-made vehicles naturally used Mitsubishi engines, while most, but not all, the Chrysler-made cars used Chrysler engines. Confusing matters, Chrysler’s midsized cars used the Mitsubishi 2.5 liter V6 until the 2.7 liter engine was ready, partly because it fit under the low hood; the 3.3 was too tall for these cars. What’s more, according to Ed Poplawski, as Chrysler started phasing them out, Mitsubishi wanted guarantees that the company would still buy around 300,000 per year to keep their factories profitable. Finally, the contracts ran out and the rebadged coupes were dropped, and the Mitsubishi engines disappeared completely from Chrysler history.
The 2.7 liter V6 was, in the words of technician Walt McCrystal, “an industry benchmark engine that Chrysler was committed to getting right.” The company published one of their rare power-and-torque charts to compare the old 3.3 with the new, more powerful 2.7; with its short stroke, the 2.7 was also engineered to rev much higher, so it was just getting started as the 3.3 had to stop at 5,200 rpm.
Compared to its larger predecessor, the 2.7 had nearly 40 more horsepower, and a tad (7 lb-ft) more torque. The 3.3 was certainly more torquey in the low revs, below 3,400 rpm or so, but the 2.7 would keep running past the 3.3’s redline. That made the 2.7 ideal for cars, and the 3.3 better for the big, heavy minivans (where it stayed—and the 2.7 never showed up).
|1998 Chrysler LH||2.7||200||Regular||$21,000|
|1997 Cadillac Catera||3.0||200||Premium||$34,750|
|1993-97 Chrysler LH||3.5||214||Mid-Grade||$24,270|
|1998 Chrysler LH||3.2||220||Regular||$24,000|
|1996 Taurus SHO||3.4||235||Premium||$28,250|
|1998 Chrysler 300M||3.5||250||Mid-Grade||$30,000|
With the 2.7, aluminum blocks (cast with a semi-permanent mold) finally arrived in the Chrysler V6 world; iron cylinder liners assured longevity, without the expense of hardening treatments.
The 2.7 was every bit as competitive as Francois Castaing had hoped. It had more horsepower than the Acura 25TL or Nissan Maxima; while the 3.2 beat the Taurus, Cadillac Catera, and the prior Chrysler 3.5.
The new 1998 version of the 3.5 liter V6 was far higher in power than any of these other engines, with 250 horses. What's more, the Acura, Catera, and Diamante all required premium (91 or 93 octane) fuel; the 3.5 took midgrade (89 octane), and the 2.7 took regular (87 octane).
Oil sludging on early engines gave the 2.7 a bad name, but these early problems were largely resolved after a couple of years. Walt wrote, “I would have no qualms against owning a 2.7 with the improved hardware. The head gaskets and bottom-ends held up well. We had coolant-heated PCV systems on Canadian and cold-climate cars to prevent PCV icing. The water pump went through a number of revisions, including a weep hole to dump coolant outside the engine, instead of into it. By 2003, it was a fine engine, as it was intended to be.” Ed Poplawski recalled, “The production engine people busted their butts to fix all the problems.”
The 3.2 liter engine didn’t make much sense, with just 20 hp more than the 2.7 and 30 hp less than the 3.5, and was eventually dropped. The 3.3 and 3.8 were both heavily revised, providing dramatic power gains, so that all the engines were competitive—though, since Chrysler was reluctant to add the 3.5 to minivans, those vehicles were not quite as quick as their competitors.
Finally, in the waning years of the Daimler occupation, Chrysler created a larger-displacement of the 3.5 liter engine to catch up to more powerful Honda and Toyota minivan engines; the new 4-liter V6, in its second year paired with a six-speed automatic, earned Chrysler the “most economical minivan” title. This engine was first optional, with the 3.3 and 3.8 below it; then it was made standard, and the 3.3 lost its place—leaving production in 2010, five million engines after the first 3.3. The 3.8 liter engine was kept going for another year, because it had found a new home under the hood of the Jeep Wrangler.
The 4-liter (241 cid) V6 was a good engine, overall; it was a stroked 3.5 liter V6, giving more torque to an alraedy strong, efficient powerplant. It generated around 255 hosrepower and 262-275 pound-feet of torque, with a broader torque curve than the 3.5 as befitted a minivan engine (minivans weighed over two tons). Other changes, besides the stroke, cut vibration at the mounts and reduced crankshaft torsionals. To make the change, the engine had new main bearing diameters, lower-mass piston and rod assemblies, a new block and oil pan structure, less bearing clearance, and an equal-length dual exhaust. It still had the clever single-cam, 24-valve design, with hydraulic lifters and rollower followers, and a timing belt.
|Bore x stroke||3.78 x 3.19||3.78 x 3.58|
|Power||250 hp @ 6400||253 hp @ 5,800|
|Torque||250 lb-ft @ 3900||262 lb.-ft. @ 4,100|
|Fuel||87 octane||89 octane|
The 4-liter was surprisingly efficient pulling the minivan, turning in better mileage than the 3.3 or 3.8 had; some of that was likely due to having enough power and torque that drivers weren’t really pushing it hard, and part was being hooked up to a more efficient six-speed automatic. (Economy in the first year was relatively poor, because gearing was too aggressive; drivers had to go easy on the throttle at stop signs and traffic lights to avoid spinning the front tires.)
The 4.0 was a good engine, but Chrysler could, and did, do better. It started working on the “Phoenix Engine” under Daimler; continued under Cerberus, despite an aborted attempt by executives to kill the project and use Nissan engines instead; and ended up arriving under Fiat. Renamed to Pentastar V6, it was designed to replace every other V6 engine, and it did—with far fewer variations than before; there were just a few basic Pentastars, including one for the Wrangler. The engine was more flexible than the past models. Many versions of it were planned, including a twin-turbo and direct injection setup, but just three were made: a 3.0 for Europe, a 3.2 for the Jeep Cherokee, and the 3.6 for everything else, including plugin hybrid minivans.
The Pentastar was, aside from the lack of direct injection, state of the art in technology. It won a spot on Ward’s Ten Best Engines list for several years, providing considerably more power (up to 305 hp) and torque than any past Chrysler six, and doing so with better fuel economy, less noise, and easier maintenance.
The basic design was adapted by Maserati for the Quattroporte and Ghibli, pushing out 404 horsepower. While it was designed to be supercharged, though, Chrysler itself never used forced induction; the performance turned out to be disappointing (as one can guess from the twin-turbo Maserati version only having 100 horsepower more than the inexpensive Dodge Challenger version). A new straight-six, based on the corporate 2-liter, was reportedly in the works from around 2017.
This engine is still the only gasoline V6 used by Chrysler, Dodge, Jeep, and Ram; and is made in plug-in and mild hybrid form.
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