Classic Engine: Jeep's Tornado Straight-Six

J engine SB1-1L II

The two faces of Tornado. The engine is shown here is from the J-Series Wagoneer or truck configuration with the standard paper air filter and a generator fitted.

 

Story by Jim Allen

Jeep's overhead-cam six, famously called the Tornado, was one of the first mass-produced overhead-cam engines built in the United States after World War II. As whiz-bang as that sounds, the engine actually has very humble roots.

Willys Motor engineer A.C. Sampietro worked out a simple plan: In 1960 he took the existing lower-end architecture from the Kaiser Supersonic/Continental Red Seal 226-cubic-inch L-head (or flathead) six and began designing a new overhead-cam engine around it.

The 226 engine had been incorporated into the Jeep lineup as the Super Hurricane in 1954, and it had an enviable reliability record. It made 105 horsepower, and when it was introduced it was a welcome addition to the horsepower-starved Jeep engine lineup. Like all flatheads, it had breathing and cooling difficulties, but the Continental-sourced engine became almost legendary for durability in Jeeps and the many other applications in which it served until 1973.

Sampietro's engine came to life in February 1961, when the prototypes were tested. By May, the engine had passed its 100-hour full-power certification tests, and the first production engines came off the line in April 1962. The 230-cubic-inch engine was dubbed Tornado, and in a strange twist of fate, the first Jeeps to have them were not the new Gladiator J-Series pickups or Wagoneer SUVs but the old Willys wagons and pickups they were designed to replace.

Although the basic architecture of the Tornado came from the 226, the blocks were considerably different, not the least of which was the lack of cast-in ports and valves used on a flathead engine and the lack of a camshaft. It was also given full-flow oil filtration, which the L226 did not have. The Tornado had the same stroke as the Super Hurricane and only a slightly larger bore. The crankshaft was more or less the same one used in the 226, but it was strengthened by Tufftriding. This was one of the first times the hardening process was used by an OEM engine builder.


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Here is the power and torque graph for the engine as designed. Note the torque line. Jeep rated the engine at 210 pounds-feet at 1,750 rpm. This curve shows it achieving 210 pounds-feet before 1,000 rpm and holding above that to about 3,700. Now that's a torque curve!

 

The overhead-cam system was unique because one cam lobe opened the intake and exhaust valves on each cylinder. This made for a unique camshaft profile, but it allowed the intake and exhaust valves to be precisely aligned in the spherical (don't call it a Hemi) combustion chamber for optimal breathing in the crossflow head. The valves were large for the displacement -- 1.88-inch intakes and 1.62-inch exhausts. A good number of parts on the engine were aluminum, including the front cover, water pump, valve cover and intake manifold. The engine weighed 575 pounds, some 40 pounds lighter than the 226 flathead.

Despite the Tornado's undersquare configuration -- a 3.34-inch bore and 4.48-inch stroke - it was a bit of a revver at heart. In fact, the engine's 140 hp at 4,000 rpm and 210 pounds-feet of torque at 1,750 rpm was underrated. When Sampietro wrote about the Tornado in November 1962, dyno testing of the two-barrel engine was yielding 155 hp and 230 pounds-feet of torque (gross) as well as BSFC (brake specific fuel consumption) below 0.45 pounds/hp/hour from 1,200 rpm all the way to 4,000 rpm. Sampietro also designed a 153-cubic-inch four-cylinder version of the Tornado that was built overseas.

On the ugly side were the problems with oil consumption and leaking issues seen mostly in the engine's early days. They were relatively easy to fix, both under warranty and in production. Because of the oil consumption and owners not checking the oil until it was too late, a relatively high number of engine failures were reported. Word spread, and even though the issues were largely solved by the next model year, the bad rap followed, and it has stuck to this day. The engine's relative complexity compared with the standard American engine of the day was also an issue for the less well-trained mechanics.

The Tornado didn't die when it was dropped from the lineup in 1965. Its design and tooling was transferred to Industries Kaiser Argentina (or IKA), which also had ties with AMC and Renault. The engine was used in the Torino, a Rambler American clone. With only a few upgrades, the engine was sold at a standard 155-hp level, and an Interceptor version with three side-draft DCOE Weber two-barrels made 176 hp. An economy 181-cubic-inch version (3.34-inch bore and 3.44-inch stroke) was built as well. In 1973, the lower end was upgraded to seven-main configuration, and by the time the engine was discontinued in 1982, there were 215-hp versions floating around. It was used extensively in racing, and it even garnered a few international victories.

The Tornado also appeared in uniform. The low-compression one-barrel version was fitted to the 1967-69 Gladiator- based M-715 military tactical truck. It was mostly the same, except for the waterproofed components and the 24-volt shielded electricals. Another difference was the elimination of the front engine mounting plate, one of the major sources for oil leaks on the civilian engine. The block had bosses, and the motor mounts were situated there to suit the locations used for the civilian 232ci AMC six.

 

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The lower end of the Tornado was unremarkable. Four-main configuration, long stroke, undersquare. The upper end was remarkable for the day, with a crossflow head and overhead cam. The high-compression (8.5:1) engines had a domed piston while the low-compression engines used flat-tops. The spherical combustion chamber allowed for good airflow. If this head were fitted to an oversquare seven-main engine, it would have been a real barn burner. In its long-stroke undersquare configuration, it had good torque with a hint of "peakyness."

 

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The 226ci L-head, whose basic lower end dimensions became the core DNA for the Tornado. It could be argued that a better engine could have been chosen for this adaptation. Engineer A.C. Sampietro's primary mandate was to develop the engine on a tight budget. This engine was originally designed by Continental Motors, a subsidiary of Kaiser Industries.

 

Comments

awsome!

the jeep/amc and whoever else put into them in all the buy ups etc. etc. 4.2 and 4.0 are two of the most durable motors ever built period

It's too bad that budget innovation had to stop. AMC seemed content to buy up the other manufacturers disposable components instead of reinventing their own which made for some pretty dismal products. R.I.P. my '81 Spirit

Given Kaiser-Jeep's limited finances, this was probably the best they could come up with. Unfortunately, the Gladiator didn't get a decent engine until the late 60's, when the Buick 350 V-8 was used. After AMC bought Jeep from Kaiser the Buick was replaced by the equally fine AMC V-8's.

Speaking of interesting 6 cylinders, how about the GMC V-6?

I do remember this engine from my U.S.Army days, and it was a fairly durable engine, but it did leak and use a lot of oil, in the Army, there is no tolerance for any oil leaks, and the trucks (Gladiators) were in the motorpool shop most of the time, but when in good running condition, they were very good runners in there trucks, witch were rated for or as a 5/4 ton with a special pick-up bed on them, very heavy duty step side type. I also remember the engine that American Motors used to replace it, it was the 3.8-4.2 6cyl. engine, that was used troughout the AMC-Jeep line, as well as in the Internation Scout, they were bulit-proof, and ran a very long time if maintaned, I had one in a CJ5 that had over 100K when I traided it in for a 73 Scout II brand new, and when I got ride of it (rust issues) it had 201K on it! with NO problems with it! at all, just oil and filter changes and points and plugs, and coolant changes, it was with a 3spd Chrysler Torque Flyt trany, that also never failed me, only had to change the trany fluid 3 times...That was a good running 4X4! but ir literaly fell apart from rust!

@bigbob the 4.3gm v6 is a great motor too you are right imo one of most durable engines you cant beat some of those old motors gms 305,350 and 4.3v6 old ford 5.0 and slant six chryslers 318/360 and slant six (225?) those motors towards the end of carbs and start of fuel injection imo are the best combination of modern and old technology they all make enough power and will outlast most of todays stuff and be alot cheaper and easier to fix

moparman he is talking about the 305 V6, i think. it was used in older gmc's. like a truck equivilant to a F-450 with a 305 c.i. V6, not 4.3 V6 or 305 c.i. V8, but GMC's 305 c.i. V6.

yeah the old gmc v6 motors 305v6 351v6 379v6 401v6 432v6 478v6 478m v6 and the monster 702 v12 http://en.wikipedia.org/wiki/GMC_V6_engine use for just bout everything from pickup trucks to gm dump trucks buses and generators

oh yea, those big block V-6 GMC engines were torque monsters, that also ran forever! my family had a trucking co. in the 60's-70's we had a fleet of those things, in GMC 7500, 9500 6wheel refer box trucks, ran well over 200K, b4 rebuild! and then ran more an more, still ran after we upgraded to diesels! they were governed to about 65mph with granny low 6spd HD truck trannys, but with a full load 28,000GVW-33,000GVW, they had plenty of power, never had to down-shift on big hills, but only got about 4-6mpg! MT not mush better! the 7500 had the 351's and the 9500 had the 401's, and one of the 9500 had a 478! 4bl carb and 7 spd! governed at 75 mph, and got maybe 2-3mpg! MT, but boy did that truck have power to spare! I could remember a load of canned goods (very heavy stuff) illeagal of naturaly, I was about 39,000GVW !!! and never had to down-shift anywhere!, when we got rid of that truck, my cousin bought it just for the engine, and put it in his 67 GMC 4X4 short bed P/U! man what a mudder, sand monster that was! those engines never even used much oil, and they held 8, 10, and 12 qts! the 478 even had 2 oil filters, and coolant filter also! they all had oil bath air filters, they were also very heavy engines, my cousin had a 306 V-6 in the truck he had originaly.

The GMC V-6s were classics just as this Jeep Tornado engine. Also the Continental staight 6s. With proper care these engines would outlast many of todays engines. These engines had lots of torque. Mark thanks again for another great article. Brings back memories.

More stories like this please.

another great straight 6 was called the Black diamond I think it was in the 50's International trucks.

Thanks for the great info about the Tornado engine. I had a '64 Jeep station wagon (last year of the old body -- the one-piece windshield version). It had the Tornado 230 and I was really impressed that a Jeep of that vintage had such a 'modern' aluminum-clad overhead-cam engine especially when I was so used to flat-head and L-head engines of that era. I was doubly impressed with the torque. The unassuming vehicle could pass without downshifting. It was almost to the point of ridiculous how free-breathing and gutsy the truck was since it was not a high-performance vehicle. It seemed unsafe over 50 miles per hour. Definitely one of my favorite vehicles.

I purchased a 1962 Jeep truck powered by the 230 Tornado engine in April 2013. I know the history of the vehicle that has 82,000 miles on it. It had been sitting for 20 years bought it in April. After installing new points/condenser and an oil change it was running. I have put about 400 miles on it, its running strong and yes it has several oil leaks. I have a lot of work to do yet including a transmission rebuild but for now the engine runs like a fine watch. Phil

I have this same truck and engine. I need a vacuum advance rebuild kit or a replacement distributor for it. I understand there is an electronic distributor for it, also.
Can u tell me some contacts for these items.
I look forward to hearing from you soon.
Rick

There`s a guy in the Baltimore area who built a custom
stainless-steel-looking flatbed pickup with the double GMC
truck V-6 set-up for a total of 702 cubic inches! That would
be two times the 351 V-6 in one tandem industrial block!
This long V-12 sits backwards on the flatbed with some
kinda Olds Toronado transaxle that sends the power
backwards to a quick-change differential. The tandem
V-6s look pretty stock as there can`t be much in the way
of speed equipment available for this engine.
You might see this thing if you attend the Mobtown
Greaseball any September, the craziest rat-rod show ever!



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