I discovered the following highly detailed article in the Google cache file for:- sadly despite considerable effort I have been unable to connect to this site, which may now be discontinued, so I hope the unnamed author* does not mind me reproducing his excellent piece again here.

*Update 2012 - the Unknown author is in fact Bill Todd (
Army Otter flying crew chief in Alaska with the 12th Aviation Company from Aug '61 to Oct '63.) who has very kindly confirmed permission to use the article and notes that the information is taken from files provided to him by Pratt & Witney. Many thanks Bill.

This is a page on the development of the R-1340 series engines. The data is from the P&W Archives section and I condensed it somewhat where necessary. I was sent some conflicting data from P&W, and am clarifying it. One document claims engine started development in 1925 and first engine built and tested in December, 1925. This data below states it was built in 1926. By adding the letter "G" to designation, any 1340 engine becomes reduction drive instead of direct drive, as in S3H1G. You may also see it expressed as S3H1-G too.


The first engine was built in April 1926. The engine had cast pistons, with 5.25:1 compression ratio; 4 rings, consisting of one oil scraper and 3 compression. The blower and rear section were of the ten-vane type. The crankshaft was a small pin, unhardened type. Cylinder and barrels were coarse finned. The cam was fine toothed and hi-lift. Rockers were small with bearings in the cylinder head. Push rod covers were telescopic, & the oil screen was inside out. Oil pump was standard single stage. Master rod bearings were babbit. Cam oiler bracket was of single piece construction. Timing was variable. Valve springs were of light construction. Knuckle pins were threaded. Cylinder hold down studs were 3/8". Crankcase front section was cast, and the engine had a small oil sump. No clutch on engines having 5:1 blower ratios; 4 surface clutch on 7:1 engines.

R-1340-A1:  ("Long nose" engine.)

6" longer than the "A" and required a new crankcase front section, crankshaft, etc. Limited quantity built, and they were obsolete.

R-1340-A2:  (Experimental)

This engine had an ell head. When first designed, the head had a one-piece cast design, and the barrel was shrunk in. Later, this design was changed to two-piece design and the upper portion bolted on. The ell head eliminated the use of push rods and rockers. In their place, a special valve tappet arrangement was used. This engine did not go beyond the single cylinder stage.

R-1340-A3:  (Low head)

This engine was of small diameter having a low head which necessitated  shortening the master rod, link rod,  length of valve guides, pistons, etc. Superceded by R-1340-F series, below.


This engine was equipped with a four surface clutch which required a new rear crankshaft. Had a larger crankpin diameter than the "A." Floating 7:1 blower gears were used in the last of these engines. Straight air scoop, hot spot with small "tees" and tubing were first used on this model. Nose section forged instead of cast. Blower and rear case were 10-vaned like the "A."


Plates were added to the clutch, making it a six surface unit. Cylinder barrels were fine finned. Cylinder heads were new, having vertical fins. Main cases were strengthened and a new cam with a forged pinion, external hydro-adjustable propeller mechanism, larger sump, new oil suction pipe, lead-bronze master rod bearing, rocker bearings in rocker, lengthened blower section, were improvements. Also a 7B carburetor was used.


Cowl bosses were added to the cylinder heads. Master rod was strengthened. One-piece lock type master rod bearings, small head diameter knuckle pins, new cam rim, hard pin crankshaft, larger oil drain pipe, angular grease fittings, seven-vaned rear section and oil regulator made optional with hot spot were improvements in this engine.


This engine was equipped with the Hasbrouck fuel injection system. This eliminated the carburetor. Only one or two of these engines were built. This type was superceded by the R-1340-D2, below.


This engine had a vaneless diffuser, eight surface clutch, main case reinforced for reduction gear, crankshaft with case hardened crankpin, oil regulator as standard. Approximately 50% of these engines had a seven-vaned rear section and blower to match, self-oiling adjusting screws, coarse tooth cam with improved profiles and a NA-Y8A or 8C carburetor was used.


These engines had a split pin crankshaft, spring type clutch, oil tight pushrod covers, larger rockers, vertical or side vacuum pump drives, bronze rear cones, tapered compression rings, two-piece intermediate gear for ratios higher than 10:1, dynamically balanced impellers, large tees and clamps for hotspot, pressure type deflectors, oil pump with integral bypass, flanged oil connection, standpipe in crankshaft, heavier valve springs, removable tappets, heavier magneto drive shaft, and a NA-Y8E or 8F self-priming carburetor. 2100 RPM used a #53 jet in crankshaft, and 2200 RPM used #60.


These engines are equipped with a Marvel Fuel charger and have a new blower and rear section. This eliminates the carburetor. The engine is like the D1 otherwise.


This engine with the exception of the 14:1 blower gears is like the D1.


These engines were of 50" diameter with fine finned cylinder heads, main case of XA-51ST aluminum, seven spring blower clutch, corrugated inlet valve locks, sodium filled TPA exhaust valves, short master rod, short articulated rods, pistons, and pushrods.


This engine is also 50" in diameter like the F. It has a stronger master rod, link rods, stronger case, an improved supercharger drive known as "the outboard type," exhaust valve with stellite faces, new design stronger and stiffer crankshaft, larger and stronger main bearings, improved supercharger spring drive (clutch,) improved reduction gear, automatic valve gear lubrication, automatic oil temperature control, self-priming carburetor, new fine fin cylinder heads, new cam mounting and drive, pressure cooling baffles, propeller control on rear of sump, new compact hot spot, new design Pratt & Whitney radio shielding. This engine could have 3:2 or 4:3 reduction gearing.


This engine was similar to the H except the diameter is like the D1 and had an outboard blower drive, NA-Y9B self-priming carburetor, flat hotspot, Cobalt chrome rotor magnetos, seven vaned rear section, split pin crankshaft, fine finned #34 alloy heads, forged cases, shelf type cam, internal hydro-control valve on rear of oil sump, large rockers, oil tight push rod covers, bronze rear cones, outside-in oil screen, exhaust ports with shrunk in liners, two breathers in blower without valves, flanged oil connections, pressure feed to rockers, seven-spring clutch with buttons, Simms magneto couplings, stellite exhaust valves and seats, heavy duty springs and washers, 3:2 steel cage reduction gear with fixed center pinions, short spline extended prop shaft, rubber o-rings under cylinder bases, and palnuts on outside of engine.


These engines of which there were but few built were exactly like the H1, except that a steel cage blower drive was used instead of the outboard blower drive.


This engine has all the features of the H, but uses fuel injection instead of carburetion.

P&W R-1340's had several configuration numbers as part of it's model number. The typical current engine's are configured, and are listed in the parts and maintenance manuals as:




R-1340-S3H1-G (geared)


The P&W historical file that describes the R-1340 in US Navy application is summarized below:*








Original rating of Engine. 375 was easily bumped to 400 HP in late engs.




Covered by Reports 1 & 2. From early series. 5:1 & 7:1 blower ratios




Carried rating to 6000 feet. (Probably with 7:1 blower?) See Report #6




Improved blower clutch, cylinder construction. See Report # 8




6:1 pistons, vaneless type diffuser. to 7500 feet. See Report #16




Compression ratio 6:1. Higher blower ratio. Rated at 5000 feet. Few mfg.




"D-1" type with 12:1. blower rated at 9k feet. USAAC, not USN




"D-1" type with 14:1 blower rated at 11k feet. Limit of single stage blower




Reduced diameter engine. Rated at 10,500 feet.  See Report #48




Rated at sea level. Not able to hold HP with current pistons & blower




Two special engines. Derated from above 750 HP engines




Engine as known today. P&W data is incomplete, and stops here

*NOTE: I've asked P&W for copies of the various reports, and will post them when available.

Development of the engine under a contract # 31111 was carried out for three engines of the "F-series" and P&W delivered three. The second engine was delivered to the NAF (Naval Aircraft Factory) for calibration. It was destroyed in a fire there. Another engine was delivered to Boeing and was installed in the XF7-B aircraft. The documentation doesn't mention where the first engine was shipped.

The data from the Archives Section becomes a bit hazy from the "F series" to the "H-series."  It appears that the USN was interested in developing a lot of power out of these engines. P&W had successfully demonstrated that the engines were capable of 500-550 HP very reliably. The high output 750 & 720 HP engines are not referenced well, but the documentation shows that two engines were shipped to the USN under Contract 31112.

It's interesting to note that one variation of the engine (R-1340-E) was run with a 14:1 blower ratio, developing 500 HP at 11,000 feet! This is the apparent limit of single stage compression, and any further increases would become marginal.  A two-speed arrangement could have been done, but this also leads to mandatory intercooling if the ratio's are really high, and that adds weight, and is counter to P&W's basic philosophy in their engines was simplicity and reliability. In fact, their motto is: "Reliable Engines." They certainly had a reliable engine in the R-1340 and it's little brother, the R-985. The bigger engines were also very reliable, and widely used. In my book I explain that some installations in a particular airframe made it a "winner." An example was the Douglas A-26. The 2800's were absolutely sweet in those wonderful birds, and I actually enjoyed working on them!

(Note: The bigger engines became more complex because of more rotating machinery. The 4360's I worked on in C-119's & B-50's had to have a hand-held circular computer to set valves, time, etc. They were complex only because of the amounts of machinery. They were basically four each, 7 cylinder engines on a single crankshaft.)

It was far simpler to go to the next bigger engine, the "Hornet A series" at 1690 cubic inches and 525 basic horsepower, or step up again to the "Hornet B series" at 1860 cubic inches and 575 basic horsepower. The R-1860 Hornet B series topped out at 875 HP. This was very comparable to the Wright R-1820 engine, P&W's biggest competitor. These engines were developed right alongside the R-1340, and as did the 1340, their horsepower creeped upwards too! 

Neither the R-1690 or the R-1860 engines was as popular as the R-1340, and were sparsely populated on a few military aircraft. I have reference to R-1860's usage on USA/USAAC/USAAF aircraft at 14 installations. The R-1690 was used in 22 installations. Gathering data from the P&W site, the R-1340 was built in a quantity nearly 35,000 engines, but the R-1690 was only built in a limited amount of nearly 3,000 engines. Compare these numbers to the R-1830 and the R-2800. Amazing? Notice also that the R-1690 engines were used in the Focke-Wolfe FW-200 Condor and the Junkers JU-52's! Manufacturing rights?

The R-1340 was also used as a tank engine, and was built with a total greater than specified by P&W.  I believe this must be just aero engines. During WW II, some other sub-manufacturer's I have seen were Lycoming, and Studebaker. I believe that Jacobs may also have been reported, but I'll try to find this out via the Archives.

For a comparison, when I did research for my book, the R-1340 was used in hundreds of applications! There are others I'm sure, but it is very, very limited, and no major field population ever existed for these two engines, the R-1690 & the R-1860. I use a source called: "US Army Aircraft 1908-1946" by James C. Fahey as my guide, also data from the P&W Website.  While it is fairly accurate, in all reports & documentation, (including mine,) errors do creep in! Please note too that it's only for Army aircraft, no Navy type aircraft data is available to me at this time.

The R-1340 engine continued development, but the documentation stops here. The "H series" is currently rated at 600 HP for T/O and 550 HP at cruise. P&W defined improved cylinder heads and an improved crankshaft for increased reliability. If you go back in the developmental cycle of the T-6/SNJ, you see where the engine was rated at 550 HP for T/O, and 500 at cruise originally. These were the military versions of the engine with dash numbers. I've asked P&W for any more continuing data in their developmental cycle.

*R-1340-4, 8, 10, 12, 16, 20, 24, 28, 30, 38, 80, 88, 92, & 96 were the USN "dash number's" of which the 80 & 90 series did not apply to the SNJ. After the -56 engine, all T-6/SNJ engines used the "AN-1" as a standard. These engines were the military derivations, and could be geared engines too.

I worked on de Havilland U-1A Otter's, using the R-1340-59 & -61 variations, and I know the US Navy had a similar model called a UC-1, and later the NU-1B. The Navy did not have had a "Navalized" version of this engine. There's no direct way to tell by the military dash numbers what gearing options, (if any) etc the engine contained.

Early Pratt & Whitney data can be found on the Internet. I downloaded the following sites:

Pratt & Whitney    "The SOURCE!"

Pratt & Whitney R-1340 Engine at "ACAM," a Canadian site



AEHS Home   Excellent source of R-1340 & other P&W series enginess

R-1340 Installations in NAA Aircraft:

Engine and dash number:





Scout trainer, similar to BC-1



Trainer;  550 HP; Flat Bottom Rudder



Same as AT-6A; Trainer 550 HP



From Y1BT-10 for Navy; 550 HP


BC-2 Grd w/3 bld prop

Developmental Trainer for So. Am.


AT-6, BC-1, 1A, 1B, 1I

Trainer, Instrument trainer 550 HP



Same as SNJ-3; Trainer 550 HP



Second Batch; Trainer 600 HP


AT-6B, C, D, F, G

Gun/photo Trainer, Inst., FAC 600 HP

Note: There were a whole raft of dash numbers that did not apply to NAA aircraft. -1, -3, -7, -9, -11,-15, -16, -17, -19, -21, -23, -27, -29, -31, -33, -35, -39, -43, -51, -53, -55, -57, -59, -61.

There were also some civilian models installed in military aircraft, R-1340-C, -D, and a very special XGRS-1340-E geared engine. There were engines with side turbo's and fuel injection! The civilian engines R-1340-AN-2 & AN-3 were taken from the military R-1340-59 & -61 respectively. There were also various versions installed in the same aircraft series as in the SNJ-3 for example.(SNJ-3 had -38's & AN-1's both installed.)

Commercial versus military equivalencies:



Blower Ratio














-48 & -57





-AN2 & -59





-AN3 & -61









The various R-1340 engines installed in H-19 (Civilian S-55) helicopters were put in at a 39 nose-up angle. This was a reversed installation, with the accessories pointed forward, making this installation easy to work on in the accessory section. The prop shaft was coupled with a clutching mechanism to connect or disconnect the rotor via the transmission. Angled engines may not have a generator pad installed on the accessory section. The generator was driven by other means. There were also some test installations of the 1340 mounted horizontal. The rear case became the sump, and the nose case became part of the venting system. They also used different thrust bearings.  These were not too successful, and never went into production, but the "little brother" R-985 used this configuration successfully in several helicopter applications.

Geared production engines used a 3:2 reduction gearing, and a 4:3 gearing was offered in the early R-1340-H series. The geared -45 engine was a 1930's developed engine with a prop governor in the rear accessory section. The -59 & -61's had a governor mounted out front like the direct drive engines as I recall (?) I never remember having to do any governor work in the accessory section on the DHC-3 Otter.

Special thanks to P&W Archives volunteer Jesse Hendershot for researching data for me!

08/05/2012 12:44:31 PM