Single stage V-1710: options for improvements?

7" stroke on the Centaurus.

Was it an 11" centre to centre distance on the master rod Greg? Which be a low rod length to stroke ratio, I would think.

I think you are right, Wayne. I misquoted the spec ... and could not really check it at the shop since we have the cylinders .... but no engine case , crankshaft, or rods. Just one cylinder and all the cylinder liners. They are very HARD metal, but are, in fact, able to be honed if you are careful and know how to hone a cylinder correctly. It displaces 3,2771.9 cubic inches, so is only slighly smaller in displacement than the Wright R-3350. Very interesting liners and cylinder. The monkey-motion sleeve valve mechanism is strange, but works. As I said, it will be the thing that fails at high rpm. But if you run it to stock rpm levels, it seems to run just fine.

The Centarus runs sweet when stock, and has plenty of power for any non-racing Sea Fury. If I had one (don't I wish!), I'd want the Centarus in stock configuration and the Sea Fury in stock configuration, too. Climbs well, is fast, handles well, and is both rugged and reliable. What more do you want from a warbird except a lower cost?

Before you start jumping the boost up with multistage multispeed superchargers, might want to consider how youre going to cool off the intake charge. Intercoolers/Aftercoolers were very essential to the Merlin and would also be to the Allison. Having said that, Id love to see a V1710 properly set up with a multispeed 3 stage supercharger and direct injection

Here is a page from the P-51J Flight Manual show the cooling arrangement for the V-1710-119. The picture of the installation was posted above earlier.

dobbie said:

Before you start jumping the boost up with multistage multispeed superchargers, might want to consider how youre going to cool off the intake charge. Intercoolers/Aftercoolers were very essential to the Merlin and would also be to the Allison. Having said that, Id love to see a V1710 properly set up with a multispeed 3 stage supercharger and direct injection

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3 stage supercharger would be really something new.
Unlike the 'something old proven', like water injection for example, used for the same purpose as the intercooling/aftercooling in V-1710.

Some of the later engines had supercharger systems that were approaching the size and weight of power section (engine block/cylinders).

Technically very interesting but the increasing complication was a headache.

Multi-stage compressors (or pumps) were nothing new, they had been used in industrial applications of decades before WW II. But they usually ran at a fixed speed ( or small speed variation) and little or no change in intake air pressure or density. Getting stages to play nicely with each other in the widely changing conditions of aircraft use was a real challenge.

AS an illustration here is a compresser map from a modern turbo:



Note that while it can reach a pressure ratio of 3:1 it is only at one specific air flow.
The curved (or wavy) lines that run from left to right with the big numbers (74990, 948?0, 135018 ) are the rpm of the impeller.
Notice that the pressure ratio falls off considerable as the airflow goes past about 22.5lbs/min. The impeller is 'choking' and cannot supply much more air.
Also note the left most line that runs from about 5lb/min and PR of about 1.4 up to about 18lb/min and just under a 3.0 pressure ratio. ANYTHING to left and the impeller is "stalling", the impeller is trying to pull a vacuum and the airflow "stalls" or slows down/stops until enough air builds up in the intake to continue flowing again, this can happen multiple times per second and if bad enough can send small shock waves back through the intake duct/s. This is the cause of the "rumbling" some F4F pilots complained about.
Rolls Royce got lucky in that the Vulture supercharger was actually a good match to the Merlin supercharger right from the start and only needed minor tweaking. Allison lost time trying to use a second same sized impeller to feed the engine supercharger. P W spent a lot of time working out the impellers and housings to eliminate the problems. Somebody at R-R was reluctant to start work on the 2 stage system because they were afraid the second stage would multiply any mistakes/problems in the first stage.

Please remember that these guys were working though ALL the problems and tricks concerning airflow though engines that we almost take for granted today.

I lived within view of Addison Texas airport just north of Dallas for a few years. The Cavanagh air museum has amongst its many interesting flyable aircraft, a P40N model. Used to look out over my balcony and see them fly it from time to time. Allisons make cool sounds lol

Yes they do and they run quite smoothly, too. We are now overhauling a really neat E-series engine for a customer and it came to us with the Aux supercharger drive atatched. It is a V-1710-93 and is exactly the same as a -117 except for 3 deviations.

1) It has a 6-counterweight crackshaft and so is a really a 3,200 rpm engine.
2) it has an "E" series nosecase so it runs a driveshaft and not a propeller.
3) They will not run the Aux stage supercharger in their application, so we will remove the Aux stage drive and not run the Aux S/C.

It MAY be that they will request the 12-counterweight crankshaft. If so, we have them and the rpm will be cleared to 3,400 and the boost to 144"of MAP. I'd assume a normal operation of 60 - 80 " of MAP. The application is interesting, but not public at this time. Not a P-82.

Suffice to say this Allison will produce 1,800 - 2,100 HP depending on what is requested by the buyer. Will probably cruise at 600 - 750 HP like most WWII engines.

tomo pauk said:

3 stage supercharger would be really something new.
Unlike the 'something old proven', like water injection for example, used for the same purpose as the intercooling/aftercooling in V-1710.

Click to expand...

It makes sense to cool the charge between multiple stage before expending energy compressing it.

The Germans planned a 3 stage supercharger:
DB 631 - A DB 603G with a three-stage supercharger. 1900hp. Abandoned.

I suspect these had infinetly variable drive. In the case of some planed engines such as the DB605 based 628 the first stage was axial and concentric with the gear case having variable pitch fans while the second stage was transverse as per the usual arrangement, this thereby allowed optimal efficiency and flow matching. Three stages should be OK on a common spool given variable speed drive.


I believe the DB603LA used in the Ta 152C had a two stage supercharger but no intercooler. The DB603L and N would have had intercooling.

The Allison V-1710-121 which had a two stage infinetly variable supercharger did not have an intercooler but was designed to work with ADI water injection.

The simplest improvement to the single stage Allison might have been an intercooler, the latter model Jumo 211 had intercooler on their single stage engines, though these were actually two speed units.

The reason I say this as there would be no changes to the dynamics of the engine or supercharger drive. It might allow a higher compression ratio.

Using a hydraulic variable speed drive would have been a natural for the US industry, with its expertise in hydraulic automatic transmissions.

Siegfried said:

It makes sense to cool the charge between multiple stage before expending energy compressing it.

Click to expand...

Agreed.

The Germans planned a 3 stage supercharger:
DB 631 - A DB 603G with a three-stage supercharger. 1900hp. Abandoned.

I suspect these had infinetly variable drive.

Click to expand...

DB 631 was to have 2 stage turbo (thing deserving an own thread?), along with 1 stage mechanical supercharger.

In the case of some planed engines such as the DB605 based 628 the first stage was axial and concentric with the gear case having variable pitch fans while the second stage was transverse as per the usual arrangement, this thereby allowed optimal efficiency and flow matching. Three stages should be OK on a common spool given variable speed drive.

Click to expand...

No common spool for the 631. I'd be cautious for the broad sweeping statements like the bolded part.

I believe the DB603LA used in the Ta 152C had a two stage supercharger but no intercooler. The DB603L and N would have had intercooling.

Click to expand...

Beats me

The Allison V-1710-121 which had a two stage infinetly variable supercharger did not have an intercooler but was designed to work with ADI water injection.

Click to expand...

Great engine, too late to matter.

The simplest improvement to the single stage Allison might have been an intercooler, the latter model Jumo 211 had intercooler on their single stage engines, though these were actually two speed units.

Click to expand...

The 2 speed unit has it's advantages, but an intercooled (or with water injection) single stage V-1710 looks like a great thing under 20000 ft.

The reason I say this as there would be no changes to the dynamics of the engine or supercharger drive. It might allow a higher compression ratio.

Click to expand...

Pressure ratio?

Using a hydraulic variable speed drive would have been a natural for the US industry, with its expertise in hydraulic automatic transmissions.

Click to expand...

Either that, or go for a two speed supercharger.

Engine (and airframe) designers were fully aware of intercoolers both before and during the war. An intercooler on a single stage engine could raise the HP by around 100HP on a 1200-1400hp engine OR raise the critical altitude by several thousand ft. However it increase drag. Benefits for bombers may be better than benefits for fighters which were more volume limited.

The intercooler increased power of the Jumo 211 (F -> J) from 1060 to 1180, high gear, Steig Kampflesitung. Cost being the lower FTH altitude for that power level ( 5,3 km -> 4,9; 1290 ft). Or, at 6 km, some 60-65 HP. The maximum gain under the FTH was some 130 HP, St Kampflst, between 3,5 and 4,9 km. The gains in low gear were, interestingly enough, lower.
You are, indeed, right that intercooler would represent the issue here, unless it's radiator is smartly faired in, like in P-51. Or using the existing intercooler in P-38 installation. That all combined with an engine with a 9.6.1 supercharger should give some 65-70 HP above 15000 ft (at 20000 ft, instead of 900-950, some 960-1010 HP). Under 13500 ft, gain of ~140 HP (at 10kft, instead of 1080 HP, some 1220). All military power (15 min rating), without going in WER (5 min rating). Not that bad, but not as capable as Merlin 20 series.
Wonder what gain in WER could've been expected (not that would make any difference above FTH)? Take off power?
The most common users of the 1 stage V-1710 would be ill able to accommodate the intercooler radiator, let alone avoid the serious drag penalty. Here the water injection would help, but the gains would be felt mostly under FTH. A P-39 that really makes 400 mph?