Japanese Zero vs Spitfire vs FW 190

[Ivan1GFP]

Not much of an economical cruise - 1240 HP in low gear. That's 20% more than max power of the late Sakae versions.

Hello Tomo Pauk,

That 1240 HP actually is pretty close to what the Army version of the Sakae (Ha-115) with water-methanol injection was making in the Ki 43-III.
The other factor here is that the airframe that is being hauled by this engine isn't the lightweight Ki 43 or A6M but something a bit more capable and carrying more equipment, fuel and protection.

664 L (175.4 US gals) of the internal fuel of the Shiden-Kai is less than 200 US gals I've proposed. Two drop tanks of 300 or 400 liters should complement that fine.
Against the Zero - yes, we have more stuff in the aircraft, but also much more power.

The fuel load of the Shiden-KAI is a bit more than you think it is.
270 Liter Forward Fuselage Tank
260 Liter Aft Fuselage Tank
2 x 93 Liter Wing Tanks
Total of 716 Liters Internal
plus
140 Liters of Water-Methanol to be able to run the engine past cruise settings.
To ignore the requirement for carrying water-methanol is to ignore the realities that the Japanese designers had to deal with as the power levels of their engines were increased.

The problem with taking the A6M as a baseline for estimates is that nearly nothing is quite big enough or strong enough in comparison to the end product. The N1K2-J actually was an existing fighter built for the Navy with many of the features you are looking for and the level of structural strength and engine power but still lacking other features and that is why I believe it makes for a better starting point.

A 10% greater RPM of 'engine X' is no match for 50% greater displacement of 'engine Y'. Everybody knew that - P&W, Wright, DB, RR, Bristol, Soviets, Japanese.

The very curious thing about "Everybody knowing that" is that just about everyone ended up increasing the maximum RPM of their later engines. The R-2800 C series ran slightly faster as did later model JuMo and Daimler Benz engines, Klimov VK-107, The Allisons installed in the P-40Q, The Sakae engines already mentioned. The Napier Sabre and Nakajima Homare engines also ran surprisingly fast.

- Ivan.

 

[XBe02Drvr]

The very curious thing about "Everybody knowing that" is that just about everyone ended up increasing the maximum RPM of their later engines.

Turning a few more revs always seems a cheap and easy way to get some additional HP, but with these large displacement engines with so much rotating and oscillating mass it comes at the cost of exponentially increased bearing loads, friction penalties, and piston speed stresses, as well as cooling loads with their added drag penalties. Sooner rather than later you come up against the limits of the metallurgy available to you.
Just a reminder to some of you folks who seem to like to throw engine numbers around like you were pulling them out of a hat.
Cheers,
Wes

 

[Ivan1GFP]

Turning a few more revs always seems a cheap and easy way to get some additional HP, but with these large displacement engines with so much rotating and oscillating mass it comes at the cost of exponentially increased bearing loads, friction penalties, and piston speed stresses, as well as cooling loads with their added drag penalties. Sooner rather than later you come up against the limits of the metallurgy available to you.
Just a reminder to some of you folks who seem to like to throw engine numbers around like you were pulling them out of a hat.

Hello XBe02Drvr,

I am in complete agreement with your summary, but you have to admit that it WAS a general tendency for just about everyone to try to increase the RPM of their engines a bit with the later models. Whether it was a good idea or not, everyone was doing it.
Now, with these larger aero engines, we are still only talking 2400 RPM to about 3200 RPM max which is just idling when compared to smaller engines like we find in Formula 1 racers and about equal to what your family sedan is doing just puttering around the neighbourhood. I was surprised as heck to find my little push lawn mower's engine was set to run at 7800 RPM. I spent an awful lot of time around auto shops as I was growing up, so I also had a chance to see what happens when certain things break. Mechanics often like to save the really interesting looking failed pieces.

- Ivan.

 

[XBe02Drvr]

Mechanics often like to save the really interesting looking failed pieces.

Ayup, got a souvenir or two lying about.

 

[Kevin J]

Hello XBe02Drvr,

I am in complete agreement with your summary, but you have to admit that it WAS a general tendency for just about everyone to try to increase the RPM of their engines a bit with the later models. Whether it was a good idea or not, everyone was doing it.
Now, with these larger aero engines, we are still only talking 2400 RPM to about 3200 RPM max which is just idling when compared to smaller engines like we find in Formula 1 racers and about equal to what your family sedan is doing just puttering around the neighbourhood. I was surprised as heck to find my little push lawn mower's engine was set to run at 7800 RPM. I spent an awful lot of time around auto shops as I was growing up, so I also had a chance to see what happens when certain things break. Mechanics often like to save the really interesting looking failed pieces.

- Ivan.

I always try and keep my turbo diesel sports saloon between 1800 and 2500 rpm so it's just cruising.

 

[tomo pauk]

Hello Tomo Pauk,

That 1240 HP actually is pretty close to what the Army version of the Sakae (Ha-115) with water-methanol injection was making in the Ki 43-III.

Yes, and that's all what it can do. We can try water injection on Kasei 20s, result being 1800+ HP to the prop.

The other factor here is that the airframe that is being hauled by this engine isn't the lightweight Ki 43 or A6M but something a bit more capable and carrying more equipment, fuel and protection.

Of course.

The fuel load of the Shiden-KAI is a bit more than you think it is.
270 Liter Forward Fuselage Tank
260 Liter Aft Fuselage Tank
2 x 93 Liter Wing Tanks
Total of 716 Liters Internal
plus
140 Liters of Water-Methanol to be able to run the engine past cruise settings.
To ignore the requirement for carrying water-methanol is to ignore the realities that the Japanese designers had to deal with as the power levels of their engines were increased.

Yes, you are right, the 664L US gals of fuel was the figure for the 1st Shiden version (one with mid-wing).
Japanese state 1430 km for the 'K1-J, and 1713 km for the 'K2-J (figures without drop tank). One drop tank adds 1100 km.
Kasei will be doing 10% less power = better mileage, another drop tank will benefit both range and radius, so will extra 40 liters of internal fuel.
I'm all for water-methanol to be carried once available.

The very curious thing about "Everybody knowing that" is that just about everyone ended up increasing the maximum RPM of their later engines. The R-2800 C series ran slightly faster as did later model JuMo and Daimler Benz engines, Klimov VK-107, The Allisons installed in the P-40Q, The Sakae engines already mentioned. The Napier Sabre and Nakajima Homare engines also ran surprisingly fast.

- Ivan.

Later R-2800 of any flavor were still inferior to the R-4360. Jumo 213 indeed revved much faster than Jumo 211, price to pay was increase of dry weight by 50% give or take. DB 603 > DB 605. VK-107 didn't make more power than AM-42. Under same conditions, V-1710 or Merlin were inferior in power to Griffon. Sakae was not making power as good as Kinsei, let alone bigger Japanese engines. Sabre did run fast, and it made twice the power than even faster revving Dagger. Homare also run fast, Nakajima was still trying with big Ha 219.
In wartime especially, it was easier to increase max RPM by 5 or 10% on any given engine, than to increase displacement of a given engine.

BTW - I'd start a thread about what Japanese might do different in ww2 WRT their aircraft & related gear in the What-if thread.

 

[XBe02Drvr]

Now, with these larger aero engines, we are still only talking 2400 RPM to about 3200 RPM max which is just idling when compared to smaller engines like we find in Formula 1 racers

True enough, but a 10-12K revving Ferrari engine wasn't going to happen in 1940 state of the art metallurgy, fuel, and lubrication wise. And the moving parts, despite their incredible speeds, are a tiny fraction of the weight of those of an R2800 or a DB601. Despite their relatively lower numbers, those engines weren't loafing; not by a long shot.
My first full time aero mechanic job involved early model RR Darts (Fokker F27) and late model PT6-67 Pratts (Shorts SD30), fairly close in SHP, but a lifetime (mine) apart in technology. The Dart (first truly successful turboprop engine) was born the same year I was, soon after WWII, and was an evolutionary "hybrid" between recip and turbine construction practices. It had a heavy, recip style engine case casting with a heavy planetary propshaft reduction gear in the nose and a two stage centrifugal compressor that looked straight out of a supercharger. This fed into individual separate burner cans that consisted of a casting and a liner, and could be unbolted and removed like recip cylinder jugs. With the entire aft section of the engine dominated by two turbine wheels (stolen from a hydropower plant, by the look of them!) and a tailpipe, where do you put the accessory case? Easy! Unbolt one from the back of a radial, rotate it to the horizontal, stuff it on a shelf over the power section/tailpipe area, and power it with a driveshaft.
Needless to say, this Rube Goldberg creation didn't spin at anywhere near the 36K RPM N1 of the PT6s. The quaint tachometers in the cockpit gave shaft and prop revs (as if it wasn't a fixed ratio!), and I seem to remember shaft topping out at about 10K. Oh, and a biggie. RR neglected to include bidirectional thrust bearings, so no reverse thrust available. You could GINGERLY ease the props into ground fine just enough to cancel the residual tailpipe thrust, but overdo it, and ground fine becomes ground bearings. Ouch$$$$!
IIRC, the Darts rated about 1850 SHP, and the Pratts (at 1/3 the weight, and <1/2 the fuel burn), about 1480.
Just another blast from the past.
Cheers,
Wes

 

[Ivan1GFP]

Yes, and that's all what it can do. We can try water injection on Kasei 20s, result being 1800+ HP to the prop.

Hello Tomo Pauk,

You were the one doing the comparison between the cruise power of Kasei and the max power of the Sakae.

Yes, you are right, the 664L US gals of fuel was the figure for the 1st Shiden version (one with mid-wing).
Japanese state 1430 km for the 'K1-J, and 1713 km for the 'K2-J (figures without drop tank). One drop tank adds 1100 km.
Kasei will be doing 10% less power = better mileage, another drop tank will benefit both range and radius, so will extra 40 liters of internal fuel.
I'm all for water-methanol to be carried once available.

From what I have been able to find, that isn't really correct for the N1K1-J either. Perhaps that was the data for the N1K1???
The N1K1-J carried
210 Liter Forward Fuselage Tank
165 Liter Aft Fuselage Tank
2 x 180 Liter Wing Tanks
Total of 735 Liters of internal fuel.

Later R-2800 of any flavor were still inferior to the R-4360. Jumo 213 indeed revved much faster than Jumo 211, price to pay was increase of dry weight by 50% give or take. DB 603 > DB 605. VK-107 didn't make more power than AM-42. Under same conditions, V-1710 or Merlin were inferior in power to Griffon. Sakae was not making power as good as Kinsei, let alone bigger Japanese engines. Sabre did run fast, and it made twice the power than even faster revving Dagger. Homare also run fast, Nakajima was still trying with big Ha 219.
In wartime especially, it was easier to increase max RPM by 5 or 10% on any given engine, than to increase displacement of a given engine.

Regarding R-2800 versus R-4360, inferior is a matter of opinion. There is no doubt the R-4360 COULD make more power but at what cost. Note that the F2G Corsair got pretty much nowhere except in civilian racing while the inferior F4U-4 seemed to do pretty well.
The point I was trying to make was that despite "everyone knowing", just about everyone tried increasing the RPM of their engines in a given model. Comparing engines across different lines can be done all day and come to no real conclusion.

- Ivan.

 

[tomo pauk]

Hello Tomo Pauk,

You were the one doing the comparison between the cruise power of Kasei and the max power of the Sakae.

Yes, indeed.

From what I have been able to find, that isn't really correct for the N1K1-J either. Perhaps that was the data for the N1K1???
The N1K1-J carried
210 Liter Forward Fuselage Tank
165 Liter Aft Fuselage Tank
2 x 180 Liter Wing Tanks
Total of 735 Liters of internal fuel.

Might be.

Regarding R-2800 versus R-4360, inferior is a matter of opinion. There is no doubt the R-4360 COULD make more power but at what cost. Note that the F2G Corsair got pretty much nowhere except in civilian racing while the inferior F4U-4 seemed to do pretty well.
The point I was trying to make was that despite "everyone knowing", just about everyone tried increasing the RPM of their engines in a given model. Comparing engines across different lines can be done all day and come to no real conclusion.

- Ivan.

The only reason why I've compared the engines is to show that a much greater displacement trumps a slight RPM advantage.

 

[XBe02Drvr]

Regarding R-2800 versus R-4360, inferior is a matter of opinion. There is no doubt the R-4360 COULD make more power but at what cost. Note that the F2G Corsair got pretty much nowhere except in civilian racing while the inferior F4U4 seemed to do pretty well.

Beat me to it, Ivan! Stole the words right out of my mouth!
I entered the Navy in the dying days of the R2800 and the R4360, and there were plenty of old time ADRs around to lament the waning of the 2800 and celebrate the decline of the 4360. "Give those lazy reservists something to keep them occupied!" And then there was the 3350 crowd, but they were quite another tribe entirely, and not considered civilized, even. "I'd throw in the towel and become a kerosene breather before I'd join that lot!"
Cheers,
Wes

 

[tomo pauk]

...
Regarding R-2800 versus R-4360, inferior is a matter of opinion. There is no doubt the R-4360 COULD make more power but at what cost.

To return here a bit. When going to the B-50, opinion of the USAAF was that 3500 HP provided by R-4360 was a superior option than whatever the R-3350 was making on it's extra 100 rpm, let alone the R-2800.

 

[XBe02Drvr]

To return here a bit. When going to the B-50, opinion of the USAAF was that 3500 HP provided by R-4360 was a superior option than whatever the R-3350 was making on it's extra 100 rpm, let alone the R-2800.

A perfectly rational decision by the bean counters and the slipstick sliders who don't have to deal with the nitty gritty. It's the operational folks, maintenance and flight crews who have to face the accusations when it doesn't live up to readiness and availability expectations and exceeds its projected maintenance budget.
"It's a POS!" is not an acceptable answer.
Cheers,
Wes

 

[Shortround6]

The R-2800 C series ran slightly faster as did later model JuMo and Daimler Benz engines, Klimov VK-107, The Allisons installed in the P-40Q,

R-2800C was a completely different engine that shared the same bore and stroke (and the starter dog?), New crankcase, new crankshaft, new con rods, new pistons.

The Klimov VK-107 took over 4 years to get into service (with such outstanding reliability {sarcasm} that it was taken out of production twice during the postwar years while problems were fixed).

The Allisons in the P-40Q (and some other late war aircraft) had a crankshaft with 27lbs worth of counter weights added.

The French Pre war Hispanos that ran at 2500rpm instead of 2400rpm had vibration dampers added in addition to a few other modifications, like changing the conrods

Yes, later engines were developed (not just allowed) to run at higher rpm but it took improved metallurgy as in different bearings or bearing material, a better understanding of vibration and how to deal with it and almost always the engines grew in weight to handle the increased stress.

Now please note that most of these engines are NOT going to get a very big increase in power from RPM alone.

The R-2800C only turned 3.7% faster than the R-2800B. The engine in the P-40Q turned 6.6% faster than a normal P-40 engine, the P-40Qs speed came from being able to use 75in of MAP at altitude and not at sea level.

WIthout comparing engines from different times we can compare the Mercedes 1939 M163 3 liter Formula one engine. However as I have said before comparing car engines to aircraft engines leaves out the aspect that in many cases the car engines were built to an artificial displacement limit. Artificial in the sense that it was either a rule imposed by the race organizers or it was way of classifying engines for a government tax. If you are going to build a 3 liter engine you have two avenues of increased power. Increase the RPM for more power strokes per minute or increase the volumetric efficiency with better breathing or supercharging.
For the aircraft engine maker the option of just making a bigger engine was usually open, at least until they hit real limits, like the speed of combustion in the cylinder limiting the bore of the cylinders.

The Mercedes engine used 67mm X 70mm cylinders. it used 4 valves per cylinder in a pent roof DOHC head. it used a real witches brew of fuel (86% methanol, 8.8 % acetone, 4.5% nitrobenzol and 0.8% sulphuric ether.. It ran at 2.31 Atm for manifold pressure (19 1/4lbs of boost?) and at 7500rpm it made 480hp, it used a two stage supercharger (one supercharger discharging into the inlet of the 2nd supercharger.) The BMEP was 305psi.

The Corrected piston speed was 3,370ft/min, a bit more on this later.

the engine weighed 603lbs. (dry weight) and this, while an extreme example, shows the problem with high rpm engines.

The P & W Wasp Junior which was hardly state of the art in 1939-41 weighed about 10% more (668lbs) was 16.1 liters (over 5 times the displacement) 132 X132mm cylinders, 2 valves per cylinder using push rods. It ran on 91 octane fuel and at 36.25 in hg (3 1/4 lbs?) at 2300rpm it made 450hp for take-off. It could also make 400hp at 5,000ft at 2200rpm for as long as the fuel lasted. The BMEP was 157psi and the piston speed was 1,988fp/min.

Since aircraft desingers don't give a rat's *ss about the displacement of an engine (unless they are building a race plane for certain set of race rules) and are very interested in power for weight, reliability and fuel consumption, heavy/high rpm engines never found much favor, Major Halford aside.

Piston speed was often used to compare engines at the time but it was not really a reflection of the stress or friction of the pistons and pistons rings but rather an easily computed number the reflected the stress on the rod bearings and reciprocating parts.
The Bristol Pegasus engine due to it's long stroke had one of the highest piston speeds of the time. 190mm (75in) times 2600rpm giving 3250fpm uncorrected. The corrected piston speed was 2850fpm to account for the light pistons (small diameter.)
The formula is twice the stroke in feet, times the rpm, then the mean piston speed is divided by the square root of the stroke/bore ratio, to reflect large diameter/heavy pistons and small diameter light pistons.

Major Halford went off on his small cylinder, high RPM tangent in an effort to build a powerful and fuel efficient engine given the fuels of the time. A small cylinder will cool better than a large cylinder (more cylinder wall per unit of volume) and he was hoping to use higher compression in the cylinders and more rpm to make power. Unfortunately for him (and Napiers) fuel improved faster than he could develop his engines and the large cylinder engine designers could simply boost pressure (and redo the broken parts) with little or no change in rpm.
The lots of little cylinders branch of development also had increased maintenance loads. One reason the R-4360 was so unpopular, 56 spark plugs to change.

 

[Ivan1GFP]

Hello Shortfound6,

Thank you for a very interesting discussion about the issues of high RPM engines. I am not entirely unfamiliar with them.
You and XBe02Drvr seem to have come to the conclusion that I was ADVOCATING increasing RPM to increase power for large aero engines.
I was actually doing nothing of the sort. I was simply making an OBSERVATION that contrary to the statement that "everybody knew it would not work", just about every company tried increasing RPM on its later engines. I never claimed it was a good idea.

The Allisons in the P-40Q (and some other late war aircraft) had a crankshaft with 27lbs worth of counter weights added.

Is there really a problem with increasing the size of counterweights on the crankshaft other than it reducing the revving response of the engine?
In my opinion, to reduce overall stresses on the engine, balancing with counterweights on the crank is much superior to a harmonic balancer on the end of the crankshaft even though the harmonic balancer is lighter overall.
I believe it tends to reduce the resonant vibrations through the engine which may be less predictable at various RPM ranges.

The Bristol Pegasus engine due to it's long stroke had one of the highest piston speeds of the time. 190mm (75in) times 2600rpm giving 3250fpm uncorrected. The corrected piston speed was 2850fpm to account for the light pistons (small diameter.)
The formula is twice the stroke in feet, times the rpm, then the mean piston speed is divided by the square root of the stroke/bore ratio, to reflect large diameter/heavy pistons and small diameter light pistons.

I understand the idea of piston speed and BMEP, but why would you divide by the square root of the stroke/bore ratio?
This is starting to remind me of discussions I had with a NASCAR engine builder who happened to work in the same shop as I did for a while.

Major Halford went off on his small cylinder, high RPM tangent in an effort to build a powerful and fuel efficient engine given the fuels of the time. A small cylinder will cool better than a large cylinder (more cylinder wall per unit of volume) and he was hoping to use higher compression in the cylinders and more rpm to make power. Unfortunately for him (and Napiers) fuel improved faster than he could develop his engines and the large cylinder engine designers could simply boost pressure (and redo the broken parts) with little or no change in rpm.
The lots of little cylinders branch of development also had increased maintenance loads. One reason the R-4360 was so unpopular, 56 spark plugs to change.

As I understand it, small diameter long stroke pistons also don't do well for overall friction either.
I wonder if these engines have an advantage in piston dwell time such as one might get by longer connecting rods?

- Ivan.

 

[XBe02Drvr]

Is there really a problem with increasing the size of counterweights on the crankshaft other than it reducing the revving response of the engine?

If you get all your resonance calculations spot on, probably not. Small errors can result in significantly higher bearing stresses. Revving response should not be an issue if you have a reasonably responsive constant speed prop and governor, as RPM shouldn't change much. Not so with some electric props whose response lag allowed RPM excursions under rapidly changing flight loads, like air combat. Years ago I remember seeing a utube video taken from inside a Cessna 152 Acrobat doing its thing, in which the tachometer and view out the windshield were both visible. The RPM fluctuations of the fixed pitch prop graphically highlighted the widely varying aerodynamic loads on the prop.
Cheers,
Wes

 

[Ivan1GFP]

If you get all your resonance calculations spot on, probably not. Small errors can result in significantly higher bearing stresses. Revving response should not be an issue if you have a reasonably responsive constant speed prop and governor, as RPM shouldn't change much. Not so with some electric props whose response lag allowed RPM excursions under rapidly changing flight loads, like air combat. Years ago I remember seeing a utube video taken from inside a Cessna 152 Acrobat doing its thing, in which the tachometer and view out the windshield were both visible. The RPM fluctuations of the fixed pitch prop graphically highlighted the widely varying aerodynamic loads on the prop.

Hello XBe02Drvr,

My knowledge of the differences is based on the differences between the old Ford 289 CID V-8 and the newer 302 CID "5.0 Liter" V-8 and also other automotive V-8 engines.
The older 289 had larger counterweights and therefore a greater rotating mass, but didn't have the same requirement for a large harmonic balancer at the end of the crankshaft to dampen vibrations along the crank because there were not as many. Each reciprocating mass of piston and connecting rod was better balanced locally.
I believe "close" is all you would ever get with an actual engine and there would always be resonances at some RPM range. They would just be worse with smaller counterweights.
This was also typical NASCAR engine practice with larger counterweights. They were willing to give up a little quick revving in acceleration in order to have better durability in sustained high RPM operation.

The Cessna 152 Aerobat is the only real aircraft *I* have actually "flown", though it is a bit of a stretch to call what I was doing "flying".
I did serve as "Ballast" (as a friend of mine calls it) in the left hand seat for a few actual aerobatic flights. Things happen very much in slow motion in that aeroplane!

- Ivan.

 

[BiffF15]

Hello XBe02Drvr,

My knowledge of the differences is based on the differences between the old Ford 289 CID V-8 and the newer 302 CID "5.0 Liter" V-8 and also other automotive V-8 engines.
The older 289 had larger counterweights and therefore a greater rotating mass, but didn't have the same requirement for a large harmonic balancer at the end of the crankshaft to dampen vibrations along the crank because there were not as many. Each reciprocating mass of piston and connecting rod was better balanced locally.
I believe "close" is all you would ever get with an actual engine and there would always be resonances at some RPM range. They would just be worse with smaller counterweights.
This was also typical NASCAR engine practice with larger counterweights. They were willing to give up a little quick revving in acceleration in order to have better durability in sustained high RPM operation.
- Ivan.

Ivan,

The Ford 289 K Code / HiPo engine used a different balancer and a hatchet counter weight on the crank to help with the RPMs. I have a 1966 Mustang GT 2+2 with this little screamer. The 66 warranties were 12 months 12k miles for the standard V8, and 3 months 4K for the K codes. Ford expected them to be abused I guess.

"The 289 High Performance balancer is larger in width at 337⁄64 inches wide. It is wider and heavier to compensate for the high revs and larger/heavier 3/8-inch rod bolts. The 1969–1970 Boss 302 balancer is also wider and on par with the 289 High Performance balancer."

Cheers,
Biff

​

Here's the 1963–1967 289 High Performance slide-on crankshaft counterweight. The Hi-Po needs a nar-rower timing sprocket and chain to make room for this counterweight.
​

 

[Shortround6]

Hello Shortfound6,

Thank you for a very interesting discussion about the issues of high RPM engines. I am not entirely unfamiliar with them.
You and XBe02Drvr seem to have come to the conclusion that I was ADVOCATING increasing RPM to increase power for large aero engines.
I was actually doing nothing of the sort. I was simply making an OBSERVATION that contrary to the statement that "everybody knew it would not work", just about every company tried increasing RPM on its later engines. I never claimed it was a good idea.

It didn't work in the sense that engine companies tried to increase RPM only without doing other things. And a number of companies either didn't increase RPM or increased it only a modest amount. P & W didn't try to use high rpm on the replacement for the R-1830 for example, they just used larger diameter pistons. A few late model R-2000s did go to 2800rpm but the majority stayed at the same 2700rpm as vast numbers of R-1830s. P & W also used higher boost (translates to higher BMEP) which seems to have been the prefered method of getting more HP in US and British engines during WW II. Of course it was the allies who had the fuel that allowed them to use this avenue. The Germans and Japanese did not (or had much less access to this avenue) and were forced to use either larger displacement or higher RPM or both.

Is there really a problem with increasing the size of counterweights on the crankshaft other than it reducing the revving response of the engine?
In my opinion, to reduce overall stresses on the engine, balancing with counterweights on the crank is much superior to a harmonic balancer on the end of the crankshaft even though the harmonic balancer is lighter overall.
I believe it tends to reduce the resonant vibrations through the engine which may be less predictable at various RPM ranges.

The increase in weight of the crankshaft probably did nothing to the rev response the engine. With a nearly 400lb propeller on the front end of the engine adding 27lbs worth of counter weights would not be noticed by the average pilot. You may be right about the counter weights being superior, the 27 counter weight crank certainly imposed much lower loads on the engine.

I understand the idea of piston speed and BMEP, but why would you divide by the square root of the stroke/bore ratio?

it tends to equalize the difference between small bore/light pistons and big bore/heavy pistons. Not very many Aircraft engines were over square but a few were decidedly undersquare and while some of them ran at a high piston speed (like the Pegasus) the small bore tended to get overlooked. Oversquare engines tend to get a pass. The 5,00 X 4.75 Napier Sabre engine's 3,058fpm (at 3,700rpm) should probably be corrected to 3,165 fpm to compare to the Griffon engine.
Yes it is a simple calculation that does not really account for different weight pistons/pins and rods but it may be better than just figuring the piston speed.

See: Mean piston speed - Wikipedia

As I understand it, small diameter long stroke pistons also don't do well for overall friction either.
I wonder if these engines have an advantage in piston dwell time such as one might get by longer connecting rods?

They probably don't have an advantage in friction, but they may have an advantage in cooling.

 

[XBe02Drvr]

My knowledge of the differences is based on the differences between the old Ford 289 CID V-8 and the newer 302 CID "5.0 Liter" V-8

The Ford 289 K Code / HiPo engine used a different balancer and a hatchet counter weight on the crank to help with the RPMs. I have a 1966 Mustang GT 2+2 with this little screamer.

It's great fun talking and reminiscing about muscle car and hotrod engines, but let's not forget, they're a whole different animal in a whole different ecosystem from a fighter engine. Let's not draw too many parallels, as their performance demands and operating profiles are so radically different, especially if the aircraft is constant speed equipped.
No automotive engine, even a Ferrari or Alfa at Le Mans, is required to run continuously at such a high percentage of its peak output as a fighter engine. OTOH, instantaneous revving response is nowhere near as critical in a fighter as in a race car.
Cheers,
Wes

 

[Ivan1GFP]

Ivan,

The Ford 289 K Code / HiPo engine used a different balancer and a hatchet counter weight on the crank to help with the RPMs. I have a 1966 Mustang GT 2+2 with this little screamer. The 66 warranties were 12 months 12k miles for the standard V8, and 3 months 4K for the K codes. Ford expected them to be abused I guess.

"The 289 High Performance balancer is larger in width at 337⁄64 inches wide. It is wider and heavier to compensate for the high revs and larger/heavier 3/8-inch rod bolts. The 1969–1970 Boss 302 balancer is also wider and on par with the 289 High Performance balancer."

Hello BiffF15,

I never actually had too many encounters with the Hi Performance 289. They were kind of rare.
From what I remember, they were about 270 HP and had solid lifters, different cam and factory headers.
I remember after a drag race in which we managed to collapse a lifter in our standard 289 4V, I was thinking solid lifters might be an idea but my Dad was of the opinion that they were too much of a maintenance hassle.

From what I remember about the old standard 289 with a 4 barrel, it was making best power at 4800 RPM but had a redline not much above that.
What is interesting in comparison is that the much newer 302 my Mustang didn't have the same counterweights and a much lower RPM for best power, (about 4200 RPM IIRC), but had a redline in theory at 6000 RPM. There is a rev limiter (ignition cutoff) that is standard that cuts at 6250 RPM and I have heard it go a few times when the car has been on a Dynojet. I always thought the Dynojet runs were a bit abusive and also expensive, so eventually I had the car weighed and switched to a GTech accelerometer to measure rear-wheel HP.

- Ivan.