On page 7:
http://www.wwiiaircraftperformance.org/japan/intelsum85-dec42.pdf
there's an example of a p-39 trying, and failing, to use 70in of boost, on US fuel.
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You had several things going on at once. The early "C" engines in the P-40B&C (Tomahawks) had a problem with the propeller reduction gears. Some of the other parts may not have been the equal of even a 1941/42 manufactured engine.
Fuel was another big "IF" factor in the early part of the war. The Allisons were developed using US spec 100 octane fuel. This is different than either British 87 octane or British 100 octane. British 87 octane fuel had a fair amount of "aeromatics" in it and performed better (allowed higher boost)than than some 87 octane fuel but it was never really measured. American 100 octane fuel had very little allowable ( 2% max) "aeromatics" and while a richer mixture allowed a bit more boost there was no real jump in allowable boost pressures. In fact a few batches of US 100 octane gas performed at worse than 100 octane rating when running rich.
British 100 octane fuel at the time of the BoB and shortly after had 20% aeromatics minimum and while not tested for a while, it performed much better under rich conditions than lean. Once they did come up with test procedures and and a rating system it was found that most batches of British 100 octane had a rich mixture response of between 115-120PN. Or 100/115-120. Once they had that figured out the British began specifying 100/130 fuel. The US meanwhile shifted to a 100/125 fuel specification.
Sorry to be a bit long winded but it helps explain why British units in North Africa could use higher boost numbers than the US army approved for it's identical engines at the same time. While few people were using 75in of boost at the time a lot of them were running way over the "BOOK" numbers of 40-44 in MAP. Some claim ( and others say they didn't) The Flying Tigers used some rather high boost settings too, but I don't know were their fuel was coming from. British or American stocks? This fuel discrepancy carried over into the P-40E's at least and maybe into the P-40Ks. At some point in 1942 the British and Americans standardized on the 100/130 fuel specification. Trying to use 60-70 in of boost on 1940 US 100 octane fuel could be a very iffy proposition. Given ideal conditions you might get away with it. Less than ideal might mean pushing into the 50s could wreck the engine.
As far as other "technology" goes a number of parts were changed along the way, Crankshafts went from "plain" to shot peened to shot peened and Nitrided (early 1942) for an almost doubled allowable stress level, and that is before the 12 counter weight crankshaft shows up in early 1944. Other parts like connecting rods changed. Valve springs changed on the later engines. Even the way the crankcases were cast was changed.
Trying to wind an early engine AS BUILT to 3400-3600rpm could (and often did) result in disaster. Doing it to a rebuilt engine using late model internal parts could very well be a different story.
The engines we build today are mostly later series and perform to stock levels. The rated rpm is 3,000 but the design was good for a LOT more. We have some customers who run them at 4,500+ rpm, but not in airplanes.
The thing is, the American engineers and Army acceptance peoplpe were very conservative. The Allison can pull over 100" of Mercury MAP, but was rated VERY conservatively and tested conservatively. You almost can't FIND a test report at over 57" of MAP and 3,000 rpm .... but we can easily get 75"+ and 3,400 - 3,600 rpm if we want. We CAN get to 115" of MAP for a race engine. Most owners don't becasue there is almost not reason to do so.
The entire point is, when we DO, the engine handles it very well!
The Allison is tougher than the Merlin and holds a tune-up MUCH longer; MUCH more trouble-free. NOTHING wrong with a Merlin; you get what you expect to get with one, no argument there. It's just that you get so much MORE than you expect with a well-overhauled and properly-tuned Allison. We have several in Jurca Spitfire replicas and they give 95+% of the performance of the real aircaft despite having only a single stage supercharger rather than a 2-stage unit. If they had an equivalent two-stage, they'd kick-butt, and do anyway in tractor pulls where sea level performance is imnportant.
No single-stage ALlison is great at 25,000+ feet compared with a 2-stage Merlin, but the aux-stage and turbo models were ... and ARE. ALL Alisons were VERY comparable to the single stage Merlins, particularly from a serviceability standpoint. They were VERY good engines hamstrung by a government committee that controlled the ordes. if they order a V-1710-39, thath's what you deliver ... not some BETTER engine. To do that would violate the contract.
In the post-war unlimited hydroplanes, the merlins that eventually took over from the Allisons were all 2-stage units. The single-stage Merlins mostly lost to the sinlge-stage Allisons. Guy Lombardo was the US Champion for 1946 - 1949 and won EVERY trophy on the circuit with Allisons. I have two pistons from one of his Championship-winning boats. When Merlins "took over," they were the 2-stage units and won mostly due to lack of knowledge of how to tune-up Allisons.
When they made the movie "Madison," Joe Yancey built the Allisons for the 20+ old hydroplane boats in the movie. He built them to STOCK configuration and they almost all ran 20+ mph faster than they did in "back-in-the-day" competion during the filming of the movie simply becasue the guys trying to "hot rod" the Allisons didn't know what they were doing. They ALSO put over 70+ hours on most of the boats during the filming and the engines never broke.
The Reno Races over the last few years have a P40, P51A and think a P38 taking laps.
There was a comment that the 3 blade prop of the Mustang and Warhawk limited the top speed.
Can a modern day Allison be built to compete with the super Unlimiteds?
Would that require a different propeller?
What HP could be expected?
Would operating at 3200/3400/3600 rpm be doable?
Conversations with Chris Fahey with Planes of Fame.
He noticed the P51A climbed a bit better than the P51D to 10000 ft.
This is when they were doing photo ops.
A newer prop might well be beneficial. However as a general rule of thumb the higher you go the more prop you need. at sea level on a 59 degree day you can use a much smaller prop than at 20,000ft even for the same power. Air density at Reno altitude and well over 100 degrees IS????
A modern day Allison might be able to compete with the unlimiteds but it needs a much different supercharger to do it. It also needs a much different cooling system. It would certainly require a new propeller as you are now dealing with 3-4000hp and not 1200-1500hp.
Using the 12 counter weight crankshaft is a start for high RPM but for how long???
Greg may have better answers
Here you need information on the two planes involved. The P-51A was lighter in military form than the P-51D.
As "warbirds" are they carrying weight to simulate guns/ammo?
I don't believe anybody is still flying with self sealing tanks/liners (they deteriorate over time and become a hazard=blocked fuel lines/filters)
Armor? new radios?
and are both pilots accurately reporting rpm and boost used in the climb?
Lot of new Allison FAA upgraded approved parts are available.
What was said in the Allison engine builders web site!Hmmmm... Please explan
From what I've read on the Soviet experience with the P-39, WEP wasn't available for use until the P-39K.With regards to post#41, a P-39 trying and failing to use 70" MAP, the date of the report is Oct 1942. Grade 150 fuel wasn't widely available until after summer 1944. I'm guessing the P-39 was running grade 100/130 fuel. Not challenging the report at all, just noting the report date and when fuel was improved to grade 150.
Reference here: 150 Grade Fuel Summarized below.
USAAF Materiel Command held a "Conference on National Advisory Committee for Aeronautics Test Program to Investigate 150 Grade Fuels" on 27-28, January 1944. It was concluded that "The program outlined should permit conclusive data to be obtained and should indicate the relative advantages of the various high octane fuel components for the preparation of satisfactory rich and lean rating fuels. It should also indicate the military value of these fuels for long range patrol or bombardment operation". It was recommended that "the program outlined should be carried out as expeditiously as is possible".
With regard to Post #48 above, ACE Allisons: They make/made new parts because they don't have any originals to speak of. I have seen at least a eight ACE Allisons while taking them apart. My recommendation is to use genuine Allison parts when you can, and they ARE available, including piston rings.
If you are serious about an Allison, ask ACE's Bud Wheeler what his Allison guarantee is and what constitutes engine abuse. Ask him to seat the rings on a run stand before he ships it. Ask him if he'll ride in it with you. Then go ask Joe Yancey (Yancey Allisons) and/or Jose Flores (Vintage V-12s). Might as well get info from several builders. Decide for yourself and good luck whatever the choice is. Last, post pics of your new Allison chariot!
And collaborate how and what to do and get them past FAA certification!
Merlin's and Allison are not experimental engines!There is NO FAA certification for experimental engine or engine parts unless there is a Type Certificate issued against that engine.
Evidently you know nothing about aircraft certification.Merlin's and Allison are not experimental engines!
Even though they are souped up!
From earlier reading I recall an Allison V1710 1,475 hp was used and the P-40Q and attained a speed of 422 mph in straight and level flight . The V1710's used in the P-38's were of the same horsepower . Although I'm not sure that this engine was installed in the P-63 . Anyone care to comment on that ?Does anyone know anything about the engine for the XP-40Q? All I have read is that it had a two-stage supercharger and a higher rated Allison. Was this the same arrangement as the P-63?