Seems the ETO P51D operated on 150 Grade.
Deliveries of Grade 100/150 aviation fuel to Eighth Air Force fighter airfields commenced in June 1944. 8 9 10 This coincidentally occured about the same time as the introduction of the P-51D into service. Even though the USAAF had cleared the P-51 for 75" Hg., the Eighth Air Force chose 72" Hg as the P-51's War Emergency Rating. 11 12 Apparently there is more to the story, however, as Encounter Reports demonstrate that 75" Hg was used operationally. 13 14
By January 1945, fourteen of the Eighth Air Force's fifteen Fighter Groups were operating Mustangs, the sole holdout being the 56th FG in P-47's. Maintenance difficulties with spark plug fouling led to the decision to convert all fighter groups to 100/150 grade fuel reformulated with increased levels of ethylene dibromide (1.5T). Deliveries of PEP, as the new 100/150 blend was called, began to be issued to all fighter groups in February 1945. The use of PEP, however, cooroded the valve seats of the V-1650 at an unacceptable level. Consequently, the standard 100/150 (1T) grade fuel was reverted to by the end of March 1945. 15 16 The Eighth Air Force also had hoped to supply the 352nd and 361st Fighter Groups based on the continent with 100/150 grade fuel.
This was deemed impractical from a logistical viewpoint, although admittedly such difficulties did not prevent the RAF's 2nd TAF from being supplied with 100/150 grade fuel. 17
Those RAF Mustang units tasked with defending against the V-1 were modified to operated at +25 lbs./sq.in. - the equivalent of 80" Hg. 21 22 On 24 August 1944, by which time the V-1 threat had subsided, the Ministry of Aircraft Production directed Rolls Royce: "all Packard Merlin V.1650-7 engines to be modified to operate at 25 lbs. boost". 23 Raising the WER rating from 67" Hg to 80" Hg increased Sea Level speed by 30 mph. 24 On 18 September 1944 ADGB noted, that with respect to the Mustang III/Packard Merlin 1650-7, "A total of over 7,000 hours have been flown at a maximum boost pressure of + 25 lbs./sq. in.". 25 The RAF's Mustang Pilot's Notes gives the Combat Engine Limitation as "81 ins. boost for 5 minutes when using 150 grade fuel". 26
Combat Reports show +25 lbs was used operationally over the continent by UK based Mustangs of ADGB. 27
Encounter Reports noting high boost obtained with 150 grade fuel
1st Lt. Raymond R. Flowers, 1 November 1944, 20th FG I closed steadily pulling over 70 inches.
1st Lt. James F. Hinchey, 14 November 1944, 353rd FG For fifteen minutes at 74 hg and indicating 600 mph
2nd Lt. Thomas R. Drybrough, 27 November 1944, 353rd FG "I had been pulling over 70" H.G. and was indicating about 425 MPH at approximately 14,000 feet."
1st Lt. Charles E. Yeager, 13 September 1944, 357th FG I rolled over and was pulling around 70Hg.
Capt. Charles E. Yeager, 6 November 1944, 357th FG I got behind him and was pulling 75 Hg.
Lt. Col. Roy A. Webb, 25 June 1944, 361st FG I closed very slowly and pulled as much as 70 inches of mercury.
1st Lt. Thomas H. Hall, 15 August 1944, 364th FG I put on 70 inches and gradually pulled up on them.
Lt. Col. Kyle L. Riddle, 24 December 1944, 479th FG "I pulled about 70" to 75" mercury..."
F/Lt Pearson, 5 April 45, 65 Squadron "Opening up to 70 inches I overtook him..."
F/Lt. G. M. Davis, 23 March 1945, 129 Squadron "Opened up to +25 lbs of boost 3,000 revs and dived down to engage."
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Summary of RAF 100\150 use.
http://www.wwiiaircraftperformance.org/150grade/appendixa.pdf