Well, if the cooling of the heads was not a problem, then the B-series R-2800 should have reached over 70" with intercooling and ADI just like V-1710 did with ADI alone. But in reality it did not do that.
Still, it’s not a “problem.” It was inherent in the design. Once the engine is designed, the way the detonation issue is dealt with is thru the induction system – by way of heat exchangers and ADI.
The B-series R-2800 would have done better with aftercooling but not very much and AFAIK series produced V-1710s with two stage mechanical superchargers never got intercooler nor aftercooler.
So says you, with no evidence to support your position. Again, Allison and P&W felt differently enough that P&W tried to develop an aftercooler, and Allison did.
Allison knew it had to find a way to increase power in its engines to be competitive and developed the V-1710-119 (F32R) for the proposed P-51J. It was rated on 100/130 grade fuel. In order to achieve the desired manifold pressures, a huge aftercooler sat on top of the superchargers. The P-51J was not developed as the Merlin P-51 was preferred.
The last plane to use an Allison was the F-82 Twin Mustang. It didn’t use an aftercooler or intercooler, but did use ADI. It wasn’t rated on 100/130 grade fuel, but rather on 115/145 grade fuel which could tolerate higher temps before detonating.
I'm merely pointing out that if the cooling of the heads would have been better in the B-series R-2800, it would have reached MAP close to V-1710 with similar induction system.
Fine. And I agree. But once the engine is developed, the way to avoid detonation is to cool the charge. The cooler the charge, the higher the MAP that can be tolerated.
And as far as the statement “B-series R-2800, it would have reached MAP close to V-1710 with similar induction” goes - it already did. For instance the maximum rating for the turbosupercharged R-2800-59 (P-47D-27 thru -40) was rated for 64” hga on 100/130 grade fuel. Maximum rating for the V-1710-111/113 (P-38L) was 60” hg on 100/130 grade fuel.
Now the V-1710-117 of the P-63C was rated at 76” hga on 100/130 grade fuel. It didn’t use an aftercooler or intercooler. But it used obscene amounts of ADI – more than 1.5 gallons per minute – to do it. It used so much ADI that it increased MAP by 15” hga over its dry WEP rating of 61” hga. That was how Allison chose to tackle their detonation issue.
The only engines I think that are really directly comparable (by virtue of their induction systems), are those on the P-38 and P-47. The induction systems on the P-63 and F4U used different methods to achieve what they did.
I wonder what you are trying to argue; no one tries to deny advantages of the charge cooling here. But if the head temperature can be reduced some how, the MAP can be increased.
What I am saying here is that improvements in MAP could be obtained without improvements in head cooling. Head temperature wasn’t a “problem” because these were good engines. If a way could be found to ever decrease the charge temp, MAP ratings would continue to rise. That happened for a while, until it was no longer a practical way to increase the efficiency of the induction system.
Detonation limitations were affected by many things, among them head temperature and induction air temperature. Induction air temperature was the more variable of them.
Basicly not so well head cooling prevented the B-series R-2800 to reach same MAPs as other engines with similar induction system.
Lemme ask you this? What was the temperature of the mixture discharged into the engine in the Corsair’s R-2800-8 engine (6.65:1 compression ratio pistons) at 60” hga? I don’t know. But I do know what it was for the Allison V-1710 and the V-1650 engines.
In the late V-1710s (6.0:1 compression ratio pistons) a mixture discharged into the engine at a temperature of 230 degrees Far developed 63” hga. (The V-1710-111/113 in the P-38L used 6.65:1 compression ratio pistons and developed a maximum of 60” hga.)
In the two stage, aftercooled V-1650 (6.0:1 compression ratio pistons) a mixture discharged into the engine at a temperature of 180 degrees Far developed 67” hga.
I think the engines are comparable enough to say that the major difference here is that the Merlin’s induction system cooled the charge better than the Allison’s so it was able to utilize higher MAPs. When Allison wanted to cool the charge more to develop higher MAP, it utilized ADI. I’d hazard to say the charge temperature in the Corsair's R-2800-8 was probably hotter than it was in the Merlin making it impossible to achieve the MAPs on the R-2800 that the Merlin could achieve on the same fuel grade.
I wonder did you understand at all what I said about turbo charged V-1710 and B-series R-2800: "The V-1710 in the P-38J could reach 60" with intercooling and without ADI, while the B-series R-2800 of the P-47D was limited to 52-54" in similar configuration and it was initially limited to 56-58" with ADI (later raised to 60-64").
This comparison shows clearly how the B-series R-2800 was more limited than the V-1710 with similar induction system. With ADI Allison tested V-1710s of P-38 at 75" which is higher than 72" claimed for C-series R-2800 of P-47M.
Those figures for the R-2800 SEEM to suggest a limitation. 64” hga doesn’t seem like much when the engine is intercooled and has ADI. In actuality, that was probably very conservative rating, and not a true reflection on the limitation of the engine. It was capable of more.
The Commanding General of the Material Air Command set those limitations (64” hag) in a letter dated 26 May 1944 – Subject: Extra Boost in P-47. He wrote that 64” hga was now approved for use in the P-47 with ADI, after acknowledging that the engine could withstand 75” hga for several hours (on 100/130 grade fuel).
There may be an element of conservatism in the MAP limitations set for the Corsair with the B series R-2800 as well. Nobody seems to have thought of that. Maybe the Corsair was like the Thunderbolt in that it had a conservative rating when it was known it actually could handle a higher boost.
But if the MAP limitations for the Corsair really were set at the point just before detonation, then it appears it was because the induction system was incapable of reducing charge temperature enough to achieve more.
Or the head temperatures of the B-series R-2800 were simply too high for 67".
Obviously not. The P-47s was rated to 64” hga, and was known to be able to withstand 75” hga. 67” hga was certainly achievable if the charge temperature could have been reduced enough. The Corsairs induction system doesn’t appear to have been able to do it.
Based on this alone, we could conclude the B-series R-2800 could handle MAPs up to and in excess of 67” on 100/130 grade fuel, because the P-47 did it. If the Corsair couldn’t, it’s because of an induction system limitation, not an engine limitation.
