enginehistory.org

[jjuutinen]

...ormance of the Merlin? Now, please forget any IMEPs. I have only interest in what is available to drive the propeller. Anyway, the highest official rating I know of the V-1710 on 100/130 fuel seems to be 1500 hp in non-turbo models. Now, the Merlin 130 is capable of 1830 hp on the same fuel. And the highest power the Allison is capable of on lean mixture seems to be around 800 hp (MAP=38in) while the Merlin 130 is capable of some 1200 hp on (boost +9) the same 100/130 fuel at lean mixture. That is 50% difference. BTW, the Allison G-series, with its reduced cr, has a max continuous boost of 44inHg on 115/145 fuel, while the Merlin 130 reaches 50 in on 100/130 fuel!!! The big question is: What did Allison screw up? Bearing in mind what Heron wrote on mild and severe engines, the Allison seems to be a much more severe engine in terms of fuel quality requirements.

[gryan]

I am interested by this as well.

I thought it intriguing that combusion chamber design of the respective engines seems to indicate the Alison would be the stronger performer. On inspecting cylinder heads, Merlin combustion chamber shape does not seem all that promising. The Allison is more like what you would find in modern practice for a 4-valve engine. Yet the Merlin does better performace wise. Nor does not seem to have had an issue with detonation.

What is going on?

[jrussell]

After searching for good pictures of V-1650 and V-1710 combustion chambers, I also came to the conclusion that the Merlin did not look like it had a clearly better chamber. As a matter of fact, an "eyeball" anaylsis tells me that a V-1710 should have been a lot closer in potential than it seems to be. Does anyone have info on the flow bench performance of the respective inlet and exhxaust ports?. At this point I am focusing on the adiabatic effiency of the respective superchargers, as it seems the most likely candidate for the performance differential. I have tried to find compressor "maps" for the two engines, and have had no luck. NARA sent me some performance charts on early Allison's, but I have'nt had the time to actually figure the effiency of the supercharger from the data.
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It runs best just before it blows!

[jjuutinen]

This supercharger issue is interesting. I hope Dan Whitney doesn´t blow up, but I really find his comments on the "greatness" of Allison two stage supercharging annoying. It is clear from the specs that the RR two stage solution was vastly superior. For example, two stage Merlins give more power at the same boost that their single stage counterparts and maintain the power to considerably higher altitude, even with low altitude models (66). This is in direct contrast to Allison whose aux stage worsened low alt performance.

Second point is that while the Allison seemed to be stuck to around 1600 hp in all series produced installations to the war´s end, a large number of Merlins were cleared for +25 boost, i.e. some 2000 hp, in the spring of 1944 without any substantial problems in service (see www.spitfireperformance.com). In my opinion the P-38 would have greatly benefitted from Merlin 66s.

It is my opinion that the best late war liquid cooled engines were the Merlin, Sabre, Griffon and the Jumo 213. By the way, it is interesting to note that the Jumo had about 25-30% lower SFC at WEP rating compared to an Allison. A clear demonstration of the superiority of direct injection.

[rlawrence]

The boys in the photo recon at Mt Farm in England installed Merlins In a 38 in 1944. It ran nicely & flew the same. They reported their findings to higher Hdqts & were promptly told to remove those engines & say no more about it under threat of court martial