That P-40 has a narrow Cowl; I don't know how well a small gasser will work or fit without cutting the cowl up a bunch, not to mention the additional weight of the ignition battery; on a 60 size p-47 the small gassers work because of the bigger cowl on these planes, a 91 4 Stroke should work without a problem, if you want more power, go with the YS 110 4 stroke.