I have the lovejoy specs in an old MSC catalog:
series | rated HP at 1750 rpm | max rpm | buna-n | urethane | hytrel |
L095 | 5.5 | 9000 | 194 inch-lbs | 291 inch-lbs | 561 inch-lbs |
L100 | 11.9 | 7000 | 417 | 626 | 1134 |
L110 | 23 | 5000 | 792 | 1188 | 2268 |
L150 | 35 | 5000 | 1240 | 1860 | 3708 |
L190 | 49 | 5000 | 1726 | 2592 | 4680 |
Spider types:
Buna-N -- oil resistant, temperature range -40 - 212F. 1º angular misalignment
Urethane -- greater torque capacity, temperature range -30 - 160F. 1º angular misalignment
Hytrel -- high torque and high temperature applications (-60 - 250F) .5º angular misalignment
An ST 7.5 head has a 38mm shaft. My catalog lists the L110 as the only series available with that shaft size.
I am using an L150 that I bored out to 38mm and I'm quite happy with it so far.
I have never found the coupling to be more than barely warm even after extended operation. The flywheel adapter only touches the flywheel in 3 places, so I suspect it tends to isolate the coupler from any engine heat.