Bring this one back from the dead. My wifes car is having the same code thrown as well only weve had the thermostat changed and it still pops up from time to time. Ym39FrM-ZBY/hqdefault.jpg' alt='How To Install Thermostat On Chevy 350' title='How To Install Thermostat On Chevy 350' />Just because your car is old doesnt mean its outdated. It Still Runs is your ultimate auto resource, whether you rotate your tires or change your oil. How To Install Thermostat On Chevy 350' title='How To Install Thermostat On Chevy 350' />Chevrolet Products. JIMMY BASICS Read Photo 1 L to Rt, 2 Top to Bottom1. Open Hemi chamber, small ports 71. Served as the only head, apparently, for 2. H head below. Compression was established by. The legendary H head open chamber, with large. Great. for performance Forged, custom piston shown. D chamber, always with a. Installed in larger GVW trucks. Great War Of Prefectures Pre Hacked Hub. An accompanying. governor limited rpms to 3,2. Also, a great performer. D chamber. Custom piston pictured. Small ports and small chamber. This head was apparently introduced about 1. These 6 engines are the small block Jimmy family. Theoretically, any of the above heads could be installed on any of the. However, the 4. 77 head would be limited in performance by the. The 4. 17 and 9. By noting the photo, it is. H. head would make less compression with the 3. The 2. 19. 48. 19 head. None of. the stock GMC pistons is recommended for a performance engine, due to.