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There is a lot of confusion on the usage of the 1115091 coil on '63 and '64 Corvettes, and part of the problem is that the JG has is wrong - or at least does not tell the complete story. It is also important to understand that various coils were also used with specific ballast resistors. The coil/ballast combinations are essentially matched pairs to provide as designed ignition system performance.
Please note that I am only discussing 091 coil useage on '63 and '64 models as I have insufficient documentation to discuss 091 coil useage prior to 1963.
All Corvette engines during EARLY 1963 production used the 091 coil in conjunction with the 1931385 (0.3 ohm) ballast resistor. This combination provided maximum primary current and spark energy, but it was tough on points and burned points became a serious enough problem with this combination (happened to me) that Chevrolet Engineering made some interim changes during the 1963 model year.
TSB DR 577, February 27, 1963 advises that beginning February 4, 1963, a different ballast resistor 1957154 (1.8 ohm) entered production for 250 and 300 HP engines, ONLY.
This change is also documented on the change record of the requisite AIM sheet (Section 6 Sheet C7.00). Also, simultaneous with the change in ballast is a change from the 091 to the 1115087 coil. Bear in mind that this sheet is for the base engine, so any changes to RPO engines must be determined by reviewing the appropriate engine RPO sections. A review these sections in the '63 AIM does not support the TSB statment that the production change(s) only affected 250 and 300 HP engines.
The L-75/L-76 section does not show any change to the coil or ballast from base production, but L-84 Sheet 7.00 shows the coil as the 087 part. This sheet was released on May 6, 1963 and added to the AIM, and I believe the coil specification is wrong! Utilization specified by the Corvette Parts Catalog for the 154 resistor is '63-'64 (second design) except SHP/FI. The 385 resistor is '63 (first design) except SHP/FI and '63-'64 with SHP/FI. This may seem confusing at first - you have to have some experience working with the Parts Catalog. I sometimes helps if you're good at figuring out riddles, so trust me, it says that all early '63 engines used the 385 ballast while all but SHP and FI changed in mid '63 to the 154 ballast. Ballast usage is important because they were matched to the specific coils. My Parts Catalogs are seventies vintage so the 202 coil is listed as the service replacement part for all point ignitions. I submit my March 19 built SHP as evidence in support of the TSB and Parts Catalog that SHP/FI engines continued to use the 091/385 combination.
BTW, the TSB suggests that SHP/FI engines be changed to the 154 ballast in cold weather (Yeah, right, like you're going to have a "winter" ballast and a "summer" ballast.), but adds that the 385 ballast will provide the best possible high speed igntion performance. The burned points problem was particularly acute in cold weather because the ballast resistance varies with temperature - the colder the temp. the lower the resistance, so burned points was a particular problem in cold winter climates.
Perhaps someone with a '64 AIM could research the appropriate sheets to confirm that coil/ballast utilization is as stated in the Parts Catalog - 087/154 on 250/300 HP engines and 091/385 on SHP/FI engines.
In 1965 this issue became moot as the 1115202 coil and 154 ballast were used for all point ignition applications until the advent of the resistor wire in the harness.
BTW the service bulletin states that the service resistors are identified by a blue stripe (154) and a black dot (385), but I am still not convinced that the resistors shipped to and used by the plant were so marked.
Duke
Please note that I am only discussing 091 coil useage on '63 and '64 models as I have insufficient documentation to discuss 091 coil useage prior to 1963.
All Corvette engines during EARLY 1963 production used the 091 coil in conjunction with the 1931385 (0.3 ohm) ballast resistor. This combination provided maximum primary current and spark energy, but it was tough on points and burned points became a serious enough problem with this combination (happened to me) that Chevrolet Engineering made some interim changes during the 1963 model year.
TSB DR 577, February 27, 1963 advises that beginning February 4, 1963, a different ballast resistor 1957154 (1.8 ohm) entered production for 250 and 300 HP engines, ONLY.
This change is also documented on the change record of the requisite AIM sheet (Section 6 Sheet C7.00). Also, simultaneous with the change in ballast is a change from the 091 to the 1115087 coil. Bear in mind that this sheet is for the base engine, so any changes to RPO engines must be determined by reviewing the appropriate engine RPO sections. A review these sections in the '63 AIM does not support the TSB statment that the production change(s) only affected 250 and 300 HP engines.
The L-75/L-76 section does not show any change to the coil or ballast from base production, but L-84 Sheet 7.00 shows the coil as the 087 part. This sheet was released on May 6, 1963 and added to the AIM, and I believe the coil specification is wrong! Utilization specified by the Corvette Parts Catalog for the 154 resistor is '63-'64 (second design) except SHP/FI. The 385 resistor is '63 (first design) except SHP/FI and '63-'64 with SHP/FI. This may seem confusing at first - you have to have some experience working with the Parts Catalog. I sometimes helps if you're good at figuring out riddles, so trust me, it says that all early '63 engines used the 385 ballast while all but SHP and FI changed in mid '63 to the 154 ballast. Ballast usage is important because they were matched to the specific coils. My Parts Catalogs are seventies vintage so the 202 coil is listed as the service replacement part for all point ignitions. I submit my March 19 built SHP as evidence in support of the TSB and Parts Catalog that SHP/FI engines continued to use the 091/385 combination.
BTW, the TSB suggests that SHP/FI engines be changed to the 154 ballast in cold weather (Yeah, right, like you're going to have a "winter" ballast and a "summer" ballast.), but adds that the 385 ballast will provide the best possible high speed igntion performance. The burned points problem was particularly acute in cold weather because the ballast resistance varies with temperature - the colder the temp. the lower the resistance, so burned points was a particular problem in cold winter climates.
Perhaps someone with a '64 AIM could research the appropriate sheets to confirm that coil/ballast utilization is as stated in the Parts Catalog - 087/154 on 250/300 HP engines and 091/385 on SHP/FI engines.
In 1965 this issue became moot as the 1115202 coil and 154 ballast were used for all point ignition applications until the advent of the resistor wire in the harness.
BTW the service bulletin states that the service resistors are identified by a blue stripe (154) and a black dot (385), but I am still not convinced that the resistors shipped to and used by the plant were so marked.
Duke
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