The 34 is a little larger and it has 80-90 more amps. That's the only difference.
Here ya go.......
Battery Model: 35
Part Number: 8020-164
NSN: Number applied for, product currently available
UPC Code: 8 11405 00164 2
Performance Data
Cold Cranking Amps: 720
Cranking Amps: 910
Nominal Voltage: 12 volts
Open Circuit Voltage (fully charged): 12.8 volts
Internal Resistance (fully charged): 0.0030 ohms
Capacity: 44 Ah (C/20)
Reserve Capacity: BCI: 100 minutes (25 amp discharge, 80°F (26.7°C), to 10.5 volts cut-off)
Physical Characteristics
Plate Design:
High purity lead-tin alloy. Wound cell configuration utilizing proprietary
SPIRALCELL TECHNOLOGY®.
Electrolyte:
Sulfuric acid, H2SO4
Case: Polypropylene
Case Color: Dark Gray
Cover Color: “OPTIMA“ Red
Group Size: BCI: 35
Post Type: SAE Post
Weight: 31.7 lb
Length: 9.38 in
Width: 6.75 in
Height: 7.69 in
And
Battery Model: 34R
Part Number: 8003-151
NSN: 6140 01 475 9357
UPC Code: 8 11405 00151 2
Performance Data
Cold Cranking Amps: 800
Cranking Amps: 1000
Nominal Voltage: 12 volts
Open Circuit Voltage (fully charged): 12.8 volts
Internal Resistance (fully charged): 0.0030 ohms
Capacity: 50 Ah (C/20)
Reserve Capacity: BCI: 100 minutes (25 amp discharge, 80°F (26.7°C), to 10.5 volts cut-off)
Physical Characteristics
Plate Design:
High purity lead-tin alloy. Wound cell configuration utilizing proprietary
SPIRALCELL TECHNOLOGY®.
Electrolyte:
Sulfuric acid, H2SO4
Case: Polypropylene
Case Color: Dark Gray
Cover Color: “OPTIMA“ Red
Group Size: BC I: 34
Post Type: SAE Post
Weight: 37.9 lb
Length: 10.06 in
Width: 6.88 in
Height: 7.88 in
Hope this helps. I know some people will only put in what the guide says, and that's fine, the 35 series will work. The 34 is just a bigger better battery.
OK. I have heard a lot about Optima batteries, I have a 2003 50th Anniv vette and a lot of the vette owners rave about them. I ordered a 34R, hope it fits good. I notice there is not a lot of slack on the negative cable to the battery.