B&M 20480 NITROUS HOLESHOT 2400 - Manual (Page 3)

worn/elongated stud holes (see Fig. 9).
The flexplate should not be “dished”
backwards. Check condition of starter
ring gear teeth. Distorted or worn
flexplates should be replaced.
STEP 14. Check the bolt pattern of
your B&M torque converter and make
sure it matches your flexplate. There
are several bolt patterns possible from
GM:
Powerglide and TH-350:
(3) 3/8" bolts on 10.75" B.C.
TH-400:
(3) 3/8" bolts on 11.5" B.C.
If your flexplate does not match up
to the bolt pattern on your B&M torque
converter, you will have to replace your
flexplate. You may enlarge your origi-
nal flexplate holes to accept larger 1/2"
bolts, if necessary. For race converters
use a 17/32" (.531") dia. drill and deburr
the holes after drilling.
Note: The flexplate you use with race
converters may require the 11-1/2" di-
ameter hole pattern.
SFI Approved B&M Flexplates
Flexplate Application
Part Number
20230 All '55-'85 Chevy Small Block V8, and '90 and earlier Big
Block with 168 Tooth Ring Gear except 400 and 454cid
20232 All '55-'85 Chevy 400cid externally balanced with 168
Tooth Ring Gear
20233 All '90 and earlier
Note: B&M AOD 40430 & 40431 Open Converters (non-split path) do not
require any transmission modifications.
VEHICLE/ENGINE FLEXPLATE P/N Starter Nosepiece P/N
Buick
All except 455 1230925 1876881
455 1233837 1876881
Chevrolet & GMC
All except 454 340296 1969309
454 3992069 196309
Oldsmobile
All except '75 400 399964 801227
'75 400 487651 801227
Pontiac
'66 - '75 & '76 455 487651 801227
'76 except 455 499857 801227
Factory part numbers are for reference only, and are not guaranteed for
accuracy.
Make sure that the replacement flexplate has an equivalent balance weight
on it. Improper flexplate balance will cause severe engine vibration.
Figure 4
Inspect converter stud holes, crankshaft
bolt holes and starter ring gear teeth for
damage, cracks and excessive wear.