Also fittment of headers is a major pain due to the proximity of the steering gear box. Factory BBC chassis frame mounts (which should have been used if some one converted your car from a SBC or L6) raise the motor on the drivers side and shift the engine to the passenger side one full inch to obtain clearance. This of course cocks the engine in the frame which requires a different transmission cross-member and a different bell crank (Z-bar). If you were to attempt to use the SBC frame mounts then the headers will hit the steering box and will not clear the Z-bar because the placement of the linkage is different on the BBC part from the SBC part as well as being a half inch longer (9.5" instead of the SBC 9").
When you go to headers the clutch linkage return spring (which is mounted to a braket bolted to your cast iron exhaust manifolds) has to be attached to something. Most just put a SS hose clamp around one of the tubes and attach it that way; others change the spring to a longer one and bore a hole in the frame mount to attach the longer spring to it. By the way the numbers matching guys over at Team Camaro want those old cast iron manifolds (the passenger side part doesn't exist in NOS or as a repop) so just don't scarp them.
I'm still working on my little treatise on SBC to BBC conversions and have learned some amazing details often over looked when swapping.
Thanks for the help. I am using an automatic trans can I modify the trans crossmember to work? I see big block frame mount for novas on ebay are these the ones I need to raise and move the engine? thanks
Is there a motor there now that you are running with? Or: are you planning to swap out an existing smallblock for a big block? (or some variant of that; as in no motor at all annd it is just a roller.)
OK so you currently have fender well headers (very rare, I would like to know who made them as I would be thinking of getting a set for myself) and want to go to the more traditional chassis style headers.
You must first asscertain if your car was converted correctly from a SBC to the BBC. Looking at the heater core open as it is I would say no. You would have to buy the following and install them if you want to use traditional chassis headers without a headache.
Dropped Air Cleaner for Holley (cars without cowl hoods)
Headers (recommend Hooker Super Comps 2" tubes)
Two and one half inch diameter tail pipes (or larger)
Pedestal Frame Mounts1
New Front Coil Springs2
Disc Brakes (RPO J52 for '68)
Big Block 4 Core Radiator
BBC Fan Shroud
BBC 7 blade thermal control clutch fan 3
BBC Heater Core & Heater Cover for BBC 4
BBC Sway Bar (if desired to go around corners)
Transmission cross-member for TH400
1 Frame mounts are no longer available from GM so you will need to find these on e-Bay 3912597 & 3912598.. Place the driver's side header into the empty engine bay first, then install the engine.
2 Eaton #MC-1266 $140
3 Classic Industries catalog number C2006 on page 690 lists a 1969 Big Block Heater Core w/o A/C (for long water pump) part number H2239 $89.95 1967-"69 Big Block Heater Core Tube Seal Ring part number T54315 $19.95 ea. 1967-"69 Big Block Heater Box w/o A/C part number AL303 $59.95
4 Fan # is 00393996 (18" diameter with 7 blades) this is a genuine GM replacement not original looking - the blades have more pitch than the original one did. Fan clutch # is 12306569 or A/C Delco # 15-4218
You can use the SBC cross member only with a manual transmission or a TH350. (but you will have to grind out the mounting holes to make mounting slots for a BBC using BBSC frame mounts.) Since the TH400 is longer and puts the transmission mount in a different location from the TH350 you will need a fabricate or buy another cross-member. On second thought I believe you can move the crossmember on Camaros and Third Gen Nova subframe to compensate for the longer TH 400.
Here are some pictures of the two for comparison (on the bottom of the chart).