632 BBC= MISERY
Posted: Mon Feb 27, 2006 10:58 pm
I recently had a customer bring in an assortment of parts to be assembled into a 632. After trial fitting I have come up with several "issues" that maybe someone with more experience can help with.
The combo is a Dart big M 10.2 block with 4.84 bore spacing. Callies 4.75 crank with Miller 6.7 rods, JE pistons. Heads are a set of maybe early 90's Pontiac 10093378 pro stock heads. Valve size are 2.48 intake, 1.9 exhaust. Head bolt holes have been sleeved for porting. Intake is sheet metal that was acquired from an entirely different engine but for the same style head. Camshaft is 288-312 @.050 .510 Intake lobe .477 exhaust lobe on 114 ls. Rockers 1.8 int, 1.7 ex. Cam is ground on .875 CORE standard BBC bearings. Engine will be used on a dragster. Rpms from 5500 to 7800. Problems are as follows:
The intake valves rub the piston reliefs everywhere. I can use .030 offset head dowels to move the valves away from the adjoining cylinder wall but that will require redrilling the head bolt holes and the sleeves. The sleeves now measure .460 ID and opening to .500 should take care of the .030 offset dowels. The head studs will almost start in the threads as is. I can machine the piston valve reliefs a little larger and take the offset into consideration. The intake valves have about .015 from the lap line to the outer valve edge. Reduce the size of the valves to 2.460 or so??? The bowl is already 91% of the 2.48 valve. Any other suggestions????
The pistons he has are for the Pontiac 427 heads and are 18 degree. The 378 heads are 15 degree as best I can measure. I have flycut one piston and roughed in the appoximate shape the valve reliefs need to be. From first appearance it seems this will probably work????
The cam lobes slightly touch every rod on the 2-4-6-8 side. The touch is so light the engine can still be rotated. Removing .030-.040 from the rod should provide enough clearance. My problems is with the anemic shaft diameter. Will flex and bending be an issue that should be addressed with a larger core that will magnify the rod/lobe interference???
Offsetting the heads also cause alignment problems with the ports. I will try to straighten everything up and use Z spar the fill any anurisms.
This is not my normal type of engine build. Hopefully some that has worked through the same problems can offer some help I have not thought of. I recently read in some forum that "God hates 632's"- I know why. Thanks in advance for any help.
The combo is a Dart big M 10.2 block with 4.84 bore spacing. Callies 4.75 crank with Miller 6.7 rods, JE pistons. Heads are a set of maybe early 90's Pontiac 10093378 pro stock heads. Valve size are 2.48 intake, 1.9 exhaust. Head bolt holes have been sleeved for porting. Intake is sheet metal that was acquired from an entirely different engine but for the same style head. Camshaft is 288-312 @.050 .510 Intake lobe .477 exhaust lobe on 114 ls. Rockers 1.8 int, 1.7 ex. Cam is ground on .875 CORE standard BBC bearings. Engine will be used on a dragster. Rpms from 5500 to 7800. Problems are as follows:
The intake valves rub the piston reliefs everywhere. I can use .030 offset head dowels to move the valves away from the adjoining cylinder wall but that will require redrilling the head bolt holes and the sleeves. The sleeves now measure .460 ID and opening to .500 should take care of the .030 offset dowels. The head studs will almost start in the threads as is. I can machine the piston valve reliefs a little larger and take the offset into consideration. The intake valves have about .015 from the lap line to the outer valve edge. Reduce the size of the valves to 2.460 or so??? The bowl is already 91% of the 2.48 valve. Any other suggestions????
The pistons he has are for the Pontiac 427 heads and are 18 degree. The 378 heads are 15 degree as best I can measure. I have flycut one piston and roughed in the appoximate shape the valve reliefs need to be. From first appearance it seems this will probably work????
The cam lobes slightly touch every rod on the 2-4-6-8 side. The touch is so light the engine can still be rotated. Removing .030-.040 from the rod should provide enough clearance. My problems is with the anemic shaft diameter. Will flex and bending be an issue that should be addressed with a larger core that will magnify the rod/lobe interference???
Offsetting the heads also cause alignment problems with the ports. I will try to straighten everything up and use Z spar the fill any anurisms.
This is not my normal type of engine build. Hopefully some that has worked through the same problems can offer some help I have not thought of. I recently read in some forum that "God hates 632's"- I know why. Thanks in advance for any help.