Checking Intake Manifold Fit After Resurfacing Heads
My first mockup of the shortblock used the new Race Tecs before the chamfer was added around the OD. The first cylinder I measured was #8, which had the largest above deck height, approximately 0.025. I brought the piston up to TDC using a bridge / indicator, then layed the 8553PT / 0.054 gasket and head on the block. I pulled the rod cap off and using a magnetic base on the pan rail, placed the indicator tip on the bottom of a connecting rod bolt, pushed the piston up until it stopped and recorded the indicator reading. The reading was 0.029. (Note that this matches (gasket thickness - deck height).
I repeated this test on cylinder #7, using the domed piston and the 0.039 gasket which resulted in piston-to-head clearance of 0.060.
At this point, I realized the chamferred edge on the piston was critical.
The machine shop added the chamferred edge to match the TRW piston. My piston-to-head measurements now, using the 0.039 gasket:
I brought the heads back to the machine shop to see if my 78cc measurements are correct. No results yet. Note that as material is removed by resurfacing, the 3.978 dia will be reduced due to the sloped surface above the spark plug.
If they are really at 78cc, which puts my DCR @ 7.22, maybe I should leave the heads alone and just change the cam. Several of the Comp profiles (252H, IVC@52*; XE250H, IVC@51*; XE256H, IVC@54) would boost my low rpm torque compared to the Mopar "761" IVC@61*. The XE250H would yield a DCR = 7.70.
I've sent my specs to Jim at Racer Brown to see what he recommends.
Some clarification on the interference problem I discovered.
My first mockup of the shortblock used the new Race Tecs before the chamfer was added around the OD. The first cylinder I measured was #8, which had the largest above deck height, approximately 0.025. I brought the piston up to TDC using a bridge / indicator, then layed the 8553PT / 0.054 gasket and head on the block. I pulled the rod cap off and using a magnetic base on the pan rail, placed the indicator tip on the bottom of a connecting rod bolt, pushed the piston up until it stopped and recorded the indicator reading. The reading was 0.029. (Note that this matches (gasket thickness - deck height).
I repeated this test on cylinder #7, using the domed piston and the 0.039 gasket which resulted in piston-to-head clearance of 0.060.
At this point, I realized the chamferred edge on the piston was critical.
The machine shop added the chamferred edge to match the TRW piston. My piston-to-head measurements now, using the 0.039 gasket:
Cylinder # /piston-to-head Cylinder # /piston-to-head
1 / 0.070 2 / 0.070
3 / 0.060 4 / 0.070
5 / 0.060 6 / 0.060
7 / 0.070 8 / 0.050
Note that the open chamber head is not round. The 4.067 piston will not fit into the chamber.1 / 0.070 2 / 0.070
3 / 0.060 4 / 0.070
5 / 0.060 6 / 0.060
7 / 0.070 8 / 0.050
If they are really at 78cc, which puts my DCR @ 7.22, maybe I should leave the heads alone and just change the cam. Several of the Comp profiles (252H, IVC@52*; XE250H, IVC@51*; XE256H, IVC@54) would boost my low rpm torque compared to the Mopar "761" IVC@61*. The XE250H would yield a DCR = 7.70.
I've sent my specs to Jim at Racer Brown to see what he recommends.
