Rocker ratio and cam advance questions

[travis]

I’m doing a cheap street build for another ford. Low mileage stock rebuilt 351w rebuilder special, 17cc dished stock style pistons .045” in the hole, stock 206/221@.050 cam on a 115 lsa/117 ica, .444/.453 lift, etc. It sank a couple of exhaust valves badly...the heads are junk. The owner ordered a set of ProMaxx 175 heads set up for an hft cam, a performer rpm non-air gap intake, and a 680 vacuum secondary QFT carb.

With the right head gaskets I should be able to get real close to 9-1 compression. If I install the cam 4* advanced that still only gets me an icl of 113* (factory cam is 2* retarded). Would 8* advance kill it? I figure it will give it some snap on the low end but that also puts that much longer exhaust lobe opening pretty early. He needs rockers too...I am not sure if 1.72’s on both intake and exhaust or 1.72’s on the intake and 1.6’s on the exhaust would be better?

The owner wants to build a better short block with more cam and compression and strength when he can afford it, so he only wants to change parts that will transfer to better motor later.

It’s a heavy car (‘72 Torino), FMX, stock converter, 3.00 gears, 1 5/8” headers, etc.

[turdwilly]

Holy hell .045" down! He must have pistons with compression height for the older 9.480" deck height block instead of the later 9.503". I don't know how thin a gasket you can get, but calculations using the promax 175 60cc chambers & 4.060" bore .025" compressed head gaskets only gets you 8.74:1 CR. Money well spent would be a set of the correct compression height pistons for the 9.503" block, possibly with a smaller dish volume.

I ran into this same situation about 35 years ago when I was dirt poor & had to run what I had. Ended up decking the block .040" but then that limits your piston selection for future builds & I also had to cut the intake.

[turdwilly]

https://www.cnc-motorsports.com/keith-b ... -bore.html

^^These pistons & standard Fel-Pro 10111/10112 head gaskets would put him around 9.8:1 CR if his block is still 9.503" & you don't want to deck it or the heads. Piston would be about .023" down & has 2 valve reliefs, 6.5cc volume.

[groberts101]

for a couple quick low budget bandaids... mill the heads .040".. maybe advance that shorter cam around 2-4°more(probably too short to do much more than that and too much EO advance will overshadow/be counterproductive beyond what the earlier IO will give and end up blowing any potential torque gains right out the exhaust pipe).. 1.72/1.6 rockers(these parts and the milling will likely require pushrod length changes).. and then add a small 2.125" choke into the likely too large 3" header collector followed by a 2.5" mandrel bent exhaust into straight thru style mufflers. Then tune for max manifold vacuum at idle/light cruise and tell him to enjoy it for what it is until he builds a real motor for it.

[Scotthatch]

With that cam 8 degrees of advance would be a good thing