I dropped off my block heads and crank the other day at the machine shop, I have 7a heads and talked with the guy about porting them for larger valves he really suggested not for 2 reasons; 1st, the larger valves don't really allow for 360 degrees of air flow @ them (more like 2/3 since they are so tight up against the walls) to justify the added expense. 2nd, the added performance is found only at the higher rpm range, still will be a torque monster at the lower end, burn the tires throw you back in the seat, as I will not be racing the thing, not sure I'll be needing the full range, just looking for nice street machine... Ok, the other question I have (tired of reading endless forums, please just enlighten me) the 7a heads should already have hardened seats??? the #5 heads have the larger valves already (found on 1968 &1969's) but would need to have the seats and guides replaced? Also, if someone could explain what makes them #5 heads "high" compression heads... I think I can get a set of #5 heads from a guy not far from here, cool old olds guy... probably for cheap.... so would these #5 heads work just fine on a '72 block? my # is 830-305-5050 if anyone cares to share their olds knowledge/recomendations with me directly... I can comfortably offer you 500 good Karma points for your trouble

 

May not answer all your questions, but the one main one, Olds compression, is not controled by the heads, but buy the pistons. If you have old heads that need to be rebult anyway, why not just put the big valves in them

 

Huh? So if you have #4's, #7s or #8 heads it won't make a difference in the compression ratio? Please explain.

 

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After the early 70's they controlled compression in the heads and kept the 14 cc dish if i remember correctly. From 64 to atleast 73 they controlled it in the piston i could be wrong. True cc varied between early heads and later heads they are all claimed to be 64 cc but it's just not true . later heads had big block like cc's to control compression. 72 7A heads and earlier are about as good as it gets the only reason i can think the 5's are better is no egr bumps. I could be wrong cutlassefi can correct me. Not all 5 heads had big valves only the w31's keep your 7A's grind down the egr bumps and they are just as good . I had a high 13 sec combo using bone stock heads with just a freshening up. You gotta look at your goals and what you want ., there are a few guys running sbo's with some great combos here .

 

Aren't the chambers smaller on the #5 heads which would be the cause of the higher compression??? just sayin', makes sense to me... but, they would need hardened seats to accommodate the unleaded gas, right???

 

im willing to put money on that if you cc the 5"s you have more than 64 cc closer to 68 . The mondello olds book states for 5 heads 68 cc give or take for 72 7A 69cc give or take., cc's varied alot you could have 5 heads with 70cc'c depends on how it was machined at the factory .Thats what i have for refrence. Im runnning 6 heads that where milled .024 and installed bigger valves . Im at 65 cc's. in 1970 they used a 14 cc dish for the low compression 9 to 1 350. In 1972 they used a 23 cc dish and dropped it to 8.5 to 1. Real compression actually varies i have had 350's with the slugs .025 in the hole and i have seen them as deep as .035 and again the cc's in the heads varry so again true compression can only be figured out by cc'ing the heads measure deck hieght and piston dish. stroke etc.