What Head Is This?

11secAvanti · Post by **11secAvanti** » Tue Apr 19, 2005 9:40 pm

Got around to rejetting my carb today and solving some ignition issues. The head casting number on my 71 SBC 350 is #3878487. It has 1.94 intake and 1.50 exhaust. Is this considered a smog head or a better flowing head for that time period. Has anyone any cfm data on this head in factory form? It is factory stock. If I could get some data I can use it in some new simulation dyno software I recently got which calculates hp and torque. Thanks.

bill jones · Post by **bill jones** » Tue Apr 19, 2005 10:55 pm

-487's are large chamber smog heads.
-typical flow numbers of stock heads (at 25" test pressure) are:

-at .100"-.200"-.300"-.400"-.500"-.600" valve lift

-int-52-103-155-177-185-193
-exh-44-81-111-128-128-128
---------------------------------
-mildly ported and with a decent valve job, valve backcuts etc, you can expect:
-int-61-124-176-207-210-224
-exh-55-106-152-177-181-188
--------------------------------------
-To convert to 28" add 6% to these 25" numbers.

11secAvanti · Post by **11secAvanti** » Wed Apr 20, 2005 8:36 am

Ok, thanks for the feedback data. Was hoping they were the better heads but I am still pleased with the street performance. Now I can play with the dyno software. Thanks.

11secAvanti · Post by **11secAvanti** » Thu Apr 21, 2005 9:52 am

For what it is worth, here are the values the dyno software gave me using the above 28" recalculated stock flow values for these heads and the Crane 2040 210/216 @ .050 cam.

rpm hp torque
1500 89 313
2000 126 331
2500 159 335
3000 194 339
3500 223 334
4000 230 302
4500 218 254
5000 189 198

When I ran the drag simulator software it put the trap speed nearly on the cars actually trap speed. 60 ft calculation also was nearly the same but overall et was off by .5 sec. Apparently I am shifting at the wrong rpm.